Detection Method of Local Leakage Window in SRAM

Abstract

The present invention provides a method for detecting leakage windows in local areas of an SRAM, comprising: exposing a test wafer using a test mask to complete overlaying of a contact hole pattern and a polysilicon gate pattern; obtaining a spacing value between the contact hole pattern and the polysilicon gate pattern; obtaining an image grayscale value of a local area; obtaining a fitting function of an overlay offset and the image grayscale value of the local area; obtaining an image grayscale value of a local area of ​​an SRAM product wafer to be tested; and obtaining a spacing value between the contact hole pattern and the polysilicon gate pattern on the SRAM to detect whether a leakage window exists in the local area of ​​the SRAM. Based on the image grayscale value of the test wafer and the spacing value between the contact hole pattern and the polysilicon gate pattern, the present invention obtains a fitting function applicable to detecting the offset from the contact hole to the polysilicon gate on an SRAM product wafer, thereby achieving online detection of whether a leakage window exists in a local area of ​​the SRAM.

Description

Technical Field

[0001] The present application relates to the technical field of integrated circuit leakage detection, and in particular to a method for detecting leakage windows in a local area of ​​an SRAM. Background Art

[0002] With the development of advanced integrated circuit manufacturing processes, especially on the 55nm technology platform, fluctuations in CT to AA / Poly overlay (the random deviation of contact hole to active area / polysilicon gate) have seriously affected product yield. After overlay, the distance between the contact hole and the active area / polysilicon gate is often too small. The contact hole needs to be filled with a metal plug that leads the active area in the substrate to the top layer. If the distance between the metal plug and the polysilicon gate is too small, leakage risk is likely to occur. Furthermore, in-line overlay makes it difficult to measure and determine whether leakage risk exists in local areas of products such as SRAM (Static Random-Access Memory). Summary of the Invention

[0003] The present application provides a method for detecting leakage windows in local areas of SRAM, which can solve at least one of the problems of random fluctuations in overlay deviation from contact holes to active areas / polysilicon gates and inability to detect online whether there is leakage risk in local areas of SRAM.

[0004] On the one hand, an embodiment of the present application provides a method for detecting a local leakage window of an SRAM, comprising:

[0005] Providing a detection mask, wherein at least a contact hole pattern and a polysilicon gate pattern are formed on the detection mask;

[0006] The test wafer is exposed at multiple levels using the inspection mask, wherein, when performing each level of exposure, the spacing between the contact hole pattern and the polysilicon gate pattern is offset to complete the overlay of the contact hole pattern and the polysilicon gate pattern, wherein the test wafer includes: a main area and multiple local areas where the contact hole pattern and the polysilicon gate pattern are formed;

[0007] Obtaining a spacing value between the contact hole pattern and the polysilicon gate pattern after each layer exposure;

[0008] Obtaining the image grayscale value of the local area after each level of exposure;

[0009] Establishing a function model of the overlay offset and the image grayscale value according to the spacing between the contact hole pattern and the polysilicon gate pattern and the image grayscale value of the local area to obtain a fitting function of the overlay offset and the image grayscale value of the local area;

[0010] Providing all SRAM product slices to be inspected, and obtaining image grayscale values ​​of local areas on the SRAM product slices to be inspected;

[0011] Based on the fitting function of the overlay offset and the image grayscale value of the local area, and the image grayscale value of the local area on the SRAM product piece to be tested, the spacing value between the contact hole pattern and the polysilicon gate pattern on the SRAM product piece to be tested is determined to detect whether there is a leakage window in the local area on the SRAM product piece to be tested.

[0012] Optionally, in the method for detecting the local area leakage window of the SRAM, the layout of the graphics on the SRAM product chip to be detected is the same as the layout of the graphics on the test wafer, wherein the graphics on the SRAM product chip to be detected include at least: the contact hole graphics and the polysilicon gate graphics.

[0013] Optionally, in the method for detecting leakage windows in local areas of the SRAM, a measurement machine is used to obtain a spacing value between the contact hole pattern and the polysilicon gate pattern after each level of exposure.

[0014] Optionally, in the method for detecting a leakage window in a local area of ​​an SRAM, the step of obtaining an image grayscale value of the local area includes:

[0015] Scanning the test wafer using an electron beam scanning device to obtain an electron beam imaging grayscale image of the test wafer;

[0016] According to the electron beam imaging grayscale image, the position information of the main area and the position information of the local area are determined, and the image grayscale value of the main area and the image grayscale value of the local area are determined.

[0017] Optionally, in the method for detecting leakage windows in local areas of SRAM, providing all SRAM product slices to be detected, and obtaining image grayscale values ​​of local areas on the SRAM product slices to be detected includes:

[0018] Providing all SRAM product slices to be tested, and obtaining electron beam imaging grayscale images of the SRAM product slices to be tested;

[0019] According to the electron beam imaging grayscale image, the image grayscale value of the main area on the SRAM product wafer to be inspected and the image grayscale value of the local area on the SRAM product wafer to be inspected are determined.

[0020] Optionally, in the method for detecting leakage windows in local areas of SRAM, an electron beam scanning device is used to scan the SRAM product wafer to be detected to obtain an electron beam imaging grayscale image of the SRAM product wafer to be detected.

[0021] Optionally, in the method for detecting a leakage window in a local area of ​​the SRAM, if the spacing value between the contact hole pattern and the polysilicon gate pattern on the SRAM product piece to be detected is less than a preset leakage distance threshold, then it is detected that there is a leakage window in the local area of ​​the SRAM product piece to be detected; if the spacing value between the contact hole pattern and the polysilicon gate pattern on the SRAM product piece to be detected is greater than or equal to the preset leakage distance threshold, then it is detected that there is no leakage window in the local area of ​​the SRAM product piece to be detected.

[0022] Optionally, in the method for detecting leakage windows in local areas of SRAM, the detection mask is used to expose at least a previous layer, a current layer, and a next layer of a test wafer.

[0023] Optionally, in the method for detecting leakage windows in local areas of an SRAM, in a local area on the SRAM product wafer to be detected, the contact hole pattern and the polysilicon pattern are adjacent to each other and maintain a certain spacing value.

[0024] Optionally, in the method for detecting leakage windows in local areas of an SRAM, the contact hole patterns include: active area contact hole patterns, inter-gate contact hole patterns, and gate-source shared contact hole patterns.

[0025] The technical solution of this application has at least the following advantages:

[0026] The present application obtains a fitting function based on the correlation fitting between the image grayscale value of the local area of ​​the test wafer and the spacing value between the contact hole pattern and the polysilicon gate pattern. The fitting function can be applied to the offset detection of the contact hole to the polysilicon gate on the SRAM product wafer, and can truly reflect the offset distribution of the contact hole to the polysilicon gate in the local area and the main area on the SRAM product wafer, thereby realizing online detection of whether there is a leakage window in the local area of ​​the SRAM product wafer, which not only expands the scanning area but also improves the detection efficiency; further, the detection data of the offset distribution of the contact hole to the polysilicon gate in the local area and the main area of ​​the present application reflects the truth and can be used for cross-layer analysis. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] In order to more clearly illustrate the specific implementation methods of the present application or the technical solutions in the prior art, the following is a brief introduction to the drawings required for use in the specific implementation methods or the description of the prior art. Obviously, the drawings described below are some implementation methods of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0028] Figure 1 Flowchart of a method for detecting a local area leakage window of an SRAM according to an embodiment of the present invention;

[0029] Figure 2 is a schematic diagram of the integrated circuit layout of a test wafer according to an embodiment of the present invention;

[0030] Figure 3 1 is a schematic diagram of a fitting curve of an image grayscale value of a first local area on a test wafer and a spacing value between a contact hole pattern and a polysilicon gate pattern according to an embodiment of the present invention;

[0031] Figure 4 1 is a schematic diagram of a fitting curve of the image grayscale value of the second local area on the test wafer and the spacing value between the contact hole pattern and the polysilicon gate pattern according to an embodiment of the present invention. DETAILED DESCRIPTION

[0032] The following is a clear and complete description of the technical solutions in this application in conjunction with the accompanying drawings. Obviously, the embodiments described are part of the embodiments of this application, not all of them. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making any creative efforts are within the scope of protection of this application.

[0033] In the description of this application, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicating orientations or positional relationships, are based on the orientations or positional relationships shown in the accompanying drawings and are intended solely to facilitate the description of this application and simplify the description. They do not indicate or imply that the devices or components referred to must have a specific orientation, be constructed, or operate in a specific orientation. Therefore, they should not be construed as limitations on this application. Furthermore, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0034] In the description of this application, it should be noted that, unless otherwise expressly specified or limited, the terms "installed," "connected," and "connected" should be understood in a broad sense. For example, they can refer to fixed connections, detachable connections, or integral connections; they can refer to mechanical connections or electrical connections; they can refer to direct connections or indirect connections through an intermediate medium; they can refer to internal connections between two components; they can refer to wireless connections or wired connections. Those skilled in the art will understand the specific meanings of the above terms in this application based on the specific circumstances.

[0035] In addition, the technical features involved in the different embodiments of the present application described below can be combined with each other as long as they do not conflict with each other.

[0036] The present application embodiment provides a method for detecting a local leakage window of an SRAM, referring to Figure 1 , Figure 1 1 is a flow chart of a method for detecting a leakage window in a local area of ​​an SRAM according to an embodiment of the present invention. The method for detecting a leakage window in a local area of ​​an SRAM comprises:

[0037] Step S10: providing a test mask, wherein at least a contact hole pattern and a polysilicon gate pattern are formed on the test mask. Specifically, the contact hole pattern includes but is not limited to: an active area contact hole pattern, an inter-gate contact hole pattern, and a gate-source shared contact hole pattern.

[0038] In this embodiment, a plurality of inspection masks may be provided, or a single inspection mask may be provided. The contact hole pattern and the polysilicon gate pattern may be formed on the same inspection mask, or may be formed on different inspection masks.

[0039] Step S20: Expose the test wafer at multiple levels using the inspection mask, wherein, during each exposure level, the spacing between the contact hole pattern and the polysilicon gate pattern is offset to complete overlay of the contact hole pattern and the polysilicon gate pattern, wherein the test wafer includes a main area and multiple local areas where the contact hole pattern and the polysilicon gate pattern are formed. Specifically, the test wafer is exposed at least on a previous layer, a current layer, and a next layer using the inspection mask to complete pattern overlay.

[0040] Furthermore, on the test wafer, the overlay deviation gradually increases or decreases in one direction, and the contact holes are arranged in the direction of the gradual change of the overlay deviation, so that in the direction of the gradual change of the overlay deviation, the position of the contact hole corresponds to the size of the overlay deviation.

[0041] refer to Figure 2 , Figure 2Schematic diagram of the integrated circuit layout of the test wafer of the embodiment of the present invention, Figure 2 As can be seen in the figure, two local areas are circled on the test wafer, namely the first local area (Area.1) and the second local area (Area.2), and the remaining uncircled areas on the test wafer can be defined as main areas.

[0042] In this embodiment, in a local area on the test wafer, the contact hole pattern and the polysilicon pattern are adjacent to each other and maintain a certain distance therebetween.

[0043] Step S30: Obtaining the spacing between the contact hole pattern and the polysilicon gate pattern after each layer of exposure. Specifically, the spacing between the contact hole pattern and the polysilicon gate pattern after each layer of exposure can be obtained using an overlay accuracy measurement machine. The spacing between the contact hole pattern and the polysilicon gate pattern can be understood as the overlay offset between the contact hole pattern and the polysilicon gate pattern.

[0044] Step S40: Obtaining the image grayscale value of the local area after each level of exposure. Specifically, the step of obtaining the image grayscale value of the local area may include:

[0045] Step S40.1: Scan the test wafer using an electron beam scanning device to obtain an electron beam imaging grayscale image of the test wafer. In this embodiment, the electron beam scanning device may be an EBI (E-Beam electron beam scanning defect scanner). The electron beam scanning defect scanner is used to perform defect detection on the main area and the local area, stimulating secondary electrons; and based on the number of secondary electrons captured at different positions, an electron beam imaging grayscale image of the main area and the local area is generated.

[0046] Step S40.2: Determine the position information of the main area and the local area according to the brightness of the main area and the local area on the electron beam imaging grayscale image, and determine the image grayscale value of the main area and the image grayscale value of the local area.

[0047] Step S50: According to the spacing between the contact hole pattern and the polysilicon gate pattern and the image grayscale value of the local area, a function model of the overlay offset and the image grayscale value is established to obtain a fitting function of the overlay offset and the image grayscale value of the local area.

[0048] refer to Figure 3 yes Figure 4 , Figure 31 is a schematic diagram of a fitting curve of the image grayscale value of the first local area on the test wafer and the spacing value between the contact hole pattern and the polysilicon gate pattern according to an embodiment of the present invention. Figure 4 The figure is a schematic diagram of a fitting curve of the image grayscale value of the second local area on the test wafer and the spacing value between the contact hole pattern and the polysilicon gate pattern according to an embodiment of the present invention. Functional models of the overlay offset and image grayscale value are established for the first and second local areas, respectively, to obtain fitting functions of the overlay offset and the image grayscale value of the local area. Each local area receives a corresponding fitting function, and the fitting functions for each local area can be the same or different. When subsequently used to monitor SRAM product wafers, each local area will be applied with its own corresponding fitting function.

[0049] Step S60: providing all SRAM product slices to be tested, and obtaining the image grayscale value of a local area on the SRAM product slice to be tested. Specifically, providing all SRAM product slices to be tested, and obtaining the image grayscale value of a local area on the SRAM product slice to be tested may include:

[0050] Step S60.1: providing all SRAM product wafers to be inspected, and obtaining electron beam imaging grayscale images of the SRAM product wafers to be inspected;

[0051] Step S60.2: Determine the image grayscale value of the main area on the SRAM product wafer to be inspected and the image grayscale value of the local area on the SRAM product wafer to be inspected according to the electron beam imaging grayscale image.

[0052] Furthermore, the layout of the pattern on the SRAM product wafer to be tested is completely identical to the layout of the pattern on the test wafer, wherein the pattern on the SRAM product wafer to be tested at least includes: the contact hole pattern and the polysilicon gate pattern.

[0053] In this embodiment, similar to the test wafer, in a local area on the SRAM product wafer to be tested, the contact hole pattern and the polysilicon pattern are adjacent to each other and maintain a certain distance value.

[0054] Step S70: Determine the spacing between the contact hole pattern and the polysilicon gate pattern on the SRAM product wafer to be tested based on a fitting function of the overlay offset and the image grayscale value of the local area, and the image grayscale value of the local area on the SRAM product wafer to be tested, so as to detect whether there is a leakage window in the local area on the SRAM product wafer to be tested. If the spacing between the contact hole pattern and the polysilicon gate pattern on the SRAM product wafer to be tested is less than a preset leakage distance threshold, it is detected that there is a leakage window in the local area on the SRAM product wafer to be tested; if the spacing between the contact hole pattern and the polysilicon gate pattern on the SRAM product wafer to be tested is greater than or equal to the preset leakage distance threshold, it is detected that there is no leakage window in the local area on the SRAM product wafer to be tested.

[0055] In the present application, a fitting function is obtained by fitting the correlation between the image grayscale value of the local area of ​​the test wafer and the spacing value between the contact hole pattern and the polysilicon gate pattern. The fitting function can be applied to the offset detection of the contact hole to the polysilicon gate on the SRAM product wafer, and can truly reflect the offset distribution of the contact hole to the polysilicon gate in the local area and the main area on the SRAM product wafer, thereby realizing online detection of whether there is a leakage window in the local area of ​​the SRAM product wafer, which not only expands the scanning area but also improves the detection efficiency; further, the detection data of the offset distribution of the contact hole to the polysilicon gate in the local area and the main area of ​​the present application reflects the truth and can be used for cross-layer analysis.

[0056] Obviously, the above embodiments are merely examples for clarity of explanation and are not intended to limit the implementation methods. Those skilled in the art will appreciate that other variations or modifications can be made based on the above description. It is not necessary and impossible to enumerate all implementation methods here. Obvious variations or modifications arising therefrom remain within the scope of protection of this application.

Claims

1. A method for detecting leakage window in a local area of ​​an SRAM, characterized in that: include: Providing a detection mask, wherein at least a contact hole pattern and a polysilicon gate pattern are formed on the detection mask; The test wafer is exposed at multiple levels using the inspection mask, wherein, when performing each level of exposure, the spacing between the contact hole pattern and the polysilicon gate pattern is offset to complete the overlay of the contact hole pattern and the polysilicon gate pattern, wherein the test wafer includes: a main area and multiple local areas where the contact hole pattern and the polysilicon gate pattern are formed; Obtaining a spacing value between the contact hole pattern and the polysilicon gate pattern after each layer exposure; Obtaining the image grayscale value of the local area after each level of exposure; Establishing a function model of overlay offset and image grayscale value according to the spacing between the contact hole pattern and the polysilicon gate pattern and the image grayscale value of the local area to obtain a fitting function of the overlay offset and the image grayscale value of the local area; Providing all SRAM product slices to be inspected, and obtaining image grayscale values ​​of local areas on the SRAM product slices to be inspected; Based on the fitting function of the overlay offset and the image grayscale value of the local area, and the image grayscale value of the local area on the SRAM product piece to be tested, the spacing value between the contact hole pattern and the polysilicon gate pattern on the SRAM product piece to be tested is determined to detect whether there is a leakage window in the local area on the SRAM product piece to be tested.

2. The method for detecting a local leakage window of an SRAM according to claim 1, wherein: The layout of the patterns on the SRAM product wafer to be tested is the same as the layout of the patterns on the test wafer, wherein the patterns on the SRAM product wafer to be tested at least include: the contact hole pattern and the polysilicon gate pattern.

3. The method for detecting the leakage window of a local area of ​​an SRAM according to claim 1, wherein: A measurement machine is used to obtain the spacing value between the contact hole pattern and the polysilicon gate pattern after each level of exposure.

4. The method for detecting the leakage window of a local area of ​​an SRAM according to claim 1, wherein: The step of obtaining the image grayscale value of the local area includes: Scanning the test wafer using an electron beam scanning device to obtain an electron beam imaging grayscale image of the test wafer; According to the electron beam imaging grayscale image, the position information of the main area and the position information of the local area are determined, and the image grayscale value of the main area and the image grayscale value of the local area are determined.

5. The method for detecting the leakage window of a local area of ​​an SRAM according to claim 1, wherein: Providing all SRAM product slices to be inspected, and obtaining the image grayscale value of a local area on the SRAM product slice to be inspected includes: Providing all SRAM product slices to be tested, and obtaining electron beam imaging grayscale images of the SRAM product slices to be tested; According to the electron beam imaging grayscale image, the image grayscale value of the main area on the SRAM product wafer to be inspected and the image grayscale value of the local area on the SRAM product wafer to be inspected are determined.

6. The method for detecting a local leakage window of an SRAM according to claim 5, wherein: The SRAM product wafer to be inspected is scanned by using an electron beam scanning device to obtain an electron beam imaging grayscale image of the SRAM product wafer to be inspected.

7. The method for detecting a local leakage window of an SRAM according to claim 1, wherein: If the spacing value between the contact hole pattern and the polysilicon gate pattern on the SRAM product piece to be tested is less than a preset leakage distance threshold, it is detected that there is a leakage window in the local area on the SRAM product piece to be tested; if the spacing value between the contact hole pattern and the polysilicon gate pattern on the SRAM product piece to be tested is greater than or equal to the preset leakage distance threshold, it is detected that there is no leakage window in the local area on the SRAM product piece to be tested.

8. The method for detecting a local leakage window of an SRAM according to claim 1, wherein: The inspection mask is used to expose at least a previous layer, a current layer and a next layer of the test wafer.

9. The method for detecting a local leakage window of an SRAM according to claim 1, wherein: In a local area on the SRAM product wafer to be inspected, the contact hole pattern is adjacent to the polysilicon gate pattern and maintains a certain distance therebetween.

10. The method for detecting a local leakage window of an SRAM according to claim 1, wherein: The contact hole patterns include active area contact hole patterns, inter-gate contact hole patterns and gate-source shared contact hole patterns.

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