JP4374986B2 - Method for manufacturing silicon carbide substrate - Google Patents

Description

  The present invention relates to a method for manufacturing a silicon carbide (SiC) substrate and a SiC substrate, and more particularly to a method for manufacturing a SiC substrate capable of efficiently correcting warpage and a SiC substrate obtained by the method.

  SiC has about 3 times the band gap, about 10 times the dielectric breakdown voltage, about 2 times the electron saturation rate, and about 3 times the thermal conductivity compared to silicon (Si). ing. In addition, SiC is a thermally and chemically stable semiconductor material. Taking advantage of these features, SiC has recently been applied to power devices that break the physical limitations of Si devices and environmentally resistant devices that operate at high temperatures. Is expected.

  On the other hand, gallium nitride (GaN) -based materials have been developed for optical device research, but SiC has a much smaller lattice mismatch to GaN than other compound semiconductors. Attention has been focused on the use as a substrate for epitaxial growth of a GaN layer.

  FIG. 4 shows a series of flows of a conventional SiC substrate manufacturing method. First, as shown in FIG. 4A, an ingot 3 is formed by bulk growth of a SiC crystal 2 on a seed crystal substrate 1 made of SiC. The bulk growth of the SiC crystal 2 is performed using, for example, an improved Rayleigh method. In the modified Rayleigh method, first, the inside of the graphite crucible containing the SiC seed crystal substrate 1 and the powdered SiC crystal is set to an inert gas atmosphere such as argon (Ar), and the inside of the crucible is heated to sublimate the SiC crystal. Let Then, the vapor formed of sublimated Si and C is transported by diffusing in an inert gas, and condensed on the SiC seed crystal substrate 1 set at a low temperature.

  Then, SiC substrate 4a shown in FIG. 4B is formed by horizontally cutting ingot 3 manufactured by the improved Rayleigh method into a predetermined thickness.

  However, as shown in FIG. 4B, there is a problem that the SiC substrate 4a obtained by cutting the ingot 3 is warped. When the SiC substrate 4a is warped, it is very difficult to perform a photolithography process or a vacuum suction fixing process of the SiC substrate 4a in a semiconductor device manufacturing process using the SiC substrate 4a. This semiconductor device could not be manufactured with a high yield.

As a method of eliminating the warp generated in the SiC substrate 4a, there is a method of polishing both the front surface and the back surface of the SiC substrate 4a. However, this method has a problem that it is not efficient because the SiC substrate 4a needs to be polished twice. There is also a problem that the SiC substrate 4a is damaged when the SiC substrate 4a is polished.
JP-A-10-125905 JP 2000-226299 A

  In view of the above circumstances, an object of the present invention is to provide an SiC substrate manufacturing method capable of efficiently correcting warpage and an SiC substrate obtained by the method.

The present invention includes a step of forming an ingot by growing a SiC crystal at a predetermined temperature and then cooling to room temperature, a step of heating the ingot to 800 ° C. or higher and 2400 ° C. or lower, and a step of heating the ingot after heating to room temperature. And a step of cutting to a predetermined thickness after cooling to a predetermined thickness.

  Here, in the manufacturing method of the SiC substrate of the present invention, it is preferable that the temperature difference between the highest temperature portion and the lowest temperature portion of the surface of the ingot when the ingot is heated is 100 ° C. or less.

Further, in the manufacturing method of the SiC substrate of the present invention, it is preferred heating time of ingot in the upper Symbol heating temperature is less than 1 hour to 100 hours. Moreover, it is preferable that the temperature increase rate to the heating temperature of the said ingot is 5 degreeC / min or more and 50 degrees C / min or less. In the present specification, “° C./min” means a temperature rising per minute.

  Moreover, in the manufacturing method of the SiC substrate of this invention, it is preferable that the cooling rate at the time of cooling an ingot is 10 to 1000 degreeC / hour. In the present specification, “° C./hour” refers to a temperature that decreases per hour.

Furthermore, in the method for producing a SiC substrate of the present invention , it is preferable to heat the ingot after taking it out of the graphite crucible.

  ADVANTAGE OF THE INVENTION According to this invention, the manufacturing method of the SiC substrate which can correct | amend a curvature efficiently, and the SiC substrate obtained by the method can be provided.

  Hereinafter, a preferred example of the method for producing a SiC substrate of the present invention will be described. In the drawings of the present specification, the same reference numerals represent the same or corresponding parts.

  FIG. 1 shows a schematic cross section of an example of a growth apparatus used in the method for producing a SiC substrate of the present invention. This growth apparatus 5 includes a graphite crucible 7 installed inside a quartz tube 6, a lid 8 of the crucible 7, and a graphite felt 9 for heat shielding installed around the crucible 7 and the lid 8. And a work coil 10 installed on the outer periphery of the quartz tube 6. A seed crystal substrate 1 made of SiC is attached to the inner surface of the lid 8, and powdered SiC crystals 2 a are filled in the crucible 7.

  The inside of the crucible 7 is set to an inert gas atmosphere such as Ar gas, and a high frequency current is passed through the work coil 10 to heat and sublimate the powdered SiC crystal 2a. Here, the inside of the crucible 7 is provided with a temperature gradient so that the temperature gradually decreases from the lower side of the crucible 7 filled with the powdered SiC crystal 2 a to the upper side of the crucible 7 with the lid 8. Therefore, the sublimation gas of the SiC crystal that has reached the vicinity of the seed crystal substrate 1 becomes supersaturated on the surface of the seed crystal substrate 1 and condenses on the seed crystal substrate 1, and the SiC crystal 2 is bulked on the seed crystal substrate 1. grow up. Then, after the bulk growth, the crucible 7 is cooled, and the seed crystal substrate 1 and the SiC crystal 2 are taken out from the growth apparatus 5 to obtain an ingot 3 as shown in FIG.

  Then, the ingot 3 is installed inside the heating furnace, and after the inside of the heating furnace is made an inert gas atmosphere such as Ar gas, the ingot 3 is heated. Alternatively, the ingot 3 can be heated in the growth apparatus 5 after the ingot 3 is cooled while the ingot 3 is installed in the growth apparatus 5.

  By heating the ingot 3 in this way, defects can be formed inside the ingot 3 and the strain existing in the ingod 3 can be alleviated. In addition, a large number of minute defects due to basal plane dislocation or the like are formed on the surface of the ingot 3.

  And after cooling the said ingot 3 after the heating, it cut | disconnects to predetermined thickness, and the SiC substrate 4 shown to typical sectional drawing of FIG. 3 is formed. Since the ingot 3 after the heating is relaxed in the strain present therein, the SiC substrate 4 obtained by cutting the ingot 3 is obtained by cutting the ingot 3 not subjected to the heat treatment. The warpage is corrected and flattened compared to the substrate.

  This was obtained by cutting the ingot containing the strain because the strain generated by the impurities and thermal stress incorporated into the SiC crystal during bulk growth or cooling of the SiC crystal exists inside the ingot. There is also distortion inside the SiC substrate. Therefore, a SiC substrate having such a strain is warped in an attempt to alleviate the strain. However, in the SiC substrate 4 obtained by cutting the ingot 3 whose strain is relaxed by heating, the strain existing in the SiC substrate 4 is eliminated, so that the flatness of the SiC substrate 4 is further increased. .

  When this flat SiC substrate 4 is used, it is very easy to perform a photolithography process, a vacuum suction fixing process, and the like in the manufacturing process of the semiconductor device. Therefore, a semiconductor layer is laminated on the flat SiC substrate 4. By doing so, a high-quality semiconductor device can be easily manufactured.

  Also, in a heating process such as the growth of a semiconductor layer or the production of an electrode in the manufacturing process of a semiconductor device, when a rapid temperature change occurs, for example, the temperature is raised from 25 ° C. to 1500 ° C. in 30 minutes. In FIG. 5, since the distortion inside the SiC substrate 4 is relaxed, the SiC substrate 4 is less likely to change its shape or crack. Therefore, the SiC substrate 4 obtained by the present invention is suitably used as a substrate for a semiconductor device.

  Here, in the present invention described above, it is preferable that the temperature difference between the highest temperature portion and the lowest temperature portion of the surface of the ingot 3 when the ingot 3 is heated is 100 ° C. or less. In this case, since defects can be formed uniformly over the entire ingot 3, distortion can be more reliably alleviated over the entire ingot 3. Here, as a method of heating so that the temperature difference between the highest temperature portion and the lowest temperature portion of the surface of the ingot 3 is 100 ° C. or less, for example, in a heating furnace in which the temperature in the furnace is set to a constant temperature There is a method of exposing the ingot 3 to an environment where the ingot 3 can be heated uniformly, such as heating the ingot 3.

  Moreover, in this invention, it is preferable that the heating temperature of the ingot 3 is 800 degreeC or more and 2400 degrees C or less. When the heating temperature of the ingot 3 is less than 800 ° C., the heating temperature tends to be too low to sufficiently relax the internal distortion of the ingot 3. When the heating temperature is higher than 2400 ° C., the heating temperature is too high. Therefore, the surface of the ingot 3 tends to deteriorate.

  Moreover, in this invention, it is more preferable that the heating time of the ingot 3 at the said heating temperature is 1 hour or more and 10 hours or less. When the heating time of the ingot 3 at the heating temperature is less than 1 hour, the heating time is too short and the internal strain of the ingot 3 tends not to be sufficiently relaxed. When the heating time is longer than 10 hours, the heating is performed. The time is too long and the production of the SiC substrate 4 tends to be inefficient.

  Moreover, in this invention, it is preferable that the heating rate to the heating temperature of the ingot 3 is 5 degreeC / min or more and 50 degrees C / min or less. If the heating speed of the ingot 3 is slower than 5 ° C./min, the heating rate tends to be too slow and the production of the SiC substrate 4 tends to be inefficient. If the heating speed is higher than 50 ° C./min, the temperature change is abrupt. Therefore, there is a tendency that an adverse effect such as cracking of the ingod 3 occurs.

  Moreover, in this invention, it is preferable that the cooling rate at the time of cooling the ingot 3 after the said heating is 10 to 1000 degreeC / hour. When the cooling rate of the ingot 3 is slower than 10 ° C./hour, the cooling rate is too slow and the production of the SiC substrate 4 tends to be inefficient, and when it is faster than 1000 ° C./hour, the temperature change is abrupt. Therefore, there is a tendency that an adverse effect such as cracking of the ingod 3 occurs.

Example 1
The SiC crystal 2 was grown in bulk on the SiC seed crystal substrate 1 using the growth apparatus 5 shown in FIG. Here, in the bulk growth, the inside of the crucible 7 is made an Ar gas atmosphere of 1.0 × 10 ⁵ Pa, and a high-frequency current is passed through the work coil 10, so that the surface temperature of the SiC seed crystal substrate 1 is a powdered SiC crystal. This was carried out by heating with a temperature gradient so as to be lower than the temperature of 2a.

Then, the ingot 3 shown in FIG. 2 composed of the SiC seed crystal substrate 1 and the SiC crystal 2 taken out from the growth apparatus 5 is placed in a heating furnace, and the inside of the heating furnace is filled with 1.0 × 10 ⁵ Pa Ar gas. After making the atmosphere, it is heated from room temperature (25 ° C.) to 800 ° C. at a heating rate of 50 ° C./min, and the difference between the highest temperature portion and the lowest temperature portion of the surface of Ingod 3 is 1 hour at a heating temperature of 800 ° C. Was heated to 100 ° C. or lower.

  Next, after the ingot 3 taken out of the heating furnace after heating is cooled to room temperature at a cooling rate of 1000 ° C./hour, the curvature radius of the SiC substrate (thickness 400 μm, aperture 2 inches) obtained by cutting the ingot 3 (M) was investigated using a flatness measuring machine. The survey results are shown in Table 1.

(Example 2)
The curvature radius (m) of the SiC substrate (thickness: 400 μm, aperture: 2 inches) was examined in the same manner as in Example 1 except that the ingot 3 was heated at a heating temperature of 2400 ° C. in a heating furnace. The survey results are shown in Table 1.

(Example 3)
The curvature radius (m) of the SiC substrate (thickness: 400 μm, aperture: 2 inches) was examined in the same manner as in Example 1 except that the ingot 3 was heated at a heating temperature of 700 ° C. in a heating furnace. The survey results are shown in Table 1.

(Example 4)
The curvature radius (m) of the SiC substrate (thickness: 400 μm, aperture: 2 inches) was investigated in the same manner as in Example 1 except that the ingot 3 was heated in a heating furnace at a heating temperature of 800 ° C. for 100 hours. The survey results are shown in Table 1.

(Example 5)
The curvature radius (m) of the SiC substrate (thickness: 400 μm, aperture: 2 inches) was examined in the same manner as in Example 1 except that the ingot 3 was heated in a heating furnace at a heating temperature of 800 ° C. for 0.5 hours. . The survey results are shown in Table 1.

(Example 6)
The curvature radius (m) of the SiC substrate (thickness: 400 μm, aperture: 2 inches) was examined in the same manner as in Example 1 except that the ingot 3 was heated at a heating temperature of 800 ° C. for 105 hours in the heating furnace. The survey results are shown in Table 1.

(Example 7)
The curvature radius of the SiC substrate (thickness: 400 μm, diameter: 2 inches) was the same as in Example 1 except that the ingot 3 was heated to a heating temperature of 800 ° C. at a rate of 5 ° C./min in the heating furnace. m) was investigated. The survey results are shown in Table 1.

(Example 8)
The curvature of the SiC substrate (thickness: 400 μm, diameter: 2 inches) in the same manner as in Example 1 except that the temperature of the ingot 3 was increased to a heating temperature of 800 ° C. at a rate of 4.5 ° C./min in the heating furnace. The radius (m) was investigated. The survey results are shown in Table 1.

Example 9
The curvature radius (m) of the SiC substrate (thickness: 400 μm, aperture: 2 inches) was examined in the same manner as in Example 1 except that the ingot 3 was cooled to room temperature at a rate of 10 ° C./hour. The survey results are shown in Table 1.

(Example 10)
The curvature radius (m) of the SiC substrate (thickness: 400 μm, aperture: 2 inches) was examined in the same manner as in Example 1 except that the ingot 3 was cooled to room temperature at a rate of 9.5 ° C./hour. The survey results are shown in Table 1.

(Comparative Example 1)
Except that the ingot 3 was not heated, the curvature radius (m) of the SiC substrate (thickness 400 μm, aperture 2 inches) was examined in the same manner as in Example 1. The survey results are shown in Table 1.

  As shown in Table 1, it was confirmed that the SiC substrates of Examples 1 to 10 increased in radius of curvature compared to the SiC substrate of Comparative Example 1 and were flat.

  In addition, as shown in Table 1, the SiC substrates of Examples 1 and 2 heated at a heating temperature of 800 ° C. or higher and 2400 ° C. or lower in the heating furnace have a larger curvature radius than the SiC substrate of Example 3 and are flat. It was confirmed that

  In addition, as shown in Table 1, the SiC substrate of Example 1 obtained by heating the ingot for 1 hour in a heating furnace has a larger radius of curvature than the SiC substrate of Example 5 heated for 0.5 hour. And confirmed to be flat.

  In addition, the SiC substrate of Example 6 obtained by heating the ingot for 105 hours in the heating furnace was heated for 5 hours more than the SiC substrate of Example 4 obtained by heating the ingot for 100 hours. Despite being obtained, the SiC substrate of Example 6 had a smaller radius of curvature than the SiC substrate of Example 4.

  Further, as shown in Table 1, the SiC substrate of Example 7 obtained by heating the ingot at a rate of 5 ° C./min up to a heating temperature of 800 ° C. was 4.5 ° C./min up to a heating temperature of 800 ° C. The curvature radius was almost the same as that of the SiC substrate of Example 8 obtained by heating the ingot at a speed of.

  Moreover, as shown in Table 1, the SiC substrate of Example 9 obtained by cooling the ingot to room temperature at a rate of 10 ° C./hour cooled the ingot to room temperature at a rate of 9.5 ° C./hour. The curvature radius was almost the same as that of the obtained SiC substrate of Example 10.

  It should be understood that the embodiments and examples disclosed herein are illustrative and non-restrictive in every respect. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

  In the method for manufacturing a SiC substrate of the present invention, a flat SiC substrate with a corrected warp can be obtained by heating the ingot in advance. In the SiC substrate of the present invention, since the distortion inside the SiC substrate is relaxed, the SiC substrate does not change its shape or crack in the heating process when the semiconductor device is manufactured using the SiC substrate of the present invention. Therefore, when the SiC substrate of the present invention is used, a high-quality semiconductor device can be manufactured with a high yield, and therefore the SiC substrate of the present invention is suitably used as a substrate for a semiconductor device.

It is typical sectional drawing which showed a preferable example of the growth apparatus used for this invention. It is typical sectional drawing which showed a preferable example of the ingot used for this invention. It is typical sectional drawing of the SiC substrate of this invention. It is the typical conceptual diagram which showed a series of flows of the manufacturing method of the conventional SiC substrate.

Explanation of symbols

  1 SiC seed crystal substrate, 2,2a SiC crystal, 3 ingot, 4,4a SiC substrate, 5 growth apparatus, 6 quartz tube, 7 crucible, 8 lid, 9 felt, 10 work coil.

Claims (6)

A step of forming an ingot by growing a silicon carbide crystal at a predetermined temperature and then cooling to room temperature, a step of heating the ingot to 800 ° C. to 2400 ° C., and cooling the ingot after heating to room temperature And a step of cutting the substrate into a predetermined thickness.   2. The method for manufacturing a silicon carbide substrate according to claim 1, wherein the temperature difference between the highest temperature portion and the lowest temperature portion of the surface of the ingot when the ingot is heated is 100 ° C. or less. The heating time of the at heating temperature ingot, characterized in that it is less than 100 hours or more 1 hour, method for manufacturing the silicon carbide substrate according to claim 1 or 2. The method for manufacturing a silicon carbide substrate according to any one of claims 1 to 3, wherein a rate of temperature rise to a heating temperature of the ingot is 5 ° C / min or more and 50 ° C / min or less. The ingot cooling speed in cooling a, characterized in that at 10 ° C. / hour or more 1000 ° C. / hour or less, the manufacturing method of a silicon carbide substrate according to any one of claims 1 to 4. Wherein the heating the ingot after removal from the graphite crucible, the method for manufacturing the silicon carbide substrate according to any one of claims 1 to 5.

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