Methods for making a photomask

Abstract

This invention provides a method for fabricating a photomask, belonging to the field of integrated circuit manufacturing. Before transferring the layout onto a photomask substrate, the method involves detecting the original layout and smoothing multiple consecutive small stepped patterns with minimum dimensions smaller than a set value on the oblique edges of the original layout. This ensures that all patterns in the corrected layout are larger than the minimum exposure size of the exposure machine. Consequently, the exposed pattern formed based on the corrected layout does not contain any patterns smaller than the minimum exposure size of the exposure machine. This improves upon the defect where normal imaging is impossible on the exposure machine due to exposure energy limitations, and enhances the consistency between the pattern formed using this photomask and the original layout.

Description

Technical Field

[0001] This invention relates to the field of integrated circuit manufacturing, and more particularly to a method for fabricating a photomask. Background Technology

[0002] A photomask is a critical component in semiconductor manufacturing. Its core function is to act as a "template" in the photolithography process, precisely transferring the layout of integrated circuits or optical devices onto a silicon wafer. It consists of a high-purity quartz substrate and a light-shielding layer (such as chromium). Pre-fabricated micro- and nano-patterns control the exposure area of ​​the photolithography machine, thereby forming the desired circuit patterns or optical structures on the silicon wafer. Photomasks are widely used in chip manufacturing (such as CPUs and memory), silicon photonic devices (such as optical waveguides), and CMOS image sensors (CIS). Their precision directly affects the performance and yield of devices, serving as a bridge between design blueprints and actual products.

[0003] Layout is the physical realization of integrated circuit or optoelectronic device design. It precisely describes the shape, size, and spatial relationships of each layer of the chip structure through geometric shapes (such as polygons, paths, and vias). Based on design rules (DRC) and process constraints, it transforms the circuit schematic into manufacturable graphical data (such as GDSII format) and optimizes it using optical proximity correction (OPC) to adapt to photolithography processes. Layout design directly affects device performance (such as signal integrity and power consumption) and yield, and is a critical link between circuit design and chip manufacturing. It is widely used in digital / analog ICs, silicon photonics chips, and sensors.

[0004] Currently, in the layout design of silicon photonics products and CMOS image sensor (CIS) products, continuous regular or irregular small stepped patterns frequently appear in the beveled edges, curved edges, or curved graphics. The reason for the formation of these small stepped patterns is as follows:

[0005] I. Resolution Limitations of Photolithography. The resolution of a photolithography machine is limited by the exposure wavelength and numerical aperture, making it impossible to directly and perfectly reproduce the ideal bevel or curve in the design. Therefore, optical correction software decomposes the bevel or curved edge into a series of stepped patterns of fixed size, ensuring that it can be correctly exposed and approximate the target shape during photolithography.

[0006] II. Optical Proximity Effect (OPE) Compensation. During photolithography, due to light diffraction and interference, adjacent patterns affect each other, causing deviations between the actual exposed pattern and the design pattern (e.g., narrower linewidth, rounded corners). Optical correction software (such as OPC) pre-calculates these deviations and adjusts the pattern in the following ways: Regularization: The hypotenuse is decomposed into multiple small rectangles (steps), and the size of each step is optimized so that the actual exposed pattern is closer to the design target. Edge Segmentation Optimization: The hypotenuse or curved edge is segmented to ensure that each segment achieves the best exposure effect during photolithography.

[0007] Third, in layout design, graphic designers may easily produce irregular, continuous small-sized graphics when defining the number of vertices of a polygon by calculation or manual setting.

[0008] During photomask exposure, semiconductor equipment aims to ensure that the exposure result closely matches the photomask. Figure 1 The electron beam lithography machine cuts the image into quadrilaterals of different sizes according to the shape of the image. The minimum exposure size (shot size) of the electron beam lithography machine is 40nm. When the quadrilateral is too small, the exposure energy cannot be captured. Such continuous small-sized stepped patterns cannot be properly imaged on the exposure machine due to the limited exposure energy, resulting in poor exposure results in this area and affecting the mask quality.

[0009] Specifically, Figure 1 It is the original map. Figure 2 yes Figure 1 Enlarged diagram of region A in the middle. Figure 3 yes Figure 1 An image showing the imaging effect of a portion of the original map after exposure, such as... Figure 1 and Figure 2 As shown, the hypotenuse of the original map has a series of small stepped shapes, such as... Figure 3 As shown, the slanted area of ​​the original map differs from the original map after exposure. The area circled in frame C is the area that should have been exposed for imaging but was not actually imaged after exposure.

[0010] Therefore, improving the consistency between the exposed graphic and the original map is one of the key research focuses. Summary of the Invention

[0011] The technical problem to be solved by the present invention is to provide a method for manufacturing a photomask that can optimize the imaging of continuous small step patterns and improve the consistency between the pattern exposed using the photomask and the original pattern.

[0012] To address the aforementioned problems, this invention provides a method for fabricating a photomask, comprising the following steps: providing an original layout; detecting the original layout; if the original layout has multiple consecutive small stepped patterns on its oblique edge, smoothing the multiple consecutive small stepped patterns to obtain a corrected layout, wherein the minimum size of the small stepped patterns is less than a set value, the set value being less than or equal to 1.5 times the minimum exposure size of the exposure machine and greater than 1 times the minimum exposure size of the exposure machine; converting the corrected layout into an exposure pattern and transferring the exposure pattern onto a photomask substrate to form a photomask.

[0013] In one specific embodiment, the method for detecting the original map includes: detection based on edge tracing.

[0014] In one specific embodiment, when the length of the region containing a series of small step patterns in the original layout is greater than a first limit value, the series of small step patterns are smoothed. The first limit value is 100 nanometers.

[0015] In one specific implementation, when the length of the region containing a series of small step shapes in the original layout is greater than a second limiting value, the series of small step shapes are segmented and smoothed, and the second limiting value is twice the first limiting value.

[0016] In one specific embodiment, the step of detecting the original layout further includes: obtaining all the step patterns of the hypotenuse of the original layout, and determining from all the step patterns whether there are multiple consecutive small step patterns.

[0017] In one specific embodiment, the set value is determined based on the density of the stepped pattern; the higher the density of the stepped pattern, the higher the set value.

[0018] In one specific embodiment, in the step of detecting the original layout, a correspondence is established between the density of the stepped pattern and the set value, and the step pattern is determined to be the small stepped pattern based on the correspondence.

[0019] In one specific embodiment, the method for smoothing the continuous series of small step shapes includes one of polygon approximation, vertex merging, and curve fitting.

[0020] In one specific embodiment, the minimum size of the small step shape is the length of the shortest side of the small step shape.

[0021] In one specific embodiment, after the step of smoothing the continuous series of small step patterns, the method further includes: comparing the corrected layout with the original layout to ensure geometric consistency.

[0022] In one specific embodiment, after the step of smoothing the continuous series of small stepped graphics, the method further includes: performing simulation processing on the corrected layout and checking whether the critical dimensions and edge placement errors meet the requirements.

[0023] The method for fabricating the mask of the present invention involves detecting the original pattern before transferring the pattern onto the mask substrate, and smoothing out multiple consecutive small stepped patterns with a minimum size smaller than a set value on the oblique edge of the original pattern. This ensures that the size of all patterns in the corrected pattern is larger than the minimum exposure size of the exposure machine. Consequently, the exposed pattern formed based on the corrected pattern does not contain any patterns smaller than the minimum exposure size of the exposure machine, thereby improving the defect that the exposure machine cannot form a normal image due to exposure energy limitations. This enhances the consistency between the pattern formed using the mask and the original pattern. Attached Figure Description

[0024] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0025] Figure 1 It is the original map;

[0026] Figure 2 yes Figure 1 Enlarged view of region A in the middle;

[0027] Figure 3 yes Figure 1 An image showing the effect of exposing a portion of the original map.

[0028] Figure 4 This is a schematic diagram illustrating the steps of a specific embodiment of the method for manufacturing a mask according to the present invention;

[0029] Figure 5 This is a partial schematic diagram of the arc-shaped area of ​​the original map;

[0030] Figure 6 This is an enlarged schematic diagram of the arc-shaped area of ​​the original map;

[0031] Figure 7 This is a partial schematic diagram of the arc-shaped area of ​​the revised map;

[0032] Figure 8 This is a schematic diagram of the exposure pattern formed by the modified layout according to the present invention;

[0033] Figure 9It is based on Figure 5 The diagram shows the exposure pattern formed from the original map. Detailed Implementation

[0034] The specific implementation method of the mask manufacturing method provided by the present invention will be described in detail below with reference to the accompanying drawings.

[0035] Figure 4 This is a schematic diagram illustrating the steps of a specific embodiment of the method for fabricating the mask of the present invention. Please refer to [link / reference]. Figure 4 The method for fabricating the mask includes: step S40, providing an original layout; step S41, detecting the original layout, and if the original layout has multiple consecutive small stepped patterns on its oblique edge, smoothing the multiple consecutive small stepped patterns to obtain a corrected layout, wherein the minimum size of the small stepped patterns is less than a set value, the set value is less than or equal to 1.5 times the minimum exposure size of the exposure machine, and greater than 1 times the minimum exposure size of the exposure machine; step S42, converting the corrected layout into an exposure pattern, and transferring the exposure pattern onto a mask substrate to form a mask.

[0036] The mask fabrication method of this invention, before transferring the pattern to the mask substrate, detects the original pattern and smooths out multiple small stepped patterns with consecutive minimum dimensions smaller than a set value on the oblique edges of the original pattern. This ensures that the dimensions of all patterns in the corrected pattern are larger than the minimum exposure size of the exposure machine. Therefore, the exposed pattern formed based on the corrected pattern does not contain any patterns smaller than the minimum exposure size of the exposure machine, thus improving the defect that prevents normal imaging on the exposure machine due to exposure energy limitations. This enhances the consistency between the pattern formed using this mask and the original pattern. The oblique edges of the original pattern refer to edges with tilt angles other than 0 degrees, 90 degrees, 180 degrees, and 270 degrees, to avoid altering the OPC-processed pattern during the smoothing of these consecutive small stepped patterns, thereby affecting the process performance.

[0037] refer to Figure 5 And step S40, providing an original map, wherein, Figure 5 This is a partial schematic diagram of the arc-shaped area of ​​the original map. The arc-shaped area of ​​the original map contains multiple stepped shapes. The edge of the arc-shaped area of ​​the original map is formed by lines connecting three consecutive vertices, creating two sides with an included angle greater than 0° and less than 180°. These two sides form a stepped shape, and the minimum size of the stepped shape refers to the length of the shortest side. Specifically, as... Figure 6As shown, it is an enlarged schematic diagram of the arc-shaped area of ​​the original map. The edge of the arc-shaped area of ​​the original map passes through three consecutive vertices 600, 601, and 602. The line connecting these three vertices 600, 601, and 602 forms two sides 610 and 611. These two sides 610 and 611 have an included angle, which is greater than 0° and less than 180°. These two sides 610 and 611 form a stepped shape. The minimum size of the stepped shape refers to the length of the shortest side, that is, the minimum size of the stepped shape is the length of the shortest side of the stepped shape.

[0038] refer to Figure 7 In step S41, the original layout is detected. If the oblique edge of the original layout contains multiple consecutive small stepped shapes, these consecutive small stepped shapes are smoothed to obtain a corrected layout. The minimum size of the small stepped shapes is less than a set value, which is less than or equal to 1.5 times the minimum exposure size of the exposure machine and greater than 1 times the minimum exposure size of the exposure machine. Figure 7 This is a partial schematic diagram of the arc-shaped area of ​​the revised map.

[0039] Because consecutive small stepped patterns will form small-sized patterns during the exposure process, these small patterns may not be properly imaged on the exposure machine due to exposure energy limitations, resulting in poor exposure results in this area and affecting mask quality. Therefore, this step detects the original pattern to determine whether there are multiple consecutive small stepped patterns on its hypotenuse. If multiple consecutive small stepped patterns are present in the original pattern, they are smoothed to correct the area of ​​consecutive small stepped patterns in the original pattern; if no multiple consecutive small stepped patterns are present in the original pattern, the smoothing step can be skipped, and subsequent steps can proceed directly.

[0040] The photomask fabrication method of this invention smooths out consecutive small stepped patterns with minimum dimensions smaller than a set value in the original pattern before forming the exposure pattern for transfer onto the photomask substrate. This avoids the formation of consecutive small-sized patterns in the exposure pattern, thus preventing defects such as partial areas of the exposure pattern failing to image properly on the exposure machine due to exposure energy limitations, and improving the consistency between the exposed pattern and the original pattern. Furthermore, by pre-forming a corrected pattern before forming the photomask, this invention eliminates the need for post-fabrication inspection to detect and correct photomask defects, significantly saving costs and improving production efficiency.

[0041] In one specific embodiment, the original layout is converted from the original design drawing into GDSII / OASIS format. The step of detecting the original layout further includes: performing grid-based representation on the original layout to convert it into grid data for subsequent processing and detection. Specifically, grid-based representation of the original layout in GDSII / OASIS format is the process of converting the continuous geometry of the original layout into discrete grid data, which facilitates subsequent graphic detection, analysis, and processing (such as the recognition of small staircase graphics). In some specific embodiments, the original layout can be quickly grid-based using Electronic Design Automation (EDA) software.

[0042] In one specific embodiment, the method for detecting the original map includes: detection based on edge tracing. Specifically, a vertex sequence is extracted along the contour of the original map, and the lengths and angles of adjacent edges are calculated to determine whether there are multiple consecutive small step shapes in the original map.

[0043] In one specific implementation, when the length of the region containing a series of small stepped patterns in the original pattern is greater than a first limit value, the series of small stepped patterns are smoothed. The first limit value is 100 nanometers. When the first limit value is too small, the presence of small stepped patterns will not affect the size of the exposed pattern, and thus will not affect normal imaging. If smoothing is still performed at this time, the program will not be simplified, and the complexity of the program processing will be increased.

[0044] In one specific embodiment, when the length of the region containing multiple consecutive small stepped graphics in the original layout is greater than a second limiting value, the graphics are smoothed in segments. The second limiting value is twice the first limiting value. If the length of the region containing the small stepped graphics is too long, smoothing all the small stepped graphics uniformly may produce a large error. In this specific embodiment, when the second limiting value is twice the first limiting value, and the length of the region containing multiple consecutive small stepped graphics in the original layout is greater than the second limiting value, the multiple consecutive small stepped graphics are divided into at least two segments, and each segment is smoothed separately. This can greatly reduce the error and make the consistency between the exposed graphic and the original layout higher. In one specific embodiment, the number of segments into which the multiple consecutive small stepped graphics are divided can be determined according to the length of the region containing the small stepped graphics. The longer the region containing the small stepped graphics is, the more segments it should be divided into.

[0045] In one specific embodiment, the step of detecting the original layout further includes: obtaining all the stepped patterns on the hypotenuse of the original layout, and determining from all the stepped patterns whether there are multiple consecutive small stepped patterns. Specifically, during the detection of the original layout, all the stepped patterns on the hypotenuse of the original layout are obtained. When the minimum size of the stepped pattern is less than the set value, the stepped pattern is determined to be a small stepped pattern that satisfies this step. The minimum size of the small stepped pattern is the length of the shortest side of the small stepped pattern, which is less than the set value.

[0046] The set value is determined based on the minimum exposure size of the exposure machine, with a maximum of 1.5 times the minimum exposure size and a minimum of 1 times the minimum exposure size. The specific value of the set value can be set according to the mask manufacturing requirements to meet those requirements. For example, the set value can be 1.5 times the minimum exposure size of the exposure machine, 1.3 times the minimum exposure size of the exposure machine, or 1 times the minimum exposure size of the exposure machine.

[0047] Furthermore, the inventors discovered that the density of the stepped patterns has a significant impact on the size of the exposed pattern; the higher the density of the stepped patterns, the greater the impact on the size of the exposed pattern. Here, the density of the stepped patterns refers to the number of stepped patterns per unit arc length. If a fixed set value is set, when the density of the stepped patterns is large and exceeds the set value, these stepped patterns are not considered small stepped patterns, but they still affect the size of the exposed pattern. Therefore, the inventors further propose dynamically determining the set value based on the density of the stepped patterns. The higher the density of the stepped patterns, the larger the corresponding set value, with the maximum set value being 1.5 times the minimum exposure size of the exposure machine and the minimum being 1 times the minimum exposure size of the exposure machine. Specifically, when the density of the stepped patterns is large, a larger set value can be set to smooth more stepped patterns, further improving image quality; when the density of the stepped patterns is small, a smaller set value can be set.

[0048] In one specific embodiment, during the step of detecting the original pattern, a correspondence is established between the density of the stepped pattern and a set value, and the correspondence is used to determine whether the stepped pattern is the small stepped pattern. This correspondence can be set based on the actual manufacturing requirements of the mask and the designer's experience.

[0049] In one specific embodiment, the method for smoothing the continuous series of small stepped shapes includes one of polygon approximation, vertex merging, and curve fitting. Polygon approximation refers to approximating the original shape with fewer but smoother edges, such as the Douglas-Peucker algorithm; vertex merging refers to merging adjacent vertices that are too close together to eliminate small steps; curve fitting refers to replacing jagged edges with Bézier curves or spline curves. In one specific embodiment, the above smoothing method can be implemented using Electronic Design Automation (EDA) software.

[0050] In one specific implementation, when smoothing the continuous series of small step shapes, the vertical step size of this step needs to be set to be less than the set value in order to achieve smoothing of the small step shapes.

[0051] In one specific embodiment, after the step of smoothing the consecutive multiple small step shapes, the method further includes: comparing the corrected layout with the original layout to ensure geometric consistency. Specifically, the corrected layout is compared with the original layout to ensure that the corrected layout is completely contained within the error band of the original layout.

[0052] In one specific embodiment, after the step of smoothing the continuous series of small step patterns, the method further includes: performing simulation processing on the corrected layout and checking whether the critical dimensions and edge placement errors meet the requirements, so as to further ensure that the corrected layout is completely contained within the error band of the original layout.

[0053] Please refer to step S42 to convert the corrected layout into an exposure pattern, and transfer the exposure pattern onto the mask substrate to form a mask.

[0054] In one specific embodiment, the method for converting the modified layout into an exposure pattern includes: cutting the modified layout into quadrilaterals of different sizes according to the shape of the modified layout based on the present invention, thereby forming an exposure pattern, such as... Figure 8 As shown, it is a schematic diagram of the exposure pattern formed by the modified layout according to the present invention.

[0055] like Figure 9 As shown, it is a schematic diagram of an exposure pattern formed based on the original map. The method for forming this exposure pattern includes: based on... Figure 5 The original map shown is cut into quadrilaterals of different sizes to form an exposure pattern. Figure 8 as well as Figure 9As can be seen, compared with the exposure pattern formed based on the original pattern, the exposure pattern formed by the pattern modified according to the present invention does not have the problem of the quadrilateral being too small, which improves the defect of being unable to form a normal image due to the limitation of exposure energy and improves the mask quality.

[0056] In one specific embodiment, the method for transferring an exposure pattern onto the mask substrate includes: writing the exposure pattern onto the mask substrate; and forming the mask by developing and etching processes and cleaning processes.

[0057] The method for fabricating the mask of the present invention involves detecting the original pattern before transferring the pattern onto the mask substrate, and smoothing out multiple consecutive small stepped patterns with minimum dimensions smaller than a set value on the oblique edge of the original pattern. This ensures that the dimensions of all patterns in the corrected pattern are larger than the minimum exposure size of the exposure machine. Consequently, the exposure pattern formed based on the corrected pattern does not contain any patterns smaller than the minimum exposure size of the exposure machine, thereby improving the defect that normal imaging cannot be achieved on the exposure machine due to exposure energy limitations. This enhances the consistency between the mask pattern formed using this mask and the original pattern.

[0058] It should be noted that the terms "comprising" and "having," and their variations, used in this invention document are intended to cover non-exclusive inclusion. The terms "first," "second," etc., are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence, unless explicitly indicated by the context; it should be understood that such use of data can be interchanged where appropriate. The term "one or more" depends at least in part on the context and can be used to describe features, structures, or characteristics in a singular sense, or in a plural sense to describe combinations of features, structures, or characteristics. The term "based on" can be understood as not necessarily intended to express an exclusive set of factors, but can instead, also at least in part on the context, allow for the presence of other factors that are not necessarily explicitly described. Furthermore, embodiments and features in embodiments of this invention can be combined with each other without conflict. In addition, descriptions of well-known components and technologies have been omitted in the above description to avoid unnecessarily obscuring the concepts of this invention. In the various embodiments described above, each embodiment focuses on its differences from other embodiments; similar / identical parts between embodiments can be referred to mutually.

[0059] The above description is only a preferred embodiment of the present invention. It should be noted that those skilled in the art can make several improvements and modifications without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method of manufacturing a reticle, characterized by, The method comprises the following steps: providing an original layout; detecting the original layout, and if there are continuous multiple small step patterns in the original layout, performing smoothing processing on the continuous multiple small step patterns to obtain a modified layout, the minimum size of the continuous multiple small step patterns being less than a set value, the set value being less than or equal to 1.5 times the minimum exposure size of an exposure machine and greater than 1 times the minimum exposure size of the exposure machine; converting the modified layout into an exposure pattern, and transferring the exposure pattern to a mask substrate to form a mask.

2. The method of manufacturing a reticle according to claim 1, wherein The method for detecting the original layout comprises edge tracking.

3. The method of manufacturing a reticle according to claim 1, wherein When the length of the region where the continuous multiple small step patterns are located in the original layout is greater than a first limit value, the continuous multiple small step patterns are subjected to smoothing processing, the first limit value being 100 nm.

4. The method of manufacturing a reticle according to claim 3, wherein When the length of the region where the continuous multiple small step patterns are located in the original layout is greater than a second limit value, the continuous multiple small step patterns are segmented and subjected to smoothing processing, the second limit value being 2 times the first limit value.

5. The method of manufacturing a reticle according to claim 1, wherein The step of detecting the original layout further comprises obtaining all step patterns of the original layout, and determining whether there are continuous multiple small step patterns from all the step patterns.

6. The method of manufacturing a reticle according to claim 5, wherein The set value is determined according to the density of the step patterns, the greater the density of the step patterns, the greater the set value.

7. The method of manufacturing a reticle according to claim 6, wherein In the step of detecting the original layout, a corresponding relationship between the density of the step patterns and the set value is set, and whether the step patterns are the small step patterns is determined according to the corresponding relationship.

8. The method of manufacturing a reticle according to claim 1, wherein The method for performing smoothing processing on the continuous multiple small step patterns comprises one of polygon approximation, vertex merging and curve fitting.

9. The method of manufacturing a reticle according to claim 1, wherein The minimum size of the small step patterns is the length of the shortest side of the small step patterns.

10. The method of manufacturing a reticle according to claim 1, wherein After the step of performing smoothing processing on the continuous multiple small step patterns, the modified layout is compared with the original layout to ensure geometric consistency.

11. The method of manufacturing a reticle according to claim 1, wherein After the step of performing smoothing processing on the continuous multiple small step patterns, simulation processing is performed on the modified layout, and whether the critical dimension and edge placement error meet the requirements is checked.

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