Mask, alignment mark and photolithography system
By using two-dimensional linear patterned masks and alignment marks in photolithography, the problem of poor overlay accuracy was solved, achieving a high-precision photolithography process, reducing rework rate and production costs, and improving product yield.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- SEMICON MFG INT (SHANGHAI) CORP
- Filing Date
- 2021-03-16
- Publication Date
- 2026-07-21
AI Technical Summary
Poor overlay accuracy in existing photolithography technologies leads to high rework rates and increased production costs. In particular, the reduced thickness of the alignment pattern during chemical mechanical polishing affects overlay accuracy and product yield.
By using a two-dimensional linear pattern mask and alignment marks, multiple spaced combination patterns and alignment patterns are formed on the mask to create periodically arranged moiré patterns, thereby increasing the intensity of the first-order diffraction signal of the alignment system and enhancing the alignment signal intensity.
It improves overlay accuracy, reduces rework rate and production costs, enhances alignment signal strength, and ensures the accuracy of the photolithography process and product yield.
Smart Images
Figure CN116097173B_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of semiconductor manufacturing, and more particularly to a photomask, alignment marks, and photolithography system. Background Technology
[0002] With the development of integrated circuit technology, the feature size that needs to be realized on the wafer is getting smaller and smaller. Therefore, the precision requirements of photolithography technology for photolithography process and photolithography system will also become higher and higher.
[0003] A complete chip manufacturing process typically involves multiple photolithography steps. Photolithography is the process of forming a mask in semiconductor production. It involves basic steps such as workpiece loading, alignment of the workpiece to be processed area with the mask, workpiece exposure, and workpiece unloading. Especially when the workpiece pattern requires multiple exposures, precise alignment of the workpiece to be processed area with the mask is a prerequisite for ensuring that the workpiece is correctly processed as the linewidth continues to shrink. In order to ensure that the pattern overlay offset between different layers is within specifications, alignment marks are formed in the previous layer for alignment during the subsequent layer photolithography process. After alignment is completed, the pattern is accurately projected onto the workpiece to be processed area, or a new layer pattern is accurately overlaid and projected onto the workpiece to be processed area where a previous pattern has been formed. Exposure of the current layer can achieve accurate transfer of the pattern from the mask to the substrate.
[0004] Before exposing the current layer, chemical mechanical polishing (CMP) is usually required on the wafer surface to improve the flatness of the wafer surface, which is beneficial for pattern transfer. The alignment technology in current high-end lithography machines is the SMASH (Smart Alignment Sensor Hybrid) system, but in the actual lithography process, there is still a problem of poor overlay accuracy. Summary of the Invention
[0005] The problem solved by the embodiments of the present invention is to provide a photomask, alignment marks, and photolithography system that improves the overlay accuracy.
[0006] To address the above problems, embodiments of the present invention provide a mask, comprising: a device mask pattern for forming a device pattern and an alignment mask pattern for forming alignment marks, wherein the alignment mask pattern comprises a two-dimensional linear pattern.
[0007] Optionally, the alignment mask pattern includes: a plurality of spaced-apart combination patterns, the combination pattern including a first mask sub-pattern extending along a first direction and a second mask sub-pattern extending along a second direction, the first mask sub-pattern and the second mask sub-pattern being sequentially and alternately connected, the first mask sub-pattern including a first end and a second end opposite to each other in the first direction, the second mask sub-pattern including a third end and a fourth end opposite to each other in the second direction, the second end and the third end being connected, and the fourth end and the first end being connected.
[0008] Optionally, the first direction and the second direction are perpendicular to each other.
[0009] Optionally, the dimensions of the first mask sub-pattern in the second direction are the same as the dimensions of the second mask sub-pattern in the first direction.
[0010] Optionally, the dimensions of the first mask sub-pattern in the first direction are the same as the dimensions of the second mask sub-pattern in the second direction.
[0011] Optionally, the spacing of the second mask sub-pattern in the first direction is equal to the spacing of the first mask sub-pattern in the second direction.
[0012] This invention provides an alignment mark, comprising: a plurality of alignment patterns arranged at intervals, wherein the alignment patterns include a first pattern extending along a first direction and a second pattern extending along a second direction, the first pattern and the second pattern being sequentially and alternately connected, the first pattern including a first end and a second end opposite to each other in the first direction, the second pattern including a third end and a fourth end opposite to each other in the second direction, the second end and the third end being connected, and the fourth end and the first end being connected.
[0013] Optionally, the first direction and the second direction are perpendicular to each other.
[0014] Optionally, the size of the first graphic in the second direction is the same as the size of the second graphic in the first direction.
[0015] Optionally, the size of the first pattern in the second direction is 50 nanometers to 300 nanometers.
[0016] Optionally, the size of the first graphic in the first direction is the same as the size of the second graphic in the second direction.
[0017] Optionally, the spacing of the second pattern in the first direction is equal to the spacing of the first pattern in the second direction.
[0018] Accordingly, embodiments of the present invention also provide a photolithography system, including: forming alignment marks using the aforementioned photomask.
[0019] Compared with the prior art, the technical solution of the embodiments of the present invention has the following advantages:
[0020] Compared with the prior art, the technical solution of the embodiments of the present invention has the following advantages: The mask provided by the embodiments of the present invention includes: a device mask pattern for forming a device pattern and an alignment mask pattern for forming alignment marks, wherein the alignment mask pattern includes a two-dimensional linear pattern. In the embodiments of the present invention, the alignment mask pattern includes a two-dimensional linear pattern, and the alignment marks subsequently formed using the alignment mask pattern of the mask proposed in the embodiments of the present invention are also two-dimensional linear patterns. Compared with the case where the alignment marks are one-dimensional linear patterns, during the alignment process using the alignment marks proposed in the embodiments of the present invention, the alignment marks macroscopically constitute periodically arranged moiré patterns. The moiré patterns enable the alignment system to obtain a larger first-order diffraction signal intensity, resulting in a larger alignment signal intensity, improved overlay accuracy (OVL), and reduced rework rate and production cost.
[0021] The alignment mark provided in this embodiment of the invention includes a plurality of alignment patterns arranged at intervals. The alignment pattern includes a first pattern extending along a first direction and a second pattern extending along a second direction. The first pattern includes a first end and a second end opposite to each other in the first direction, and the second pattern includes a third end and a fourth end opposite to each other in the second direction. The second end and the third end are connected, and the fourth end and the first end are connected. The alignment pattern is a two-dimensional linear pattern. Compared with the case where the alignment mark is a one-dimensional linear pattern, in the process of alignment using the alignment mark proposed in this embodiment of the invention, the alignment mark forms a periodically arranged moiré pattern on a macroscopic scale. The moiré pattern enables the alignment system to obtain a larger first-order diffraction signal intensity, resulting in a larger alignment signal intensity, improving overlay accuracy (OVL), and reducing rework rate and production cost.
[0022] In an alternative embodiment, the dimensions of the first pattern in the second direction are the same as those of the second pattern in the first direction, and the dimensions of the first pattern in the second direction are 50 nanometers to 300 nanometers. Compared with the cases where the dimensions of the first pattern in the second direction are in the micrometer range and the dimensions of the second pattern in the first direction are in the micrometer range, the widths of the first and second patterns are smaller. Consequently, during the chemical mechanical polishing process of the wafer, the area where the alignment pattern reacts chemically with the polishing slurry is smaller, making it difficult to reduce the thickness of the alignment pattern (the dimension of the alignment pattern in the normal direction of the wafer surface). This is because the magnitude of the alignment signal intensity is proportional to the thickness of the alignment pattern during photolithography. Therefore, a larger alignment pattern thickness results in a larger alignment signal intensity generated by the alignment mark, leading to higher overlay accuracy (OVL) and reduced rework rate and production costs. Attached Figure Description
[0023] Figure 1This is a schematic diagram of the alignment mark structure in the SMASH alignment system.
[0024] Figure 2 yes Figure 1 A magnified view of a section at point B in the middle.
[0025] Figure 3 Based on Figure 1 Electron microscopy cross-sectional view of the semiconductor structure obtained by alignment marks.
[0026] Figure 4 This is a schematic diagram of the structure of the mask plate aligned with the mask pattern in an embodiment of the present invention.
[0027] Figure 5 yes Figure 4 A magnified view of a portion of the image.
[0028] Figure 6 This is a schematic diagram of the alignment mark structure according to an embodiment of the present invention.
[0029] Figure 7 yes Figure 6 A magnified view of a portion of the image.
[0030] Figure 8 This is an electron microscope cross-sectional view of a semiconductor structure obtained based on the alignment marks in an embodiment of the present invention. Detailed Implementation
[0031] As the background technology shows, poor overlay accuracy still exists in the actual photolithography process. This paper combines... Figures 1 to 3 To analyze the reasons for the poor stability of alignment marks in photolithography.
[0032] Figure 1 This is a schematic diagram of the alignment mark 10 in the SMASH alignment system. Figure 2 for Figure 1 The enlarged view at point B shows that the alignment mark 10 includes a plurality of periodically arranged alignment patterns 20. The alignment pattern 20 is a one-dimensional linear pattern. In the extension direction perpendicular to the alignment pattern 20, the line width m1 of the alignment pattern 20 is 1.13 μm. The spacing between the alignment patterns 20 is the same as the line width of the alignment pattern 20, which is 1.13 μm.
[0033] like Figure 2 As shown, during the photolithography process, the diffracted light of a one-dimensional linear pattern at a 45° angle can be decomposed into a first direction (Iy) and a second direction (Ix). The signal intensity of the first direction can be used for positioning in the first direction during the alignment process, and the signal intensity of the second direction can be used for positioning in the second direction during the alignment process.
[0034] During the photolithography process, the pattern density of one-dimensional linear patterns is relatively low. When the photolithography machine aligns the one-dimensional linear patterns according to the alignment marks 10 of the previous layer, the intensity of the first-order diffraction signal obtained by the one-dimensional linear patterns is relatively low, that is, the alignment signal intensity is relatively low, resulting in low overlay accuracy (OVL), high rework rate and high production cost.
[0035] Furthermore, during the chemical mechanical polishing (CMP) process on the wafer, the alignment pattern 20 comes into contact with the polishing slurry (a mixture of ultrafine particles, chemical oxidants, and liquid media). The alignment pattern 20 reacts chemically with the polishing slurry, resulting in a reduction in the thickness of the alignment pattern 20 (the dimension of the alignment pattern 20 in the direction normal to the wafer surface). The larger the linewidth m1 of the alignment pattern 20, the larger the contact area between the alignment pattern 20 and the polishing slurry, and the more chemical reactions occur, leading to a more severe loss of the alignment pattern 20's thickness. Consequently, the alignment pattern 20 has a smaller thickness. During photolithography, the alignment signal strength is directly proportional to the thickness of the alignment pattern 20. Because the alignment pattern 20 has a smaller thickness, the alignment signal strength generated by the alignment mark 10 of the previous layer is weaker, resulting in poor overlay accuracy (OVL) between the previous and subsequent layers. Overlay errors can take many forms, including translation, rotation, and expansion. If the overlay error exceeds the tolerance, various problems will occur. For example, the produced circuit may experience open or short circuits due to displacement, thus affecting product yield.
[0036] like Figure 3 As shown, it is based on Figure 1 Electron microscopy cross-sectional view of the semiconductor structure obtained by alignment marks.
[0037] based on Figure 3 Measurements show that the target thickness originally aligned with pattern 20 was... The final thickness of aligned pattern 20 is only The thickness was reduced by 50% compared to the target thickness. The signal strength corresponding to the alignment mark 10 at the final thickness was only 0.5%, resulting in poor overlay accuracy (OVL) between the front and back layers. This greatly increased the photolithography rework caused by overlay deviation, leading to low yield of the semiconductor structure.
[0038] In addition, existing technologies have proposed methods to break up one-dimensional linear patterns to improve the alignment signal strength of alignment marks 10. However, during the chemical mechanical polishing process of the wafer, the broken one-dimensional linear patterns will still react with the polishing slurry, resulting in a smaller thickness of the alignment pattern 20. Consequently, during photolithography alignment based on the alignment marks 10 with broken one-dimensional linear patterns, the alignment signal strength is not improved, and the problems of low overlay accuracy (OVL), high rework rate, and high production cost still exist.
[0039] To address the aforementioned technical problem, embodiments of the present invention provide an alignment mark, comprising: a plurality of alignment patterns arranged at intervals, wherein the alignment pattern includes a first pattern extending along a first direction and a second pattern extending along a second direction, the first pattern including a first end and a second end opposite to each other in the first direction, and the second pattern including a third end and a fourth end opposite to each other in the second direction, the second end and the third end being connected, and the fourth end and the first end being connected.
[0040] The alignment mark provided in this embodiment of the invention includes a plurality of alignment patterns arranged at intervals. The alignment pattern includes a first pattern extending along a first direction and a second pattern extending along a second direction. The first pattern includes a first end and a second end opposite to each other in the first direction, and the second pattern includes a third end and a fourth end opposite to each other in the second direction. The second end and the third end are connected, and the fourth end and the first end are connected. The alignment pattern is a two-dimensional linear pattern. Compared with the case where the alignment mark is a one-dimensional linear pattern, in the process of alignment using the alignment mark proposed in this embodiment of the invention, the alignment mark forms a periodically arranged moiré pattern on a macroscopic scale. The moiré pattern enables the alignment system to obtain a larger first-order diffraction signal intensity, resulting in a larger alignment signal intensity, improving overlay accuracy (OVL), and reducing rework rate and production cost.
[0041] To make the above-mentioned objectives, features and advantages of the embodiments of the present invention more apparent and understandable, specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings.
[0042] refer to Figure 4 and Figure 5 , Figure 4 This is a schematic diagram of the structure of the photomask for aligning the mask pattern according to an embodiment of the present invention. Figure 5 yes Figure 4 A magnified view of a portion of the image.
[0043] The mask includes a device mask pattern for forming a device pattern and an alignment mask pattern 100 for forming alignment marks, wherein the alignment mask pattern 100 includes a two-dimensional linear pattern.
[0044] In this embodiment of the invention, the alignment mask pattern 100 includes a two-dimensional linear pattern. The alignment marks formed subsequently using the alignment mask pattern 100 of the mask proposed in this embodiment of the invention are also two-dimensional linear patterns. Compared with the case where the alignment marks are one-dimensional linear patterns, during the alignment process using the alignment marks proposed in this embodiment of the invention, the alignment marks form periodically arranged moiré patterns on a macroscopic scale. The moiré patterns enable the alignment system to obtain a larger first-order diffraction signal intensity, resulting in a larger alignment signal intensity, improved overlay accuracy (OVL), and reduced rework rate and production cost.
[0045] In this embodiment, the mask also includes a device mask pattern. Accordingly, alignment marks and device patterns can be formed simultaneously in one exposure step based on the mask, which can save a photomask, reduce production costs, and simplify the process.
[0046] In this embodiment, the alignment system includes the SMASH alignment system.
[0047] like Figure 5 As shown, the alignment mask pattern 100 includes a plurality of spaced-apart combination patterns 101. The combination pattern 101 includes a first mask sub-pattern 102 extending along a first direction (x) and a second mask sub-pattern 103 extending along a second direction (y). The first mask sub-pattern 102 includes a first end a1 and a second end a2 opposite to each other in the first direction. The second mask sub-pattern 103 includes a third end a3 and a fourth end a4 opposite to each other in the second direction. The second end a2 and the third end a3 are connected, and the fourth end a4 and the first end a1 are connected.
[0048] The first mask sub-pattern 102 extends along a first direction, and the second mask sub-pattern 103 extends along a second direction. The extension directions of the first mask sub-pattern 102 and the second mask sub-pattern 103 are different. Therefore, during the formation of alignment marks based on the alignment mask pattern 100, the formed alignment pattern includes a first pattern extending along the first direction and a second pattern extending along the second direction. The first pattern is formed based on the first mask sub-pattern 102, and the second pattern is formed based on the second mask sub-pattern 103. Compared to the case where the alignment mask pattern is a one-dimensional linear pattern, the alignment marks formed in this embodiment are two-dimensional linear patterns. Compared to the case where the alignment mask pattern is a one-dimensional linear pattern and the resulting alignment marks are also one-dimensional linear patterns, during alignment using the alignment marks proposed in this embodiment, the alignment marks macroscopically constitute periodically arranged moiré patterns. These moiré patterns enable the alignment system to obtain a larger first-order diffraction signal intensity, resulting in a larger alignment signal intensity, improved overlay accuracy (OVL), and reduced rework rate and production costs.
[0049] In this embodiment, the first mask sub-pattern 102 includes a first end a1 and a second end a2 opposite to each other in the first direction, and the second mask sub-pattern 103 includes a third end a3 and a fourth end a4 opposite to each other in the second direction. The second end a2 and the third end a3 are connected, and the fourth end a4 and the first end a1 are connected, so that the combined pattern 101 is a pattern arranged in a stepped manner.
[0050] In this embodiment, the first direction and the second direction are perpendicular. Thus, the first pattern formed based on the first mask sub-pattern 102 and the second pattern formed based on the second mask sub-pattern 103 are perpendicular. During alignment according to the alignment marks, the light emitted from the alignment light source is easily decomposed into the first and second perpendicular directions. The alignment system can easily obtain signals of first-order diffracted light existing in both the first and second directions simultaneously, enabling subsequent mask positioning in both directions.
[0051] In this embodiment, the dimensions of the first mask sub-pattern 102 in the first direction are the same as the dimensions of the second mask sub-pattern 103 in the second direction. Therefore, the extension direction of the combined pattern 101 forms an equidistant line M with the first and second directions. Figure 5 The extension direction is the same as that shown in the figure. Accordingly, the size of the first pattern formed according to the first mask sub-pattern 102 in the first direction is the same as the size of the second pattern formed according to the second mask sub-pattern 103 in the second direction, and the macroscopic extension direction of the alignment pattern formed according to the alignment mask pattern is the same as the extension direction of the bisector M that forms the angle between the first direction and the second direction.
[0052] It should be noted that, because the first direction and the second direction are perpendicular, and the first mask pattern 102 has a dimension x1 in the first direction (e.g., ... Figure 5 As shown) and the second mask pattern 103 in the second direction, the dimension y1 (as shown) is... Figure 5 As shown in the figure, the angle between the bisector M and the first and second directions is 45°. Therefore, during the alignment process based on the alignment mark, it is beneficial to make the decomposition ratio of the light emitted by the alignment light source in the first direction the same as that in the second direction. As a result, the signal intensity of the first-order diffracted light in the first and second directions is easy to be the same, which can make the subsequent mask well positioned in the first and second directions.
[0053] In this embodiment, the second mask pattern 103 has an interval of x2 in the first direction (e.g., ...). Figure 5 As shown) is equal to the spacing y2 of the first mask pattern 102 in the second direction (as shown). Figure 5(As shown). The resulting second pattern has a spacing in the first direction equal to the spacing in the second direction of the first pattern. During subsequent alignment based on the alignment marks, it is easy to make the ratio of the diffracted light in the first direction decomposed according to the spacing between the first patterns to the diffracted light in the second direction decomposed according to the spacing between the second patterns the same. This makes it easy to make the signal intensity of the first-order diffracted light in the first and second directions the same, which can effectively enable the subsequent mask to be positioned in the first and second directions, improve the overlay accuracy, and reduce the rework rate and production cost.
[0054] It should be noted that the spacing of the second mask sub-pattern 103 in the first direction is equal to the spacing of the first mask sub-pattern 102 in the second direction. This can improve the uniformity of the spacing of the alignment pattern at various locations, making it easier to keep the period of the moiré pattern as consistent as possible. During the alignment process, this allows the alignment system to obtain a larger first-order diffraction signal intensity, resulting in a larger alignment signal intensity, improved overlay accuracy (OVL), and reduced rework rate and production cost.
[0055] In this embodiment, the dimension y3 of the first mask sub-pattern 102 in the second direction is the same as the dimension x3 of the second mask sub-pattern 103 in the first direction. This is beneficial because the width of the first pattern formed based on the first mask sub-pattern 102 is the same as the width of the second pattern formed based on the second mask sub-pattern 102. During the subsequent alignment process based on the alignment marks, it is easy to make the ratio of the diffracted light decomposed in the first direction based on the first pattern to the diffracted light decomposed in the second direction based on the second pattern the same. This makes it easy to make the signal intensity of the first-order diffracted light in the first and second directions the same, which can effectively enable the subsequent mask to be positioned in the first and second directions, improve the overlay accuracy, and reduce the rework rate and production cost.
[0056] It should also be noted that the dimensions of the first mask sub-pattern 102 in the second direction are the same as those of the second mask sub-pattern 103 in the first direction. This is beneficial to improving the width uniformity of the alignment pattern 200 at various locations, making it easier to keep the period of the moiré pattern as consistent as possible. During the alignment process, this allows the alignment system to obtain a larger first-order diffraction signal intensity, resulting in a larger alignment signal intensity, improved overlay accuracy (OVL), and reduced rework rate and production cost.
[0057] refer to Figure 6 and Figure 7 , Figure 6 This is a schematic diagram of the alignment mark 300 according to an embodiment of the present invention. Figure 7 yes Figure 6 A magnified view of a portion of the image.
[0058] The alignment mark 300 includes a plurality of alignment patterns 200 arranged at intervals. The alignment pattern 200 includes a first pattern 201 extending along a first direction (x) and a second pattern 202 extending along a second direction (y). The first pattern 201 and the second pattern 202 are connected alternately in sequence. The first pattern 201 includes a first end A1 and a second end A2 opposite to each other in the first direction. The second pattern 202 includes a third end A3 and a fourth end A4 opposite to each other in the second direction. The second end A2 and the third end A3 are connected, and the fourth end A4 and the first end A1 are connected.
[0059] The alignment mark provided in this embodiment of the invention includes a plurality of alignment patterns 200 arranged at intervals. The alignment pattern 200 includes a first pattern 201 extending along a first direction and a second pattern 202 extending along a second direction. The first pattern 201 includes a first end and a second end opposite to each other in the first direction, and the second pattern 202 includes a third end and a fourth end opposite to each other in the second direction. The second end and the third end are connected, and the fourth end and the first end are connected. The alignment pattern 200 is a two-dimensional linear pattern. Compared with the case where the alignment mark is a one-dimensional linear pattern, in the process of alignment using the alignment mark proposed in this embodiment of the invention, the alignment mark forms a periodically arranged moiré pattern on a macroscopic scale. The moiré pattern enables the alignment system to obtain a larger first-order diffraction signal intensity, and the corresponding alignment signal intensity is larger, which improves the overlay accuracy (OVL) and reduces the rework rate and production cost.
[0060] In this embodiment, the alignment system includes the SMASH alignment system.
[0061] like Figure 7 As shown, in this embodiment, the first pattern 201 includes a first end A1 and a second end A2 opposite to each other in the first direction, and the second pattern 202 includes a third end A3 and a fourth end A4 opposite to each other in the second direction. The second end A2 and the third end A3 are connected, and the fourth end A4 and the first end A1 are connected, so that the alignment pattern 200 is a pattern arranged in a stepped manner.
[0062] In this embodiment, the first direction and the second direction are perpendicular. During the alignment process based on the alignment marks, the light emitted by the alignment light source can be easily decomposed into the first direction and the second direction, which are perpendicular to each other. The alignment system can easily obtain the signals of the first-order diffracted light existing in the first direction and the second direction at the same time, which can effectively enable the subsequent mask to be positioned in the first direction and the second direction.
[0063] In this embodiment, the first graphic 201 has a dimension X1 in the first direction (e.g., Figure 7 As shown) and the second graphic 202 in the second direction Y1 (e.g.) Figure 7The dimensions are the same as those shown. Therefore, the bisector M (as shown) of the angle formed between the extension direction of the alignment pattern 200 and the first and second directions. Figure 7 The extension direction is the same as that shown. Thus, the extension direction of the alignment graphic macroscopically is the same as the extension direction of the bisector M that forms the angle between the first direction and the second direction.
[0064] It should be noted that, because the first direction and the second direction are perpendicular, and the size of the first pattern 201 in the first direction is the same as the size of the second pattern 202 in the second direction, the angle between the bisector M and the first direction and the second direction is 45°. Therefore, during the alignment process based on the alignment mark, it is beneficial to make the decomposition ratio of the light emitted by the alignment light source in the first direction the same as the decomposition ratio in the second direction. As a result, the signal intensity of the first-order diffracted light in the first direction and the second direction is easily the same, which can make the subsequent mask well positioned in the first and second directions.
[0065] In this embodiment, the second pattern 202 is spaced X2 in the first direction (e.g., Figure 7 As shown) is equal to the interval Y2 of the first pattern 201 in the second direction (as shown) Figure 7 (As shown). During the subsequent alignment process based on the alignment marks, it is easy to make the ratio of the diffracted light in the first direction decomposed according to the interval between the first patterns 201 and the diffracted light in the second direction decomposed according to the interval between the second patterns 202 the same. This makes it easy to make the signal intensity of the first-order diffracted light in the first and second directions the same, which can effectively enable the subsequent mask to be positioned in the first and second directions, improve the overlay accuracy, and reduce the rework rate and production cost.
[0066] It should be noted that the spacing X2 of the second pattern 202 in the first direction is equal to the spacing Y2 of the first pattern 201 in the second direction. This can improve the uniformity of the spacing of the alignment pattern at various locations, making it easier to keep the period of the moiré pattern as consistent as possible. During the alignment process, this allows the alignment system to obtain a larger first-order diffraction signal intensity, resulting in a larger alignment signal intensity, improved overlay accuracy (OVL), and reduced rework rate and production cost.
[0067] In this embodiment, the first pattern 201 has a dimension Y3 in the second direction (e.g., ...). Figure 7 (as shown) and the second graphic 202 in the first direction, dimension X3 (e.g.) Figure 7As shown, during the subsequent alignment process based on the alignment marks, it is easy to make the ratio of the diffracted light in the first direction decomposed according to the first pattern to the diffracted light in the second direction decomposed according to the second pattern the same. This makes it easy to make the signal intensity of the first-order diffracted light in the first and second directions the same, which can effectively enable the subsequent mask to be positioned in the first and second directions, improve the overlay accuracy, and reduce the rework rate and production cost.
[0068] It should be noted that the dimension of the first pattern 201 in the second direction should not be too large or too small. If the dimension is too large, during the chemical mechanical polishing (CMP) process on the wafer, the area where the alignment pattern 200 reacts chemically with the polishing slurry is larger, which easily reduces the thickness of the alignment pattern 200 (the dimension of the alignment pattern in the direction normal to the wafer surface). Consequently, the alignment signal strength generated by the alignment mark 300 is smaller, the overlay accuracy (OVL) is poorer, and the rework rate and production cost are higher. If the dimension is too small, it easily increases the difficulty of forming the alignment mark 300, which is not conducive to saving semiconductor structure process costs.
[0069] In this embodiment, the first pattern 201 has a size of 50 nanometers to 300 nanometers in the second direction, and correspondingly, the second pattern 202 has a size of 50 nanometers to 300 nanometers in the first direction. Compared with the cases where the size of the first pattern 201 in the second direction is at the micrometer level and the size of the second pattern 202 in the first direction is at the micrometer level, the widths of the first pattern 201 and the second pattern 202 are smaller. Consequently, during the chemical mechanical polishing (CMP) process on the wafer, the area where the alignment pattern 200 reacts chemically with the polishing slurry is smaller, making it difficult to reduce the thickness of the alignment pattern 200 (the size of the alignment pattern in the direction normal to the wafer surface). This is because the magnitude of the alignment signal intensity is proportional to the thickness of the alignment pattern 200 during photolithography. Therefore, a larger thickness of the alignment pattern 200 results in a larger alignment signal intensity generated by the alignment mark 300, leading to higher overlay accuracy (OVL) and reduced rework rate and production costs.
[0070] It should be noted that the dimensions of the first pattern 201 in the second direction are the same as those of the second pattern 202 in the first direction. In other words, the width of the first pattern 201 is the same as the width of the second pattern 202. This is beneficial to improving the uniformity of the width of the alignment pattern 200 at various locations, making it easier to keep the period of the moiré pattern as consistent as possible. During the alignment process, this allows the alignment system to obtain a larger first-order diffraction signal intensity. The corresponding alignment signal intensity is larger, which improves the overlay accuracy (OVL) and reduces the rework rate and production cost.
[0071] It should be noted that the parameters such as the spacing of the first pattern 201 in the second direction, the spacing of the second pattern 202 in the first direction, the size of the first pattern 201 in the second direction, the size of the second pattern 202 in the first direction, the size of the first pattern in the first direction, and the size of the second pattern in the second direction in the alignment mark 300 can be adjusted according to the actual photolithography illumination process capability.
[0072] This invention also provides a photolithography system. The photolithography system uses the aforementioned photomask to form alignment marks.
[0073] The alignment marks formed using the aforementioned mask are two-dimensional linear patterns. Compared to the case where the alignment marks are one-dimensional linear patterns, during the alignment process using the alignment marks proposed in this embodiment of the invention, the alignment marks macroscopically form periodically arranged moiré patterns. The moiré patterns enable the alignment system to obtain a larger first-order diffraction signal intensity, resulting in a larger alignment signal intensity, improved overlay accuracy (OVL), and reduced rework rate and production costs.
[0074] In the step of forming the alignment mark, the alignment mark is formed within the dicing channel on the wafer. The dicing channel is subsequently used for cutting, and the alignment mark formed within the dicing channel on the wafer does not affect device formation, while improving wafer area utilization.
[0075] The method for forming the semiconductor structure includes: forming alignment marks on the wafer, and then performing a chemical mechanical polishing (CMP) process on the wafer, wherein the wafer after the CMP process still has at least the alignment marks. Having at least the alignment marks enables photolithographic alignment to be performed based on the alignment marks during subsequent photolithographic alignment processes.
[0076] It should be noted that before chemical mechanical polishing, the top surface of the alignment mark can be higher or lower than the top surface of the layer to be polished; during chemical mechanical polishing, the alignment mark can be thinned to a certain extent so that the top surface of the alignment mark is flush with the top surface of the layer to be polished.
[0077] like Figure 8 The figure shows an electron microscope cross-sectional view of a semiconductor structure obtained based on the alignment marks of an embodiment of the present invention. It can be seen from the figure that the thickness of the alignment pattern 200 is increased. Because the strength of the alignment signal is proportional to the thickness of the alignment pattern 200 during photolithography, a larger thickness of the alignment pattern 200 results in a stronger alignment signal generated by the alignment marks, leading to higher overlay accuracy (OVL) and reduced rework rate and production costs.
[0078] While the embodiments of the present invention have been disclosed above, the present invention is not limited thereto. Any person skilled in the art can make various modifications and alterations without departing from the spirit and scope of the embodiments of the present invention. Therefore, the scope of protection of the embodiments of the present invention should be determined by the scope defined in the claims.
Claims
1. A photomask, characterized in that, include: Device mask pattern for forming device patterns and alignment mask pattern for forming alignment marks, the alignment mask pattern including two-dimensional linear patterns; The alignment marks macroscopically form a periodically arranged moiré pattern; the alignment mask pattern includes: a plurality of spaced-apart combined patterns, the combined pattern including a first mask sub-pattern extending along a first direction and a second mask sub-pattern extending along a second direction, the first mask sub-pattern and the second mask sub-pattern being sequentially and alternately connected, the first mask sub-pattern including a first end and a second end opposite to each other in the first direction, the second mask sub-pattern including a third end and a fourth end opposite to each other in the second direction, the second end and the third end being connected, the fourth end and the first end being connected; the first direction and the second direction are perpendicular to each other; the size of the first mask sub-pattern in the second direction is the same as the size of the second mask sub-pattern in the first direction.
2. The photomask as described in claim 1, characterized in that, The dimensions of the first mask sub-pattern in the first direction are the same as the dimensions of the second mask sub-pattern in the second direction.
3. The photomask as described in claim 2, characterized in that, The spacing of the second mask sub-pattern in the first direction is equal to the spacing of the first mask sub-pattern in the second direction.
4. An alignment mark, characterized in that, include: Multiple alignment patterns are arranged at intervals. The alignment patterns include a first pattern extending along a first direction and a second pattern extending along a second direction. The first and second patterns are sequentially connected alternately. The first pattern includes a first end and a second end opposite each other in the first direction. The second pattern includes a third end and a fourth end opposite each other in the second direction. The second end and the third end are connected. The fourth end and the first end are connected. The alignment marks form a periodically arranged moiré pattern on a macroscopic scale. The first direction and the second direction are perpendicular to each other. The size of the first pattern in the second direction is the same as the size of the second pattern in the first direction.
5. The alignment mark as described in claim 4, characterized in that, The first pattern has a size of 50 nanometers to 300 nanometers in the second direction.
6. The alignment mark as described in any one of claims 4 to 5, characterized in that, The size of the first graphic in the first direction is the same as the size of the second graphic in the second direction.
7. The alignment mark as claimed in claim 6, characterized in that, The spacing of the second shape in the first direction is equal to the spacing of the first shape in the second direction.
8. A photolithography system, characterized in that, Alignment marks are formed using a mask as described in any one of claims 1 to 3.