An adaptive step optical proximity correction method
By adopting an adaptive step size optical proximity correction method, the problem of unsatisfactory OPC correction quality in complex chip design layouts is solved, achieving higher precision optical proximity correction and improving the accuracy of chip design.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- SHANGHAI HUALI INTEGRATED CIRCUIT CORP
- Filing Date
- 2023-05-30
- Publication Date
- 2026-07-14
AI Technical Summary
In the existing technology, the optical proximity correction method with a fixed single step length has unsatisfactory correction quality on complex chip design layouts, resulting in inaccurate correction results and a large difference between the corrected graphic contour and the target graphic contour.
An adaptive step-size optical proximity effect correction method is adopted. By edge cutting of the target graphic, adaptive moving step size and cyclic optimization, combined with weighting factors and mean square error objective function, the position of the graphic is gradually adjusted to meet the accuracy requirements.
It significantly improves the OPC correction effect of complex chip design layouts, enhances the accuracy and precision of pattern correction, and reduces the negative impact of optical proximity effect.
Smart Images
Figure CN116643447B_ABST
Abstract
Description
Technical Field
[0001] This application relates to the field of semiconductor technology, and specifically to an adaptive step size optical proximity effect correction method. Background Technology
[0002] With the rapid development of integrated circuits and the expansion of wafer foundries, Moore's Law has reached its practical application limit. Especially after 55nm, the requirements for photolithography in integrated circuit manufacturing are becoming increasingly stringent. Effectively suppressing the deformation and data deviation of patterns on the layout after photolithography, and reducing the negative impact of the optical proximity effect (OPE), has become a core factor in improving chip yield.
[0003] To address the impact of OPE (Optical Proximity Effect), the primary method currently used is Optical Proximity Correction (OPC) to correct the layout and minimize the influence of beam interference and diffraction effects on the pattern shape. The industry commonly employs an OPC method based on a segmented classification approach. While this method offers some effectiveness in correcting layout proximity effects, its fixed single-step length for cutting the pattern edges and fixed movement distance limits the correction quality for complex chip designs, leading to inaccurate results and significant differences between the corrected and target pattern outlines. Summary of the Invention
[0004] In view of the shortcomings of the prior art described above, the purpose of this application is to provide an adaptive step size optical proximity effect correction method to solve the problem of unsatisfactory correction quality of OPC for complex chip design layouts in the prior art.
[0005] To achieve the above and other related objectives, this application provides an adaptive step-size optical proximity effect correction method, comprising:
[0006] Step 1: Edge cutting of the target graphic;
[0007] Step 2, adaptive movement step size;
[0008] Step 3: Optimize the target graphic repeatedly until the preset accuracy requirements are met.
[0009] Preferably, in step one, during the graphic preprocessing stage, the cutting step size to be taken for the target graphic is determined based on the minimum line width of the graphic to be corrected and the photolithography wavelength.
[0010] Preferably, when the minimum linewidth of the pattern is less than the photolithography wavelength, one-fifth of the minimum linewidth is used as the basic step size for pattern cutting; when the minimum linewidth of the pattern is greater than the photolithography wavelength, one-fifth of the photolithography wavelength is used as the basic step size for pattern cutting.
[0011] Preferably, the cutting step length is obtained by weighted calculation of the base step length, that is, the cutting step length = the base step length of the target graphic * weight factor + the base step length of the environment graphic * weight factor, where the weight factor of the target graphic to be corrected is 1 and the weight factor of the environment graphic is 2.
[0012] Preferably, in step two, for the target line segment that has been cut and marked as a line segment, line end, or corner type, when moving the whole line segment during correction, the distance between the imaging point corresponding to the midpoint of the line segment and the expected point is selected as the initial movement step size.
[0013] Preferably, in step two, during the Nth iteration of correction (N>1) before the optimization target is reached, the distance between the imaging point corresponding to the midpoint of the target line segment in the N-1th iteration results and the expected point is used as the movement step size in the Nth iteration of correction.
[0014] Preferably, in step three, the cutting line segment is used as the basic unit of the correction process. The correction process processes each line segment in a clockwise direction along the boundary of the target graphic, and the optimized position of each line segment is obtained through cyclic correction.
[0015] Preferably, during the correction process, the new position of other line segments after correction is taken as the environmental line segment of the current correction line segment.
[0016] Preferably, the number of cycles of correction depends on the required correction accuracy.
[0017] Preferably, in cyclic correction, the mean square difference e(α) between the target point and the expected point is used. ij e(α) is the objective function for line segment optimization. ij It can be expressed by the following formula:
[0018] e(α ij )=∫[I(x,y)-I γ (x, y)] 2 dxdy
[0019] Where I(x,y) represents the target point of the corrected line segment; I γ (x,y) represents the expected points of the corrected line segment; i,j=1,2,…,N.
[0020] As described above, the adaptive step size optical proximity effect correction method provided in this application has the following beneficial effects: by fully considering the OPC correction requirements of complex chip design layouts and the influence of optical proximity effect inside the image, it can significantly improve the OPC correction effect on wafer design layouts. Attached Figure Description
[0021] To more clearly illustrate the technical solutions in the specific embodiments of this application or the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this application. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.
[0022] Figure 1 The flowchart shown is a method for optical proximity effect correction with adaptive step size provided in an embodiment of this application.
[0023] Figure 2 The flowchart shown is a method for calculating the cutting step size of an image edge in the adaptive step size optical proximity effect correction method provided in the embodiments of this application;
[0024] Figure 3 The diagram shows the adaptive movement step size in the adaptive step size optical proximity effect correction method provided in the embodiments of this application;
[0025] Figure 4 The image shown is a graphical profile after multiple cyclic corrections using the adaptive step size optical proximity effect correction method provided in the embodiments of this application. Detailed Implementation
[0026] The following specific examples illustrate the implementation of this application. Those skilled in the art can easily understand other advantages and effects of this application from the content disclosed in this specification. This application can also be implemented or applied through other different specific embodiments, and various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of this invention.
[0027] The technical solutions of this application will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this application. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.
[0028] In the description of this application, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," indicating orientation or positional relationships, are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation 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.
[0029] In the description of this application, it should be noted that, unless otherwise expressly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal connection of two components; and they can refer to a wireless connection or a wired connection. Those skilled in the art can understand the specific meaning of the above terms in this application based on the specific circumstances.
[0030] Furthermore, the technical features involved in the different embodiments of this application described below can be combined with each other as long as they do not conflict with each other.
[0031] Currently, the most commonly used optical proximity correction method in OPC technology is an optical proximity correction method based on the idea of segmentation and classification. This method uses a fixed single-step length to cut the edge of the pattern and a fixed moving distance to correct the optical proximity effect. For complex chip design layouts, this limits the correction quality of OPC and will cause inaccurate correction results. The corrected pattern outline and the target pattern outline will have a large difference.
[0032] To address this issue, this application provides an adaptive step size optical proximity effect correction method.
[0033] Please see Figure 1 The diagram shows a flowchart of the adaptive step size optical proximity effect correction method provided in the embodiments of this application.
[0034] like Figure 1 As shown, the adaptive step-size optical proximity effect correction method includes the following steps:
[0035] Step 1: Edge cutting of the target graphic;
[0036] Step 2, adaptive movement step size;
[0037] Step 3: Optimize the target graphic repeatedly until the preset accuracy requirements are met.
[0038] For edge cutting of target graphics, current OPC correction methods use a single step size to cut the boundary of the target graphics into small line segments during the graphics preprocessing stage. Whether the cutting result is reasonable has a great impact on the correction accuracy of OPC. However, existing methods ignore the ambient light intensity distribution characteristics of complex design layouts.
[0039] In step one, such as Figure 2 As shown, in the pattern preprocessing stage, the cutting step size to be taken for the target pattern is determined based on the minimum line width of the pattern to be corrected and the photolithography wavelength.
[0040] Based on the principles of optics and finite element method, when the minimum linewidth of the pattern is less than the lithography wavelength, one-fifth of the minimum linewidth is used as the basic step size for pattern cutting; when the minimum linewidth of the pattern is greater than the lithography wavelength, one-fifth of the lithography wavelength is used as the basic step size for pattern cutting, in order to ensure the integrity of the resulting small line segments and facilitate numerical calculations by the system's optical simulator.
[0041] The cutting step size is calculated using a weighted average of the base step size, i.e., Cutting Step Size = Target Image Base Step Size * Weight Factor + Environment Image Base Step Size * Weight Factor. The target image weight factor is 1, and the environment image weight factor is 2. The environment image refers to the surrounding images that significantly affect the target image's optical proximity. The base step size of the environment image is determined in the same way as the target image base step size.
[0042] In step two, the correction of the target image uses an adaptive movement step size to correct each target line segment. For target line segments that have been cut and marked as line segments, line ends, or corners, during the overall movement in the correction, the distance between the imaging point corresponding to the midpoint of the line segment and the expected point is selected as the initial movement step size, such as... Figure 3 As shown. In the Nth iteration of correction (N>1) before the optimization target is reached, the distance between the imaging point corresponding to the midpoint of the target line segment in the N-1th iteration result and the expected point is used as the moving step size in the Nth iteration of correction. This is more conducive to approximating the optimization target.
[0043] In the cyclic optimization of the target graphic, the cutting line segment is used as the basic unit of the correction process. The correction process processes each line segment in a clockwise direction along the boundary of the target graphic, and obtains the optimized position of each line segment through cyclic iteration.
[0044] like Figure 3As shown, the solid lines represent the positions of line segments on the corrected photomask, while the dashed lines represent the original positions of line segments in the target graphic. When correcting a small line segment within the target graphic, since all line segments belong to the same graphic and are close to each other, especially adjacent segments, the change in the position of the line segment before and after correction has different effects on the optical proximity of the next line segment, resulting in different correction results. Current OPC correction always uses the original line segments as the environment, ignoring the changes in the position of the corrected line segments, leading to inaccurate correction results.
[0045] In step three, during the correction process, the new position of other line segments after correction is taken as the environmental line segment of the current correction line segment. The correction accuracy problem caused by the change of environmental line segments is fully considered. Thus, through several cycles of correction, a more accurate correction result is finally obtained. The number of cycles can be determined according to the correction accuracy requirements.
[0046] In cyclic correction, the mean square difference e(α) between the target point and the expected point is used. ij e(α) is the objective function for line segment optimization. ij It can be expressed by the following formula:
[0047] e(α ij )=∫[I(x,y)-I γ (x, y)] 2 dxdy
[0048] Where I(x,y) represents the target point of the corrected line segment; I γ (x,y) represents the expected points of the corrected line segment; i,j=1,2,…,N.
[0049] like Figure 4 As shown, Figure 4 (a) shows the target graphic. Figure 4 (b) shows Figure 4 (a) An uncorrected image of the target image shown. Figure 4 (c) shows Figure 4 (a) The target graphic shown is a graphic corrected using existing technology. Figure 4 (d) shows Figure 4 (c) shows the image of the graphic. Figure 4 (e) shows Figure 4 (a) The target graphic shown is the graphic after being corrected by the adaptive step size optical proximity effect correction method provided in the embodiments of this application. Figure 4 (f) shows the image obtained after multiple iterations of correction. By comparison, it can be found that after multiple iterations, the corrected outline of the image is closer to the outline of the target image.
[0050] It should be noted that the illustrations provided in this embodiment are only schematic representations of the basic concept of this application. Therefore, the drawings only show the components related to this invention and are not drawn according to the actual number, shape and size of the components. In actual implementation, the form, quantity and proportion of each component can be arbitrarily changed, and the layout of the components may also be more complex.
[0051] In summary, the adaptive step-size optical proximity correction method provided in this application fully considers the OPC correction requirements of complex chip design layouts and the influence of internal optical proximity effects in images, and can significantly improve the OPC correction effect on wafer design layouts. Therefore, this application effectively overcomes the various shortcomings of the prior art and has high industrial application value.
[0052] The above embodiments are merely illustrative of the principles and effects of this application and are not intended to limit this application. Any person skilled in the art can modify or alter the above embodiments without departing from the spirit and scope of this application. Therefore, all equivalent modifications or alterations made by those skilled in the art without departing from the spirit and technical concept disclosed in this invention should still be covered by the claims of this application.
Claims
1. A method for correcting the optical proximity effect with an adaptive step size, characterized in that, The method includes: Step 1: Edge cutting of the target graphic. In the graphic preprocessing stage, the cutting step size for the target graphic is determined based on the minimum linewidth of the graphic to be corrected and the lithography wavelength: if the minimum linewidth of the graphic is less than the lithography wavelength, one-fifth of the minimum linewidth is used as the basic cutting step size; if the minimum linewidth of the graphic is greater than the lithography wavelength, one-fifth of the lithography wavelength is used as the basic cutting step size. The cutting step size is obtained by weighted calculation of the basic step size, i.e., cutting step size = target graphic basic step size * weight factor + environment graphic basic step size * weight factor, where the weight factor of the target graphic to be corrected is 1 and the weight factor of the environment graphic is 2. Step 2, Adaptive movement step size: For target line segments that have been cut and marked as line segments, line ends or corners, when moving the whole line segment during correction, the distance between the imaging point corresponding to the midpoint of the line segment and the expected point is selected as the initial movement step size. In the Nth cycle of correction (N>1) before the optimization target is reached, the distance between the imaging point corresponding to the midpoint of the target line segment and the expected point in the N-1th cycle result is used as the movement step size in the Nth cycle of correction. Step 3: Continuously optimize the target graphic until the preset accuracy requirements are met. Using line segments as the basic unit of correction, the correction process sequentially processes each line segment in a clockwise direction along the boundary of the target graphic. The optimized position of each line segment is obtained through iterative correction. During the correction process, the new positions of other corrected line segments are taken as the environmental line segments of the currently corrected line segment. In the iterative correction, the mean square difference e(α) between the target point and the expected point is used. ij () is used as the objective function for line segment optimization.
2. The method according to claim 1, characterized in that, The number of cycles for correction depends on the required correction accuracy.
3. The method according to claim 1, characterized in that, The mean square error e(α) ij It can be expressed by the following formula: e(α ij )=∫[I(x,y)-I γ (x,y)] 2 dxdy Where I(x,y) represents the target point of the corrected line segment; I γ (x,y) represents the expected points of the corrected line segment; i,j=1,2,…,N.