Method for evaluating crystallinity of 3C-SiC film

Abstract

Provided is a method for evaluating the crystallinity of a 3C-SiC film heteroepitaxially grown on a single crystal silicon substrate, the method being characterized in that the crystallinity of the 3C-SiC film is evaluated on the basis of the WARP value using the heteroepitaxial wafer and the stress value applied to the substrate obtained using the Stokes equation. And determining the crystallinity of the 3C-SiC film of the heteroepitaxial wafer. As a result, the crystallinity of a 3C-SiC film heteroepitaxially grown on a single crystal silicon substrate can be evaluated easily and non-destructively without requiring wafer processing work.

Description

Technical Field

[0001] This invention relates to a method for evaluating the crystallinity of 3C-SiC films. Background Technology

[0002] SiC (silicon carbide) is a material with a wide band gap of 2.2 to 3.3 eV, which gives it high insulation breaking strength and a relatively high thermal conductivity. Therefore, it is expected to be used as a semiconductor material for various semiconductor devices such as power devices and high-frequency devices.

[0003] In addition, the utilization of gallium nitride (GaN) growth platforms (e.g., Patent Document 1) continues to advance. However, on the other hand, SiC wafers are mainly small in diameter, and in the fields of power devices and high-frequency devices, there is a demand for larger diameters. Therefore, as long as a high-quality 3C-SiC single crystal film can be deposited on a large-diameter substrate, in addition to utilizing the 3C-SiC single crystal film itself, it is also possible to fabricate a large-diameter heteroepitaxial wafer with a high-quality GaN layer.

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

[0005] Patent Document 1: Japanese Patent Publication No. 2018-522412 Patent Document 2: Japanese Patent Application Publication No. 2021-20819 Summary of the Invention The technical problem that the invention aims to solve

[0006] TEM and XRD are well-suited for obtaining information on localized crystallization states, but they require processing such as meticulously dividing the heteroepitaxial wafer into small pieces before measurement, which results in a significant time consumption for crystallinity assessment.

[0007] This invention was made to solve the above-mentioned problems, and its purpose is to provide a method for evaluating the crystallinity of 3C-SiC films, which can evaluate the crystallinity of 3C-SiC films heteroepitaxially grown on single-crystal silicon substrates in a simple and non-destructive manner without the need for wafer processing. Technical means to solve the problem

[0008] This invention was made to achieve the above-mentioned objective, providing a method for evaluating the crystallinity of 3C-SiC films. The method for evaluating the crystallinity of 3C-SiC films heteroepitaxially grown on monocrystalline silicon substrates is characterized by using a reduced-pressure CVD apparatus to heteroepitaxially grow 3C-SiC films on multiple monocrystalline silicon substrates with known WARP values ​​under different conditions, thus preparing multiple reference value samples with different crystallinity of the 3C-SiC films. The WARP values ​​of each of the multiple reference value samples are measured. The WARP values ​​before and after heteroepitaxial growth are substituted into the Stoney equation to calculate the stress values ​​applied to the monocrystalline silicon substrates of the multiple reference value samples. XRD measurements are then performed on the multiple reference value samples, and the obtained XRD spectra are used to evaluate the multiple reference values. To determine the crystallinity of the 3C-SiC film of the sample, in the evaluation of crystallinity using the XRD spectrum, among the reference value setting samples judged to have good crystallinity, the stress value of the sample with the lowest stress value is set as the reference stress value. 3C-SiC heteroepitaxial growth is carried out on a single-crystal silicon substrate with a known WARP value. The WARP value of the evaluation object, i.e., the heteroepitaxial wafer, is measured. The WARP values ​​before and after heteroepitaxial growth are substituted into the Stoney equation to calculate the stress value applied to the single-crystal silicon substrate of the evaluation object, i.e., the heteroepitaxial wafer. The reference stress value is compared with the stress value of the evaluation object. If the stress value of the evaluation object is above the reference stress value, it is determined that the 3C-SiC film of the heteroepitaxial wafer of the evaluation object has good crystallinity.

[0009] Based on this crystallinity assessment method, the crystallinity of 3C-SiC films heteroepitaxially grown on single-crystal silicon substrates can be assessed simply and nondestructively by substituting the WARP value, one of the indicators representing wafer shape, into the stress value calculated by the Stoney equation.

[0010] At this time, in the crystallinity evaluation of the sample using the reference value setting of the XRD spectrum, 3C-SiC with single crystals can be determined as having good crystallinity, and 3C-SiC with polycrystalline growth can be determined as having poor crystallinity.

[0011] Therefore, it is easy to assess whether a 3C-SiC film grown heteroepitaxially on a single-crystal silicon substrate is single-crystal or polycrystalline. Invention Effects

[0012] As described above, the crystallinity evaluation method for 3C-SiC films according to the present invention can evaluate the crystallinity of 3C-SiC films heteroepitaxially grown on single-crystal silicon substrates based on the stress value calculated by substituting the WARP value, one of the indicators representing wafer shape, into the Stoney equation. Therefore, the crystallinity can be evaluated easily and non-destructively without wafer processing. Attached Figure Description

[0013] Figure 1 This is an example of the process for evaluating the crystallinity of 3C-SiC according to the present invention. Figure 2 It represents the stress value of the 3C-SiC heteroepitaxial wafer under various conditions during film formation, calculated based on the Stoney equation. Detailed Implementation

[0014] The present invention will now be described in detail, but it is not limited thereto.

[0015] As described above, an evaluation method is sought that can assess the crystallinity of 3C-SiC films heteroepitaxially grown on single-crystal silicon substrates in a simple and non-destructive manner without requiring wafer fabrication.

[0016] The inventors dedicated themselves to researching the aforementioned technical problems and discovered a method for evaluating the crystallinity of 3C-SiC films. This method allows for a simple and non-destructive evaluation of the crystallinity of 3C-SiC films heteroepitaxially grown on monocrystalline silicon substrates by substituting the WARP value (one of the indicators of wafer shape) into the Stoney equation to calculate the stress value. This led to the completion of this invention: a method for evaluating the crystallinity of 3C-SiC films heteroepitaxially grown on monocrystalline silicon substrates. The method is characterized by using a reduced-pressure CVD apparatus to heteroepitaxially grow 3C-SiC films on multiple monocrystalline silicon substrates with known WARP values ​​under different conditions, preparing multiple reference value samples with different crystallinity of the 3C-SiC films. The WARP values ​​of each of these reference value samples are measured. The WARP values ​​before and after heteroepitaxial growth are then substituting into the Stoney equation to calculate the stress value applied to the monocrystalline silicon substrates of the multiple reference value samples. The stress value was measured using XRD on samples with multiple reference values. The crystallinity of the 3C-SiC film of the samples with multiple reference values ​​was evaluated using the obtained XRD spectra. In the evaluation of crystallinity using the XRD spectra, the stress value of the sample with the lowest stress value among the reference value samples that were determined to have good crystallinity was set as the reference stress value. 3C-SiC heteroepitaxial growth was carried out on a single-crystal silicon substrate with a known WARP value. The WARP value of the evaluation object, i.e., the heteroepitaxial wafer, was measured. The WARP values ​​before and after heteroepitaxial growth were substituted into the Stoney equation to calculate the stress value applied to the single-crystal silicon substrate of the evaluation object, i.e., the heteroepitaxial wafer. The reference stress value was compared with the stress value of the evaluation object. If the stress value of the evaluation object was higher than the reference stress value, it was determined that the 3C-SiC film of the heteroepitaxial wafer of the evaluation object had good crystallinity.

[0017] The following is for reference Figure 1 The method for evaluating the crystallinity of the 3C-SiC film according to embodiments of the present invention will be described. Figure 1 This is a diagram illustrating an example of the crystallinity evaluation method flow for the 3C-SiC film of the present invention.

[0018] [Reference Stress Value Setting] First, such as Figure 1 As shown in S1, multiple monocrystalline silicon substrates are prepared, and their respective WAPR values ​​are measured. Furthermore, the prepared monocrystalline silicon substrates are preferably of the same specifications as the monocrystalline silicon substrate being evaluated.

[0019] Next, as Figure 1As shown in S2, a single-crystal silicon substrate with a known WAPR value is placed in a reduced pressure (RP)-CVD apparatus, and heteroepitaxial growth of 3C-SiC is performed using various film deposition conditions to prepare multiple reference value samples with different crystallinity of 3C-SiC films. Since there is approximately a 20% lattice constant difference between Si and 3C-SiC, tensile stress is applied when 3C-SiC is deposited on a silicon substrate, causing the substrate to warp and become a downwardly convex shape.

[0020] Next, as Figure 1 As shown in S3, the shape of the samples was measured for the obtained reference value, and WARP, which is used as an indicator of the amount of warpage, was measured.

[0021] Next, as Figure 1 As shown in S4, the stress value applied to the single-crystal silicon substrate of the reference value setting sample is calculated by substituting the WARP values ​​before and after heteroepitaxial growth into the following Stoney equation, which can calculate the stress based on the warpage of the substrate.

[0022] Mathematical Formula 1 Here, σ f Let f represent stress, E represent the elastic modulus (Young's modulus), t represent thickness, ν represent Poisson's ratio, R1 represent the radius of curvature of the wafer after film deposition, and R0 represent the radius of curvature of the wafer before film deposition. (f represents the 3C-SiC film, and s represents the substrate.) In addition, the radius of curvature R can be expressed by the following formula.

[0023] Mathematical formula 2 Here, r represents the substrate radius, and d represents the warpage (WARP).

[0024] When growing 3C-SiC with low crystallinity, the WARP value decreases due to lattice relaxation caused by numerous mismatched dislocations in the film, and the stress value calculated based on the Stoney equation also decreases. Conversely, when growing 3C-SiC with high crystallinity, the WARP value increases because there are fewer dislocation defects in the film and lattice relaxation is less likely to occur, and the stress value calculated based on the Stoney equation also increases.

[0025] In addition, such as Figure 1 As shown in S5, XRD measurements were performed on the sample used for benchmark setting, and the crystallinity of the 3C-SiC film of the sample used for benchmark setting was evaluated using the obtained XRD spectra.

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

[0027] Specific examples will be used to illustrate this. Figure 2 The paper shows the relationship between crystallinity and stress value obtained by using seven monocrystalline silicon substrates with pre-determined WARP values ​​as reference samples, growing 3C-SiC under different growth conditions, and measuring WARP values, calculating stress values, and investigating crystallinity. Figure 2 As shown, XRD spectroscopy confirmed the growth of single-crystal 3C-SiC in the films formed using conditions 1-3, indicating good crystallinity. Conversely, XRD spectroscopy confirmed the growth of polycrystalline 3C-SiC in the films formed using conditions 4-7, indicating poor crystallinity. Based on these results, the stress value (1.13 GPa) for condition 3 can be set as the reference stress value.

[0028] In evaluating the crystallinity of samples using the aforementioned XRD spectral reference values, 3C-SiC films with grown monocrystalline 3C-SiC can be classified as having good crystallinity, while 3C-SiC films with grown polycrystalline 3C-SiC can be classified as having poor crystallinity. Therefore, it is easy to assess whether a 3C-SiC film heteroepitaxially grown on a monocrystalline silicon substrate is monocrystalline or polycrystalline.

[0029] [Evaluation of the crystallinity of the 3C-SiC film being evaluated] Next, the method for evaluating the crystallinity of the 3C-SiC film heteroepitaxially grown on a single-crystal silicon substrate using the reference stress value obtained by the above method will be described.

[0030] First, such as Figure 1 As shown in S7, the WAPR value of the single-crystal silicon substrate for 3C-SiC heteroepitaxial growth, which is the subject of evaluation, is measured in advance.

[0031] Next, as Figure 1 As shown in S8, a single-crystal silicon substrate with a known WAPR value is placed in a reduced pressure (RP)-CVD apparatus to perform heteroepitaxial growth of 3C-SiC, and the WAPR value of the obtained wafer is measured.

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

[0033] Finally, as Figure 1As shown in S10, the reference stress value is compared with the stress value of the evaluation target wafer. If the stress value of the evaluation target wafer is above the reference stress value, it is determined that the 3C-SiC film of the evaluation target wafer has good crystallinity.

[0034] exist Figure 2 In the example, the stress value of condition 3 is set as the reference stress value. Therefore, when the stress value of the actual evaluation wafer is above the reference stress value, i.e., 1.13 GPa, the crystallinity of the 3C-SiC film is judged to be good. When it is below the reference stress value, the crystallinity of the 3C-SiC film is judged to be poor.

[0035] If the evaluation method of the present invention is used, the crystallinity of the 3C-SiC film heteroepitaxially grown on a single-crystal silicon substrate can be evaluated based on the stress value calculated by substituting the WARP value, one of the indicators representing the wafer shape, into the Stoney equation. Therefore, the crystallinity can be evaluated simply and non-destructively.

[0036] Furthermore, when the evaluation method of the present invention is applied, as described above, if 3C-SiC is deposited on a silicon substrate, tensile stress is applied, and the substrate will warp into a downward convex shape. Therefore, it is preferred to apply it to a wafer in which 3C-SiC heteroepitaxial growth is performed on a single-crystal silicon substrate with an upward convex warp. [Example]

[0037] The present invention will be specifically described below with reference to specific embodiments, but these embodiments do not limit the present invention.

[0038] (Example) Seven single-crystal silicon substrates with known WARP values ​​were prepared. The prepared single-crystal silicon substrates were 300 mm in diameter, (111) facet orientation, P-type, and 10 Ω·cm. The single-crystal silicon substrates with known WARP values ​​were placed on the base inside the reactor of the vacuum CVD apparatus, and heteroepitaxial growth of 3C-SiC was carried out using seven different film formation conditions.

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

[0040] When the obtained 3C-SiC films were further subjected to XRD under in-plane diffraction conditions, the 3C-SiC films formed under conditions 1 to 3 showed only peaks originating from the (220) plane based on the XRD spectrum, thus confirming the growth of single-crystal 3C-SiC and determining that the crystallinity was good. In addition, the 3C-SiC films formed under conditions 4 to 7 showed peaks originating from the (220) plane as well as peaks originating from the (111) and (311) planes based on the XRD spectrum, thus confirming the growth of polycrystalline 3C-SiC and determining that the crystallinity was poor (hereinafter, also referred to as good / poor XRD determination).

[0041] Among the stress values ​​of wafers rated as good by XRD (conditions 1 to 3), the lowest is the stress value of condition 3 (1.13 GPa), which is used as the reference stress value.

[0042] Figure 2 This shows the stress values ​​of 3C-SiC heteroepitaxial wafers formed under various conditions. For example... Figure 2 As shown, wafers classified as good under conditions 1 and 2 all had stress applied to the substrate that was above the reference stress value, while wafers classified as bad under conditions 4 to 7 had stress applied to the substrate that was below the reference stress value.

[0043] Next, the 3C-SiC film of the actual evaluation object was evaluated. The single-crystal silicon substrate used was 300 mm in diameter, with a face orientation of (111), P-type, and 10 Ω·cm. First, when the WARP value of the single-crystal silicon substrate on which the 3C-SiC film was heteroepitaxially grown was measured, 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. The WARP value was 19.97 μm. Next, the WARP values ​​before and after heteroepitaxial growth were substituted into the Stoney equation, and the stress value applied to the single-crystal silicon substrate of the fabricated heteroepitaxial wafer was calculated to be 1.19 GPa. Figure 2 It can be determined that this value is above the stress value (1.13 GPa) of condition 3, which is set as the reference stress value, and therefore has good crystallinity.

[0044] In fact, when the fabricated heteroepitaxial wafer was subjected to XRD measurement and the spectrum was confirmed, a single-crystal 3C-SiC film was obtained.

[0045] As described above, according to embodiments of the present invention, the crystallinity of 3C-SiC can be determined based on the stress applied to a substrate on which a 3C-SiC heteroepitaxial film is formed using different conditions.

[0046] It should be noted that the present invention is not limited to the embodiments described above. The embodiments described above are examples, and embodiments having the same structure and achieving the same effect as those described in the claims of the present invention are all included within the technical scope of the present invention.

Claims

1. A method for evaluating the crystallinity of a 3C-SiC film, which is a method for evaluating the crystallinity of a 3C-SiC film heteroepitaxially grown on a single-crystal silicon substrate, characterized in that... Using a reduced-pressure CVD apparatus, 3C-SiC heteroepitaxial growth was performed on multiple single-crystal silicon substrates with known WARP values ​​under different conditions to prepare samples with varying crystallinity for setting reference values ​​for the 3C-SiC films. For each of the aforementioned reference values, the WARP value was measured using samples. Substituting the WARP values ​​before and after heteroepitaxial growth into the Stony equation, the stress values ​​applied to the single-crystal silicon substrates of the multiple reference value setting samples are calculated. XRD measurements were performed on the samples used to set the multiple reference values, and the crystallinity of the 3C-SiC films in the samples was evaluated using the obtained XRD spectra. In the evaluation of crystallinity using the XRD spectra, among the samples used for setting the reference value that are determined to have good crystallinity, the stress value of the sample with the lowest stress value is used as the reference stress value. 3C-SiC heteroepitaxial growth was performed on a single-crystal silicon substrate with a known WARP value. The WARP value of the evaluated object, i.e., the heteroepitaxially grown wafer, was measured and evaluated. Substituting the WARP values ​​before and after heteroepitaxial growth into the Stony equation, the stress value applied to the evaluation object, i.e., the single-crystal silicon substrate of the heteroepitaxial wafer, is calculated. By comparing the reference stress value with the stress value of the evaluation object, if the stress value of the evaluation object is above the reference stress value, it is determined that the 3C-SiC film of the heteroepitaxial wafer of the evaluation object has good crystallinity.

2. The method for evaluating the crystallinity of 3C-SiC films according to claim 1, characterized in that, In the crystallinity assessment of the sample using the reference value setting of the XRD spectrum, 3C-SiC films with single-crystal 3C-SiC growth are judged as having good crystallinity, and 3C-SiC films with polycrystalline 3C-SiC growth are judged as having poor crystallinity.

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