Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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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
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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
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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
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- , . 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
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. , , , 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.
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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.
12 BRIEF DESCRIPTION
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
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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.
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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
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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
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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
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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
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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
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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
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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
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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
CA 02305974 2000-04-19
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
16
CA 02305974 2000-04-19
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
17
CA 02305974 2000-04-19
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.
18
CA 02305974 2000-04-19
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
19
CA 02305974 2000-04-19
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.
CA 02305974 2000-04-19
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).
21
