|Publication number||US3337304 A|
|Publication date||Aug 22, 1967|
|Filing date||Mar 15, 1965|
|Priority date||Mar 15, 1965|
|Also published as||DE1519793A1|
|Publication number||US 3337304 A, US 3337304A, US-A-3337304, US3337304 A, US3337304A|
|Inventors||Lorenzini Robert E|
|Original Assignee||Elmat Corp|
|Export Citation||BiBTeX, EndNote, RefMan|
|Patent Citations (3), Referenced by (3), Classifications (9)|
|External Links: USPTO, USPTO Assignment, Espacenet|
A1181 1967 R. E. LORENZINI CRYSTAL GROWTH SAMPLER 2 Sheets-Sheet 1 Filed March 15, 1965 ATTORNEYS ROBE? T f. LORENZ/All F I E 3 INVENTOR.
FIE--1- United States Patent 3,337,304 CRYSTAL GROWTH SAMPLER Robert E. Lorenzini, Mountain View, Calif., assignor to Elmat Corporation, a corporation of California Filed Mar. 15, 1965, Ser. No. 439,813 2 Claims. (Cl. 23273) This invention relates to an improvement in a crystal growing furnace and to a method of operating such a furnace. More particularly, the invention relates to a crystal growing furnace having a unique double window structure therein and the method of utilizing such a furnace wherein one or more samples are withdrawn and analyzed before a crystal is grown to insure that the ultimate crystal will be of the desired chemical composition and will contain a minimum number of dislocations.
It is an object of the present invention to provide a crystal growing furnace having a double window therein so that the window can be kept clear at all times.
A further object of this invention is to provide a double acting window wherein the window can be used to seal both an opening of a crystal growing furnace and to seal off a portion of the crystal growing chamber, permitting analytical samples to be taken during the course of a melt.
Another object of this invention is to provide a melt sampling method whereby one is insured that the ultimate crystal which is grown is of a desired, definite chemical composition.
Still another object of this invention is to provide an interlock system whereby the crucible may be recharged with material without having to cool the furnace and disassemble it, thereby increasing the amount of crystal produced per unit time.
Other objects and features of the advantage of the invention will be apparent from the specification which follows.
In the drawings forming part of this application:
FIGURE 1 is a perspective View of a crystal growing furnace embodying the present invention and showing. a crystal being grown. I
FIGURE 2 is a section on the line 2-2 of FIGURE 1.
FIGURE 3 is a section generally on the line 33 of FIGURE 2 but showing the position of the parts when a sample is being taken.
FIGURE 4 is a perspective view of a sample and resistance probe showing an analytical method which may be used.
FIGURE 5 is a view similar to FIGURE 3 but illustrating the method of recharging the crucible.
The basic crystal growing furnace of the present invention is described and claimed in a copending patent application and the basic structure, therefore, will not be here described in detail. Suffice it to say that the present invention is applicable to a crystal growing apparatus embodying a double-walled vessel 56 having a relatively large lower portion 57 and an elongated neck portion 59. Within the chamber a quartz crucible 75 is contained in a graphite holder 77, the latter being mounted for rotation on a tubular member 79. The crucible is surrounded by a resistance heating element 103, which is mounted on brackets 105 and 107 attached to rods 109 and 111, respectively, it being understood that the rods and brackets serve the dual purpose of mechanically supporting the heater and also supplying electricity thereto. Further, means are provided for moving the rods so that the heating element can be lowered as the surface of the melt becomes lower due to the growth of a crystal. The double-walled vessel is supplied with a cooling fluid such as Water which flows between the walls of the vessel.
The water inlet and outlet have been omitted from the drawings for the sake of simplicity. The interior of the vessel is flushed with an inert gas such as argon which can be introduced through line 71 to either the top portion 59 or the bottom portion 57 or both by appropriate manipulating of valves 71A and 71B. Valve 71A is normally open, while valve 71B is normally closed. Gas can be exhausted through line 73, which is open at all times or may be exhausted through line 190 by opening valve 190A, as is hereinafter explained. The base of the vessel 56 is fastened to a furnace base member 65 which rests on a support member 17, the vessel being held in substantially air-tight relationship by means of the clamps 69. It will be understood that the rods 1-09 and 111 as well as tube 79 pass through base 65 in sealing relationship. A crystal growing rod 49, to which is attached a seed crystal 50, extends downwardly through the vessel 59 into the vessel 57.
The parts thus far described are parts which are common to the parts set forth in my copending patent application and only sufficient detail has been given to enable one to understand the present invention. Thus, means are provided for rotating and lowering, and ultimately slowly raising, the crystal growth rod 49; for rotating the crucible and for lowering the heating element as crystal growth proceeds.
The upper chamber 59 has a top 188 held by clamps 188A and at the center has a Teflon bushing 189 through which rod 49 can pass. The lower section 57 and the upper section 59 of chamber 56 are interconnected by a flat, horizontal portion having a composite window, generally designated 151, therein. The window 151 has a lower sealing member 155 and an upper sealing member 157. At least the upper, and preferably both windows have a center, transparent portion, preferably of quartz. The lower sealing member 155 has a groove 159 which corresponds in diameter both to a lip 161 which extends downwardly from the inner wall of the upper portion of the vessel 59 and also a similar lip 163 which extends downwardly from the window aperture. In addition, groove 159 has a sealing gasket 165 therein. The window 155 is pivoted on the pin 167, the outer end of the pin terminating in a handle 169'. Thus the window 155 can be turned to a first position where it acts as a seal for the window 151, to a second position where it acts as a seal for the top portion of the vessel 59 (see FIGURE 3) or to a third or intermediate position (as in dash lines in FIG- .URE 2) between the first andsecond positions. Window element 157 has a downturned rim 171 so that it is capable of sealing the window aperture from the top.
The double window arrangement serves three useful purposes in conjunction with the making of crystals. In the first place, the crystalline materials, such as silicon and germanium, vaporize and the vapor condenses on .any relatively cool surface such as a window and soon forms a deposit which makes the window opaque. The double window arrangement permits one to always have a clear window without permitting the contamination which might ensue if one merely lifted out a window and cleaned it. Thus, if the window 157 becomes opaque due to the deposit of material on the inner surface thereof, one merely swings window 155 into sealing position on lip 163 of the window aperture. Window 157 can be removed, cleaned and replaced without danger of contaminating the interior of the crystallization vessel. After the window 157 is replaced, the window 155 is swung out of the way and the clean window 157 is now used for observation purposes.
Another important function of the window is illustrated in FIGURES 3 and 4. In making a crystal of a material such as hyperpure silicon to which has been added a small amount of a doping material, the composition of the crystal will bear a known relationship to the composition of the melt. Since it is most advantageous to know the precise composition of the melt and therefore of the resultant crystal, I herein descn'be a method whereby this invention can be used to monitor the composition of the melt without contaminating the melt with air or other gases. Thus, before crystal formation is started, the Window 155 can be moved to the sealing position on lip 161 shown in FIGURE 3. At the same time, the flow of inert gas from line 71 is diverted by closing valve 71A and opening valve 713. The seed shaft is then removed and replaced by a quartz tube 177 of like dimension so as to form a good seal through Teflon bushing 189. Valve 190 on the upper exhaust port (normally closed) is then opened and window 155 is moved aside. Quartz tube 177 is then lowered into the molten material, with bulb 179 being compressed and a sample (181) of material is drawn into the tube. Tube 177 is then pulled up into chamber 59 and window 155 is again sealed on lip 161. After being allowed to cool for approximately 5 minutes, tube 177 is completely withdrawn from top 188. Tube 177, together with the crystalline material 181, which solidifies therein, is ground and polished toa flat surface as at 183 and 187, A resistance probe 185 is then applied to the surface 187 of the crystalline material and a resistance reading taken. Since pure silicon has substantially an infinite resistance and since the chemical nature of the doping materials which lend conductivity to the silicon are known, the resistance of the sample thus taken will give an accurate indication of the chemical composition of the upper surface of the melt. If the composition is correct, seed rod 49 is inserted through bushing 189, valve 71A is opened, valve 71B is closed and chamber 59 is allowed to purge with inert gas which has entered through valve 71A into chamber 59 and subsequently exhausts through line 190. After the purge cycle, window 155 is moved aside and valve 190A is closed, thereby allowing the normal gas flow through valve71A, downwards through chambers 59 and 57 and out exhaust 73.
Seed rod 49 with seed 50 attached, is dipped into the surface of the melt and slowly withdrawn to form a large crystal 153 as shown in FIGURE 1.
If the composition after sampling was not correct, another quartz tube similar to 177 is inserted into the melt as explained in the sampling process. However, instead of withdrawing a sample of melt, pellets of doping chemicals are dropped into the tube in order to change the chemical composition of the melt to that desired. The sampling and doping procedure can then be repeated until the desired composition is attained.
A third useful purpose of the double window arrangement is to allow the melt to be replenished with material without turning the furnace oflf. This is illustrated in FIG- URE 5. Historically, crystal growing has been a batch process whereby one crystal was grown from a crucible charge, the furnace turned off and allowed to cool, the chamber disassembled and cleaned and a new charge placed in the crucible. This process resulted in a considerable amount of unproductive time spent on the furnace and also resulted in the loss of a crucible after each run since the small amount of silicon left in the crucible expands during freezing and breaks every crucible.
By recharging the crucible while the furnace is hot, a considerable savings in both of the above areas takes place.
To recharge the furnace valve 71B and 190A are opened, 71A is closed, and window is brought into position to seal on lip 161. Top 188 is removed and stainless steel tube 191 is inserted in bushing 189. Tube 191 includes a center rod 192 which terminates at its upper end in a knob 193 and at its lower end in three or more incurved fingers 194 which are biased in grasping relationship by spring 195. The fingers are expanded in order to grasp a large piece of silicon 196. The entire assembly is clamped back onto chamber 59, valve 71A is opened, 71B is closed and chamber 59 allowed to purge. Valve A is then closed while window 155 is moved aside. Tube 191 with silicon attached is moved down into crucible 75, knob 193 is depressed and the silicon 196 dropped into the mother liquid. Tube 191 is then withdrawn and replaced 'by seed rod 49 as per same procedure as the sampling technique.
Although a specific embodiment of the invention has been illustrated, it will be understood by those skilled in the art that this is for purposes of illustration only and that departures may be made in the exact structure and method without departing from the spirit of the invention. For instance, a specific rotating handle and pin arrangement has been shown for moving the interior window to its various positions; other means of moving the window might be employed.
1. In a crystal growing furnace wherein a crystal is grown in an enclosed crystallization vessel from a melt, said crystallization vessel having a crucible with heating means in surrounding relationship therewith and having a reduced diameter portion extending upwardly from the vessel, means for inserting a crystal growing rod through the reduced diameter portion overlying the crucible and for withdrawing said rod and growing a crystal thereon, said reduced diameter portion having a horizontally disposed opening with a sealing lip extending around the periphery of said opening, a composite window in the crystallization vessel, said window comprising an aperture in the vessel, said aperture having a sealing lip of substantially the same diameter and located horizontally adjacent the said opening, an interior window movable within said vessel, the interior window being movable by means of an external rotary handle to seal selectively the aperture or the opening.
2. The structure of claim 1 wherein said aperture has an exterior window which can be removed or inserted in said aperture whereby the exterior window can be removed and cleaned when the interior window is in sealing relationship with said aperture.
References Cited UNITED STATES PATENTS 2,908,254 10/1959 Mangold 88-1 3,145,705 8/1964 Bruce 88-1 3,249,005 5/1966 Foguel 88l NORMAN YUDKOPF, Primary Examiner.
WILBUR L. BASCOMB, Examiner.
G. HINES, Assistant Examiner,
|Cited Patent||Filing date||Publication date||Applicant||Title|
|US2908254 *||Dec 2, 1955||Oct 13, 1959||Nat Lead Co||Shutter assembly|
|US3145705 *||Oct 25, 1962||Aug 25, 1964||Riley Stoker Corp||Furnace observation window|
|US3249005 *||Feb 24, 1964||May 3, 1966||Yissum Res Dev Co||Pinhole projector for viewing furnace interiors|
|Citing Patent||Filing date||Publication date||Applicant||Title|
|US5373807 *||Nov 8, 1993||Dec 20, 1994||Memc Electronic Materials, Inc.||Apparatus for growing multiple single crystals|
|US7118626||Aug 29, 2003||Oct 10, 2006||University Of Alabama In Huntsville||Crystallization cassette for the growth and analysis of macromolecular crystals and an associated method|
|US20050045094 *||Aug 29, 2003||Mar 3, 2005||University Of Alabama In Huntsville||Crystallization cassette for the growth and analysis of macromolecular crystals and an associated method|
|U.S. Classification||117/203, 117/214, 359/513, 23/301, 117/932, 117/936|