Method for growing silicon carbide crystals

Abstract

To provide a method for growing a silicon carbide crystal having uniform resistivity.SOLUTION: A method for growing a silicon carbide crystal includes the steps of: supplying a raw material including a carbon element and a silicon element and a seed crystal positioned on the raw material into a reactor; and performing the process of growing a silicon carbide crystal, including heating the reactor and the raw material to form the silicon carbide crystal on the seed crystal. The growth process controls a ratio difference (▵Tz / ▵Tx) between the axial direction temperature gradient (▵Tz) of the silicon carbide crystal and the diameter direction temperature gradient (▵Tx) within 0.5-3 to form the silicon carbide crystal, and the silicon carbide crystal formed by the growth method has a uniform resistivity distribution and excellent geometric performance.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to silicon carbide crystals, and more particularly to a method for growing silicon carbide crystals. [Background technology]

[0002] At present, silicon wafers are widely used in the semiconductor industry. Many electronic devices are equipped with silicon wafers manufactured from silicon wafers. However, in order to improve the performance of the wafers, many manufacturers have tried to use silicon carbide wafers as materials to manufacture silicon carbide chips. Silicon carbide wafers have the advantages of high temperature resistance and high stability.

[0003] As far as the prior art is concerned, when growing N-type silicon carbide crystals, there is generally a problem that the resistivity of the formed crystal is non-uniform. If the resistivity distribution of the silicon carbide crystal is uniform, the crystal stress can be reduced and the shape of the processed wafer can be improved. Furthermore, the electrical properties and performance of the silicon carbide device manufactured therefrom are also improved. In view of the above, how to manufacture silicon carbide crystals with uniform resistivity is a problem to be solved. Summary of the Invention [Problem to be solved by the invention]

[0004] It is an object of the present invention to provide a method for growing silicon carbide crystals having uniform resistivity. [Means for solving the problem]

[0005] By controlling the ratio difference between the axial temperature gradient and the radial temperature gradient of the silicon carbide crystal and adjusting the doping amount of nitrogen concentration, it is possible to produce silicon carbide crystals having uniform resistivity.

[0006] The method for growing silicon carbide crystals includes the following steps: A raw material containing carbon and silicon elements and a seed crystal located on the raw material are supplied into a reactor; A silicon carbide crystal growth process is carried out, including heating the reactor and the raw material to form a silicon carbide crystal on the seed crystal; In the growth process, the ratio difference (△Tz / △Tx) between the axial temperature gradient (△Tz) and radial temperature gradient (△Tx) of the silicon carbide crystal is adjusted to control the ratio difference within a range of 0.5 to 3 to form the silicon carbide crystal.

[0007] In one embodiment of the present invention, the ratio difference is controlled within the range of 2 to 3 to form silicon carbide crystals.

[0008] In one embodiment of the present invention, the ratio difference is controlled to a range of 2.5 to 3 to form silicon carbide crystals.

[0009] In one embodiment of the present invention, the method further comprises increasing the doping amount of the nitrogen concentration during the growth process, such that the nitrogen concentration increases from a first concentration to a second concentration.

[0010] In one embodiment of the present invention, the first concentration is 2 × 10 18 atom / cm 3 and the second concentration is 3 × 10 18 atom / cm 3 It is.

[0011] In one embodiment of the present invention, the first concentration is 2.2 × 10 18 atom / cm 3 and the second concentration is 2.9 × 10 18 atom / cm 3 It is.

[0012] In one embodiment of the present invention, the first concentration is 2.5 × 10 18 atom / cm 3 and the second concentration is 2.8 × 10 18atom / cm 3 It is.

[0013] In one embodiment of the present invention, the nitrogen concentration increases linearly.

[0014] In one embodiment of the present invention, the nitrogen concentration is increased in stages.

[0015] In one embodiment of the present invention, the increase in the doping amount of nitrogen concentration is performed by increasing the nitrogen flow rate in the reactor, and the increase in the nitrogen flow rate is controlled in the range of 10 sccm to 50 sccm.

[0016] The present invention provides a silicon carbide wafer, the single crystal ratio of which is 100%, the resistivity of which is within a range of 15 mΩcm to 20 mΩcm, and the deviation in uniformity of the resistivity of the silicon carbide wafer is less than 0.4%.

[0017] In one embodiment of the present invention, the silicon carbide wafer has a single crystal ratio of 100%, a resistivity of the silicon carbide wafer is in the range of 19 mΩcm to 20 mΩcm, and a deviation in the uniformity of the resistivity of the silicon carbide wafer is less than 0.4%.

[0018] In one embodiment of the present invention, the deviation in resistivity uniformity is less than 0.01%.

[0019] In one embodiment of the present invention, the silicon carbide wafer has a basal plane dislocation (BPD) of 200 / cm 2 is less than.

[0020] In one embodiment of the present invention, the silicon carbide wafer has a basal plane dislocation (BPD) of 140 / cm 2 is less than.

[0021] In one embodiment of the present invention, the silicon carbide wafers have less than 5 bar stacking faults (BSF) per wafer. Effect of the Invention

[0022] From the above, the N-type silicon carbide wafer formed by the silicon carbide crystal growth method according to the embodiment of the present invention has a uniform resistivity distribution. Therefore, the silicon carbide wafer obtained after the processing step has a lower wafer stress and can improve the wafer shape after processing. [Brief description of the drawings]

[0023] The accompanying drawings are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification. The drawings illustrate exemplary embodiments of the invention and, together with the description, serve to explain the principles of the invention. [Figure 1] FIG. 1 is a schematic diagram of a crystal growing apparatus according to one embodiment of the present invention. [Diagram 2] 1 is a flow chart of a method for growing silicon carbide crystals in accordance with one embodiment of the present invention. [Figure 3A] 4 is a chart illustrating different doping adjustment methods to increase the nitrogen concentration in a silicon carbide crystal growth method according to one embodiment of the present invention. [Figure 3B] 4 is a chart illustrating different doping adjustment methods to increase the nitrogen concentration in a silicon carbide crystal growth method according to one embodiment of the present invention. [Figure 3C] 4 is a chart illustrating different doping adjustment methods to increase the nitrogen concentration in a silicon carbide crystal growth method according to one embodiment of the present invention. [Figure 3D] 4 is a chart illustrating different doping adjustment methods to increase the nitrogen concentration in a silicon carbide crystal growth method according to one embodiment of the present invention. [Figure 4] 4 is a schematic flow chart of a crystal growth method according to another embodiment of the present invention. [Diagram 5] 1 is a schematic flow chart of a process for preparing a first seed crystal used in a crystal growth method according to one embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0024] Fig. 1 is a schematic diagram of a crystal growth apparatus according to one embodiment of the present invention. Fig. 2 is a flow chart of a method for growing silicon carbide crystals according to one embodiment of the present invention. A method for growing silicon carbide crystals according to some embodiments of the present invention will be described with reference to the crystal growth apparatus shown in Fig. 1 and the flow chart shown in Fig. 2.

[0025] As shown in S10 of FIG. 1 and FIG. 2, in the crystal growth process, a source material 110 including carbon and silicon elements and a seed crystal 106 on the source material 110 are fed into the reactor 102. For example, the source material 110 is silicon carbide powder, which is placed at the bottom of the reactor 102 and used as a solid sublimation source. The seed crystal 106 is placed at the top of the reactor 102. In some embodiments, the seed crystal 106 can be fixed on a seed crystal mounting platform (not shown) by an adhesive layer. The material of the seed crystal 106 includes silicon carbide. For example, the seed crystal 106 is 6H-silicon carbide or 4H-silicon carbide. In other embodiments, the seed crystal 106 includes 6H-silicon carbide and 4H-silicon carbide.

[0026] As shown in S20 of FIG. 1 and FIG. 2, in some embodiments, a silicon carbide growth process is performed to form a silicon carbide crystal 108. For example, the growth process further includes performing steps S22 and S24. In step S22, the reactor 102 and the source material 110 are heated to form a silicon carbide crystal 108 on the seed crystal 106. In step S24 of the growth process, the ratio difference (ΔTz / ΔTx) between the axial temperature gradient (ΔTz) and the radial temperature gradient (ΔTx) of the silicon carbide crystal 108 is adjusted to control the ratio difference within a range of 0.5 to 3 to form the silicon carbide crystal.

[0027] In the above steps S22 and S24, silicon carbide crystals 108 are formed on the seed crystal 106 by physical vapor transport (PVT). In some embodiments, the reactor 102 and the source material 110 are heated by the induction coil 104 to form the silicon carbide crystals 108 on the seed crystal 106. During the manufacturing process, the seed crystal 106 receives the source material 110 (silicon carbide powder) that is solidified from a gaseous state, and a semiconductor crystal is slowly formed on the seed crystal 106 until a silicon carbide crystal 108 having a desired size is obtained. Then, referring to step S30 of FIG. 1 and FIG. 2, after the silicon carbide crystal 108 grows to a desired size, the reactor 102 and the source material 110 are cooled to obtain a silicon carbide ingot composed of the silicon carbide crystal 108. In some embodiments, the ingot formed may have different crystal structures depending on the orientation of the single crystal seed crystal used. For example, silicon carbide ingot includes 4H-silicon carbide, 6H-silicon carbide, etc. Both 4H-silicon carbide and 6H-silicon carbide belong to the hexagonal crystal system.

[0028] In the above-mentioned embodiment, when the reactor 102 and the feedstock 110 are heated to form the silicon carbide crystal 108, the axial temperature gradient (ΔTz) refers to the temperature gradient in the thickness direction of the silicon carbide crystal 108, and the radial temperature gradient (ΔTx) refers to the temperature gradient of the silicon carbide crystal 108 in the horizontal direction perpendicular to the thickness direction. In some embodiments, the temperature difference is adjusted by utilizing the difference in the growth rate of each crystal orientation to achieve a ratio difference (ΔTz / ΔTx) within the range of 0.5 to 3. In general, the growth rate of the <11-20> crystal orientation is greater than that of the <1-100> crystal orientation. In the embodiment of the present invention, the growth rates of the two crystal orientations are controlled to be the same, and the crystals in each axial / radial direction can obtain a constant growth rate by adjusting the ratio difference (ΔTz / ΔTx) within the range of 0.5 to 3.

[0029] In some embodiments, the silicon carbide crystal 108 is formed by controlling the ratio difference (ΔTz / ΔTx) between the axial temperature gradient (ΔTz) and the radial temperature gradient (ΔTx) to within a range of 0.5 to 3. In some embodiments, the silicon carbide crystal 108 is formed by controlling the ratio difference (ΔTz / ΔTx) between the axial temperature gradient (ΔTz) and the radial temperature gradient (ΔTx) to within a range of 2 to 3. In some embodiments, the silicon carbide crystal 108 is formed by controlling the ratio difference (ΔTz / ΔTx) between the axial temperature gradient (ΔTz) and the radial temperature gradient (ΔTx) to within a range of 2.5 to 3. By controlling the ratio difference (ΔTz / ΔTx) between the axial temperature gradient (ΔTz) and the radial temperature gradient (ΔTx) to within the above range, the silicon carbide crystal 108 formed may have better uniformity of resistivity.

[0030] In some embodiments, when the reactor 102 and the feedstock 110 are heated to form the silicon carbide crystals 108, i.e., during the growth process of the silicon carbide crystals 108, the doping amount of nitrogen concentration is further increased to nitrogen The element concentration increases from a first concentration to a second concentration. In some embodiments, the first concentration is 2 × 10 18 atoms / cm 3 and the second concentration is 3 × 10 18 atoms / cm 3 In some embodiments, the first concentration is 2.2 × 10 18 atoms / cm 3 and the second concentration is 2.9 × 10 18 atoms / cm 3 In some embodiments, the first concentration is 2.5 × 10 18 atoms / cm 3 and the second concentration is 2.8 × 10 18 atoms / cm 3 By controlling the doping amount of nitrogen concentration within the above range, the uniformity of the resistivity of the silicon carbide crystal formed can be further optimized.

[0031] In the above embodiments, the nitrogen concentration can be increased linearly or stepwise. For example, a doping adjustment method with different nitrogen concentrations will be described with reference to Figures 3A to 3D.

[0032] 3A-3D are charts showing different doping adjustment methods for increasing the nitrogen concentration in a silicon carbide crystal growth method according to an embodiment of the present invention. As shown in FIG. 3A, in this embodiment, the flow rate of nitrogen gas increases linearly with respect to time, so the nitrogen concentration also increases linearly. As shown in FIG. 3B, in this embodiment, the flow rate of nitrogen gas increases stepwise with respect to time, so the nitrogen concentration also increases stepwise. As shown in FIG. 3C, in this embodiment, the flow rate of nitrogen gas increases stepwise with respect to time. However, in the embodiment shown in FIG. 3C, the flow rate of nitrogen gas is directly increased at the beginning of the process, unlike the process shown in FIG. 3B, in which the flow rate of nitrogen gas is stabilized at 10 sccm for a certain period of time and then the concentration increases stepwise. As shown in FIG. 3D, in this embodiment, the flow rate of nitrogen gas increases stepwise with respect to time. However, in the embodiment of FIG. 3D, the flow rate of nitrogen gas increases in each stepwise process is different, and the residence time at a particular nitrogen flow rate is also different.

[0033] In the embodiment of the present invention, the increase in the doping amount of nitrogen concentration is performed by increasing the flow rate of nitrogen gas in the reactor, so that the increase in the nitrogen flow rate is controlled within the range of 10 sccm to 50 sccm, and the nitrogen concentration can be increased linearly or stepwise using the method shown in Figures 3A to 3D above. In some embodiments, the increase in the nitrogen flow rate is controlled within the range of 10 sccm to 30 sccm.

[0034] When silicon carbide crystals are formed using the above method, the single crystal ratio of the formed silicon carbide crystal and the silicon carbide wafer obtained after processing is 100%, the resistivity of the silicon carbide crystal / wafer is in the range of 15 mΩcm to 20 mΩcm, preferably in the range of 9 mΩcm to 20 mΩcm, and the deviation of the resistivity uniformity of the silicon carbide wafer is less than 0.4%. In some embodiments, the deviation of the resistivity uniformity of the silicon carbide wafer is less than 0.01%. Furthermore, in some embodiments, the basal plane dislocations (BPDs) of the silicon carbide crystal / wafer are less than 200 / cm 2 In some embodiments, the silicon carbide crystals / wafers have a basal plane dislocation (BPD) of less than 140 / cm 2 In some embodiments, the silicon carbide crystals / wafers have less than 5 columnar stacking faults (BSFs) per wafer. This results in silicon carbide crystals / wafers with uniform resistivity distribution, and the silicon carbide crystals / wafers are formed with relatively low stress and improved wafer shape after processing.

[0035] FIG. 4 is a schematic flow chart of a crystal growth method according to another embodiment of the present invention. In some embodiments, the crystal growth process can be carried out using the silicon carbide crystal growth method described above. As shown in FIG. 4, in the crystal growth method according to the embodiment of the present invention, a first seed crystal 202 having a first single crystal ratio and a first size is provided. In some embodiments, the first single crystal ratio is 70%-80% and the first size is 200 mm.

[0036] As shown in FIG. 4, a first crystal growth process (N=1) is performed using a first seed crystal 202 to obtain an intermediate crystal 204 with an increased single crystal ratio. If it is confirmed that the single crystal ratio of the intermediate crystal 204 is not 100%, the intermediate crystal 204 is cut to obtain a growth seed crystal 204A. The previously obtained growth seed crystal 204A can then be used as a seed crystal for the next crystal growth process. For example, in a second crystal growth process (N=2), a crystal growth process is performed using the growth seed crystal 204A to obtain an intermediate crystal 206 with an increased single crystal ratio. If it is confirmed that the single crystal ratio of the intermediate crystal 206 is not 100%, the intermediate crystal 206 is cut to obtain a growth seed crystal 206A. Thus, the crystal growth process can be repeated multiple times (N=X) until the single crystal ratio of the intermediate crystal formed by the final seed crystal SD1 becomes 100%, and such intermediate crystal can be designated as a second crystal 250, completing the crystal growth method according to the embodiment of the present invention.

[0037] In the above example, the crystal growth process is performed N times on the first seed crystal 202, with each crystal growth process increasing the first single crystal ratio, and N crystal growth processes are performed until a second crystal 250 with a single crystal ratio of 100% is obtained. In other words, when an intermediate crystal with a single crystal ratio of 100% is identified, the crystal growth process is stopped to form the second crystal 250. In some embodiments, N times includes more than three crystal growth processes. In some embodiments, N times includes more than three and less than eight crystal growth processes. In some embodiments, N times includes more than four and less than six crystal growth processes.

[0038] Further, in the above embodiment, each crystal growth process includes adjusting the ratio difference (ΔTz / ΔTx) between the axial temperature gradient (ΔTz) and the radial temperature gradient (ΔTx) of the crystal to control the ratio difference within a range of 0.5 to 3. In the above embodiment, each crystal growth process includes adjusting the doping amount of nitrogen concentration by 2. × 10 18 a tom / cm 3 ~3 ×10 18 a tom / cm 3 In some embodiments, each crystal growth process is different. For example, in the embodiments of the present invention, the ratio difference (ΔTz / ΔTx) between the axial temperature gradient (ΔTz) and the radial temperature gradient (ΔTx) in each crystal growth process is different, and / or the doping amount of nitrogen concentration is different, but the ratio difference and the doping amount of nitrogen concentration are still controlled within the above range. By using the above method, it is possible to grow from a B-class crystal (low single crystal ratio) to an A-class crystal (100% single crystal ratio) with a certain number of crystal growth processes. Therefore, the time required to form a large-diameter crystal with a high single crystal ratio can be significantly reduced.

[0039] FIG. 5 is a schematic flow chart of the preparation of a first seed crystal used in a crystal growth method according to an embodiment of the present invention. In some embodiments, a smaller size seed crystal can be used to expand the diameter and form a larger size crystal. As shown in FIG. 5, in some embodiments, a preliminary seed crystal PX1 is provided, and the preliminary seed crystal PX1 has a size A and a single crystal ratio A'. In some embodiments, the size A is smaller than the first size of the first seed crystal 202, and the single crystal ratio A' is larger than the first single crystal ratio of the first seed crystal 202. For example, the first single crystal ratio of the first seed crystal 202 is 70% to 80%, the first size is 200 mm, the single crystal ratio A' of the preliminary seed crystal PX1 is 100%, and the size A of the preliminary seed crystal PX1 is 150 mm.

[0040] As shown in Fig. 5, the preliminary seed crystal PX1 is used to perform a crystal growth process to obtain a first crystal PX2 having the above-mentioned first size and the above-mentioned first single crystal ratio. In an embodiment of the present invention, the crystal growth process of the preliminary seed crystal PX1 is performed by adjusting the ratio difference (ΔTz / ΔTx) between the axial temperature gradient (ΔTz) and the radial temperature gradient (ΔTx) of the crystal to control the ratio difference within a range of 0.5 to 3 and the doping amount of nitrogen concentration to 2. × 10 18 atoms / cm3 ~3 × 10 18 atoms / cm 3 After the first crystal PX2 is obtained, the first crystal PX2 is cut to obtain the above-mentioned expanded first seed crystal 202, and the process shown in FIG. 4 is carried out using the first seed crystal 202 to obtain a second crystal 250 with a single crystal ratio of 100%. By using the above method, a grade A seed crystal (single crystal ratio 100%) can be grown and expanded to form a larger size grade A crystal (single crystal ratio 100%) within a certain number of crystal growth processes. Therefore, the time required to form a large diameter crystal with a high single crystal ratio can be significantly shortened, and the conventional multiple diameter expansion steps and diameter expansion period of several years required for crystal expansion can be avoided.

[0041] Working Example

[0042] The following examples are carried out and described to demonstrate that the method of the present invention is capable of producing silicon carbide crystals having uniform resistivity and significantly reduces the time required to form large crystals with a high proportion of single crystals.

[0043] First example:

[0044] In the first example, (i) the ratio difference (ΔTz / ΔTx) between the axial temperature gradient (ΔTz) and the radial temperature gradient (ΔTx), (ii) the nitrogen concentration doping variation method, and (iii) the nitrogen concentration doping amount in Examples 1 to 7 and Comparative Examples 1 to 4 were adjusted as shown in Tables 1 and 2 below. Furthermore, a growth process was carried out to form silicon carbide crystals using the method described in Figures 1 and 2. Evaluations of the basal plane dislocations (BPDs), wafer single crystal rate, wafer resistivity, wafer resistivity uniformity deviation, and columnar stacking faults (BSFs) of the obtained silicon carbide crystal wafers are also shown in Tables 1 and 2.

[0045] [Table 1]

[0046] [Table 2]

[0047] According to the experimental results of Examples 1 to 7 shown in Table 1, the ratio difference (ΔTz / ΔTx) between the axial temperature gradient (ΔTz) and the radial temperature gradient (ΔTx) was controlled within the range of 0.5 to 3, the doping change method of the nitrogen concentration was adjusted from low to high, and the doping amount of the nitrogen concentration was increased by 2. × 10 18 atoms / cm 3 ~3 × 10 18 atoms / cm 3 When the resistivity is controlled within the range, the single crystal ratio of the obtained silicon carbide crystal is 100%, and the silicon carbide wafer obtained after processing has a uniform resistivity distribution (the deviation of the resistivity uniformity is less than 0.4%) and the basal plane dislocation of the wafer is small. ( BPD) is 200 / cm 2 The number of columnar stacking faults is controlled to less than 5 / wafer (ea / wf), and the wafer resistivity (15-20 mΩ·cm) is also within an ideal range, preferably within the range of 19 mΩcm-20 mΩcm.

[0048] Going one step further, the ratio difference (ΔTz / ΔTx) is controlled within the range of 2 to 3, and the nitrogen doping amount is set to 2.1 × 10 18 atoms / cm 3 ~2.9 × 10 18 atoms / cm 3 When the ratio difference (ΔTz / ΔTx) was controlled within the range of 2.5 to 3, and the doping amount of nitrogen concentration was controlled within the range of 2.4, the silicon carbide wafer obtained after processing the silicon carbide crystal had a better uniformity of resistivity distribution and fewer wafer defects and columnar stacking faults were observed. × 10 18 atoms / cm 3 ~.8 × 10 18 atoms / cm 3When the resistivity distribution was controlled within this range, the silicon carbide wafer obtained had the most uniform resistivity distribution and the fewest defects such as basal plane dislocations (BPDs) and columnar stacking faults (BSFs) were observed. Therefore, the silicon carbide wafer obtained by processing the N-type silicon carbide crystal formed by the silicon carbide crystal growth method according to the embodiment of the present invention has a uniform resistivity distribution, low crystal stress, and improved wafer shape after processing.

[0049] In contrast, in the experimental results shown in Table 2, referring to Comparative Example 1, the ratio difference (ΔTz / ΔTx) was not controlled within the range of 0.5 to 3, the nitrogen doping method was not changed, and the nitrogen concentration was 1 × 10 18 atoms / cm 3 When a fixed doping concentration of 1000 nm was used, the uniformity of the resistivity distribution of the obtained silicon carbide wafer was not good. ( With reference to Comparative Example 2, even if the ratio difference (ΔTz / Δx) is controlled within the range of 0.5 to 3, when the nitrogen concentration doping method is not changed and a fixed doping concentration is used, the resistivity uniformity of the obtained silicon carbide wafer is still not good (uniformity deviation >4%), and the results of defects such as basal plane dislocations (BPDs) and columnar stacking faults (BSFs) are also not good. With reference to Comparative Examples 3 and 4, although the nitrogen concentration doping is changed from a low concentration to a high concentration, the ratio difference (ΔTz / Δx) is not controlled within the range of 0.5 to 3, and the doping amount of the nitrogen concentration is 2. × 10 18 atoms / cm 3 ~3 × 10 18 atoms / cm 3 When the resistivity distribution is not controlled within the range, although the uniformity of the resistivity distribution is slightly improved compared to Comparative Examples 1-2 (deviation of uniformity > 1.5%), the uniformity of the resistivity distribution is still not within the ideal range, and the results of defects such as basal plane dislocations (BPDs) and columnar stacking faults (BSFs) are still not good.

[0050] Second Example

[0051] In the second example, (i) the ratio difference (ΔTz / ΔTx) between the axial temperature gradient (ΔTz) and the radial temperature gradient (ΔTx), (ii) the doping variation method of the nitrogen concentration, and (iii) the doping amount of the nitrogen concentration in the crystal growth processes of Examples 8 to 11 and Comparative Examples 5 to 8 were adjusted as shown in Tables 3 to 10 below. Furthermore, a crystal growth process was performed using a first seed crystal by the method described in FIG. 4 to form a silicon carbide crystal. The evaluations of basal plane dislocations (BPDs), single crystal ratio, resistivity, deviation of resistivity uniformity, and rod-column stacking faults (BSFs) in each crystal growth process of the obtained silicon carbide crystal are also shown in Tables 3 to 10.

[0052] [Table 3]

[0053] [Table 4]

[0054] [Table 5]

[0055] [Table 6]

[0056] [Table 7] JPEG0007650918000008.jpg249155

[0057] [Table 8] JPEG0007650918000010.jpg249159

[0058] [Table 9] JPEG0007650918000012.jpg249155

[0059] [Table 10] JPEG0007650918000014.jpg249159

[0060] As can be seen from the experimental results of Examples 8 to 11 shown in Tables 3 to 6 above, the ratio difference (ΔTz / ΔTx) was controlled within the range of 0.5 to 3, and the doping amount of nitrogen concentration was 2. × 10 18 atoms / cm 3 ~3 × 10 18 atoms / cm 3 When the nitrogen concentration is controlled within this range, a B-class seed crystal (with a low single crystal ratio) can be grown into an A-class crystal (100% single crystal ratio) in no more than six crystal growth processes (N=6), regardless of how the nitrogen doping method is changed, and the basal plane dislocations (BPDs), resistivity, resistivity uniformity, and columnar stacking faults (BSFs) are all controlled within ideal ranges; for example, the BSFs are controlled to 5 sheets / wafer or less.

[0061] In comparison, as can be seen from the experimental results of Comparative Examples 5 to 8 shown in Tables 7 to 10 above, when the ratio difference (ΔTz / ΔTx) between the axial temperature gradient (ΔTz) and the radial temperature gradient (ΔTx) in each crystal growth process does not satisfy the above range and the doping amount of nitrogen concentration is outside the above range, even if the crystal growth process is performed 11 to 13 times, it is not possible to grow a B-class seed crystal (low single crystal ratio) and form a crystal with a single crystal ratio of 100%, and the results of basal plane dislocations (BPDs), resistivity uniformity, and columnar stacking faults are also insufficient. Therefore, it can be seen that according to the crystal growth method of the present invention, the time required to form a large-diameter crystal with a high single crystal ratio can be significantly shortened.

[0062] Third Example

[0063] In the third example, (i) the ratio difference (ΔTz / ΔTx) between the axial temperature gradient (ΔTz) and the radial temperature gradient (ΔTx), (ii) the doping variation method of the nitrogen concentration, and (iii) the doping amount of the nitrogen concentration in the crystal growth process of Example 12 and Comparative Example 9 were adjusted as shown in Tables 11 to 12 below. In addition, as shown in FIG. 5, a smaller-sized seed crystal was used in the preliminary process (N=0), and the diameter of the smaller-sized crystal was expanded to form a larger-sized crystal, which was then cut to form a first seed crystal. Then, a crystal growth process was performed using the first seed crystal by the method shown in FIG. 4 to form a silicon carbide crystal. Tables 11 to 12 also show the evaluations of basal plane dislocations (BPDs), single crystal ratio, resistivity, deviation in resistivity uniformity, and columnar stacking faults (BSFs) in each crystal growth process of the obtained silicon carbide crystal.

[0064] [Table 11]

[0065] [Table 12] JPEG0007650918000017.jpg249144

[0066] As can be seen from the experimental results of Example 12 shown in Table 11 above, a smaller-sized A-class spare seed crystal (single crystal ratio 100%) was used to expand the diameter and form a first seed crystal, and the ratio difference (ΔTz / ΔTx) between the axial temperature gradient (ΔTz) and the radial temperature gradient (ΔTx) in each crystal growth process was controlled within the range of 0.5 to 3, and the doping amount of nitrogen concentration was increased to 2. × 10 18 atoms / cm 3 ~3 × 10 18 atoms / cm 3When the nitrogen concentration is controlled within this range, a smaller-sized A-grade seed crystal (single crystal ratio 100%) can be grown into a large-sized A-grade crystal (single crystal ratio 100%) that is expanded in a crystal growth process within one pre-expansion and four times (N=4), regardless of how the nitrogen concentration doping method is changed, and the basal plane dislocations (BPDs), resistivity, resistivity uniformity, and columnar stacking faults (BSFs) are all controlled within ideal ranges; for example, the BSFs are controlled to 5 sheets / wafer or less.

[0067] In contrast, as can be seen from the experimental results of Comparative Example 9 shown in Table 12 above, when the ratio difference (ΔTz / ΔTx) between the axial temperature gradient (ΔTz) and the radial temperature gradient (ΔTx) in each crystal growth process does not satisfy the above range and the doping amount of nitrogen concentration is outside the above range, even if the preliminary diameter expansion is performed once and the crystal growth process is performed ten times, it is not possible to grow a small-diameter A-class seed crystal (single crystal ratio 100%) to form a larger crystal with a single crystal ratio of 100%, and the results of basal plane dislocations (BPDs), resistivity uniformity, and columnar stacking faults are also insufficient. Therefore, it can be understood that the crystal growth method of the embodiment of the present invention can significantly shorten the time required to form a large-sized crystal with a high single crystal ratio, and therefore can avoid the multiple diameter expansion steps and the diameter expansion period of several years required in the conventional crystal diameter expansion.

[0068] In summary, the N-type silicon carbide crystal formed by the silicon carbide crystal growth method of the embodiment of the present invention has a uniform resistivity distribution. Therefore, the crystal stress of the formed silicon carbide crystal is low, and the shape of the wafer after processing is improved. In addition, according to the crystal growth method of the present invention, the time required to form a large crystal with a high single crystal ratio can be significantly shortened, and large diameter crystals and / or crystals with a single crystal ratio of 100% can be obtained within a certain number of crystal growth processes.

[0069] It will be apparent to one skilled in the art that various modifications and variations can be made to the disclosed embodiments without departing from the scope or spirit of the invention. In view of the above, it is intended that the present invention cover modifications and variations provided they come within the scope of the appended claims and their equivalents. [Industrial Applicability]

[0070] The silicon carbide crystal growth method of the present invention can be applied to the formation of silicon carbide wafers having lower wafer stress and improved wafer shape. [Explanation of symbols]

[0071] 102: Reactor 104: Induction coil 106: Seed Crystal 108: Silicon carbide crystal 110: Raw materials 202: First seed crystal 204, 206: Intermediate crystals 204A, 206A: Growth seed crystal 250: Second Crystal PX1: spare seed crystal PX2: First Crystal S10, S20, S22, S24, S30: Process SD1: Seed crystal

Claims

1. Supplying a raw material containing carbon and silicon elements into a reactor and a seed crystal located on the raw material; conducting a silicon carbide crystal growth process including heating the reactor and the feedstock to form a silicon carbide crystal on the seed crystal; In the growth process, a ratio difference (ΔTz / ΔTx) between an axial temperature gradient (ΔTz) and a radial temperature gradient (ΔTx) of the silicon carbide crystal is adjusted to be controlled within a range of 0.5 to 3, thereby forming the silicon carbide crystal; The axial temperature gradient (ΔTz) is the temperature gradient in the thickness direction of the silicon carbide crystal, and the radial temperature gradient (ΔTx) is the temperature gradient in the silicon carbide crystal in the horizontal direction perpendicular to the thickness direction. The method for growing silicon carbide crystals further comprises increasing a doping amount of the nitrogen concentration during the growth process, such that the nitrogen concentration increases from a first concentration to a second concentration, the first concentration being 2×10 18 atoms / cm 3 and the second concentration being 3×10 18 atoms / cm 3 , and the doping amount of the nitrogen concentration does not decrease during the growth process.

2. The method of claim 1, wherein the ratio difference is controlled in the range of 2 to 3 to form the silicon carbide crystals.

3. The method according to claim 2, wherein the ratio difference is controlled in the range of 2.5 to 3 to form silicon carbide crystals. ××

4. The first concentration is 2.1×10 １８ atom / cm ３ and the second concentration is 2.9×10 １８ atom / cm ３ The method of claim 1, wherein

5. The first concentration is 2.4×10 １８ atom / cm ３ and the second concentration is 2.8×10 １８ atom / cm ３ The method of claim 1, wherein

6. The method of claim 1 , wherein the nitrogen concentration increases linearly.

7. The method of claim 1 , wherein the nitrogen concentration is increased in steps.

8. 2. The method of claim 1, wherein the step of increasing the doping amount of the nitrogen concentration is performed by increasing a nitrogen flow rate in the reactor, and the increase in the nitrogen flow rate is controlled within a range of 10 sccm to 50 sccm.

9. A method for producing a silicon-based catalyst comprising: supplying a raw material containing carbon and silicon elements into a reactor; and a seed crystal located on the raw material; conducting a silicon carbide crystal growth process including heating the reactor and the feedstock to form a silicon carbide crystal on the seed crystal; In the growth process, a ratio difference (ΔTz / ΔTx) between an axial temperature gradient (ΔTz) and a radial temperature gradient (ΔTx) of the silicon carbide crystal is adjusted to be controlled within a range of 0.5 to 3, thereby forming the silicon carbide crystal; The axial temperature gradient (ΔTz) is the temperature gradient in the thickness direction of the silicon carbide crystal, and the radial temperature gradient (ΔTx) is the temperature gradient in the silicon carbide crystal in the horizontal direction perpendicular to the thickness direction. The method for growing silicon carbide crystals further comprises increasing a doping amount of the nitrogen concentration during the growth process, such that the nitrogen concentration increases from a first concentration to a second concentration, wherein the step of increasing the doping amount of the nitrogen concentration is performed by increasing a nitrogen flow rate in the reactor, and the increase in the nitrogen flow rate is controlled within a range of 10 sccm to 50 sccm.

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