METHOD FOR EVALUATING CRYSTALLINITY OF 3C-SiC FILM

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 technology]

[0002] SiC has a wide band gap of 2.2 to 3.3 eV, which gives it high dielectric breakdown strength. It also has high thermal conductivity, making it a promising material for use as a semiconductor material in various semiconductor devices such as power devices and high-frequency devices.

[0003] Furthermore, its use as a platform for gallium nitride (GaN) growth (e.g., Patent Document 1) is also progressing, but at the same time, small diameter SiC wafers are the norm, and larger diameters are required for power devices and high-frequency devices. If high-quality 3C-SiC single crystal films could be formed on large-diameter substrates, in addition to using the 3C-SiC single crystal film itself, it would be possible to produce large-diameter heteroepitaxial wafers with high-quality GaN layers.

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

[0005] [Patent Document 1] Special Publication No. 2018-522412 [Patent Document 2] Patent Publication No. 2021-20819 Summary of the Invention [Problem to be solved by the invention]

[0006] TEM and XRD are very suitable for obtaining information on local crystalline states, but they require processing such as dividing the heteroepitaxial wafer into small pieces before measurement, and they have the drawback of taking a long time to evaluate crystallinity.

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

[0008] The present invention has been made to achieve the above-mentioned object, and provides a method for evaluating the crystallinity of a 3C-SiC film heteroepitaxially grown on a single crystal silicon substrate, comprising: using a low-pressure CVD apparatus, heteroepitaxially growing 3C-SiC under different conditions on a plurality of single crystal silicon substrates whose WARP values ​​are known, to prepare a plurality of reference value setting samples having different crystallinity of the 3C-SiC film; measuring the WARP value of each of the plurality of reference value setting samples; substituting the WARP values ​​before and after the heteroepitaxial growth into Stoney's equation to calculate stress values ​​applied to the single crystal silicon substrates of the plurality of reference value setting samples; performing XRD measurement on the plurality of reference value setting samples; evaluating the crystallinity of the 3C-SiC film of the plurality of reference value setting samples using the obtained XRD spectrum; the stress value of a sample having the lowest stress value among the samples for setting a reference value that are determined to have good crystallinity in a crystallinity evaluation using a spectrometer is set as a reference stress value; the WARP value of a heteroepitaxial wafer to be evaluated is obtained by heteroepitaxially growing 3C-SiC on a single crystal silicon substrate whose WARP value is known; the WARP values ​​before and after the heteroepitaxial growth are substituted into Stoney's formula to calculate a stress value applied to the single crystal silicon substrate of the heteroepitaxial wafer to be evaluated; the reference stress value is compared with the stress value of the evaluation target; and if the stress value of the evaluation target is equal to or greater than the reference stress value, it is determined that the 3C-SiC film of the heteroepitaxial wafer to be evaluated has good crystallinity.

[0009] According to this crystallinity evaluation method, the crystallinity of a 3C-SiC film heteroepitaxially grown on a single crystal silicon substrate can be easily and non-destructively evaluated by the stress value calculated by substituting the WARP value, which is one of the indicators that represents the wafer shape, into the Stoney equation.

[0010] In this case, in evaluating the crystallinity of the reference value setting sample using the XRD spectrum, the crystallinity can be judged to be good when single crystal 3C-SiC is grown, and the crystallinity can be judged to be poor when polycrystalline 3C-SiC is grown.

[0011] This makes it possible to easily evaluate whether a 3C-SiC film heteroepitaxially grown on a single crystal silicon substrate is single crystal or polycrystalline. Effect 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 that represents the shape of the wafer, into the Stoney equation, making it possible to evaluate the crystallinity easily and non-destructively without the need for wafer processing. [Brief description of the drawings]

[0013] [Figure 1] An example of a flow of evaluation of 3C-SiC crystallinity according to the present invention is shown below. [Diagram 2] The stress values ​​of 3C-SiC heteroepitaxial wafers during film formation under various conditions, calculated using the Stoney formula, are shown below. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

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

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

[0016] As a result of intensive investigations into the above-mentioned problems, the present inventors have discovered a method for evaluating the crystallinity of a 3C-SiC film heteroepitaxially grown on a single crystal silicon substrate, comprising: using a low-pressure CVD apparatus to heteroepitaxially grow 3C-SiC under different conditions on a plurality of single crystal silicon substrates whose WARP values ​​are known, to prepare a plurality of reference value setting samples having different crystallinity of the 3C-SiC film; measuring the WARP value of each of the plurality of reference value setting samples; substituting the WARP values ​​before and after the heteroepitaxial growth into Stoney's formula to calculate stress values ​​applied to the single crystal silicon substrates of the plurality of reference value setting samples; performing XRD measurement on the plurality of reference value setting samples; evaluating the crystallinity of the 3C-SiC film of the plurality of reference value setting samples using the obtained XRD spectrum; and determining, from among the reference value setting samples whose crystallinity is determined to be good in the evaluation of crystallinity using the XRD spectrum, the sample with the lowest stress value. The inventors have found that a method for evaluating the crystallinity of a 3C-SiC film, which comprises setting a stress value as a reference stress value, measuring the WARP value of a heteroepitaxial wafer to be evaluated, which is formed by heteroepitaxially growing 3C-SiC on a single crystal silicon substrate whose WARP value is known, substituting the WARP values ​​before and after the heteroepitaxial growth into the Stoney formula to calculate a stress value applied to the single crystal silicon substrate of the heteroepitaxial wafer to be evaluated, comparing the reference stress value with the stress value of the evaluation target, and judging that the 3C-SiC film of the evaluation target has good crystallinity if the stress value of the evaluation target is equal to or greater than the reference stress value, enables the crystallinity of a 3C-SiC film heteroepitaxially grown on a single crystal silicon substrate to be easily and nondestructively evaluated by a stress value calculated by substituting the WARP value, which is one of the indexes representing the shape of the wafer, into the Stoney formula, and thus completed the present invention.

[0017] Hereinafter, a method for evaluating the crystallinity of a 3C-SiC film according to an embodiment of the present invention will be described with reference to Fig. 1. Fig. 1 shows an example of a flow chart of the method for evaluating the crystallinity of a 3C-SiC film according to the present invention.

[0018] [Reference stress value setting] First, as shown in S1 of Fig. 1, multiple single crystal silicon substrates are prepared and the WAPR value of each is measured. Note that it is preferable that the prepared single crystal silicon substrates are of the same specifications as the single crystal silicon substrate to be evaluated.

[0019] Next, as shown in S2 in Figure 1, a single crystal silicon substrate with a known WAPR value is placed in a reduced pressure (RP)-CVD apparatus, and 3C-SiC is heteroepitaxially grown under various deposition conditions to prepare multiple samples with different crystallinity of the 3C-SiC film for setting reference values. There is a lattice constant difference of about 20% between Si and 3C-SiC, and when 3C-SiC is deposited on a silicon substrate, tensile stress is applied, causing the substrate to warp in a downward convex shape.

[0020] Next, as shown in S3 of FIG. 1, the shape of each of the obtained samples for setting the reference values ​​is measured, and WARP, which is an index showing the amount of warping, is measured.

[0021] Next, as shown in S4 of FIG. 1, the WARP values ​​before and after the heteroepitaxial growth are substituted into the following Stoney equation, which can calculate stress from the warpage of the substrate, to calculate the stress value applied to the single crystal silicon substrate of the reference value setting sample.

[0022]

number

[0023]

number

[0024] When 3C-SiC with low crystallinity is grown, the WARP value becomes smaller due to lattice relaxation caused by the numerous misfit dislocations generated in the film, and the stress value calculated from the Stoney formula becomes lower.On the other hand, when 3C-SiC with high crystallinity is grown, there are fewer dislocation defects in the film, making lattice relaxation less likely to occur, so the WARP value becomes larger and the stress value calculated from the Stoney formula becomes higher.

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

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

[0027] A concrete example will be used for explanation. Figure 2 shows the relationship between crystallinity and stress value obtained by growing 3C-SiC under different growth conditions using seven single crystal silicon substrates with WARP values ​​measured in advance as samples for setting the reference value, measuring the WARP value, calculating the stress value, and investigating the crystallinity. As shown in Figure 2, the 3C-SiC films grown under conditions 1 to 3 were confirmed to have grown as single crystal 3C-SiC from the XRD spectrum, and were judged to have good crystallinity. Also, the 3C-SiC films grown under conditions 4 to 7 were confirmed to have grown as polycrystalline 3C-SiC from the XRD spectrum, and were judged to have poor crystallinity. From this result, the stress value under condition 3 (1.13 GPa) can be set as the reference stress value.

[0028] In the crystallinity evaluation of the reference value setting sample using the above XRD spectrum, it is possible to judge that the crystallinity is good when single crystal 3C-SiC is grown and that the crystallinity is poor when polycrystalline 3C-SiC is grown. This makes it easy to evaluate whether the 3C-SiC film heteroepitaxially grown on the single crystal silicon substrate is single crystal or polycrystalline.

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

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

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

[0032] Next, as shown in S9 of FIG. 1, the WARP values ​​before and after the heteroepitaxial growth are substituted into the Stoney formula to calculate the stress value acting on the single crystal silicon substrate of the evaluation target wafer.

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

[0034] In the example of Figure 2, the stress value of condition 3 is set as the reference stress value, so if the stress value of the actual wafer being evaluated is equal to or greater than the reference stress value of 1.13 GPa, the crystallinity of the 3C-SiC film is judged to be good, and if it is less than 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 a stress value calculated by substituting the WARP value, which is one of the indicators that represents the shape of the wafer, into the Stoney equation, making it possible to evaluate the crystallinity simply and non-destructively.

[0036] In applying the evaluation method of the present invention, since, as described above, forming a film of 3C-SiC on a silicon substrate applies tensile stress, causing the substrate to warp in a downward convex shape, it is preferable to apply the method to a wafer in which 3C-SiC is heteroepitaxially grown on a single crystal silicon substrate that has an upward convex warp. EXAMPLES

[0037] The present invention will be specifically described below with reference to examples, but the present invention is not limited thereto.

[0038] (Example) Seven single crystal silicon substrates were prepared for measuring the WARP value. The single crystal silicon substrates had a diameter of 300 mm, a (111) surface orientation, P-type, and a value of 10 Ω·cm. The single crystal silicon substrates with known WARP values ​​were placed on a susceptor in the reactor of a low-pressure CVD apparatus, and 3C-SiC was heteroepitaxially grown under seven different deposition conditions.

[0039] The WARP values ​​of the seven types of wafers obtained were measured, and the WARP values ​​before and after the film formation were substituted into the Stoney formula to calculate the stress value acting on each wafer.

[0040] Furthermore, when the obtained 3C-SiC films were subjected to XRD measurement under in-plane diffraction conditions, the 3C-SiC films formed under conditions 1 to 3 had only a peak derived from the (220) plane detected in the XRD spectrum, confirming that single-crystal 3C-SiC had grown, and were judged to have good crystallinity. The 3C-SiC films formed under conditions 4 to 7 had peaks derived from the (111) and (311) planes in addition to the peak derived from the (220) plane in the XRD spectrum, confirming that polycrystalline 3C-SiC had grown, and were judged to have poor crystallinity (hereinafter also referred to as XRD judgment good / poor).

[0041] Among the stress values ​​of the wafers under conditions 1 to 3 for which the XRD judgment was good, the lowest was the stress value under condition 3 (1.13 GPa), which was set as the reference stress value.

[0042] The stress values ​​of 3C-SiC heteroepitaxial wafers grown under each condition are shown in Figure 2. As shown in Figure 2, the wafers under conditions 1 and 2, which were judged as good by XRD, all had a stress applied to the substrate that was equal to or greater than the standard stress value, while the wafers under conditions 4 to 7, which were judged as bad by XRD, all had a stress applied to the substrate that was less than the standard stress value.

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

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

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

[0046] The present invention is not limited to the above-described embodiment. The above-described embodiment is merely an example, and anything that has substantially the same configuration as the technical idea described in the claims of the present invention and exhibits similar effects is included in the technical scope of the present invention.

Claims

1. A method for evaluating the crystallinity of a 3C-SiC film heteroepitaxially grown on a single crystal silicon substrate, comprising: Using a low-pressure CVD apparatus, 3C-SiC is heteroepitaxially grown under different conditions on a plurality of single crystal silicon substrates having known WARP values, to prepare a plurality of reference value setting samples having different crystallinity of the 3C-SiC film; measuring the WARP value for each of the plurality of reference value setting samples; The WARP values ​​before and after the heteroepitaxial growth are substituted into Stoney's formula to calculate stress values ​​applied to the single crystal silicon substrates of the plurality of reference value setting samples; XRD measurements are performed on the plurality of reference value setting samples, and the crystallinity of the 3C-SiC film of the plurality of reference value setting samples is evaluated using the obtained XRD spectra; Among the samples for setting the reference value, which are determined to have good crystallinity in the evaluation of crystallinity using the XRD spectrum, the stress value of the sample having the lowest stress value is set as a reference stress value; Measure the WARP value of a heteroepitaxial wafer to be evaluated, which is obtained by heteroepitaxially growing 3C-SiC on a single crystal silicon substrate having a known WARP value; The WARP values ​​before and after the heteroepitaxial growth are substituted into the Stoney formula to calculate a stress value applied to the single crystal silicon substrate of the heteroepitaxial wafer to be evaluated; A method for evaluating crystallinity of a 3C-SiC film, comprising: comparing the reference stress value with a stress value of the evaluation object; and judging that the 3C-SiC film of the evaluation object heteroepitaxial wafer has good crystallinity if the stress value of the evaluation object is equal to or greater than the reference stress value.

2. The method for evaluating the crystallinity of a 3C-SiC film as described in claim 1, characterized in that, in evaluating the crystallinity of a reference value setting sample using the XRD spectrum, a sample on which single-crystalline 3C-SiC has been grown is judged to have good crystallinity, and a sample on which polycrystalline 3C-SiC has been grown is judged to have poor crystallinity.

Images