Terrace width measuring method, defect measuring method, and measuring apparatus

Abstract

To provide a measuring method and a measuring device of a terrace width capable of measuring quickly and accurately the terrace width existing in an outer peripheral part of a laminated wafer.SOLUTION: A method for measuring a terrace width of a terrace portion formed in an outer peripheral portion of a bonded wafer including a substrate and a thin film bonded on the substrate, the method comprising: disposing the bonded wafer on a front surface side of a reflector having an outer edge larger than an outer diameter of the bonded wafer; irradiating a region including a front surface of the bonded wafer and a front surface of the reflector outside an outer peripheral portion of the bonded wafer with vertical incident light; and receiving vertical reflected light from the bonded wafer and the reflector to measure the terrace width.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a terrace width measurement method, a defect measurement method, and a measurement apparatus. [Background technology]

[0002] In recent years, SOI wafers, which have an SOI structure in which an SOI (Silicon On Insulator) layer is formed on an electrically insulating silicon oxide film, have been attracting particular attention as high-performance LSI wafers for electronic devices due to their excellent device speed, low power consumption, high voltage resistance, and environmental resistance. Furthermore, materials such as gallium arsenide (GaAs), indium phosphide (InP), gallium nitride (GaN), and silicon carbide (SiC) are expected to replace conventional silicon, as well as piezoelectric materials used to improve RF filters. Development is also underway to bond wafers in which these materials are directly bonded to a substrate, as well as Piezoelectric-On-Insulator (POI) and GaN-on-SOI wafers. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2002-305292 [Patent Document 2] Japanese Patent Application Laid-Open No. 2006-080339 Summary of the Invention [Problem to be solved by the invention]

[0004] When bonded wafers such as SOI wafers are fabricated using the bonding method, regions where bonding does not occur occur on the periphery due to the shape of the material wafers. Even in regions where bonding does occur, there are regions on the periphery where the bonding strength is insufficient, raising concerns about delamination during the device fabrication process. Therefore, the semiconductor layer (e.g., SOI layer) in those regions may be removed in advance. These regions where semiconductor layer does not exist (regions where bonding does not occur and regions where semiconductor layer has been intentionally removed) are called terrace regions.

[0005] FIG. 5 shows an SOI wafer 30 as an example of a bonded wafer. As shown in FIG. 5, the SOI wafer 30 includes a base wafer 31, a BOX layer 32, and an SOI layer (semiconductor layer) 33. In a terrace portion 34, the BOX layer 32 and the SOI layer 33 are not present on the base wafer 30. The width of this terrace portion 34 is typically about 1 to 3 mm, but because no SOI layer 33 is formed on the terrace portion 34, devices cannot be fabricated on the terrace portion 34. For this reason, delivery specifications for the width of the terrace portion are determined for each user in order to guarantee the effective area of ​​the semiconductor layer on which devices can be fabricated. Therefore, the width of the terrace portion must be measured accurately. Furthermore, in actual manufacturing inspections, measurements must be performed simply and quickly.

[0006] Various methods have been proposed for measuring the width of terrace portions. For example, Patent Document 1 describes measuring terrace widths using a microscope. While the method described in Patent Document 1 is highly accurate, it requires a high level of operator proficiency and has the problem of taking a long time to measure. Furthermore, Patent Document 2 proposes a method for evaluating bonded wafers that measures the width of terrace portions using a reflection method using a magic mirror (the magic mirror method). The magic mirror method described in Patent Document 2 is a rapid measurement method, but has the problem of making it difficult to accurately measure terrace widths because reflected light from the chamfered portion of the substrate cannot be obtained.

[0007] The present invention has been made to solve the above problems, and an object of the present invention is to provide a terrace width measurement method and measurement apparatus that can quickly and accurately measure the terrace width present on the outer periphery of a bonded wafer. [Means for solving the problem]

[0008] The present invention has been made to achieve the above-mentioned object, and provides a method for measuring a terrace width of a terrace portion formed on the outer periphery of a bonded wafer comprising a substrate and a thin film bonded on the substrate, the method comprising: placing the bonded wafer on the surface side of a reflector having an outer edge larger than the outer diameter of the bonded wafer; irradiating a region including the surface of the bonded wafer and the surface of the reflector outside the outer periphery of the bonded wafer with perpendicular incident light; and receiving perpendicular reflected light from the bonded wafer and the reflector to measure the terrace width.

[0009] According to this method for measuring the terrace width, the terrace width present on the outer periphery of the bonded wafer can be measured quickly and accurately.

[0010] In this case, the method for measuring the terrace width may be such that the surface of the reflector is a mirror surface or a light scattering surface.

[0011] This allows for more stable measurement of the terrace width.

[0012] In this case, the method for measuring the terrace width can be such that the reflector is used as a wafer stage for placing the bonded wafer thereon.

[0013] This makes it possible to measure the terrace width more easily.

[0014] In this case, the method for measuring the terrace width may be such that the wavelength of the perpendicular incident light is selected from a wavelength range in which the contrast of the perpendicular reflected light is high for the bonded wafer and the material of the terrace portion.

[0015] This allows the terrace width to be measured more stably and with higher accuracy.

[0016] In this case, the method can be a defect measurement method for measuring defects in the bonded wafer by using the perpendicularly reflected light in the terrace width measurement method.

[0017] This makes it possible to measure the size, area and shape of defects in the bonded wafer quickly and accurately, while simultaneously measuring the terrace width.

[0018] The present invention also provides a measuring device for measuring a terrace width of a terrace portion formed on the outer periphery of a bonded wafer comprising a substrate and a thin film bonded on the substrate, the measuring device comprising: a reflector having an outer edge larger than an outer diameter of the bonded wafer and arranged on the back side of the bonded wafer; and a terrace width measurement system that irradiates a surface of the bonded wafer and a surface of the reflector with perpendicular incident light and receives perpendicular reflected light from the bonded wafer and the reflector to measure the terrace width.

[0019] Such a measuring device can quickly and accurately measure the terrace width present on the outer periphery of a bonded wafer with a simple configuration.

[0020] In this case, the surface of the reflector may be a specular surface or a light-scattering surface.

[0021] This allows the terrace width to be measured more stably.

[0022] In this case, the reflector can be a measuring device that is a wafer stage on which the bonded wafer is placed.

[0023] This results in a simpler device configuration.

[0024] In this case, the measuring device can be one that can measure the terrace width and defects of the bonded wafer at the same time, and that is equipped with a display means for displaying the measured terrace width and the defects.

[0025] This makes it possible to measure and evaluate the defects quickly and accurately at the same time as measuring the terrace width. [Effects of the Invention]

[0026] As described above, the terrace width measuring method of the present invention makes it possible to quickly and accurately measure the terrace width present on the outer periphery of a bonded wafer. The measuring apparatus of the present invention has a simple configuration and can quickly and accurately measure the terrace width present on the outer periphery of a bonded wafer. [Brief explanation of the drawings]

[0027] [Figure 1] 1 is a diagram illustrating a measuring device and a method for measuring a terrace width according to the present invention. [Figure 2] 1 is a diagram showing a comparison of measurement results obtained by the measurement method of the present invention (Example 1) and conventional measurement methods (Comparative Examples 1 and 2). [Figure 3] 1 is a diagram showing a comparison of measurement results obtained by the measurement method of the present invention (Example 1) and a conventional measurement method (Comparative Example 2). [Figure 4] 10 is a diagram showing the results of measuring the entire surface of a bonded wafer by the measuring method of the present invention (Example 2). [Figure 5] 1 is a diagram illustrating the structure of a bonded wafer. DETAILED DESCRIPTION OF THE INVENTION

[0028] The present invention will be described in detail below, but the present invention is not limited thereto.

[0029] As described above, there has been a demand for a method and apparatus for measuring terrace widths that can quickly and accurately measure the widths of terraces present on the outer periphery of a bonded wafer.

[0030] As a result of extensive investigation into the above-mentioned problems, the present inventors have found that a method for measuring the terrace width of a terrace portion formed on the outer periphery of a bonded wafer comprising a substrate and a thin film bonded on the substrate, the method comprising: placing the bonded wafer on the surface side of a reflector having an outer edge larger than the outer diameter of the bonded wafer; irradiating a region including the surface of the bonded wafer and the surface of the reflector outward from the outer periphery of the bonded wafer with perpendicular incident light; and receiving perpendicular reflected light from the bonded wafer and the reflector to measure the terrace width, thereby finding that the terrace width present on the outer periphery of a bonded wafer can be measured quickly and accurately, and have completed the present invention.

[0031] The present inventors have also found that a measuring apparatus for measuring the terrace width of a terrace portion formed on the outer periphery of a bonded wafer comprising a substrate and a thin film bonded on the substrate, the measuring apparatus comprising: a reflector having an outer edge larger than the outer diameter of the bonded wafer and arranged on the back side of the bonded wafer; and a terrace width measurement system that irradiates a front surface of the bonded wafer and a front surface of the reflector with perpendicular incident light and receives perpendicular reflected light from the bonded wafer and the reflector to measure the terrace width, making it possible to quickly and accurately measure the terrace width present on the outer periphery of a bonded wafer, and have completed the present invention.

[0032] The following description will be given with reference to the drawings. The bonded wafers that are the subject of the terrace width measuring device and method of the present invention include SOI wafers as well as direct bonded wafers in which Si, GaAs, InP, SiC, and GaN are bonded without an insulating layer. Other examples include POI wafers bonded with a piezoelectric material, and are not particularly limited. The number of layers on the base wafer in the bonded wafer is also not particularly limited, and may be a single layer or two or more layers.

[0033] [Measuring equipment] An outline of the measurement apparatus according to the present invention is shown in Fig. 1. Note that Fig. 1 also shows a bonded wafer, which is the object to be measured, in order to explain the positional relationship with the object to be measured and the method for measuring the terrace width, but it goes without saying that the bonded wafer is not a component constituting the measurement apparatus according to the present invention.

[0034] As shown in FIG. 1 , a measuring apparatus 100 according to the present invention includes a reflector 2 having an outer edge larger than the outer diameter of the bonded wafer 30 and disposed on the backside of the bonded wafer 30, and a terrace width measurement system 1 that irradiates the front surface of the bonded wafer 30 and the front surface of the reflector 2 with perpendicular incident light L1 and receives perpendicularly reflected light L2 from the bonded wafer 30 and the reflector 2 to measure a terrace width 34. When the perpendicularly reflected light L2 is measured, the SOI layer (semiconductor layer) 33 of the bonded wafer 30, the flat region of the terrace portion 34, the chamfered portion, and the reflector 2 are observed as different contrasts, so that the measuring apparatus can accurately measure the terrace width present on the outer periphery of the bonded wafer. Furthermore, this method eliminates the time and effort required for setting conditions, as in conventional microscopy, and enables rapid measurement with a simple apparatus configuration.

[0035] (Terrace width measurement system) The terrace width measurement system 1 can be configured, for example, as shown in FIG. 1 , with a measurement optical system including a light source 3 that emits vertically incident light L1 and a camera 4 that receives vertically reflected light L2. The light source 3 is preferably a light source whose wavelength range can be easily selected and set. For example, an LED can be used. More specifically, the terrace width measurement system 1 can use a high-brightness LED as the light source 3. The short-wavelength light from the high-brightness LED is collimated and then passed through a telecentric lens to project highly accurate vertical light coaxially onto the surface of the bonded wafer. The vertically reflected light from the bonded wafer can then be captured by a digital camera.

[0036] (reflector) The reflector 2 has an outer edge that is larger than the outer diameter of the bonded wafer 30, and is disposed on the back surface side of the bonded wafer 30. In other words, when the bonded wafer 30 is placed on the reflector 2 and the front surface of the bonded wafer 30 is viewed from the vertical direction, the front surface of the reflector 2 is visible outside the outer periphery (edge) of the bonded wafer 30.

[0037] Since the measuring device according to the present invention receives the vertically reflected light L2 from the bonded wafer 30 and the reflector 2, the surface condition of the reflector 2 is not particularly limited as long as it receives the vertically incident light L1 and reflects the vertically reflected light L2. Reflecting the vertically reflected light L2 does not necessarily mean that all of the vertically incident light is reflected in the vertical direction, but rather that the reflected light contains a vertical component. Therefore, the surface of the reflector can be a mirror surface or a light-scattering surface. In the case of a light-scattering surface, it may be a surface sprayed with powder. Furthermore, it is more preferable that the wavelength characteristics of the vertically reflected light L2 are nearly flat (uniform). In particular, a mirror surface is more preferable because the wavelength characteristics of the vertically reflected light L2 are more flat (uniform), which enhances the contrast between the vertically reflected light and the chamfered portion of the bonded wafer.

[0038] The reflector disposed on the backside of the bonded wafer is not particularly limited as long as it has an outer edge larger than the outer diameter of the bonded wafer 30. It may support the entire underside of the bonded wafer 30, or may be, for example, a donut-shaped reflector that supports only the outer periphery of the bonded wafer as shown in FIG. 1. In particular, it is preferable to use a wafer stage on which the bonded wafer is placed, as this simplifies the device configuration. In other words, the wafer stage on which the bonded wafer is placed may have an outer edge larger than the outer diameter of the bonded wafer, and the surface condition of the stage may be such that it receives perpendicular incident light and reflects perpendicularly reflected light, as described above.

[0039] (others) The measuring device according to the present invention is preferably equipped with a display means for displaying the measured terrace width and defects. The inventors have found that the measuring device according to the present invention measures perpendicularly reflected light, and therefore can accurately measure the size, area, and shape of defects on the wafer surface. That is, the measuring device according to the present invention is equipped with a display means for displaying the measured terrace width and defects, and can measure defects on bonded wafers simultaneously with terrace width measurement. Details of defect measurement will be described later.

[0040] [Measurement method] Next, a terrace width measurement method of the present invention will be described. The terrace width measurement method of the present invention is a method for measuring the terrace width of a terrace portion formed on the outer periphery of a bonded wafer comprising a substrate and a thin film bonded to the substrate. For example, the method can be performed using the measuring device according to the present invention as described above. Items mentioned in the description of the measuring device above may be omitted as appropriate.

[0041] As shown in FIG. 1 , the bonded wafer 30 is placed on the surface side of a reflector 2 having an outer edge larger than the outer diameter of the bonded wafer 30. Then, a region including the surface of the bonded wafer 30 and the surface of the reflector 2 outside the outer periphery of the bonded wafer 30 is irradiated with perpendicular incident light L1, and perpendicularly reflected light L2 from the bonded wafer 30 and the reflector 2 is received to measure the terrace width. With this terrace width measurement method, when the perpendicularly reflected light L2 is measured, different contrasts are observed for the SOI layer (semiconductor layer) 33 of the bonded wafer 30, the flat region of the terrace portion 34, the chamfered portion, and the reflector, making it possible to accurately measure the terrace width of the terrace portion 34 present on the outer periphery of the bonded wafer. Furthermore, this method eliminates the time and effort required for setting conditions, as in conventional microscopy, and enables rapid measurement of the terrace width.

[0042] The measurement area may be any area including the surface of the bonded wafer 30 and the surface of the reflector 2 outside the outer periphery of the bonded wafer 30, and a part or the entire surface of the bonded wafer 30 may be the measurement target.

[0043] In the terrace width measuring method of the present invention, a reflector having a mirror surface or a light-scattering surface can be used as the reflector 2. In particular, a mirror surface of the reflector 2 is preferred because it enhances the contrast with the chamfered portion of the bonded wafer.

[0044] It is also preferable to use the reflector 2 as a wafer stage for placing the bonded wafer 30. Generally, when measuring the shape of a wafer, the wafer is placed on a stage for measurement, and therefore, if the reflector 2 is used as a wafer stage for placing the bonded wafer, the terrace width can be measured more easily.

[0045] It is preferable to select the wavelength of the perpendicular incident light L1 in a wavelength range that provides high contrast for the perpendicular reflected light L2 with respect to the bonded wafer 30 and the material of the terrace portion. Higher contrast allows for more stable and more accurate measurement of the terrace width.

[0046] Furthermore, a defect measurement method can be provided for measuring defects on a bonded wafer using the vertically reflected light L2 in the above-described terrace width measurement method. Since the terrace width measurement method according to the present invention measures vertically reflected light, it is also possible to accurately measure the size, area, and shape of defects on the wafer surface. That is, it is possible to measure defects on a bonded wafer simultaneously with measuring the terrace width. For example, an image such as that shown in FIG. 4 can be obtained by irradiating the entire surface of a bonded wafer with vertically incident light and measuring the vertically reflected light. Based on such an image, it is possible to simultaneously measure the terrace width and defects.

[0047] Measurable defects include slip dislocations that occur on the outer periphery of the bonded wafer, as well as various defects (voids, blisters, scratches, etc.) that occur in the SOI layer inside the terrace of the bonded wafer. [Example]

[0048] The present invention will be specifically explained below with reference to examples, but the present invention is not limited to these examples.

[0049] Example 1 A 200 mm (8 inch) diameter SOI wafer was used as a measurement sample. The SOI wafer was placed on a stage (reflector) with a mirrored surface and a diameter of 208 mm, which was larger than the diameter of the SOI wafer. Light was irradiated perpendicularly to the SOI wafer surface, and the perpendicularly reflected light from the SOI wafer surface was captured by a camera to measure the terrace width. More specifically, the stage consisted of a high-resolution θ stage capable of full 360° rotation and a 300 mm stroke linear stage. The SOI wafer was adsorbed onto the stage using vacuum air. Since particularly high precision is preferred for the perpendicularity of the linear stage and the optical axis, one with an error of 10 μm or less for a 200 mm stroke was used. The diameter of the reflector was sufficient as long as the number of pixels of the reflector captured by the camera was greater than a certain value. In Example 1, the diameter was 100 pixels.

[0050] A high-brightness LED was used as the light source for the measurement device, and the short-wavelength (450 nm) light from the high-brightness LED was collimated and passed through a telecentric lens to project extremely high-precision perpendicular light coaxially onto the surface of the bonded wafer, and the perpendicular reflected light from the bonded wafer was captured by a digital camera. The telecentric lens used had a low optical magnification of 0.23x and high resolution. The digital camera used was a camera equipped with a 1 / 3" image sensor. The observation field was 50 mm x 40 mm. In addition, a dedicated image processing unit was provided to highlight changes in the surface condition of defective areas in real time and to optimize the concentration distribution, etc. Note that for the SOI wafer in Example 1, an LED with a wavelength of 450 nm, which provides high contrast between the bonded wafer and the terrace portion, is used, but the LED wavelength is selected according to the specifications of the bonded wafer. The equipment in Example 1 allows selection of LED light sources of 450 nm, 525 nm, or 630 nm, but an LED with a wavelength that provides high contrast is installed to match the bonded wafer and terrace portion material. In addition, the magnification and observation field differ depending on specification requirements such as measurement precision and throughput.

[0051] Example 2 The same SOI wafer as that measured in Example 1 was used, and the entire surface of the SOI wafer was measured using the measuring device of Example 1.

[0052] (Comparative Examples 1 and 2) The same SOI wafer as the measurement target in Example 1 was used, and the width of the terrace portion was measured by a conventional microscope method (Comparative Example 1) and the magichou method described in Patent Document 2 (Comparative Example 2).

[0053] FIG. 2 shows the results of measurements using the terrace width measurement method of the present invention (Example 1), as well as the results of measurements using the conventional microscopy method (Comparative Example 1) and the Magichomb method (Comparative Example 2). FIG. 3 is a diagram illustrating the differences between Example 1 and Comparative Example 2. As shown in FIG. 2, the terraces, including the chamfered portions, could be observed using the microscopy method (Comparative Example 1), but the actual measurements required time for sample placement, focusing, and determining the light intensity conditions. As shown in FIGS. 2 and 3, in the measurement using the Magichomb method (Comparative Example 2), the flat portions of the terraces could be observed as differences in contrast, but the chamfered portions could not be distinguished, resulting in the terrace width measurement being smaller by the amount of the chamfered portions.

[0054] On the other hand, according to the terrace width measurement method of the present invention (Example 1), the flat portion of the terrace, the chamfered portion, and the stage (reflector) on the backside of the SOI wafer were observed as different contrasts, as shown in Figures 2 and 3. The chamfered portion has a mirror surface and does not reflect incident light in the vertical direction, so the contrast appears black when vertically reflected light is received. From these results, it was possible to accurately measure the terrace width, which is the sum of the flat portion and the chamfered portion of the terrace, in a short time.

[0055] The measurement results of Example 2 are shown in Figure 4. As shown in Figure 4, void defects in the bonded wafer could be observed simultaneously with the terrace width measurement. The void defects had the same contrast as the terrace portion, which is the area without the bonded layer, making it possible to accurately measure the size of the defects.

[0056] As described above, according to the embodiment of the present invention, it is possible to accurately measure the terrace width of a bonded wafer in a short time using a measuring device with a simple configuration. Furthermore, it is possible to measure defects present in the surface of the bonded wafer simultaneously with the measurement of the terrace width.

[0057] The present specification includes the following aspects. [1]: A method for measuring a terrace width of a terrace portion formed on the outer periphery of a bonded wafer having a substrate and a thin film bonded on the substrate, comprising: placing the bonded wafer on a surface side of a reflector having an outer edge larger than an outer diameter of the bonded wafer; irradiating a region including the surface of the bonded wafer and the surface of the reflector outside the outer periphery of the bonded wafer with normal incident light; a terrace width measuring method for measuring the terrace width by receiving perpendicularly reflected light from the bonded wafer and the reflector; [2]: The method for measuring the terrace width according to [1] above, wherein the reflector has a mirror surface or a light-scattering surface. [3]: The method for measuring a terrace width according to [1] or [2] above, wherein the reflector is used as a wafer stage for placing the bonded wafer thereon. [4]: The method for measuring the terrace width according to [1], [2] or [3] above, wherein the wavelength of the perpendicular incident light is selected from a wavelength range in which the contrast of the perpendicular reflected light is high for the bonded wafer and the material of the terrace portion. [5]: A defect measurement method for measuring defects in the bonded wafer using the vertically reflected light in the terrace width measurement method according to [1], [2], [3] or [4] above. [6]: A measuring apparatus for measuring a terrace width of a terrace portion formed on the outer periphery of a bonded wafer having a substrate and a thin film bonded on the substrate, a reflector having an outer edge larger than an outer diameter of the bonded wafer and disposed on the back surface side of the bonded wafer; a terrace width measurement system that irradiates a surface of the bonded wafer and a surface of the reflector with perpendicular incident light and receives perpendicular reflected light from the bonded wafer and the reflector to measure the terrace width; A measuring device comprising: [7]: The measuring device according to [6], wherein the surface of the reflector is a specular surface or a light-scattering surface. [8]: The measuring device according to [6] or [7], wherein the reflector is a wafer stage for placing the bonded wafer thereon. [9]: The measuring device according to [6], [7] or [8] above, which is capable of measuring defects in the bonded wafer simultaneously with measuring the terrace width, and is equipped with a display means for displaying the measured terrace width and the defects.

[0058] The present invention is not limited to the above-described embodiments. The above-described embodiments are merely examples, and anything that has substantially the same configuration as the technical idea described in the claims of the present invention and that exhibits similar effects is included within the technical scope of the present invention. [Explanation of symbols]

[0059] 1... terrace width measurement system, 2... reflector, 3... light source, 4... camera, 30...SOI wafer, 31...base wafer, 32...BOX layer, 33...SOI layer (semiconductor layer), 34...terrace portion, 100...measuring device. L1...Vertical incident light, L2...Vertical reflected light.

Claims

1. A method for measuring a terrace width of a terrace portion formed on an outer periphery of a bonded wafer including a substrate and a thin film bonded on the substrate, comprising: placing the bonded wafer on a surface side of a reflector having an outer edge larger than an outer diameter of the bonded wafer; irradiating a region including the surface of the bonded wafer and the surface of the reflector outside the outer periphery of the bonded wafer with normal incident light; a terrace width measuring method, characterized in that the terrace width is measured by receiving perpendicularly reflected light from the bonded wafer and the reflector.

2. 2. The method for measuring terrace width according to claim 1, wherein the reflector has a surface that is a mirror surface or a light scattering surface.

3. 2. The terrace width measuring method according to claim 1, wherein the reflector is used as a wafer stage for placing the bonded wafer thereon.

4. 2. The method for measuring a terrace width according to claim 1, wherein the wavelength of the perpendicular incident light is selected from a wavelength range in which the contrast of the perpendicular reflected light is high with respect to the bonded wafer and the material of the terrace portion.

5. 5. A defect measuring method, comprising measuring defects in the bonded wafer by using the vertically reflected light in the terrace width measuring method according to claim 1.

6. A measuring apparatus for measuring a terrace width of a terrace portion formed on an outer periphery of a bonded wafer including a substrate and a thin film bonded on the substrate, comprising: a reflector having an outer edge larger than an outer diameter of the bonded wafer and disposed on the back surface side of the bonded wafer; a terrace width measurement system that irradiates a surface of the bonded wafer and a surface of the reflector with perpendicular incident light and receives perpendicular reflected light from the bonded wafer and the reflector to measure the terrace width; A measuring device comprising:

7. 7. The measuring apparatus according to claim 6, wherein the surface of the reflector is a specular surface or a light-scattering surface.

8. 7. The measuring apparatus according to claim 6, wherein the reflector is a wafer stage for placing the bonded wafer thereon.

9. 9. The measuring device according to claim 6, wherein the measuring device is capable of measuring defects on the bonded wafer simultaneously with measuring the terrace width, and further comprises a display means for displaying the measured terrace width and the defects.

Images