Optical proximity correction method and system, mask, apparatus, and storage medium

Abstract

An optical proximity correction method and system, a mask, a device and a storage medium, the method comprising: providing a first corrected pattern, the first corrected pattern being obtained by an initial target pattern through an optical proximity correction process, the first corrected pattern having a first minimum simulation pattern; detecting whether the first minimum simulation pattern has a pattern loss defect; in the case that the first minimum simulation pattern has the pattern loss defect, performing an amplification process on the initial target pattern; performing the optical proximity correction process on the initial target pattern after the amplification process to obtain a second corrected pattern and a second minimum simulation pattern corresponding to the second corrected pattern; detecting whether the second minimum simulation pattern has the pattern loss defect, and in the case that the second minimum simulation pattern has the pattern loss defect, continuing to perform the amplification process, the optical proximity correction process and the detection of the pattern loss defect on the initial target pattern after the amplification process. The present application improves the accuracy of the optical proximity correction process.

Description

Technical Field

[0001] The present invention relates to the field of semiconductor manufacturing, and more particularly to an optical proximity correction method and system, a photomask, an apparatus, and a storage medium. Background Technology

[0002] To transfer a pattern from a photomask to the surface of a silicon wafer, it typically involves an exposure step, a development step following the exposure step, and an etching step following the development step.

[0003] However, as device dimensions shrink, the difference between the pattern on the chip surface and the original photomask pattern increases after photolithography. To avoid inconsistencies between the pattern on the chip and the photomask pattern caused by optical proximity effect, the current solution is usually to perform optical proximity correction (OPC) on the photomask pattern, and then perform pattern transfer based on the corrected photomask pattern.

[0004] However, the current optical proximity correction still has some defects, and further repair processing is required after optical proximity correction. Summary of the Invention

[0005] The problem solved by the embodiments of the present invention is to provide an optical proximity correction method and system, mask, device and storage medium to improve the accuracy of optical proximity correction processing.

[0006] To address the aforementioned problems, embodiments of the present invention provide an optical proximity correction method, comprising: providing a layout, including a first corrected graphic, the first corrected graphic being obtained from an initial target graphic through optical proximity correction processing, the first corrected graphic having a first minimum simulated graphic; detecting whether the first minimum simulated graphic has a graphic loss defect; if the first minimum simulated graphic has a graphic loss defect, enlarging the initial target graphic; performing optical proximity correction processing on the enlarged initial target graphic to obtain a second corrected graphic and a second minimum simulated graphic corresponding to the second corrected graphic; detecting whether the second minimum simulated graphic has a graphic loss defect, and if it is determined that the second minimum simulated graphic has a graphic loss defect, continuing to enlarge the enlarged initial target graphic, perform optical proximity correction processing, and detect graphic loss defects until the second minimum simulated graphic does not have a graphic loss defect; and using the second corrected graphic as a photomask graphic.

[0007] Accordingly, embodiments of the present invention also provide an optical proximity correction system, comprising: a pattern providing module for providing a layout, including a first corrected pattern, the first corrected pattern being obtained from an initial target pattern through optical proximity correction processing, the first corrected pattern having a first minimum simulated pattern; a detection module for detecting whether the first minimum simulated pattern has a pattern loss defect; a magnification processing module for magnifying the initial target pattern when the first minimum simulated pattern has a pattern loss defect; an optical proximity correction module for performing optical proximity correction processing on the magnified initial target pattern to obtain a second corrected pattern and a second minimum simulated pattern corresponding to the second corrected pattern; a loop processing module for detecting whether the second minimum simulated pattern has a pattern loss defect, and when it is determined that the second minimum simulated pattern has a pattern loss defect, continuing to perform magnification processing, optical proximity correction processing, and pattern loss defect detection on the magnified initial target pattern until the second minimum simulated pattern does not have a pattern loss defect; and a photomask pattern determining module for using the second corrected pattern as a photomask pattern.

[0008] Accordingly, embodiments of the present invention also provide a photomask, including a pattern obtained using the optical proximity correction method provided in embodiments of the present invention.

[0009] Accordingly, embodiments of the present invention also provide an apparatus including at least one memory and at least one processor, wherein the memory stores one or more computer instructions, wherein the one or more computer instructions are executed by the processor to implement the optical proximity correction method provided in embodiments of the present invention.

[0010] Accordingly, embodiments of the present invention also provide a storage medium storing one or more computer instructions, which are used to implement the optical proximity correction method provided in embodiments of the present invention.

[0011] Compared with the prior art, the technical solution of the embodiments of the present invention has the following advantages:

[0012] In the optical proximity correction method provided by this invention, when the first minimum simulated image has a pattern loss defect, the initial target image is magnified, and optical proximity correction is performed on the magnified initial target image to obtain a second corrected image and a second minimum simulated image corresponding to the second corrected image. The method detects whether the second minimum simulated image has a pattern loss defect, and if it is determined that the second minimum simulated image has a pattern loss defect, the magnified initial target image continues to undergo magnification, optical proximity correction, and pattern loss defect detection. During the optical proximity correction process, if the first minimum simulated image is too small, it can easily lead to pattern loss during subsequent exposures. This invention reduces the probability of pattern loss defects by magnifying the initial target image and correspondingly magnifying the first minimum simulated image. Furthermore, the first minimum simulated image is a process variation loop. Enlarging the smallest ring in the PVBand (Publication Band) helps reduce the size of the PVBand, which is beneficial for subsequent manufacturing processes. In addition, compared with the scheme of improving defects by enlarging the first corrected image, the present invention improves defects by enlarging the initial target image, eliminating the edge-finding operation used to find the line segment corresponding to the defect in the first corrected image, simplifying the correction process. At the same time, it also helps to reduce the restrictions of the mask manufacturability rule (MRC) on the enlarged initial target image, which helps to improve the flexibility of optical proximity correction processing, thereby improving the accuracy of optical proximity correction processing. Attached Figure Description

[0013] Figure 1 This is a flowchart of an optical proximity correction method;

[0014] Figure 2 This is a schematic diagram of an optical proximity correction method;

[0015] Figure 3 This is a flowchart of an embodiment of the optical proximity correction method of the present invention;

[0016] Figures 4 to 7 This is a schematic diagram of each step in one embodiment of the optical proximity correction method of the present invention;

[0017] Figure 8 This is a functional block diagram of an embodiment of the optical proximity correction system of the present invention;

[0018] Figure 9 This is a hardware structure diagram of an embodiment of the device provided by the present invention. Detailed Implementation

[0019] The accuracy of optical proximity correction processing needs improvement. This paper analyzes the reasons why the accuracy of optical proximity correction processing needs further improvement, using one such method as an example.

[0020] Figure 1 This is a flowchart of an optical proximity correction method. (Refer to reference.) Figure 2 The diagram shows the optical proximity correction method, which includes:

[0021] Step s1: Provide a first corrected image 13 of the initial target image 10. The first corrected image 13 is obtained by optical proximity correction processing of the initial target image 10. The first corrected image 13 has a first minimum simulated image 11.

[0022] Step s2: Detect whether the first minimum simulated graphic 11 has a graphic loss defect;

[0023] Step s3: If the first minimum simulation graphic 11 does not have graphic loss defects, the first corrected graphic 13 is used as the photomask graphic;

[0024] Step s4: If the first minimum simulation graphic 11 has a graphic loss defect, perform one or more iterative repair processes on the first corrected graphic 13. The repair process includes:

[0025] Step s41: Adjust the first corrected graphic 13;

[0026] Step s42: Obtain the second minimum simulation graph (not shown) corresponding to the adjusted first corrected graph 13;

[0027] Step s43: Detect whether the second minimum simulation graphic has a graphic loss defect. If the second minimum simulation graphic has a defect, return to step s41.

[0028] Step s5: When the second minimum simulation pattern has no defects, the repair process is completed, and the adjusted first corrected pattern 13 is used as the photomask pattern.

[0029] In the process of optical proximity correction, in order to adapt to the various subsequent processes to form corresponding patterns, each initial target pattern 10 usually corresponds to a first minimum simulated pattern 11 and a first maximum simulated pattern 12. When the first minimum simulated pattern 11 is too small, it is easy to cause pattern loss in the subsequent exposure process. Moreover, the first minimum simulated pattern 11 is the smallest loop in the process variation band (PVBand). If the first minimum simulated pattern 11 is too small, it is also easy to increase the size d of the PVBand, thereby affecting the subsequent manufacturing process. In the case of pattern loss defects in the first minimum simulated pattern 11, the first minimum simulated pattern 11 is enlarged by adjusting the first corrected pattern 13. It is necessary to perform an edge-finding operation to find the line segment corresponding to the defect in the first corrected pattern 13. The correction process is relatively complex. At the same time, due to the limitations of the mask manufacturability rule (MRC) on the adjustment of the first corrected pattern 13, the repair process has significant limitations, thereby affecting the accuracy of the repair process.

[0030] To address the aforementioned technical problem, embodiments of the present invention provide an optical proximity correction method. (Reference) Figure 3 The flowchart of an embodiment of the optical proximity correction method of the present invention is shown.

[0031] In this embodiment, the optical proximity correction method includes the following basic steps:

[0032] Step S1: Provide a layout, including a first corrected graphic, which is obtained from an initial target graphic through optical proximity correction processing, and the first corrected graphic has a first minimum simulated graphic;

[0033] Step S2: Detect whether the first minimum simulated graphic has a graphic loss defect;

[0034] Step S3: If the first minimum simulated graphic has a graphic loss defect, the initial target graphic is enlarged.

[0035] Step S4: Perform optical proximity correction processing on the magnified initial target image to obtain a second corrected image and a second minimum simulation image corresponding to the second corrected image;

[0036] Step S5: Detect whether the second minimum simulated graphic has a graphic loss defect, and when it is determined that the second minimum simulated graphic has a graphic loss defect, continue to perform magnification processing, optical proximity correction processing and graphic loss defect detection on the magnified initial target graphic until the second minimum simulated graphic does not have a graphic loss defect;

[0037] Step S6: Use the second modified pattern as the photomask pattern.

[0038] In the process of optical proximity correction, if the first minimum simulated pattern is too small, it can easily lead to pattern loss during subsequent exposure. This embodiment of the invention reduces the probability of pattern loss defects by enlarging the initial target pattern and correspondingly enlarging the first minimum simulated pattern. Moreover, since the first minimum simulated pattern is the smallest loop in the Process Variation Band (PVBand), enlarging the first minimum simulated pattern also helps to reduce the size of the PVBand, which is beneficial for subsequent manufacturing processes. In addition, compared with the scheme of improving defects by enlarging the first corrected pattern, this embodiment of the invention improves defects by enlarging the initial target pattern, eliminating the edge-finding operation used to find the line segment corresponding to the defect in the first corrected pattern, simplifying the correction process. At the same time, it also helps to reduce the restrictions of the mask manufacturability rule (MRC) on the enlargement of the initial target pattern, which helps to improve the flexibility of optical proximity correction and thus improve the accuracy of optical proximity correction.

[0039] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0040] Figures 4 to 7 This is a schematic diagram of each step in one embodiment of the optical proximity correction method of the present invention.

[0041] refer to Figure 4 Step S1: Provide a layout, including a first corrected pattern 103, which is obtained by optical proximity correction processing from the initial target pattern 100. The first corrected pattern 103 has a first minimum simulated pattern 101.

[0042] The first corrected pattern 103 is the pattern obtained after optical proximity correction processing of the design pattern. The design pattern is the pattern transferred onto the wafer. After optical proximity correction processing of the design pattern, the first corrected pattern 103 is used to make a photomask, and then photolithography is performed on the photomask to form the corresponding photomask pattern on the wafer. If the first corrected pattern 103 still has defects, it needs to be repaired. The repaired first corrected pattern 103 is used to make a photomask.

[0043] The simulated pattern is a simulated exposure pattern of the initial target pattern 100. Different processes will be used to form the pattern corresponding to the initial target pattern 100. Therefore, the initial target pattern 100 will have different simulated exposure patterns for different processes. Accordingly, in the optical proximity correction process, in order to adapt to the use of different processes to form the pattern corresponding to the initial target pattern 100, each initial target pattern 100 usually has a first minimum simulated pattern 101 and a first maximum simulated pattern 102. When the first minimum simulated pattern 101 is too small, it is easy to cause pattern loss in the subsequent exposure process. Moreover, the first minimum simulated pattern 101 is the smallest loop in the process deviation loop. If the first minimum simulated pattern 101 is too small, it is also easy to increase the size d of the PVBand, thereby affecting the subsequent manufacturing process. Therefore, it is necessary to detect whether the first minimum simulated pattern 101 has pattern loss defects.

[0044] In this embodiment, the layout also includes an initial auxiliary graphic 110 located around the initial target graphic 100.

[0045] In this embodiment, the initial target pattern 100 is an exposing pattern, and the initial auxiliary pattern 110 is an unexposing pattern. Therefore, the initial auxiliary pattern 110 is a scattering bar (SB), and the linewidth of the initial auxiliary pattern 110 is greater than or equal to the minimum linewidth of the mask writing rule, and less than or equal to the resolution of the photolithography process, so that the initial auxiliary pattern can be written into the template, but will not be exposed.

[0046] Setting scattering strips around the initial target pattern 100 helps improve light intensity contrast, reduce edge placement error (EPE), and also helps increase the depth of focus, thereby improving the lithography process window.

[0047] In this embodiment, the layout includes through-holes. The initial target pattern 100 includes through-hole patterns for forming through-holes between metal interconnects. Therefore, in this embodiment, the shape of the initial target pattern 100 includes a square.

[0048] Continue to refer to Figure 4 Step S2: Detect whether the first minimum simulated graphic 101 has a graphic loss defect.

[0049] The detection of whether the first minimum simulated graphic 101 has graphic loss defects is used to determine whether the initial target graphic 100 needs further processing.

[0050] In this embodiment, the area of ​​the graphic is used as the detection standard to detect whether the first minimum simulated graphic 101 has a graphic loss defect.

[0051] The first minimum simulated graphic 101 is a simulated exposure graphic of the initial target graphic 100. When the first minimum simulated graphic 101 is too small, it is easy to cause the problem of graphic loss in the subsequent exposure process. Therefore, this embodiment uses the graphic area as the detection standard. When the graphic area of ​​the first minimum simulated graphic 101 is too small, the first minimum simulated graphic 101 has a graphic loss defect.

[0052] Specifically, in this embodiment, the step of detecting whether the first minimum simulated graphic 101 has a graphic loss defect includes: obtaining the area of ​​the first minimum simulated graphic 101 and the corresponding initial target graphic 100; comparing the area of ​​the first minimum simulated graphic 101 and the area ratio of the corresponding initial target graphic 100 with a preset threshold, and determining that the first minimum simulated graphic 101 has a graphic loss defect when the area ratio is less than the preset threshold.

[0053] Different initial target graphics 100 have different area sizes. Using the area of ​​the first minimum simulated graphic 101 and the ratio of its area to the area of ​​the corresponding initial target graphic 100 as the judgment standard is beneficial for flexible adaptation to each initial target graphic 100 on the layout. This makes the judgment on whether the first minimum simulated graphic 101 has a graphic loss defect more accurate. When the area ratio is less than a preset threshold, it indicates that the area of ​​the corresponding first minimum simulated graphic 101 is too small compared to the initial target graphic 100, and the first minimum simulated graphic 101 has a graphic loss defect.

[0054] It should be noted that the preset threshold should not be too large or too small. If the preset threshold is too large, the criterion for determining whether the first minimum simulated pattern 101 has a pattern loss defect is too stringent. When the area of ​​the first minimum simulated pattern 101 is large, it may still meet the condition that the area ratio is less than the preset threshold, thus determining that the first minimum simulated pattern 101 has a pattern loss defect, requiring subsequent processing, which may increase unnecessary calculations and increase processing costs. If the preset threshold is too small, the criterion for determining whether the first minimum simulated pattern 101 has a pattern loss defect is too lenient. When the area of ​​the first minimum simulated pattern 101 is small, it may not meet the condition that the area ratio is less than the preset threshold, thus determining that the first minimum simulated pattern 101 does not have a pattern loss defect. This may easily lead to the omission of the first minimum simulated pattern 101 with a pattern loss defect. Without subsequent processing, it is difficult to reduce the probability of pattern loss problems in subsequent exposure processes, affecting subsequent manufacturing processes. Therefore, in this embodiment, the preset threshold is 70% to 90%. As an example, the preset thresholds are 75%, 80%, or 85%.

[0055] In this embodiment, if the first minimum simulation graphic 101 does not have graphic loss defects, the first corrected graphic 103 is used as the photomask graphic.

[0056] The photomask pattern is used to create a photomask, which is then used in the photolithography process to form the corresponding photomask pattern on the wafer.

[0057] Step S3: If the first minimum simulation graphic 101 has a graphic loss defect, the initial target graphic 100 is enlarged.

[0058] The initial target graphic 100 is enlarged, which in turn enlarges the first minimum simulated graphic 101, thereby reducing the probability of graphic loss defects.

[0059] In the process of optical proximity correction, when the first minimum simulated pattern 101 is too small, it is easy to cause pattern loss in subsequent exposure processes. This embodiment reduces the probability of pattern loss defects by enlarging the initial target pattern 100 and correspondingly enlarging the first minimum simulated pattern 101. Moreover, since the first minimum simulated pattern 101 is the smallest loop in the process deviation loop, enlarging the first minimum simulated pattern 101 is also beneficial to reducing the size d of the PVBand, which is beneficial to subsequent manufacturing processes. In addition, compared with the scheme of improving defects by enlarging the first corrected pattern, this embodiment improves defects by enlarging the initial target pattern 100, which eliminates the edge-finding operation used to find the line segment corresponding to the defect in the first corrected pattern 103, simplifying the correction process. At the same time, it is also beneficial to reduce the restrictions of the mask manufacturability rule (MRC) on the enlargement of the initial target pattern 100, which is beneficial to improve the flexibility of optical proximity correction and thus improve the accuracy of optical proximity correction.

[0060] In this embodiment, the step of enlarging the initial target graphic 100 includes: shifting each side of the initial target graphic 100 outward by a preset size at equal distances to form a closed graphic, which serves as the enlarged initial target graphic 200.

[0061] The initial target image 100 is translated outward at equal distances to obtain the enlarged initial target image 200. This makes the enlargement of the initial target image 100 more uniform, and consequently makes the changes of the second corrected image and the second minimum simulated image corresponding to the second corrected image more uniform after the optical proximity correction processing is performed on the enlarged initial target image 100.

[0062] It should be noted that in the step of equidistantly translating each edge of the initial target pattern 100 outwards, the preset size w should not be too large or too small. If the preset size w is too large, the step size of subsequent processing iterations will be too large, and the amplification of the initial target pattern 100 each time will be too large. This can easily cause the amplified initial target pattern 100 to deviate too much from the better correction result. It can also easily oscillate back and forth around the better correction result during the adjustment process, making it difficult to eliminate defects. Furthermore, because the amplification is too large, other types of defects can easily be generated, thereby increasing the difficulty and number of subsequent processing steps, and thus affecting the processing efficiency. If the preset size w is too small, the step size of subsequent processing iterations will be too small, and the amplification of the initial target pattern 100 each time will be too small. This can easily lead to too many iterations, increasing the processing time and unnecessary time and computational costs. Therefore, in this embodiment, in the step of equidistantly translating each edge of the initial target pattern 100 outwards, the preset size w is 0.1nm to 0.25nm.

[0063] Continue to refer to Figure 5 In this embodiment, before enlarging the initial target graphic 100, the method further includes marking the initial target graphic 100 with graphic loss defects.

[0064] In the layout, marking the initial target graphic 100 with graphic loss defects is beneficial for subsequent processing of the initial target graphic 100 with graphic loss defects, thereby improving processing efficiency.

[0065] In this embodiment, the step of marking the initial target graphic 100 with graphic loss defects includes: forming a marking area 300 with the center of the initial target graphic 100 as the origin, and the marking area 300 covering the initial target graphic 100.

[0066] In this embodiment, the initial target graphic 100 is square in shape. Therefore, forming a square marking area 300 with the center of the initial target graphic 100 as the origin is beneficial for matching the shape of the initial target graphic 100 and selecting all of the initial target graphic 100.

[0067] It should be noted that in the step of forming the square marking area 300, the side length c of the square area is set according to the actual situation of the initial target graphic 100 in the layout.

[0068] refer to Figure 6 Step S4: Perform optical proximity correction processing on the magnified initial target image 200 to obtain the second corrected image 203 and the second minimum simulation image 201 corresponding to the second corrected image 203.

[0069] The initial target pattern 100 has been enlarged, and its shape and size have changed. Therefore, it is necessary to perform optical proximity correction processing on the enlarged initial target pattern 200 to obtain the second corrected pattern 203 and the second minimum simulated pattern 201 corresponding to the second corrected pattern 203. Correspondingly, the second minimum simulated pattern 201 is also enlarged compared to the first minimum simulated pattern 101, thereby reducing the probability of pattern loss defects. At the same time, it is also beneficial to reduce the size d of the PVBand, which is beneficial to subsequent manufacturing processes.

[0070] Furthermore, performing optical proximity correction on the enlarged initial target image 200 enables uniform processing of the entire image of the processed initial target image 200, resulting in better consistency of the optical proximity correction results.

[0071] In this embodiment, before detecting whether the second minimum simulated graphic 201 has a graphic loss defect after the initial target graphic 100 is magnified, the method further includes: adding an auxiliary graphic 120 based on the magnified initial target graphic 200.

[0072] In this embodiment, the shape and size of the initial target graphic 100 are changed. Accordingly, the initial auxiliary graphic 110 is difficult to apply to the enlarged initial target graphic 200. Therefore, an auxiliary graphic 120 is added based on the enlarged initial target graphic 200.

[0073] After magnification, the initial target pattern 200 is an exposing pattern, and the auxiliary pattern 120 is an unexposing pattern. Therefore, the auxiliary pattern 120 is a scattering bar, and the line width of the auxiliary pattern 120 is greater than or equal to the minimum line width of the mask writing rule, and less than or equal to the resolution of the photolithography process, so that the auxiliary pattern can be written into the template, but will not be exposed.

[0074] Setting scattering strips around the initial target pattern 200 after magnification helps improve light intensity contrast, reduce edge placement error, and also helps increase the depth of focus, thereby improving the photolithography process window.

[0075] Furthermore, after enlarging the initial target graphic 100, adding auxiliary graphics 120 based on the enlarged initial target graphic 200 allows for a comprehensive consideration of the mutual influence of the enlarged initial target graphic 200 across the entire map, which helps to make the setting results of the auxiliary graphics 120 across the entire map more accurate.

[0076] refer to Figure 7Step S5: Detect whether the second minimum simulated graphic 201 has a graphic loss defect. If it is determined that the second minimum simulated graphic 201 has a graphic loss defect, continue to perform magnification processing, optical proximity correction processing and graphic loss defect detection on the magnified initial target graphic until the second minimum simulated graphic 201 does not have a graphic loss defect.

[0077] In this embodiment, detecting whether the second minimum simulation graphic 201 has a graphic loss defect is used to determine whether the adjusted second minimum simulation graphic 201 still needs further processing.

[0078] In this embodiment, the area of ​​the graphic is used as the detection standard to detect whether the adjusted second minimum simulated graphic 201 has a graphic loss defect.

[0079] The second minimum simulated graphic 201 is a simulated exposure graphic of the initial target graphic 200 after magnification. When the second minimum simulated graphic 201 is too small, it is easy to cause graphic loss in subsequent exposure processes. Therefore, this embodiment uses graphic area as the detection standard. When the graphic area of ​​the second minimum simulated graphic 201 is too small, the second minimum simulated graphic 201 has graphic loss defects.

[0080] Specifically, in this embodiment, the step of detecting whether the adjusted second minimum simulated graphic 201 has a graphic loss defect includes: obtaining the area of ​​the second minimum simulated graphic 201 and the area of ​​the corresponding enlarged initial target graphic 200; comparing the area of ​​the second minimum simulated graphic 201 with the area ratio of the corresponding enlarged initial target graphic 200 with a preset threshold, and determining that the second minimum simulated graphic 201 has a graphic loss defect when the area ratio is less than the preset threshold.

[0081] The initial target graphic 200 after different magnification processes has different area sizes. Using the area of ​​the second minimum simulated graphic 201 and the ratio of the area of ​​the corresponding magnified initial target graphic 200 as the judgment standard is beneficial to flexibly adapt to each magnified initial target graphic 200 on the layout. This makes the judgment on whether the second minimum simulated graphic 201 has graphic loss defects more accurate. When the area ratio is less than a preset threshold, it indicates that the area of ​​the corresponding second minimum simulated graphic 201 is too small compared to the magnified initial target graphic 200, and the second minimum simulated graphic 201 has graphic loss defects.

[0082] Similarly, in this embodiment, the preset threshold is 70% to 90%.

[0083] When the second minimum analog pattern 201 has a pattern loss defect, the magnification process and optical proximity correction process continue until the second minimum analog pattern 201 does not have a pattern loss defect.

[0084] Step S6: Use the second modified pattern 203 as the photomask pattern.

[0085] When the second minimum simulation pattern 201 does not have pattern loss defects, the second corrected pattern 203 is used as the photomask pattern.

[0086] The photomask pattern is used to create a photomask, which is then used in the photolithography process to form the corresponding photomask pattern on the wafer.

[0087] In this embodiment, after determining that the second minimum simulated graphic 201 does not have graphic loss defects, the method further includes: performing an optical proximity correction process on the corrected layout to verify the graphic transmission accuracy of the corrected layout.

[0088] After completing the correction process, verifying the entire layout is beneficial for verifying the accuracy of subsequent pattern transfer to the wafer based on the entire layout, and for preparing for pattern verification on the wafer based on the verification results.

[0089] Accordingly, the present invention also provides an optical proximity correction system. Figure 8 This is a functional block diagram of an embodiment of the optical proximity correction system of the present invention.

[0090] In this embodiment, the optical proximity correction system 50 includes: a pattern providing module 501, used to provide a layout, including a first corrected pattern, which is obtained by optical proximity correction processing of an initial target pattern, and the first corrected pattern has a first minimum simulated pattern; a detection module 502, used to detect whether the first minimum simulated pattern has a pattern loss defect; a magnification processing module 503, used to magnify the initial target pattern if the first minimum simulated pattern has a pattern loss defect; an optical proximity correction module 504, used to perform optical proximity correction processing on the magnified initial target pattern to obtain a second corrected pattern and a second minimum simulated pattern corresponding to the second corrected pattern; a loop processing module 505, used to detect whether the second minimum simulated pattern has a pattern loss defect, and when it is determined that the second minimum simulated pattern has a pattern loss defect, to continue to magnify, perform optical proximity correction processing, and detect pattern loss defects on the magnified initial target pattern until the second minimum simulated pattern does not have a pattern loss defect; and a photomask pattern determination module 506, used to use the second corrected pattern as a photomask pattern.

[0091] The graphic providing module 501 is used to provide a layout, including a first modified graphic, which is obtained by optical proximity correction processing from an initial target graphic, and the first modified graphic has a first minimum analog graphic.

[0092] The first corrected pattern is the pattern obtained after optical proximity correction processing of the design pattern. The design pattern is the pattern transferred onto the wafer. After optical proximity correction processing of the design pattern, the first corrected pattern is used to make a photomask, and then photolithography is performed on the photomask to form the corresponding photomask pattern on the wafer. If the first corrected pattern still has defects, it needs to be repaired. The repaired first corrected pattern is used to make a photomask.

[0093] The simulated pattern is a simulated exposure pattern of the initial target pattern. Different processes will be used to form the pattern corresponding to the initial target pattern. Therefore, the initial target pattern will have different simulated exposure patterns for different processes. Correspondingly, in the optical proximity correction process, in order to adapt to the different processes used to form the pattern corresponding to the initial target pattern, each initial target pattern usually has a first minimum simulated pattern and a first maximum simulated pattern. When the first minimum simulated pattern is too small, it is easy to cause pattern loss in the subsequent exposure process. Moreover, the first minimum simulated pattern is the smallest loop in the process deviation loop. If the first minimum simulated pattern is too small, it is also easy to increase the size d of the PVBand, thereby affecting the subsequent manufacturing process. Therefore, it is necessary to detect whether the first minimum simulated pattern has pattern loss defects.

[0094] In this embodiment, the layout also includes initial auxiliary graphics located around the initial target graphic.

[0095] In this embodiment, the initial target pattern is an exposing pattern, and the initial auxiliary pattern is an unexposing pattern. Therefore, the initial auxiliary pattern is a scattering bar, and the linewidth of the initial auxiliary pattern is greater than or equal to the minimum linewidth of the mask writing rule, and less than or equal to the resolution of the photolithography process, so that the initial auxiliary pattern can be written into the template, but will not be exposed.

[0096] Setting scattering strips around the initial target pattern helps improve light intensity contrast, reduce edge placement errors, and also helps increase the depth of focus, thereby improving the lithography process window.

[0097] In this embodiment, the layout includes through-holes, and the initial target pattern includes through-hole patterns for forming through-holes between metal interconnects. Therefore, in this embodiment, the shape of the initial target pattern includes a square.

[0098] The detection module 502 is used to detect whether the first minimum simulated graphic has a graphic loss defect.

[0099] The detection of whether the first minimum simulated graphic has graphic loss defects is used to determine whether the initial target graphic needs further processing.

[0100] In this embodiment, the area of ​​the graphic is used as the detection standard to detect whether the first smallest simulated graphic has a graphic loss defect.

[0101] The first minimum simulated graphic is a simulated exposure graphic of the initial target graphic. When the first minimum simulated graphic is too small, it is easy to cause graphic loss in subsequent exposure processes. Therefore, this embodiment uses graphic area as the detection standard. When the graphic area of ​​the first minimum simulated graphic is too small, the first minimum simulated graphic has graphic loss defects.

[0102] Specifically, in this embodiment, detecting whether the first minimum simulated graphic has a graphic loss defect includes: obtaining the area of ​​the first minimum simulated graphic and the corresponding initial target graphic; comparing the area of ​​the first minimum simulated graphic and the ratio of the area of ​​the corresponding initial target graphic with a preset threshold, and determining that the first minimum simulated graphic has a graphic loss defect when the area ratio is less than the preset threshold.

[0103] Different initial target graphics have different area sizes. Using the area of ​​the first minimum simulated graphic and the ratio of the area of ​​the corresponding initial target graphic as the judgment standard is beneficial to flexibly adapt to each initial target graphic on the layout. This makes the judgment on whether the first minimum simulated graphic has graphic loss defects more accurate. When the area ratio is less than a preset threshold, it indicates that the area of ​​the corresponding first minimum simulated graphic is too small compared to the initial target graphic, and the first minimum simulated graphic has graphic loss defects.

[0104] It should be noted that the preset threshold should not be too large or too small. If the preset threshold is too large, the criterion for determining whether the first minimum simulated pattern has a pattern loss defect is too stringent. Even when the area of ​​the first minimum simulated pattern is large, it may still meet the condition that the area ratio is less than the preset threshold, thus determining that the first minimum simulated pattern has a pattern loss defect and requiring subsequent processing, which may increase unnecessary calculations and processing costs. If the preset threshold is too small, the criterion for determining whether the first minimum simulated pattern has a pattern loss defect is too lenient. Even when the area of ​​the first minimum simulated pattern is small, it may not meet the condition that the area ratio is less than the preset threshold, thus determining that the first minimum simulated pattern does not have a pattern loss defect. This may easily lead to the omission of first minimum simulated patterns with pattern loss defects. Without subsequent processing, it is difficult to reduce the probability of pattern loss problems during subsequent exposure, affecting subsequent manufacturing processes. Therefore, in this embodiment, the preset threshold is 70% to 90%. As an example, the preset threshold is 75%, 80%, or 85%.

[0105] If the first minimal simulation graphic does not have graphic loss defects, the first corrected graphic is used as the photomask graphic.

[0106] The photomask pattern is used to create a photomask, which is then used in the photolithography process to form the corresponding photomask pattern on the wafer.

[0107] The magnification processing module 503 is used to magnify the initial target graphic when the first minimum simulated graphic has graphic loss defects.

[0108] The initial target graphic is enlarged, which in turn enlarges the first minimum simulated graphic, thereby reducing the probability of graphic loss defects.

[0109] In the process of optical proximity correction, if the first minimum simulated pattern is too small, it can easily lead to pattern loss in subsequent exposures. This embodiment reduces the probability of pattern loss defects by enlarging the initial target pattern and correspondingly enlarging the first minimum simulated pattern. Moreover, since the first minimum simulated pattern is the smallest loop in the process deviation loop, enlarging the first minimum simulated pattern also helps to reduce the size d of the PVBand, which is beneficial for subsequent manufacturing processes. In addition, compared with the scheme of improving defects by enlarging the first corrected pattern, this embodiment improves defects by enlarging the initial target pattern, eliminating the edge-finding operation used to find the line segment corresponding to the defect in the first corrected pattern, simplifying the correction process. At the same time, it also helps to reduce the restrictions of the mask manufacturability rule (MRC) on the enlargement of the initial target pattern, which helps to improve the flexibility of optical proximity correction and thus improve the accuracy of optical proximity correction.

[0110] In this embodiment, the process of enlarging the initial target graphic includes: shifting each edge of the initial target graphic outward by a preset size at equal distances to form a closed graphic, which serves as the enlarged initial target graphic.

[0111] The initial target image is translated outward at equal distances along each edge to obtain the magnified initial target image. This makes the magnification of the initial target image more uniform, and consequently, the changes in the second corrected image and the second minimum simulated image corresponding to the second corrected image are more uniform after the optical proximity correction is performed on the magnified initial target image.

[0112] It should be noted that in the step of equidistantly translating each edge of the initial target graphic outwards, the preset size w should not be too large or too small. If the preset size w is too large, the step size of subsequent processing iterations will be too large, and the amplification of the initial target graphic each time will be too large. This can easily cause the amplified initial target graphic to deviate too much from the better correction result. It can also easily oscillate back and forth around the better correction result during the adjustment process, making it difficult to eliminate defects. Furthermore, because the amplification is too large, other types of defects can easily be generated, thereby increasing the difficulty and number of subsequent processing steps, and thus affecting the processing efficiency. If the preset size w is too small, the step size of subsequent processing iterations will be too small, and the amplification of the initial target graphic each time will be too small. This can easily lead to too many iterations, increasing the processing time and unnecessary time and computational costs. Therefore, in this embodiment, in the step of equidistantly translating each edge of the initial target graphic outwards, the preset size w is 0.1nm to 0.25nm.

[0113] In this embodiment, before enlarging the initial target graphic, the method further includes marking the initial target graphic that has graphic loss defects.

[0114] In the layout, marking the initial target graphics with graphic loss defects is beneficial for subsequent processing of the initial target graphics with graphic loss defects, thereby improving processing efficiency.

[0115] In this embodiment, marking the initial target graphic with graphic loss defects includes: forming a marking area with the center of the initial target graphic as the origin, and the marking area covering the initial target graphic.

[0116] In this embodiment, the initial target graphic is square. Therefore, forming a square marking area with the center of the initial target graphic as the origin is beneficial for matching the shape of the initial target graphic and selecting all of the initial target graphic.

[0117] It should be noted that in the step of forming the square marking area, the side length c of the square area is set according to the actual situation of the initial target graphic in the layout.

[0118] The optical proximity correction module 504 is used to perform optical proximity correction processing on the magnified initial target image to obtain a second corrected image and a second minimum simulation image corresponding to the second corrected image.

[0119] The initial target image has been enlarged, and its shape and size have changed. Therefore, it is necessary to perform optical proximity correction on the enlarged initial target image to obtain a second corrected image and a second minimum simulated image corresponding to the second corrected image. Correspondingly, the second minimum simulated image is also enlarged compared to the first minimum simulated image, thereby reducing the probability of image loss defects. At the same time, it is also beneficial to reduce the size d of the PVBand, which is beneficial to subsequent manufacturing processes.

[0120] Furthermore, performing optical proximity correction on the enlarged initial target image enables uniform processing of the entire image, resulting in better consistency of the optical proximity correction results.

[0121] In this embodiment, before detecting whether the second minimum simulated graphic has graphic loss defects after the initial target graphic is magnified, the method further includes: adding auxiliary graphics based on the magnified initial target graphic.

[0122] In this embodiment, the shape and size of the initial target graphic are changed. Consequently, the initial auxiliary graphic is difficult to apply to the enlarged initial target graphic. Therefore, an auxiliary graphic is added based on the enlarged initial target graphic.

[0123] The initial target pattern after magnification is an exposing pattern, and the auxiliary pattern is an inexposing pattern. Therefore, the auxiliary pattern is a scattering bar, and the line width of the auxiliary pattern is greater than or equal to the minimum line width of the mask writing rule, and less than or equal to the resolution of the photolithography process, so that the auxiliary pattern can be written into the template, but will not be exposed.

[0124] Setting scattering strips around the initial target pattern after magnification helps improve light intensity contrast, reduce edge placement errors, and also helps increase the depth of focus, thereby improving the lithography process window.

[0125] Furthermore, by enlarging the initial target graphic and then adding auxiliary graphics based on the enlarged initial target graphic, the mutual influence of the enlarged initial target graphics in the entire map can be taken into account, which helps to make the setting results of the auxiliary graphics in the entire map more accurate.

[0126] The loop processing module 505 is used to detect whether the second minimum simulated graphic has a graphic loss defect. When it is determined that the second minimum simulated graphic has a graphic loss defect, the initial target graphic after magnification is further magnified, optical proximity correction is performed, and graphic loss defect is detected again until the second minimum simulated graphic does not have a graphic loss defect.

[0127] In this embodiment, detecting whether the second minimum simulated graphic has a graphic loss defect is used to determine whether the adjusted second minimum simulated graphic still needs further processing.

[0128] In this embodiment, the area of ​​the graphic is used as the detection standard to detect whether the adjusted second minimum simulated graphic has a graphic loss defect.

[0129] The second minimum simulated image is a simulated exposure image of the initial target image after magnification. When the second minimum simulated image is too small, it is easy to cause image loss in subsequent exposure processes. Therefore, this embodiment uses the image area as the detection standard. When the image area of ​​the second minimum simulated image is too small, the second minimum simulated image has an image loss defect.

[0130] Specifically, in this embodiment, detecting whether the adjusted second minimum simulated graphic has a graphic loss defect includes: obtaining the area of ​​the second minimum simulated graphic and the area of ​​the corresponding enlarged initial target graphic; comparing the area of ​​the second minimum simulated graphic and the ratio of the area of ​​the corresponding enlarged initial target graphic with a preset threshold, and determining that the second minimum simulated graphic has a graphic loss defect when the area ratio is less than the preset threshold.

[0131] Different initial target graphics have different area sizes after different magnification processes. Using the area of ​​the second minimum simulated graphic and the ratio of the area of ​​the corresponding magnified initial target graphic as the judgment standard is beneficial for flexible adaptation to various magnified initial target graphics on the layout. This makes the judgment on whether the second minimum simulated graphic has graphic loss defects more accurate. When the area ratio is less than a preset threshold, it indicates that the area of ​​the corresponding second minimum simulated graphic is too small compared to the magnified initial target graphic, and the second minimum simulated graphic has graphic loss defects.

[0132] Similarly, in this embodiment, the preset threshold is 70% to 90%.

[0133] The mask pattern determination module 506 is used to use the second modified pattern as the mask pattern.

[0134] The photomask pattern is used to create a photomask, which is then used in the photolithography process to form the corresponding photomask pattern on the wafer.

[0135] In this embodiment, after determining that the first minimum simulated graphic does not have graphic loss defects, the method further includes: performing optical proximity correction processing on the corrected layout to verify the graphic transmission accuracy of the corrected layout.

[0136] After completing the correction process, verifying the optical proximity correction process on the entire layout is beneficial for verifying the accuracy of subsequent pattern transfer to the wafer based on the entire layout, and for preparing for pattern verification on the wafer based on the verification results.

[0137] Accordingly, the present invention also provides a photomask, comprising: a pattern obtained using the optical proximity correction method provided in the embodiments of the present invention.

[0138] As can be seen from the foregoing embodiments, during the optical proximity correction process, when the first minimum simulated pattern is too small, it is easy to cause pattern loss in subsequent exposure processes. This embodiment of the invention reduces the probability of pattern loss defects by enlarging the initial target pattern and correspondingly enlarging the first minimum simulated pattern. Moreover, since the first minimum simulated pattern is the smallest loop in the process variation band (PVBand), enlarging the first minimum simulated pattern also helps to reduce the size of the PVBand, which is beneficial to subsequent manufacturing processes. In addition, compared with the scheme of improving defects by enlarging the first corrected pattern, this embodiment of the invention improves defects by enlarging the initial target pattern, eliminating the edge-finding operation used to find the line segment corresponding to the defect in the first corrected pattern, simplifying the correction process. At the same time, it also helps to reduce the restrictions of the mask manufacturability rule (MRC) on the enlargement of the initial target pattern, which helps to improve the flexibility of the optical proximity correction process, thereby improving the accuracy of the optical proximity correction process. Correspondingly, after forming the mask pattern on the wafer using a mask, the matching degree between the mask pattern formed on the wafer and the target pattern is improved.

[0139] This invention also provides a device that can implement the optical proximity correction method provided in this invention by loading a program, as described above. An optional hardware structure of the terminal device provided in this invention can be as follows: Figure 9 As shown, it includes: at least one processor 01, at least one communication interface 02, at least one memory 03, and at least one communication bus 04.

[0140] In this embodiment, the number of processor 01, communication interface 02, memory 03, and communication bus 04 is at least one, and the processor 01, communication interface 02, and memory 03 communicate with each other through communication bus 04. Communication interface 02 can be an interface of a communication module for network communication, such as the interface of a GSM module. Processor 01 may be a central processing unit (CPU), an application-specific integrated circuit (ASIC), or one or more integrated circuits configured to implement embodiments of the present invention. Memory 03 may include high-speed RAM and may also include non-volatile memory (NVM), such as at least one disk storage device. Memory 03 stores one or more computer instructions, which are executed by processor 01 to implement the optical proximity correction method provided in this embodiment of the present invention.

[0141] It should be noted that the aforementioned terminal device may also include other devices (not shown) that may not be essential to understanding the content disclosed in the embodiments of the present invention; given that these other devices may not be essential for understanding the content disclosed in the embodiments of the present invention, the embodiments of the present invention will not describe them one by one.

[0142] This invention also provides a storage medium storing one or more computer instructions for implementing the optical proximity correction method provided in this invention.

[0143] In the optical proximity correction method provided by this invention, when the first minimum simulated pattern is too small during the optical proximity correction process, it is easy to cause pattern loss in subsequent exposure processes. This invention reduces the probability of pattern loss defects by enlarging the initial target pattern and correspondingly enlarging the first minimum simulated pattern. Moreover, since the first minimum simulated pattern is the smallest loop in the Process Variation Band (PVBand), enlarging the first minimum simulated pattern also helps to reduce the size of the PVBand, which is beneficial to subsequent manufacturing processes. In addition, compared with the scheme of improving defects by enlarging the first corrected pattern, this invention improves defects by enlarging the initial target pattern, eliminating the edge-finding operation used to find the line segment corresponding to the defect in the first corrected pattern, simplifying the correction process. At the same time, it also helps to reduce the restrictions of the mask manufacturability rule (MRC) on the enlargement of the initial target pattern, which helps to improve the flexibility of the optical proximity correction process, thereby improving the accuracy of the optical proximity correction process.

[0144] The embodiments of the present invention described above are combinations of elements and features of the present invention. Unless otherwise stated, the elements or features described are optional. Individual elements or features may be practiced without combination with other elements or features. Furthermore, embodiments of the present invention may be constructed by combining some elements and / or features. The order of operations described in the embodiments of the present invention may be rearranged. Some constructions of any embodiment may be included in another embodiment and may be replaced by corresponding constructions of another embodiment. It will be apparent to those skilled in the art that claims in the appended claims that are not expressly referenced to each other may be combined to form embodiments of the present invention, or may be included as new claims in amendments made after the filing of this application.

[0145] Embodiments of the present invention can be implemented by various means, such as hardware, firmware, software, or combinations thereof. In a hardware configuration, the method according to an exemplary embodiment of the present invention can be implemented by one or more application-specific integrated circuits (ASICs), digital signal processors (DSPs), digital signal processing devices (DSPDs), programmable logic devices (PLDs), field-programmable gate arrays (FPGAs), processors, controllers, microcontrollers, microprocessors, etc. In a firmware or software configuration, embodiments of the present invention can be implemented in the form of modules, processes, functions, etc. Software code can be stored in memory units and executed by a processor. The memory units are located inside or outside the processor and can send data to and receive data from the processor via various known means.

[0146] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is accorded the widest scope consistent with the principles and novel features disclosed herein.

[0147] While the present invention has been disclosed above, it is not limited thereto. Any person skilled in the art can make various modifications and alterations without departing from the spirit and scope of the invention; therefore, the scope of protection of the present invention should be determined by the scope defined in the claims.

Claims

1. An optical proximity correction method, characterized in that, include: Provide a layout, including a first corrected graphic, which is obtained from an initial target graphic through optical proximity correction processing, and the first corrected graphic has a first minimum simulated graphic; Detect whether the first minimum simulated graphic has a graphic loss defect; If the first minimum simulated graphic has a graphic loss defect, the initial target graphic is enlarged. The enlarged initial target image is subjected to optical proximity correction processing to obtain a second corrected image and a second minimum simulation image corresponding to the second corrected image; The process involves detecting whether the second minimum simulated graphic has a graphic loss defect, and if it is determined that the second minimum simulated graphic has a graphic loss defect, the process continues to perform magnification processing, optical proximity correction processing, and graphic loss defect detection on the magnified initial target graphic until the second minimum simulated graphic does not have a graphic loss defect. When the second minimum simulation graphic does not have graphic loss defects, the second corrected graphic is used as the photomask graphic.

2. The optical proximity correction method as described in claim 1, characterized in that, Using the area of ​​the graphic as the detection standard, the first smallest simulated graphic is used to detect whether it has a graphic loss defect.

3. The optical proximity correction method as described in claim 2, characterized in that, The step of detecting whether the first minimum simulated graphic has a graphic loss defect includes: obtaining the area of ​​the first minimum simulated graphic and the corresponding initial target graphic; comparing the area of ​​the first minimum simulated graphic and the area ratio of the corresponding initial target graphic with a preset threshold, and determining that the first minimum simulated graphic has a graphic loss defect when the area ratio is less than the preset threshold.

4. The optical proximity correction method as described in claim 3, characterized in that, The preset threshold is 70% to 90%.

5. The optical proximity correction method as described in claim 1, characterized in that, The step of enlarging the initial target graphic includes: shifting each side of the initial target graphic outward by a preset size at equal distances to form a closed graphic, which is the enlarged initial target graphic.

6. The optical proximity correction method as described in claim 5, characterized in that, The preset size is 0.1nm to 0.25nm.

7. The optical proximity correction method as described in claim 1, characterized in that, After determining that the second minimum simulated graphic does not have graphic loss defects, the method further includes: performing an optical proximity correction verification process on the corrected layout to verify the graphic transfer accuracy of the corrected layout.

8. The optical proximity correction method as described in claim 1, characterized in that, After enlarging the initial target image, the method further includes: adding an auxiliary image based on the enlarged initial target image, wherein the auxiliary image is used to reduce the edge placement error of the initial target image.

9. The optical proximity correction method as described in claim 1, characterized in that, Before enlarging the initial target graphic, the method further includes: marking the initial target graphic that has graphic loss defects.

10. The optical proximity correction method as described in claim 9, characterized in that, The step of marking the initial target graphic that has a graphic loss defect includes: forming a marking region with the center of the initial target graphic as the origin, the marking region covering the initial target graphic.

11. An optical proximity correction system, characterized in that, include: A graphics providing module is used to provide a layout, including a first corrected graphics, which is obtained from an initial target graphics through optical proximity correction processing, and the first corrected graphics has a first minimum analog graphics; The detection module is used to detect whether the first minimum simulated graphic has a graphic loss defect; The magnification processing module is used to magnify the initial target graphic when the first minimum simulated graphic has a graphic loss defect; An optical proximity correction module is used to perform optical proximity correction processing on the magnified initial target image to obtain a second corrected image and a second minimum simulation image corresponding to the second corrected image. The loop processing module is used to detect whether the second minimum simulated graphic has a graphic loss defect, and when it is determined that the second minimum simulated graphic has a graphic loss defect, the initial target graphic after magnification processing is further magnified, optical proximity correction processing is performed, and graphic loss defect detection is performed until the second minimum simulated graphic does not have a graphic loss defect. The photomask pattern determination module is used to use the second corrected pattern as the photomask pattern when the second minimum simulation pattern does not have a pattern loss defect.

12. A photomask, characterized in that, include: The image obtained using the optical proximity correction method as described in any one of claims 1-10.

13. A terminal device, characterized in that, It includes at least one memory and at least one processor, the memory storing one or more computer instructions, wherein the one or more computer instructions are executed by the processor to implement the optical proximity correction method as described in any one of claims 1-10.

14. A storage medium, characterized in that, The storage medium stores one or more computer instructions for implementing the optical proximity correction method as described in any one of claims 1-10.

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