Method for evaluating shape of wafer

Abstract

To provide a method for evaluating a shape of a wafer which can properly evaluate a shape of a wafer with a notch.SOLUTION: The method for evaluating the shape of the wafer includes the steps of: measuring the flatness of a plurality of regions in an outer peripheral part of the wafer; and evaluating a shape of the wafer on the basis of a difference between an average value or a center value of the flatnesses of regions not including notches of a plurality of regions and the flatnesses of the regions including the notches.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a method for evaluating a shape of a wafer. [Background technology]

[0002] When a wafer having a notch is subjected to a double-side polishing process for polishing both main surfaces, a notch mirror polishing process for mirror polishing the chamfered portion of the notch, a peripheral mirror polishing process for mirror polishing the chamfered portion of the periphery, and a finish polishing process for finish polishing one of the main surfaces, the edge roll-off of the boundary between the one of the main surfaces and the notch chamfered portion of the notch (hereinafter sometimes referred to as "sagging of the notch portion") tends to be larger than the edge roll-off of the boundary between the one of the main surfaces and the peripheral chamfered portion of the wafer (hereinafter sometimes referred to as "sagging of the peripheral portion"). If the difference between the sagging of the notch portion and the sagging of the peripheral portion is large, it is likely to cause defects in subsequent processes. As a method for evaluating the occurrence of such sagging, Patent Document 1 discloses a method in which the ESFQR (Edge flatness metric, Sector based, Front surface referenced, least squares fit reference plane, Range of the data within sector) of a wafer is measured, and the occurrence of edge roll-off (sagging) of a notch chamfer is evaluated based on the difference between the ESFQR of a notch site including the notch and the maximum ESFQR of a site not including the notch. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2020-104210 A Summary of the Invention [Problem to be solved by the invention]

[0004] However, the evaluation method described in Patent Document 1 may not be able to appropriately evaluate the sagging of the notch portion.

[0005] An object of the present invention is to provide a wafer shape evaluation method capable of appropriately evaluating the shape of a wafer having a notch. [Means for solving the problem]

[0006] The wafer shape evaluation method of the present invention is a method for evaluating the shape of a wafer having a notch, which measures the flatness of a plurality of regions in the outer periphery of the wafer, and evaluates the shape of the wafer based on the difference between the average or median flatness of the regions among the plurality of regions that do not include the notch and the flatness of the region that includes the notch.

[0007] The wafer shape evaluation method of the present invention is a method for evaluating the shape of a wafer having a notch, which measures the flatness of a plurality of regions in the outer periphery of the wafer, and evaluates the shape of the wafer based on the difference between the average or median flatness of the plurality of regions and the flatness of a region among the plurality of regions that includes the notch.

[0008] In the wafer shape evaluation method of the present invention, the index representing the flatness is preferably ESFQR. [Brief description of the drawings]

[0009] [Figure 1] 1 is a block diagram showing a wafer and a wafer shape evaluation system according to an embodiment; [Diagram 2] 3 is a flowchart showing a wafer shape evaluation method according to the embodiment. [Diagram 3] 11 is a graph showing an example of a measurement result of ESFQR according to the embodiment. [Figure 4] FIG. 13 is a schematic diagram showing the shape of sagging in the notch portion and the average shape of sagging in the outer periphery of wafers of levels A and B according to the embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] [Embodiment] <Configuration of wafers to be evaluated> First, a configuration of a wafer to be evaluated by a wafer shape evaluation system according to an embodiment of the present invention will be described. FIG. 1 is a block diagram showing a wafer and a wafer shape evaluation system. 1, the wafer W to be evaluated by the shape evaluation system 1 has a notch Wn formed at one location on the outer periphery. The wafer W is subjected to a double-sided polishing process, a notch mirror polishing process, a peripheral mirror polishing process, and a finish polishing process before being evaluated by the shape evaluation system 1. Note that, before the double-sided polishing process, the wafer W may be subjected to a chamfering process in which an edge of the wafer W is chamfered. After the above-mentioned process, sagging occurs at the boundary between one main surface and the notch chamfer and at the boundary between one main surface and the outer peripheral chamfer of the wafer W. The sagging of the notch is larger than that of the outer peripheral. The notch mirror polishing step may be carried out before the double-side polishing step. The wafer W may also be made of materials such as silicon, germanium, gallium arsenide, gallium phosphide, and indium phosphide.

[0011] <Configuration of shape evaluation system> Next, the shape evaluation system 1 for the wafer W will be described. The wafer shape evaluation system 1 includes a measurement device 2 and a shape evaluation device 3 .

[0012] The measuring device 2 measures ESFQR as the flatness of the outer periphery of the wafer W. The measurement of ESFQR is performed for each site, which is an annular region between a position 2 mm in from the outermost periphery of the wafer W toward the center of the wafer and a position 32 mm in from the outermost periphery of the wafer W (an annular region with a width of 30 mm excluding the outermost periphery of the edge 2 mm) divided into 72 equal parts in the circumferential direction. The measuring device 2 transmits the ESFQR measurement result to the shape evaluation device 3 together with wafer identification information that identifies the wafer W to be measured.

[0013] The shape evaluation device 3 evaluates the shape of the wafer W based on the measurement result of the ESFQR by the measurement device 2. The shape evaluation device 3 includes an input unit 31, a display unit 32, a storage unit 33, and a control unit .

[0014] The input unit 31 is configured with, for example, a touch panel or physical buttons. The input unit 31 is used to input various information, and outputs a signal corresponding to the input to the control unit .

[0015] The display unit 32 displays various information based on the control of the control unit .

[0016] The storage unit 33 is configured with a well-known storage device such as an HDD (Hard Disk Drive). The storage unit 33 stores the measurement results of the ESFQR and the evaluation results of the wafer W in association with information for identifying the wafer W to be evaluated, so as to be readable by the control unit 34. The information for identifying the wafer W to be evaluated may be acquired from the measurement device 2 or may be input by the input unit 31.

[0017] The control unit 34 is configured by a computer including a CPU, and realizes various functions by the CPU executing the programs stored in the storage unit 33. The control unit 34 includes a measurement result acquisition unit 341 and an evaluation unit 342. The measurement result acquisition unit 341 acquires the wafer identification information and the ESFQR measurement results transmitted from the measurement tool 2. The evaluation unit 342 performs a calculation process of a sag evaluation value (hereinafter sometimes referred to as a "notch sag amount evaluation value") of a notch site including the notch Wn as an evaluation process of the shape of the wafer W based on the measurement results of ESFQR acquired by the measurement result acquisition unit 341.

[0018] <Shape evaluation method> Next, a method for evaluating the shape of the wafer W will be described. Fig. 2 is a flow chart showing a method for evaluating the shape of a wafer, and Fig. 3 is a graph showing an example of the measurement results of ESFQR.

[0019] As shown in FIG. 1, the wafer shape evaluation method includes a wafer preparation step (step S1), a peripheral flatness measurement step (step S2), and an evaluation step (step S3).

[0020] In the wafer preparation process of step S1, an operator prepares a wafer W to be measured that has been subjected to a double-sided polishing process, a notch mirror polishing process, a peripheral mirror polishing process, and a finish polishing process, and sets it in the measuring device 2 as shown by the two-dot chain line in Figure 1.

[0021] In the outer periphery flatness measurement process of step S2, the measurement device 2 measures ESFQR as the flatness of the outer periphery of the wafer W to be measured. The measurement device 2 obtains, for example, a measurement result as shown in FIG. 3. The measurement device 2 transmits the wafer specific information and the measurement result of ESFQR to the shape evaluation device 3. The measurement result acquisition unit 341 of the control unit 34 constituting the shape evaluation device 3 obtains the wafer specific information and the measurement result of ESFQR transmitted from the measurement device 2, and stores the obtained information in the storage unit 33 in association with each other. The measurement result acquisition unit 341 may obtain the wafer specific information input by an operator operating the input unit 31.

[0022] In the evaluation process of step S3, the evaluation unit 342 of the control unit 34 constituting the shape evaluation device 3 evaluates the shape of the wafer W. First, the evaluation unit 342 calculates the average value of ESFQR of the sites other than the notch site (hereinafter, “first outer periphery ESFQR average value”). Then, the evaluation unit 342 calculates the notch droop evaluation value V based on the following formula (1-1). V=ESFQR_N-ESFQR_mean … (1-1) ESFQR_N: ESFQR of the notch site (ESFQR of the notch site) ESFQR_mean1: First outer ESFQR mean value

[0023] The evaluation unit 342 stores the calculation result of the notch sagging evaluation value V in association with the wafer identification information and the measurement result of ESFQR stored in the storage unit 33. The evaluation unit 342 may cause the display unit 32 to display the calculation result of the notch sagging evaluation value V.

[0024] <Effects of the embodiment> The shape evaluation system 1 measures the flatness of a plurality of sites on the outer periphery of the wafer W, and evaluates the shape of the wafer W based on the difference between the average flatness of the plurality of sites including the notch site and the flatness of the notch site. For example, when the measurement result of ESFQR shown in FIG. 3 is obtained, in the evaluation method described in Patent Document 1, the notch droop evaluation value Vp is calculated based on the following formula (2). Vp = ESFQR_N - ESFQR_max … (2) ESFQR_max: Maximum ESFQR value for sites other than the notch site (maximum outer ESFQR value) The notch sagging evaluation value Vp obtained in this manner represents the difference in ESFQR between the notch site and one specific site, as shown in Fig. 3, and therefore cannot represent the difference between the sagging of the notch portion and the sagging tendency of the entire outer periphery. In particular, since the notch sagging evaluation value Vp represents the difference between the portion of the notch portion and the outer periphery where the sagging is the largest, even if the difference between the sagging of the notch portion and the sagging tendency of the entire outer periphery is large enough to cause defects, the sagging of the notch portion may be evaluated as being of a size that does not cause defects based on the notch sagging evaluation value Vp.

[0025] On the other hand, the notch sagging evaluation value V obtained based on the formula (1-1) in this embodiment is obtained by subtracting the first outer circumference ESFQR average value representing the tendency of sagging of the entire outer circumference from the notch site ESFQR, so that it can represent the difference between the sagging of the notch part and the tendency of sagging of the entire outer circumference as shown in FIG. 3. Therefore, for example, when the notch sagging evaluation value V is equal to or greater than the first threshold, it can be evaluated that the difference between the sagging of the notch part and the tendency of sagging of the entire outer circumference is large enough to cause a defect, and when it is less than the first threshold, it can be evaluated that the difference between the sagging of the notch part and the tendency of sagging of the entire outer circumference is small enough not to cause a defect. Alternatively, when the notch sagging evaluation value V is equal to or greater than the second threshold, it can be evaluated that there is a possibility that an abnormality has occurred in the polishing conditions of the wafer W or the polishing device, and when it is less than the second threshold, it can be evaluated that there is no possibility that an abnormality has occurred in the polishing conditions of the wafer W or the polishing device. Therefore, based on the notch sagging evaluation value V, the shape of the wafer W having the notch Wn can be appropriately evaluated.

[0026] [Variations] Although an embodiment of the present invention has been described in detail above with reference to the drawings, the specific configuration is not limited to this embodiment, and various improvements and design changes that do not deviate from the gist of the present invention are also included in the present invention.

[0027] For example, the evaluation unit 342 may calculate the median value of ESFQR of sites other than the notch site (hereinafter, may be referred to as the “first outer periphery ESFQR median value”), and calculate the notch droop evaluation value V based on the following formula (1-2). V=ESFQR_N-ESFQR_median1 … (1-2) ESFQR_median1: The first outer perimeter ESFQR median The notch sagging evaluation value V obtained based on such formula (1-2) can represent the difference between the sagging of the notch portion and the tendency of sagging of the entire outer periphery, as shown in Fig. 3. Therefore, the shape of the wafer W having the notch Wn can be appropriately evaluated based on the notch sagging evaluation value V.

[0028] Furthermore, the evaluation unit 342 may calculate an average value of ESFQR of all sites (hereinafter, may be referred to as a "second outer periphery ESFQR average value"), and calculate a notch droop evaluation value V based on the following formula (1-3). V=ESFQR_N-ESFQR_mean2 … (1-3) ESFQR_mean2: Second outer circumference ESFQR mean value Furthermore, the evaluation unit 342 may calculate the median value of ESFQR of all sites (hereinafter, may be referred to as the "second outer periphery ESFQR median value"), and calculate the notch droop evaluation value V based on the following formula (1-4). V=ESFQR_N-ESFQR_median2 … (1-4) ESFQR_median2: The second perimeter ESFQR median

[0029] The calculation process of the notch sagging evaluation value based on the above-mentioned formulas (1-1) to (1-4) may be performed by an operator. Instead of ESFQR, ESFQD (Edge Site Flatness Front Reference Least Square Deviation), ZDD (Z-height Double Differentiation), ESBID (Edge Site Flatness Back Reference Ideal Deviation), or ESBIR (Edge Site Flatness Back Reference Ideal Range) may be used as an index representing flatness. EXAMPLES

[0030] Next, examples of the present invention will be described, but the present invention is not limited to the examples.

[0031] [Example 1] First, one wafer each of level A and level B was prepared. The level A and B wafers were subjected to a double-side polishing process, a notch mirror polishing process, a peripheral mirror polishing process, and a finish polishing process, in that order. Figure 4 shows a schematic diagram of the shape of the sagging of the notch portion and the average shape of the sagging of the peripheral portion of the level A and B wafers W. As shown in Figure 4, the shapes of the sagging of the notch portion of the level A and B wafers are different from each other. Furthermore, the average shapes of the sagging of the peripheral portion of the level A and B wafers are also different from each other. The ESFQR of the outer periphery of the wafers of levels A and B was measured using a flatness measuring device Wafersight2 (manufactured by KLA-Tencor). The notch site ESFQR, the maximum peripheral ESFQR value, and the first peripheral ESFQR average value for the wafers of levels A and B are shown in Table 1.

[0032] [Table 1]

[0033] Next, the notch sites ESFQR in the wafers of levels A and B were taken as the notch sagging evaluation values ​​of Comparative Example 1-1. Moreover, the notch droop evaluation value of Comparative Example 1-2 was calculated based on the above formula (2). Moreover, the notch droop evaluation value of Example 1 was calculated based on the above formula (1-1). The calculation results of the notch droop evaluation values ​​of Comparative Examples 1-1 and 1-2 and Example 1 are shown in Table 2.

[0034] [Table 2]

[0035] Here, as shown in Table 1 and Figure 4, the sagging of the notch portion was larger in the wafer of level B than in the wafer of level A, but the average sagging of the outer periphery was also larger in the wafer of level B than in the wafer of level A. In this case, it is preferable to consider that the difference between the sagging of the notch portion and the tendency of sagging of the entire outer periphery is almost the same for the wafers of level A and level B.

[0036] As shown in Table 2, the notch sagging evaluation value of Comparative Example 1-1 was larger for the wafer of Level B than for the wafer of Level A. Since the sagging amount evaluation value of the notch site of Comparative Example 1-1 is the notch site ESFQR, it is not possible to express the difference between the sagging of the notch portion and the sagging tendency of the entire outer periphery based on the sagging amount evaluation value of the notch site of Comparative Example 1-1. Moreover, like the notch sagging evaluation value of Comparative Example 1-1, the notch sagging evaluation value of Comparative Example 1-2 was larger for the wafer of level B than for the wafer of level A. Since the notch sagging evaluation value of Comparative Example 1-2 represents the difference in ESFQR between the notch site and one specific site, it is not possible to represent the difference between the sagging of the notch portion and the sagging tendency of the entire outer periphery based on the sagging amount evaluation value of the notch site of Comparative Example 1-2. On the other hand, the notch sagging evaluation values ​​of Example 1 were the same for the level A wafers and the level B wafers. The notch sagging evaluation value of Example 1 represents the difference between the ESFQR of the notch site and the average value of the ESFQR of sites other than the notch site, and therefore, based on the sagging amount evaluation value of the notch site of Example 1, it is possible to represent the difference between the sagging of the notch portion and the sagging tendency of the entire outer circumferential portion. From the above, it was confirmed that the shape of a wafer having a notch can be appropriately evaluated based on the notch sagging evaluation value of the present invention.

[0037] [Example 2] First, we prepared one wafer each of level C and level D. The wafers of levels C and D were subjected to the same polishing process as the wafer of level A. Using the above-mentioned flatness measuring device Wafersight 2, the ESFQR of the outer periphery of the wafers of levels C and D was measured. Then, the notch sagging evaluation value was calculated based on the above formula (1-1). The notch site ESFQR, the first peripheral ESFQR average value, and the notch sagging evaluation value for the wafers of levels C and D are shown in Table 3.

[0038] [Table 3]

[0039] As shown in Table 3, the sagging of the notch portion was the same for the standard C wafers and the standard D wafers, but the average shape of the sagging of the outer periphery was larger for the standard C wafers than for the standard D wafers. In this case, it is preferable to consider that the difference between the sagging of the notch portion and the tendency of the sagging of the entire outer periphery is larger for the standard D wafers than for the standard C wafers. The notch droop evaluation value of level D was greater than the notch droop evaluation value of level C. Therefore, based on the notch sagging evaluation value of the present invention, it is possible to evaluate whether the difference between the sagging of the notch portion and the sagging tendency of the entire outer periphery is large enough to cause a defect, or whether there is a possibility that an abnormality has occurred in the polishing conditions of the wafer or in the polishing apparatus, and it was confirmed that the shape of a wafer having a notch can be appropriately evaluated. [Explanation of symbols]

[0040] W...wafer, Wn...notch.

Claims

1. A method for evaluating a shape of a wafer having a notch, comprising the steps of: measuring flatness of a plurality of regions in an outer periphery of the wafer; A wafer shape evaluation method, comprising: evaluating a shape of the wafer based on a difference between an average value or a median value of flatness of regions among the plurality of regions that do not include the notch and a flatness of a region that includes the notch.

2. A method for evaluating a shape of a wafer having a notch, comprising the steps of: measuring flatness of a plurality of regions in an outer periphery of the wafer; A wafer shape evaluation method, comprising: evaluating a shape of the wafer based on a difference between an average value or a median value of flatness of the plurality of regions and a flatness of a region including the notch among the plurality of regions.

3. 3. The method for evaluating a shape of a wafer according to claim 1, further comprising: The method for evaluating a shape of a wafer, wherein the index representing flatness is ESFQR.

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