CA2305974C

CA2305974C - Method and apparatus for growing crystals

Info

Publication number: CA2305974C
Application number: CA002305974A
Authority: CA
Inventors: Vladimir A. Klipov
Original assignee: Sawyer Res Products Inc
Current assignee: Sawyer Res Products Inc
Priority date: 2000-04-19
Filing date: 2000-04-19
Publication date: 2006-01-31
Anticipated expiration: 2020-04-19
Also published as: CA2305974A1

Abstract

A method and apparatus for hydrothermally growing crystals in a pressure vessel containing feed crystals immersed in a mineralizing solution. The apparatus is disposed in the pressure vessel, above the mineralizing solution. The apparatus includes an enclosure having opposing major walls with passages extending therethrough.
The enclosure completely surrounds a seed plate having opposing major faces. A restraining structure holds the seed plate within the enclosure such that the major faces of the seed plate are spaced inwardly from the major walls.

Description

METHOD AND APPARATUS FOR GROWING CRYSTALS
BACKGROUND OF THE INVENTION
The present invention relates to the growth of artificial crystals, and more particularly to a method and apparatus for controlling hydrvmrermal crystal growth to produce crystals with a specific shape.
Hydrothermal crystal growth is the growth of crystals from solution at a high temperature and a high pressure.
In a typical commercial process, a vertical autoclave holds a supply of nutrient material immersed in an aqueous solution. An upper portion of the autoclave includes a number of suspended seed plates. The autoclave is heated to increase the temperature and pressure sufficiently to dissolve the nutrient material in the aqueous solution and thereby form a nutrient solution. Typically, the autoclave is raised to a temperature of around 350°C and a pressure of 10,000 p.s.i. A temperature gradient inside the autoclave creates convective currents, which carry the nutrient solution upward. The nutrient solution then cools and is deposited on the seed plates, thereby causing crystal growth. , Hydrothermal crystal growth is used to grow crystals composed of nutrient materials having very low solubilities in pure water. Some of these materials include quartz (SiOZ), zinc oxide (Zn0), calcite (CaCO3) and aluminum oxide (A1203). Although these materials are more soluble under hydrothermal conditions, mineralizers are typically included in the aqueous solution to achieve reasonable solubilities. In commercial crystal growing, the 1 mineralizers are almost always alkaline (NaOH and Na2C03 are 2 common choices) but neutral or acidic materials can also be 3 used. The choice of mineralizes depends on the material 4 being grown and the impurities which are acceptable.
The most commercially significant crystals that are 6 grown hydrothermally are quartz crystals. Quartz crystals 7 are commonly used in the electronics industry to 8 manufacture quartz oscillator plates. Quartz crystals are 9 also used in optical spectrographs and other optical devices. After being artificially grown, quartz crystals ii are lumbered and cut to form quartz wafers. Currently, 12 most of the purchasers of quartz wafers desire quartz 13 wafers having a circular shape with a portion cut away to 14 form a reference flat. The length of a wafer extending perpendicularly from the reference flat to the outer edge 16 of the wafer is often referred to as the segment height of 17 the wafer. Typically, purchasers require the circular 18 quartz wafers to have a diameter of either three inches 19 (3") or one hundred millimeters (100 mm).
In the science of crystallography, the axes of a 21 crystal are normally designated the x, y and z axes, each 22 axis being angularly related to each of the other two axes.
23 A naturally-occurring quartz crystal is elongated and has a 24 generally hexagonal cross-section with pyramidal ends of six facets each. The z axis of the naturally occurring 26 quartz crystal extends longitudinally thereof, while there 27 are three x and three y axes perpendicular to the z axis.
28 The x axes intersect the angles formed by the sides of the 29 crystal, while the y axes are perpendicular to such sides.
In commercial growing processes, crystal growth in the 31 direction of the z-axis is typically preferred over growth 32 in the direction of the y-axis or growth in the direction 33 of the x- axis. In the direction of the y-axis, growth is 34 practically non-existent. In the direction of the x-axis, growth quickly tapers to an edge. Growth in the direction 36 of the z-axis, however, is fast and does not quickly taper 37 to an edge. In addition, growth in the direction of the z-axis results in considerably less impurity incorporation than in the other directions.
Seed crystals have been adapted to take advantage of the preferred growth in the direction of the z-axis. Expired U.S. Patent No. 3,291,575 to Sawyer shows a seed plate having its greatest length in the direction of the y-axis and its shortest length in the direction of the z-axis. In this manner, the seed plate has a length in the direction of the y-axis, a width in the direction of the x-axis and a thickness in the direction of the z-axis.
Such a seed plate is often referred to as having a z-cut. A z-cut seed plate has a major face disposed substantially perpendicular to the z-axis or substantially parallel to a plane defined by the x and y axes. This major face and its companion major face on the opposite side of the z-cut seed plate are the greatest areas on the z-cut seed plate.
In this manner, the z-cut seed plate promotes crystal growth in the preferred direction of the z-axis.
In many prior art commercial growing processes, seed plates are freely suspended in the autoclave. As a result, crystal growth often occurs in undesirable directions, such as in the direction of the x-axis. Crystal growth in such undesirable directions tends to be flawed and produces crystals having a shape and size that is not conducive to efficient commercial utilization.
In order to prevent undesirable crystal growth, some prior art processes suppress crystal growth in the direction of the x-axis using restrictor plates or shields. Examples of such prior art processes include those shown in U.S. Patent No. 5,069,744 to Borodin et al., U.S. Patent No. 3,607,108 to Genres, U.S. Patent No. 3,013,867 to Sawyer, U.S. Patent No. 2,674,520 to Sobek, and Sawyer 575'.
Even if crystal growth in undesirable directions is suppressed in a process by restrictor shields, the crystals that are grown in the process will still have a shape that - , . 4 1 is not conducive to efficient commercial utilization. The 2 restrictor shields will produce crystals with planar sides 3 and sharp angles. These planar sides and sharp angles will 4 have to be eliminated by a substantial amount of lumbering in order to produce the desired circular wafers.
6 Based upon the foregoing, there is a need in the art 7 for a method and apparatus for forming crystals having a 8 shape conducive to efficient utilization. The present 9 invention is directed to such a method and apparatus.
SUMMARY OF THE INVENTION
11 It therefore would be desirable, and is an advantage 12 of the present invention, to provide a method and apparatus 13 for forming crystals having a shape conducive to efficient 14 utilization. In accordance with the present invention, an apparatus is provided for shaping a crystal grown from a 16 seed crystal. The apparatus includes an enclosure for 17 disposal around the seed crystal. The enclosure has a 18 plurality of passages extending therethrough. The 19 apparatus also includes a retaining structure for holding the seed crystal within the enclosure.
21 Also provided in accordance with the present invention 22 is an assembly for hydrothermally growing a crystal. The 23 assembly includes a pressure vessel containing a basket 24 filled with feed material and a mineralizing solution. The basket is immersed in the mineralizing solution. A rack is 26 provided having a mounting frame. The rack is disposed 27 within the pressure vessel, above the mineralizing 28 solution. A seed plate is provided having opposing major 29 faces. An apparatus is suspended from the mounting frame.
The apparatus includes an enclosure and a retaining 31 structure. The enclosure surrounds the seed plate. The 32 retaining structure holds the seed plate within the 33 enclosure such that the seed plate is fully disposed within 34 the enclosure.
Also provided in accordance with the present invention 36 is a method of producing a crystal. Pursuant to the . , , , r 1 method, a pressure vessel, a mineralizing solution, feed 2 material, a feed basket, and a seed plate having major 3 faces are selected. An apparatus having an enclosure for 4 surrounding the seed plate is also selected. The pressure vessel is partially filled with the mineralizing solution, 6 and the feed basket is filled with the feed material. The 7 feed basket is disposed in the pressure vessel such that 8 the feed basket is immersed in the mineralizing solution.

9 The seed plate is mounted within the enclosure such that the seed plate is fully disposed within the enclosure. The 11 apparatus is suspended inside the pressure vessel, above 12 the mineralizing solution. The pressure vessel is sealed 13 and heated to a temperature wherein hydrothermal crystal 14 growth occurs on the seed plate.

Also provided in accordance with the present 16 invention is a method of producing generally circular 17 crystal wafers. In this method, a pressure vessel is 18 selected containing a basket filled with feed material and 19 a mineralizing solution. The basket is immersed in the mineralizing solution. A seed plate having major faces is 21 selected. An apparatus is selected having an enclosure for 22 surrounding the seed plate. The enclosure has a generally 23 elliptical cross-section with major and minor axes. The 24 seed plate is mounted within the enclosure such that the major faces of the seed plate are disposed along the major 26 axis of the cross-section. The apparatus is suspended 27 inside the pressure vessel, above the mineralizing 28 solution. The pressure vessel is sealed and heated to a 29 temperature wherein hydrothermal crystal growth occurs on the seed plate. Crystal growth is allowed to continue on 31 the seed plate until crystal growth on the major faces 32 reach the enclosure and a generally cylindroidal crystal is 33 thereby formed. The apparatus is removed from the pressure 34 vessel and the crystal is removed from the apparatus. A

plurality of parallel cuts are made through the crystal 36 transverse to the longitudinal axis of the crystal and at 37 an acute angle thereto.

1 Also provided in accordance with the present invention 2 is a method of producing a crystal, wherein a vessel, feed 3 material, and a seed crystal are selected. The apparatus 4 has an enclosure for surrounding the seed crystal. The enclosure has a plurality of passages extending 6 therethrough. The vessel is partially filled with the feed 7 material. The seed crystal is mounted within the enclosure 8 such that the seed crystal is fully disposed within the 9 enclosure. The apparatus is disposed inside the vessel and the vessel is heated to a temperature wherein crystal 11 growth occurs on the seed crystal.

OF THE DRAWINGS

13 The features, aspects, and advantages of the present 14 invention will become better understood with regard to the following description and accompanying drawings where:

16 Fig. 1 shows a schematic view of an autoclave;

17 Fig. 2 shows a front perspective view of a first seed-18 holding assembly;

19 Fig. 3 shows a bottom view of the first seed-holding assembly;

21 Fig. 4 shows a sectional view of an upper 22 protuberance;

23 Fig. 5 shows a sectional view of a lower protuberance;

24 Fig. 6 shows a rear perspective view of a second seed-holding assembly;

26 Fig. 7 shows a front perspective view of a third seed-27 holding assembly; and 28 Fig. 8 shows a top view of the third seed-holding 29 assembly.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
31 It should be noted that in the detailed description 32 which follows, identical components have the same reference 33 numerals, regardless of whether they are shown in different 34 embodiments of the present invention. It should also be noted that in order to clearly and concisely disclose the 1 present invention, the drawings may not necessarily be to 2 scale and certain features of the invention may be shown in 3 somewhat schematic form.
4 Referring now to Fig. l, there is shown a schematic view of an autoclave 10 in which the method and apparatus 6 of the present invention may be used. The autoclave 10 is 7 generally cylindrical and has an inside diameter of 8 approximately 13 inches (33 centimeters) and an interior 9 volume of about 78.2 gallons (296 liters). The autoclave 10 has a top opening that is sealed with a plug 12. The 11 plug 12 can be of the 8ridgman type or the Grayloc type.

12 The autoclave 10 has a mineral-dissolving region, or 13 supply chamber 14, and a seed-growing chamber 16. The 14 supply chamber 14 and the seed-growing chamber 16 are separated by a perforated baffle 18. Electrically 16 resistive heaters 20 are secured around an exterior surface 17 of the autoclave 10. A control system (not shown) is 18 connected to the heaters 20 and provides independent 19 control of the temperatures in the supply chamber 14 and the seed-growing chamber 16. A data acquisition system 21 (not shown) may be provided to monitor the operating 22 parameters inside the autoclave l0, such as temperature and 23 pressure.
24 It is considered apparent that the present invention is not limited to the foregoing autoclave. Rather, other 26 autoclaves may be employed with equal functionality and 27 without departing from the scope and spirit of the present 28 invention as embodied in the claims appended hereto.
29 A feed basket 22 is filled with feed stock crystal 24.
Preferably, the feed stock crystal 24 is comprised of 31 quartz. However, other types of feed stock crystal may be 32 used, such as zinc oxide (Zn0), calcite (CaC03) and aluminum 33 oxide (A1203). The feed basket 22 with the feed stock 34 crystal or "lascas" 24 is disposed in the supply chamber 14. Disposed within the seed-growing chamber 16 is a rack 36 26 having a plurality of vertically-spaced mounting frames 37 28 defining a plurality of vertical seed-growing tiers 30.

1 A plurality of seed-holding assemblies 32 are hung from 2 each of the mounting frames 28. The seed-holding 3 assemblies 32 each hold a seed crystal or seed plate 33 4 (shown in Fig. 2).
A mother liquor or mineralizing solution preferably 6 composed of sodium carbonate or sodium hydroxide, or a 7 mixture of both is added to the autoclave 10 and immerses 8 the lascas 24. Preferably, about 78% of the free volume of 9 the autoclave 10 is filled with the mineralizing solution.
Preferably, about a 7% sodium carbonate solution, or about 11 a 5% sodium hydroxide solution is used.
12 Referring now to Fig. 2 there is shown a front 13 perspective view of one of the seed-holding assemblies 32 14 with a portion cut away to better show the interior thereof. The seed-holding assembly 32 is constructed in 16 accordance with a first embodiment of the present invention 17 and generally includes an enclosure or restrictor 34, an 18 upper support 36, and a lower support 38. The seed-19 holding assembly 32 is utilized to grow a single quartz crystal from which a plurality of circular quartz wafers 21 may be obtained.
22 The restrictor 34 has a hollow interior and open top 23 and bottom ends 40, 42. The restrictor 34 is preferably 24 formed from a sheet of low carbon steel having first and second side portions 44, 46 (shown best in Fig. 3). The 26 sheet is configured so as to provide the restrictor 34 with 27 a cylindroidal shape. As best shown in Fig. 3, the 28 restrictor 34 has a cross-section (taken at a right angle 29 to a longitudinal axis of the restrictor 34) that is shaped like an ellipse with a portion cut away to form a straight 31 edge. Since the cross-section is generally elliptical, the 32 restrictor 34 has a width along the major axis of the 33 cross-section and a depth along the minor axis of the 34 cross-section. As will be described in more detail later, the width and the depth of the restrictor 34 are dependent 36 upon the size of the quartz wafers that are desired to be 37 produced. If 3" wafers are desired, the width of the 1 restrictor 34 is preferably in a range of about 3.0" to 2 3.75", more preferably about 3.25", and the depth is 3 preferably in a range of about 2.3" to 3.3", more 4 preferably about 2.8". If 100 mm wafers are desired, the width of the restrictor 34 is preferably in a range of 6 about 4.0" to 4.75", more preferably about 4.25", and the 7 depth is in a range of about 3.3" to 4.3", more preferably 8 about 3.8". The restrictor 34 has a length preferably in a 9 range of about 12" to 18", more preferably about 12.5".
It should be appreciated that the restrictor 34 can be 11 sized to produce wafers other than 3" or 100 mm wafers.
12 For example, the restrictor 34 can also be sized to produce 13 6" wafers.
14 Referring now also to Fig. 3, the restrictor 34 has first and second major walls 48, 50 and an arcuate first 16 side wall 52. The first and second side portions 44, 46 17 overlap each other and are releasably secured together by 18 upper and lower fasteners 54, 55 so as to form a second 19 side wall 53. The upper and lower fasteners 54, 55 may be generally U-shaped staples having a pair of legs extending 21 from a bight.
22 The first and second side portions 44, 46 of the 23 restrictor 34 each define a pair of upper holes (not shown) 24 and a pair of lower holes (not shown). The upper and lower holes in the first side portion 44 are respectively aligned 26 with the upper and lower holes in the second side portion 27 46. The legs of the upper staple 54 extend through the 28 upper openings, while the legs of the lower staple 55 29 extend through the lower openings. With regard to each of the upper and lower fasteners 54, 55, the legs are bent 31 inward, toward each other, so to clasp the first and second 32 side portions 44, 46 between the bight and the legs.
33 When the legs of the upper and lower fasteners 54, 55 34 are unclasped, the first and second side portions 44, 4~6 can be moved apart to open the restrictor 34 and thereby 36 provide access to the interior of the restrictor 34. In 37 Fig. 3, the upper and lower fasteners 54, 55 are shown 1 unclasped and the second side portion 46 is shown extending 2 outward, away from the first side portion 44.
3 A plurality of upper protuberances 56 and a plurality 4 of lower protuberances 58 are formed in the first and second major walls 48, 50 of the restrictor 34. The upper 6 protuberances 56 are arranged in a pattern having an upper 7 boundary spaced downward from the top end 40 of the 8 restrictor 34 and a lower boundary located approximately 9 midway along the length of the restrictor 34. The lower protuberances 58 are arranged in a pattern having a bottom 11 boundary spaced upward from the bottom end 42 of the 12 restrictor 34 and an upper boundary located approximately 13 midway along the length of the restrictor 34, adjacent the 14 lower boundary of the upper protuberances 56.
Each of the upper and lower protuberances 56, 58 is 16 generally semi-conical in shape. The upper and lower 17 protuberances 56, 58, however, are oppositely directed.
18 The upper protuberances 56 each flare outwardly and 19 upwardly from a closed bottom end to a top end defining an upwardly-directed opening 60, while the lower protuberances 21 58 each flare outwardly and downwardly from a closed top 22 end to a bottom end defining a downwardly-directed opening 23 62 (shown in Fig. 3).
24 Referring now to Figs. 4 and 5, there is respectively shown a sectional view of one of the upper protuberances 56 26 and one of the lower protuberances 58. The upper 27 protuberance 56 defines an upper passage 57 that extends 28 arcuately upward through the restrictor 34, from the 29 interior to the exterior thereof. The lower protuberance 58 defines a lower passage 59 that extends arcuately 31 downward through the restrictor 34, from the interior to 32 the exterior thereof. The upper and lower passages 57, 59 33 do not extend linearly through the restrictor 34 in a 34 direction parallel to the cross-section of the restrictor 34. In contrast, crystal growth on the major faces 94 of 36 the seed plate 33 extends linearly in a direction parallel 37 to the cross-section of the restrictor, as will be 1 discussed more fully later. Thus, the crystal that is 2 grown inside the restrictor 34 cannot grow through the 3 upper and lower passages 57, 59.
4 Although the crystal cannot grow through the upper and lower passages 57, 59, growing solution can flow through 6 the upper and lower passages 57, 59. In this manner, the 7 upper and lower passages 57, 59 permit growing solution to 8 be conveyed or transferred through the first and second 9 major walls 48, 50 so as to contact the major faces 94 of the seed plate 33. This transfer of growing solution 11 through the first and second major walls 48, 50 is critical 12 when the crystal inside the restrictor 34 approaches the 13 first and second major walls 48, 50. If growing solution 14 is not transferred through the first and second major walls 48, 50 at this point, the major faces 94 starve of growing 16 solution and crystal growth terminates short of the first 17 and second major walls 48, 50. Thus, the upper and lower 18 passages 57, 59 permit the crystal to grow up to, but not 19 through the first and second major walls 48, 50.
Referring back to Fig. 2, the upper support 36 21 includes an elongated top bar 64 mounted to the restrictor 22 34, toward the top end 40. An end of the top bar extends 23 through an opening formed in the first side wall 52 of the 24 restrictor 34, while an opposite end (not -shown) of the top bar extends through aligned openings formed in the first 26 and second side portions 44, 46 of the restrictor 34. The 27 top bar 64 is disposed along the major axis of the cross 28 section of the restrictor 34 and is slidable through the 29 openings in the restrictor 34.
The upper support 36 also includes a mounting plate 66 31 and a top clip 68. The mounting plate 66 is secured to the 32 top bar 64 and is connected to a top end of a spring 70.
33 The top clip 68 has an elongated body with opposing end 34 portions. A pair of spaced-apart arms 72 extend downwardly from each of the end portions. The body of the top clip 68 36 is secured to a bottom end of the spring 70 so as to be 1 resiliently connected to the mounting plate 66. The arms 2 72 clasp a top portion of the seed plate 33.
3 The lower support 38 includes an elongated bottom bar 4 80 mounted to the restrictor 34, toward the bottom end 42.
An end of the bottom bar 80 extends through an opening 6 formed in the first side wall 52 of the restrictor 34, 7 while an opposite end (not shown) of the bottom bar 80 8 extends through aligned openings formed in the first and 9 second side portions 44, 46 of the restrictor 34. The bottom bar 80 is aligned with the top bar 64 of the upper 11 support 36 and, thus, is disposed along the major axis of 12 the cross section of the restrictor 34. The bottom bar 80 13 is slidable through the openings in the restrictor 34.
14 The lower support 38 includes a bottom clip 82. The bottom clip 82 has an elongated body with opposing end 16 portions. A pair of spaced-apart lower arms 84 extend 17 downwardly from each of the opposing end portions. Two 18 pairs of spaced-apart upper arms 86 extend upward from the 19 body, in between the lower arms 84. The lower arms 84 clasp the bottom bar 80, while the upper arms 86 clasp a 21 lower portion of the seed plate 33.
22 The seed plate 33 is generally rectangular and has a 23 z-cut. As such, the seed plate 33 has a length in the 24 direction of its crystallographic y-axis, a width in the direction of its crystallographic x-axis and a thickness in 26 the direction of its crystallographic z-direction. In this 27 manner, the seed plate 33 has top and bottom edges 88, 90 28 perpendicular to the y-axis, side edges 92 perpendicular to 29 the x-axis and opposing major faces 94 perpendicular to the z-axis.
31 With the top portion of the seed plate 33 clasped 32 between the arms 72 of the top clip 68 and the bottom 33 portion of the seed plate 33 clasped between the upper arms 34 86 of the bottom clip 82, the seed plate 33 is securely disposed within the interior of the restrictor 34. The top 36 edge 88 of the seed plate 33 abuts the body of the top clip 37 68, while the bottom edge 90 of the seed plate 33 abuts the 1 body of the bottom clip 82. The width of the seed plate 33 2 extends along the major axis of the cross section of the 3 restrictor 34, and the side edges 92 of the seed plate 33 4 respectively abut the first side wall 52 in the restrictor 34 and the first side portion 44 of the restrictor 34. The 6 major faces 94 of the seed plate 33 are disposed 7 perpendicular to the cross-section of the restrictor 34 and 8 are spaced inward from the first and second major walls 48, 9 50 of the restrictor 34. Thus, the major faces 94 of the seed plate 33 are directed toward the upper and lower 11 passages 57, 59 in the restrictor 34 and the z-axis of the 12 seed plate 33 extends parallel to the cross-section of the 13 restrictor 34. Accordingly, the upper and lower passages 14 57, 59 are non-linear in the direction of the z-axis of the seed plate 33.
16 Once all of the seed plates 33 are mounted inside the 17 seed-holding assemblies 32 in the foregoing manner, the 18 seed-holding assemblies 32 are hung from the mounting 19 frames 28 of the rack 26. The seed-holding assemblies 32 are spaced apart within each tier 30 and between tiers 30 21 so as to permit fluid to flow around each seed-holding 22 assembly 32. If the restrictors 34 are sized to produce 3"
23 wafers, preferably five (5) seed-growing tiers 30 are 24 utilized, with preferably eight (8) seed-growing assemblies 32 being disposed in each tier 30, for a total of forty 26 (40) seed-growing assemblies 32. If the restrictors 34 are 27 sized to produce 100 mm wafers, preferably five (5) seed-28 growing tiers 30 are utilized, with preferably six (6) 29 seed-growing assemblies 32 being disposed in each tier 30, for a total of thirty (30) seed-growing assemblies 32.
31 After all of the seed-holding assemblies 32 have been hung 32 from the mounting frames 28, the rack 26 is inserted into 33 the autoclave 10 through the top opening. Inside the 34 autoclave 10, the restrictors 34 are disposed with their lengths extending vertically.
36 Once the seed-holding assemblies 32 are loaded into 37 the autoclave lo, the plug 12 is sealed and the heaters 20 1 are energized by the control system. The heaters 2o raise 2 the temperature of the seed-growing chamber 16 and the 3 supply chamber 14 until setpoint temperatures are reached.
4 The control system then manipulates the heaters 20 to maintain the seed-growing chamber 16 and the supply chamber 6 14 at the setpoint temperatures. Preferably, the setpoint 7 temperature for the supply chamber 14 is programmed for a 8 temperature in a range of about 345°C to 360°C. The 9 setpoint temperature for the seed-growing chamber 16 is preferably programmed to be between 5°C to to°C cooler than 11 the setpoint of the supply chamber 14 so as to create a 12 temperature gradient across the baffle 18. The pressure 13 within the autoclave 10 is maintained at a pressure in a 14 range of about 11,000 psi to 13,000 psi, more preferably about 12,000 psi.
16 The elevated temperature and pressure of the autoclave 17 10 causes the lascas 24 in the feed basket 22 to dissolve 18 in the mineralizing solution and form a growing solution.
19 Due to the temperature differential between the supply chamber 14 and the seed-growing chamber 16, thermal 21 currents of growing solution flow upward from the supply 22 chamber 14 and enter the seed-growing chamber 16. The 23 thermal currents flow upward along an upflow portion of the 24 seed-growing chamber 16 and then, toward the top opening, change direction and flow downward along a downflow portion 26 of the seed-growing chamber 16. In this manner, a circular 27 flow of growing solution continually moves between the 28 supply chamber 14 and the seed-growing chamber 16.
29 With regard to each of the seed-holding assemblies 32, the circular flow of growing solution enters the restrictor 31 34, contacts the seed plate 33 and then exits the 32 restrictor 34. If the seed-holding assembly 32 is located 33 in the upflow portion of the seed-growing chamber 16, the 34 growing solution enters the restrictor 34 through the bottom end 42 and the lower passages 59 in the restrictor 36 34, and exits the restrictor 34 through the top end 40 and 37 the upper passages 57 in the restrictor 34. Conversely, if 1 the. seed-holding assembly 32 is located in the downFlow 2 portion of the seed-growing chamber 16, the growing 3 solution enters the restrictor 34 through the top end 40 4 and the upper passages 57 in the restrictor 34, and exits the restrictor 34 through the bottom end 4Z and the lower 6 passages 59 in the rQStrictor 34. In this manner, the restrictor 3a accommodates the circular flow of the growing 8 solution regardless where the restrictor 34 is placed in the seed-growing chamber 16.
l0 Within the seed-growing chamber 16, the growing 11 solution cools and bQCOmes super-saturated with respect to 12 the dissolved quartz. As a result, the growing solution i3 deposits quartz on the seed plates 33 as the growing Z4 solution flows over the sqAd plates 33, thereby causing crystal growth.
16 With regard to each seed plate 33, crystal growth on 17 the side edges 9z in the direction of the x-axis is 18 effectively suppresseB by the first side wall 52 of the 19 restrictor 34 and the first side portion 44 of the restrictor 34_ Growth on the top and bottom edgee .88, 90 21 in the direction of the y-axis is negligible. Growth in 22. the direction of the z-axis, however, is fast. Therefore, z3 crystal growtri occurs almost entirely on the major faces 94 24 zn the direction of the z-axis, which is perpendicular tv the major faces 94 of the seed plate 33 and is parallel to z6 trie cross-sQCtion of the restrictor 34.
As thA crystal grows, rhombohedral surfaces form in zs non-favored directions, i.e., directions other than the z-29 axis. crystal growth on these rhombohedral surfaces in the 3o non-favored directions, however, is slower than crystal 3Z growth on the major faces 94 in the direction of the 2-32 axis.
33 Crystal growth in the direction of the z-axis 34 continues until it rEaches the restrictor 34, at Which point it is physically suppressed by the first and second 36 major walls 48, 60. Since the crystal growth is linear in 37 the direction of the z-axis and the upper and lower 1 passages 57, 59 are non-linear in the direction of the z-2 axis, the crystal growth cannot extend through the upper 3 and lower passages 57, 59. Thus, crystal growth in the 4 direction of the z-axis stops.
It should be appreciated from the foregoing that it is 6 critical that the upper and lower passages 57, 59 do not 7 extend linearly through the restrictor 34 in the direction 8 of the z-axis of the seed plate 33. The upper and lower 9 passages 57, 59, however can have configurations different from those described herein. For example the upper and 11 lower passages 57, 59 can be serpentine.
12 Even though crystal growth in the direction of the z-13 axis is suppressed, crystal growth on the rhombohedral 14 surfaces in the non-favored directions continues and, in fact, speeds up. This crystal growth in the non-favored 16 directions continues until it reaches the restrictor 34, at 17 which point it is also physically suppressed. In this 18 manner, the crystal fills out the internal dimensions of 19 the restrictor 34 and thereby assumes a cylindroidal shape having a cross-section shaped like an ellipse with a 21 portion cut away to form a reference flat.
22 From extensive crystal growing data, the growth of a 23 crystal in the autoclave 10 for a given set of operating 24 parameters can be tracked with a substantial degree of accuracy. Therefore, the time it will take for the crystal 26 to fill in the restrictor 34 can be determined with a 27 substantial degree of accuracy without using gammagraph 28 measurements of the crystal. Since the restrictor 34 29 completely suppresses crystal growth after the crystal fills in the restrictor 34, over-growth of the crystal is 31 not a concern. Therefore, extra time can be added to the 32 calculated growth time to ensure complete crystal growth.
33 The growth time is approximately four months for a crystal 34 that produces 3" wafers and six months for a crystal that produces 100 mm wafers.
36 Once the run of the autoclave 10 is complete, the 37 control system turns off the heaters 20 and the autoclave 1 10 is permitted to cool. Subsequently, the plug 12 is 2 opened and the rack 26 is removed from the autoclave 10.
3 The seed-holding assemblies 32 are then taken off the rack 4 26 and the crystals removed from the interiors thereof.
With regard to each of the seed-holding assemblies 32, the 6 crystal is removed from the seed-holding assembly 32 by 7 unclasping the upper and lower fasteners 54, 55 and 8 separating the first and second side portions 44, 46 so as 9 to open the restrictor 34. The crystal is then removed from the seed-holding assembly 32 through the restrictor 11 34, with or without the upper and lower supports 36, 38.
12 After the crystal has been removed from the seed-13 holding assembly 32, the crystal may be cut into a 14 plurality of wafers. Specifically, a plurality of parallel cuts may be made through the crystal transverse to the 16 crystal's longitudinal axis (the crystallographic y-axis).
17 The cuts are each made at an acute angle to the z-axis.
18 This angle is determined by customer specification and is 19 typically in a range of about 31° to 43°. Of course, cuts at angles outside this range can also be made. Cutting the 21 crystal at an acute angle forms generally circular wafers.
22 More specifically, the wafers are circular with a portion 23 cut away to form a reference flat.
24 As can be appreciated from the foregoing, the depth of each restrictor 34 is determined by the angle at which the 26 crystal is to be cut and the desired diameter of the 27 resulting wafers. Specifically, the depth is equal to the 28 desired diameter (plus a machining tolerance) multiplied by 29 the COSINE of the angle at which the crystal is to be cut.
In order to avoid having a multitude of differently-sized 31 restrictors 34, the depth of each restrictor 34 may be 32 calculated using an angle of 31° since most crystals are 33 cut at an angle of at least 31°. If the angle for a 34 particular crystal is greater than 31°, the crystal can be lumbered to reduce the width of the crystal. As set forth 36 earlier, if the restrictor 34 is to produce 3" wafers, the 37 depth is preferably about 2.8" and if the restrictor 34 is 1 to produce 100 mm wafers, the depth is preferably about 2 3.8".
3 The width of each restrictor 34 is determined by the 4 segment height of the wafers. Specifically, the width is equal to the segment height plus a machining tolerance. As 6 set forth earlier, if the restrictor 34 is to produce 3"
7 wafers, the width is preferably about 3.25" and if the 8 restrictor 34 is to produce 100 mm wafers, the width is 9 preferably about 4.25".
Once the crystal has been cut, the wafers are 11 temporarily glued back together to re-form the crystal.
12 The crystal is then lumbered on a lathe to remove any 13 surface irregularities that may be present. After 14 lumbering, the glue is dissolved to reobtain the wafers.
It should be appreciated that the present invention is 16 not limited to a restrictor having a cylindroidal shape 17 with a generally elliptical cross-section. Restrictors 18 having a different shape can be provided. The desired 19 shape of a crystal that is to be produced determines the shape of the restrictor 34 that is used.
21 Referring now to Fig. 6, there is shown a second 22 embodiment of the present invention. Specifically, Fig. 6 23 is a rear perspective view of a second seed-holding 24 assembly 100 having essentially the same construction as the seed-holding assembly 32 of the first embodiment except 26 for the differences to be hereinafter described. The 27 restrictor 34 has been replaced by a second restrictor 102.
28 The second restrictor 102 is preferably comprised of a 29 sheet of low carbon steel configured to have a rectangular shape. The second restrictor 102 includes the first and 31 second side portions 44, 46, as well as planar major walls 32 104, 106, and first and second side walls 108, 109. The 33 upper and lower protuberances 56, 58 are formed in the 34 major walls 104, 106 in the same patterns as in the restrictor 34. The first and second side portions 44, 46 36 are releasably secured together in the same manner as in 37 the restrictor 34 so as to form the second side wall 109.

1 The seed plate 33 is securely disposed within the 2 interior of the second restrictor 102. The side edges 92 3 of the seed plate 33 respectively abut the first side wall 4 108 and the first side portion 44 of the second restrictor 102, and the major faces 94 of the seed plate 33 are 6 directed toward the upper and lower passages 57, 59 in the 7 second restrictor 102. The second restrictor 102 is 8 disposed in the autoclave 10 with its length extending 9 vertically.
Under conditions similar to those described above for 11 the first embodiment, a second crystal is grown in the 12 second restrictor 102. The second crystal, however, is 13 substantially rectangular instead of being generally 14 cylindroidal. The second crystal can be cut to form a plurality of rectangular y-cut wafers, or a plurality of 16 rectangular seed plates. In order to produce rectangular 17 y-cut wafers, a plurality of parallel cuts are made through 18 the crystal substantially perpendicular to the crystal's 19 longitudinal axis (the crystallographic y-axis). In order to produce rectangular seed plates, a plurality of parallel 21 cuts are made through the crystal parallel to the 22 crystallographic y-axis.
23 It should also be appreciated that the present 24 invention is not limited to use with a z-cut seed plate.
Other seed plates having different cuts can be used.
26 Referring now to Figs. 7 and 8, there is shown a third 27 embodiment of the present invention. Specifically, Figs. 7 28 and 8 respectively show a schematic front view and a 29 schematic top sectional view of a third seed-holding assembly 110 having essentially the same construction as 31 the seed-holding assembly 32 of the first embodiment except 32 for the differences to be hereinafter described. The 33 restrictor 34 has been replaced by a third restrictor 112 34 and the upper and lower supports 36, 38 have been replaced by a plurality of side clips 114. The third restrictor 112 36 has essentially the same construction as the restrictor 34 37 except top and bottom end portions of the restrictor 34 1 have been cut away at an angle to provide the third 2 restrictor 112 with angled ends 116 that are parallel to 3 each other. In this manner, the third restrictor 112 has a 4 profile that resembles a parallelogram.
A second seed plate 118 is mounted inside the third 6 restrictor 112 by the side clips 114. The second seed 7 plate 118 is substantially circular and is cut parallel to 8 a rhombohedral face of a parent crystal. For this reason, 9 a seed plate such as the second seed plate 118 is referred to as having a rhombohedral or rhomb cut. The second seed 11 plate 118 has opposing major faces 120 and a 12 circumferential edge 122. The major faces 120 intersect 13 the crystallographic z-axis of the second seed plate 118 at 14 an angle of about 38.25°.
The second seed plate 118 is disposed within the third 16 restrictor 112 so as to have the major faces 120 disposed 17 parallel to the angled ends 116. The circumferential edge 18 122 adjoins the first and second major walls 48, 50 as well 19 as the first side wall 52 and the first side portion 44 of the third restrictor 112.
21 The third seed-growing assembly 110 is hung from one 22 of the mounting frames 28 of the rack 26 by wires (not 23 shown) connected to the third restrictor 112 such that the 24 width of the third restrictor 112 is vertically extending.
In this manner, the second seed plate 118 is disposed in 26 the autoclave 10 with the major faces 120 extending 27 substantially vertical as shown in Fig. 7.
28 Under conditions similar to those described above for 29 the first embodiment, a third crystal is grown in the third restrictor 112. The third crystal is generally 31 cylindroidal with a reference flat, and has opposing angled 32 ends that are parallel with each other. The third crystal 33 is ideally suited to produce seed-less circular wafers. In 34 order to produce seed-less circular wafers, a plurality of parallel cuts are made through the third crystal parallel 36 to the second seed plate 118.

1 Although the preferred embodiments of this invention 2 have been shown and described, it should be understood that 3 various modifications and rearrangements of the parts may 4 be resorted to without departing from the scope of the invention as disclosed and claimed herein. For example, 6 the restrictor 34, the second restrictor 102, and the third 7 restrictor 112 can be composed of materials other than low 8 carbon steel. In addition, passages having configurations 9 different from the upper and lower passages 57, 59 can be formed through the restrictor 34, the second restrictor 102 11 and the third restrictor 112. Also, the upper and lower 12 passages 57, 59 can be located all over the restrictor 34, 13 the second restrictor 102 and the third restrictor 112 14 instead of being located just on the front walls 48, 104 and the rear walls 50, 106.
16 It should also be understood that the present 17 invention can be used to grow crystals other than quartz 18 crystals, such as zinc oxide (Zn0), calcite (CaC03) and 19 aluminum oxide (A1203).

Claims

1. An apparatus for shaping a crystal grown from a seed crystal, said apparatus comprising:
an enclosure for disposal around the seed crystal, said enclosure having a plurality of passages extending therethrough; and a retaining structure for holding the seed crystal within the enclosure.

2. The apparatus of claim 1, wherein the passages are non-linear in a direction parallel to a cross-section of the enclosure.

3. The apparatus of claim 1 or 2, wherein the enclosure has opposing open ends.

4. The apparatus of claim 3, wherein the enclosure is comprised of opposing major walls and opposing first and second side walls, said major walls having the passages formed therein.

5. The apparatus of claim 4, wherein the major walls and the first side wall are arcuate, and the second side wall is planar.

6. The apparatus of claim 4 or 5, wherein the major walls and the first and second side walls are integrally formed from a metal sheet having opposing side portions.

7. The apparatus of claim 6, wherein the side portions of the metal sheet are secured together by a fastener so as to form the second side wall; and wherein the fastener can be released to permit the side portions of the metal sheet to be moved apart, thereby providing access to the interior of the enclosure.

8. The apparatus of any one of claims 4 to 7, wherein the passages in each of the major walls are comprised of a plurality of upwardly-directed passages and a plurality of downwardly-directed passages.

9. The apparatus of claim 8, wherein a plurality of upper protuberances and a plurality of lower protuberances are formed in each of the major walls; and wherein the upper protuberances define the upwardly-directed passages, and the lower protuberances define the downwardly-directed protuberances.

10. The apparatus of claim 9, wherein the upper and lower protuberances are generally semi-conical.

11. The apparatus of any one of claims 1 to 10, wherein the enclosure has a generally elliptical cross-section.

12. The apparatus of any one of claims 1 to 10, wherein the enclosure is rectangular.

13. An assembly for hydrothermally growing a crystal, said assembly comprising:
a pressure vessel containing a basket filled with feed material and a mineralizing solution, said basket being immersed in the mineralizing solution;
a rack having a mounting frame, said rack being disposed within the pressure vessel, above the mineralizing solution;
a seed plate having opposing major faces; and an apparatus suspended from the mounting frame, said apparatus including:

an enclosure that, when viewed in a cross section taken at a right angle to a longitudinal axis of the enclosure, completely surrounds the seed plate; and a retaining structure that holds the seed plate within the enclosure such that the seed plate is fully disposed within the enclosure.

14. The assembly of claim 13, wherein the feed material and the seed plate are comprised of quartz.

15. The assembly of claim 13 or 14, wherein the enclosure is comprised of opposing major walls and opposing first and second side walls, said major walls each having a plurality of passages formed therein.

16. The assembly of claim 15, wherein the enclosure further comprises opposing open ends.

17. The assembly of claim 16, wherein the retaining structure holds the seed plate within the enclosure such that the major faces are directed toward, and spaced inward from, the major walls.

18. The assembly of claim 17, wherein the seed plate is substantially rectangular and has a z-cut; and wherein the retaining structure holds the seed plate such that a z-axis of the seed plate is parallel to a cross-section of the enclosure.

19. The assembly of claim 18, wherein the passages are non-linear in the direction of the z-axis of the seed plate.

20. The assembly of claim 16, wherein the retaining structure holds the seed plate within the enclosure such that the major faces are directed toward, and spaced inward from, the open ends.

21. The assembly of claim 20, wherein the seed plate is substantially circular and has a rhombohedral cut.

22. An apparatus for shaping a crystal grown from a seed crystal, said apparatus comprising:
an enclosure for disposal around the seed crystal, said enclosure having open ends and at least one passage extending therethrough, said passage being non-linear in a direction parallel to a cross-section of the enclosure taken at a right angle to a longitudinal axis of the enclosure;
and a retaining structure for holding the seed crystal within the enclosure such that the seed crystal is substantially disposed within the enclosure.

23. The apparatus of claim 22, wherein the enclosure is comprised of opposing major walls, one of which has the passage extending therethrough.

24. The apparatus of claim 23, wherein the major walls are arcuate.

25. The apparatus of any one of claims 22 to 24, wherein the enclosure has a generally elliptical cross-section.

26. A method of producing a crystal, said method comprising the steps of:
selecting a pressure vessel;
selecting a mineralizing solution;
selecting feed material;

selecting a feed basket;
selecting a seed plate having major faces;
selecting an apparatus having an enclosure provided with a plurality of passages extending therethrough for surrounding the seed plate;
partially filling the pressure vessel with the mineralizing solution;
filling the feed basket with the feed material;
disposing the feed basket in the pressure vessel such that the feed basket is immersed in the mineralizing solution;
mounting the seed plate within the enclosure such that the seed plate is fully disposed within the enclosure;
suspending the apparatus inside the pressure vessel, above the mineralizing solution;
sealing the pressure vessel; and heating the pressure vessel to a temperature wherein hydrothermal crystal growth occurs on the seed plate.

27. The method of claim 26, wherein the feed material and the seed plate are comprised of quartz.

28. The method of claim 26 or 27, wherein the passages are non-linear in the direction of a z-axis of the seed plate.

29. The method of any one of claims 26 to 28, wherein the enclosure is formed from a metal sheet having opposing side portions, said metal sheet being configured such that the side portions overlap each other.

30. The method of claim 29, wherein the cross-section of the enclosure is generally elliptical.

31. The method of claim 29 or 30, wherein the side portions of the metal sheet are secured together by a fastener; and wherein the fastener can be released to permit the side portions of the metal sheet to be moved apart, thereby providing access to the interior of the enclosure.

32. The method of claim 29, further comprising the steps of:
allowing crystal growth to continue on the seed plate until crystal growth on the major faces reach the enclosure;
cooling the pressure vessel;
opening the pressure vessel;
removing the apparatus from the pressure vessel;
releasing the fastener of the enclosure;
moving the side portions of the metal sheet apart; and removing the crystal from the enclosure.

33. A method of producing generally circular crystal wafers, said method comprising the steps of:
selecting a pressure vessel containing a basket filled with feed material and a mineralizing solution, said basket being immersed in the mineralizing solution;
selecting a seed plate having major faces;
selecting an apparatus having an enclosure for surrounding the seed plate, said enclosure having a generally elliptical cross-section with major and minor axes;
mounting a seed plate within the enclosure such that the major faces of the seed plate are disposed along the major axis of the cross-section;
suspending the apparatus inside the pressure vessel, above the mineralizing solution;
sealing the pressure vessel;
heating the pressure vessel to a temperature wherein hydrothermal crystal growth occurs on the seed plate;
allowing crystal growth to continue on the seed plate until crystal growth on the major faces reach the enclosure and a generally cylindroidal crystal is thereby formed;

removing the apparatus from the pressure vessel;
removing the crystal from the apparatus; and making a plurality of parallel cuts through the crystal transverse to the longitudinal axis of the crystal and at an acute angle thereto.

34. The method of claim 33, wherein the feed material and the seed plate are comprised of quartz.

35. The method of claim 39, wherein the enclosure has a plurality of passages extending therethrough.

36. The method of claim 35, wherein the passages are non-linear in the direction of a z-axis of the seed plate.

37. A method of producing a crystal, said method comprising the steps of:
selecting a vessel;
selecting feed material;
selecting a seed crystal;
selecting an apparatus having an enclosure for surrounding the seed crystal, said enclosure having a plurality of passages extending therethrough;
partially filling the vessel with the feed material;
mounting the seed crystal within the enclosure such that the seed crystal is fully disposed within the enclosure;
disposing the apparatus inside the vessel; and heating the vessel to a temperature wherein crystal growth occurs on the seed crystal.

38. The method of claim 37, wherein the feed material and the seed crystal are comprised of quartz.

39. The method of claim 37 or 38, wherein the passages are non-linear in the direction of a z-axis of the seed crystal.

40. The method of claim 39, wherein the enclosure is comprised of: opposing open ends, opposing major walls, and opposing first and second side walls, said major walls being arcuate and having the passages formed therein.

41. The method of claim 40, wherein the seed crystal is a plate having opposing major faces; and wherein the seed crystal is mounted within the enclosure such that the major faces are directed toward, and spaced inward from, the major walls.