Defect inspection method for composite substrate

Abstract

To provide a defect inspection method for composite substrates that can detect defects in a composite substrate, in which a semiconductor layer is formed through an insulating layer on a translucent substrate, in good condition.SOLUTION: The present invention is a defect inspection method for detecting defects in a semiconductor layer in a composite substrate 1, in which the semiconductor layer is formed through an insulating layer on a translucent substrate, light 4 is incident on the main surface of the composite substrate 1, and defects in the semiconductor layer are detected based on the intensity of transmitted light 5 transmitted through the composite substrate.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a method for inspecting defects in a composite substrate that detects defects in a semiconductor layer in a composite substrate in which a semiconductor layer is formed on a translucent substrate via an insulating layer.

Background Art

[0002] By bonding different materials together, it becomes possible to achieve performance that did not exist conventionally and to manufacture large semiconductor substrates. This bonding is called a bonding technique. However, in order to directly bond substrates together, flatness of the surfaces to be bonded is required, and an insulating layer such as silicon oxide is used for the purpose of filling the unevenness on the substrate surface. By forming a layer such as silicon oxide on the surface of the substrate to fill the valleys of the unevenness and then flattening the layer by polishing, the smoothness of the surface necessary for direct bonding can be obtained, and a layer having another function can be bonded to the substrate surface to form a layer having another function on the substrate surface. Here, smoothness means that both flatness with small undulations and deformation and surface roughness representing fine unevenness on the surface are small, and the surface is flat and has small unevenness.

[0003] As an example of a composite substrate obtained by directly bonding a substrate and a layer, there is a composite substrate described in Patent Document 1, which is a combination of a ceramic substrate and a semiconductor layer obtained by bonding a semiconductor layer to a ceramic substrate. In this composite substrate, a ceramic substrate having a thermal expansion coefficient matched to that of single-crystalline GaN was used for the purpose of forming a GaN crystal layer on the composite substrate by epitaxial growth. Further, in this composite substrate, a single-crystalline Si layer was bonded to the ceramic substrate, and a single-crystalline Si layer was provided on the ceramic substrate as a seed crystal for epitaxial growth. Thereby, the generation of defects in the GaN crystal layer due to thermal stress generated when cooling to room temperature after epitaxial growth is prevented.

[0004] The composite substrate produced by bonding must have its bonding surface finished to a very smooth surface. If the bonding surface is rough, there will be a part where the two bonding surfaces are separated between the two bonding surfaces, and a void will occur in that part. Therefore, during heating, the gas expansion in the void may cause the seed crystal layer to peel off from the ceramic substrate, or the bonding strength may be insufficient, resulting in defects in the seed crystal layer starting from that part. For this reason, in Patent Document 1, a bonding layer is formed on the surface of the ceramic substrate, the valleys on the surface of the ceramic substrate are filled with the bonding layer, and the bonding layer formed on the surface of the ceramic substrate is finished flat by grinding or polishing to create a surface state suitable for bonding. In Patent Document 1, a barrier layer is formed before forming the bonding layer to prevent impurities from the ceramic substrate. In this way, in Patent Document 1, by planarizing the bonding layer, a single-crystalline Si layer, which is a semiconductor layer, is formed on the surface of the ceramic substrate by transfer.

[0005] The surface of the ceramic substrate has unevenness of several microns due to damage generated during grinding or polishing processes, and the detachment of particles from the boundaries (grain boundaries) of particles. This unevenness is filled with a material such as silicon oxide for the bonding layer, and further planarization processing is performed. In order to fill the valleys of the unevenness on the surface of the ceramic substrate, for example, silicon oxide is deposited on the surface of the ceramic substrate so as to be thicker than the valleys, and a silicon oxide layer with a thickness of about 10 μm is formed on the surface of the ceramic substrate. After heat treatment, the surface of the ceramic substrate is processed by polishing so that the thickness of the silicon oxide layer becomes about 1 μm from the surface of the ceramic substrate, and a smooth surface necessary for direct bonding is obtained. At this time, in order to fill the valleys on the surface of the ceramic substrate, silicon oxide is deposited thickly. However, it is difficult to finish the thickness of the silicon oxide layer uniformly in the plane by polishing, and variations occur in the thickness of the silicon oxide layer in the plane. Also, regarding the deposition of silicon oxide, in the film formation using plasma, since the ceramic substrate is insulating, electrical differences are generated due to structures necessary for transporting the substrate, such as lift pins and transfer forks in the lower electrode, and variations occur in the thickness of the formed silicon oxide layer. This variation in the thickness of the silicon oxide layer appears as color unevenness of the reflected light over the entire composite substrate due to the interference of the reflected light on the surface of the ceramic substrate where the silicon oxide layer is formed. When the structure of the surface layer of the composite substrate is Si / SiO2 / barrier layer / ceramic substrate, the reflected light interferes with each other at the Si surface, the Si / SiO2 interface, and the SiO2 / barrier layer interface. And since the state of interference changes depending on the wavelength, the color tone changes depending on the film thickness of each layer. Although there is no problem with this itself, when inspecting the defects of the single crystal Si layer that becomes the seed crystal for epitaxial growth, the intensity of this reflected light causes problems.

[0006] Taking a single-crystalline Si layer as an example, the semiconductor layer will be described (hereinafter, the single-crystalline Si layer may be simply referred to as the Si layer). In the following example, the Si layer corresponds to the semiconductor layer, and the silicon oxide layer corresponds to the insulating layer. Usually, for the defect inspection of the Si layer, as shown in FIG. 2, illumination is applied and the surface of the substrate is magnified and observed with a camera or a microscope, and defects and scratches in the Si layer are detected by the difference in brightness from the surroundings. Although not shown in FIG. 2, the entire composite substrate is inspected by moving the composite substrate relative to the camera. The type of camera used and the combination of lenses for magnifying the field of view are selected according to the size of the defect to be detected. The defect detection method using the reflected light in FIG. 2 will be described with reference to FIG. 3. As shown in FIG. 3, a part of the illumination light 4 is reflected on the surface of the Si layer 11. Conversely, since there is less light reflection in the part without the Si layer and the light is transmitted to the substrate 10, it becomes dark, and a part darker than the surroundings can be recognized as a defect. However, in the case of a composite substrate provided with a silicon oxide layer 12 under the Si layer 11, as shown in FIG. 4, the light transmitted through the Si layer 11 and the silicon oxide layer 12 is reflected at the interface between the Si layer 11 and the silicon oxide layer 12 or at the interface between the silicon oxide layer 12 and the substrate 10. Since the optical path length of the reflected light inside is different from that of the reflected light on the surface, light interference occurs, and the intensity of the reflected light varies depending on the thickness of the transmitted layer. Therefore, due to the difference in layer thickness, a difference in brightness occurs, and there are cases where the presence of a defect in the Si layer 11 cannot be determined simply by being darker than the surroundings. That is, depending on the combination of the thicknesses of each layer, even if there is no defect in the Si layer, very bright and dark parts may occur, and false detection of defects may occur due to the difference in brightness. When the number is small, a person can compare the actual object with the inspection result to determine whether it is a false detection. Industrially, it is required to be automatically inspected by an inspection device, and the pass / fail is mechanically determined there.

[0007] There is also a method that uses an apparatus with a high-magnification lens to observe only the surface of the semiconductor layer. By doing so, the inspection range (field of view) can be narrowed, and the imaging depth (range of in-focus height) can also be narrowed. As a result, it is possible to make it less susceptible to the color of ambient reflected light and to mitigate the interference of the reflected light itself. However, in this case, it is possible to detect very small defects (e.g., 0.1 μm to several tens of μm), but larger defects (0.1 mm to several mm) are detected separately, and it is not easy to detect larger defects. Therefore, there is a need for a method to accurately and quickly detect defects in the semiconductor layer on the surface layer of the composite substrate.

Prior Art Documents

Patent Documents

[0008]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0009] The present invention has been made in view of the above circumstances, and an object thereof is to provide a method for inspecting defects in a composite substrate that can satisfactorily detect defects in a composite substrate in which a semiconductor layer is formed on a translucent substrate via an insulating layer.

Means for Solving the Problems

[0010] As a result of intensive research and repeated trial and error to solve this problem, the present inventor has found that defects in the semiconductor layer can be satisfactorily detected based on the intensity of the transmitted light of the light that has entered the main surface of the composite substrate and passed through the composite substrate, and has thus completed the present invention. The gist of the present invention is as follows. [1] A method for inspecting defects in a composite substrate for detecting defects in the semiconductor layer in a composite substrate in which a semiconductor layer is formed on a translucent substrate via an insulating layer, wherein light is made to enter the main surface of the composite substrate, and defects in the semiconductor layer are detected based on the intensity of the transmitted light of the light that has passed through the composite substrate. [2] The method for inspecting defects of the composite substrate according to [1] above, wherein the light-transmissive substrate is made of at least one material selected from the group consisting of glass, sapphire, synthetic quartz, quartz crystal, and ceramic.

Advantages of the Invention

[0011] According to the present invention, it is possible to provide a method for inspecting defects of a composite substrate that can favorably detect defects of a composite substrate in which a semiconductor layer is formed on a light-transmissive substrate with an insulating layer interposed therebetween.

Brief Description of the Drawings

[0012]

Figure 1

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Embodiments for Carrying Out the Invention

[0013] [Method for Inspecting Defects of Composite Substrate] The method for inspecting defects of a composite substrate of the present invention is a method for inspecting defects of a semiconductor layer in a composite substrate in which a semiconductor layer is formed on a light-transmissive substrate with an insulating layer interposed therebetween. Light is made incident on the main surface of the composite substrate, and defects of the semiconductor layer are detected based on the intensity of the transmitted light of the light transmitted through the composite substrate.

[0014] (Composite Substrate) The composite substrate to be inspected by the method for inspecting defects of a composite substrate of the present invention is one in which a semiconductor layer is formed on a light-transmissive substrate with an insulating layer interposed therebetween.

[0015] <Light-Transmissive Substrate> The light-transmissive substrate of the composite substrate is not particularly limited as long as it is a substrate having light-transmittance, but it is preferably a substrate made of at least one material selected from the group consisting of glass, sapphire, synthetic quartz, quartz crystal, and ceramics. Examples of the ceramics used for the light-transmissive substrate include aluminum nitride, aluminum oxide, PLZT, titanium oxide, yttria-based light-transmissive ceramics, zirconia-based light-transmissive ceramics, magnesia-based light-transmissive ceramics, and the like. These light-transmissive materials can be used alone or in combination of two or more. From these, the material is selected according to the purpose, from the thermal expansion coefficient, crystallinity, optical properties, etc. For semiconductor applications, synthetic quartz with few impurities, sapphire from the crystal lattice size, and aluminum nitride with a thermal expansion coefficient close to that of GaN single crystal are selected.

[0016] The thickness of the light-transmissive substrate is not particularly limited. For example, for a substrate with a diameter of 150 mm, it is 600 - 1,000 μm, and for a substrate with a diameter of 200 mm, it is 700 - 1,000 μm. The thickness of the light-transmissive substrate is selected according to the constraints of semiconductor devices. Also, from the perspective of the strength of the material, a light-transmissive substrate with a thickness outside these ranges may be used.

[0017] <Semiconductor layer> The semiconductor layer of the composite substrate is not particularly limited as long as it is a layer of a single-crystal material having light-transmittance and semiconductor characteristics. Examples of the materials constituting the semiconductor layer include Si, Ge, ZnSe, CdS, ZnO, GaAs, InO, GaN, SiC, SiGe, and the like. From these, a material appropriate for the target characteristics and epitaxial growth is selected. For example, for a seed crystal for GaN growth, single-crystal Si with a crystal orientation of (111) is optimal. Also, if it is desired to form an optically transparent transistor circuit thereon, a structure in which single-crystal Si is formed on a synthetic quartz substrate is optimal. Although single-crystal Si is originally opaque to visible light, light can pass through in the case of a thin film.

[0018] The method of forming a semiconductor layer on a light-transmissive substrate via an insulating layer is not particularly limited, but it is preferably formed by a transfer method. For example, after ion implantation is performed on a semiconductor substrate, the ion-implanted portion of the semiconductor substrate is transferred to the insulating layer described later as a thin film, that is, after transferring the semiconductor substrate to the insulating layer, the semiconductor layer can be formed by peeling off the semiconductor substrate. Ion implantation may be performed by a normal method. Ion implantation is a method of ionizing an atom or molecule for implantation in a vacuum, accelerating it from several keV to several MeV, and implanting it into a solid. Examples of the ions to be implanted include hydrogen (H), helium (He), argon (Ar), etc. For ion implantation, for example, an ion implantation apparatus is used. The ion implantation apparatus is a miniaturized high-energy accelerator and isotope separator, and is composed of an ion source, an accelerator, a mass separator, a beam scanning unit, an implantation chamber, etc. In addition, it is preferable to polish the semiconductor layer transferred to the insulating layer on the light-transmissive substrate to smooth the surface of the semiconductor layer.

[0019] The thickness of the semiconductor layer is not particularly limited, but for example, it is 100 to 1,000 nm, preferably 100 to 300 nm. This is determined by the thickness of the semiconductor layer required in the device to be manufactured, but when used as a seed crystal, if the thickness exceeds this value, the problem of thermal stress cannot be ignored, which will affect the film quality in epitaxial growth. Also, if the thickness is more than this, light will not be transmitted, and defect inspection in the present invention may not be possible.

[0020] <Insulating layer> The insulating layer of the composite substrate is not particularly limited as long as it is a layer of a light-transmissive insulator material. Examples of the material constituting the insulating layer include SiO2, SiN, SiO x N y (where x = 0 to 2, y = 0 to 1.5, x + y > 0), etc. Among these, SiO2 and SiN are preferable. This is because the deposition apparatus and method have been established, deposition can be easily performed, and the polishing method has also been established.

[0021] The insulating layer may be composed of a single layer or multiple layers. When the insulating layer is composed of multiple layers, it is preferably composed of 2 to 3 layers. Further, when the insulating layer is composed of multiple layers, the materials constituting each layer may be the same as each other or different from each other.

[0022] The method of forming the insulating layer on the translucent substrate is not particularly limited, but a chemical vapor deposition method (CVD method) is preferred.

[0023] The thickness of the insulating layer is not particularly limited, but for example, it is 0.1 to 5 μm, preferably 0.5 to 2 μm. This is determined from the balance between the magnitude of the unevenness on the substrate surface before deposition and the film thickness uniformity during polishing. A thinner thickness can reduce the deposition time and polishing time, but in order to obtain the flatness and smoothness required for bonding, it is better to deposit thicker and perform longer polishing. However, if the polishing time is long, there is a problem that a large amount of the outer peripheral portion is polished and the film thickness uniformity is impaired.

[0024] (Light source) The light source used to irradiate light onto the main surface of the composite substrate is not particularly limited, and examples of the light source include an LED, a fluorescent lamp, a halogen lamp, a xenon lamp, etc. Among these light sources, an LED capable of uniform surface emission is preferred. Recently, there are various-shaped and brightness LED illuminations for image processing, so it is advisable to select one that suits the arrangement during inspection from among them.

[0025] (Wavelength of light) The wavelength of the light incident on the main surface of the composite substrate is not particularly limited, but preferably it is 400 to 800 nm in the visible light range. Depending on the film configuration, it is also possible to narrow the wavelength range in order to mitigate the influence of interference light.

[0026] (Intensity of transmitted light) The device for measuring the intensity of transmitted light that has passed through the composite substrate is not particularly limited as long as it can measure the intensity of the transmitted light. The device capable of measuring the intensity of the transmitted light is preferably a line sensor type camera. While moving the composite substrate, the transmitted light is continuously photographed with a line sensor type camera, and by connecting the signals of the line sensor over time, the intensity of the transmitted light across the entire surface of the composite substrate can be obtained as a two-dimensional map. Then, based on this two-dimensional map, defects in the semiconductor layer can be detected. Note that the intensity of the transmitted light at the defective part is higher than that at the non-defective part. Line sensors for image processing are available from various manufacturers. For example, when using the CMOS line scan camera "Basler racer raL12288-8gm" from BASLER, since it has 12,000 pixels, the resolution can be increased, and when scanning multiple times, the number of scans can be reduced. Additionally, there is a camera called a TDI (Time Delay Integration) sensor, which has multiple pixels in the scanning direction and can perform high-sensitivity imaging by overlapping the exposure for the movement by matching the moving speed and the CCD readout speed, and this can also be used. Examples of TDI cameras include "C10000-801" from Hamamatsu Photonics and the VT series from Nippon Viewworks Co., Ltd.

[0027] In the conventional method for inspecting defects in a composite substrate that uses reflected light, in addition to defects in the semiconductor layer, due to the interference of the reflected light caused by variations in the thickness of the bonding layer for filling the unevenness under the semiconductor layer on the surface, light and dark patterns of the reflected light occur. As a result, defects in the semiconductor layer are detected even though there are no defects in the semiconductor layer, leading to false detections in defect detection. On the other hand, in the method for inspecting defects in the composite substrate of the present invention, since transmitted light is used instead of reflected light, the problem of the above-mentioned false detections does not occur.

[0028] As described above, the method for inspecting defects in a composite substrate of the present invention is a method for inspecting defects in a semiconductor layer in a composite substrate in which a semiconductor layer is formed on a light-transmissive substrate via an insulating layer. Light is incident on the main surface of the composite substrate, and defects in the semiconductor layer are detected based on the intensity of the transmitted light of the light transmitted through the composite substrate. This is a method for inspecting defects in a composite substrate, characterized by this. As described above, in the case of a composite substrate produced by bonding, in order to improve the surface state of the light-transmissive substrate and improve the bonding quality, an insulating layer (for example, a layer of silicon oxide) is formed on the light-transmissive substrate and flattened by polishing or the like. Variations in the thickness of the insulating layer that occur during this flattening cause interference between the reflected light from the inside and the surface reflected light due to the reflection of the inspection light after the semiconductor layer is formed on the surface, generating light intensity unrelated to defects and causing false detection in defect inspection. This is because defect detection is performed based on the intensity (brightness) of the reflected light, and although only the portion without the semiconductor layer where the reflected light of the original defect is reduced should be detected, even if there are no defects in the semiconductor layer, the portion darkened due to the interference of the reflected light is also recognized as a defect. In the case of a light-transmissive substrate, when the composite substrate is irradiated with inspection light, transmitted light can be obtained on the opposite surface with brightness corresponding to the transmittance. This transmitted light is bright in the portion without the semiconductor layer (defect portion) and dark in the portion where the semiconductor layer is normally present, so defects can be detected by the intensity (brightness) of the transmitted light. Also, this transmitted light is less affected by the thickness of the insulating layer like the surface reflected light, making it easy to distinguish the presence or absence of the semiconductor layer and the presence or absence of defects in the semiconductor layer.

Example

[0029] Hereinafter, the present invention will be described more specifically with reference to examples, but the present invention is not limited thereto.

[0030] [Manufacture of Composite Substrate] As a light-transmitting substrate, a circular aluminum nitride substrate with a diameter of 150 mm and a thickness of 635 μm, having a single-crystalline Si layer on its surface, was prepared. A flat notch with a length of 47.5 mm indicating the crystal orientation of the single-crystalline Si layer provided on the surface was formed in a part of the outer periphery of this aluminum nitride substrate. On the surface of this light-transmitting substrate, a 300-nm-thick silicon oxide layer was deposited by the LPCVD method (low-pressure chemical vapor deposition method), and further, a 300-nm-thick silicon nitride layer was deposited thereon to form a barrier layer for preventing impurity diffusion from the aluminum nitride substrate. A 3-μm-thick silicon oxide layer was deposited on the surface of the light-transmitting substrate by the plasma CVD method and baked at a temperature of 1000°C. The 3-μm-thick silicon oxide layer was polished until it became about 1 μm thick, and this was used as an insulating layer. Separately, a single-crystalline Si substrate with a surface oxidized and having a crystal orientation of <111> was prepared, and hydrogen ions were implanted to a depth that would become the peeling interface to be used as a donor substrate. Plasma was irradiated onto the surface of the donor substrate and the surface of the insulating layer to activate them, and their surfaces were joined together, and heat treatment was performed to further increase the bonding force between the single-crystalline Si substrate and the insulating layer. After the heat treatment, a blade was inserted to peel the Si substrate, and a composite substrate having a single-crystalline Si layer formed on the light-transmitting substrate was obtained. There was a variation in the thickness of the silicon oxide layer of this substrate, and the thickness had a variation in the in-plane direction of 0.6 to 1.4 μm with respect to the finishing target of 1 μm, and by visually observing the appearance, a change in the color of the reflected light could be seen in the portion where the thickness was changing.

[0031] [Comparative Example 1] When the above composite substrate was inspected with a conventional defect inspection apparatus using reflected light as shown in FIG. 2, many defects were detected in the portion where the color changed due to the change in film thickness. However, when the defective portion was observed at a high magnification using a microscope, no defects were found in the composite substrate. From this, it was found that this defect detection was a false detection. This false detection can be prevented by making the thickness of the silicon oxide layer, which is the bonding layer, uniform or making the thickness less likely to cause interference. However, for the purpose of filling the unevenness on the surface of the light-transmitting substrate, it is necessary to make the thickness of the bonding layer more than a certain thickness, and since the polishing amount of the bonding layer also becomes relatively large, it is difficult to adopt such a method.

[0032] [Example 1] As shown in FIG. 1, a camera was placed on the front side of the composite substrate, lighting was placed on the opposite side (back side) of the composite substrate, and defects were detected based on the intensity of the light (transmitted light) that had passed through the composite substrate. A line sensor type camera was used, and continuous shooting was performed while moving the composite substrate. By connecting the signals of the line sensor over time, the light intensity across the entire composite substrate was obtained as a two-dimensional map. The number of pixels of the line sensor was 8,192. To observe a composite substrate with a diameter of 150 mm, the arrangement and lens were selected such that the width of the field of view was 180 mm. To observe 180 mm with 8,192 pixels, the observation width per pixel was 22 μm. The moving speed of the composite substrate was calculated and set based on the line rate of the line sensor used and the observation width per pixel (22 μm). With such a configuration, the measurement of the intensity of the transmitted light of the aforementioned composite substrate was performed. The brightness of the lighting was adjusted so that the defective portions could be recognized. In this configuration, the change in the brightness of the transmitted light due to the presence or absence of the semiconductor layer, that is, the defect of the semiconductor layer, was larger than the change in the transmitted light due to the film thickness. Therefore, the defective portions could be easily detected.

[0033] In Example 1, a camera is used as a line sensor. However, the sensitivity can be increased by matching the moving speed of the substrate and the scanning time of the camera using a method called a TDI (Time Delay Integration) sensor, or the composite substrate can be fixed and the camera and lighting can be moved. A high-pixel area sensor can be used to image the composite substrate in several parts to obtain a two-dimensional map of the intensity of the transmitted light across the entire surface. Note that the configuration of the inspection apparatus described in this example is merely an example. As shown in FIG. 6, an illumination for transmitted light can be added to an apparatus capable of performing inspection using reflected light, and a configuration that can switch between reflected light and transmitted light for inspection is also possible as an application example.

[0034] [Example 2] Regarding an SOS (Silicon on Sapphire) substrate, which is a sapphire substrate having a single-crystalline Si layer on its surface as a transparent substrate, it was investigated whether defect detection could be performed in the same manner as in Example 1. The used transparent substrate was a sapphire substrate with a diameter of 150 mm and a thickness of 625 μm, with one side finished to a mirror surface, and the surface on the opposite side of the single-crystalline Si layer side was a lapped surface in a rough and cloudy state. The surface of the single-crystalline Si substrate was thermally oxidized to prepare a single-crystalline Si substrate having a SiO2 layer with a thickness of 50 nm on its surface. Hydrogen ions were implanted into this single-crystalline Si substrate to a depth corresponding to the thickness of the release layer to obtain a donor substrate. The surfaces of the donor substrate and the mirror surface side (SiO2 layer side) of the sapphire substrate were irradiated with plasma to be activated, and the surfaces were joined together and heat-treated to further increase the bonding strength between the sapphire substrate and the single-crystalline Si substrate. After the heat treatment, a blade was inserted to peel the single-crystalline Si substrate from the sapphire substrate, and a composite substrate (SOS substrate) with a single-crystalline Si layer formed on the sapphire substrate was obtained. This single-crystalline Si layer was polished to the target thickness (200 nm). An attempt was made to detect defects in the single-crystalline Si layer of this composite substrate using the transmission light defect detection device with the configuration shown in FIG. 1. As a result, the same defects as those detected by the conventional reflection-type defect inspection device were detected, indicating that there is no problem with defect detection by transmission light.

[0035] In the above Example 1 and Example 2, in a composite substrate in which a semiconductor layer is formed on a transparent substrate via an insulating layer, even when there is a change in the intensity of reflected light due to the film thickness of the semiconductor layer or the insulating layer below it, by making light incident on the main surface of the composite substrate and detecting defects in the semiconductor layer based on the intensity of transmitted light of the light transmitted through the composite substrate, defects in the semiconductor layer could be detected well. On the other hand, in Comparative Example 1, due to the change in the intensity of reflected light caused by the film thickness of the semiconductor layer or the insulating layer below it, defects in the semiconductor layer could not be detected well.

Description of Reference Numerals

[0036] 1 Composite substrate 2 Camera 3 Light source 4 Illumination light 5 Light transmitted through the substrate 6 Reflected light (interference light) 10 Substrate 11 Si layer 12 Silicon oxide layer 13 Incident light 14 Reflected light 20 Light source for observing reflected light 21 Light source for observing transmitted light

Claims

**Claim 1** A method for inspecting defects in a composite substrate that forms a semiconductor layer via an insulating layer on a light-transmissive substrate, the method comprising: A method for inspecting defects in a composite substrate, the method comprising: irradiating light onto a main surface of the composite substrate and detecting defects in the semiconductor layer based on the intensity of transmitted light that has passed through the composite substrate. **Claim 2** The method for inspecting defects in a composite substrate according to claim 1, wherein the light-transmissive substrate is made of at least one material selected from the group consisting of glass, sapphire, synthetic quartz, quartz crystal, and ceramics.

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