阅读说明：本技术 一种大尺寸低缺陷碳化硅单晶的制造方法 (Method for manufacturing large-size low-defect silicon carbide single crystal ) 是由 娄艳芳 刘春俊 彭同华 王波 赵宁 杨建� 于 2019-05-14 设计创作，主要内容包括：本发明针对在籽晶接长时发生位错等缺陷大幅增加问题,提供了一种从生长的初期阶段开始显著降低位错密度的SiC单晶的生长方法,从而制造出位错密度从生长初期到末期都较低的SiC单晶。本发明涉及一种碳化硅单晶块的制造方法,其是在由碳化硅单晶形成的籽晶的生长面上使用升华再结晶法使碳化硅单晶生长而制造碳化硅单晶块的方法,其中,在晶体生长初期,采用1200℃-2000℃的温度范围,保持10分钟以上,之后,控制压力在100 Pa到10Kpa之间,保持炉体压力恒定,向生长炉内通入一定流量的碳氢气体,使籽晶表面以小于50μ?/h的速度同质生长,生长一段时间之后,以一定的速度将温度和压力调节至常规生长条件,获得目标厚度的SiC单晶锭。(The present invention provides a method for growing a SiC single crystal in which the dislocation density is significantly reduced from the initial stage of growth, in order to produce a SiC single crystal having a low dislocation density from the initial stage to the final stage of growth, in order to solve the problem that defects such as dislocations are greatly increased during seed crystal growth. The invention relates to a method for manufacturing a silicon carbide single crystal block, which is a method for manufacturing the silicon carbide single crystal block by growing the silicon carbide single crystal on a growth surface of a seed crystal formed by the silicon carbide single crystal by using a sublimation recrystallization method, wherein, in the initial stage of the crystal growth, the temperature range of 1200-2000 ℃ is adopted and kept for more than 10 minutes, then, the pressure is controlled between 100Pa and 10Kpa, the pressure of a furnace body is kept constant, hydrocarbon gas with a certain flow rate is introduced into a growth furnace, so that the surface of the seed crystal grows homogeneously at the speed of less than 50 mu ⅿ/h, and after a period of growth, the temperature and the pressure are adjusted to the conventional growth condition at a certain speed, and the SiC single crystal ingot with the target thickness is obtained.)

1. A method for producing a silicon carbide single crystal, comprising the steps of providing a crucible container main body and a crucible cover, disposing a seed crystal comprising silicon carbide on the crucible cover, disposing a silicon carbide raw material in the crucible container main body,

firstly, carrying out in-situ treatment on the surface of a seed crystal: vacuumizing the furnace body to enable the internal pressure of the growth chamber to be less than 1 Pa, heating the crucible to 1200-2000 ℃, keeping the temperature of the raw material higher than the temperature of the seed crystal and the temperature difference less than 100 ℃, and keeping the temperature for more than 10 minutes; then, low-temperature slow homoepitaxial growth is carried out: stopping vacuumizing, introducing argon into the furnace body, controlling the pressure between 100Pa and 10Kpa, and keeping the pressure of the furnace body constant; introducing hydrocarbon gas with a certain flow into the crucible to ensure that the surface of the seed crystal grows homogeneously at a speed of less than 50 mu m/h until the thickness of the grown massive silicon carbide single crystal is increased by no more than 1 mm; secondly, ending the low-temperature slow homoepitaxial growth, and heating: introducing Ar gas with the pressure of more than 30KPa into the furnace chamber, increasing the temperature to 2100-2500 ℃ at the temperature change speed of less than 50 ℃ per hour, and reducing the pressure to 100-8 KPa at the pressure change speed of less than 1000Pa per hour; finally, conventional SiC single crystal growth is performed: the silicon carbide crystal is grown by a sublimation recrystallization method at the temperature of 2100-2500 ℃ and under the pressure of 100 Pa-8 KPa.

2. The method of producing a silicon carbide single crystal according to claim 1, wherein the seed crystal surface is subjected to in situ treatment at a temperature preferably in the range of 1500 ℃ to 1800 ℃.

3. The method of producing a silicon carbide single crystal according to claim 1, wherein the seed crystal surface in-situ treatment is performed at a temperature preferably in the range of 1500 ℃ to 1650 ℃.

4. the method of producing a silicon carbide single crystal according to claim 1, wherein the seed crystal surface is subjected to in situ treatment at a temperature more preferably within a range of 1550 ℃ to 1625 ℃.

5. A method for producing a silicon carbide single crystal according to claim 1, wherein a constant flow rate of hydrogen gas or silicon hydrogen gas is introduced into the crucible when the surface of the seed crystal is treated in situ.

6. A method for producing a silicon carbide single crystal according to claim 1, wherein a flow of hydrogen gas or silicon hydrogen gas is directly introduced into the crucible through a graphite tube hollow in the bottom of the crucible when the surface of the seed crystal is treated in situ.

7. The method of producing a silicon carbide single crystal according to claim 1, wherein the time for performing the seed crystal surface treatment is preferably 30 minutes or more.

8. a method for producing a silicon carbide single crystal according to claim 1, wherein the seed crystal has a thickness of less than 300 microns, preferably less than 150 microns.

9. The method of producing a silicon carbide single crystal according to claim 1, wherein the rate of low-temperature slow homoepitaxial growth is 20 μ ⅿ/h or less.

10. The method of producing a silicon carbide single crystal according to claim 1, wherein the rate of low-temperature slow homoepitaxial growth is 10 μ ⅿ/h or less.

11. The method of producing a silicon carbide single crystal according to claim 1, wherein the rate of low-temperature slow homoepitaxial growth is 5 μ ⅿ/h or less.

12. A method for producing a silicon carbide single crystal according to claim 1, wherein the thickness of the bulk silicon carbide single crystal grown by low-temperature slow homoepitaxy is increased by not more than 0.5 mm.

13. A method for producing a silicon carbide single crystal according to claim 1, wherein the thickness of the bulk silicon carbide single crystal grown by low-temperature slow homoepitaxy is increased by not more than 0.1 mm.

14. the method of producing a silicon carbide single crystal according to claim 1, wherein a hydrocarbon gas is introduced into the crucible at a constant flow rate by adding a hollow graphite tube to the bottom of the crucible when the low-temperature slow-rate homoepitaxial growth is performed.

Technical Field

The present invention relates to a method for producing a silicon carbide single crystal having a low dislocation density and a high crystal quality. The silicon carbide single crystal wafer produced by the production method of the present invention is mainly used as various semiconductor electronic devices or their substrates. In particular, the present invention relates to a silicon carbide single crystal wafer cut out from a bulk silicon carbide single crystal grown by sublimation recrystallization, wherein the dislocation density of the wafer cut out from the initial stage of growth of the bulk silicon carbide single crystal is not significantly increased.

Background

Silicon carbide (SiC) is a new third-generation semiconductor material, compared with the first-generation silicon and the second-generation gallium arsenide, the silicon carbide (SiC) has the breakdown field strength which is 10 times that of silicon and 5 times that of gallium arsenide, the thermal conductivity which is 3 times that of silicon and 7 times that of gallium arsenide, the theoretical working temperature reaches 600 ℃, and the SiC semiconductor material has obvious performance advantages. In the fields of aerospace, new energy automobiles, smart power grids, microwave communication, solid-state lighting and the like, a new generation of devices based on silicon carbide has a series of advantages of high pressure resistance, high temperature resistance, irradiation resistance, light weight, small volume, energy conservation and the like, and can gradually replace the existing devices. The research of people is always the key point in order to improve various performance indexes, reliability and stability of SiC-based devices, reduce the defect density in SiC crystals and continuously improve the quality of the SiC crystals. With the appearance of zero micropipe density crystals and the gradual solution of macroscopic defects such as mixed crystals, planar hexagonal cavities, inclusions, micropipes, polytype, small-angle grain boundaries and the like, SiC epitaxy and device manufacturers put higher requirements on the quality of SiC substrates, and microscopic defects represented by dislocations gradually enter the visual field of research and development personnel. According to the research on dislocation analysis [ see non-patent document 1(n. Ohtani et al/Journal of Crystal Growth 386 (2014) 9-15 ]), and the experimental results of patent document 1 (CN 107208311 a) ] and our experimental results (see fig. 5), it was revealed that various dislocations (including edge dislocations, screw dislocations, and basal plane dislocations) are sharply increased at the initial stage of growing SiC single Crystal by the normal sublimation recrystallization method (rayleigh method or modified rayleigh method), and the dislocation density is decreased to different degrees depending on the Growth process parameters as the Growth time is prolonged. Therefore, decreasing the dislocation density at the initial stage of growth or decreasing the amount of increase in the dislocation density at the initial stage of growth generally decreases the dislocation density of the entire columnar crystal.

In recent years, many studies have been reported on the reduction of dislocations in SiC crystals, and patent document 1 (CN 107208311 a) reports growth of a silicon carbide single crystal by a sublimation recrystallization method in which a step cluster having a step height of 10 um ~ 1mm and a terrace width of 200 um ~ 1mm is formed on a growth surface of an off-angle seed crystal by a solution growth method, and the seed crystal is used.

Patent document 2 (CN 103620095 a) reports a method for producing a silicon carbide single crystal by a stepwise process, in which in the 1 st growth step, a silicon carbide single crystal is grown to a thickness of at least 0.5mm under a growth atmosphere pressure of 3.9kPa to 39.9kPa, and a growth temperature at which the temperature of a seed crystal is 2100 ℃ to less than 2300 ℃; in the 2 nd growth step, a silicon carbide single crystal is grown thicker than in the 1 st growth step, with an atmospheric pressure of 0.13kPa to 2.6 kPa inclusive and a seed crystal temperature being higher than the 1 st growth temperature and lower than 2400 ℃. The invention enables the screw dislocation of the peripheral area of the 0.5 radius circle taking the central point as the center of the SiC substrate to be reduced by more than 20 percent compared with the internal area of the 0.5 radius circle. Obviously, the amplitude and area of the dislocation density reduced by the method are far from meeting the application of the substrate in high-performance SiC devices.

Patent document 3 (CN 105074059A) reports that the dislocation density is low (300/cm) using the large Bouguese vector b (b > < 0001 > +1/3 < 11-20 >)²Below even 100/cm²Below) and large declination angle (surface)having a range of 10 degrees in the < 11-20 > direction with respect to the {0001} plane) as a seed crystal, and cutting the grown crystal into a large off-angle substrate as a seed crystal to grow, repeating the steps for a plurality of times, thereby growing a SiC single crystal having a low large berge vector dislocation density. The method only aims at the dislocation of the large Berger vector, and has the defect of low sheet yield due to large seed crystal deflection angle. Patent document 4 (CN 105525350 a) also reports a method of reducing dislocations by repeated growth using an off-angle seed crystal as described above, and according to our experimental conclusion, the yield and the dislocation reduction rate of this method are very low.

Patent document 5 (CN 107002281 a) reports that before the main growth step, a sub-step of growing a crystal at a growth atmosphere pressure of 3.9kPa or more and 39.9kPa or less and a seed crystal temperature of 2100 ℃ or more and less than 2300 ℃ is used, in which the pressure is higher than that of the main step and the temperature is lower than that of the main step, in order to reduce the growth rate in the elongation stage and reduce the amount of dislocation increase in the initial growth stage. Since the temperature of the sub-process is still above the growth temperature, the control range of the pressure is large, and the growth rate is difficult to control. In addition, the pressure is too low, the growth speed is fast, the pressure is too high, the seed crystal is seriously evaporated, the surface of the seed crystal is seriously damaged and can be seriously amplified and even penetrate, and the increase rate of dislocation is more severe.

Disclosure of Invention

Problems to be solved by the invention

The present invention has been made in view of the situation reported in the above-mentioned publication, and an object thereof is to provide a method for reducing the dislocation density of a full-column SiC crystal by reducing the dislocation density increase rate at the initial stage of SiC single crystal growth.

Means for solving the problems

The present inventors have conducted intensive studies on a method for suppressing an increase in dislocation density at the interface between a seed crystal and a growing SiC single crystal, i.e., at the initial stage of crystal growth, using a sublimation recrystallization method, and as a result, have found that: on one hand, the surface of the seed crystal is treated in situ to remove pollutants and a damaged layer on the surface of the seed crystal, eliminate the root source generated by partial dislocation, and simultaneously slightly amplify the original dislocation on the seed crystal, thereby being beneficial to the lateral growth rate in the slow growth process to be greater than the vertical growth rate, and effectively healing partial original dislocation; on the other hand, at the growth temperature close to homoepitaxy, the Si steam preferentially evaporated from the raw material reacts with the externally introduced hydrocarbon gas to deposit on the surface of the seed crystal, so that the initial growth atmosphere silicon-carbon ratio and the single crystal growth speed can be effectively controlled, the increase rate of defects such as dislocation, inclusion and the like is reduced, the defects such as dislocation, inclusion and the like of the whole column of crystal are reduced, and the quality of the single crystal is improved.

The principle of in situ treatment of our seed is as follows:

In the temperature range of 1200 ℃ to 2000 ℃, Si atoms on the surface of the seed crystal are preferentially evaporated, and C atoms are left; controlling the temperature of the raw material to be higher than the temperature of the seed crystal and the temperature difference to be less than 100 ℃, wherein Si atoms in the raw material are preferentially evaporated, the evaporation speed is higher than that of Si atoms on the surface of the seed crystal, and because the temperature of the raw material is slightly higher than the temperature of the surface of the seed crystal, the evaporated Si atoms in the raw material migrate to the surface of the seed crystal and react with C atoms on the surface of the seed crystal to generate SiC and Si₂C and SiC₂Silicon carbon gases, which are drawn out of the crucible along with the Si vapor; so that the surface of the seed crystal is exposed to the fresh atom surface, and simultaneously, because Si atoms are more easily evaporated at the defect position compared with the complete crystal surface, the defects such as dislocation and the like are slightly amplified in the process.

similar to the principle, the hydrogen introduced into the crucible can react with C atoms on the surface of the seed crystal at high temperature to generate hydrocarbon gas, so that the seed crystal is exposed out of the fresh surface; or Si vapor decomposed from the silicon hydrogen gas introduced into the crucible at high temperature can accelerate the exposure of the fresh surface of the seed crystal.

The principle of low-speed epitaxial homogrowth is as follows:

at a temperature ranging from 1200 ℃ to 2000 ℃, the silicon carbide raw material begins to sublimate to generate SiC and Si₂C and SiC₂When the temperature is relatively low, the Si/C atomic ratio in the atmosphere is far greater than 1, and the main atmosphere is a silicon-containing atmosphere, which results in a plurality of silicon dropletsIt is generated on the surface of the seed crystal, and high-quality epitaxial growth cannot be carried out. Therefore, the invention provides that hydrocarbon gas with a certain flow rate is introduced into the crucible, and the hydrocarbon gas reacts with Si vapor evaporated from the raw materials to generate SiC and Si₂C and SiC₂And (3) waiting carbon silicon gas, maintaining the silicon-carbon ratio of the atmosphere to be near 1, depositing on the surface of the seed crystal at a deposition speed which is higher than the evaporation speed of atoms on the surface of the seed crystal, and enabling the surface of the seed crystal to grow homogenously at a speed of less than 50 mu m/h.

The gist of the present invention is as follows:

A method for producing a silicon carbide single crystal, comprising the steps of providing a crucible container main body and a crucible cover, disposing a seed crystal comprising silicon carbide on the crucible cover, disposing a silicon carbide raw material in the crucible container main body,

Firstly, carrying out in-situ treatment on the surface of a seed crystal: under the state of always vacuumizing and the pressure less than 1 Pa, heating the crucible to the temperature range of 1200-2000 ℃, keeping the temperature of the raw material higher than the temperature of the seed crystal and the temperature difference less than 100 ℃, and keeping the temperature for more than 10 minutes;

Further, when the in-situ treatment of the surface of the seed crystal is performed, the temperature of the seed crystal is preferably in the range of 1500 ℃ to 1800 ℃.

Further, when the surface of the seed crystal is treated in situ, the temperature of the seed crystal is preferably 1500 ℃ to 1650 ℃.

Further, when the in-situ treatment of the surface of the seed crystal is performed, the temperature of the seed crystal is preferably in the range of 1550 ℃ to 1625 ℃.

In order to accelerate the etching treatment of the surface of the seed crystal, hydrogen or silicon hydrogen gas with certain flow can be directly introduced into the crucible through a hollow graphite pipeline at the bottom of the crucible.

Further, the time for performing the in-situ treatment of the surface of the seed crystal is preferably 20 minutes or more.

Further, the time for performing the in-situ treatment of the surface of the seed crystal is preferably 30 minutes or more.

Then, low-temperature slow homoepitaxial growth is carried out: stopping vacuumizing, introducing argon into the furnace body, controlling the pressure between 100Pa and 10Kpa, and keeping the pressure of the furnace body constant; introducing a certain flow of hydrocarbon gas into the crucible by adding a hollow graphite pipeline at the bottom of the crucible, and adjusting the flow of the hydrocarbon gas to adjust the speed of homoepitaxial growth so that the surface of the seed crystal grows homologously at a speed of less than 50 mu m/h;

further, the control pressure for low-temperature slow homoepitaxial growth is between 1KPa and 5KPa,

Further, the low-temperature slow homoepitaxial growth is carried out at a rate of 20 μm/h or less.

Further, the low-temperature slow homoepitaxial growth is carried out at a rate of 10 μm/h or less.

Further, the low-temperature slow homoepitaxial growth is carried out at a rate of 5 μm/h or less.

The growth rate of homoepitaxy should not be too fast in order to reduce the growth rate of dislocations, and the thickness of homoepitaxy should not be too thick in order to save the total growth time, so that the thickness of bulk silicon carbide single crystal grown at the homoepitaxy stage is increased by no more than 1 mm.

Further, the thickness of the bulk silicon carbide single crystal subjected to homoepitaxial growth is increased by not more than 0.5 mm.

Further, the thickness of the bulk silicon carbide single crystal subjected to homoepitaxial growth is increased by not more than 0.1 mm.

and thirdly, finishing the low-temperature slow homoepitaxial growth, and heating: introducing Ar gas with the pressure of more than 3 ten thousand Pa into the furnace chamber, raising the temperature to 2100-2500 ℃ at the temperature change speed of less than 50 ℃ per hour, and reducing the pressure to 100-8 KPa at the pressure change speed of less than 1000Pa per hour.

finally, conventional SiC single crystal growth is performed: the silicon carbide crystal is grown by a sublimation recrystallization method at the temperature of 2100-2500 ℃ and under the pressure of 100 Pa-8 KPa.

compared with the prior art, the invention has the advantages that:

1. Seed crystal surface in-situ treatment: the conventional method is that the seed crystal is ground and polished by using a polishing reagent to obtain a surface with the least relative damage, then the seed crystal is fixed on a graphite support by using glue or a mechanical structure, and then the seed crystal and a crucible are assembled and put into a single crystal furnace for single crystal growth. Since the SiC-based epitaxy and the device are both carried out on the Si surface, most researches are mainly focused on the surface treatment process of the Si surface, most of the related polishing solutions sold in the market are related to the Si surface treatment process, and the surface treatment process of the C surface is still in an immature stage. The seed crystal surface in-situ treatment method disclosed by the invention solves the problem of great difficulty in the existing C surface polishing technology on the one hand. On the other hand, the in-situ treatment method avoids secondary damage to the surface of the seed crystal in the operation links of seed crystal adhesion or fixation and the like in the non-in-situ treatment process, and is beneficial to industrialized popularization.

2. The low-temperature slow homoepitaxial growth on the C surface can effectively solve the dislocation multiplication problem in the seed crystal growth process: on one hand, when the seed crystal is processed in situ in the first step, the surface damage layer is effectively removed, meanwhile, the dislocation on the seed crystal is slightly amplified during the in situ etching processing, and when the epitaxial growth is carried out on the basis, the lateral growth speed of the dislocation is higher than the vertical growth speed, so that the healing of partial dislocation is facilitated.

On the other hand, the evaporation capacity of Si in the raw material is far greater than that of C at low temperature, and by introducing hydrocarbon gas with a certain flow into the crucible, the silicon-carbon ratio in the atmosphere can be effectively controlled, the silicon-carbon ratio of low-temperature epitaxial growth is kept stable, and defects such as silicon inclusion and the like in the growing process are reduced, so that the dislocation is reduced; meanwhile, compared with the conventional high-temperature silicon carbide growth process, the low-temperature extension is beneficial to reducing the dislocation in the grown SiC material, and the thermal expansion difference among the seed crystal, the seed crystal support and the epitaxial layer is considered to be smaller at low temperature, and the thermal stress among the seed crystal, the seed crystal support and the epitaxial layer is also smaller, so that the dislocation of the grown SiC material caused by the thermal stress is reduced.

3. The transition between the slow growth and the fast growth is carried out in a slow heating and slow pressure reduction mode, which is beneficial to reducing the growth rate of various dislocations.

4. The invention can use a seed crystal of thin thickness: the thickness of the seed crystal is generally more than 350 microns or thicker by the conventional method, the thickness of the seed crystal is less than 300 microns, preferably less than 150 microns, and the cost of growing the silicon carbide single crystal is reduced. In the conventional method, the initial growth temperature is raised to the formal growth temperature of 2100-2500 ℃, and seed crystal ablation is easily caused due to improper parameters such as seed crystal position, temperature or pressure, and the like.

Drawings

The above and other objects, configurations, and advantages of the present invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings. In the drawings, there is shown in the drawings,

Fig. 1 is a graph showing the trend of the SiC single crystal ingot grown using example 1 with the growth time.

Fig. 2 is a typical optical microscope photograph of a dislocation of a single crystal ingot head of SiC grown using example 1.

Fig. 3 is a graph showing the trend of the SiC single crystal ingot grown using example 2 with the growth time.

Fig. 4 is a typical optical microscope photograph of a dislocation of a single crystal ingot head of SiC grown using example 2.

FIG. 5 is a graph showing the trend of the SiC single crystal ingot grown using the comparative example with the growth time.

Fig. 6 is a typical optical microscope photograph of a dislocation of a single crystal ingot head of SiC grown using a comparative example.

Detailed Description

The present invention will be described in detail below.

When the sublimation recrystallization method is used for SiC single crystal growth, firstly, the temperature range of 1200 ℃ to 2000 ℃ is maintained under the condition that the vacuumizing pressure is less than 1 Pa, the temperature of the raw material is higher than the temperature of the seed crystal, the temperature difference is less than 100 ℃, the surface of the seed crystal is etched for more than 10 minutes, the vacuumizing is stopped, argon is introduced into a furnace body, the pressure is controlled between 100Pa and 10Kpa, the pressure of the furnace body is kept constant, then, hydrocarbon gas with a certain flow rate is introduced into a crucible, the surface of the seed crystal grows homogeneously at the speed of less than 50 mu ⅿ/h, the thickness of the grown massive silicon carbide single crystal is increased to be not more than 1mm, Ar gas with the pressure of more than 3 ten thousand Pa is rapidly introduced into the furnace chamber, the temperature is increased to 2100 ℃ to 2500 ℃, the pressure is reduced to between 100Pa and 8 Kpa, and the silicon carbide growth by the.

In the invention, firstly, the silicon vapor preferentially evaporated from the raw material is used for carrying out in-situ etching on the seed crystal at the temperature of 1200-2000 ℃, the surface state is removed, the original dislocation appearance is slightly amplified, and then hydrocarbon gas with a certain flow is introduced into the furnace body, so that the silicon vapor preferentially evaporated from the raw material reacts with the hydrocarbon gas on the surface of the seed crystal to generate SiC and Si₂C and SiC₂And gas is subjected to equal deposition on the surface of the seed crystal, so that a layer of SiC homoepitaxial film is generated on the surface of the seed crystal, the growth speed is close to the speed of SiC homoepitaxial, the lateral growth speed at the slightly amplified dislocation is higher than the vertical growth speed, the healing of partial dislocation is facilitated, transition is carried out between slow growth and fast growth in a mode of slow temperature rise and slow pressure drop, and the growth rate of various dislocation densities is facilitated to be reduced.