Optical proximity effect correction method to improve imaging contrast

Abstract

The present invention provides a method for correcting optical proximity effects to enhance imaging contrast. The method comprises providing a target pattern, optically correcting the target pattern to obtain a mask pattern, obtaining an exposed pattern of the mask pattern such that the edge placement error between the exposed pattern and the target pattern is less than a first threshold; forming a tangent line, and determining whether the spatial image contrast of the exposed pattern on either side of the tangent line is greater than a second threshold; if so, further correcting the mask pattern such that its edge placement error is less than the first threshold and its spatial image contrast is greater than the second threshold, and then publishing the mask pattern; if not, publishing the mask pattern. After completing the optical proximity effect correction, the method selects layouts with low spatial image contrast. In addition to the target critical dimension, the spatial image contrast is added as an indicator to guide the final converged mask pattern to have a greater imaging contrast, thereby reducing the risk of line breakage.

Description

Technical Field

[0001] The present invention relates to the field of semiconductor technology, and in particular to an optical proximity effect correction method for improving imaging contrast. Background Art

[0002] Optical proximity correction (OPC) is a lithography resolution enhancement technique that uses computational methods to modify the pattern on the mask so that the pattern projected onto the photoresist closely matches the design requirements. Optical proximity correction (OPC) is a technique that adjusts the topology of the pattern in the light-transmitting areas of the photolithography mask or adds small sub-resolution auxiliary patterns to the mask to ensure that the resulting image in the photoresist closely matches the mask pattern. OPC also compensates for degradation in the lithography system's imaging quality by altering the amplitude of light transmitted through the mask.

[0003] OPC is primarily used in the production of semiconductor devices. During the photolithography process, the pattern on the mask is projected onto the photoresist through an exposure system. Due to optical system imperfections and diffraction effects, the pattern on the photoresist and the pattern on the mask are not completely consistent. If these distortions are not corrected, they can significantly alter the electrical performance of the resulting circuit.

[0004] In the existing technology, only the target critical dimension used in optical proximity effect correction is used as an indicator to reduce the single-side error to zero. This approach has a certain degree of randomness and may increase the risk of wire breakage under certain layouts.

[0005] For example, see Figure 1 , Figure 1 The target pattern is 101, the corrected mask pattern is 102, the simulated exposure profile of the mask pattern 102 is the exposed pattern 103, and the distance between the exposed pattern 103 and the target pattern 101 is the edge placement error. Figure 2A is the tangent line at the pattern 103 after exposure, Figure 2B The photoresist forming condition at the tangent line is shown. Due to the low image contrast, the photoresist forming will be affected (such as Figure 2C shown).

[0006] In order to solve the above problems, it is necessary to propose a new optical proximity effect correction method to improve imaging contrast. Summary of the Invention

[0007] In view of the shortcomings of the prior art described above, the present invention aims to provide a method for correcting the optical proximity effect to improve imaging contrast. This method is used to address the problem in the prior art of reducing the unilateral error to zero by only using the target critical dimension used in optical proximity effect correction. This approach has a certain degree of randomness and may increase the risk of wire breakage under certain layouts.

[0008] To achieve the above-mentioned and other related objectives, the present invention provides a method for correcting the optical proximity effect for improving imaging contrast, which at least comprises:

[0009] Step 1: providing a target pattern, optically correcting the target pattern to obtain a mask pattern, and obtaining an exposed pattern of the mask pattern so that an edge placement error between the exposed pattern and the target pattern is less than a first threshold;

[0010] Step 2: forming a tangent line, and determining whether the aerial image contrast of the exposed pattern on both sides of the tangent line is greater than a second threshold; wherein the aerial image contrast refers to the ratio of the difference between the maximum light intensity and the minimum light intensity in the region having the bright and dark images divided by the sum of the two;

[0011] If yes, continue to correct the mask pattern so that its edge placement error is less than the first threshold and the aerial image contrast is greater than the second threshold, and then publish the mask pattern;

[0012] If not, the mask pattern is published.

[0013] Preferably, the shape of the target graphic in step 1 is an irregular polygon composed of multiple rectangles.

[0014] Preferably, the method of optically correcting the target pattern to obtain the mask pattern in step 1 includes: using OPC software to form a plurality of continuous line segments based on the contour of the target pattern, and then moving the line segments to obtain the mask pattern. Preferably, the method of obtaining the exposed pattern of the mask pattern in step 1 includes: using OPC software to simulate the exposure result of transferring the mask pattern to the photoresist layer, thereby obtaining the exposed pattern.

[0015] Preferably, the tangent line in step 2 is formed between angular line segment patterns on the mask pattern, and the angular line segment pattern is a pattern of a concave portion of the mask pattern.

[0016] Preferably, the tangent line in step 2 is formed at the midpoint of the bottom edge of the angle segment pattern, so that the shapes of the exposed pattern along both sides of the tangent line are approximately the same.

[0017] Preferably, the angle segment graphic in step 2 is one.

[0018] Preferably, in step 2, there are two angle segment graphics.

[0019] Preferably, the two angle segment graphics in step 2 are symmetrical structures to each other.

[0020] Preferably, the mask pattern published in step 2 is a closed pattern composed of multiple line segments.

[0021] As described above, the optical proximity effect correction method for improving imaging contrast of the present invention has the following beneficial effects:

[0022] After completing the optical proximity effect correction, the method of the present invention selects layouts with low spatial image contrast. In addition to the target critical dimension, the spatial image contrast is added as an indicator to guide the final converged mask layout to have a larger imaging contrast, thereby reducing the risk of line breakage. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 Shown is a schematic diagram of a layout OPC of the prior art;

[0024] Figure 2A Shown is a schematic diagram of the layout tangent position of the prior art;

[0025] Figure 2B Shown is a schematic diagram of a photoresist molding structure at a tangent line of the prior art;

[0026] Figure 2C Shown is a schematic diagram of photoresist molding data in the prior art;

[0027] Figure 3A Shown is a schematic diagram of an improved OPC according to the second embodiment of the present invention;

[0028] Figure 3B Shown is a schematic diagram of improved OPC photoresist molding data according to embodiment 2 of the present invention;

[0029] Figure 4A The second embodiment of the present invention is shown in the OPC schematic diagram of the prior art;

[0030] Figure 4B Shown is a schematic diagram of an improved OPC according to the second embodiment of the present invention;

[0031] Figure 4C A schematic diagram showing comparison of photoresist molding data of the prior art and the improved OPC;

[0032] Figure 5 It is a schematic diagram of the optical proximity effect correction method for improving imaging contrast according to the present invention. DETAILED DESCRIPTION

[0033] The following describes the embodiments of the present invention through specific examples. Those skilled in the art will readily understand the other advantages and benefits of the present invention from the disclosure herein. The present invention may also be implemented or applied through various other specific embodiments, and the details in this specification may be modified or altered based on different viewpoints and applications without departing from the spirit of the present invention. Example 1

[0034] See also Figure 5 The present invention provides a method for correcting the optical proximity effect to improve imaging contrast, which at least comprises:

[0035] Step 1: providing a target pattern 101, optically correcting the target pattern 101 to obtain a mask pattern 102, and obtaining an exposed pattern 103 of the mask pattern 102 so that an edge placement error between the exposed pattern 103 and the target pattern 101 is less than a first threshold;

[0036] In an embodiment of the present invention, the shape of the target graphic 101 in step 1 is an irregular polygon composed of multiple rectangles.

[0037] In an embodiment of the present invention, the method of optically correcting the target pattern 101 to obtain the mask pattern 102 in step 1 includes: using OPC software to form multiple continuous line segments according to the outline of the target pattern 101, and then moving the line segments to obtain the mask pattern 102.

[0038] In an embodiment of the present invention, the method for obtaining the exposed pattern 103 of the mask pattern 102 in step 1 is: using OPC software to simulate the exposure result of transferring the mask pattern 102 to the photoresist layer, thereby obtaining the exposed pattern 103.

[0039] Step 2: Form a tangent line 104 and determine whether the aerial image contrast of the exposed pattern 103 and the mask pattern 102 on both sides of the tangent line 104 is greater than a second threshold. That is, during the photolithography process, the imaging contrast of the photoresist layer is measured along the tangent line 104. Aerial image contrast refers to the ratio of the difference between the maximum and minimum light intensities in the region with bright and dark images divided by the sum of the two.

[0040] If yes, continue to correct the mask pattern 102 so that its edge placement error is less than the first threshold and the aerial image contrast is greater than the second threshold, and then publish the mask pattern 102;

[0041] If not, the mask pattern 102 is published. In conventional optical proximity effect correction, the target critical dimension is used as the sole convergence indicator. The present invention measures image contrast along the cutline 104 , which can improve the image contrast by approximately 10% compared to conventional techniques, thereby reducing the risk of layout breakage.

[0042] In an embodiment of the present invention, the tangent line 104 in step 2 is formed between the corner segment patterns 105 on the mask pattern 102. The corner segment patterns 105 are the patterns at the concave parts of the mask pattern 102. The patterns at the corner segment patterns 105 are relatively complex and will affect the photolithography effect.

[0043] In an embodiment of the present invention, the tangent line 104 in step 2 is formed at the midpoint of the bottom edge of the angle segment pattern 105, so that the partial or complete shapes of the pattern 103 on both sides of the tangent line 104 after exposure are close to the same.

[0044] In an embodiment of the present invention, the number of angle segment graphics 105 in step 2 is one.

[0045] In an embodiment of the present invention, there are two angle segment graphics 105 in step 2.

[0046] In the embodiment of the present invention, the two angle segment graphics 105 in step 2 are symmetrical structures to each other.

[0047] In an embodiment of the present invention, the mask pattern 102 generated in step 2 is a closed pattern composed of multiple line segments. Example 2

[0048] For example, see Figure 1 , Figure 1 The target pattern is 101, the corrected mask pattern is 102, the simulated exposure profile of the mask pattern 102 is the exposed pattern 103, the exposed pattern 103 is a structure that is approximately symmetrical to each other, and the distance between the exposed pattern 103 and the target pattern 101 is the edge placement error. Figure 2A is the tangent line 104 at the pattern 103 after exposure, Figure 2B The photoresist forming condition at the cut line 104 is shown. Due to the low image contrast, the photoresist forming is affected (eg Figure 2C shown).

[0049] Please refer to the figure after correction using the method of the present invention. Figure 3A , that is, a tangent line 104 is formed between the two corner line segments of the mask pattern, and spatial image contrast is introduced in the correction. The photoresist molding result at the tangent line 104 can be found in Figure 3B , which was improved by 9%. Example 3

[0050] For example, see Figure 4A , Figure 4A The target pattern is 101, the corrected mask pattern is 102, the simulated exposure profile of the mask pattern 102 is the exposed pattern, the exposed pattern is an asymmetric structure, and the distance between the exposed pattern and the target pattern 101 is the edge placement error. Only the edge prevention error is introduced as the OPC indicator in the correction.

[0051] Please refer to the figure after correction using the method of the present invention. Figure 4B , that is, a tangent line 104 is formed between the two corner line segments 105 of the mask pattern, and spatial image contrast is introduced in the correction. The photoresist molding results at the tangent line 104 before and after the improvement can be found in Figure 4C , which was improved by 28.6%.

[0052] It should be noted that the illustrations provided in this embodiment are only used to schematically illustrate the basic concept of the present invention. Therefore, the illustrations only show components related to the present invention and are not drawn according to the number, shape and size of components in actual implementation. In actual implementation, the type, quantity and proportion of each component can be changed at will, and the component layout type may also be more complicated.

[0053] In summary, after correcting for optical proximity effects, the method of the present invention selects layouts with low spatial image contrast. In addition to the target critical dimension, this method incorporates spatial image contrast as a metric, guiding the final converged reticle layout to have greater imaging contrast, thereby reducing the risk of line breakage. Therefore, this method effectively overcomes the shortcomings of existing technologies and possesses high industrial value.

[0054] The above embodiments are merely illustrative of the principles and effects of the present invention and are not intended to limit the present invention. Anyone skilled in the art may modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by one of ordinary skill in the art without departing from the spirit and technical principles disclosed herein are intended to be covered by the claims of the present invention.

Claims

1. A method for correcting the optical proximity effect to improve imaging contrast, characterized in that: At least: Step 1: providing a target pattern, optically correcting the target pattern to obtain a mask pattern, and obtaining an exposed pattern of the mask pattern so that an edge placement error between the exposed pattern and the target pattern is less than a first threshold; Step 2: forming a tangent line, and determining whether the aerial image contrast of the exposed pattern on both sides of the tangent line is greater than a second threshold; the tangent line is formed at the midpoint of the bottom edge of an angular line segment pattern on the mask pattern, so that the shapes of part or all of the exposed pattern along both sides of the tangent line are approximately the same, and the angular line segment pattern is the pattern of the concave portion of the mask pattern; there are two angular line segment patterns, and the two angular line segment patterns are symmetrical to each other; wherein the aerial image contrast refers to the ratio of the difference between the maximum light intensity and the minimum light intensity in the area having the bright and dark images divided by the sum of the two; If the aerial image contrast is not greater than the second threshold, then continue to correct the mask pattern so that its edge placement error is less than the first threshold and the aerial image contrast is greater than the second threshold, and then publish the mask pattern; If the aerial image contrast is greater than the second threshold, the mask pattern is published.

2. The method for correcting the optical proximity effect for improving imaging contrast according to claim 1, wherein: The shape of the target graphic in step 1 is an irregular polygon composed of multiple rectangles.

3. The method for correcting the optical proximity effect for improving imaging contrast according to claim 1, wherein: The method of optically correcting the target pattern to obtain a mask pattern in step 1 includes: using OPC software to form a plurality of continuous line segments according to the outline of the target pattern, and then moving the line segments to obtain the mask pattern.

4. The method for correcting the optical proximity effect for improving imaging contrast according to claim 3, wherein: The method for obtaining the exposed pattern of the mask pattern in step 1 is: using OPC software to simulate the exposure result of transferring the mask pattern to the photoresist layer, thereby obtaining the exposed pattern.

5. The method for correcting the optical proximity effect for improving imaging contrast according to claim 1, wherein: The angle segment graphic in step 2 is one.

6. The method for correcting the optical proximity effect for improving imaging contrast according to claim 1, wherein: The mask pattern published in step 2 is a closed pattern composed of multiple line segments.

Images