Method for evaluating the crystallinity of 3C-SiC films

Abstract

To provide a method for evaluating the crystallinity of a 3C-SiC film in which 3C-SiC is heteroepitaxially grown on a single crystal silicon substrate simply and in a non-destructive manner without requiring a processing work of a wafer.SOLUTION: There is provided a method for evaluating the crystallinity of a 3C-SiC film in which 3C-SiC is heteroepitaxially grown on a single crystal silicon substrate, where the crystallinity of the 3C-SiC film of the hetero epitaxial wafer is determined on the basis of a WARP value of the hetero epitaxial wafer and a stress value applied to the substrate obtained by using Stoney's equation.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a method for evaluating the crystallinity of a 3C-SiC film.

Background Art

[0002] SiC has a high breakdown strength because it has a wide bandgap of 2.2 to 3.3 eV, and also has a high thermal conductivity, so it is a material expected to be used as a semiconductor material for various semiconductor devices such as power devices and high-frequency devices.

[0003] Also, although its use as a platform for gallium nitride (GaN) growth (for example, Patent Document 1) is also being advanced, on the other hand, SiC wafers are mainly small in diameter, and there is a demand for larger diameters for power devices and high-frequency devices. If a high-quality 3C-SiC single crystal film can be formed on a large-diameter substrate, in addition to the use of the 3C-SiC single crystal film itself, it becomes possible to fabricate a heteroepitaxial wafer having a high-quality GaN layer with a large diameter.

[0004] As a method for increasing the diameter of SiC wafers, epitaxial growth on a silicon substrate with good compatibility with device processes has been studied (for example, Patent Documents 1 and 2). In order to use a heteroepitaxial wafer formed by heteroepitaxially growing 3C-SiC on a silicon substrate for power devices and the like, it is necessary to grow a 3C-SiC film with excellent crystallinity, and the crystal state of the heteroepitaxial layer has been determined by transmission electron microscopy (TEM) and X-ray diffraction (XRD) measurement.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

[0006] While TEM and XRD are very suitable for obtaining information about local crystal states, they have the drawback of requiring processing such as dividing heteroepitaxial wafers into small pieces before measurement, which makes crystallinity evaluation very time-consuming.

[0007] The present invention was made to solve the above problems, and aims to provide a simple and non-destructive method for evaluating the crystallinity of a 3C-SiC film grown heteroepitaxially on a single-crystal silicon substrate without requiring wafer processing. [Means for solving the problem]

[0008] The present invention was made to achieve the above objective, and is a method for evaluating the crystallinity of a 3C-SiC film heteroepitaxially grown on a single-crystal silicon substrate, wherein 3C-SiC is heteroepitaxially grown on multiple single-crystal silicon substrates with known WARP values ​​under different conditions using a reduced-pressure CVD apparatus to prepare multiple reference value setting samples with different crystallinity of the 3C-SiC film, the WARP value is measured for each of the multiple reference value setting samples, the WARP values ​​before and after heteroepitaxial growth are substituted into Stoney's equation to calculate the stress value applied to the single-crystal silicon substrate of the multiple reference value setting samples, XRD measurements are performed on the multiple reference value setting samples, and the crystallinity of the 3C-SiC film of the multiple reference value setting samples is evaluated using the obtained XRD spectra, and the XRD spectra The present invention provides a method for evaluating the crystallinity of a 3C-SiC film, characterized in that, among the reference value setting samples that were judged to have good crystallinity in the evaluation of crystallinity using a criterion, the stress value of the sample with the lowest stress value is set as the reference stress value, the WARP value of the heteroepitaxial wafer to be evaluated is measured by heteroepitaxial growth of 3C-SiC on a single-crystal silicon substrate with a known WARP value, the WARP values ​​before and after heteroepitaxial growth are substituted into Stoney's equation to calculate the stress value acting on the single-crystal silicon substrate of the heteroepitaxial wafer to be evaluated, the reference stress value and the stress value of the target to be evaluated are compared, and if the stress value of the target to be evaluated is equal to or greater than the reference stress value, it is determined that the 3C-SiC film on the heteroepitaxial wafer to be evaluated has good crystallinity.

[0009] This crystallinity evaluation method allows for the simple and non-destructive assessment of the crystallinity of a 3C-SiC film grown heteroepitaxially on a single-crystal silicon substrate by substituting the WARP value, one of the indicators representing the wafer shape, into Stoney's equation to calculate the stress value.

[0010] In this case, when evaluating the crystallinity of the reference value setting sample using the XRD spectrum, it is possible to determine that samples with single-crystal 3C-SiC growth have good crystallinity, and samples with polycrystalline 3C-SiC growth have poor crystallinity.

[0011] This makes it easy to evaluate whether a 3C-SiC film grown heteroepitaxially on a single-crystal silicon substrate is a single crystal or a polycrystalline film. [Effects of the Invention]

[0012] As described above, according to the 3C-SiC crystallinity evaluation method of the present invention, the crystallinity of a 3C-SiC film heteroepitaxially grown on a single-crystal silicon substrate can be evaluated from the stress value calculated by substituting the WARP value, which is one of the indicators representing the shape of the wafer, into Stoney's formula. Therefore, it is possible to evaluate the crystallinity simply and non-destructively without requiring wafer processing work. [Brief explanation of the drawing]

[0013] [Figure 1] An example of the flow chart for evaluating the crystallinity of 3C-SiC according to the present invention is shown. [Figure 2] The stress values ​​of 3C-SiC heteroepitaxial wafers during film deposition under various conditions, calculated using Stoney's formula, are shown. [Modes for carrying out the invention]

[0014] The present invention will be described in detail below, but the present invention is not limited to these descriptions.

[0015] As described above, there was a need for a simple and non-destructive method to evaluate the crystallinity of 3C-SiC films grown heteroepitaxially on single-crystal silicon substrates, without requiring wafer processing.

[0016] The present inventors, after diligently studying the above problem, have provided a method for evaluating the crystallinity of a 3C-SiC film grown heteroepitaxially on a single-crystal silicon substrate, wherein 3C-SiC is heteroepitaxially grown on multiple single-crystal silicon substrates with known WARP values ​​under different conditions using a reduced-pressure CVD apparatus to prepare multiple reference value setting samples with different crystallinity of the 3C-SiC film, the WARP value is measured for each of the multiple reference value setting samples, the WARP values ​​before and after heteroepitaxial growth are substituted into Stoney's equation to calculate the stress value applied to the single-crystal silicon substrate of the multiple reference value setting samples, XRD measurements are performed on the multiple reference value setting samples, the crystallinity of the 3C-SiC film of the multiple reference value setting samples is evaluated using the obtained XRD spectra, and among the reference value setting samples that are judged to have good crystallinity in the evaluation of crystallinity using the XRD spectra, the sample with the lowest stress value is... The present invention was completed by discovering that the crystallinity of a 3C-SiC film can be easily and nondestructively evaluated by using a stress value calculated by substituting the WARP value, which is one of the indicators representing the shape of the wafer, into Stoney's formula. This method involves setting a stress value as a reference stress value, measuring the WARP value of a heteroepitaxial wafer to be evaluated by heteroepitaxial growth of 3C-SiC on a single-crystal silicon substrate with a known WARP value, substituting the WARP values ​​before and after heteroepitaxial growth into Stoney's formula to calculate the stress value acting on the single-crystal silicon substrate of the heteroepitaxial wafer to be evaluated, comparing the reference stress value with the stress value of the wafer to be evaluated, and determining that the 3C-SiC film on the heteroepitaxial wafer to be evaluated has good crystallinity if the stress value of the wafer to be evaluated is equal to or greater than the reference stress value.

[0017] The following describes a method for evaluating the crystallinity of a 3C-SiC film according to an embodiment of the present invention, with reference to Figure 1. Figure 1 shows an example of a flowchart for the method of evaluating the crystallinity of a 3C-SiC film according to the present invention.

[0018] [Setting of reference stress value] First, as shown in S1 of FIG. 1, prepare a plurality of single-crystal silicon substrates, and measure the WAPR value of each. It is preferable that the single-crystal silicon substrates to be prepared are of the same standard as the single-crystal silicon substrates to be evaluated.

[0019] Next, as shown in S2 of FIG. 1, place the single-crystal silicon substrate with a known WAPR value in a reduced-pressure (RP)-CVD apparatus, and heteroepitaxially grow 3C-SiC under various film-forming conditions to prepare a plurality of samples for setting reference values with different crystallinities of the 3C-SiC film. There is a lattice constant difference of about 20% between Si and 3C-SiC. When 3C-SiC is formed on the silicon substrate, tensile stress is applied, and the substrate warps into a downwardly convex shape.

[0020] Next, as shown in S3 of FIG. 1, perform shape measurement on each of the obtained samples for setting reference values, and measure the WARP which is an index indicating the amount of warping.

[0021] Next, as shown in S4 of FIG. 1, substitute the WARP values before and after heteroepitaxial growth into the following Stoney's formula by which stress can be calculated from the warping of the substrate, and calculate the stress value applied to the single-crystal silicon substrate of the sample for setting reference values.

[0022] [Equation] Here, σ f represents stress, E represents the elastic modulus (Young's modulus), t represents the thickness, ν represents the Poisson's ratio, R1 represents the radius of curvature of the wafer after film formation, R0 represents the radius of curvature of the wafer before film formation. ( f represents the 3C-SiC film, s represents the substrate.) Also, the radius of curvature R is represented by the following formula.

[0023]

number

[0024] When low-crystallinity 3C-SiC is grown, the WARP value decreases due to lattice relaxation caused by numerous misfit dislocations in the film, resulting in a lower stress value calculated from Stoney's equation. Conversely, when high-crystallinity 3C-SiC is grown, there are fewer dislocation defects in the film, making lattice relaxation less likely, resulting in a higher WARP value and a higher stress value calculated from Stoney's equation.

[0025] Furthermore, as shown in S5 of Figure 1, XRD measurements are performed on the reference value setting sample, and the crystallinity of the 3C-SiC film of the reference value setting sample is evaluated using the obtained XRD spectrum.

[0026] Next, as shown in S6 of Figure 1, among the samples for setting the reference value that were judged to have good crystallinity in the evaluation of crystallinity using XRD spectroscopy, the stress value of the sample with the lowest stress value is set as the reference stress value.

[0027] Let's explain using a specific example. Figure 2 shows the relationship between crystallinity and stress values ​​obtained by growing 3C-SiC under different growth conditions using seven single-crystal silicon substrates whose WARP values ​​were measured in advance, as samples for setting reference values, and then measuring the WARP values, calculating stress values, and investigating crystallinity. As shown in Figure 2, the 3C-SiC deposited under conditions 1 to 3 was confirmed to have grown as single crystal 3C-SiC based on the XRD spectrum, and was judged to have good crystallinity. On the other hand, the 3C-SiC deposited under conditions 4 to 7 was confirmed to have grown as polycrystalline 3C-SiC based on the XRD spectrum, and was judged to have poor crystallinity. From these results, the stress value for condition 3 (1.13 GPa) can be set as the reference stress value.

[0028] In evaluating the crystallinity of reference value setting samples using the above XRD spectrum, samples grown as single crystals of 3C-SiC can be determined to have good crystallinity, while samples grown as polycrystalline 3C-SiC can be determined to have poor crystallinity. This makes it easy to evaluate whether a 3C-SiC film grown heteroepitaxially on a single-crystal silicon substrate is single-crystal or polycrystalline.

[0029] [Evaluation of the crystallinity of the 3C-SiC film being evaluated] Next, we will describe a method for evaluating the crystallinity of a 3C-SiC film grown heteroepitaxially on a single-crystal silicon substrate, which is the subject of evaluation, using the reference stress values ​​obtained by the above method.

[0030] First, as shown in S7 of Figure 1, the WAPR value of the single-crystal silicon substrate on which the 3C-SiC to be evaluated will be grown heteroepitaxially is measured in advance.

[0031] Next, as shown in S8 of Figure 1, a single-crystal silicon substrate with a known WARP value is placed in a reduced-pressure (RP)-CVD apparatus, 3C-SiC is grown heteroepitaxially, and the WARP value of the resulting wafer is measured.

[0032] Next, as shown in S9 of Figure 1, the WARP values ​​before and after heteroepitaxial growth are substituted into Stoney's equation to calculate the stress value applied to the single-crystal silicon substrate of the wafer under evaluation.

[0033] Finally, as shown in S10 of Figure 1, the reference stress value is compared with the stress value of the wafer under evaluation. If the stress value of the wafer under evaluation is equal to or greater than the reference stress value, it is determined that the 3C-SiC film of the wafer under evaluation has good crystallinity.

[0034] In the example in Figure 2, the stress value for condition 3 was set as the reference stress value. Therefore, if the actual stress value of the wafer being evaluated is 1.13 GPa or higher (the reference stress value), the crystallinity of the 3C-SiC film is judged to be good, and if it is below the reference stress value, the crystallinity of the 3C-SiC film is judged to be poor.

[0035] By using the evaluation method of the present invention, the crystallinity of a 3C-SiC film heteroepitaxially grown on a single-crystal silicon substrate can be evaluated from the stress value calculated by substituting the WARP value, which is one of the indicators representing the shape of the wafer, into Stoney's equation. This makes it possible to evaluate the crystallinity simply and nondestructively.

[0036] Furthermore, when applying the evaluation method of the present invention, as described above, when 3C-SiC is deposited on a silicon substrate, tensile stress is applied, causing the substrate to warp in a convex shape downwards. Therefore, it is preferable to apply the method to a wafer on which 3C-SiC has been heteroepitaxially grown on a single-crystal silicon substrate that has a convex shape upwards. [Examples]

[0037] The present invention will be described in detail below with reference to examples, but this is not intended to limit the present invention.

[0038] (Examples) Seven single-crystal silicon substrates were prepared to measure their warp values. The prepared single-crystal silicon substrates had a diameter of 300 mm, a crystal orientation of (111), were P-type, and had a resistance of 10 Ω·cm. The single-crystal silicon substrates with known warp values ​​were placed on a susceptor in the reactor of a reduced-pressure CVD apparatus, and 3C-SiC was heteroepitaxially grown under seven different deposition conditions.

[0039] The WARP values ​​of the seven obtained wafers were measured, and the WARP values ​​before and after film deposition were substituted into Stoney's formula to calculate the stress values ​​applied to each wafer.

[0040] Furthermore, when the obtained 3C-SiC films were subjected to XRD measurements under in-plane diffraction conditions, the 3C-SiC films deposited under conditions 1 to 3 showed only peaks originating from the (220) plane in the XRD spectra, confirming that single-crystal 3C-SiC had grown and that the crystallinity was good. On the other hand, the 3C-SiC films deposited under conditions 4 to 7 showed peaks originating from the (111) and (311) planes in addition to the peak originating from the (220) plane in the XRD spectra, confirming that polycrystalline 3C-SiC had grown and that the crystallinity was poor (hereinafter, this will also be referred to as good / bad XRD judgment).

[0041] Among the wafers under conditions 1 to 3, which showed good XRD results, the lowest stress value was that of condition 3 (1.13 GPa), and this was set as the reference stress value.

[0042] Figure 2 shows the stress values ​​of 3C-SiC heteroepitaxial wafers deposited under each condition. As shown in Figure 2, wafers under conditions 1 and 2, which had good XRD results, all had stresses on the substrate that were above the reference stress value, while wafers under conditions 4 to 7, which had poor XRD results, all had stresses on the substrate that were below the reference stress value.

[0043] Next, the 3C-SiC film to be evaluated was performed. The single-crystal silicon substrate used had a diameter of 300 mm, a crystal orientation (111), was P-type, and had a stress of 10 Ω·cm. First, the WARP value of the single-crystal silicon substrate on which the 3C-SiC film was heteroepitaxially grown was measured, and the WARP value was 4.36 μm. The 3C-SiC film was heteroepitaxially grown on this single-crystal silicon substrate, and the WARP value of the resulting heteroepitaxial wafer was measured. This WARP value was 19.97 μm. Next, the WARP values ​​before and after heteroepitaxial growth were substituted into Stoney's equation to calculate the stress value applied to the single-crystal silicon substrate of the fabricated heteroepitaxial wafer, which was 1.19 GPa. As can be seen from Figure 2, this value is greater than the stress value of condition 3 (1.13 GPa), which was used as the reference stress value, and it was determined that the wafer had good crystallinity.

[0044] In fact, when we performed XRD measurements on the fabricated heteroepitaxial wafer and examined the spectrum, we were able to confirm that a single-crystal 3C-SiC film had been obtained.

[0045] As described above, according to the embodiments of the present invention, it has been confirmed that the crystallinity of 3C-SiC can be determined from the stress applied to a substrate on which a 3C-SiC heteroepitaxial film has been deposited under different conditions.

[0046] It should be noted that the present invention is not limited to the embodiments described above. The embodiments described above are illustrative, and any configuration that is substantially identical to the technical idea described in the claims of the present invention and achieves similar effects is included within the technical scope of the present invention.

Claims

1. A method for evaluating the crystallinity of a 3C-SiC film grown heteroepitaxially on a single-crystal silicon substrate, Using a reduced-pressure CVD apparatus, 3C-SiC was heteroepitaxially grown on multiple single-crystal silicon substrates with known WARP values ​​under different conditions to prepare multiple reference value setting samples with different crystallinity of 3C-SiC films. The WARP value was measured for each of the aforementioned multiple reference value setting samples. The WARP values ​​before and after heteroepitaxial growth are substituted into Stoney's equation to calculate the stress values ​​applied to the single-crystal silicon substrates of the multiple reference value setting samples. XRD measurements were performed on the aforementioned multiple reference value setting samples, and the crystallinity of the 3C-SiC film of the aforementioned multiple reference value setting samples was evaluated using the obtained XRD spectra. In the evaluation of crystallinity using the XRD spectrum, among the samples for setting the reference value that were judged to have good crystallinity, the stress value of the sample with the lowest stress value is set as the reference stress value. The WARP value of the heteroepitaxial wafer to be evaluated was measured by heteroepitaxial growth of 3C-SiC on a single-crystal silicon substrate with a known WARP value. The WARP values ​​before and after heteroepitaxial growth are substituted into Stoney's formula to calculate the stress value applied to the single-crystal silicon substrate of the heteroepitaxial wafer being evaluated. A method for evaluating the crystallinity of a 3C-SiC film, characterized by comparing the reference stress value with the stress value of the subject to evaluation, and determining that the 3C-SiC film of the heteroepitaxial wafer subject to evaluation has good crystallinity if the stress value of the subject to evaluation is equal to or greater than the reference stress value.

2. The method for evaluating the crystallinity of a 3C-SiC film according to claim 1, characterized in that, in the evaluation of the crystallinity of a reference value setting sample using the aforementioned XRD spectrum, samples in which single crystal 3C-SiC has been grown are determined to have good crystallinity, and samples in which polycrystalline 3C-SiC has been grown are determined to have poor crystallinity.

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