Wafer inspection method

Abstract

This application provides a wafer inspection method applicable to the semiconductor technology field. In this application, a reflective film is placed at the outer edge of a support stage to acquire an image (e.g., a grayscale image) of the chamfered area of ​​the wafer and the reflective film. Because the reflective film is reflective, under bright light, the light is reflected to a camera (e.g., a monochrome camera), resulting in a white image. Since the chamfered area of ​​the wafer is curved, it appears black in the image. Therefore, the chamfered area can be identified based on the grayscale difference between the chamfered area and the reflective film in the grayscale image. Then, an inspection program is set, and an optical inspection machine is run to achieve the purpose of measuring the wafer edge and detecting wafer edge defects.

Description

Technical Field

[0001] This application relates to the field of semiconductor technology, and in particular to a wafer inspection method. Background Technology

[0002] Optical wafer inspection equipment is an automated device used in semiconductor manufacturing to detect defects on the surface and inside of wafers, playing a crucial role in quality control and yield improvement in the semiconductor industry. Wafer edge region (crystal edge) inspection is an indispensable part of the inspection process of optical wafer inspection equipment, which can identify defects such as edge scratches, particles, and defocus, thereby avoiding product yield loss.

[0003] To perform wafer edge inspection, it is first necessary to identify the wafer chamfer region (also known as the bevel section). The wafer chamfer region is an arc-shaped transition surface formed by specific processing of the wafer edge, located between the front and back sides of the wafer. Its width is typically only a few hundred micrometers to one or two millimeters, and it is part of the wafer edge. Existing optical inspection equipment cannot identify the chamfer region because the chamfer region is a curved surface, and light will be reflected outside the camera's range, causing the camera to be unable to image the chamfer region. If wafer edge inspection is to be performed, a fixed value is directly compensated in the chamfer region. The edge of the chamfer region is determined by a fixed value preset by the software, rather than by the actual edge of the chamfer region. Therefore, this method cannot accurately calculate the actual width of the chamfer region and cannot meet the user's needs for accurate measurement of wafer edges and detection of wafer edge defects. Summary of the Invention

[0004] The purpose of this application is to provide a wafer inspection method that solves the problem that existing optical wafer inspection equipment cannot accurately measure the wafer edge and detect wafer edge defects.

[0005] To address the aforementioned technical problems, this application provides a wafer inspection method applied to an optical inspection machine, wherein the optical inspection machine includes a support stage for supporting the wafer, and may include at least the following steps:

[0006] A reflective film is provided on the outer edge of the support platform;

[0007] The wafer is placed on the support platform, and the edge of the wafer has a chamfered area, and there is a grayscale difference between the chamfered area and the reflective film.

[0008] Obtain images of the chamfered area of ​​the wafer and the reflective film;

[0009] The chamfered region is identified based on the grayscale difference between the chamfered region of the wafer and the reflective film in the image.

[0010] Furthermore, the support platform is circular.

[0011] Furthermore, the edge of the support platform has a stepped structure with a height lower than the support platform, and the reflective film is fixed to the surface of the stepped structure.

[0012] Furthermore, the reflective film is fixed to the surface of the stepped structure by means of adhesive bonding, magnetic attraction, or snap-on fastening.

[0013] Furthermore, the stepped structure is annular.

[0014] Furthermore, the reflective film is annular, and the center of the reflective film is concentric with the center of the support platform.

[0015] Furthermore, the outer radius of the reflective film is larger than the radius of the wafer.

[0016] Furthermore, the identification of the chamfered region based on grayscale differences includes:

[0017] In the image, the chamfered area presents a first grayscale range, and the reflective film presents a second grayscale range, wherein the grayscale value of the first grayscale range is less than the grayscale value of the second grayscale range;

[0018] The image processing algorithm captures the pixel locations where the grayscale gradient change is greater than a preset threshold, and these pixel locations are the beveled regions.

[0019] Furthermore, after identifying the chamfered region, the process also includes:

[0020] Calculate the width of the chamfered region;

[0021] Set up the detection program;

[0022] The optical inspection machine is operated according to the inspection program to measure the wafer edge region and detect defects in the wafer edge region.

[0023] Furthermore, the chamfered area also includes at least one notch.

[0024] Compared with the prior art, the technical solution of this application has at least one of the following beneficial effects:

[0025] In the wafer inspection method provided in this application, a reflective film is set on the outer edge of the support stage to acquire an image, such as a grayscale image, of the chamfered area of ​​the wafer and the reflective film. Since the reflective film is reflective, under bright light, the light is reflected to the camera, such as a black and white camera, so the image appears white. However, since the chamfered area of ​​the wafer is curved, it appears black. Therefore, the chamfered area can be identified based on the grayscale difference between the chamfered area of ​​the wafer and the reflective film in the grayscale image. Then, the inspection program is set, and the optical inspection machine is run to achieve the purpose of measuring the wafer edge and detecting wafer edge defects. Attached Figure Description

[0026] The accompanying drawings are provided to further illustrate the present application and form part of the specification. They are used together with the following detailed description to explain the present application, but do not constitute a limitation thereof. In the drawings:

[0027] Figure 1 This is a flowchart of a wafer inspection method in one embodiment of this application;

[0028] Figure 2 This is a schematic diagram of a wafer inspection process in one embodiment of this application;

[0029] Figure 3 This is a top view of the support platform and reflective film in one embodiment of this application;

[0030] Figure 4 This is an image of the chamfered area at the wafer notch location when using the wafer inspection method provided in the prior art;

[0031] Figure 5 This is an image of the chamfered area at the wafer notch location when using the wafer inspection method provided in one embodiment of this application.

[0032] in, Figures 2-3 The specific reference numerals in the attached figures are as follows:

[0033] 1-Supporting stage; 2-Step structure; 3-Reflective film; 4-Light source / camera; 5-Wafer; 5a-Chamfered area.

[0034] In the accompanying drawings, the same parts are referred to by the same reference numerals, and the drawings are not drawn to scale. Detailed Implementation

[0035] To make the technical solutions and advantages of the embodiments of this application clearer, the technical solutions of this application will be further described in detail below with reference to the accompanying drawings and embodiments. Although exemplary implementation methods of this application are shown in the accompanying drawings, it should be understood that this application can be implemented in various forms and should not be limited to the implementation methods described herein. Rather, these implementation methods are provided to enable a more thorough understanding of this application and to fully convey the scope of this application to those skilled in the art.

[0036] The present application is described in more detail below by way of example with reference to the accompanying drawings. The advantages and features of the present application will become clearer from the following description and claims. It should be noted that the drawings are in a very simplified form and are only used to facilitate and clarify the illustration of the embodiments of the present application. It is understood that the meanings of "on," "above," and "over" in the present application should be interpreted in the broadest sense, such that "on" not only means "on" something without any intervening feature or layer (i.e., directly on something), but also includes "on" something with an intervening feature or layer. In the embodiments of the present application, the terms "first," "second," etc., are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be noted that the technical solutions described in the embodiments of the present application can be arbitrarily combined without conflict.

[0037] As described in the background section, optical wafer inspection equipment is an automated device used in semiconductor manufacturing to detect surface and internal defects on wafers, playing a crucial role in quality control and yield improvement in the semiconductor industry. Edge inspection is an indispensable part of the inspection process in optical wafer inspection equipment, capable of identifying defects such as edge scratches, particles, and defocusing, thereby avoiding product yield losses. To perform edge inspection, it is first necessary to identify the wafer chamfer area. The wafer chamfer area is the transition surface between the front and back sides of the wafer. Existing optical inspection equipment cannot identify the chamfer area because it is a curved surface, causing light to reflect outside the camera's range, resulting in the camera being unable to image in the chamfer area. If edge inspection is to be performed, a fixed value is directly compensated in the chamfer area; however, this method cannot accurately calculate the actual width of the chamfer area, failing to meet the user's needs for precise measurement of edge and detection of edge defects.

[0038] To address the above issues, this application proposes an improved solution: a reflective film is placed on the outer edge of the support stage to acquire images, such as grayscale images, of the chamfered area of ​​the wafer and the reflective film. Since the reflective film is reflective, under bright light, the light is reflected to a camera, such as a monochrome camera, resulting in a white image. However, the chamfered area of ​​the wafer, being a curved surface, appears black. Therefore, the chamfered area can be identified based on the grayscale difference between the chamfered area of ​​the wafer and the reflective film in the grayscale image. Then, a detection program is set, and an optical inspection machine is run to achieve the purpose of measuring the wafer edge and detecting wafer edge defects.

[0039] refer to Figure 1 , Figure 1 This is a schematic flowchart of the wafer inspection method provided in the embodiments of this application; as shown Figure 1 As shown, the wafer inspection method may include the following steps:

[0040] Step S101: A reflective film is provided on the outer edge of the support platform;

[0041] Step S102: Place the wafer on the support platform. The edge of the wafer has a chamfered area, and there is a grayscale difference between the chamfered area and the reflective film.

[0042] Step S103: Obtain images of the chamfered area of ​​the wafer and the reflective film;

[0043] Step S104: Identify the chamfered region based on the grayscale difference between the chamfered region of the wafer and the reflective film in the image.

[0044] The wafer inspection method proposed in this application will be further described in detail below with reference to the accompanying drawings and specific embodiments. The advantages and features of this application will become clearer from the following description. It should be noted that the drawings are all in a very simplified form and use non-precise proportions, and are only used to facilitate and clarify the illustration of the embodiments of this application. Many specific details are set forth in the following description to provide a thorough understanding of this application; however, this application may also be implemented in other ways different from those described herein, and therefore this application is not limited to the specific embodiments disclosed below.

[0045] See Figures 2-3The wafer inspection method is applied to optical inspection equipment, particularly automated optical inspection (AOI) equipment. In this embodiment, the optical inspection equipment includes a support platform 1 for carrying the wafer 5 and a light source / camera 4. The support platform 1 is circular, and its edge has a stepped structure 2 with a height lower than the support platform 1. The stepped structure 2 is annular, and its center is concentric with the center of the support platform 1. In step S101, a reflective film 3 is provided on the outer edge of the support platform 1, that is, the reflective film 3 is fixed to the surface of the stepped structure 2. Specifically, the reflective film 3 can be fixed to the surface of the stepped structure 2 by adhesive, magnetic attraction, or snap-fit. The reflective film 3 is annular, with its center concentric with the center of the support platform 1, and its outer radius is larger than the radius of the wafer 5.

[0046] In step S102 above, the wafer 5 is removed from the wafer cassette by a robotic arm and then placed on the support stage 1, ensuring that the wafer 5 is approximately in the center area of ​​the support stage 1. Then, a high-precision positioning system is activated for fine calibration to ensure that the chamfered area 5a is exactly in the center of the field of view of the camera 4. The wafer 5 has a chamfered area 5a at its edge. Because the chamfered area 5a is curved, light shining on it is reflected outside the range of the camera 4, causing the camera 4 to be unable to image the chamfered area 5a. When the camera 4 is a monochrome camera, the chamfered area 5a will appear black in the image. However, because the reflective film 3 is reflective, light shining on it is reflected back to the camera 4. Therefore, when the camera 4 is a monochrome camera, the reflective film 3 will appear white in the image. Thus, there will be a significant grayscale difference between the images of the chamfered area 5a and the reflective film 3 captured by the camera 4 (e.g., a monochrome camera), facilitating subsequent identification of the chamfered area 5a.

[0047] In step S103 above, images of the wafer 5 (including the chamfered region 5a) and the reflective film 3 are captured by camera 4. In this embodiment, camera 4 is preferably a monochrome camera, and the image is a grayscale image. The captured image effect is as follows. Figure 5 As shown, the chamfered area 5a is black; the reflective film 3 is white; the area outside the chamfered area 5a of the wafer 5 exhibits uneven grayscale variation because the wafer surface is not a plane with uniform optical properties, but is composed of different materials, different heights and different structures, which will produce different reflection effects after light is irradiated.

[0048] In step S104 above, the chamfered region 5a is identified based on the grayscale difference between the chamfered region 5a and the wafer 5 region outside the chamfered region 5a in the grayscale image, and between the chamfered region 5a and the reflective film 3. The method for identifying the chamfered region 5a based on grayscale difference includes: in the grayscale image, the chamfered region 5a presents a first grayscale range (e.g., black 0), the reflective film 3 presents a second grayscale range (e.g., white 255), the grayscale value of the first grayscale range is less than the grayscale value of the second grayscale range, and the region of the wafer 5 outside the chamfered region 5a presents an uneven grayscale change; starting from the outermost edge of the wafer 5, scanning towards the center, the first pixel position where the grayscale value gradient change is greater than a preset threshold is captured by the image processing algorithm and marked as the starting point of the chamfered region 5a, and the second pixel position where the grayscale value gradient change is greater than the preset threshold is marked as the ending point of the chamfered region 5a, and all pixels between the starting point and the ending point can be identified as the chamfered region 5a. The preset threshold is determined manually through empirical optimization; wherein, the grayscale gradient change refers to the grayscale difference between the current pixel and its neighboring pixels.

[0049] After identifying the chamfered region 5a in step S104 above, the wafer inspection method provided in this application embodiment further includes:

[0050] Step S104.1: Calculate the width of the chamfered region 5a using a software algorithm;

[0051] Step S104.2: Set the detection program (recipe), including setting the radial range of the detection box, setting the starting position of the edge search, adjusting the gradient threshold, setting the width anomaly judgment criteria, and determining the sampling density, etc.

[0052] Step S104.3: Run the optical inspection machine according to the detection program to measure the crystal edge and detect defects such as scratches, particles, and defocusing, thereby avoiding product yield loss. Specifically, the detection program first uses the measurement function to determine the precise position of the crystal edge, generates a dynamic detection mask, then acquires a series of images along the circumference, and then comprehensively applies algorithms such as dynamic thresholding, edge curvature analysis, and differential filtering to capture grayscale anomalies, shape anomalies, and texture anomalies, thereby detecting defects in the crystal edge.

[0053] like Figures 4-5 As shown, when using the wafer inspection method provided in this embodiment, the chamfered region 5 (i.e., the wafer notch position) is located at the wafer notch. Figure 5 The bevel segment in the middle) and the reflective film 3 (i.e. Figure 5The grayscale difference between the reflective film and the background is obvious and can be easily captured by image processing algorithms. However, when using the wafer inspection method provided by the existing technology, the chamfer area at the notch port is the same color as the background, making it difficult to identify.

[0054] Those skilled in the art will understand that the wafer inspection method provided in this application is applicable to the identification of chamfered regions at wafer notch locations, and also applicable to the identification of chamfered regions at wafer non-notch locations, because wafer notch locations are more complex. The method can identify chamfered regions at wafer notch locations, and can also identify chamfered regions at wafer non-notch locations.

[0055] In summary, in the wafer inspection method provided in this application, a reflective film is set on the outer edge of the support stage to acquire an image (e.g., a grayscale image) of the chamfered area of ​​the wafer and the reflective film. Since the reflective film is reflective, under bright light, the light is reflected to the camera (e.g., a black and white camera), so the image appears white. However, the chamfered area of ​​the wafer, being a curved surface, appears black. Therefore, the chamfered area can be identified based on the grayscale difference between the chamfered area of ​​the wafer and the reflective film in the grayscale image. Then, an inspection program is set, and the optical inspection machine is run to achieve the purpose of measuring the wafer edge and detecting wafer edge defects.

[0056] It should be noted that although preferred embodiments have been disclosed above in this application, these embodiments are not intended to limit this application. For any person skilled in the art, many possible variations and modifications can be made to the technical solutions of this application based on the disclosed technical content, or equivalent embodiments can be modified accordingly, without departing from the scope of the technical solutions of this application. Therefore, any simple modifications, equivalent changes, and modifications made to the above embodiments based on the technical essence of this application, without departing from the content of the technical solutions of this application, shall still fall within the scope of protection of the technical solutions of this application.

Claims

1. A wafer inspection method, applied to an optical inspection machine, the optical inspection machine comprising a support stage for holding a wafer, characterized in that, The detection method includes: A reflective film is provided on the outer edge of the support platform; The wafer is placed on the support platform, and the edge of the wafer has a chamfered area, and there is a grayscale difference between the chamfered area and the reflective film. Obtain images of the chamfered area of ​​the wafer and the reflective film; The chamfered region is identified based on the grayscale difference between the chamfered region of the wafer and the reflective film in the image.

2. The method as described in claim 1, characterized in that, The support platform is circular.

3. The method as described in claim 1, characterized in that, The edge of the support platform has a stepped structure with a height lower than the support platform, and the reflective film is fixed to the surface of the stepped structure.

4. The method as described in claim 3, characterized in that, The reflective film is fixed to the surface of the stepped structure by adhesive, magnetic attraction or snap-on method.

5. The method as described in claim 3, characterized in that, The stepped structure is circular.

6. The method as described in claim 5, characterized in that, The reflective film is circular, and the center of the reflective film is concentric with the center of the support platform.

7. The method as described in claim 6, characterized in that, The outer radius of the reflective film is greater than the radius of the wafer.

8. The method as described in claim 1, characterized in that, The method of identifying the chamfered region based on grayscale differences includes: In the image, the chamfered area presents a first grayscale range, and the reflective film presents a second grayscale range, wherein the grayscale value of the first grayscale range is less than the grayscale value of the second grayscale range; The image processing algorithm captures the pixel locations where the grayscale gradient change is greater than a preset threshold, and these pixel locations are the beveled regions.

9. The method as described in claim 1, characterized in that, After identifying the chamfered region, the process also includes: Calculate the width of the chamfered region; Set up the detection program; The optical inspection machine is operated according to the inspection program to measure the wafer edge region and detect defects in the wafer edge region.

10. The method as described in claim 1, characterized in that, The chamfered area also includes at least one notch.

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