Shape measurement method and polishing method for DIC defects in silicon wafers

Abstract

The present invention provides a method for measuring the shape of a DIC defect on a silicon wafer, comprising the following steps: detecting a DIC defect on the main surface of the silicon wafer using a particle counter; identifying the position coordinates of the detected DIC defect; and using the identified position coordinates to measure the shape of the detected DIC defect, including at least its height or depth, using phase-shift interferometry. This method provides a method for simply and accurately measuring the shape, including the dimensions, of a DIC defect generated on the main surface of a silicon wafer.

Description

Technical Field

[0001] The present invention relates to a shape measurement method and a polishing method for DIC defects generated in a silicon wafer. Background Art

[0002] If DIC defects occur on the surface of silicon wafers, they can affect defects and cause defocusing during CMP during device fabrication. Therefore, to reduce or suppress DIC defects, Patent Documents 1 to 3 describe improvements to abrasives, polishing heads, and polishing cloths, respectively. Furthermore, Patent Documents 4 and 5 describe methods for measuring DIC defects.

[0003] Here, the DIC defect is explained. DIC is the first letter of the word Differential Interference Contrast, which means differential interference contrast. DIC defects are also described in patent documents 3 to 5. They are mainly defects detected using evaluation devices such as SP2 or SP3 of the SurfScan series of particle counters manufactured by KLA-Tencor, and further using the DIC mode of bright field observation. The characteristic of DIC defects is that they are shallow and flat defects, and there are both raised convex shapes and depressed concave shapes on the surface of the silicon wafer. Specifically, as a common shape, it is characterized by a height or depth of several nanometers to tens of nanometers, a width of tens of micrometers to hundreds of micrometers, and a ratio of height or depth to width (aspect ratio) of thousands of times.

[0004] Prior art literature

[0005] Patent Literature

[0006] Patent Document 1: Japanese Patent Application Publication No. 2019-021719

[0007] Patent Document 2: Japanese Patent Application Publication No. 2019-058955

[0008] Patent Document 3: Japanese Patent Application Publication No. 2019-125722

[0009] Patent Document 4: Japanese Patent Application Publication No. 2018-101698

[0010] Patent Document 5: Japanese Patent Application Laid-Open No. 2010-021242

[0011] Patent Document 6: Japanese Patent Application Laid-Open No. 2016-027407 Summary of the Invention

[0012] (1) Technical issues to be resolved

[0013] DIC defect detection methods typically use a particle counter, as described above. However, this method suffers from the following problem: it can only pinpoint the coordinates of the DIC defect on the silicon wafer surface; it cannot determine the shape, including the dimensions, of the DIC defect. Patent Document 5 describes a method for measuring DIC defects using a microscope using general interferometry, but does not disclose specific numerical values. Consequently, no literature has yet accurately described the height and width of DIC defects.

[0014] The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to provide a method capable of simply and accurately measuring the shape including the size of a DIC defect generated on the main surface of a silicon wafer.

[0015] (2) Technical solution

[0016] The present invention is completed to achieve the above-mentioned purpose and provides a DIC defect shape measurement method, which measures the shape of a DIC defect on a silicon wafer, including the following steps: using a particle counter to detect the DIC defect on the main surface of the silicon wafer; specifying the position coordinates of the detected DIC defect; and using the specified position coordinates, measuring the shape of the detected DIC defect including at least the height or depth by phase shift interferometry.

[0017] According to such a DIC defect shape measurement method, the shape including the height dimension of a DIC defect generated on the main surface of a silicon wafer can be measured simply and with high accuracy.

[0018] At this time, in the DIC defect shape measurement method, the main surface of the silicon wafer may be a device fabrication surface.

[0019] This makes it possible to accurately and easily evaluate DIC defects that affect the device manufacturing process.

[0020] In this case, in the silicon wafer polishing method, the silicon wafer may be polished by setting a polishing allowance based on the shape of the DIC defect measured by the above-mentioned DIC defect shape measurement method.

[0021] As a result, silicon wafers with reduced DIC defect levels can be manufactured efficiently, at low cost, and with high productivity.

[0022] (3) Beneficial effects

[0023] As described above, the DIC defect shape measurement method of the present invention can simply and accurately measure the shape, including the height dimension, of a DIC defect generated on the main surface of a silicon wafer. Furthermore, by using the measured DIC defect shape, including the height dimension, the polishing allowance can be accurately set to reduce DIC defects, thereby shortening polishing time and reducing polishing costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 This is a flowchart showing the DIC defect shape measurement method of the present invention.

[0025] Figure 2 An example of a DIC defect map evaluated by a particle counter in an embodiment of the present invention is shown.

[0026] Figure 3 An example of a phase-shift interference image obtained in an embodiment of the present invention is shown.

[0027] Figure 4 An example of a distribution map obtained by performing phase analysis of a DIC defect described in this embodiment is shown. DETAILED DESCRIPTION

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

[0029] As described above, there is a demand for a DIC defect shape measurement method that can easily and accurately measure the shape, including the size, of a DIC defect generated on the main surface of a silicon wafer.

[0030] The inventors of this case have conducted repeated and in-depth research on the above-mentioned problems, and as a result, they have discovered a method for measuring the shape of DIC defects in silicon wafers, and completed the present invention. Through this method, the shape of the DIC defect generated on the main surface of the silicon wafer, including the height dimension, can be measured simply and with high precision. The method includes the following steps: using a particle counter to detect the DIC defect on the main surface of the silicon wafer; specifying the position coordinates of the detected DIC defect; and using the specified position coordinates, measuring the shape of the detected DIC defect, including at least the height or depth, by phase shift interferometry.

[0031] Hereinafter, a shape measuring method and a silicon wafer polishing method according to an embodiment of the present invention will be described with reference to the accompanying drawings.

[0032] Figure 1 This is a flow chart showing the method for measuring the shape of a DIC defect and the method for polishing a silicon wafer according to the present invention. Figure 1The front end of the described process (before S1) may include processes such as the production of single crystal silicon ingots, ingot slicing, etching, grinding, and heat treatment. The most representative process for generating DIC defects is the grinding process. In this grinding process, a suspension called slurry is used. DIC defects are believed to be caused by failure to properly process the slurry after grinding. However, there are many unclear points regarding the generation of DIC defects, and the grinding process described above cannot currently be identified as the only generation process.

[0033] In the DIC defect shape measurement method of the present invention, Figure 1 The process of detecting DIC defects on the main surface of the silicon wafer using a particle counter as shown in S1, and the process of determining the position coordinates of the specifically detected DIC defects as shown in S2, and then performing shape measurement of the coordinates as described in S3. As mentioned above, the particle counter used in the detection of DIC defects is generally the SurfScan series manufactured by KLA-Tencor Corporation, but even other devices can be used as long as they can detect DIC defects. Furthermore, it is preferred if it is a device that can output the position coordinates of the detected DIC defects. In this case, the process of S1 and the process of determining the position coordinates of the specifically detected DIC defects as shown in S2 can be performed approximately at the same time, and the coordinate position can be determined quickly and with high precision compared to the case where the coordinate position is determined by manual operation as described later. In this way, the shape measurement method of the DIC defect of the present invention includes the case where the processes of S1 and S2 are implemented approximately at the same time.

[0034] Here, we'll explain how to specify coordinates. While the SurfScan series can output coordinates, other evaluation devices and methods that don't use particle counters can output coordinates. It's also possible to output a map or observation image of the entire silicon wafer surface showing detected DIC defects, and manually specify and acquire the coordinates. The coordinate system is not limited; any coordinate system can be used, whether XY coordinates or r-θ coordinates, also known as polar coordinates, as long as the DIC defect's location can be determined.

[0035] Then, if Figure 1As shown in S3 of , the following process is performed: using the position coordinates of a specific DIC defect, the shape of the detected DIC defect, including at least the height or depth, is measured by phase shift interferometry. In addition, the phase shift interferometry method is described in Patent Document 6. In short, it is a measurement method that obtains nanometer-level height resolution by observing the interference fringes of monochromatic light while changing the observation height and performing phase analysis. This phase shift interferometry method is an increasingly popular observation method as an observation method using interference. In this way, using phase shift interferometry, the shape of DIC defects, which are shallow and flat defects, can be measured simply and with high precision, especially the shape including the height dimension.

[0036] In the DIC defect shape measurement method of the present invention, the device production surface (also referred to as the "main front side" to distinguish between the front and back sides of the wafer) is preferably used as the main surface of the silicon wafer for DIC defect shape measurement. DIC defects on the device production surface are generally problematic during the device production process. Evaluating the device production surface allows for accurate and simple evaluation of DIC defects that may affect the device production process.

[0037] Furthermore, the inventors of this application have discovered that by using the shape of the DIC defects, particularly the height and depth data obtained as described above, it is possible to significantly improve the efficiency when polishing a silicon wafer having DIC defects to reduce the DIC defects.

[0038] For silicon wafers where DIC defects are detected, DIC defects can be reduced by properly polishing them. Previously, it was impossible to measure the shape of DIC defects detected on each wafer, especially their height dimensions. Therefore, machining allowances were uniformly set to match the shape of the typical DIC defects.

[0039] However, if Figure 1 As shown in S4, if the grinding allowance is set based on the shape of the DIC defect measured using the DIC defect shape measurement method and the silicon wafer is ground, an appropriate grinding allowance can be set for each silicon wafer, thereby avoiding unnecessary grinding. Therefore, productivity can be improved and costs can be reduced. In addition, the grinding allowance to be set is preferably set within a range of 5 times or more of the height or depth of the measured DIC defect. For example, if it is set to 5 to 50 times, preferably 10 to 20 times, DIC defects can be reduced more reliably and efficiently.

[0040] Example

[0041] Hereinafter, the present invention will be described in detail with reference to Examples, but the present invention is not limited thereto.

[0042] (Example)

[0043] In this embodiment, a silicon wafer with a diameter of 300 mm and a (100) main surface was used. The silicon wafer used is a product of the production process of single crystal silicon ingot production, ingot slicing, chamfering, lapping, etching, grinding, and cleaning.

[0044] Figure 2 This is an example of a graph obtained by evaluating a sample of the cleaned silicon wafer using a particle counter. The particle counter used was a SurfScan SP3 manufactured by KLA-Tencor, and measurements were performed in the DIC mode of bright field observation. Figure 2 It can be seen that 4 DIC defects (indicated by black dots) were detected in the sample used. In addition, the position coordinates of each of the 4 locations are also output as coordinate data. The detection of the DIC defect and the output of the position coordinates are equivalent to Figure 1 The S1 and S2 processes.

[0045] Next, proceed Figure 1 The position coordinates of the DIC defects output in step S2 were observed using phase-shift interferometry. This observation used an OPTELICS hybrid microscope manufactured by Lasertec, equipped with a 10x double-beam interferometry objective lens. Furthermore, a movable stage with micron-level position coordinate accuracy was fabricated and installed on the hybrid microscope to enable direct observation of the position coordinates output by the particle counter.

[0046] Figure 3 This is an example of a phase shift interference image obtained by observing the position coordinates of the DIC defect output in S1. Figure 3 This figure shows an example of a convex DIC defect. The black and white shades in the figure represent the height of the DIC defect, and the whitest portion in the center of the figure represents the peak of the DIC defect.

[0047] exist Figure 4 The hybrid microscope is used to Figure 3 The phase-resolved distribution diagram of a DIC defect is shown in Figure 1. In this example, the DIC defect height is measured to be 30nm and the DIC defect width is 190μm. Figure 2 As shown in FIG, the silicon wafer used has four DIC defects. However, after investigation by the inventors of this case, it was found that the multiple DIC defects detected in the same wafer were of approximately the same height or depth. Figure 3 、 4 There is no problem even if the other three points other than the DIC defect are displayed with similar values, so the following Figure 3 、 Figure 4The result of measuring one DIC defect is shown as a representative value of the size of the DIC defect of the sample (silicon wafer). Figure 1 In this way, the shape of the DIC defect of the sample (silicon wafer) including the height dimension is measured.

[0048] Next, based on the measured shape of the DIC defects, including their height and depth, the polishing allowance is set, and reprocessing is performed. Reprocessing involves reprocessing a product with DIC defects through the polishing and cleaning steps. The goal is to eliminate DIC defects and reduce their number, height, and depth.

[0049] The number of samples used here is 10, all of which are samples in which DIC defects were detected by the particle counter SP3 mentioned above. The height of the DIC defect at one location on each of the 10 samples was measured, and the reprocessing allowance was set to match each sample and polished, and the reprocessing time was measured. In addition, for reprocessing, the DIC defects were eliminated or the number of DIC defects or the height and depth of the DIC defects were reduced by setting the processing allowance to 10 to 20 times the height and depth of the DIC defects. Table 1 shows the DIC defect height and reprocessing time of each sample. In addition, the "reprocessing time" mentioned here is the time required for polishing during reprocessing (excluding the cleaning process, etc.).

[0050] (Comparative Example)

[0051] The comparative example shows the conditions for reprocessing with a uniform reprocessing margin when the occurrence of DIC defects is detected by a particle counter as in the conventional art. Specifically, the margin is set to 2 μm and the reprocessing time is set to 5 minutes (Table 1).

[0052] [Table 1]

[0053]

[0054] It can be seen that the shape measurement method of DIC defects according to the present invention can accurately and easily measure the height (or depth) of DIC defects. In addition, if the DIC defect height calculated as in the example is used to set the grinding allowance for reprocessing, as shown in Table 1, the reprocessing time is reduced by up to 80% compared to the comparative example, and even a total of 10 sheets is reduced by 65%, resulting in a significant reduction compared to the comparative example. In addition, the quality of the DIC defects after reprocessing can also be confirmed to be equivalent to that of the comparative example. Thus, it can be seen that the shape measurement method of DIC defects according to the present invention can achieve various effects such as not only shortening reprocessing time but also reducing costs and improving productivity.

[0055] The present invention is not limited to the above-described embodiments. The above-described embodiments are merely examples, and any configuration having substantially the same structure and achieving the same function and effect as the technical concept described in the claims of the present invention is encompassed within the technical scope of the present invention.

Claims

1. A method for measuring the shape of a DIC defect on a silicon wafer, characterized in that: The following steps are included: detecting DIC defects on the main surface of the silicon wafer using a particle counter; Outputting the position coordinates of the detected DIC defect from the particle counter to a phase shift interferometry detection device; as well as The phase shift interferometry detection device is set based on the output position coordinates, and the shape of the detected DIC defect including at least the height or the depth is measured by phase shift interferometry. The DIC defect is a defect detected by differential interference contrast, and has a width ranging from tens to hundreds of microns.

2. The method for measuring the shape of a DIC defect according to claim 1, wherein: The main surface of the silicon wafer is the device manufacturing surface.

3. A method for polishing a silicon wafer, characterized in that: The silicon wafer is polished by setting a polishing allowance based on the shape of the DIC defect measured by the DIC defect shape measurement method according to claim 1 or 2.

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