阅读说明：本技术 一种氮化铝籽晶高温粘接方法 (High-temperature bonding method for aluminum nitride seed crystals ) 是由 吴亮 雷丹 王琦琨 李哲 黄嘉丽 张刚 赵寅廷 于 2021-08-11 设计创作，主要内容包括：本发明公开了一种氮化铝籽晶高温粘接方法。将氮化铝籽晶、籽晶支撑件、以及高纯氮化铝原料放置于一封闭结构的坩埚内,籽晶支撑件及籽晶置于坩埚底部、氮化铝原料固定于籽晶上方位置；在高温炉中完成粘接。粘接工艺主要包括以下步骤(1)高温炉抽真空,通入高纯氮气,升温至一定温度,且该过程籽晶温度大于原料温度；(2)继续升温,但原料升温速度大于籽晶升温速度,形成籽晶温度小于原料温度的梯度,升温至设定高温后,保温,保温期间籽晶与籽晶支撑件热粘接,同时籽晶表面有氮化铝沉积；(3)最后降温至室温。本发明的高温粘接方法,解决了籽晶化学粘接及机械固定方法中易脱落、形成孔洞、受杂质污染、生长面受到破坏等技术问题。(The invention discloses a high-temperature bonding method for aluminum nitride seed crystals. Placing aluminum nitride seed crystals, seed crystal supporting pieces and high-purity aluminum nitride raw materials in a crucible with a closed structure, placing the seed crystal supporting pieces and the seed crystals at the bottom of the crucible, and fixing the aluminum nitride raw materials above the seed crystals; and (4) completing bonding in a high-temperature furnace. The bonding process mainly comprises the following steps of (1) vacuumizing a high-temperature furnace, introducing high-purity nitrogen, heating to a certain temperature, wherein the seed crystal temperature is higher than the raw material temperature in the process; (2) continuing to heat, but the heating speed of the raw material is higher than that of the seed crystal, forming a gradient that the temperature of the seed crystal is lower than that of the raw material, keeping the temperature after the temperature is raised to a set high temperature, thermally adhering the seed crystal to the seed crystal support during the heat preservation, and simultaneously depositing aluminum nitride on the surface of the seed crystal; (3) and finally, cooling to room temperature. The high-temperature bonding method solves the technical problems that the seed crystal is easy to fall off, form holes, be polluted by impurities, damage to a growth surface and the like in the chemical bonding and mechanical fixing method of the seed crystal.)

1. A high-temperature bonding method of aluminum nitride seed crystals is characterized in that a high-temperature furnace and a crucible with a closed structure used in the high-temperature furnace are used, and the method comprises the following steps:

s1, the piece to be bonded is a seed crystal support piece and an aluminum nitride seed crystal, the seed crystal support piece is placed at the bottom in the crucible, the aluminum nitride seed crystal is placed on the surface of the seed crystal support piece, an aluminum nitride raw material is fixed above the aluminum nitride seed crystal in the crucible, and then the crucible with the piece to be bonded and the aluminum nitride raw material assembled is placed in a high-temperature furnace;

s2, vacuumizing the high-temperature furnace to reach a set vacuum degree, introducing nitrogen into the high-temperature furnace, performing positive gradient temperature rise on the seed crystal and the raw material, and raising the temperature T2 of the raw material to a first set temperature;

wherein the positive gradient temperature rise means that the temperature T1 at the seed crystal is always kept to be more than T2 in the temperature rise process, and a certain temperature difference is maintained;

after the air pressure in the furnace reaches a set constant pressure, keeping the air pressure in the subsequent furnace at the set constant pressure until the whole bonding process is finished;

s3, continuing to perform reverse gradient temperature rise on the seed crystal and the raw material, namely the temperature rise rate of the raw material is higher than that of the seed crystal, and finally T1 is less than T2, so that a temperature reverse gradient is formed, namely the temperature T2 of the raw material is higher than that of the seed crystal T1; t1 rising to a second set temperature, and keeping the temperature for a period of time;

and S4, cooling after the heat preservation is finished, taking out the bonded aluminum nitride seed crystal from the furnace body after cooling, and finishing the whole bonding process.

2. The aluminum nitride seed crystal high-temperature bonding method according to claim 1, characterized in that: the aluminum nitride seed crystal in the step S1 is selected from an aluminum nitride wafer, an aluminum nitride bulk crystal grain or an ingot.

3. The aluminum nitride seed crystal high-temperature bonding method according to claim 1, characterized in that: the crucible is made of one or more high-temperature-resistant materials of tungsten, tantalum, molybdenum, tantalum carbide, tungsten carbide, boron nitride and graphite; the seed crystal support is made of any one high-temperature-resistant material of tungsten, tantalum, molybdenum, tantalum carbide, tungsten carbide, boron nitride and graphite.

4. The aluminum nitride seed crystal high-temperature bonding method according to claim 1, characterized in that: the high-purity aluminum nitride raw material is selected from aluminum nitride powder, aluminum nitride ceramic material, aluminum nitride porous crystallization material or aluminum nitride bulk crystal; the fixing method of the high-purity aluminum nitride raw material in the step S1 is any one of a lay-up method, a suspension method, a thermal bonding method, a chemical bonding method, a crystallization method and a magnetic suspension method.

5. The aluminum nitride seed crystal high-temperature bonding method according to claim 1, characterized in that: in step S2, the set vacuum degree is less than 1 Pa; the set constant pressure is 0.3-1.5 bar.

6. The aluminum nitride seed crystal high-temperature bonding method according to claim 1, characterized in that: the first set temperature in step S2 is 1600-1900 ℃.

7. The aluminum nitride seed crystal high-temperature bonding method according to claim 1, characterized in that: the maintenance of a certain temperature difference in step S2 means that the difference T1 > T2 is in the range of 10-100 ℃.

8. The aluminum nitride seed crystal high-temperature bonding method according to claim 1, characterized in that: in the step S3, the second set temperature is 1900-; the heat preservation for a period of time refers to heat preservation for 0.5-100 h.

9. The aluminum nitride seed crystal high-temperature bonding method according to claim 1, characterized in that: the difference between the temperature T2 of the raw material at the step S3 and the temperature T1 of the seed crystal is 10-100 ℃.

10. The aluminum nitride seed crystal high-temperature bonding method according to claim 1, characterized in that: in the cooling process of the step S4, the temperature T2 is always more than or equal to T1, and the temperature T2-T1 is less than or equal to 10 ℃.

Technical Field

The invention relates to the technical field of semiconductor material preparation, in particular to a seed crystal fixing method in crystal growth by a physical vapor transport method.

Background

Aluminum nitride (AlN) is a wide bandgap semiconductor material with great application potential, the bandgap width is as high as 6.2eV, and the AlN has high breakdown field strength, high saturated electron drift rate and excellent heat conduction and radiation resistance, and is an optimal substrate material for ultraviolet/deep ultraviolet LEDs and an ideal substrate material for GaN power devices. The natural AlN mineral substance is rich in Al element and N element, but does not exist in natural form. At present, Physical Vapor Transport (PVT) is recognized as the best method for preparing AlN crystals, and homoepitaxy process based on high quality AlN seed crystals is the most ideal way to obtain high quality, large size AlN crystals.

Seed crystal epitaxial growth based on a physical vapor transport method is a common method for preparing large-size AlN single crystals, wherein seed crystal fixation is a key link. At present, chemical bonding or mechanical fixing of the seed crystal is a commonly adopted scheme for fixing the AlN seed crystal wafer. However, the chemical bonding method is liable to generate bubbles at high temperature, which on the one hand is liable to cause peeling; on the other hand, under the driving of the temperature gradient, bubbles reversely flow from the low-temperature region to the interior of the high-temperature crystal, so that a large number of holes are formed in the interior of the crystal to damage the quality of the crystal. Meanwhile, the chemical adhesive is easy to cause the surface of the seed crystal to be polluted by impurities and damage the growth surface, and in the subsequent high-temperature process, the impurities on the growth surface enter the inside of the crystal to increase point defects and influence the optical properties of the crystal and the like. The solution of mechanically fixing the seed crystal is liable to generate a large number of holes during the crystal growth process due to the inevitable existence of a gap between the two, and at the same time, the crystal ingot is cracked due to the thermal mismatch of the two materials.

Disclosure of Invention

Based on the problems in the prior art, the invention provides a high-temperature bonding method for aluminum nitride seed crystals, which solves the technical problems of easy falling, hole formation, impurity pollution, damage to the growth surface and the like in the chemical bonding and mechanical fixing method for the seed crystals.

In order to achieve the above purpose, the invention adopts the following technical scheme.

A high-temperature bonding method of aluminum nitride seed crystals uses a high-temperature furnace and a crucible with a closed structure used in the high-temperature furnace, and comprises the following steps:

s1, the piece to be bonded is a seed crystal support piece and an aluminum nitride seed crystal, the seed crystal support piece is placed at the bottom in the crucible, the aluminum nitride seed crystal is placed on the surface of the seed crystal support piece, a high-purity aluminum nitride raw material is fixed above the aluminum nitride seed crystal in the crucible, and then the crucible with the piece to be bonded and the aluminum nitride raw material assembled is placed in a high-temperature furnace. Wherein the aluminum nitride seed is selected from the group consisting of an aluminum nitride wafer, a bulk grain of aluminum nitride, or an ingot. The crucible is made of one or more high-temperature-resistant materials of tungsten, tantalum, molybdenum, tantalum carbide, tungsten carbide, boron nitride and graphite. The seed crystal support can be made of any high-temperature-resistant material of tungsten, tantalum, molybdenum, tantalum carbide, tungsten carbide, boron nitride and graphite. The high-purity aluminum nitride raw material is selected from aluminum nitride powder, aluminum nitride ceramic material, aluminum nitride porous crystallization material or aluminum nitride bulk crystal. The fixing method of the high-purity aluminum nitride raw material is any one of a laying method, a suspension method, a thermal bonding method, a chemical bonding method, a crystallization method or a magnetic suspension method.

S2, vacuumizing the high-temperature furnace to a set vacuum degree, introducing nitrogen into the high-temperature furnace, after the air pressure in the furnace reaches a set constant pressure, performing positive gradient temperature rise at the seed crystal and the raw material, and raising the temperature T1 at the seed crystal and the temperature T2 at the raw material to a first set temperature, wherein the positive gradient temperature rise means that the temperature T1 is more than T2 and the temperature difference between the two is within the range of 10-100 ℃ all the time in the temperature rise process; and the air pressure in the furnace is kept at the set constant pressure until the whole bonding process is finished. In the process, due to the action of the positive temperature gradient, impurities, organic matters, particle impurities and residual damage layers on the surface of the seed crystal can be effectively removed; this provides quality assurance for the aluminum nitride crystal deposit on the surface of the seed crystal in the subsequent step.

Further, in step S2, the high-temperature furnace is vacuumized until the degree of vacuum is less than 1 Pa; wherein the constant pressure is set to 0.3-1.5 bar; the first set temperature is 1600-1900 ℃.

S3, continuing to perform reverse gradient temperature rise on the seed crystal and the raw material, namely, the temperature rise rate of the raw material is higher than that of the seed crystal, and finally reaching T1 < T2 to form a temperature reverse gradient; the temperature T1 is raised to a second set temperature, the temperature T2 at the raw material is about 10-100 ℃ higher than the temperature T1 at the seed crystal, and the temperature is kept for a period of time under the condition of the temperature. In the heat preservation process, on one hand, the back of the seed crystal is thermally bonded with the seed crystal support under the action of high temperature and temperature gradient, and on the other hand, the raw material is decomposed and sublimated to generate gas phase substances of Al gas and N gas₂The gas is transmitted to the direction of the seed crystal and is deposited on the surface of the seed crystal to form a high-quality crystal surface growing at low speed.

Further, the second set temperature in step S3 is 1900-; the heat preservation for a period of time refers to heat preservation for 0.5-100 h;

s4, cooling after the heat preservation is finished, wherein T2 is not less than T1 and a small temperature difference is formed in the cooling process, and T2-T1 is not more than 10 ℃. In the cooling process, the surface of the seed crystal is still in a substance deposition state, and the problems of stress, cracks and the like in the cooling process are avoided by the small temperature difference. And after cooling, taking out the bonded aluminum nitride seed crystal from the furnace body.

The technical effects are as follows: 1) the method of high-temperature bonding in a nitrogen environment is adopted, the seed crystal can be effectively and firmly fixed on the surface of the seed crystal support and is not easy to fall off, the seed crystal and the surface are not polluted by other impurities, and compared with the traditional seed crystal fixing method, the defects of air holes and the like are effectively reduced; 2) in the process of seed crystal bonding, organic substances, oxide films, particle impurities and polishing damage layers on the surfaces of the seed crystals are also effectively removed; the quality of the seed crystal is improved, and the defects of impurities, dislocation, mismatch and the like are reduced during the subsequent epitaxial growth of the crystal; 3) and further, a layer of high-quality AlN single crystal grows on the surface of the seed crystal at a low speed, a natural high-quality growth surface is provided for the subsequent crystal growth, and the subsequent high-quality ingot growth is facilitated.

Drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings needed to be used in the description of the embodiments or the prior art are briefly introduced below, it is obvious that the drawings in the following description are only some embodiments described in the present invention, and for those skilled in the art, other drawings can be obtained according to the drawings without creative efforts.

FIG. 1 is a schematic view of a crucible used in an embodiment of the present invention.

Fig. 2 is a schematic assembly diagram of a seed crystal bonding process performed in an embodiment of the present invention.

FIG. 3 is a schematic view of the process curve of high temperature bonding of aluminum nitride seed crystals according to the present invention.

FIG. 4 is a graph showing the results of high temperature bonding of M-oriented aluminum nitride seed wafers bonded according to the method of the embodiment of the present invention.

FIG. 5 is a graph showing the results of high temperature bonding of C-oriented aluminum nitride seed wafers bonded according to the method of the embodiment of the present invention.

Wherein: 1 is a crucible cover; 2 is an aluminum nitride raw material; 3 is a porous tungsten sheet; 4 is aluminum nitride seed crystal; 5 is a sleeve; 6 is a bottom container; and 7 is a seed crystal support.

Detailed Description

The invention relates to a high-temperature bonding method of aluminum nitride seed crystals, wherein the bonding process is completed in a high-temperature furnace. In the bonding process, the aluminum nitride seed crystal to be bonded, the seed crystal support piece and the high-purity aluminum nitride raw material are placed in a crucible, the crucible is of a closed structure and is made of a high-temperature-resistant material. The bonding process mainly comprises the following steps: 1. the seed crystal support piece is arranged at the bottom of the crucible, the seed crystal is arranged on the surface of the seed crystal support piece, and the high-purity aluminum nitride raw material is fixed at a position above the seed crystal in the crucible; then placing the crucible in a high-temperature furnace; 2. vacuumizing the high-temperature furnace, introducing high-purity nitrogen, and starting positive gradient temperature rise, namely the temperature of the seed crystal is higher than that of the raw material; 3. the temperature rise of the reverse gradient is carried out to form a temperature reverse gradient, the temperature rise of the reverse gradient refers to that the temperature rise speed of the raw material is greater than that of the seed crystal, the temperature reverse gradient refers to that the temperature T1 of the seed crystal is less than the temperature T2 of the raw material, the temperature is preserved for a period of time after the temperature rise of the reverse gradient is carried out to a set high temperature, the seed crystal is thermally bonded with the seed crystal support during the heat preservation, and meanwhile, the surface of the seed crystal is deposited with aluminum nitride; 4. cooling to room temperature and opening the furnace.

In the embodiment of the invention, the crucible is used as shown in figure 1, and comprises a bottom container, a sleeve and a crucible cover, wherein the sleeve is arranged in the bottom container, and the crucible cover is overlapped on the sleeve through a step surface to form a closed structure. In the embodiment of the invention, when the bonding process is executed, the seed crystal supporting piece is arranged in the bottom container of the crucible, the aluminum nitride seed crystal is arranged on the surface of the seed crystal supporting piece, and the sleeve is arranged on the seed crystal supporting piece; the aluminum nitride raw material is placed on a porous tungsten sheet by a placing method, the size of the porous tungsten sheet is correspondingly matched with the sleeve and the crucible cover of the crucible, the porous tungsten sheet is placed on the sleeve, the crucible cover is lapped on the porous tungsten sheet, and the crucible with the assembled raw material is shown in figure 2.

The invention will be described in more detail below with reference to the accompanying drawings and specific embodiments. These embodiments are not intended to limit the present invention, and structural, methodological, or functional changes made by those skilled in the art according to these embodiments are included in the scope of the present invention.

Example 1:

the aluminum nitride seed crystal high-temperature bonding process of the embodiment adopts the crucible device shown in fig. 1, and raw material assembly is carried out according to the mode shown in fig. 2, and the whole process comprises the following steps:

(1) in the embodiment, the aluminum nitride seed crystal is an aluminum nitride seed wafer, is an aluminum nitride wafer with the diameter of 15mm, has the thickness of 1mm, and is subjected to double-sided fine polishing, so that the surface roughness (Ra) of the growing surface of the aluminum nitride seed crystal reaches 0.5 nm.

Placing an aluminum nitride seed crystal wafer on the surface of a seed crystal support made of tungsten, wherein the surface of the support is polished into a mirror surface; the aluminum nitride raw material is high-purity aluminum nitride crystallization block-shaped material, and the aluminum nitride crystallization block-shaped material is placed on the porous tungsten sheet and placed in the middle as much as possible, so that the volatilization of the material is guaranteed, and the transmission is uniform. And placing the seed crystal support with the seed crystal wafer placed in the bottom container, placing the sleeve on the seed crystal support, then placing the porous tungsten sheet with the aluminum nitride raw material on the sleeve, and finally overlapping the crucible cover on the porous tungsten sheet. After the assembly is finished, a closed environment is integrally formed in the crucible;

(2) placing the crucible with the assembled raw materials into a high-temperature furnace, and vacuumizing the high-temperature furnace to 1 x 10^-3Pa or less. Referring to fig. 3, a process curve for high temperature bonding of aluminum nitride seed crystals is shown. And after the vacuum pumping is finished, the temperature of the high-temperature furnace starts to rise, when the temperature of the infrared thermometer on the bottom of the bottom container is higher than 900-1200 ℃, high-purity nitrogen is introduced into the furnace body to reach a constant pressure of 50Kpa, and the constant pressure is maintained until the whole bonding process is finished.

(3) The temperature of the seed crystal and the raw material is continuously increased, the temperature T1 of the seed crystal and the temperature T2 of the raw material are increased to 1600-1900 ℃, the temperature T1 is more than T2 is kept in the temperature increasing process, namely, the temperature is increased in a positive gradient, and the temperature difference between the two is in the range of 10-100 ℃. In the process, impurities and residual damaged layers on the surface of the seed crystal can be removed through positive gradient temperature rise, and the problems of mixed crystals, parasitic nucleation and the like caused by mixed dirt on the surface of the seed crystal are avoided.

(4) Continuously carrying out reverse gradient temperature rise on the seed crystal and the raw material, namely the temperature rise rate of the raw material is higher than that of the seed crystal, and finally reaching T1 to T2 to form a temperature reverse gradient; the surface temperature T1 of the seed crystal is raised to 2100-2200 ℃, and the temperature of the raw material is higher than the temperature of the seed crystal by 50-60 ℃. Keeping the temperature for 10h under the temperature condition. In the heat preservation process, the back of the seed crystal is thermally bonded with the seed crystal support under the action of high temperature and temperature gradient, and meanwhile, the raw material substance is sublimated and deposited on the surface of the seed crystal to form low-speed high-quality crystal growth.

(5) And after the heat preservation is finished, the temperature is reduced, the nitrogen pressure in the furnace body is unchanged, the temperature T2 is kept higher than T1 in the temperature reduction process, and the temperature difference is within 5 ℃. And after cooling, taking out the bonded aluminum nitride seed crystal from the furnace body.

By adopting the high-temperature bonding method of the embodiment, the aluminum nitride seed wafers with different orientations (M direction and C direction) can obtain high-quality seed bonding effect, and as shown in fig. 4 and 5, the result of the high-temperature bonding of the M-oriented aluminum nitride seed wafer and the C-oriented aluminum nitride seed wafer bonded by the method of the embodiment is respectively shown. The aluminum nitride seed crystal has good light transmission, no bubble, no pore, no impurity and other defects in the seed crystal and on the surface of the seed crystal, and uniform bonding and no cavity and other defects can be seen on the bonding interface of the aluminum nitride seed crystal and the seed crystal support. In addition, the inventor uses the bonded aluminum nitride seed crystal to carry out the subsequent AlN crystal ingot growth, and compared with the crystal ingot obtained by the subsequent growth of the seed crystal by using the conventional bonding technology, the AlN crystal ingot obtained by the subsequent growth has the advantages of improving the defects of impurities, dislocation, mismatch and the like, thereby achieving the purpose of the invention.

Compared with the prior art, the embodiment of the invention achieves the aim from the following aspects. By adopting positive gradient temperature rise, organic substances, oxide films, particle impurities and polishing damage layers on the surfaces of the seed crystals can be effectively removed, the surface quality of the seed crystals is further optimized, and the influence of defects caused in the seed crystal processing process on the epitaxial quality of the seed crystals is avoided; the adoption of the high-purity blocky raw materials can not only provide material transmission raw materials for seed crystal bonding, but also avoid the pollution to the surface of the seed crystal caused by the falling of the material on the outer surface of the raw materials in the sublimation process of the raw materials; the reverse gradient heat preservation can ensure that the raw material is sublimated and deposited on the surface of the seed crystal, so that the sublimation of the seed crystal is avoided; the high-temperature thermal bonding can effectively and firmly fix the seed crystal on the surface of the seed crystal support piece, the seed crystal is not easy to fall off, and the seed crystal and the surface are not polluted by other impurities. In a word, the high-temperature seed crystal bonding process is a stable seed crystal bonding process and can provide a smooth high-quality growth surface for subsequent crystal growth, and is beneficial to subsequent high-quality ingot growth epitaxy.

On the basis of the above embodiment, the technical scheme of the invention can adjust the process parameters in a certain range, such as the step (2) above, wherein the high-temperature furnace is vacuumized, and the vacuum degree can be controlled within the range of less than 1 Pa; wherein the high-purity nitrogen reaches the constant pressure within the range of 0.3-1.5 bar; step (4), raising the temperature of the surface T1 of the seed crystal to be within the range of 1900-2350 ℃, and preserving the temperature for 0.5-100h, wherein the temperature of the raw material is 10-100 ℃ higher than that of the seed crystal; keeping the temperature T2 higher than T1 within about 10 ℃ in the temperature reduction process in the step (5). These parameters were adjusted within the above ranges, and the aluminum nitride seed crystal adhesion effect comparable to that of the above-described embodiment of the present invention was also achieved.

The technical scheme of the invention is not limited to the growth of the aluminum nitride crystal, and can also be applied to other crystal growth, such as an aluminum nitride-based crystal, and more specifically, an AlScN crystal. The above description of the embodiments is only intended to facilitate the understanding of the method of the invention and its core idea. It should be noted that, for those skilled in the art, it is possible to make various improvements and modifications to the present invention without departing from the principle of the present invention, and those improvements and modifications also fall within the scope of the claims of the present invention.