Etching method
By using a method of etching in stages and using a cover plate to block out light, different etching conditions are applied to patterns with different transmittance, which solves the problem of uneven linewidth caused by differences in transmittance on the photomask, improves product quality and saves costs.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- 兴华芯(绍兴)半导体科技有限公司
- Filing Date
- 2026-02-25
- Publication Date
- 2026-05-15
AI Technical Summary
Existing etching processes result in uneven linewidth distribution in areas with significant differences in light transmittance on photomasks, leading to a decline in product quality.
Based on the light transmittance of the area to be etched, etching is performed in stages, and a cover plate is used to block other areas outside the area to be etched. Different etching conditions are used, and the optimal etching conditions are determined through pre-testing.
This resulted in a more uniform linewidth distribution, improved product quality, reduced photomask consumption, and cost savings.
Smart Images
Figure CN122054928A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of semiconductor fabrication technology, and in particular to an etching method. Background Technology
[0002] Plasma etching is a dry etching process that achieves precise nanoscale pattern transfer on wafer surfaces through the combined effects of chemical reactions and physical bombardment of plasma. It enables precise etching of wafer surfaces. First, in a photolithography machine, the circuit pattern on a photomask is precisely transferred to the photoresist layer on the silicon wafer through a photochemical reaction of photoresist. Figure 1 As shown, plasma is then used to selectively etch the underlying film (film) that is not protected by photoresist, ultimately allowing the photoresist pattern to be precisely replicated onto the functional film on the wafer, such as... Figure 2 As shown.
[0003] Existing etching processes typically involve etching the entire photomask under plasma. When the pattern distribution on a photomask is relatively uniform and without significant differences, such as... Figure 3 As shown, the linewidth error caused by etching is often small, such as Figure 4 As shown, after correction by the exposure machine, it can meet the actual production requirements. However, in actual production, the photomask often includes several parts of the pattern with large differences in transmittance, such as... Figure 5 As shown. Under the same etching conditions, the linewidth values of the corresponding parts after etching also differ significantly, and the linewidth distribution uniformity is poor, such as... Figure 6 As shown. Summary of the Invention
[0004] To address some or all of the problems in existing technologies, and in order to achieve a more uniform linewidth distribution and improve product quality when there are significant differences in light transmittance across different areas of the wafer, this invention provides an etching method, comprising: Based on the light transmittance of the pattern in the area to be etched, etching is performed in stages, with the light transmittance of the pattern area being the same or similar in each etch, and different etching conditions are used for patterns with different light transmittance.
[0005] Furthermore, the etching method includes: During each etching process, a cover plate is used to shield the area outside the area to be etched.
[0006] Furthermore, the cover plate is made of silicon dioxide.
[0007] Furthermore, the etching conditions for images with different transmittance were determined through prior testing.
[0008] Furthermore, the pre-test includes: The photomask is divided into several areas, and one area is etched at a time while the others are covered with a cover plate. The etching conditions are different for each etching. Based on the etching performance of each region, the relationship between etching conditions and etching performance was determined; and Based on the desired etching performance, the final etching conditions are determined, wherein the etching performance includes etching rate, critical dimension linearity (CD), proximity effect, and etching bias, and the etching conditions include: chamber pressure, power, etching temperature, etching gas, and gas flow rate.
[0009] Furthermore, the pre-test includes: Only one etching condition is modified at a time.
[0010] Furthermore, the areas of the pre-tested regions are all the same size.
[0011] Furthermore, the cover plate used in the pre-test includes: The first cover plate is L-shaped, with its vertical and horizontal sides equal to the length and width of the photomask, respectively, and the area of its right-angled chamfer is 20% of the area of the photomask; and The second cover plate is shaped like a grid, with the four corner areas having the same shape and size, and the area of the blank space in its center is equal to 20% of the photomask.
[0012] Furthermore, the pre-test includes: The photomask is shielded by a second cover plate, and the first etching is performed. The photomask is shielded by a first cover plate, and a second etching is performed. After rotating the first cover plate by 90° to block the photomask, a third etching is performed; After rotating the first cover plate another 90° to block the photomask, a fourth etching is performed; and After rotating the first cover plate 90°, it blocks the photomask and performs the fifth etching.
[0013] This invention provides an etching method that uses a cover plate to divide patterns with different transmittance. Different etching conditions are applied to patterns with different transmittance, resulting in more uniform linewidth across the entire image. Furthermore, using a cover plate in pre-testing reduces the consumption of photomasks, improving efficiency and saving costs. Attached Figure Description
[0014] To further illustrate the above and other advantages and features of the various embodiments of the present invention, a more specific description of the various embodiments of the present invention will be presented with reference to the accompanying drawings. It is to be understood that these drawings depict only typical embodiments of the invention and are therefore not intended to limit its scope. In the drawings, identical or corresponding parts will be indicated by identical or similar reference numerals for clarity.
[0015] Figure 1 A partial schematic diagram of the wafer before etching is shown; Figure 2 A partial schematic diagram of the wafer after etching is shown; Figure 3 A schematic diagram of a photomask with a relatively uniform pattern distribution is shown. Figure 4 This diagram illustrates the distribution of linewidth error obtained by etching a photomask with a relatively uniform pattern distribution. Figure 5 A schematic diagram of a photomask with significant differences in light transmittance is shown. Figure 6 This diagram illustrates the distribution of linewidth errors obtained by etching photomasks with significant differences in pattern transmittance. Figure 7 A schematic flowchart of an etching method according to an embodiment of the present invention is shown; Figure 8 A schematic diagram of the structure of a first cover plate according to an embodiment of the present invention is shown; and Figure 9 A schematic diagram of the structure of the second cover plate according to an embodiment of the present invention is shown. Detailed Implementation
[0016] In the following description, the invention is described with reference to various embodiments. However, those skilled in the art will recognize that the embodiments may be practiced without one or more specific details or with other alternatives and / or additional methods, materials, or components. In other instances, well-known structures, materials, or operations are not shown or described in detail so as not to obscure the inventive points of the invention. Similarly, for illustrative purposes, specific quantities, materials, and configurations are set forth to provide a comprehensive understanding of embodiments of the invention. However, the invention is not limited to these specific details. Furthermore, it should be understood that the embodiments shown in the drawings are illustrative representations and are not necessarily drawn to scale.
[0017] In this specification, references to "an embodiment" or "this embodiment" mean that a particular feature, structure, or characteristic described in connection with that embodiment is included in at least one embodiment of the invention. The phrase "in one embodiment" appearing throughout this specification does not necessarily refer to the same embodiment in all instances.
[0018] It should be noted that the embodiments of the present invention describe the process steps in a specific order; however, this is only for illustrating the specific embodiment and not for limiting the order of the steps. On the contrary, in different embodiments of the present invention, the order of the steps can be adjusted according to the process.
[0019] In dry etching processes such as plasma etching, after exposure and development, a precise photoresist pattern forms on the surface of the wafer. Areas of the wafer that need to be retained are covered by photoresist, while areas that need to be removed are unexposed. The wafer is then fed into the process chamber of a plasma etching machine for selective plasma etching. Specifically, the process chamber is evacuated to the required pressure, a specific etching gas is introduced, and the gas is ionized using radio frequency (RF) power to generate high-density, highly reactive plasma. The plasma reacts chemically and physically with the underlying thin film not protected by photoresist, removing the film in that area. Areas covered by photoresist, without plasma contact or reaction, retain their film intact. After etching, endpoint detection methods such as spectral analysis of gaseous products and film thickness measurement determine whether the film in the unprotected areas has been etched to the target depth. Once the target depth is reached, the plasma is shut off, stopping the etching process. At this point, the photoresist's masking effect ends. The photoresist on the wafer surface is then removed through oxygen plasma ashing or wet stripping, ultimately forming a physical pattern on the underlying thin film that is identical to the original photoresist. In plasma etching, the etching of the underlying thin film by plasma is not a simple chemical reaction; therefore, the transmittance of the pattern significantly affects the final linewidth error. The inventors discovered that by using different etching conditions—such as gas ratio, power, and gas pressure—for patterns with different transmittance, the linewidth difference in the corresponding parts after etching can be reduced, thereby minimizing the impact of transmittance on linewidth. Based on this, the present invention provides an etching method that uses different etching conditions for patterns with different transmittances on the same photomask, resulting in a more uniform linewidth distribution.
[0020] The technical solution of the present invention will be further described below with reference to the accompanying drawings of the embodiments.
[0021] Figure 7 This diagram illustrates a flow chart of an etching method according to an embodiment of the present invention. Figure 7 As shown, an etching method includes: First, in step 701, the wafer to be etched is divided into regions. Based on the light transmittance of the pattern in the region to be etched, the wafer is divided into multiple regions; Next, in step 702, a portion of the area is blocked. A portion of the wafer to be etched is blocked so that the light transmittance of the remaining area is the same or similar. In one embodiment of the invention, the same or similar light transmittance means that the difference in light transmittance is no greater than 50%. In one embodiment of the invention, the wafer to be etched is blocked by a cover plate, wherein the cover plate is made of a pure quartz substrate, and its core material is silicon dioxide. Next, in step 703, etching is performed. Based on the light transmittance of the unobstructed area, etching conditions (etch recipe) are determined, and etching is carried out; and Finally, in step 704, it is determined whether all areas have been etched. If so, subsequent processes such as photoresist removal are performed. Otherwise, the process returns to step 702, partially obscuring the area of the wafer to be etched, exposing one or more areas with the same or similar light transmittance, and continuing etching under different conditions.
[0022] In one embodiment of the invention, the etching conditions for images with different transmittance are determined through prior testing. In another embodiment of the invention, the etching conditions for images with different transmittance are determined based on historical experience.
[0023] In one embodiment of the present invention, the pre-test includes etching patterns with the same transmittance under different etching conditions, and / or etching patterns with different transmittances under the same etching conditions, to determine the impact of various etching conditions on etching performance, and thus determine the required etching conditions for the desired etching performance. The etching performance includes, but is not limited to, etching rate, critical dimension linearity (CD), proximity effect, and etching bias, etc., and the etching conditions include, but are not limited to, chamber pressure, power, etching temperature, etching gas, and gas flow rate.
[0024] To reduce testing costs and save on blank substrate usage, in one embodiment of the present invention, multiple etching conditions are tried on a blank substrate. Specifically, the photomask is divided into several regions, and one region is etched at a time, wherein the etching conditions are different each time. While etching one region, the other regions are covered with a cover plate as described above.
[0025] To better confirm the relationship between different etching conditions and the final etching performance, in one embodiment of the present invention, only one etching condition is modified in each attempt compared to the previous attempt. However, it should be understood that in other embodiments of the present invention, multiple etching conditions may be adjusted based on actual needs.
[0026] In one embodiment of the present invention, during pre-testing, the areas of each region are identical. For example, the area of each etched region is 1 / N of the area of the photomask, where N is the number of times the same blank substrate is etched. Based on this, the shape of the cover plate can be designed according to the shape, size, etc. of each etched region. For example, in one embodiment of the present invention, two different shaped cover plates are used for pre-testing. The first cover plate is L-shaped, such as... Figure 8 As shown, the second cover plate is in a grid shape, as... Figure 9 As shown. Among them, as Figure 8 As shown, the vertical and horizontal sides of the first cover plate 800 are equal in length and width to the photomask, respectively, and the area of the right-angled chamfer is 20% of the area of the photomask. Figure 9 As shown, the four corner regions of the second cover plate 900 have the same shape and size, and the area of the blank area in its central region is equal to 20% of the photomask. Rotating the first cover plate three times, plus the second cover plate, allows etching of five positions on the same photomask. These five positions have equal areas, thus facilitating adjustments to different etching conditions for testing. Specifically, the second cover plate is used to cover the photomask for the first etching. Then, the first cover plate is used to cover the photomask for the second etching. The first cover plate is then rotated 90° to cover the photomask for the third etching. The first cover plate is then rotated 90° again to cover the photomask for the fourth etching. Finally, the first cover plate is rotated 90° again to cover the photomask for the fifth etching. Each rotation is in the same direction, for example, either clockwise or counterclockwise.
[0027] Based on this, when adjusting etching performance such as etching rate, critical dimension linearity (CD), proximity effect, and etching bias, five etching conditions can be tried on a single blank substrate, thereby reducing testing costs and saving the amount of blank substrate used. Simultaneously, this method can determine the etching conditions required to achieve the same or similar etching performance under different pattern transmittances. Therefore, when there are significant differences in transmittance across different areas of the wafer, etching conditions can be specifically set for distributed etching, resulting in a more uniform linewidth distribution and improved product quality.
[0028] Although various embodiments of the invention have been described above, it should be understood that they are presented by way of example only and not as limitations. It will be apparent to those skilled in the art that various combinations, modifications, and alterations can be made without departing from the spirit and scope of the invention. Therefore, the breadth and scope of the invention disclosed herein should not be limited by the exemplary embodiments disclosed above, but should be defined solely by the appended claims and their equivalents.
Claims
1. An etching method, characterized in that, include: Based on the light transmittance of the pattern in the area to be etched, etching is performed in stages, wherein the difference in light transmittance of the pattern area etched in each stage is not greater than a preset value, and different etching conditions are used for patterns with different light transmittance.
2. The etching method as described in claim 1, characterized in that, The preset value is 50% light transmittance.
3. The etching method as described in claim 1, characterized in that, include: During each etching process, a cover plate is used to shield the area outside the area to be etched.
4. The etching method as described in claim 3, characterized in that, The cover plate is made of silicon dioxide.
5. The etching method as described in claim 1, characterized in that, Etching conditions for images with different transmittance were determined through prior testing.
6. The etching method as described in claim 5, characterized in that, The pre-test includes: The photomask is divided into several areas, and one area is etched at a time while the others are covered with a cover plate. The etching conditions are different for each etching. Based on the etching performance of each region, the relationship between etching conditions and etching performance was determined; and Based on the desired etching performance, the final etching conditions are determined, wherein the etching performance includes etching rate, critical dimension linearity, proximity effect, and etching deviation, and the etching conditions include: chamber pressure, power, etching temperature, etching gas, and gas flow rate.
7. The etching method as described in claim 6, characterized in that, The pre-test includes: Only one etching condition is modified at a time.
8. The etching method as described in claim 6, characterized in that, The areas tested in the pre-test were all the same size.
9. The etching method as described in claim 6, characterized in that, The cover plate used in the pre-test includes: The first cover plate is L-shaped, with its vertical and horizontal sides equal to the length and width of the photomask, respectively, and the area of its right-angled chamfer is 20% of the area of the photomask; and The second cover plate is shaped like a grid, with the four corner areas having the same shape and size, and the area of the blank space in its center is equal to 20% of the photomask.
10. The etching method as described in claim 9, characterized in that, The pre-test includes: The photomask is shielded by a second cover plate, and the first etching is performed. The photomask is shielded by a first cover plate, and a second etching is performed. After rotating the first cover plate by 90° to block the photomask, a third etching is performed; After rotating the first cover plate another 90° to block the photomask, a fourth etching is performed; and After rotating the first cover plate 90°, it blocks the photomask and performs the fifth etching.