Method for improving photoetching performance of dipole light source

Abstract

The invention discloses a method for improving photoetching performance of a dipole light source. The method comprises the following steps of: finding out a selected area with an OPC (Optical Proximity Correction) segment coupling effect in a layout graph, selecting a plurality of adjacent selected OPC segments in the selected area, and combining the selected OPC segments to form a segment group; the row number and the column number of the Jacobian matrix are equal to the number of the selected OPC segments, and each element of a row vector of the Jacobian matrix is a derivative of the light intensity of one selected OPC segment corresponding to the row vector to the position coordinate of each selected OPC segment; each element of a column vector of the Jacobian matrix is a derivative of the light intensity of each selected OPC segment to the position coordinates of one selected OPC segment corresponding to the column vector. A Jacobian matrix is added into a cost function, then MB-OPC correction is carried out, and a light source in an OPC model subjected to MB-OPC correction is a dipole light source. According to the invention, the OPC convergence speed of an area with a strong OPC segmented coupling effect can be accelerated, and the contrast ratio can be improved.

Description

Technical Field

[0001] The present invention relates to a method for manufacturing a semiconductor integrated circuit, and in particular to a method for improving the photolithography performance of a dipole light source. Background Art

[0002] In the photolithography process, the choice of lighting method must take into account the requirements of different graphics, and each lighting method has different effects on the photolithography process. Generally, annular lighting and mixed lighting can better take into account the process windows of various graphics. However, uniform lighting will cause background exposure during imaging, which reduces the overall contrast of the graphics. For graphics with high resolution, this type of lighting cannot meet the photolithography process requirements.

[0003] As the design layout cycle continues to shrink, the pattern density continues to increase and the direction is single. In order to obtain a larger lithography process window, a dipole light source or a quasi-dipole light source with a large off-axis angle becomes the optimal illumination method. However, because the dipole light source removes the DC component in the other direction, the contrast of the structure in the other direction (such as the grating line end) is very poor. At the same time, it will make it difficult or even impossible to converge the line end during OPC correction.

[0004] The advantages and disadvantages of ring light sources, hybrid light sources and dipole light sources are:

[0005] For Ring Lights and Mixed Lights:

[0006] The advantage is: it better takes into account the process window of various graphics; the disadvantage is: the overall contrast of the graphics is relatively small.

[0007] For a dipole source:

[0008] The advantage is that it has the best contrast for imaging dense grating patterns in a single direction; the disadvantage is that it can only take care of patterns in a fixed direction, and the contrast in other directions is very poor.

[0009] like Figure 1 , which is a schematic diagram of an existing dipole light source; Figure 1 The DC component of the light source 101 shown in the figure is located in the X direction. The X-direction dipole light source is very friendly to the process window of the 1D pattern in the Y direction, but the contrast of the 2D line ends is very poor, making it difficult or even impossible to converge the line ends during OPC correction.

[0010] like Figure 2Figure 2 shows the OPC simulation image and layout pattern generated after eight iterations of MB-OPC using a conventional dipole light source. The designed layout pattern 201 is a bar with line ends extending in the Y direction. Therefore, the area outside the line ends is a 1D Y-direction pattern, while the line ends are a 2D pattern. During OPC correction, the edges of layout pattern 201 are segmented. The area between lines 203 is an OPC segment 204, and the middle of each OPC segment 204 is typically selected as the OPC segment evaluation point 205. Sub-resolution prevention auxiliary patterns 202 are also placed around the periphery of layout pattern 201.

[0011] OPC correction usually adopts model-based (MB) OPC, namely MB-OPC correction. OPC correction will go through multiple iterations. During the iteration process, the cost function includes the sum of the squares of the edge placement errors of each OPC segment 204, which is expressed as:

[0012]

[0013] Here, cost function represents a cost function, EPE represents an edge placement error, and x represents the position coordinate of the corresponding OPC segment 204 .

[0014] Figure 2 The OPC simulation image 201a is the contour image formed after 8 iterations of OPC simulation. It can be seen that the deviation between the image and the target is large at the end of the line, and convergence cannot be achieved. In other words, the OPC EPE cannot converge. In order to achieve convergence, the only option is to further increase the number of OPC correction iterations.

[0015] For example, increasing the iteration to 15 times, the OPC-EPE results gradually converge, but the runtime increases by two times. Figure 3 As shown, the OPC simulation imaging pattern and layout pattern formed after 15 iterations of the existing MB-OPC using dipole light source lithography; Figure 3 is Figure 2 The number of iterations is increased based on , that is, the OPC simulation imaging pattern 201b is the contour pattern formed after 15 iterations of OPC simulation. It can be seen that after 15 iterations, the OPC-EPE results at the line ends gradually converge, but the calculation time increases.

[0016] In addition, the slope of the imaging intensity distribution at the edge of the ideal line width, namely the image logarithmic slope (ILS), is an important indicator for evaluating lithography performance. The typical image logarithmic slope is generally taken as the value at the boundary of the ideal imaging of the mask pattern. Figure 4, which is a schematic diagram of the logarithmic slope of an existing image. During exposure, the mask 206 opens the pattern area, and then the exposure is performed. Curve 207 represents the light intensity during exposure, i.e., the imaging intensity curve. The imaging emphasizes that the distribution of the open area of ​​the mask 206, i.e., the pattern area, is uneven, with the peak located in the middle area. The slope of the edge area indicated by the dotted circle 208 is ILS, which can be expressed as:

[0017] The image logarithmic slope is expressed as follows:

[0018]

[0019] Wherein, ILS represents the logarithmic slope of the image, I represents the light intensity, and x represents the position coordinate.

[0020] Under the existing conventional MB-OPC correction, the ILS comparison of 1D and 2D line-end graphics with different numbers of iterations is as follows:

[0021] like Figure 5 As shown, Figure 2 The ILS values ​​at various locations in the OPC simulated imaging pattern are shown. It can be seen that the ILS of light intensity curve 207a at the line end (arrow line 209, i.e., the 2D graph) is less than 15, while the ILS of light intensity curve 207b at the line area (arrow line 210, i.e., the 1D graph) is greater than 30. A larger ILS indicates better image contrast. Clearly, a smaller ILS at the line end indicates poorer contrast.

[0022] like Figure 6 As shown, Figure 3 The ILS values ​​at various locations in the OPC simulation image are shown. It can be seen that the ILS of the light intensity curve 207c at the line end is less than 15, and the ILS of the light intensity curve 207d in the line area is greater than 30. It can be seen that even after the number of iterations increases, the ILS at the line end remains small, and the contrast remains poor.

[0023] Even if OPC can achieve 2D line-end EPE convergence by increasing the number of iterations and sacrificing runtime, it cannot effectively improve the contrast of the 2D line end, which has a great impact on the lithography process window and subsequent etching performance. Summary of the Invention

[0024] The technical problem to be solved by the present invention is to provide a method for improving the photolithography performance of a dipole light source, which can accelerate the OPC convergence speed in areas with strong OPC segment coupling effects and improve the contrast.

[0025] To solve the above technical problems, the present invention provides a method for improving the lithography performance of a dipole light source, comprising the steps of:

[0026] A selected area with OPC segment coupling effect in a publication pattern is found, a plurality of adjacent selected OPC segments are selected in the selected area, and the selected OPC segments are combined to form a segment group.

[0027] A Jacobian Matrix corresponding to the segment group is formed, wherein the number of rows and columns of the Jacobian matrix is ​​equal to the number of the selected OPC segments, each element of the row vector of the Jacobian matrix is ​​the derivative of the light intensity of one of the selected OPC segments corresponding to the row vector with respect to the position coordinates of each of the selected OPC segments, and each element of the column vector of the Jacobian matrix is ​​the derivative of the light intensity of each of the selected OPC segments with respect to the position coordinates of one of the selected OPC segments corresponding to the column vector.

[0028] The Jacobian matrix is ​​added to the cost function, and then MB-OPC correction is performed. The light source in the OPC model of the MB-OPC correction is a dipole light source.

[0029] A further improvement is that the selected area includes line ends.

[0030] A further improvement is that the line end is the end of a bar graph.

[0031] The length direction of the strip pattern is perpendicular to the direction of the dipole light source.

[0032] A further improvement is that the selected OPC segments include OPC segments formed by the width edges at the line ends and OPC segments located on the length edges, and the selected OPC segments located on the length edges are symmetrically arranged on both sides of the width edges.

[0033] A further improvement is that the number of the selected OPC segments includes more than 3;

[0034] A further improvement is that the cost function further includes the sum of squares of edge placement errors of each of the OPC segments.

[0035] A further improvement is that it also includes: forming an image logarithmic slope of the layout pattern outside the selected area, and the cost function also includes the image logarithmic slope.

[0036] The present invention selects an area with an OPC segment coupling effect, groups the selected OPC segments in the selected area into a segment group, and then forms a corresponding Jacobian matrix. In the Jacobian matrix, the factors affecting the change of the light intensity of each selected OPC segment include the position coordinates of all selected OPC segments in the selected area, so it can accurately reflect the influence of the OPC segment coupling effect, thereby accelerating the OPC convergence speed in the area with a strong OPC segment coupling effect, for example, it can complete convergence with a fewer number of iterations; at the same time, after the OPC correction is completed, the image logarithmic slope at each OPC segment in the selected area can be improved, thereby improving the contrast.

[0037] The present invention is particularly applicable to improving the OPC correction of the line end of a dipole light source, increasing the OPC convergence speed and ultimately improving the lithography contrast. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments:

[0039] Figure 1 is a schematic diagram of an existing dipole light source;

[0040] Figure 2 It is the OPC simulation imaging pattern and layout pattern formed after 8 iterations of the existing MB-OPC lithography using a dipole light source;

[0041] Figure 3 It is the OPC simulation imaging pattern and layout pattern formed after 15 iterations of the existing MB-OPC lithography using a dipole light source;

[0042] Figure 4 is a schematic diagram of the logarithmic slope of the existing image;

[0043] Figure 5 yes Figure 2 The ils values ​​of the OPC simulation imaging graph at various positions are shown;

[0044] Figure 6 yes Figure 3 The ils values ​​of the OPC simulation imaging graph at various positions are shown;

[0045] Figure 7 is a flow chart of a method for improving the lithography performance of a dipole light source according to an embodiment of the present invention;

[0046] Figure 8 A schematic diagram of finding a selected area in a layout pattern in a method for improving the lithography performance of a dipole light source according to an embodiment of the present invention;

[0047] Figure 9The OPC simulation imaging pattern and layout pattern, as well as the ils values ​​at each position of the OPC simulation imaging pattern, are formed after eight iterations of MB-OPC correction according to the method for improving the lithography performance of a dipole light source according to an embodiment of the present invention. DETAILED DESCRIPTION

[0048] like Figure 7 FIG. 1 is a flow chart of a method for improving the lithography performance of a dipole light source according to an embodiment of the present invention. The method for improving the lithography performance of a dipole light source according to an embodiment of the present invention comprises the following steps:

[0049] Step S101: Figure 8 As shown, a selected area 401 having a coupling effect of the OPC segments 304 is found in the publication pattern 301 , and a plurality of adjacent selected OPC segments are selected in the selected area 401 and the selected OPC segments are combined to form a segment group.

[0050] In the embodiment of the present invention, the selected area 401 includes line ends.

[0051] The layout pattern 301 is a bar pattern. The line end is the end of the bar pattern.

[0052] The length direction of the strip pattern is perpendicular to the direction of the dipole light source.

[0053] Depend on Figure 8 As shown, the line segments of the layout pattern 301 between lines 303 are OPC segments 304, and the middle position of the OPC segment 304 is usually selected as the OPC segment evaluation point 305. Sub-resolution auxiliary patterns 302 are also prevented on the periphery of the layout pattern 301.

[0054] The selected OPC segments include the OPC segments 304 formed by the width edge at the line end and the OPC segments 304 located on the length edge. The selected OPC segments located on the length edge are symmetrically arranged on both sides of the width edge.

[0055] In some embodiments, the number of the selected OPC segments is 3 or more.

[0056] Figure 8 In the figure, the number of the selected OPC segments is 5, which are labeled 1 to 5. Increasing the number of the selected OPC segments increases the computational complexity. The actual number of the selected OPC segments can be selected based on the computational complexity and the improvement of the MB-OPC correction result of the selected area 401.

[0057] Step S102: Form a Jacobian matrix corresponding to the segment group, wherein the number of rows and columns of the Jacobian matrix is ​​equal to the number of the selected OPC segments, each element of the row vector of the Jacobian matrix is ​​the derivative of the light intensity of one of the selected OPC segments corresponding to the row vector with respect to the position coordinates of each of the selected OPC segments, and each element of the column vector of the Jacobian matrix is ​​the derivative of the light intensity of each of the selected OPC segments with respect to the position coordinates of one of the selected OPC segments corresponding to the column vector.

[0058] The matrix expression of the Jacobian matrix is:

[0059]

[0060] Wherein, ILS() represents the Jacobian matrix, x1, x2, x3, x4 and x5 represent the position coordinates of the 5 selected OPC segments respectively, and I1, I2, I3, I4 and I5 represent the light intensities of the 5 selected OPC segments.

[0061] Step S103: adding the Jacobian matrix to the cost function, and then performing MB-OPC correction, wherein the light source in the OPC model of the MB-OPC correction is a dipole light source.

[0062] In the embodiment of the present invention, the cost function further includes the sum of squares of edge placement errors of the OPC segments 304 .

[0063] The method further includes forming a logarithmic slope of the image of the layout graphic 301 outside the selected area 401 , and the cost function also includes the logarithmic slope of the image.

[0064] The image logarithmic slope is expressed as follows:

[0065]

[0066] Wherein, ILS represents the logarithmic slope of the image, I represents the light intensity, and x represents the position coordinate.

[0067] As can be seen from the above, the light intensity of the ILS in formula (1) is only related to the position coordinates of the same OPC segment, and does not need to consider the coupling between adjacent OPC segments. In contrast, in formula (2), the five light intensities in ILS() need to consider the coupling effects of adjacent selected OPC segments. Therefore, in the embodiment of the present invention, the ILS in the selected area is improved using the disclosed ILS() in (2), so that the coupling effects of adjacent selected OPC segments can be reflected, which is beneficial to accelerate the convergence of OPC correction and ultimately improve contrast.

[0068] In the embodiment of the present invention, a region having a coupling effect of the OPC segment 304 is selected, and each selected OPC segment of the selected region 401 is grouped into a segment group, and then a corresponding Jacobian matrix is ​​formed. In the Jacobian matrix, factors affecting the change in the light intensity of each selected OPC segment include the position coordinates of all selected OPC segments in the selected region 401. Therefore, the influence of the coupling effect of the OPC segment 304 can be accurately reflected, thereby accelerating the OPC convergence speed in the region where the coupling effect of the OPC segment 304 is strong, for example, achieving convergence with a fewer number of iterations. At the same time, after the OPC correction is completed, the logarithmic slope of the image at each OPC segment 304 in the selected region 401 can be improved, thereby improving the contrast.

[0069] The embodiments of the present invention are particularly suitable for improving the OPC correction of the line end of a dipole light source, increasing the OPC convergence speed and ultimately improving the lithography contrast.

[0070] like Figure 9 As shown, the OPC simulation imaging pattern and the layout pattern 301 are formed after 8 iterations of MB-OPC correction according to the method for improving the lithography performance of the dipole light source according to an embodiment of the present invention, as well as the ils values ​​at each position of the OPC simulation imaging pattern. Figure 9 In the figure, the OPC simulation imaging pattern 301a is the contour pattern formed by simulating the layout pattern 301 after the OPC correction. It can be seen that Figure 2 The corresponding OPC simulation imaging pattern 201a, Figure 9 The OPC simulation imaging graph 301a in the embodiment achieves convergence. Figure 3 In contrast, the embodiment of the present invention only needs 8 iterations to achieve convergence, so the number of iterations is less than Figure 3 There are few corresponding existing methods, so the embodiments of the present invention can accelerate convergence.

[0071] Figure 9 Also shown is the light intensity curve 404a at the line end position corresponding to the arrow line 402, i.e., the 2D graph position, and the light intensity curve 404b at the line area corresponding to the arrow line 403, i.e., the 1D graph position. It can be seen that the ILS of the light intensity curve 404a is greater than 15, and the ILS of the light intensity curve 404b is greater than 30. Figure 5 The light intensity curve 207a and Figure 6 As can be seen from the comparison with the light intensity curve 207c, the ILS of the light intensity curve 404a is increased, so the embodiment of the present invention can well improve the contrast of the line end.

[0072] The OPC segment coupling effect near 2D line ends is very strong, and the movement between them greatly affects each other, so more iterations are required to converge the results. The embodiments of the present invention achieve rapid OPC convergence at 2D line ends and can also help improve the lithography performance of line ends under dipole light sources.

[0073] This embodiment of the present invention combines segmentation during OPC correction, grouping the five segments near the 2D line end into a single group. This grouping is then expressed using a Jacobian matrix, based on the ILS parameter, the most important parameter affecting lithography performance. Each row represents the ILS of a single segment as affected by the movement of all segments within the group. The Jacobian matrix is ​​a key mathematical tool used to describe the derivative of a vector-valued function, representing the optimal linear approximation of a differentiable equation to a given point. Adding this matrix to the cost function can help achieve rapid convergence of 2D line end OPC, while also yielding a more optimal and stable solution.

[0074] The comparison between conventional MB-OPC correction and ILS with Jacobian matrix correction is shown in Table 1:

[0075] Table 1

[0076]

[0077]

[0078] In Table 1, EPE based OPC Iteration = 8 means, Figure 2 Correspondingly, 8 iterations were performed using the existing method; EPE based OPC Iteration = 15 means, Figure 3 Correspondingly, 15 iterations were performed using the existing method; EPE based + Jacobian Matrix Iteration = 8 means that 8 iterations were performed using the method of the embodiment of the present invention; 1D means that the line area is as follows Figure 5 The area corresponding to the arrow line 210, 2D represents the line end position area as shown in FIG. Figure 5 The area corresponding to arrow 209 in the middle shows that the ILS in the 1D region is greater than 30. In the 2D region, only the embodiment of the present invention achieves an ILS greater than 15. Furthermore, a comparison of convergence reveals that the existing method requires 15 iterations to achieve convergence, while the embodiment of the present invention achieves convergence in just 8. Therefore, the method of the embodiment of the present invention can accelerate convergence and increase line end contrast.

[0079] It's also important to note that this embodiment of the present invention is effective only for situations where the coupling effect of 2D line-end OPC segments is very strong and convergence is difficult, such as under a dipole light source. The number of OPC segments within the Jacobian matrix group used in this embodiment of the present invention affects the computational complexity; adding too many segments will result in an unfeasible implementation due to the excessive computational complexity.

[0080] The present invention has been described in detail above by means of specific embodiments, but these do not constitute limitations of the present invention. Without departing from the principles of the present invention, those skilled in the art may make many variations and improvements, which should also be considered as the scope of protection of the present invention.

Claims

1. A method for improving the lithography performance of a dipole light source, characterized in that: Including steps: Finding a selected area with an OPC segment coupling effect in a publication pattern, selecting a plurality of adjacent selected OPC segments in the selected area and combining the selected OPC segments to form a segment group; Forming a Jacobian matrix corresponding to the segment group, wherein the number of rows and columns of the Jacobian matrix is ​​equal to the number of the selected OPC segments, each element of a row vector of the Jacobian matrix is ​​a derivative of the light intensity of one of the selected OPC segments corresponding to the row vector with respect to the position coordinates of each of the selected OPC segments, and each element of a column vector of the Jacobian matrix is ​​a derivative of the light intensity of each of the selected OPC segments with respect to the position coordinates of one of the selected OPC segments corresponding to the column vector; The Jacobian matrix is ​​added to the cost function, and then MB-OPC correction is performed. The light source in the OPC model of the MB-OPC correction is a dipole light source.

2. The method for improving the lithography performance of a dipole light source according to claim 1, wherein: The selected area includes line ends.

3. The method for improving the lithography performance of a dipole light source according to claim 2, wherein: The line end is the end of the bar graph; The length direction of the strip pattern is perpendicular to the direction of the dipole light source.

4. The method for improving the lithography performance of a dipole light source according to claim 3, wherein: The selected OPC segments include OPC segments formed by the width edges at the line ends and OPC segments located on the length edges. The selected OPC segments located on the length edges are symmetrically arranged on both sides of the width edges.

5. The method for improving the lithography performance of a dipole light source according to claim 4, wherein: The number of the selected OPC segments includes 3 or more.

6. The method for improving the lithography performance of a dipole light source according to claim 1, wherein: The cost function also includes a sum of squares of edge placement errors of each of the OPC segments.

7. The method for improving the lithography performance of a dipole light source according to claim 4, wherein: Also includes: An image logarithmic slope of the layout pattern outside the selected area is formed, and the cost function also includes the image logarithmic slope.

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