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Publication numberUS3713883 A
Publication typeGrant
Publication dateJan 30, 1973
Filing dateMay 27, 1970
Priority dateMay 27, 1970
Also published asCA964968A1, DE2126487A1, DE2126487B2, DE2126487C3
Publication numberUS 3713883 A, US 3713883A, US-A-3713883, US3713883 A, US3713883A
InventorsS Lien
Original AssigneeWestern Electric Co
Export CitationBiBTeX, EndNote, RefMan
External Links: USPTO, USPTO Assignment, Espacenet
Method of and apparatus for growing crystals from a solution
US 3713883 A
Abstract
A mixture (liquid or solid), including a solvent, a solute (comprising the constituents of a crystal to be grown), and any desired dopant, is placed in a drum rotatable on a major (and preferably generally vertical) axis. Substrates are mounted in the drum above the mixture level. The mixture is heated to dissolve the solute and form a solution. The solution is moved over and covers the substrates via a centrifugally induced forced vortex by rotating the drum. The system is controllably cooled, or otherwise affected, to effect crystal growth on the substrate. Expedients are provided to accomodate substrates both denser than and less dense than the solution and to obviate undesirable effects of contaminants in the solution. Defects in the grown crystals caused by temperature gradients, solution concentration gradients and turbulence are also obviated by appropriate facilities.
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United States Patent 1 1 Lien 1 1 Jan. 30, 1.973

[75] Inventor: Suei-Yuen Paul Lien, Morrisville,

[73] Assignee: Western Electric Company, Incorporated, New York, N.Y.

[22] Filed: May 27,1970

[2]] Appl. No.: 40,854

UNITED STATES PATENTS 3,033,159 5/1962 OBrien ..l17/101 X 3,097,112 7/1963 Schutze et a1... ..117/101 X 3,212,929 10/1965 Pliskin et a1. 1 1 ..117/201 3,298,875 l/l967 Schink 1 ..117/106 X 3,429,295 2/1969 Shapiro ..117/101 X Primary Examiner-Ralph S. Kendall Attorney-W. M. Kain, R. P. Miller and R. C. Winter 57 ABSTRACT A mixture (liquid or solid), including a solvent, a solute (comprising the constituents of a crystal to be grown), and any desired dopant, is placed in a drum rotatable on a major (and preferably generally vertical) axis. Substrates are mounted in the drum above the mixture level. The mixture is heated to dissolve the solute and form a solution. The solution is moved over and covers the substrates via a centrifugally induced forced vortex by rotating the drum. The system is controllably cooled, or otherwise affected, to effect crystal growth on the substrate. Expedients are provided to accomodate substrates both denser than and less dense than the solution and to obviate undesirable effects of contaminants in the solution. Defects in the grown crystals caused by temperature gradients, solution concentration gradients and turbulence are also obviated by appropriate facilities.

63 Claims, 14 Drawing Figures PAIENTEnmao 191a 3.713.883

sum nor 4 fiwmemam) 5 75 BACKGROUND OF THE INVENTION In an even more specific sense, the present invention contemplates so called liquid .phase epitaxy (LPE),

vthat is, the controlled precipitation and epitaxial In all three methods appropriate dopants (e.g., oxygen, zinc) may be used to cause the grown crystal compound to emit light of a predetermined wavelength.

First, the compounds may be grown by a non-epitaxial, bulk method from a stochiometric or nearstochiometric melt, followed, if necessary, by zone refining. Present melt-growth methods have been 1 found to be deficient for a number of reasons. Among growth of single crystalline material from a supersatu- Y rated solution onto a seed or substrate. Such single crystalline material may be a so-called Ill-V or lI-VI semiconductive, electroluminescent compound. However, as discussed subsequently, the present invention is not necessarily limited to the growth of only such compounds.

2. Discussion of the Prior Art semiconductive, electroluminescent diodes and other devices, for example those made of crystal compounds such as gallium phosphide [GaP] orgallium arsenid'e-phosphide [GaAs,,P, are the most efficient light sources known. Specifically, the electroluminescence of these compounds is due to the band-gap energies of their constituents being in the visible region of the radiationspect'rum. More specifically; electroluminescence is caused by exciton recombination mechanism or by direct band-gap electron hole recombination. Usually, the. constituents of an electroluminescent compound arejselected as follows: I

' a. one or more element from column [ll ,of the Periodic Table one or more elementlfrom Column V of the Periodic Table; or

these reasons are the necessity of high pressures (30-45 atm), high temperatures (=l500" c), and elaborate facilities; the unwanted introduction of impurities from crucibles at the pressures and temperatures necessarily utilized; and the inability to consistently grow high quality crystals.

In a second method, the compounds may be grown by epitaxial growth via vapor transport. Present vapor transport growth methods produce, at rather slow rates, crystal compounds having electroluminescent efficiencies somewhat lower than compounds grown by other methods.

Third, the compounds may be grown from solutions (LPE). Specifically, a heated liquid-solvent phase of a solution (e.g., gallium) is used to dissolve a solid-solute phase (e.g., gallium-phosphide). The desired compound is permitted to precipitate out either randomly or controllably (the latter being onto-a seed or substrate) by slowly lowering the temperature of the solution (whicheffects supersaturation thereof) to prevent polycrystalline growth and to encourage single crystal growth.

b. one or more element from Column ll of the Periodic Table one or more element from Column VI of the Periodic Table.

Thus, in describing.electroluminescent compounds,

there are derived the terms Ill-V and ll-VI.

Further information concerning these compounds may be found in the following references: Morpholo' gy of Gallium Phosphide Crystals Grown by VLS Mechanism with Gallium as Liquid-Forming Agent, by W. C. Ellis, C. J. Fros'ch and R. B. Zetterstrom in Journal Of Crystal "Growth,'2 (1968), pages 61 68 (printed in the Netherlands); Visible Light from Semiconductors, by MaxR; Lorenz in Science, Mar. 29,1968, Vol. 159, No.'3822, pages-14194423; and Solid State-Light" by A. S. Epstein and N. l-lolo'nyak in Science JournaL'January, 1969, pages 68-7 3. f

(Besides being efficient, electroluminescentdiodes and devices are more sturdy, reliable and longer-lived than, and are accordingly replacing, conventional incandescent lamps in a number of applications. .Additionally, such diodes are compact, compatible with solid state circuitry and require'very little power for operation. e

Nevertheless, difficulties have been experienced in rapidly, efficiently, and cheaply growing uniform, large area, single crystal, epitaxial compounds from which f Solution growth is potentially more desirable than the other two prior art methods because it uses lower temperatures "(901l00C) and lower pressures ambient), and produces strain'free crystal diodes having the highest known electroluminescent efficiency (about 3XX higher than the first two methods). Solution growth is rather slow (usually one-at-a-time), however, and has been found to often produce crystals having structural defects caused by, inter alia, solution concentration gradients, temperature gradients,.turbulence and the capturing of undissolved dopants'in the grown crystal. a,

.Thepresent invention, asnoted above,'is an improvement of the third prior art method, viz., the growth of crystalsfrorn a solution (LPE). Accordingly, another object of this invention is an improved method of the type last mentioned. v

As noted previously, the present invention is not limited to the epitaxial growth of single crystal, elecof, and a primary object of this invention, is the growth of crystals from a supersaturated solution which contains a solvent and a solute, the crystals resulting from controlled precipitati'on of the dissolved solute. I

A simple example of the type of crystal growth improved by the present invention may entail the growth of crystals of ordinary table salt. First, the table salt (the solute) is dissolved in a solvent therefor, such as water. If during the dissolutionof the salt, the water is heated, a saturated salt solution results upon addition of sufficient salt. If, now, this saturated solution is cooled, supersaturation results and the salt precipitates as solid, particulate crystalline matter. Such precipitation is generally random due to the generally random location of nucleating sites, salt. concentration provided in the solution, and if the thermal properties I and turbulence of the solution are appropriately adjusted and-controlled, the salt will precipitate on and adhere to the substrate or seed. I

Methods similar to'the above-described precipitation of table salt are found in prior art methods generally used to grow from solutions epitaxial layers of semiconductor materials. Such a method is described in U.S. Pat. application Ser. No. 556,192, filed June 8, 1966, and assigned to Bell Telephone Laboratories, lncorporated; and in U.S. Pat. No. 3,463,680. This method is usually referred to as the tipping method.

Specifically, in the tipping method of theprior art a graphite boat is positioned in a tiltable furnace. A substrate or seed is held at one end of the boat, which is tilted to raise the substrate. The lowered diametric side of the boat has placed therein a solution which includes a solvent (e.g., gallium), saturated with a solute (e.g., GaP) plus a dopant, if desired.

The furnace-boat system is closed and the boat is heated to dissolve the solute and the dopant. When the substrate and the solution reach an appropriate temperature, the boat is tipped to cover the substrate with the heated solution. The temperatureis then controllably lowered both to supersaturate the solution and to effect epitaxial deposition onto the substrate.

It should here be noted that the terms fseed and substrate are used interchangeably, the term seed" being the more generic term.Specifically, a seed is defined as a single crystal ofa'material on which it is desired to grow a crystal. A substrate, on the other hand, is a slice of a seed. Thus, the only difference between the two terms is their physical shape.

The above-described tipping method and methods derived therefrom are, at present, the best known methods of growing single crystal layers from a solution. As mentioned above, these methods are however, plagued with difficulties which render them somewhat less than desirable.- v

' A first difficulty involves the inability of the prior art tipping methods to effect the growth of single crystal epitaxial layers simultaneously on a large numberof substrates or seeds; Specifically, as described previously,epit'axial crystal growth involves the cooling of a saturated solution to a point where supersaturation ocours and the desired material precipitates from the now supersaturated solution onto the substrate or seed. Typically, prior art tipping methods have treated one substrate at a time, which is most inefficient, and, of course, costly and slow. The reason for-one-at-a-time treatment is related in part to difficult-to-analyze temperature gradients within the'super-saturated saturated solution when a large number of substrates are present. ln'view of the different cooling rates-of the solution and of a single substrate thereinafter tipping, the presence of numerous substrates generates many different temperature gradientsat different points within the supersaturated solution. These temperature gradients render unpredictablethe' exact rate at which the desired crystal precipitates the'refrom,that rate being temperature dependent. Moreover, these same gradients lead to a lack of a uniform substrate temperature. This, in turn results in the crystalline layers grown on the different substrates varying in character from substrate to substrate. Anobject of the present invention is to eliminate these temperature gradient problems in crystal growth.

A second difficulty with prior art crystal growth -tipping methods relates to the dopants which are often between the substrate-solvent interface making the grown crystalline layer either unacceptable or unpredictable in quality. Another object of this invention, then, is 'to eliminate such trapping of dopants and immundities inherent in prior art crystal growing processes. i

A third problem involved in prior art tipping processes is related to so-called concentration gradients. Specifically, the substrate is maintained at the bottom of or within the saturated solution as the solutionis cooledto grow on the substrate the desired crystal. Such growth is due to precipitation ,of the solute and'dopant from the cooled and now supersaturated solution. Such precipitation is not uniform throughout the solution due to temperature gradients and mobility considerations. Thus, precipitation generally first occurs from that portion of the solution immediately adjacent 1 the substrate. Because this precipitation causes a depletion of the solute and dopant from such portions of the-solution, the solute and dopant concentration in that portion is decreased.

A decrease in the solute and dopant concentration in thesolution portion immediatelyadjacent the substrate affects the density of that portion. Thatis', the density of thesolution portion may be rendered either greater or less than that of the rest of the solution.

The first situation is where the lower concentration portion of the solution has a density greater than the remainder of the solution. Because all of the solute and dopant that can precipitate from the supersaturated solution does precipitate from that portion of the solution immediately adjacent the substrate, further precipitation cannot take place untilthc solution immediately adjacent the substrate has been replenished with the solute. Such replenishment may be effected by stirring the solution. However, such stirring may cause the temperature gradients in the solution to become non-uniform and randomlylocated, thus, giving rise to the first problem of the tipping method discussed above. I

On the other hand, replenishment by naturaldiffusion may be allowed to take place. This, however, requires long time intervals making the process very slow and inefficient.

The second possibility, where a portion of the solution undergoes a density change, is for that density to be less than that .of the remainder'of the solution. The less dense solution will tend to rise generating either the temperature gradient problem or the turbulence problems discussed below.'-

Accordingly, yet another object of the present invention is to obviate concentration gradient problems, such as described immediately above.

The fourth major difficulty with prior art crystal growing tipping processes is related to turbulence. Some of the difficulties caused by turbulence have been discussed previously. In addition, turbulence immediately adjacent the substrate is usually undesirable since it causes variations in the thickness of (and the chemical and electrical characteristics of) the grown crystalline layer. It has been observed that turbulence typically leads to striations in the grown crystalline layers. Another object of this invention is to eliminate the turbulence difficulties of the prior art methods.

Some workers in the art have attempted to eliminate the temperature gradient problems in the following way: The substrate is positioned at the bottom of a very deep solution mass. An appropriate temperature gradient is then imposed on the system, the hope being that the large solution mass will stabilize the thermal gradient. Such, however, has not been the case due to increased turbulence effects. Specifically, such increased turbulence is due to the so-called Rayleigh Number exceeding 1700.

The Rayleigh, Number R is defined for the fluid-filled space between two parallel horizontal places as where y coefficient of thermal expansion of the fluid;

0 -0 the temperature difference between the two I planes; a

g gravitational acceleration;

d= the separation between the planes;

v= kinematic viscosity of the fluid; and

K the thermal conductivity of the fluid.

Convection currents appear when R 1700.

As discussed below, LPE is best effected with the substrate positioned within the solution at the cold end of a thermal gradient therewithin. Thus, for LPE (O -0 may be quite large. As a consequence, all else being equal, convection currents may be realistically eliminatedby minimizing the d3 term. Obviously, the deep solution mass does just the opposite, i.e., it maximizes the d term. In fact convection cells have been observedwhen the deep solution mass is used. Such cells create the undesirable turbulence effects noted previously, e.g., striations in the grown crystal layer. Moreover, rather than stabilizing the thermal gradient, the deep solution mass, in causing the convection cells, effects local temperature differences not only on a single substrate, but also from substrate to substrate, where several are used. Accordingly, another object of this invention is to prevent undesirable convection cells by minimizing the Rayleigh Number in'an LPE process.

Typically, as noted above, it has been found desirable to locate the substrate at the colder end of the thermal gradient in the solution between the substrate and the heat source. Specifically, the most desirable position for the substrate has been found to be one wherein a surface of the substrate, on which surface crystal growth is to take place, faces the heat source heating the solution, and is, therefore, at the cold end of the temperature gradient within the solution between that surface and the heat source. Such positioning enhances the growth of the epitaxial crystal in only one direction, namely, perpendicular to the surface of the substrate. Effecting this optimum positioning of the substrate while eliminating the above prior art difficulties has, until this invention, proved impossible.

SUMMARY OF THE INVENTION With the above-mentioned and other objects in view, the present" invention contemplates a new and improved method of and apparatus for growing crystals and more especially to a new and improved method of and apparatus for epitaxially growing crystalsfrom 'a solution. I

In a preferred form of the present invention in its broadest aspects, a solvent and a solute are placed in a generally cylindrical drum or container rotatable on a major axis. The solute comprises the constituents of (and dopants in) a crystal which is to be grown, Also placed in the drum, above the solution level therein, is a substrate or a plurality thereof.

The solvent and solute are heated to dissolve the solute (and dopants, if any) to form a solution. While the heat is maintained, the drum is rotated at aspeed sufficient to both move the solution up the side wall of the drum by centrifugal force in a so called forced vortex, and to hold the substrate against the side wall. Ultimately the substrate is covered by the solution at which time the entire system is cooled. Such cooling supersaturates the solution to effect the desired crystal growth on the substrate. When appropriate crystal growth is effected, rotation of the drum is' stopped and the solution falls to its natural level below the substrate. In a first alternate embodiment, the substrate placed within the drum is constrained against vertical movement and movement parallel to the rotation of the drum, but is horizontally movable, radially from the drum axis, between a first and a second stop member. In this first embodiment heating is performed by, one of two heat sources, namely, a first heat source outside of andsurrounding the drum, or, a second heat source inside the drum and surroundedthereby.

The first external heat source is used when the substrate is less dense than the solution. Specifically, the rotation of the drum initially forces the horizontally movable substrate outwardly against the first stop member via centrifugal action. When the substrate is covered by the solution (due to centrifugal force acting on the solution), the substrate floats thereon, i.e., it moves inwardly toward the drum's axis until it abuts the second stop members exposing to the solution that surface thereof which faces the heat source.

Accordingly, the exposed surface is ideally located, i.e., facing the heat source and at the cold end of the temperature gradient within the solution between the surface and the heat source.

The second internal heat source is used when the substrate is denser than the solution. Specifically, the rotation of the drum initially forces the horizontally movable substrate outwardly against the first stop member via centrifugal action. When the substrate is covered by the solution, it remains against the first stop members exposing to the surface that surface thereof which faces the heat source. Again, the ideal location of the exposed substrate surface is effected.

A second alternative embodiment recognizes the presence of either denser or less dense immundities in the solution. Such immundities may be the dopant skin or scum, previously referred to, or may be other unwanted and undissolved immundities.

In the second alternative embodiment the drum is divided by a cylindrical wall into an inner region and an outer annular region. The two regions are interconnected for solution flow therebetween above the level of the solution which is put in the inner region. The substrate is'placed in the outer region in accordance with either the description of the broader aspects of this invention, or of the first alter'native'embodiment, above.

A heat sourceis energized. This heat source is one of the two types describedabove. The drum is rotated to move the solution up the outer side wall of the inner region by centrifugal action in a first forced vortex. Immundi'ties denser than the solution remain at the bottom thereof. lmmundi'ties less dense than the solution float on the solution stopping their upward travel at some point below the interconnection between the two regions as determined .by their density and the rotational velocity of the drum.

After the solute isv dissolved in the solvent, the drum is rotated at a speed sufficient to further move the solution up to the interconnection, whereupon the immuninvention which may be included with the apparatus depicted in FIGS. 3, 4, SA, 58 and 6A-6F.

DETAILED DESCRIPTION Referring to FIG; 1 there is shown a product 20 of the type which is produced by the present invention.

The product 20 includes a crystal layer 21 grown by the method of the present invention on a substrate or seed crystal of, for example, a III-V or a lI-VI electroludity-freesolution spills into the outer annular region.

Rotation of the drum continues until sufficient immundity-free solution is present in the outer annular region to cover the substrates -by' a second forced vortex. Crystal growth is effected, again, by cooling the system to supersaturate the solution. a

Other embodiments and modifications are discussed in detail below.

BRIEF 'DESCRIPT'IONOF THE DRAWINGS substrate or a seed in accordance with the principlesof the present invention; 1

FIG. 2 is a stylized representation of the prior art tipping" method of growing the crystal of FIG. 1, which prior art method is improved upon by the present invention; r

7 FIG. 3 is partially cross-sectioned elevation of apparatus by which the broadest aspects of the method of the present invention are effected to grow the crystal layer shown in FIG. 1;

FIG. 4 illustrates a first alternative embodiment of the invention depicted in FIG. 3;

FIGS. 5A-5C are partial cross-sectional, elevational views illustrating the apparatus of FIG. 3 as modified by FIG. 4 to carry out the first alternative embodiment of the method of the present invention;

FIGS. 6-6F illustrate a second alternative embodiment of FIG. 3 as. well as the various stages of the present method, which stages are also carried out by, but are not specifically'shown in connection with, the apparatus of FIGS. 3 4 and SA-SB;

FIG. 7 is-a partially cross-sectioned elevation of another embodiment of apparatus usable in the present minescent compound appropriately doped. Typically, where the crystal layer 21 is an epitaxial, electroluminescent compound, the constituents of the layer 21 may be gallium and arsenic [GaAs], gallium and phosphorus [GaP] or gallium, arsenic phosphorus [GaAs,P The present invention is not, however, intended to be limited to such compounds and, in fact, contemplates the growth of any crystal whether or not epitaxial or electroluminescent, which can be grown from a solution. v

Referring now to FIG. 2, stylized apparatus is shown for effecting the prior art tipping method of growing the crystal layer 21, for example a gallium-phosphide [GaP] crystal layer, on the substrate 22 of FIGQl. The prior art utilizes a furnace 23 tiltable from side-to-side on a pivot 24. The furnace 23 is hea'table by any convenient heat source, such as the RF coils 26, as shown. Included within the furnace 23'is a graphite boat 28 having a convenient configuration.

One side of the boat 28 is provided with a substrate or seed holder 29 of vany'conventional type. The substrate or seed 22 on which it is desired to grow the crystal layer 21 is held at the bottom of the boat 28 by the holder 29. I

In use, the furnace 23 .is tilted, for example, to the left, to lower the end 28a of the boat 28.which is diametrically opposite the substrate22 and the holder 29. Into this lowered end 280 of the boat 28 are placed a solvent 30, such as a gallium solution, and a particulate solute 31, which includes the constituents of the crystal to be .grown as well asany desired dopants. If the crystal layer 21 is to comprise gallium phosphide the particular matter will include gallium phosphid particles. I

The furnace 23 is'sealed and the RF coils 26 are energized to heat the furnace 23. Heating the furnace 23 aids in the dissolution of the particulate matter 31' in the solvent 30. A sufficient excess of particulate matter 31 is included so that further heating eventually produces a saturated solution 32. Next, the furnace 23 is tilted so that the heated saturated solution 32 flows over and covers the heated substrate 22. The furnace 23 and, accordingly, the solution 32 and the substrate 22 is slowly and controllably cooled by appropriated control of the RF coils 26. Such cooling, as previously described, effects the growth, epitaxial or otherwise, of the crystal layer 21 on the substrate 22 by supersaturating the solution 32 and by precipitation of-the solute from the solution 32. v

The above-described prior art crystal growing method -.is plagued with numerous difficulties and problems which have been-previously discussed. The apparatus of the present invention described immediately below is intended to obviate and eliminate all of the difficulties and problems of the prior art.

Referring now to FIG. 3, there is shown 'novel apparatus 38 for carrying out the present process in its broadest aspects.

The apparatus. 38 includes a drum 40 located within a furnace 41 and rotatable by any convenient means (not shown), as shown by the arrow 42, on a major axis 43 thereof. The axis 43 may conveniently be generally vertically disposed. The drum 40 is heated by any convenient heating means. Such heating means may include either a heat source, such as RF coils 45 surrounding the exterior of the drum 40, or a heat source, such as RF coils 46 located within a tube 47 surrounded by the drum 40. Both heat sources 45 and 46 (and the tube 47) are generally coaxial with the major axis 43 of the drum 40.

The drum 40 is partially filled with the solvent 30 and the particulate solute 31 similar to the solvent and particulate solute used in the prior art and described above in the description of FIG. 2. Moreover, the solvent-particulate mixture 30 31 fills the drum 40 to some convenient height H,.

Placed within the drum 40 in any convenient manner is at least one substrate 22, but preferably a plurality thereof. The substrates 22 may be held in the drum 40 by J-shaped holders 50 at a minimum height H greater than the height P1,. The holders 50 may hold the substrates 22 in either of the orientations shown in FIG. 3. Specifically, the holders 50 may expose a first surface 51 of the substrates 22 by maintaining the substrates 22 against a side wall 52 of the drum 40. Alternatively, the holders 50 may expose a second surface 53 of the substrates 22 by maintaining the substrates 22 against the tube 47 or against a radial extension 54 of the tube 47. In practice both of the holder arrangements are not used at the same time and are shown in FIG. 3 only for convenience. The I substrates 22 may be vertically stacked as shown, as long as the relationship H l-I, obtains.

One of the heat sources 45 M46 is now energized depending on the orientation of the substrates 22. Specifically, the heat source 45 or 46 energized is that heat source which directly faces the exposed substrate surfaces 51 which faces toward the major axis 43 and 53. If the first substrate surface 51 is exposed, the internal heat source 46 is energized; if the second surface 53 which faces away from the major axis 43 is exposed, the external heat source 45 is energized.

. Energization of the appropriate heat source 45 or 46 heats the solvent-solute mixture 30-31 and the substrates 22. Heatingis carried out until the solvent-particulate mixture 30-31 and the substrates 22 reach an appropriatetemperature and, if necessary, until the solvent 30 is saturated with the solute 31 to produce the solution 32.

Next, the drum 40 is rotated as-shown by the arrow 42. Such rotation effects the movement of the saturated solution 32 up the side wall 52 of the drum 40 by the action of centrifugal force. The rotational speed of the drum is selected so that ultimately the solution 32 assumes a forced vortex configuration 55 shown in cross section by the dotted and dashed line. As is known forced vortices are paraboloid in cross section.

The solution 32 assumes the forced vortex configuration 55 and the substrates 22 are covered thereby, as shown, at an appropriate rotational velocity of the drum 40. While rotation of the drum 40 continues, the heat source 45 or 46 is appropriately adjusted to begin slow cooling of the solution 32 and of the substrates 22. Such cooling, as described previously, supersaturates the solution 32 to effect the growth of the crystal layer 21 on the substrates 22 FIG. 1).

After the crystal layer 21 has been grown on the substrates 22, rotation of the drum 40 is stopped. In order to prevent further crystal growth, where such is not desired, a sudden stopping is used. Such stopping eliminates the centrifugal force acting on the solution 32 and the forced vortex collapses. As such collapse occurs, the solution 32 runs down the side wall 52 of the drum 40 to the bottom thereof at the height 11,. Because H, is still less than H, all crystal growth ceases.

The above-described apparatus 38 eliminates the difficulties of the prior art crystal growing tipping processes. Specifically, the apparatus 38 permits the simple and expeditious growth of the uniformlyv good crystal layers 21 on a large number of substrates 22 in a single operation. I

The heating sources 45 and 46 should bepreferably stationary because the drum 40 rotates either within or around the energized heat sources 45 or 46 respectively, the heating of both the substrates 2 and of the solution 32 which has moved up the side wall 52 of the drum 40 is substantially equal over the entire drum 40. That is, all of the substrates 22 and all portions of the solution 32'are exposed to the heat output of all the entire periphery of the heat source 45 or 46 as the drum 40 rotates. Thus, an averaging or integration" of the heat input to the various parts of the drum 40 takes place. In other words, the temperature gradient problem of the prior art is eliminated. Moreover, due to the fact that all of thesubstrates are maintained at the same temperature, with respect to each other, the growth rate of the crystal layer 21 on each substrate 22 is the same.

A second problem of the prior art eliminated by use of the apparatus 38 relates to improperly dissolved or partially dissolved dopants and to other immundities present in the solution 32 (and in the solvent 30). As discussed previously, the improperly or partially dissolved dopants often form a skin or a scum layer which may have a density greater than or less than that of the solution 32. Moreover, other immundities in the solution 32 may also havedensities greater than or less than that of the solution 32.

, In FIGS. 6D and 6E is shown drum filled with solution 32 containing both types of immundities, that is, those arising from undissolved dopants and those arising from other immundities and are represented by particles 56a and 56b. For the purposes of discussing the behavior of the particles 56a and.56b, drum 70 of FIGS. 6D and 6E is equivalent to drum 40 of FIG. 3. The particles 56a are those particles or either type which are less dense than and, accordingly, float on the surface of the solution 32 (and of the solvent 30). The particles 56b are those particles of either type which are denser than and sink to the bottom of the solution 32 (and of the solvent 30). Upon rotation of the drum 70 as shown by the arrow 42 in FIG. 6E, the solution 32, as previously described, assumes the forced vortex configuration 55, that is, on and up the side wall 79 of the drum 70. .It has been found that the particles 56a and 56b move -to definitely locatable positions upon such rotation of the drum 40.

Specifically,.the denser particles 56b are thrown, by centrifugal action, as is well known, against the bottom of the side wall 79 of the drum 70. Depending upon the rotational velocity of the drum 70, the denser particles 56b may tend to climb the side wall 79 in a manner similar to the solution 32; however, such rotational velocity may be empirically selected to insure that these particles 56b remain at or near the bottom of the solution 32. k

The particles 56a which are less dense than the solu- I tion 32 have been found to continue to float on the solution 32 as that solution assumes the forced vortex configuration 55. The average height H,, at which such particles 56a float on the solution 32 is easily empirically determined and depends, inter alia, on such con ditions as both the relative densities of the particles 560 I and of the solution 32 andon the rotational velocity of the drum-70. It has been found that'for a given set of these conditions, the top of the forced vortex solution configuration 55, will rise to a miximum height X but particles 56a.will rise only'tothe intermediate height I-I,,; Ultimately, if the height H of the substrates 22' held by the holders 50 (as shown in FIG. '3) is selected to be greater than the'height H, and less than X, the impurities 56a do not interfere with the growth of the crystal layer 21. Also, if it is desired to permit the-flow of that portion of the solution through a passageway 73 (as shown in FIGS. 6A through 7,particularly FIGS. 6C and 6F),"the position of the passageway 73 should be at a height H, (FIGS, 6A) which is greater than the height H, but less than the height X.

Thus, the problems generated in prior art crystal growing processes by undissolved dopants or by other impurities are also obviated by the use of this invention.

Also, it has been found quite easy, using the apparatus 38 of FIG. 3, to eliminate the turbulence and convection cell problems of the prior art. Both of these problems are easily overcome due to the fact that the height I-Iof the substrates 22 may quite simply be kept at a point where the thickness of a layer of the solution 32 in the forced vortex 55 thereover is quite thinQThis thinness, as described earlier, minimizesthe d term. in the Rayleigh Number formula, thus eliminating turbulence and convection cells. It is observed that near the top ofthe paraboloid forced vortex 55, the layer of the solution 32 is quite thin.

As can thus be seen, the apparatus 38 of FIG. 3 properly effects the necessary thermal gradient while expeditiously permitting the growth on a large number of substrates of uniform crystal layers. The thermal, turbulence, concentration and convection problems of the prior artare also resolved at the same time.

Referring now to FIG. 4,. there is shown a firstalternative embodiment of the invention depicted in FIG. 3. While any convenient form of substrate holder, such as the'J-shaped holders 50 ma'y be used, a holder 57, as shown in FIG. 4 maybe preferred due to its versatility.

Specifically, the holder 57 may include the side wall 60 of the radialgextension 54 (shown in FIG. 3) of the tube-47 and the side wall 52 of thedrum 40 defining an annular substrate-receiving groove 58 therebetween. The holder 57 further comprises some convenient means, such as upper and lower annular screens 59 or other mesh-like or porous material within-the groove 58. The screens 59 prevent vertical movement of the substrates 22. within the groove 58, but permit limited movement thereof between the surface 60 of the tube 47 and the side wall 52 of the drum 40. Thus, the tube surface 60 serves as a first stop member and the drum side wall 52 serves as a second stop member. Any conventional means, such as pairs of radial members 61, positioned about midway between the screens 59, may

also be used in the groove 58 to limit movement of the favorable substrate orientation, viz., the surface 53 on substrates 22 parallel to the direction of rotation of the drum 40.

The holder 57 is especially convenient, when a single embodiment, such as the apparatus 38 of FIG. 3, is intended to be used with substrates 22 which are either less dense than or denser than the solution 32. I

Specifically, assuming centrifugal action to have already filled the groove 58 with the solution upon rotation of, the drum 40, a less dense substrate floats on the solution 32 (which passes upwardly through the screens 59) Such. floating forces the substrate 22 toward the axis 43 and against the first stop member, i.e., the surface 60 of the tube 47 to' expose the second substrate surface-53. Where'this is the case, the heat source utilized is the RF coils 45 exterior of the drum 40. Thus there is effected the previously. described which the crystal layer 21 is be to grown is at the cold end of the thermal gradient in the solution 32.

A more dense substrate 22, on the other hand, is forced by the centrifugal action away from the axis 43 and against the second stop member, i.e., the sidewall 52 of the drum 40. In this position of the substrate 22, the first surface 51 thereof is exposed.- I-Iere, the heat source 46'is used. Again the favorable substrate orientation in the thermal gradient is effected.

The substrate 22 does not, in reality, assume the position shown in FIG. 4 (nor in FIGS. 68 and 7). Rather, as indicated by the double-headed arrow 62, the substrate 22, moves against either. the first or the I second stop member 60 or 52, respectively, depending on the density thereof.

Referring now to FIGS. 5A and 58, there are shown two modifications derived from the embodiments shown in FIGS. 3 and 4 and which embody the princifurnace 41 is the heat source,which may comprise the ble from the drum 40. The inside wall 65 of the member 64 and the outside surface 60' of the extension 54' define an annular, substrate-receiving compartment 58' similar to the groove 58. The substrates 22 are held within this compartment 58' by any convenient means such as the'J-shaped holders 50, or more preferably a holder permitting the same limited substrate movement as the holder 57 of FIG. 4.

, Also asshown in FIG. SB the outside surface 60' of the extension 54 may have, rather than a regular, annular configuration, a polygonal configuration such as an octagon. In this case the apexes of the octagon contact the inside surface 65 of the member 64 to define a plurality of sector-shaped compartments 58" which confine the substrates 22 in a direction parallel to the rotation of the drum 40. Here, the J-shaped holder 50 or the holder'57 may, of course, be used to constrain the substrates 22 vertically.

The bottom of the drum 40 includes a region 66 (FIGS. A and 5B) depressed below the bottom of the extension 54'. This depressed region 66 includes a solution-containing well 67 into which either the solventsolute mixture 30-31 or the saturated solution 32 is placed. The depressed region 66 communicates with the substrate-receiving compartment 58 (or 58") via a plurality of holes 68 formed through the tongue-like member 63.

In operation, either the solvent-solute mixture 30-31 or the saturated solution 32 is placed in the well 66 and, as before, the RF coils 45 maintain the system in a hightemperature condition until the solution 32 results. Rotation of the drum 40 is initiated to cause, via centrifugal action, the solution 32 to move out across the' bottom of the depressed region 66 up through the holes 68 and into the compartment 58' or 58'. Ultimately, the substrates 22 within the compartment 58' or 58" are covered by the solution 32. The RF coils 45 are then controlled to lower the temperature slowly, thus growing the crystal layers 21 on the substrates 22 as previously described. I

When proper crystal growth has been effected, the drum 40 is stopped, the solution 32 returning to the well 67 via the holes 68.

In the modification shown in FIG. 5A is assumed that the substrates 22 are less dense than the solution 32. Accordingly, when that solution fills the compartment 58' or 58" the substrates 22 float thereon and move inwardly toward the axis 43 of the drum 40 and against the surface 60 of the extension 54', which surface 60' serves as the first stop member. Such movement exposes the second surface 53 of the substrates 22. It is on this surface 53 that the crystal layer 21 is to be grown. Moreover, as shown in FIG. 5A if the substrates 22 are less dense than the solution 32, the heat source 45 exterior of the drum 40 is used. This positions the second surface 53 of the substrates 22 at the cold end of the thermal gradient existing in the solution 32 occupying the compartment 58' or 58". The order of things 'as viewed from the drum axis 43 is: the outside surface 60' of the extension 54', the substrates 22, the second surface 53 thereof, the solution 32 within the compartment 58' or 58" which covers the second surface 53, the inside wall 65 of the member 64, and the heat source 45. As previously mentioned, this is the ideal location for the second substrate surface 53.

The modification depicted in FIG. 5C is very similar to that of FIGS. 5A and 5B with the exception that the heat source 46 located within the tube 47 is used. The reason for the use of heat source 46 is that the substrates 22 shown in FIG. 5C are denser than the solution 32. Accordingly, upon rotation of the drum 40 the solution 32 moves up through the holes 68 into the compartment 58' or 58". The denser substrates 22 move against the surface 65 of the angled member 64 exposing the first surface 51 thereof. Thus, the first surface 51 faces the heat source 46. The order of things, then, as viewed from the exterior of the drum 40 is: the surface 65 of the member 64, the substrates 22, the first exposed surface 51 thereof, the solution 32 covering the first surface 51, the outside surface of the extension 54 and the heat source 46. ,Thus, again, the ideal location of the first substrate surface 51, namely at the cold end of the thermal gradient within the solution 32, is effected.

I In the modification shown in FIGS. 5A5C any convenient form of substrate holder may be used. To iterate, such holders preferably (but not necessarily) permit generally horizontal movement of the substrates 22 either toward or away from the axis 43 of the drum 40. The holders should, however, constrain the substrates 22 in the vertical direction and also in a direction parallel with the rotational movement of the drum 40. Such a holder 57 is shown in FIG. 4 and may comprise the mesh-like members, such as the screens 59, therein depicted.

It is apparent that the modifications of FIGS. 5A and 5C could be easily combined by havingavailable for use both heat sources 45 and 46. Centrifugal action due to rotation of the drum 40 and/or the relative densities of the substrates 22 and thesolution 32 position the substrates 22 against either the first stop member (the surface 60') or the second stop member (the surface depending on the density of the substrate 22. Preknowledge of the density of' the substrates 22 then permits energizing the appropriate heat source depending upon which surface 51 or 53 of the substrates 22 will be exposed. I

Referring now to FIGS. 6A6F, there is shown a second alternative embodiment of the present invention.

Contained within the furnace 41 is the drum 40 rotatable upon its major axis 43 as shown by the arrow 42. Both types of heat sources 45 and 46 may be included depending upon the substrate density considerations above-described.

Within the drum 40 is a second drum generally coaxial therewith. The drums 40 and 70 thus define an inner region 71 and an outer annular region 72. If the tube 47 is present within the drum 70 the inner region 71 is also annular. If the tube 47 is not used, the inner region is not, of course, annular. The regions 71 and 72 intercommunicate via a plurality of passageways 73 formed through the wall of the drum 70. The passageways 73 are located at av height H, which is greater than the height H, to whichthe less dense floating impurity particles 56a rise upon rotation of the drums 40 and 70, but is no higher than (and is preferably lower than) a height X to which the solution 32 is able to rise in the forced vortex configuration 55 (FIGS. 3 and 6E). The floating." of the particles 56a was described above in the description of FIG. 3.

The substrates 22 are mounted within the outer an-' nular region 72 by any convenient means. Such mount ing means may (as in FIG. 5B) comprise sector-shaped compartments 58" or (as in FIGS. 3 and 6A) comprise the J-shaped holders 50, previously described, which may hold the substrates 22 against either the exterior wall 74 of the drum 70 (right-hand side of FIG. 6A) or the outer, interior wall 75 of the drum 40 (left-hand side of FIG. 6A). Preferably, the mounting means (as shown in FIG. 6B) comprises the type of holder 57 shown in FIG. 4. As described with reference to FIG..4'

the holder 57 permits horizontal movement of the substrates 22 but constrains the substrates 22 vertically. and in a direction parallel to the rotation of the drums 40 and 70. In this instance, if the holder 57 is used, when the outer annular region 72 is filled with the'solution 32 the substrates 22 (a) move inwardly toward the axis 43 against the wall 74 of the drum 70 if they are less dense than the solution 32 and (b) move outwardly away from the axis 43 against the wall 75 of the drum 40 if they are denser than the solution 32. Thus, the walls 74 and 75 serve, respectively, as the first and second stop surfaces.

FIGS. 6A and 6D depict the situation prior to initiationof rotation of drums 40 and 70. FIG. 6D, as mentioned previously, shows the location of immundity particles 56a and 56b prior to rotation.

FIG. 6B shows an intermediate state in the process of this invention wherein rotation of the drums 40 and 70 has been initiated and the solution 32'has deformed into an intermediate forced'vortex configuration 55 tending toward the forced vortex configuration 55 shown in FIG. 3. As shown in FIG. 6B, the immundity particles 56a and 56b assume the positions previously described. It should be noted that the height H, to which the'immundities 56a rise is below the height H, of the passages 73.

Accordingly, as shown in FIG. 6C, continued rotation of the drums 40 and 70 causes the solution 32 to rise up to the passageways 73 and to begin flowing (numeral 76) therethrough into the outer annular region 72.'Because of the location of the immundities 56a and 56b, as' shown in FIG. 6E, substantially immundity-free solution 32 passes into the outer annulai region 72.

Ultimately, as shown in FIG. 6F, the solution 32 in the outer annular region 72 is moved up the inner wall 75 of the drum 40 by centrifugal force into a second forced .vortex configuration 77. Such movement of the solution 32 covers the substrates 22 therewith. Moreover, if the type of holder 57 depicted in FIG. 4 is used, either the first or the second surface 51 or 53 (see FIG. 6B), respectively, of the substrates 22 will be.

covered by and exposed to the solution 32 within the outer annular region 72, as indicated by the arrow 62 in FIG. 63. Control of the appropriate heat source 45 or 46 to cool the system is now effective to grow the crystal layer 21 on the substrates 22.

In the embodiment ofFIGS. 3 and 5A-5C, after the crystal layer 21 had been grown, cessation of the rotation of the drum caused the solution 32 to retreat from the substrates 22. In FIG. 3 the relation H I-I, is always true; in FIGS. 5A-5C, the solution 32 returns to the well-67 via theholes 68. In FIGS. 6A-6F either ap proach may be taken. As shown in FIG. 6F the height H of the lowest substrates may be chosenso that upon the drums 40 and 70 stopping I-I I-I, where'H, is the height of the solution 32 in theouter region '72.

On the other hand, as shown in FIG. 6C another approach maybe taken. Specifically, coaxially mounted to the drum 40 is a cup 90 defining an annular solution height and need not be greater than H, in the outer region 72.

A modification of the second alternative embodiment of FIG. 6 is depicted in FIG. 7. This modification is not limited to the apparatus of FIG. 6, however, and may easily be adapted to the embodiments shown in FIGS. 3 and 5.

In the modification of FIG. 7 the substrates 22 are mounted by any appropriate holder, such as the J- shaped holder 50 (left-hand side of FIG. 7) or the holder 57 (right-hand side of FIG. 7 )within an annular chamber 77 "of a mesh-like cage 78. The cage 78 comprises a pair of coaxial mesh cylinders 80 and 81 defining the chamber and joined by amesh bottom 82. The cage bottom 82 contains a hole 83'large enough to fit over the drum 40.

The cage 78 is designed to fit into the outer annular region 72 and to rotate along with the drums 40 and by any convenient means, for example, by a key-in-slot arrangement (not shown). The substrates 22 are loaded into the chamber 77 of the cage 78 which initially resides in an upraised position as shown in FIG. 7. After such loading the cage 78 is moved downwardly by means (not shown) into the outer outer annular region 72, as shown by the arrows 84. Operation of the apparatus of FIG. 7 then proceedsasin the description of FIGS. 6A-6F. After the crystal layers 21 have been grown on the substrates 22 the cage 78 is lifted out of the outer annular region 72, the substrates 22 being easily transported without being contaminated within thecage78. Where the holder 57 is used, the walls of the cylinders and 81 serve, respectively, as the first and second stop members. l

The cage 78 may, accordingly, be viewed either as a handling expedient, as an alternative to, the passageway-valve-receptacle 92-93-91 arrangement of FIG. 6C (upward movement of the cage 78 may terminate crystal layer growth notwithstanding the relation ofH to IL), or both.

Thus, there has been described a method, and apparatus for effecting that method, which method permits the convenient growth of crystal layers of any type from a solution on'one or on a plurality of substrates simultaneously while eliminating all of the difficulties of prior art processes and apparatus. It should be noted that the above-described embodiments of this crystal growing-method are simplyillustrative of the principles of the present invention. Numerous other arrangements and modifications may be devised'by one skilled in the art without departing from the spirit and scope of this invention. For example, the forced vortex 55 may be generated by an impeller arrangement (not shown) within and generally coaxial with either of the drums 40 and 70. Such impeller arrangement may be similar to the impeller of a centrifugal pumpor of a conventional cream separator. 1

Moreover, it is not necessary that the forced vortex 55 be generated simultaneously with the cooling of the saturated solution 32. Specifically, as described previously, if the saturated solution 32 is cooled to the point of super-saturation without the substrate or seed being present, solid, particulate crystalline matter randomly precipitates therein. If the seed or substrate 22 is present in the solution 32 at supersaturation, the crystal layer 21 is grown thereon. Many saturated solutions 32 have been'found to possess a property whereby the temperature at which random precipitation occurs is lower than the temperature at which the controlled growth of the crystal layer 2l occurs. Accordingly, the present invention may be used in the following manner: The particulate solute 31 is dissolved in the solvent 30 at an elevated temperature to produce the saturated solution 32. The saturated solution 32 is then cooled to a point where supersaturation occurs but the random precipitation does not occur. The substrate 22 is next placed in the drum 40 and is maintained at a temperature at which crystal growth thereon will take place. The forced vortex configuration 55 may now be imposed on the supersaturated solution so that the substrate 22 is at least momentarily covered thereby.

Growth of the crystal layer 21 occurs.

In order that those skilled in the art may more fully understand the inventive concept herein present, the following examples are given by way of illustration and not limitation.

EXAMPLE I Apparatus similar to that illustrated in FIG. 5A was employed. The apparatus comprised an ultra-pure graphite drum 40 and an ultra-pure graphite tube 47. A suitable p-type doped GaP substrate 22, grown by standard liquid encapsulated pulling techniques and cut to size, was selected. Thesubstrate 22 was placed within a substrate-receiving compartment 58 of the apparatus, defined by the inside wall 65 of member 64 and the outside surface 60' of extension 54' of the tube 47 A gallium GaP Ga O Zn mixture 30-31 was prepared by weighing out 0.931 mole of high purity gallium, 0.0015 mole of zinc, 0.0035 mole of Ga o and 0.064 mole GaP. The resultant mixture 30-31 was placed in a well 67 of region 66 of the apparatus. The amount of Ga? present in the mixture 30-31 was such as to give a GaP saturated gallium solution doped with oxygen and zinc at a temperature of l050 C. An ambientatmosphere of argon was maintained within drum 40 and furnace 41 of the apparatus and the furnace 41 was heated, by means of RF coils 45, to the temperature of 1050" C, thereby forming the Gal saturated gallium solution 32.

When the temperature of,l050 C was reached, the drum 40 was rotated, by conventional means, at a rate of 750 to 850 revolutions/minute. The rotation of the drum 40 caused, via centrifugal force, or action, the solution 32 to move into compartment 58 and cover the substrate 22. Crystal growth was then initiated by lowering the temperature ata rate of 100 C/minute. Upon reaching a temperature at 700 C the spinning was stopped, thereby terminating the crystal growth. Theapparatus was cooled to room temperature and the substrate 22 was removed. I

An epitaxial layer having a thickness of about lp.m was obtained. The thickness uniformity obtained was 18 good, as evidenced by a Taly-Surf measured central line average of0.5p.m.

EXAMPLE II The procedure of Example I was repeated except that the rotation was at a rate of 850 to 950 revolutions/minute, and the rotation was terminated at a temperature of 750 C. An epitaxial layer of about p.m was obtained having a central line average of l.0p.m.

What is claimed is: 1. In a method of growing a crystal layer on a substrate from a liquid body rich in the constituents of the layer, which method includes at least a step of contacting the substrate with the liquid, the improvement comprising:

' configurating the liquid body in a forced vortex to effeet the contacting where the distance between the substrate and the free surface of said forced vortex is such that the Rayleigh Number is less than about 1700. I

.2. In a method of growing a crystal layer on a selected portion of a substrate from a liquid body rich in the constituents of the layer the improvement comprising:

configurating the liquid body in a forced vortex; and

contacting the selected substrate portion with said forced vortex, the distance between the substrate portion and the free surface of said forced vortex during said contacting being such that the Rayleigh Number is less than about 1700.

3. The method of claim 2 which includes the further step of: I

positioning the substrate in a container and wherein said configurating step includes,

placing the liquid body in said container,.and

rotating the container.

4. The method ofvclaim 3 wherein during said contacting step the rotational velocity of said container during said contact is a velocity at which the distance between the selected substrate portion and the free surface of said forced vortex is such that the Rayleigh Number within said distance is less than about 1700.

' 5. The method of claim 4 wherein said contacting step iseffected as a consequence of the effectuationof said configurating step.

6. In a method of growing a crystal layer on at least a portion of a selected surface of a substrate in a container from a solution rich in a solute of the crystals constituents wherein (i) a solvent in the container out of contact with the substrate is saturated at anelevated temperature with the solute to produce the solution, (ii) the selected substrate surface is contacted with the solution, and (iii) the solution is cooled to a supersaturated condition, the improvement comprising:

imposing on the solution a forced vortex configuration which contacts the selected substrate surface portion to effect step (ii), the distance between the portion of the selected surface and the free surface of said forced vortex during step (ii) being such that the Rayleigh Number is less than about 1700. 7. The method of claim 6 wherein said forced vortex is imposed on the solution by rotating the container.

8. The method of claim 7 wherein the rotational velocity of the container during said contact is a velocityat which the distance between the selected substrate surface portion and the free surface of said forced solution vortex, measured generally perpendicular to said selected substrate surface is such that the Rayleigh Number with said distance is less than about 1700.

9. In a method of growing a crystal layer on a selected surface of a substrate in a container from a solution rich in a solute of the crystals constituents wherein (i) a solvent in the containerout of contact with the substrate is saturated at an elevated temperature with the solute to produce the solution, (ii) the selected substrate surface is contacted with the solution, and (iii) the solution is cooled to a supersaturated condition, the improvement comprising:

generating a forced vortex of the solution, which solution vortex covers the selected substrate surface to effect step (ii), the distance between the selected substrate surface and thefree surface of said forced vortex during step (ii) being such that the Rayleigh Number is less than about 1700.

10. The method of claim 9 wherein said forced vor tex is generated by rotating'the container.

11. The method of claim 10 wherein the rotational velocity of the container during said contact is a velocity at which the distance between the selected substrate surface and the free surface of said forced solution vortex, measured generally perpendicular to said selected substrate surface is such that the Rayleigh Number within said distance is less than about 1700.

12. In a method of growing a crystal layer on a substrate in a container. from a solution rich in a solute of the crystals constituents wherein (i) a solvent in the container out of contact with the substrate is saturated at an elevated temperature with the solute to produce the solution, (ii) the substrate is contacted by the solution, and (iii) the solution is cooled until supersaturation occurs, the improvement comprising:

rotating the container on a symmetrical axis thereof until the solution is moved in a forced vortex which contacts the substrate in such a manner that the distance between the substrate and the free surface of said forced vortex during step (ii) leads to a Rayleigh Number which is less than about t 1700. 13. The method of claim 12 wherein step (iii) is effected after step (ii).

14. The method of claim fected before step (ii).

15. The method of claim 12 wherein steps (ii) and (iii) are effected simultaneously.

16. The methodo'f claim 12 which the step of;

effecting relative movement between-said forced 12 wherein step (iii) is effurther includes solution vortex and the substrate for terminating the contact therebetwee'n to terminate the growth of the crystal layer. l7. The'method ,of claim movement is effected by:

stopping said container rotation for effecting the collapse of said forced vortex.

18. The method of claim 12 wherein: said container is drum-like and, rotatable on said axis which is generally vertical and includes a side wall generally coaxial with said axis, and wherein said rotation is effected generally horizontally about said axis.

16 wherein said relative 19. The method of claim 18 wherein the rotationalvelocity of said drum-like container during said contact is a velocity at which the distance between the substrate and the free surface of said forced vortex is such that the Rayleigh Number is less than about 1700.

20. The method of claim 19 wherein the solution contains immundities having densities greater than or less than the solution and wherein the rotational velocity of said drum-like container during said contact is a velocity at which the denser immundities remain at the bottom of the container and the less dense immundities float on said forced vortex out of contact with the substrate.

21. The method of claim 18 wherein the solution contains immundities having densities greater than or less than the solution and wherein the rotational velocity of said drum-like container during said contact is a velocity at which the denser immundities remain at the bottom of the container and the less dense immundities float on said forced vortex out of contact with the substrate.

22. The method of claim 18 which further includes the step of:

positioning the substrate within said drum-like container to be constrained against vertical movement and radially movable horizontally toward and away from said axis between a first and a second stop member, respectively.

23. The method of claim '22 in which the substrate is less dense than the solution and effectuation of the rotating step further includes:

contacting the substrate with the solution to move the substrate toward said axis and against said first stop member to expose a first surface thereof facing away from said axis and to impinge the solution on said first surface.

24. The method of clairn'23which further includes the step of i surrounding the exterior of said drum-like container with a first source of heat flux generally coaxial with said axis to orient said first surface at the cold end of the thermal gradient within the solution between sad first heat flux source and said first surface.

25. The rnethod of claim 22 in which the substrate is denser than the solution and effectuation of the rotating step further includes contacting the substrate with the solution to move the substrate away from said axis and against said second stop member to expose'a second surface thereof facing toward said axis and to impinge the solution on said second surface.

26. The method of claim 25 which further includes the step of:

surrounding a second source of heat flux with said drum-like container, said second heat flux source being generally coaxial with said axis tolorient said second surface at the cold end of the thermal gradient within the solution between said second heat flux source'and said second surface.

27. In a method of growing a crystal layer on a substrate from a heated, saturated solution rich in a solute made up of the crystals constituents, which method includes contacting the substrate with the solution, the solution including immundities having densities greater than or less than the solution, the improvement comprising: i

a. placing the solution in an inner, fluid-receiving region of a drum rotatable on a major axis, the drum further including an outer annular region, both regions including side walls generally coaxial with said axis and interconnected at a position above the level of the solution within said inner region;

. positioning at least one substrate within said outer annular region;

c. rotating said drum until centrifugal action moves the solution in a first forced vortex up said side wall of said inner region, through said interconnection, and into said outer annular region, to contact the substrate with a second forced solution vortex, such that the distance of the substrate and the free surface of said second forced solution vortex dur-' ing said contacting is one whereby the Rayleigh Number is less than about 1700, the denser immundities remaining at the bottom of the solution in said inner region, the less dense immundities floating on said first forced solution vortex at a level below said. interconnection; and d. cooling the solution to effect growth of the crystal layer on the substrate by supersaturating the solution. 28. The method of claim 27 wherein step (b) includes: I

positioning the substrate within said outer annular region so'that the substrate is constrained against vertical movement and is radially movable horizontally toward and away from said axis between a firstand a second stop member, respectively. 29. The method of claim 28 in which the substrate is less dense than the solution and effectuation of step (c) further includes:

contacting the substrate with the solution to move the substrate toward said axis and against said first stop member to expose a first surface thereof fac- -ing away from said axis and to impinge the solution of said second forced vortex on said first surface. 30. The method of claim 29 which further includes the step of: v

surrounding the exterior of said drum with a first source of heat flux generally coaxial with said axis to orient said first surface at the cold end of the thermal gradient within said second forced solution vortex between said first heat source and said first surface. p 31. The method of claim 28 in which the substrate is denser than the solution and effectuation of step (c) further includes:

contacting the substrate with the solution to move the substrate away from said axis and against said second stop member to expose a second surface thereof facing toward said axis and to impinge the solution of said second forced vortex on said second surface. 32. The method of claim 31 which further includes the step of:

surrounding a second source of heat flux with said drum, said second. heat source being generally coaxial with said axis, to orient said second surface at the cold end of the thermal gradient within said I second forced solution vortex between said second heat source and second surface.

selected surface ofthe substrate in a container from a supersaturated solution containing the constituents of the layer, the improvement comprising:

forming the solution by centrifugal force into a forced vortex having an-immundity-free substrate contacting layer. I

35. A method of growing a crystal layer on a selected portion of a substrate from a liquid body, rich in the constituents of the layer, the improvement comprising:

configurating the liquid body in a forced vortex, and contacting theselected substrate portion with said forced vortex such that any immundities present in the liquid body lie without a region bounded by the distance between the selected substrate portion and said forced vortex. i 36. The method of claim 35 which includes the further step of:

positioning the substrate in' a container and wherein said configurating step includes: placing the liquid body in saidcontainer, and rotating the container. A 37. The method of claim 36 wherein during said contacting step the rotational velocity of said container during said contact is a velocity at which the distance between the selected substrate portion and the free surface of said forced vortex is such that'the Rayleigh Number within said distance is less than about 1700.

38. The method of claim 37 wherein said contacting step is effected as a consequence of the effectuation of said configurating step.

39. in a method of growing a crystal layer'on at least a portion of a selected surfaceof a substrate in a container from a solution rich in a solute of the crystals constituents wherein (i) a solvent in the container out of contact with the substrate is saturated at an elevated temperature with the solute to produce the solution, (ii) the selected substrate surface is contacted'with the solution, and (iii) the solution is cooled to a supersaturated condition, the improvement comprising:

imposing on the solution a forced vortex configuration which contacts the-selected substrate surface portion to effect step (ii) in such a manner that any immundities contained in the solution lie without a region bounded by the distance between the selected surface and the free surface of said forced vortex. 40. The method of claim 39 wherein said forced vortex is imposed on the solution by rotating the container. 41. The method of claim-40 wherein the rotational velocity of the container during said contact is a velocity at which the distance between the selected substrate surface portion and the free surface of said forced solution vortex, measured generallyperpendicuselected substrate surface is contacted with the solu-' tion, and (iii) the solution is cooled to a supersaturated condition, the improvement comprising:

generating a forced vortex of the solution to cover the selected substrate surface therewith to effect step (ii) in such a manner that any immundities contained in the solution lie without a region bounded by the distance between the selected substrate surface and the free surface of said forced vortex.

43. The method of claim 42 wherein said forced vortex is generated by rotating the container.

44. The method of claim 43 wherein the rotational velocity of the container during said contact is a velocity at which the distance between the selected substrate surface and the freesurface of said forced solution vortex, measured generally perpendicular to said selected substrate surface is such that the Rayleigh Number without said distance is less than about 1700.

45.ln a method of growing a crystal layer on a substrate in a container from a solution rich in a solute of the crystals constituents wherein (i) a solvent in the container out of contactwith the substrate is saturated at an elevated temperature with the solute to produce the solution, (ii) the substrate is contacted by the solution, and (iii) the'solution is cooled until supersaturation occurs, the improvement comprising:

rotating the container on a symmetrical axis thereof at a sufficient rotational velocity to (1) move the solution in a forced vortex which contacts the substrate to effect step (ii), (2) effect retention atthe bottom of the containerof any immundities having a density greater than the solution and (3) effect a floating on said forced vortex out of contact with the substrate of any immundities having a density less than the solution.

v46. The method .of claim 45 wherein step (iii) is effected after step (ii). 5

. 47,Th'e method of claim .45 wherein step (iii) is ef fected before step (ii).

48. The method of claim '45 wherein step (ii) and (iii) are effected simultaneously.

49. The method-of claim 45-which further includes the step of:

effecting relative movement between said forced solution vortex and the substrate for terminating the contact therebetween to terminate the growth of the crystal layer.

50. The method of claim 49 wherein said relative movement is effected by: n

stopping said container rotation for effecting the lapse of said forced vortex. I

5 L-The method of claim"45 wherein:

said container is drum-like and rotatableon said axis which is generally vertical and includes a side wall generally coaxial with said axis, and wherein col- ' the container, of:

said rotation is effected generally horizontally about said axis.

52. The method of claim 51 wherein the rotational velocity of said drum-like container during said contact is a velocity at which the distance between the substrate and the free surface of said forced vortex is such that the Rayleigh Number is less than about 1700.

53.. The method of claim 51 which further includes the step-of:

' positioning the substrate within said drum-like container to be constrained against vertical movement and radially movable effectuation toward and away from said axis between a first and a second stop member, respectively.

54. The method of claim 53 in which the substrate is less dense than the solution and effectutation of the rotating step further includes:

contacting the substrate with the solution to move the substrate toward said axis and against said first stop member to expose a first surface thereof facing away from said axis and to impinge the solution on said firstsurface.

55. The method of claim 54 which further includes the step of:

surrounding the exterior of said drum-like container with a first source of heat flux generally coaxial with said axis to orient said first surface at the cold end of the thermal gradient within the solution between said first heat flux source and said first surface.

56. The method of claim 53 in which the substrate is denser than the solution and effectuation of the rotating step further includes:

contacting the substrate with the solution to move the substrate away from said axis and against said second stop member to expose a second surface thereof facing toward said axis and to impinge the solution on said second surface.

57. The method of claim 56 which further includes surrounding a second source of heat flux with said drum-like container said second heat flux source being generally coaxial with said axis to orient said second surface at the cold end of the thermal gradient within thesolution between said second heat flux source and said second surface.

58. In a method of growing a crystal layer on a substrate from a heated, saturated solution rich in a solute made up of the crystals constituents,which method includes contacting the substrate withthe solution, the solution including immundities having densities greater than or less than the solution, the improvement comprising: v

a. placing the solution in an inner, fluid-receiving region of a drum rotatable on a major axis, the drum further including an outer annular region, both regions including side walls generally coaxial with said axis and interconnected at a position above the level of the solution within said innerregion; positioning at least one substrate within said outer annular region; rotatingsaid drum until centrifugal action moves the solution in a first forced vortex up said side wall of said inner region, through said interconnection, and into said outer annular region, to contact the substrate with a second forced solution vortex, the denser immundities remaining at the bottom of the solution in said inner region, the less dense immundities floating on said first forced solution vortex at a level below said interconnection; and d. cooling the solution to effect growth of the crystal layer on the substrate by supersaturating the solution. I 59. The method of claim 58 wherein step (b) includes:

positioning the substrate within said outer annular region so that the substrate is constrained against vertical movement and is radially movable horizontally toward and away from said axis between a first and a second stop member, respectively. 60. The method of claim 59 in which the substrate is less densethan the solution and effectuation of step further includes:

contacting the substrate with the solution to move the substrate toward said axis and against said first stop member to expose a first surface thereof facing away from said axis and to impinge the solution of said second forced vortex'on said first surface. 61. The method of claim 60 which further includes the step of:

surrounding the exterior of said drum with a first source of heat flux generally coaxial with said axis to orient said first surface at the cold end of the thermal gradient within said second forced solution vortex between said first heat source and said first surface. r 62. The method of claim 59 in which the substrate is denser than the solution and effectuation of step (c) further includes:

contacting the substrate with the solution to move the substrate away from said axis and against said second stop member to expose a second surface thereof facing toward said axis and to impinge the solution of said second forced vortex on said second surface. 63. The method of claim 62 which further includes the step of:

surrounding a second source of heat flux with said drum, said second heat source being generally coaxial with said axis, to orient said second surface at the cold end of the thermal gradient within said second forced solution vortex between said second heat source and said second surface.

' I Eli

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Referenced by
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US3957547 *Apr 8, 1974May 18, 1976Beckman Instruments G.M.B.H.Method for doping semiconductors in centrifuge
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Classifications
U.S. Classification117/64, 117/67, 148/DIG.600, 148/105, 148/DIG.107, 117/953, 427/240, 117/54, 117/956, 117/955, 118/52, 117/954
International ClassificationH01L21/00, C30B19/06
Cooperative ClassificationC30B19/066, Y10S148/107, Y10S148/006, H01L21/00
European ClassificationH01L21/00, C30B19/06K
Legal Events
DateCodeEventDescription
Mar 19, 1984ASAssignment
Owner name: AT & T TECHNOLOGIES, INC.,
Free format text: CHANGE OF NAME;ASSIGNOR:WESTERN ELECTRIC COMPANY, INCORPORATED;REEL/FRAME:004251/0868
Effective date: 19831229