CN111155173B - Sapphire and annealing method of sapphire crystal - Google Patents
Sapphire and annealing method of sapphire crystal Download PDFInfo
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- CN111155173B CN111155173B CN201811318560.6A CN201811318560A CN111155173B CN 111155173 B CN111155173 B CN 111155173B CN 201811318560 A CN201811318560 A CN 201811318560A CN 111155173 B CN111155173 B CN 111155173B
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- C—CHEMISTRY; METALLURGY
- C30—CRYSTAL GROWTH
- C30B—SINGLE-CRYSTAL GROWTH; UNIDIRECTIONAL SOLIDIFICATION OF EUTECTIC MATERIAL OR UNIDIRECTIONAL DEMIXING OF EUTECTOID MATERIAL; REFINING BY ZONE-MELTING OF MATERIAL; PRODUCTION OF A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; SINGLE CRYSTALS OR HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; AFTER-TREATMENT OF SINGLE CRYSTALS OR A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; APPARATUS THEREFOR
- C30B29/00—Single crystals or homogeneous polycrystalline material with defined structure characterised by the material or by their shape
- C30B29/10—Inorganic compounds or compositions
- C30B29/16—Oxides
- C30B29/20—Aluminium oxides
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- C—CHEMISTRY; METALLURGY
- C30—CRYSTAL GROWTH
- C30B—SINGLE-CRYSTAL GROWTH; UNIDIRECTIONAL SOLIDIFICATION OF EUTECTIC MATERIAL OR UNIDIRECTIONAL DEMIXING OF EUTECTOID MATERIAL; REFINING BY ZONE-MELTING OF MATERIAL; PRODUCTION OF A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; SINGLE CRYSTALS OR HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; AFTER-TREATMENT OF SINGLE CRYSTALS OR A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; APPARATUS THEREFOR
- C30B33/00—After-treatment of single crystals or homogeneous polycrystalline material with defined structure
- C30B33/02—Heat treatment
Abstract
The invention relates to the field of sapphire preparation, and discloses an annealing method for sapphire and sapphire crystals, which comprises the following steps: heating the sapphire crystal for 30-36h in a pulse heating mode, so that the difference delta T between the highest temperature and the lowest temperature of an annealing system meets the following conditions: 0 ℃ less than or equal to 100 ℃. Wherein, the pulse heating mode includes: a. heating to 1900-2100 ℃ at T1 and keeping T1 at 0.5-2 h; b. cooling to T2 of 1800-2000 ℃ and keeping T2 of 0.1-1 h; c. step a and step b are cyclically alternated. The sapphire crystal prepared by the annealing method has high crystallization quality and smooth surface, and the stress generated in the processing process of the sapphire is effectively reduced.
Description
Technical Field
The invention relates to the field of sapphire preparation, in particular to an annealing method for sapphire and sapphire crystals.
Background
The sapphire has high hardness and good wear resistance, and can be used for touch screens of electronic products such as mobile phones and the like.
Sapphire single crystals develop stress during growth, processing or slicing, and high temperature annealing is generally used to reduce the stress.
CN105525355A discloses an in-situ annealing process for large-size sapphire crystals, which comprises that after the sapphire crystals grown by the kyropoulos method are finished, the sapphire crystals are kept in-situ annealed. The annealing process comprises five stages: in the first stage, the temperature is raised and then lowered, and the temperature is kept for 0.5 h; and a second stage: reducing the temperature to 1750 ℃, and preserving the temperature for 4 hours; and a third stage: heating and then cooling, and keeping the temperature for 0.5 h; a fourth stage: cooling to 800 ℃, and preserving heat for 4 hours; the fifth stage: and cooling to room temperature.
CN103643300A discloses an annealing method used in sapphire processing, which mainly comprises: step one, filling nitrogen into an annealing furnace; step two, heating up to 8h to 1450 ℃ at the speed of 3 ℃/min; step three, continuing for 8 hours at 1450 ℃; step four, reducing the temperature to 150 ℃ at the speed of 1.25 ℃/min.
CN106435741A discloses a processing method of a large-size sapphire annealing process, wherein the annealing process in the method comprises 42 stages, the first nine stages comprise the step of gradually heating from room temperature to 1680 ℃, and the temperature is kept for 22 min; the subsequent stage includes the temperature reduction from 1680 deg.c to 290 deg.c in 21 stages.
In the prior art, annealing temperature is controlled to be slowly reduced in the annealing procedures, the temperature control procedure is complex, the time is long, and the stress of the sapphire in the processing process can not be effectively reduced.
Disclosure of Invention
The invention aims to solve the problems that the annealing procedure is complex and the internal stress of sapphire cannot be effectively reduced in the prior art, and provides sapphire and an annealing method of sapphire.
In order to achieve the above object, a first aspect of the present invention provides a method of annealing sapphire, the method comprising:
heating the sapphire crystal for 30-36h in a pulse heating mode, so that the difference delta T between the highest temperature and the lowest temperature of an annealing system meets the following conditions: 0 ℃ less than or equal to 100 ℃.
In a second aspect, the present invention provides a sapphire, and a method for preparing the sapphire comprises the annealing method described in the first aspect.
In the invention, in the annealing process of the sapphire, the sapphire is treated in advance in a pulse heating mode and then is matched with a cooling process of reducing the temperature to room temperature. By adopting the mode, the internal stress generated during sapphire processing can be effectively reduced, the flatness of sapphire can be improved, and the yield is improved.
Drawings
FIG. 1 is a stress test graph of sapphire S1 made in example 1;
fig. 2 is a stress detection graph of sapphire D1 prepared in comparative example 1.
Detailed Description
The endpoints of the ranges and any values disclosed herein are not limited to the precise range or value, and such ranges or values should be understood to encompass values close to those ranges or values. For ranges of values, between the endpoints of each of the ranges and the individual points, and between the individual points may be combined with each other to give one or more new ranges of values, and these ranges of values should be considered as specifically disclosed herein.
The invention provides a sapphire annealing method in a first aspect, which comprises the following steps:
heating the sapphire crystal for 30-36h in a pulse heating mode, so that the difference delta T between the highest temperature and the lowest temperature of an annealing system meets the following conditions: 0 ℃ less than or equal to 100 ℃.
In the present invention, the sapphire processing method may employ melt growth, solution growth, vapor phase growth and solid phase growth, and preferably employs a kyropoulos method in melt growth.
The kyropoulos method mainly comprises seeding, shoulder-expanding growth, equal-diameter growth, ending extraction and annealing.
In the seeding step, the rotation speed of the seed rod is 1-5r/min, and the temperature is 2000-.
In the shoulder-expanding growth step, the shoulder expansion is preferably carried out twice, and the conditions of the first shoulder expansion comprise: the growth speed of the crystal is 0.1-0.2kg/h, and the pulling speed is 0.1-1 mm/h; the conditions of the second shoulder-expanding comprise: the crystal growth speed is 0.2-0.3kg/h, and the pulling speed is 1.5-3 mm/h.
In the step of equal-diameter growth, the growth speed of the crystal is 0.25-0.4kg/h, and the pulling speed is 0.1-0.5 mm/h.
In the final stripping step, the temperature is kept constant for 2-3h under the temperature of 1800-2000 ℃; then, the pulling speed is set to 5-8mm/h, so that the crystal is separated from the bottom of the crucible.
The annealing step employs the annealing method provided in the first aspect of the invention.
The annealing method of the present invention is suitable for sapphire crystals produced by any of the above methods. In the present invention, the sapphire crystal may be a crystal of various conventional forms, for example, a sapphire ingot and/or a sapphire wafer. The invention adopts a pulse heating mode to replace a constant temperature annealing mode in the prior art, and the sapphire crystal is annealed at a relatively high temperature and a relatively low temperature alternately, so that residual thermal stress gathered in the processing process is released, and the internal stress of the sapphire crystal is reduced.
The invention adopts a pulse heating mode to keep for 30-36h, and then cools the sapphire crystal to room temperature, thereby effectively reducing the stress of the sapphire crystal, reducing the crystal face warpage of the sapphire crystal, improving the surface flatness of the sapphire crystal and improving the yield of the product.
In order to further reduce the internal stress of sapphire and improve the flatness of the surface of the crystal, preferably, the pulse heating mode comprises the following steps:
a. heating the annealing system to T1 of 1900-2100 ℃ and keeping T1 of 0.5-2 h;
b. cooling the annealing system to T2 of 1800-2000 ℃ and keeping T2 of 0.1-1 h;
c. step a and step b are cyclically and alternately carried out;
wherein the temperature of 0 ℃ is less than or equal to 100 ℃ (T1-T2).
In the pulse heating method of the present invention, the order of the steps a and b is not limited, and for example, the steps a and b may be performed first, and then the steps a and b may be sequentially circulated. Alternatively, step b may be performed first, step a may be performed again, and then step b and step a may be circulated in sequence. As long as the step a and the step b can be performed alternately.
In the pulse heating process, the high-temperature section of the pulse is 1900-2100 ℃, preferably 2000-2100 ℃, and is higher than the melting point of the sapphire; the low temperature section of the pulse is 1800-2000 ℃, preferably 1900-2000 ℃. Annealing treatment is carried out in the temperature interval, so that the annealing effect of the sapphire crystal can be improved, and the internal stress of the sapphire crystal is effectively reduced; the crystallization performance of the sapphire crystal can be improved, and the surface of the sapphire crystal is not easy to warp.
The temperature difference Δ T between the high-temperature stage and the low-temperature stage is preferably 20 to 80 ℃ and more preferably 30 to 60 ℃. By adopting the method to carry out annealing treatment on the sapphire, the internal stress of the sapphire can be effectively reduced, and the crystallization performance of the sapphire is improved.
Preferably, the rate of temperature increase in step a is from 15 to 30 deg.C/min, more preferably from 20 to 25 deg.C/min. Under the temperature rise rate, the internal stress of the sapphire crystal can be effectively reduced, and the process time is shortened.
Preferably, the cooling rate in step b is 15-25 deg.C/min, more preferably 20-25 deg.C/min. Under the cooling rate, the residual stress in the sapphire crystal can be released more effectively, and the annealing effect is improved.
In the invention, in the pulse heating mode, the temperature rising rate and the temperature lowering rate are in the range, so that the crystallization effect of the sapphire can be further improved, and the flatness of the crystal face of the sapphire can be improved.
Preferably, in the pulse heating mode, t2< t1, the dwell time of the pulse heating in the low temperature section is preferably shorter than that in the high temperature section. By adopting the heating mode, the stress of the sapphire can be further reduced. More preferably, 0.5 h.ltoreq (t1-t 2). ltoreq.2 h.
In order to further reduce the internal stress of sapphire and improve the flatness of the crystal face, the method preferably further comprises cooling to room temperature (e.g., 10-40 ℃), wherein the cooling rate is 10-25 ℃/min, more preferably 10-15 ℃/min.
The invention adopts a pulse heating mode for heat preservation for 30-36h, and then is matched with temperature reduction at the speed of 10-25 ℃/min, and the annealing method can further effectively release the internal stress gathered in the processing process of the sapphire, simultaneously improve the flatness of the crystal face, shorten the process time and improve the yield.
The annealing method of the present invention can be selectively performed under vacuum condition, preferably, vacuum degree is 10-3-10-4Pa。
The annealing process of the present invention may also optionally be carried out in an inert atmosphere, preferably provided by nitrogen and/or argon, at a flow rate of 3-5L/min.
In the present invention, the annealing process of sapphire is performed under the vacuum condition or in an inert gas, which can further improve the crystallization property of sapphire.
In a second aspect, the present invention provides a sapphire, and a method for preparing the sapphire comprises the annealing method described in the first aspect.
The sapphire prepared by the annealing method has a flatter crystal face and lower internal stress. The sapphire can effectively improve the phenomena of crystal cracking and wafer warping deformation in the subsequent cutting, grinding or polishing process, and the yield of products is improved.
The present invention will be described in detail below by way of examples. In the following examples of the present invention,
"Room temperature" means "25 ℃";
the stress detection of the sapphire adopts a polarized light stress meter to be placed under polarized light at room temperature for detection.
Example 1
In this example, sapphire was prepared by the kyropoulos method.
1. Seeding
Adhering seed crystals on a seed crystal rod, and putting the seed crystal rod into a crystal growth furnace for growth for 24 hours, wherein the rotating speed of the seed crystal rod is 3r/min, and the temperature of the crystal growth furnace is adjusted to 2100 ℃.
2. Growth by shoulder enlargement
Two times of shoulder-expanding growth are adopted. The conditions for the first shoulder-expanding growth are as follows: the growth speed is 0.15kg/h, the pulling speed is 0.5mm/h, and the growth time is 24 h; the conditions for the second shoulder-expanding growth are as follows: the growth rate is 0.2kg/h, the pulling rate is 2mm/h, and the growth time is 12 h.
3. Growth in equal diameter
The growth rate of the crystal is adjusted to be 0.3kg/h, the pulling rate is 0.3mm/h, and the growth time is 170 h.
4. Carry and take off at the end
Adjusting the temperature of the crystal growth furnace to 2000 ℃, and keeping the temperature for 2 hours; and then, the pulling speed is increased by 5mm/h, so that the sapphire crystal is separated from the bottom of the crucible.
5. Annealing
Carrying out in-situ annealing on the sapphire crystal prepared in the step 4, and carrying out vacuum pumping treatment on the crystal growth furnace, wherein the vacuum degree is 10- 3Pa. The annealing step comprises:
(1) pulse heating:
a. the temperature of the sapphire crystal is increased to T1 at the temperature increasing rate of 25 ℃/min, the temperature of T1 is 2100 ℃, the temperature is kept constant at T1 at 2100 ℃, and the temperature of T1 is 1 h;
b. the sapphire crystal treated in the step a is reduced to T2 at the cooling rate of 20 ℃/min, the temperature of T2 is 2000 ℃, the temperature is kept constant at 2000 ℃ for T2, and the temperature of T2 is 0.5 h;
c. and (4) circulating the sapphire crystal subjected to the treatment of the step b for 20 times in total, wherein the whole pulse heating time is 33 h.
(2) Cooling to room temperature:
and (3) cooling the sapphire crystal processed in the step (1) to room temperature at a cooling rate of 15 ℃/min to obtain sapphire S1, wherein the stress detection result is shown in figure 1. As can be seen from fig. 1, the sapphire crystal prepared by the method of the present embodiment has no large residual stress therein, and does not crack or warp during the subsequent cutting process.
Example 2
In this example, sapphire was prepared by the kyropoulos method.
1. Seeding
Adhering seed crystals on a seed crystal rod, and putting the seed crystal rod into a crystal growth furnace for growth for 24 hours, wherein the rotating speed of the seed crystal rod is 5r/min, and the temperature of the crystal growth furnace is adjusted to 2000 ℃.
2. Growth by shoulder enlargement
Two times of shoulder-expanding growth are adopted. The conditions for the first shoulder-expanding growth are as follows: the growth speed is 0.2kg/h, the pulling speed is 1mm/h, and the growth time is 24 h; the conditions for the second shoulder-expanding growth are as follows: the growth rate is 0.3kg/h, the pulling rate is 3mm/h, and the growth time is 12 h.
3. Growth in equal diameter
The growth rate of the crystal is adjusted to be 0.4kg/h, the pulling rate is 0.5mm/h, and the growth time is 170 h.
4. Carry and take off at the end
Adjusting the temperature of the crystal growth furnace to 1800 ℃ and keeping the temperature for 3 hours; and then, the pulling speed is increased by 8mm/h, so that the sapphire crystal is separated from the bottom of the crucible.
5. Annealing
And 4, carrying out in-situ annealing on the sapphire crystal prepared in the step 4, and introducing nitrogen into the crystal growing furnace, wherein the flow of the nitrogen is 3L/min. The annealing step comprises:
(1) pulse heating:
a. the temperature of the sapphire crystal is increased to T1 at the temperature increasing rate of 20 ℃/min, the temperature of T1 is 1900 ℃, the temperature is kept constant at 1900 ℃ for T1, and the temperature of T1 is 2 h;
b. the sapphire crystal treated in the step a is reduced to T2 at a cooling rate of 25 ℃/min, the temperature of T2 is 1840 ℃, and the temperature is kept constant at 1840 ℃ for T2, and the temperature of T2 is 1 h;
c. and (4) circulating the sapphire crystal subjected to the step b in the steps a and b for 10 times in total, wherein the whole pulse heating time is about 30.9 h.
(2) Cooling to room temperature:
and (3) cooling the sapphire crystal treated in the step (1) to room temperature at a cooling rate of 10 ℃/min to obtain sapphire S2. The stress detection result of the sapphire S2 prepared in the embodiment is similar to that of the sapphire prepared in the embodiment shown in FIG. 1, no large stress remains in the sapphire, and the surface is flat. And in the subsequent cutting process, the phenomena of cracking and buckling deformation can not occur.
Example 3
In this example, sapphire was prepared by the kyropoulos method.
1. Seeding
Adhering seed crystals on a seed crystal rod, and putting the seed crystal rod into a crystal growth furnace for growth for 24 hours, wherein the rotating speed of the seed crystal rod is 1r/min, and the temperature of the crystal growth furnace is adjusted to 2000 ℃.
2. Growth by shoulder enlargement
Two times of shoulder-expanding growth are adopted. The conditions for the first shoulder-expanding growth are as follows: the growth speed is 0.1kg/h, the pulling speed is 1mm/h, and the growth time is 24 h; the conditions for the second shoulder-expanding growth are as follows: the growth rate is 0.2kg/h, the pulling rate is 3mm/h, and the growth time is 12 h.
3. Growth in equal diameter
The growth rate of the crystal is adjusted to be 0.4kg/h, the pulling rate is 0.5mm/h, and the growth time is 170 h.
4. Carry and take off at the end
Adjusting the temperature of the crystal growth furnace to 1900 ℃, and keeping the temperature for 3 hours; and then, the pulling speed is increased by 8mm/h, so that the sapphire crystal is separated from the bottom of the crucible.
5. Annealing
And 4, carrying out in-situ annealing on the sapphire crystal prepared in the step 4, and filling nitrogen and argon into the crystal growth furnace, wherein the flow of the nitrogen is 3L/min, and the flow of the argon is 5L/min. The annealing step comprises:
(1) pulse heating:
a. the temperature of the sapphire crystal is increased to T1 at the temperature increasing rate of 15 ℃/min, the temperature of T1 is 2050 ℃, the temperature is kept constant at 2050 ℃ for T1, and the temperature of T1 is 2 h;
b. the sapphire crystal treated in the step a is reduced to T2 at a cooling rate of 20 ℃/min, wherein T2 is 1980 ℃, and T2 and T2 are kept at the temperature of 1980 ℃ for 0.1 h;
c. and (4) circulating the sapphire crystal subjected to the treatment of the step b by the steps a and b for 15 times in total, wherein the whole pulse heating time is about 33.6 h.
(2) Cooling to room temperature:
and (3) cooling the sapphire crystal treated in the step (1) to room temperature at a cooling rate of 15 ℃/min to obtain sapphire S3. The stress detection result of the sapphire S3 prepared in the embodiment is similar to that of the sapphire prepared in the embodiment shown in FIG. 1, no large stress remains in the sapphire, and the surface is flat. And in the subsequent cutting process, the phenomena of cracking and buckling deformation can not occur.
Example 4
The process according to example 1, with the difference that: the annealing processes are different.
Carrying out in-situ annealing on the sapphire crystal prepared in the step 4, and carrying out vacuum pumping treatment on the crystal growth furnace, wherein the vacuum degree is 10- 3Pa. The annealing step comprises:
(1) pulse heating:
a. the temperature of the sapphire crystal is increased to T1 at the temperature increasing rate of 35 ℃/min, the temperature of T1 is 2100 ℃, the temperature is kept constant at T1 at 2100 ℃, and the time of T1 is 1 h;
b. the sapphire crystal treated in the step a is reduced to T2 at the cooling rate of 20 ℃/min, the temperature of T2 is 2000 ℃, the temperature is kept constant at 2000 ℃ for T2, and the temperature of T2 is 0.5 h;
c. and (4) circulating the sapphire crystal subjected to the step b through the steps a and b for 20 times in total, wherein the whole pulse heating time is about 32.6 h.
(2) Cooling to room temperature:
and (3) cooling the sapphire crystal treated in the step (1) to room temperature at a cooling rate of 15 ℃/min to obtain sapphire S4. The stress detection result of the sapphire S4 prepared in the embodiment is similar to that of the sapphire prepared in the embodiment shown in FIG. 1, no large stress remains in the sapphire, and the surface is flat.
Example 5
The method of example 1 is followed with the difference that the annealing process is different.
Carrying out in-situ annealing on the sapphire crystal prepared in the step 4, and carrying out vacuum pumping treatment on the crystal growth furnace, wherein the vacuum degree is 10- 3Pa. The annealing step comprises:
(1) pulse heating:
a. the temperature of the sapphire crystal is increased to T1 at the temperature increasing rate of 25 ℃/min, the temperature of T1 is 2100 ℃, the temperature is kept constant at T1 at 2100 ℃, and the temperature of T1 is 1 h;
b. the sapphire crystal treated in the step a is reduced to T2 at the cooling rate of 35 ℃/min, the temperature of T2 is 2000 ℃, the temperature is kept constant at 2000 ℃ for T2, and the temperature of T2 is 0.5 h;
c. and (4) circulating the sapphire crystal subjected to the step b through the steps a and b for 20 times in total, wherein the whole pulse heating time is about 32.3 h.
(2) Cooling to room temperature:
and (3) cooling the sapphire crystal treated in the step (1) to room temperature at a cooling rate of 15 ℃/min to obtain sapphire S5. The stress detection result of the sapphire S5 prepared in the embodiment is similar to that of the sapphire prepared in the embodiment shown in FIG. 1, no large stress remains in the sapphire, and the surface is flat.
Example 6
The method of example 1 is followed with the difference that the annealing process is different.
Carrying out in-situ annealing on the sapphire crystal prepared in the step 4, and carrying out vacuum pumping treatment on the crystal growth furnace, wherein the vacuum degree is 10- 3Pa. The annealing step comprises:
(1) pulse heating:
a. the temperature of the sapphire crystal is increased to T1 at the temperature increasing rate of 25 ℃/min, the temperature of T1 is 2100 ℃, the temperature is kept constant at T1 at 2100 ℃, and the temperature of T1 is 1 h;
b. the sapphire crystal treated in the step a is reduced to T2 at the cooling rate of 20 ℃/min, the temperature of T2 is 2000 ℃, the temperature is kept constant at 2000 ℃ for T2, and the temperature of T2 is 1.2 h;
c. and (4) circulating the sapphire crystal subjected to the treatment of the step b by the steps a and b for 15 times in total, wherein the whole pulse heating time is 35.25 h.
(2) Cooling to room temperature:
and (3) cooling the sapphire crystal treated in the step (1) to room temperature at a cooling rate of 15 ℃/min to obtain sapphire S6. The stress detection result of the sapphire S6 prepared in the embodiment is similar to that of the sapphire prepared in the embodiment shown in FIG. 1, no large stress remains in the sapphire, and the surface is flat.
Comparative example 1
The method of example 1 is followed with the difference that the annealing process is different.
And 4, carrying out in-situ annealing on the sapphire crystal prepared in the step 4, wherein the annealing step comprises the following steps:
(1) the sapphire crystal prepared in the step 4 is subjected to heat preservation treatment at 2000 ℃ for 33 h;
(2) and (2) cooling the sapphire crystal treated in the step (1) to room temperature at a cooling rate of 15 ℃/min to obtain sapphire D1, wherein the stress detection result is shown in figure 2. As can be seen from fig. 2, the sapphire manufactured by the method has a large stress inside, and the wafer is warped and deformed.
Comparative example 2
The method of example 1 is followed with the difference that the annealing process is different.
And 4, carrying out in-situ annealing on the sapphire crystal prepared in the step 4, wherein the annealing step comprises the following steps:
(1) the temperature of the sapphire crystal prepared in the step 4 is increased to 2100 ℃ at the heating rate of 25 ℃/min, and the temperature is kept constant for 32.9 hours at 2100 ℃;
(2) and (3) reducing the sapphire crystal treated in the step (1) to room temperature at a cooling rate of 20 ℃/min to obtain sapphire D2, wherein the surface of the wafer of D2 has a warping phenomenon.
Comparative example 3
The method of example 1 is followed with the difference that the annealing process is different.
And 4, carrying out in-situ annealing on the sapphire crystal prepared in the step 4, wherein the annealing step comprises the following steps:
(1) reducing the temperature of the sapphire crystal prepared in the step 4 to 1800 ℃ at a cooling rate of 5 ℃/min, and keeping the temperature of 1800 ℃ for 32.3 h;
(2) and (3) reducing the sapphire crystal treated in the step (1) to room temperature at a cooling rate of 20 ℃/min to obtain sapphire D3, wherein large stress is left in D3, and the wafer is not flat.
Comparative example 4
The method of example 1 is followed with the difference that the annealing process is different.
And 4, carrying out in-situ annealing on the sapphire crystal prepared in the step 4, wherein the annealing step comprises the following steps:
(1) reducing the temperature of the sapphire crystal prepared in the step 4 to 1800 ℃ at a cooling rate of 35 ℃/min, and keeping the temperature of 1800 ℃ for 32.9 hours;
(2) and (3) reducing the sapphire crystal treated in the step (1) to room temperature at a cooling rate of 20 ℃/min to obtain sapphire D4, wherein a stress test chart of D4 is similar to that of figure 2, and the surface of a wafer has a warping phenomenon.
Comparative example 5
The process according to example 1 is distinguished by different annealing process conditions:
carrying out in-situ annealing on the sapphire crystal prepared in the step 4, and carrying out vacuum pumping treatment on the crystal growth furnace, wherein the vacuum degree is 10- 3Pa. The annealing step comprises:
(1) pulse heating:
a. the temperature of the sapphire crystal is increased to T1 at the temperature increasing rate of 25 ℃/min, the temperature of T1 is 2100 ℃, the temperature is kept constant at T1 at 2100 ℃, and the temperature of T1 is 1 h;
b. the sapphire crystal treated in the step a is reduced to T2 at the cooling rate of 20 ℃/min, the temperature of T2 is 1900 ℃, the temperature is kept constant at 1900 ℃ for T2, and the temperature of T2 is 0.5 h;
c. and (4) circulating the sapphire crystal subjected to the treatment of the step b in the steps a and b for 19 times in total, wherein the whole pulse heating time is about 34.1 h.
(2) Cooling to room temperature:
and (3) cooling the sapphire crystal treated in the step (1) to room temperature at a cooling rate of 15 ℃/min to obtain sapphire D5, wherein large stress is remained in D5.
According to the data, the sapphire crystal prepared by the method has the advantages of no large stress residue inside the sapphire, flat surface and high yield. If the conventional constant-temperature annealing mode in the prior art is adopted for annealing or the pulse heating mode is adopted, but the difference between the highest temperature and the lowest temperature in the annealing system is more than 100 ℃, the sapphire prepared has larger stress residue inside.
The preferred embodiments of the present invention have been described above in detail, but the present invention is not limited thereto. Within the scope of the technical idea of the invention, many simple modifications can be made to the technical solution of the invention, including combinations of various technical features in any other suitable way, and these simple modifications and combinations should also be regarded as the disclosure of the invention, and all fall within the scope of the invention.
Claims (11)
1. A method of annealing a sapphire crystal, the method comprising:
heating the sapphire crystal for 30-36h in a pulse heating mode, so that the difference delta T between the highest temperature and the lowest temperature of an annealing system meets the following conditions: 0 ℃ less than or equal to 100 ℃;
the pulse heating mode comprises the following steps:
a. heating the annealing system to T1 of 1900-2100 ℃ and keeping T1 of 0.5-2 h;
b. cooling the annealing system to T2 of 1800-2000 ℃ and keeping T2 of 0.1-1 h;
c. step a and step b are cyclically and alternately carried out;
wherein the temperature of 0 ℃ is less than or equal to 100 ℃ (T1-T2).
2. The method according to claim 1, wherein the temperature rise rate in step a is 15-30 ℃/min.
3. The method according to claim 1, wherein the cooling rate in step b is 15-25 ℃/min.
4. The method of claim 1, wherein t2< t 1.
5. The method of claim 4, wherein 0.5h ≦ (t1-t 2). ltoreq.2 h.
6. The method of claim 1, further comprising cooling to room temperature at a rate of 10-25 ℃/min.
7. The method of claim 6, wherein the rate of temperature reduction is 10-15 ℃/min.
8. The process according to any one of claims 1 to 7, wherein the process is carried out in a vacuum or an inert atmosphere.
9. The method of claim 8, wherein the inert atmosphere is provided by nitrogen and/or argon.
10. The method of claim 8, wherein the flow rate of the gas providing the inert atmosphere is 3-5L/min.
11. The method of claim 8, wherein the vacuum condition has a vacuum degree of 10-3-10-4Pa。
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