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Publication numberUS2858730 A
Publication typeGrant
Publication dateNov 4, 1958
Filing dateDec 30, 1955
Priority dateDec 30, 1955
Also published asDE1165163B
Publication numberUS 2858730 A, US 2858730A, US-A-2858730, US2858730 A, US2858730A
InventorsJames S Hanson
Original AssigneeIbm
Export CitationBiBTeX, EndNote, RefMan
External Links: USPTO, USPTO Assignment, Espacenet
Germanium crystallographic orientation
US 2858730 A
Abstract  available in
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Claims  available in
Description  (OCR text may contain errors)

1953 J. 5. HANSON 2,858,730

J GERMANIUM CRYSTALLOGRAPHIC ORIENTATIQN I Filed Dec. 50, 1955 5 Sheets-Sheet 1 FIG.1

/ U ms INVENTOR.

' Y JAMES s. HANSON AGENT Nov. 4, 1958 J. S. HANSON GERMANIUM CRYSTALLOGRAPHIC ORIENTATION Filed Dec. 30, 1955 3 Sheets-Sheet 2 N aw N T A NH ws ms E M A J AGENT Nov. 4,,1958 J. 5. HANSON 2,858,730

GERNANIUM CRYSTALLOGRAPHIC ORIENTATION Filed Dec. =30, i955 s Sheets-Sheet s 'FIG.'4"

22 21 mvsmoa I JAMES s. HANSON AG-ENTH United States Patent This invention relates to semiconductor technology and in particular to a method of orienting a monocrystalline ingot of germanium so that it may be cut parallel to a particular crystallographic plane.

In the art of manufacturing semiconductor devices such as diodes and transistors, it is standard practice to form the bodies of these devices from portions of a large monocrystalline semiconductor ingot. The portions of the large ingot are cut into small wafer-shaped dice and appropriate electrodes are applied to certain surfaces of the dice. The crystallographic structure of the monocrystalline semiconductor material is similar to that of the diamond and is known as a body centered cubic structure. It has recently developed in the art that a number of advantages in performance of semiconductor devices can be realized if the dicing of the monocrystalline ingotinto wafers is performed so that a particular crystallographicplane of the body centered cubic structure is parallel to the major surfaces of the die. In the case of transistors, semiconductor wafers cut parallel to the [111] crystallographic plane have been found togive superior performance. To provide such crystallographic orientation in semiconductor devices it is necessary to very accurately establish a crystallographic orientation of the ingot from which the wafers are cut. are grown under agitation and because most seed crystals from which the ingots are grown are of uncertain orientation accuracy, if the orientation is known at all, it is difficult to find a reference plane with respect to the ingot so that cuts that are accurately parallel to a particular crystallographic plane may be made.

This invention is directed to a novel method of optically orienting a monocrystalline germanium ingot so that a particular crystallographic axis of the ingot will coincide with reference surfaces of the base on which the-ingot will eventually be mounted. Then the ingot is so'mounted with respect, for example, to the [111] crystallographic axis, cuts made normal to these reference surfaces will produce germanium wafers having a [111] crystallographic plane of the cubic structure parallel to the major faces of the wafer, and once the orientation is established the ingot may be cut parallel to any desired crystallographic plane by cutting the ingot at the proper angles with respect to the reference surfaces.

Accordingly, a primary object of this invention is to provide an optical means of orienting a monocrystalline ingot so as to establish the location of a particular crystallographic plane within the ingot.

Another object is to provide a means of orienting a monocrystalline ingot so as to establish the location of a [111] crystallographic plane.

Another object is to provide a means of mounting the monocrystalline ingot for dicing normal to a particular axis of the crystal structure.

A related object is a method of determining the error angle made by a cut crystal surface with respect to a particular crystollagraphic plane.

Another related object is to provide a method of form- 2,858,730 Patented Nov. 4, 1958 Other objects of the invention will be pointed out in the following description and claims and illustrated in the accompanying drawings, which disclose, by way of example, the principle of the invention and the best mode, which has been contemplated, of applying that principle.

' In the drawings: I

Figure 1 is a view of an octahedron crystalline structure having two of its [111] faces corresponding to the X2 plane.

Figure 2 shows a monocrystalline germanium ingot showing the [111] plane flats and serrations.

' Figure 3 is a view of the monocrystalline ingot mounted in an orienting fixture.

Figure 4 is a technique of orientation using a narrow beam of sunlight.

- Figure 5 is another technique of orientation showing collirnated artificial light.

Since the germanium ingots Figure 6 is a view of the oriented crystal mounted for' cutting into wafers.

It has been discovered as a germanium crystal grows into a large monocrystalline ingot, the ingot tends to grow in the form of an octahedron having flat areas on its surface that are parallel to the [111] crystallographic plane.

However, due to the many disturbances that can occur at freezing interface as the monocrystalline ingot grows the true octahedron shape is seldom readily observed in an ingot. Thus in order to establish an accurate reference so that an ingot may be cut parallel to a particular crystallographic plane it is necessary in the method of this invention to position the ingot so that its [111] axis or its [100] axis coincides with the [111] axis or [100] axis of the octahedron. The manner in which this is done and the reasons for the method employed will be brought out in the following description.

Considering first the [111] axis and referring to Fig-. I ure 1, an octahedron is shown that corresponds to the ultimate shape that is approached by the ingot. It is to be noted that all faces of the octahedron in this position are parallel to the [1111 faces of the cubic structure and that two of these faces correspond to the XZ plane.

, Thus flie Y axis is normal to these two faces and has ing a body for a semiconductor device having a selected been labeled the [111] axis. The term [111] axis is then used to designate an axis through the octahedron that is normal to the [111] crystallographic plane. It may now be seen that if the ingot is so oriented that its [111] axis is normal to the cutting plane, then from the geometry shown in Figure 1, cuts made in the germanium crystal ingot from the axis will then be parallel to" the [111] plane as represented by the [111] faces of the octahedron in Figure 1 that correspond to the XZ plane. In order to do this to a high degree of accuracy it is necessary to establish the location of the [111] axis of the'c'ry'stalline ingot. This is done in this method by reflecting a light from three equally spaced optically reflective areas located on the surface of one end of the ingot.

The octahedron of Figure 1 has corners labeled A, B, C, D, E 'and F. All surfaces correspond to [111] crystallographic plane surfaces and the planes represented by quadrilaterals ABDE, ACEF, and BCDF correspond to what is known in the art as the crystallographic plane.

Referring again to Figure 1, there is a first group of three [111]-plane surfaces of the octahedron labeled ACD, ABF, and BOB-respectively, each forming the same acute angle with respect to the [111] axis and each intersecting this axis at the same point. This angle in practice hasbeen found to be on the order of 19 /2 and is labeled in the figure-as alpha (or); Similarly, there is a second group of three [111]-plane surfaces ofthe octahedron rotated 60 about the Y or '[111] axis from the first group and labeled CDE, BEF, and ADF; each plane forming the same acute angle with the [111] axis as the first group but at a different point from the first group as shown. These angles are labeled a. Angles a and a are equal. The remaining two planes of the octahedron that are parallel to the X2 plane are ABC and DEF. By virtue of the fact that all three planes of each of these groups intersect the [111] axis at the same angle, a light beam from a single source will be reflected to the same position from each of the three planes of a single group if the octahedron is rotated about the [111] axis. Then, since the crystal ingot tends to grow in an octahedron shape it is possible to establish on the surface of the ingot three properly spaced optically reflective areas corresponding to either of the groups of planes ACD, ABF, and BCE, or CDE, BEF, and ADF.

Referring now to Figure 2 a pictorial view is presented of a typical germanium ingot. This ingot has been grown by the technique known as Crystal Pulling that is standard practice in the art. However, the method of this invention, as will be apparent from the following discussion, is not limited to ingots grown by a particular method since the octahedron shape is a property of the crystallographic structure and not of the method of growing. The ingot 1 of Figure 2 has a body 2 of monocrystalline germanium that was grown from a seed crystal 3 provided with reference surfaces 4 and 5 which will be described in detail later. On most ingots areas termed ingot flats 6 are found. A group of flats found near the seed 3 end of the ingot corresponds to the first group of [111] planes ACD, ABF, and BCE of the octahedron. The flats are spaced approximately 120 apart around the ingot. Another group of flats at the opposite end of the ingot corresponds to the second group of [111] planes CDE, BEF, and ADF. The flats on the seed 3 end of the ingot are rotated 60 around the ingot from those on the opposite end. The tendency to form flats varies tremendously from ingot to ingot; some ingots are decidedly triangular or square depending on the crystallographic orientation of the seed, while others are almost perfect solids of revolution with only microscopic traces of flats. A close inspection of these flats reveals that they are made up of a multitude of steps, similar to a flight of stairs with the stair treads representing fairly flat reflecting surfaces or facets parallel to a [111] plane. These steps are labeled 7 in Figure 2. From the foregoing, an ingot flat may consist of anywhere from one or two to several hundred facets, depending on the many disturbances that can occur at the liquidus-solidus interface during freezing of the ingot from the melt. Thus, it can be seen that cylindrical and octahedron shapes form the two extremes in grown monocrystalline ingots.

On an ingot in which all of the flats 6 of a particular group are present the facets of these areas may serve as optically reflective areas as described above. In a few ingots, some or even all of these flats 6 may be missing. In such cases it is necessary to establish by artificial means the desired three optically reflective areas corresponding to one of the groups of planes of Figure 1. Where one or two of the necessary three flats 6 of Figure 2 are missing, the remaining flat or flats can serve as'a guide to locate those that are missing. The missing areas can be synthesized by abrading, lapping, or similar means. It has been found that crystal ingots tend to exhibit facets on the surfaces of the above described flats 6 as indicated by the reference numeral 7 in Figure 2 and that these facets are parallel to the [111] crystallographic plane. In general these facets are of more than suflicient reflective quality to serve as an optically reflective area in the desired location. The manner of properly synthesizing spaced areas with sufficient optical reflectivity where natural flats 6 are missing will be described in detail below. The worst case would occur when there were no flats 6 at allon the crystal ingot and there were no facets of sufl'icient quality to be useable. In this case, the three flats 6 would have to be established by abrading in connection with an etching step to be described below. Some trial and error will be necessary to locate the required three properly spaced facets corresponding to a particular group of planes but from the knowledge of their general location as shown in Figure 1, namely 120 spacing rotated 60 from the second group of planes, the required facets may be located.

There are a group of etching reagents known in the art that are preferential to exposing the [111] crystallographic plane. Some of these reagents are discussed in an article by Ray C. Ellis, Jr., Etching of single crystal germanium spheres-Journal of Applied Physics, vol. 25, No. 12, December 1954, pages 1497-1499. The combination known as Superoxol (20'parts by volume H Odistilled; 5 parts by volume HFconcentrated; and 5 parts by volume H O 37% concentrated) is a member of this group. It has been found that a flat abraded area of an ingot when etched will exhibit triangular etch pits when viewed under a microscope if the area roughly coincides with the [111] crystallographic plane and that the etch pits will be rectangular if the area roughly coincides with the crystallographic plane. These reagents are useful in determining whether or not an area is a [111] plane, and in connection with reflected light whether an area corresponds to a member of a certain group of planes, and in improving the optical quality of an area. Thus, each area selected or provided as one of the required group of three areas is etched to establish that it is a [111] plane, that it is a member of the proper group of planes, and to give it satisfactory optical quality. The preferential etch by its nature creates etch pit surfaces that are parallel to a [111] crystallographic plane. As may be seen from Figure 1, if the etched area is not a member of the same group of planes, the angle of reflection of a light source will be so different from the angle of reflection of the other planes in the group that no reflection will be observed at the place in which the reflected light would normally fall. The optical quality of a particular area for the purposes of this method is indicated by the quantity of directly reflected light from the area in relation to the quantity of randomly reflected or diffused light from the area. Since this method relies for its accuracy on a comparison of the position of a spot of light reflected from each of the three areas the more light that is reflected and the more sharply defined and more concentrated the spot into which that light is focused, the greater will be the accuracy of the method. An area is of satisfactory optical quality for this method when the light reflected from the area forms a spot which can be easily distinguished from the background reflected diffused light.

The ingot having the three required optically reflecting areas established is now positioned in a suitable fixture so that the ingot may be adjusted for rotation about its [111] axis. An example of such a fixture is shown in Figure 3 wherein the crystal 1 has a shaft 8 affixed to one end as through the use of a sealing wax or similar cement. The shaft 8 is supported in a cylinder 9 by two sets of three screws each, respectively sets 10 and 11.

The cylinder 9 rests in a pair of V-shaped supports 12- and 13 so that it is free to rotate about its geometric axis. The purpose of this fixture is to permit the [111] axis of the ingot to be shifted to coincide with the rotational axis of the cylinder 9. This is accomplished by adjusting the two sets of screws 10 and 11.

In order to determine when the ingot is adjusted in the fixture so that it rotates on the [111] axis use is made of the fact that the three [111] plane surfaces of one group of faces on the octahedron of Figure 1 all form the same angle or. with the [111] axis. Since the ingot tends to grow as an octahedron and since facets of the three areas have been established on the surface of the ingot corresponding to these planes, then if, when the ingot is rotated, the'light from a single source is reflected from the facets of each of these three areas to the same position, the ingot will be rotating about the [111] axis. Two methods of providing this light are shown in Figures 4 and 5. In both instances an eifort has been made to provide collimated light so as to make the reflected light spot more pronounced. In Figure 4, the sun, being at almost infinite distance provides the parallel light beam. In Figure 5 an artificial light source isrrestricted by apertures to produce the parallel beam. So long as the reflected spot is distinguishable from the background light the'method is operable, but for accuracy a small intense spot reflected to a target at the longest practical distance is best.

Referring now to Figure 4, the ingot 1 is shown mounted in the fixture as in Figure 3. A target 14 is mounted at a suitable distance from the crystal. Six feet has been found to be a very satisfactory distance from target to ingot for crystallographic orientation within i0.5 tolrance. The crystal and its fixture are mounted in such a manner that sun light or light from some other suitably collimated source is reflected from a mirror 15 to one of the required three areas on the crystal and is further reflected to the target 14. The crystal is then turned by rotating the cylinder 9 through approximately 120 to bring the next flat area into position for reflection. The position of the reflected sun light on the target will be an indication of the amount and the direction in which the [111] axis of the crystal must be tilted to bring it into parallel with the rotational axis of the cylinder 9. Adjustment of the two sets of screws 10 and 11 will accomplish this movement. -The crystal is again rotated to the third flat area and the position of the reflected light on the target is again observed and proper adjustment of the crystallographic axis of .the ingot is again made. This is continued until a reflected light spot from each of the three flat areas passes in turn through the same point on the target as the cylinder 9 is rotated.

It has been found that the smaller the flat area, the greater the distance from the crystal to the target, and the more parallel the light beam, the greater the accuracy will be.

Referring now to Figure 5, a technique is shown whereby the artificial collimated light beam is provided. In the technique of Figure 5 a light 16 is provided shining through a small aperture 17 such as a hole in, a piece of cardboard onto a mirror 18. The light is reflected from the mirror 18,.through a second aperture 19, to the flat areas of the ingot 1, back through the aperture 19, to an observer 20 looking through a pin hole in the silver of the mirror 18. It has been found if the light 16 is located around 5 to feet from the crystal 1, although once again greater distances provide greater accuracy, and the aperture 19 is located approximately one foot from the crystal, results at least comparable to the sun light method described above will be acquired.

Having oriented the crystal so that its [111] axis is parallel to the axis of rotation, the crystal now may be mounted in a suitable fixture for cutting, if cutting is desired. This may be seen in Figure 6 wherein the cylinder 9 is mounted at the intersection of two sets of parallel blocks 21 and 22, and 23 and 24. The crystal 1 is mounted as through the use of sealing wax or a suitable cement to a supporting surface so that saw 25 may now cut the ingot 1 at right angles to the axis of the cylinder 9 and since the cylinder axis now coincides with V the [111] axis of the ingot, the germanium wafers so obtained will have a [111] crystallographic plane parallel to the major face of the wafer.

Wafers may also be cut parallel to other desired crystallographic planes provided the ingot is rotationally positioned about its [111] axis with respect to the fixture reference surfaces so that a [111] facet on the ingot corresponding to a particular one of a group of planes of the octahedron of Figure 1 makes one particular angle with this reference surface, and that the saw cut itself shall make another particular angle with the [111] axis of the ingot. The determination of the above mentioned angles may be readily made by one skilled in the art by application of the geometry of the octahedron of Figure 1 to the ingot. 1

At this point it is to be noted that the saw 25 may also cut seed crystals having suflicient reference information sites so that they may be oriented with respect to the [111] axis through the use of these sites. A seed crystal is shown as 3 in Figure 2 and in this case the reference sites are surfaces 4 and 5, parallel to the [111] axis and at to each other. It should be understood, however, that the seed crystal is not limited to a particular shape nor are the reference sites limited to a particular type so long as there is sufficient geometric information present in the reference sites or in the combination of seed crystal shape and reference sites so that orientation with respect to the [111] axis can be performed.-

These properly oriented seed crystals many then be used to grow [111] oriented ingots which will not require further optical orientation. Such ingots may be mounted for wafering in a manner similar to Figure 6, except that the reference information sites of the seed are utilized to establish the [111] axis position of the ingot. It should not be noted that rotational positioning of the ingot about the [111] axis can be controlled by means of seeds cut from ingots that have been rotationally oriented in accordance with the above teaching with reference to the cutting of wafers at any desired crystallographic plane. 7

Considering next the axis, from the foregoing descriptions and the octahedron of Figure 1 it may be seen that if at least three reflecting facets of the four are provided on-the ingot corresponding to one group of planes ABC, BCE, CDE, and ACD or a second group of planes ABF, BEF, DEF and ADF of the octahedron of Figure 1 then it is possible to orient the crystal by the method of this invention along a [100] axis passing through points F and C of the octahedron, which axis is normal to the E100] crystallographic plane ABED. Similar orientations with other [100] axes may readily be performed by one skilled in the art by applying the geometry of the octahedron to the ingot.

It should be noted that octahedron relationships can be further utilized by one skilled in the art in determining error angles between cut surfaces on ingots, Wafers, etc., and the desired crystallographic plane by means of the rotational cylinder device of Figure 3, and utilizing optical reflections from etch pit facets in the cut surfaces corresponding to the [111] octahedron plane ABC, or DEF of Figure 1.

In summary, what has been described is a method of orienting a monocrystalline germanium ingot whereby the discoveries that the ingot tends to grow as an octahedron and that optically reflective areas on the surface of the ingot are identifiable with the certain planes of the octahedron are utilized to permit the application of the geometricalrelationships of the octahedron to the ingot. These relationships then identify the position of any crystallographic plane in theingot. Cutting or other operations may then be performed on the ingot wit-h reference to a particular crystallographic plane, if desired.

While there have been shown and described and pointed out the fundamental novel features of the invention as applied to a preferred embodiment, it will be understood that various omissions and substitutions and changes in the form and details of the device illustrated and in its operation may be made by those skilled in the art without departing from the spirit of the invention; For example the use of X-rays or sonic vibrations may be employed instead of the preferred embodiment of light in the identification of the planes of the ingot with the planes of the octahedron. it is the intention therefore, to be limited only as indicated by the scope of the following claims.

What is claimed is:

1. The method of positioning a germanium monocrystalline ingot on an axis of rotation coinciding with either a [100] or a [111] crystallographic axis of said ingot, each said [100] or said [111] axis respectively being intersected at the same angle and at essentially the same point by at least three planes of a group of planes of the crystalline octahedron and said [100] or said [111] axis respectively being normal to a fourth [100] or [111] crystallographic plane not a member of said group comprising in combination the steps of identifying the location of at least three reflecting areas on said ingot each said area corresponding to a different plane of said group of planes of said octahedron, adjustably mounting said ingot for rotation, directing energy from a single source on said ingot in the vicinity of said areas and adjusting the axis of rotation of said ingot so that energy is reflected to the same position from each of said areas as said ingot is rotated.

2. The method of positioning a germanium monocrystalline ingot on an axis of rotation coinciding with either a [100] or a [111] crystallographic axis of said ingot, each said [100] or said [111] axis respectively being intersected at the same angle and at essentially the same point by at least three planes of a group of planes of the crystalline octahedron and said [100] or said [111] axis respectively being normal to a fourth [100] or [111] crystallographic plane not a member of said group comprising in combination the steps of etching said ingot with a crystallographic plane preferential etching solution, identifying the location of at least three reflecting areas on said ingot each said area corresponding to a different plane of said group of planes of said octahedron, adjustably mounting said ingot for rotation, di recting energy from a single source on said ingot in the vicinity of said areas and adjusting the axis of rotation of said ingot so that energy is reflected to the same position from each of said areas as said ingot is rotated.

3. The method of orienting a germanium monoc-rystalline ingot with respect to the [111] axis thereof, comprising in combination the steps of determining the location of at least three reflecting areas on the surface of said ingot, each said area being parallel with a different plane of a corresponding group of planes of the crystalline octahedron that intersect at the same angle and at the same point said axis, said axis being normal to a fourth [111] plane not a member of said group of planes of the crystalline octahedron, adjustably mounting said ingot for rotation, impinging light from a single source on said ingot in the vicinity of said areas and adjusting the axis of rotation of said ingot so that said light is reflected to the same position from each of said areas when said ingot is rotated.

4. The method of orienting a germanium monocrystalline ingot with reference to the [100] crystallographic plane comprising in combination the steps of determining the location of at least three reflecting surfaces on said ingot, each of said surfaces being parallel to a different plane of a corresponding group of planes of the crystalline octahedron, each plane intersecting the same [100] axis at the same angle and at the same point; said [100] axis being normal to a fourth [100] plane of said octahedron not a member of said group, adjustably mounting said ingot for rotation; impinging light from a single source on said ingot in the vicinity of said reflecting surfaces; and adjusting the axis of rotation of said ingot so' that said light falls on the same position when reflected from each of said three surfaces in turn as said ingot is rotated.

5. The method of orienting a germanium monoc-rystalline ingot with reference to the [111] crystallographic plane comprising in combination the steps of identifying at least three areas on said ingot, each of said areas being approximately parallel to a different plane of a corresponding group of three planes of the crystalline octahedron, each plane intersecting the same [111] axis at the same angle and at the same point; said [111] axis being normal to a fourth [111] plane of said octahedron not a member of said group treating each of said areas with a [111] plane preferential etching solution; adjustably mounting said ingot for rotation; impinging light from'a single source on said ingot in the vicinity of said areas; and adjusting the axis of rotation of said ingot so that said light is reflected to the same position from each of said three areas as said ingot is rotated.

6. The method of orienting a monocrystalline germanium ingot with respect to the crystallographic plane comprising in combination the steps of treating flat areas on the surface of said ingot with a [100] plane preferential etching solution; selecting three of said treated areas, each selected area being parallel to a different plane of a corresponding group of three planes of the crystalline octahedron, each plane of said group intersecting the same [100] axis of said octahedron at the same angle and at the same point; said [100] axis being normal to a fourth [100] plane of said octahedron not a member of said group, adjustably mounting said ingot for rotation; impinging light from a single source on said ingot in the vicinity of said areas; and adjusting the axis of rotation of said ingot so that said light is reflected to the same position from each of said three areas when said ingot is rotated.

7. A method of acquiring suflicient information for the geometrical determination of the relationship of a monocrystalline ingot of germanium with respect to a desired crystallographic plane comprising in combination the steps of determining the location of at least three reflecting areas on the surface of said ingot, each said area being parallel with a different plane of a corresponding group of planes of the crystalline octahedron, each plane of which intersects at the same angle and at the same points a [111] axis of said octahedron; said [111] axis being normal to a fourth [111] plane of said octahedron not a member of said group, adjustably mounting said ingot for rotation; impinging light from a single source on said ingot in the vicinity of said areas; adjusting the axis of rotation of said ingot so that said light is reflected to the same position from each of said areas when said ingot is rotated; and rotationally positioning said ingot so that one of said reflecting areas is in a known position with respect to a surface parallel to said axis.

8. A method of orienting a monocrystalline ingot of germanium with respect to a desired crystallographic plane comprising in combination the steps of determining the location of at least three reflecting areas on the surface of said ingot, each said area being parallel with a different plane of a corresponding group of planes of the crystalline octahedron that intersect a [100] axis of said octahedron at the same angle and at the same point; said [100] axis being normal to a fourth [100] plane of said octahedron not a member of said group, adjustably mounting said ingot for rotation; impinging light from a single source on said ingot in the vicinity of said areas, adjusting the axis of rotation of said ingot so that said light is reflected to the same position from each of said areas when said ingot is rotated, and rotating one of said areas into a particular geometric relationship with said axis whereupon the geometric relationships applicable to said octahedrons are applicable to said ingot to determine the location of said desired crystallographic plane within said ingot.

ReferencesCited in the file of this patent UNITED STATES PATENTS 2,423,357 Watrobski July 1, 1947

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Classifications
U.S. Classification356/31, 438/16, 125/30.1, 438/7, 23/301, 117/902, 117/936, 257/627
International ClassificationB28D5/00, C30B15/36, B28D5/02, H01L21/00
Cooperative ClassificationC30B15/36, B28D5/0082, Y10S117/902, B28D5/022, H01L21/00
European ClassificationH01L21/00, C30B15/36, B28D5/00H6, B28D5/02C