Method for reducing silicon inclusion defect in silicon carbide single crystal
By performing microwave sintering and water washing treatment on silicon carbide powder before growth, the problem of silicon inclusion defects in silicon carbide single crystals was solved, improving crystal quality and device performance.
Patent Information
- Application Number
- CN202511995593.4
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-12-26
- Publication Date
- 2026-02-06
AI Technical Summary
Existing technologies are insufficient to effectively reduce silicon inclusion defects in silicon carbide single crystals, especially since silicon inclusion defects caused by Si-rich gas phase during growth severely affect lattice integrity and device performance.
Before the growth of silicon carbide powder, microwave sintering is carried out under vacuum conditions and a protective atmosphere in three stages, including low-temperature degassing, rapid heating and holding for silicon release, followed by water washing and drying. The sintering process is optimized to improve the Si/C stoichiometric imbalance.
It effectively reduces the density of silicon inclusion defects and the content of free silicon in silicon carbide single crystals, improves crystal integrity and device performance, and avoids avalanche breakdown and leakage current problems caused by Si-rich gas phase.
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Abstract
Description
TECHNICAL FIELD
[0001] The application belongs to the technical field of silicon carbide crystal preparation, and particularly relates to a method for reducing silicon inclusions in a silicon carbide single crystal. BACKGROUND
[0002] In recent years, silicon carbide materials gradually replace silicon-based materials to become a new third-generation semiconductor material due to the characteristics of strong radiation resistance, wide band gap, high breakdown electric field, high electron mobility, etc.
[0003] Among several common defects of a silicon carbide wafer, such as inclusions, polytypes, dislocations, microtubules, etc., inclusions are a kind of defects with extremely great harm. The mismatch between inclusions and a silicon carbide lattice can introduce defects such as stress and dislocations at the defects, which seriously damages the integrity of the lattice and can cause device failure and cracking of the crystal.
[0004] Common inclusions in a silicon carbide wafer include carbon inclusions, silicon inclusions, carbon-silicon compound inclusions, etc. Silicon inclusions formed by liquid silicon drops at high temperatures can induce substrate effects, causing local electric field concentration in the growth process of silicon carbide epitaxy, resulting in problems such as avalanche breakdown or increased leakage current. SUMMARY
[0005] The purpose of the present application is to provide a method for reducing silicon inclusions in a silicon carbide single crystal. The method in the present application can effectively improve the silicon inclusions directly generated due to gas phase Si enrichment in the growth process.
[0006] The present application provides a method for reducing silicon inclusions in a silicon carbide single crystal. Before growing a silicon carbide crystal from silicon carbide powder, the following pretreatment is performed:
[0007] A) Under vacuum conditions and a protective atmosphere, microwave sintering is performed on the silicon carbide powder;
[0008] The microwave sintering includes a first stage, a second stage and a third stage;
[0009] In the first stage, the silicon carbide powder is heated from room temperature to a temperature T1 at a microwave power P1, and is kept at the temperature T1 for a time t1;
[0010] In the second stage, the silicon carbide powder is heated from the temperature T1 to a temperature T2 at a microwave power P2;
[0011] In the third stage, the temperature T2 is maintained constant at a microwave power P3 for a time t2;
[0012] P2>P1, and P3≤P2;
[0013] T1 is 300-600℃, and T2 is 1400-1800℃.
[0014] B) The microwave-sintered silicon carbide powder is washed with water and dried to obtain pretreated silicon carbide powder.
[0015] Preferably, the silicon carbide powder in step A) has a purity of >99.99% and a particle size of 0.25mm~1.00mm.
[0016] Preferably, the vacuum degree of the microwave sintering is 200~500Pa.
[0017] Preferably, P1 is 1~3KW, and the heating rate in the first stage is 300~500℃ / h.
[0018] Preferably, t1 is 10~30 min.
[0019] Preferably, P2 is 6~10KW; the heating rate of the second stage is 500~1000℃ / h.
[0020] Preferably, P3 is 5~10KW and T2 is 30~120min.
[0021] Preferably, the drying temperature in step B) is 100~200℃ and the drying time is 15~25h.
[0022] Preferably, the silicon carbide powder is placed in a growth crucible for microwave sintering;
[0023] The crucible is a graphite crucible, and the crucible is covered with a graphite crucible lid.
[0024] Preferably, the pretreated silicon carbide powder is used to grow silicon carbide crystals using the PVT method.
[0025] This invention provides a method for reducing silicon inclusion defects in silicon carbide single crystals. Before growing silicon carbide crystals from silicon carbide powder, the following pretreatment is performed: A) Microwave sintering of silicon carbide powder under vacuum and a protective atmosphere; the microwave sintering includes a first stage, a second stage, and a third stage; the first stage heats the silicon carbide powder from room temperature to temperature T1 using microwave power P1, and holds it at temperature T1 for time t1; the second stage heats the silicon carbide powder from temperature T1 to temperature T2 using microwave power P2; the third stage maintains a constant temperature T2 using microwave power P3, and holds it at temperature t2; P2 > P1, P3 ≤ P2; T1 is 300~600℃, and T2 is 1400~1800℃; B) The microwave-sintered silicon carbide powder is washed with water and dried. This invention employs a microwave sintering method and sets up a corresponding sintering program to improve the gas-phase Si-rich phenomenon caused by Si / C stoichiometry imbalance in the early stage of silicon carbide growth, thereby effectively improving the silicon inclusion defects directly caused by gas-phase Si-richness during the growth process. Attached Figure Description
[0026] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.
[0027] Figure 1 This is a schematic diagram of the apparatus for the preprocessing method in an embodiment of the present invention;
[0028] 1 is the crucible, 2 is the silicon carbide powder, 3 is the crucible lid, and 4 is the hole in the crucible lid. Detailed Implementation
[0029] This invention provides a method for reducing silicon inclusion defects in silicon carbide single crystals, comprising the following pretreatment before growing silicon carbide crystals from silicon carbide powder:
[0030] A) Microwave sintering of silicon carbide powder under vacuum conditions and a protective atmosphere;
[0031] The microwave sintering includes a first stage, a second stage, and a third stage;
[0032] In the first stage, silicon carbide powder is heated from room temperature to temperature T1 using microwave power P1, and held at temperature T1 for time t1.
[0033] The second stage uses microwave power P2 to heat the silicon carbide powder from temperature T1 to temperature T2;
[0034] The third stage maintains a constant temperature T2 using microwave power P3 for a holding time t2.
[0035] P2>P1,P3≤P2;
[0036] T1 is 300~600℃, and T2 is 1400~1800℃;
[0037] B) Wash and dry the microwave-sintered silicon carbide powder.
[0038] The present invention first loads silicon carbide powder into a growth crucible and places the growth crucible in the resonant cavity of a microwave sintering furnace.
[0039] In this invention, the silicon carbide powder preferably has a purity of >99.99% and a particle size of 0.25mm~1.00mm. This invention does not have special requirements for the source of the silicon carbide powder; it can be purchased as a commercial product or prepared by itself according to methods known in the art.
[0040] In this invention, the growth crucible is preferably a graphite crucible, and the crucible lid is preferably a graphite crucible lid. Preferably, the silicon carbide powder is evenly spread and placed inside the growth crucible for pre-firing.
[0041] In this invention, the crucible lid of the growth crucible has small holes to facilitate the escape of gas.
[0042] In this invention, the microwave sintering furnace is equipped with a non-contact infrared thermometer for accurately detecting microwave power and temperature.
[0043] After placing the growth crucible containing silicon carbide powder into the microwave sintering furnace, close the furnace door, start the vacuum pump group, and evacuate the pressure in the furnace cavity to the preset vacuum level. Then, fill the furnace cavity with a protective atmosphere to near atmospheric pressure, and perform the vacuuming operation again. Repeat this process 2 to 3 times to fully replace the air in the furnace cavity.
[0044] In this invention, the vacuum degree is preferably 200~500Pa, more preferably 300~400Pa, and the protective atmosphere is preferably high-purity nitrogen and / or high-purity argon.
[0045] After completing the above-mentioned vacuuming and atmosphere replacement, the present invention starts the microwave source and performs microwave sintering of silicon carbide powder according to the preset heating program.
[0046] In this invention, the microwave sintering sequentially includes a first stage, a second stage, and a third stage;
[0047] The first stage is the low-temperature degassing stage, in which the silicon carbide powder is slowly heated from room temperature to temperature T1 using microwave power P1, and held at temperature T1 for time t1, so that the moisture and gas adsorbed in the powder can be slowly released, avoiding spraying caused by rapid heating.
[0048] The second stage is the rapid heating stage, in which the microwave power is increased to P2, and the silicon carbide powder is heated from temperature T1 to the target temperature T2 at a relatively fast heating rate.
[0049] The third stage is the heat preservation and silicon release stage. The microwave power is adjusted to P3 to maintain the temperature at a constant T2. The temperature is maintained at T2 for a time t2. During this process, the free silicon in the powder is heated and evaporated, and the silicon vapor is extracted under the negative pressure environment of the furnace cavity.
[0050] In this invention, P1 is preferably 1~3KW, more preferably 1~2KW; T1 is preferably 300~600℃, more preferably 400~500℃, such as 300℃, 350℃, 400℃, 450℃, 500℃, 550℃, 600℃, preferably a range of values with any of the above values as the upper or lower limit; t1 is preferably 10~30min, more preferably 15~25min, such as 10 min, 15 min, 20 min, 25 min, 30 min, preferably a range of values with any of the above values as the upper or lower limit; the heating rate of the first stage is preferably 300~500℃ / h, more preferably 350~450℃ / h, such as 300℃ / h, 350℃ / h, 400℃ / h, 450℃ / h, 500℃ / h, preferably a range of values with any of the above values as the upper or lower limit.
[0051] In this invention, P2 is preferably 6~10KW, more preferably 7~9KW, such as 6 KW, 7 KW, 8 KW, 9 KW, 10KW, preferably values within the range of any of the above values as the upper or lower limit; T2 is preferably 1400~1800℃, more preferably 1500~1700℃, such as 1400℃, 1450℃, 1500℃, 1550℃, 1600℃, 1650℃, 1700℃, 1750℃, 1800℃, preferably values within the range of any of the above values as the upper or lower limit; the heating rate of the second stage is preferably 500~1000℃ / h, more preferably 600~900℃ / h, such as 500℃ / h, 550℃ / h, 600℃ / h, 650℃ / h, 700℃ / h, 750℃ / h, 800℃ / h, 850℃ / h, 900℃ / h, 950℃ / h, 1000℃ / h, preferably values within the range of any of the above values as the upper or lower limit.
[0052] In this invention, P3 is preferably 5~10KW, more preferably 6~9KW, such as 5 KW, 6 KW, 7 KW, 8 KW, 9 KW, 10 KW, and preferably a range of values with any of the above values as the upper or lower limit; t2 is preferably 30~120min, more preferably 50~100min, such as 30 min, 35 min, 40 min, 45 min, 50 min, 55 min, 60 min, 65 min, 70 min, 75 min, 80 min, 85 min, 90 min, 95 min, 100 min, 105 min, 110 min, 115 min, 120min, and preferably a range of values with any of the above values as the upper or lower limit.
[0053] After the heat preservation is completed, the microwave source is turned off, and after cooling, the microwave sintered silicon carbide powder is taken out. In this invention, the sintered silicon carbide powder is washed with pure water and dried to obtain pretreated silicon carbide powder.
[0054] In this invention, the pure water used for cleaning has a resistivity greater than 1 MΩ·cm, a conductivity less than 1µS / cm, and a total organic carbon content less than 50 ppb.
[0055] In this invention, the drying temperature is preferably 100~200℃, more preferably 120~180℃, such as 100℃, 110℃, 120℃, 130℃, 140℃, 150℃, 160℃, 170℃, 180℃, 190℃, 200℃, preferably a range of values with any of the above as the upper or lower limit; the drying time is preferably 15~25h, more preferably 18~20h.
[0056] After pretreatment, silicon carbide powder can be used to grow silicon carbide crystals using the PVT (physical vapor transport) method. This invention does not impose any special restrictions on the process parameters for growing silicon carbide crystals using the PVT method; conventional processes for growing silicon carbide crystals from silicon carbide powder using PVT in this field can be used.
[0057] This invention provides a method for reducing silicon inclusion defects in silicon carbide single crystals. Before growing silicon carbide crystals from silicon carbide powder, the following pretreatment is performed: A) Microwave sintering of silicon carbide powder under vacuum and a protective atmosphere; the microwave sintering includes a first stage, a second stage, and a third stage; the first stage heats the silicon carbide powder from room temperature to temperature T1 using microwave power P1, and holds it at temperature T1 for time t1; the second stage heats the silicon carbide powder from temperature T1 to temperature T2 using microwave power P2; the third stage maintains a constant temperature T2 using microwave power P3, and holds it at temperature t2; P2 > P1, P3 ≤ P2; T1 is 300~600℃, and T2 is 1400~1800℃; B) The microwave-sintered silicon carbide powder is washed with water and dried. This invention employs a microwave sintering method and sets up a corresponding sintering program to improve the gas-phase Si-rich phenomenon caused by Si / C stoichiometry imbalance in the early stage of silicon carbide growth, thereby effectively improving the silicon inclusion defects directly caused by gas-phase Si-richness during the growth process.
[0058] To further illustrate the present invention, the following describes in detail a method for reducing silicon inclusion defects in silicon carbide single crystals provided by the present invention with reference to embodiments, but it should not be construed as limiting the scope of protection of the present invention.
[0059] Example 1
[0060] Select a graphite crucible with an outer diameter of 25cm, an inner diameter of 23cm, and a height of 30cm;
[0061] Select silicon carbide powder with a purity greater than 99%;
[0062] refer to Figure 1 Spread silicon carbide powder evenly in a graphite crucible, and place a graphite crucible lid on top of the crucible;
[0063] Silicon carbide raw materials were pre-calcined using a microwave method. In the first stage, P1 was set to 2.5KW with a heating rate of 500℃ / h, T1 was controlled at 500℃, and t1 time was set to 20min. In the second stage, P2 was set to 8KW with a heating rate of 1000℃ / h and T2 was controlled at 1600℃. In the third stage, P3 was set to 8KW with t2 set to 4h.
[0064] The pre-calcined silicon carbide powder was collected, washed with pure water, and dried.
[0065] Silicon carbide crystals were grown using the PVT method with treated powder.
[0066] Example 2
[0067] Silicon carbide powder was subjected to a three-stage sintering pretreatment and growth to obtain silicon carbide crystals according to the method in Example 1. The difference is that t2 in Example 2 is 6h.
[0068] Example 3
[0069] Silicon carbide powder was subjected to a three-stage sintering pretreatment and growth to obtain silicon carbide crystals according to the method in Example 1. The difference is that the temperature T2 in Example 3 was 1400℃.
[0070] Comparative Example 1
[0071] Silicon carbide powder was subjected to a three-stage sintering pretreatment and growth to obtain silicon carbide crystals according to the method in Example 1. The difference is that in Comparative Example 1, the induction coil method was used instead of the microwave sintering furnace to sinter the silicon carbide powder.
[0072] Comparative Example 2
[0073] Silicon carbide crystals were grown using silicon carbide powder according to the method in Example 1. The difference between Example 1 and Comparative Example 2 is that no pretreatment was performed on the silicon carbide powder, and silicon carbide crystals were grown directly.
[0074] Comparative Example 3
[0075] Silicon carbide crystals were grown using silicon carbide powder according to the method in Example 1. However, unlike Example 1, Comparative Example 3 only performed two-stage pretreatment on the silicon carbide powder, skipping the low-temperature degassing stage and directly heating it from room temperature to T2 at power P2, followed by heat preservation to release silicon.
[0076] The silicon carbide crystals prepared in the examples and comparative examples were sliced and polished to obtain the test samples. The performance of the test samples was tested according to the following methods, and the results are shown in Table 1.
[0077] 1) Record the electrical energy consumed during the pre-burning process using a high-precision digital energy meter;
[0078] 2) The mass percentage of free silicon in the powder was calculated using inductively coupled plasma atomic emission spectrometry;
[0079] 3) Detect the density of defects in wafer inclusions using an automated microscope.
[0080] Table 1. Performance of silicon carbide crystals in the examples and comparative examples.
[0081]
[0082] As can be seen from Examples 1-3, Comparative Examples 1 and 2 and Table 1, the pretreatment method of the present invention can effectively reduce the density of silicon encapsulation in the wafer and the free silicon content in the raw materials.
[0083] As can be seen from Examples 1-3 and Table 1, the increase in pre-firing time leads to an increase in the density of silicon inclusions, proving that appropriate pre-firing time and temperature can reduce the density of silicon inclusions in silicon carbide crystals. However, excessive time or temperature will lead to excessive evaporation of silicon and graphitization of the powder, resulting in negative effects. Therefore, in this invention, the pre-firing time and temperature of the powder have a direct improving effect on the density of silicon inclusions and the free silicon content in the raw materials.
[0084] As can be seen from Example 1, Comparative Example 3 and Table 1, the low-temperature degassing stage for processing silicon carbide powder in this invention can reduce the density of silicon inclusions.
[0085] Combined with Example 1, Comparative Example 1 and Table 1, it can be seen that different pre-burning methods affect the density of silicon encapsulation and the content of free silicon. Although Comparative Example 1 uses the same heating procedure, the induction coil method is effective for carbon encapsulation, but for silicon encapsulation, there is a significant difference in effect compared with the pretreatment method in this application.
[0086] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.
Claims
1. A method for reducing silicon inclusion defects in silicon carbide single crystals, characterized in that, Before growing silicon carbide crystals from silicon carbide powder, the following pretreatment is performed: A) Microwave sintering of silicon carbide powder under vacuum conditions and a protective atmosphere; The microwave sintering includes a first stage, a second stage, and a third stage; In the first stage, silicon carbide powder is heated from room temperature to temperature T1 using microwave power P1, and held at temperature T1 for time t1. The second stage uses microwave power P2 to heat the silicon carbide powder from temperature T1 to temperature T2; The third stage maintains a constant temperature T2 using microwave power P3 for a holding time t2. P2>P1,P3≤P2; T1 is 300~600℃, and T2 is 1400~1800℃; B) The microwave-sintered silicon carbide powder is washed with water and dried to obtain pretreated silicon carbide powder.
2. The method for reducing silicon inclusion defects in silicon carbide single crystals according to claim 1, characterized in that, The silicon carbide powder in step A) has a purity of >99.99% and a particle size of 0.25mm~1.00mm.
3. The method for reducing silicon inclusion defects in silicon carbide single crystals according to claim 1, characterized in that, The vacuum degree of the microwave sintering is 200~500Pa.
4. The method for reducing silicon inclusion defects in silicon carbide single crystals according to claim 1, characterized in that, P1 is 1~3KW, and the heating rate in the first stage is 300~500℃ / h.
5. The method for reducing silicon inclusion defects in silicon carbide single crystals according to claim 1, characterized in that, t1 is 10~30 min.
6. The method for reducing silicon inclusion defects in silicon carbide single crystals according to claim 1, characterized in that, P2 is 6~10KW; the heating rate in the second stage is 500~1000℃ / h.
7. The method for reducing silicon inclusion defects in silicon carbide single crystals according to claim 1, characterized in that, P3 is 5~10KW, T2 is 30~120min.
8. The method for reducing silicon inclusion defects in silicon carbide single crystals according to claim 1, characterized in that, The drying temperature in step B) is 100~200℃, and the drying time is 15~25h.
9. The method for reducing silicon inclusion defects in silicon carbide single crystals according to claim 1, characterized in that, The silicon carbide powder was placed in a growth crucible and microwave sintered. The crucible is a graphite crucible, and the crucible is covered with a graphite crucible lid.
10. The method for reducing silicon inclusion defects in silicon carbide single crystals according to claim 1, characterized in that, The pretreated silicon carbide powder was used to grow silicon carbide crystals using the PVT method.