US3650701A

US3650701A - Apparatus for growing crystalline bodies

Info

Publication number: US3650701A
Application number: US57139A
Authority: US
Inventors: Francis Forrat
Original assignee: Commissariat a lEnergie Atomique CEA
Current assignee: Commissariat a lEnergie Atomique et aux Energies Alternatives CEA
Priority date: 1970-07-22
Filing date: 1970-07-22
Publication date: 1972-03-21
Anticipated expiration: 1989-03-21

Abstract

The apparatus comprises a gastight furnace locating a crucible which may be rotated by a motor located under the furnace. A rod vertically movable in a tubular extension of the furnace cover is adapted to pull a crystal from a melt in the crucible. The cover has a side arm which is pivotally connected to a lateral extension of a vertical shaft adapted to swing about its axis into a position where the crystal clears the furnace only after the shaft has been raised to a predetermined position. Additional pivotal movement of the side arm then provides access to the furnace body if necessary.

Description

llited States Patent l on-at [4 1 Mar. 21, 11972 [73] Assignee:

[54] APPARATUS FOR GROWING Commissariat A LEnergie Atomique, Paris, France [22] Filed: July 22,1970

[21] Appl.No.: 57,139

3,185,551 5/1965 Djevahirdjian ..23/273 3,275,417 9/1966 Hunt ..23/273 FOREIGN PATENTS OR APPLICATIONS 792,038 3/1958 Great Britain........................23/273 Primary ExaminerNorman Yudkoff Assistant ExaminerR. T. Foster Attorney-Cameron, Kerkam & Sutton ABSTRACT The apparatus comprises a gastight furnace locating a crucible which may be rotated by a motor located under the furnace. A rod vertically movable in a tubular extension of the furnace cover is adapted to pull a crystal from a melt in the crucible. The cover has a side arm which is pivotally connected to a lateral extension of a vertical shaft adapted to swing about its axis into a position where the crystal clears the furnace only after the shaft has been raised to a predetermined position. Additional pivotal movement of the side arm then provides access to the furnace body if necessary.

8 Claims, 4 Drawing Figures Patented March 21, 1972 3,650,701

5 Sheets-Sheet 1 Patented Ma rc-h 21, 1972 I v 7 3,650,701

' 5 Sheets- Sheet 2 x APPARATUS FOR GROWING CRYSTALLINE BODIES BACKGROUND OF THE INVENTION One commonly used method of growing crystals consists of contacting the surface of a melt with a seed crystal and then pulling a monocrystal from the melt. Numerous systems have been developed in the prior art which comprise a leaktight furnace locating a crucible. The crucible is provided with electrical resistance heaters connected to a control device located outside the crucible for maintaining the temperature of an appropriate melt in the crucible at a predetermined value. A vertical rod slidably sealingly projects through the cover of the furnace and is connected to a motor which raises slowly the rod for growing the crystal.

SUMMARY OF THE INVENTION It is an object of the invention to provide on apparatus which operates to grow a monocrystalline body from a melt and which comprises a furnace consisting of several parts, such apparatus being easier to operate and to maintain than the prior art devices.

According to the invention there is provided an apparatus for growing crystalline bodies comprising: a leaktight furnace for containing a crystal growing melt in a crystal growing environment, said furnace having a tubular body and a cover in which means are vertically movable for pulling a crystalline body from said melt, and support means which includes a side arm secured to said cover and pivotally connected to a lateral extension of a vertical shaft vertically movable between a lower position and an upper position, said shaft being restrained against rotation from an angular position where said cover is aligned with said body by means which are inoperative when said shaft is in an upper position.

The invention will be better understood from a consideration of the following description of an embodiment of the invention given by way of non-limitative example.

The description refers to the accompanying drawings wherein:

FIG. 1 schematically illustrates the apparatus in partial sectron;

FIG. 2 is an enlarged schematic fragmentary view of the shaft and ofthejack assembly of the apparatus of FIG. 1;

FIG. 3 is a fragmentary section along line III-III of FIG. 1 with the cover fully offset laterally;

FIG. 4 is a fragmentary elevation of the seed pulling mechanism, on an enlarged scale and in partial section.

DESCRIPTION OF THE PREFERRED EMBODIMENT FIG. 1 shows a closed furnace consisting of a generally cylindrical body 10, a lower plate 12 and a domical cover 14. The body 10 is double walled and cooling water is circulated in the annular space between the walls during operation. rings (not shown) are located between the mating surfaces of the body 10, lower plate 12 and cover 14 for retaining an appropriate atmosphere within the furnace. The furnace cover is formed with a tubular extension 18 which provides room for vertical movement of a crystal pulling rod 20. A telescope 22 projecting through the cover is equipped with a calibrated graduated scale which makes it possible to measure the diameter of the crystal as it is being grown from the melt. A loophole 24 closed by a quartz window (not shown) permits to monitor the crystal growth. The lower plate 12 of the crucible is carried by a support bracket 26 securely connected to a vertical frame 28 of channeled cross section (FIG. 3). The frame 28 is carried by a base plate 30 which supports the whole apparatus.

The crucible 16 containing the melt 34 is supported on a rod 32 which is vertically movable through an opening in the lower plate 12. The melt 34 is heated by electrical resistors 36 surrounding the crucible l6 and whose terminals 38 project out of the lower plate for connection with a control apparatus associated with suitable temperature sensors (not shown).

A plenum chamber 40 is formed under the lower plate 12 for receiving the atmosphere to be maintained in the furnace.

Chamber 40 is limited by the lower plate 12, a ring 42 having a gas inlet 44 and a sealing assembly 46. Stationary O-ring seals 47 are located between the mating surfaces of the ring 42, lower plate 12 and sealing assembly 46. A pair of lip seals 48 carried by the two walls of assembly 46 provide a sliding fluidtight connection between the assembly 46 and the rod 32 which projects out of the assembly. In the embodiment illustrated in FIG. 1, the assembly 52 includes a water box provided with an inlet and an outlet for cooling water.

The rod is secured to the shaft of a low-speed rotary motor 50 which rests on a vertically movable support 52: as a result, the crucible l6 and rod 32 are carried by the support 52 and vertical movement of the latter permits to adjust the height of the crucible and the level of the melt in the furnace.

The mechanism for raising and loweringthe support 52 comprises a vertical column 54 mounted between the base plate 30 and bracket 26 by suitable means such as screws or bolts. A rotatable axial screw (not shown) retained against axial movement in the column 54 may be rotated either by a low-speed motor 56 or by a high-speed motor 58. The support 52 is provided with a sleeve which carries rollers 60 received in an axial groove 62 of the column, thereby providing a splined connection, and with a rotatable nut threaded on the screw: as a consequence, rotation of either motor results in upward or downward movement of support 52 and crucible 16.

The cover 14 and extension 18 may be lifted and rotated by an assembly which also supports the seed pulling mechanism, as will appear later. The extension is formed with a radial flange 64 secured to a side arm 66. The side arm 66 is pivotally connected by a vertical pin 68 in a lateral extension 70 of a vertical shaft 72 (FIG. 1 and 3). A releasable latch 71 normally retains the extension 70 and side arm 66 in alignment. The shaft 72 is guided by bearings 74 secured to the frame 28 and keys 76 carried by the shaft are slidably engaged in keyways 78 of the bearing and retain the shaft 72 against rotation except when the shaft is in the vertical position illustrated in FIG. 2. Vertical movement of the shaft 72 is controlled by an electric jack whose cylinder 80 is connected to a bracket 82 of the frame by a pin 84 and whose piston rod 86 is pivotally connected to the shaft.

As shown on FIG. 1 -2, the shaft is free to rotate only after is has been raised from the position which corresponds to closed condition of the furnace by an amount sufficient for the lower key 76 to clear the corresponding keyway 78 (FIG. 2), but smaller than that which would correspond to engagement of the upper key 76 with the corresponding beyway. Angular movement of the shaft when in the location of FIG. 2 is however restrained by the size of openings 77 inthe stationary frame 28 to a predetermined angle a (FIG. 3). The angle a is so selected as to correspond to a location of the cover for which the seed pulling mechanism is laterally displaced beyond the body of the crucible, making it possible to withdraw the crystal by separating it from the mechanism and removing it downwardly.

The components of the seed pulling mechanism (FIG. 1 and 4) are similar to those of the mechanism for rotating the crucible and moving it vertically. The seed pulling rod 20 has a terminal chuck (not shown) and projects through a water-cooled sealing assembly provided with lip seals 48'. The rod is supported by a rotating motor 50 carried by a support 52. The support 52 is adapted to be raised and lowered by a screw and nut connection actuated either by a high-speed motor 58' or by a low-speed motor 56' carried by a transverse arm 88 of the shaft 72. The screw 92 is retained against axial movement in column 54' by bearings 94 while the nut 96 is connected by a pin 98 to a sleeve integral with slide arm 52' and slidably nonrotatably engaging the sides of a longitudinal slit I00 of the column. Metal bellows 102 provide a flexible gastight connection between the upper opening of the tubular extension 18 and the sealing assembly.

In order to grow a crystalline body, the crucible 16 is charged with an appropriate melt while the furnace is in the open condition illustrated in FIG. 3. The furnace is then closed. For this purpose, the cover 14 and the tubular extension 18 are rotated about pin 68 until the side arm 66 and lateral extension 70 are in aligned condition. The latch 71 is inserted and locks the side arm 66 and lateral extension in aligned relationship. The shaft 72 is rotated in turn to the angular position of FIG. 2 for which the cover 14 confronts the body 10. The liftingjack is deactivated and the shaft 72 moves down along with cover 14. During that movement, the lower key 78 engages the corresponding keyway 76 thereby guiding the cover into accurate engagement with the upper surface of the body. Fast action fasteners 104 are then locked manually to retain the cover.

The furnace is purged and an appropriate atmosphere is admitted into the furnace through inlet 44. Such inert gases as nitrogen, argon and helium are generally used although in certain cases a chemically reducing atmosphere or a vacuum may be preferable. The electrical resistance heater 36 is then energized until the charge in crucible 16 is melted and a suitable temperature is attained.

From this point on the sequence of operation is conventional. It may however be noted that during the crystal growing operation the melt 34 is continuously rotated by motor 50 and the interface is maintained at a substantially constant level using the low-speed motor 56. The rod 20 is also rotated by motor 50 and slowly lifted by the low-speed motor 56' which permit to adjust the speed of growth of the crystal; on the contrary the high-speed motors 58 and 58' are used for movement of the crucible and rod prior to initiation of the crystal pulling Step.

When a crystal body of sufficient length has been pulled, contact is broken between the body and melt by an increase of the speed of pull for a short time duration. The pulling mechanism is deactivated until the crystal has cooled down. Access may be gained to the crystal for removal thereof by energization of the jack 80 for lifting the shaft 72 from the position of FIG. 1 to the position of FIG. 2. The cover crystal pulling mechanism and shaft 72 are then rotated about the shaft axis by an angle (1 thereby bringing the crystal to a position making it possible to remove it downwardly without interference with the body of the furnace. Care is of course to be taken to avoid that the lower end of the crystal projects down to a level below that ofthe upper surface of body 10. If in addition the crucible and/or the inner surface of the furnace are to be cleaned, access may be had to them after the cover has been rotated about pin 78 by an additional angle B (FIG. 3). This may be done after the latch 71 has been removed.

Although a single embodiment of the invention has been illustrated and described in full detail, it will be apparent to those skilled in the art that numerous modifications are possible. It should be understood that the invention is not limited to the preceding description, but only by the appended claims.

We claim:

1. An apparatus for growing crystalline bodies comprising:

a leaktight furnace for containing a crystal growing melt in a crystal/environment, said furnace having a tubular body and a cover,

means vertically movable in said cover for pulling a crystalline body from said melt,

and support means for said cover, said support means including:

a side arm secured to said cover,

a vertical shaft having a lateral extension pivotally connected to said side arm, and vertically movable,

and means for preventing said shaft from rotating from an angular position where said cover is vertically aligned with said body, said means being inoperative when said shaft is at a predetermined level for which said cover is out of engagement with said body.

2. An apparatus according to claim 1, including means for limiting the extent of pivotal movement of said shaft when in said predetermined position.

3. An apparatus according to claim 2, wherein the extent of angular movement of said shaft is just sufficient for the crystal pulling mechanism to clear the body laterally.

4. An apparatus according to claim 2, having manually releasable locking means for retaining said lateral extension and side arm in aligned condition.

5. An apparatus according to claim 4, having means for restraining pivotal movement of said side arm to an extentjust sufficient for the cover to clear said body upon combined pivotal movement of said sode arm and shaft.

6. An apparatus according to claim 1, including a splined connection between said shaft and a stationary frame, said connection being inoperative when said shaft is at said predetermined level.

7. An apparatus according to claim 1, wherein said shaft carries said crystal pulling means.

8. An apparatus according to claim 1, having a crucible in said furnace, a vertical rod slidably sealingly projecting through a bottom assembly of said furnace, motor means for rotating said rod and crucible, and motor means for moving said rotating means, rod and crucible vertically as a whole.

Claims

2. An apparatus according to claim 1, including means for limiting the extent of pivotal movement of said shaft when in said predetermined position.
3. An apparatus according to claim 2, wherein the extent of angular movement of said shaft is just sufficient for the crystal pulling mechanism to clear the body laterally.
4. An apparatus according to claim 2, having manually releasable locking means for retaining said lateral extension and side arm in aligned condition.
5. An apparatus according to claim 4, having means for restraining pivotal movement of said side arm to an extent just sufficient for the cover to clear said body upon combined pivotal movement of said sode arm and shaft.
6. An apparatus according to claim 1, including a splined connection between said shaft and a stationary frame, said connection being inoperative when said shaft is at said predetermined level.
7. An apparatus according to claim 1, wherein said shaft carries said crystal pulling means.
8. An apparatus according to claim 1, having a crucible in said furnace, a vertical rod slidably sealingly projecting through a bottom assembly of said furnace, motor means for rotating said rod and crucible, and motor means for moving said rotating means, rod and crucible vertically as a whole.