Method for improving radiation type line width difference of photomask
By dividing the correction partitions on the mask substrate and calculating the secondary exposure amount, the problem of radiation line width difference of the mask plate is solved and the quality of the mask plate is improved.
Patent Information
- Application Number
- CN202511079890.4
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-08-04
- Publication Date
- 2025-10-17
AI Technical Summary
In the prior art, during the production process of photomasks, there is a problem of large differences in the width of the radiation lines, which affects the quality of the photomasks.
By dividing the mask substrate into multiple correction zones, calculating the secondary exposure amount of each zone, and superimposing the secondary exposure amount on the basis of the preset exposure amount, secondary exposure is performed to compensate for the line width difference caused by uneven development and etching rates, and the exposure correction gear of the exposure machine is set.
The difference in the radiation line width of the mask is significantly reduced, and the quality of the mask is improved.
Smart Images
Figure CN120802571A_ABST
Abstract
Description
TECHNICAL FIELD
[0001] The present application relates to the technical field of semiconductor mask, and particularly relates to a method for improving radiation type line width difference of a mask. BACKGROUND
[0002] A general mask substrate includes three layers of materials, from bottom to top, quartz glass, chromium and photoresist. After the substrate is subjected to exposure, development, etching and photoresist removal in sequence, a mask reticle is obtained. The main function of the mask reticle is to transfer the circuit design pattern to the surface of a semiconductor wafer through photolithography technology. In the semiconductor production process, the circuit pattern is stored on the mask reticle, and the pattern will be irradiated onto the silicon wafer coated with photoresist during the exposure process. The photoresist will undergo chemical changes according to the intensity of the exposure, thereby forming the circuit pattern on the silicon wafer.
[0003] In the production process of the mask reticle, a designer creates a design pattern of the mask reticle according to the circuit drawing of a chip, and the design pattern includes a circuit structure. Then, the mask substrate is exposed by an exposure machine, and the design pattern is transferred to the mask substrate. Then, the exposed mask substrate is developed and etched to obtain a corresponding pattern on the mask substrate.
[0004] The line width difference refers to the fact that after the same specification of wire patterns in the design pattern is transferred and etched on the mask substrate, the widths of the etched wire patterns are not uniform.
[0005] In related technologies, single exposure is performed on the mask substrate with a preset exposure amount. During development and etching, as shown in FIG. 1, the developer is sprayed on the rotating mask substrate. Since the developer is sprayed on the substrate at a certain angle, the development or etching rate is inconsistent in the radial direction of rotation, as shown in FIG. 2. Thus, the image line width on the developed or etched mask substrate presents a gradually decreasing trend from the center to the outside, resulting in radiation type line width difference. Figure 2 Figure 3 The line width difference is an important standard for evaluating the quality of the mask reticle. Therefore, the mask reticle obtained by the related technologies has poor quality.
[0006] The main purpose of the present application is to provide a method for improving radiation type line width difference of a mask, which aims to solve the technical problem of large radiation type line width difference of the mask reticle. SUMMARY
[0007] The main purpose of the present application is to provide a method for improving radiation type line width difference of a mask, which aims to solve the technical problem of large radiation type line width difference of the mask reticle.
[0008] To achieve the above purpose, the present application provides a method for improving radiation type line width difference of a mask, comprising the following steps:
[0009] S1, randomly select a piece of mask substrate from a batch of mask substrates, and sequentially perform exposure with a preset exposure amount, development, etching and photoresist removal treatment to obtain a mask test piece; the mask test piece has a cross pattern array etched thereon;
[0010] S2, measure the line width of each cross pattern in the cross pattern array on the mask test piece, and divide N concentric squares from the geometric center of the mask test piece outward, and the non-overlapping area of two adjacent concentric squares constitutes a correction subzone;
[0011] S3, according to the difference between the maximum line width of the pattern on the mask test piece and the average line width of the pattern in each correction subzone, calculate the secondary exposure amount of each correction subzone, and set the exposure correction file of the exposure machine based on the secondary exposure amount of each correction subzone; the secondary exposure amount is less than the preset exposure amount;
[0012] S4, for the remaining other mask substrates in the same batch of mask substrates, perform exposure with a preset exposure amount, then perform secondary exposure through the exposure correction file, and then sequentially perform development, etching and photoresist removal treatment to obtain a mask mask.
[0013] Further, the preset exposure amount ranges from 5 μC / cm² to 30 μC / cm².
[0014] Further, N ranges from 3 to 5.
[0015] Further, a first preset difference and a second preset difference are set, and the first preset difference is less than the second preset difference.
[0016] Measure the line width of each cross pattern in the cross pattern array on the mask test piece, and calculate the line width difference between the cross pattern at the center of the mask test piece and the cross pattern at the edge.
[0017] When the line width difference is less than the first preset difference, set N=3; when the line width difference is greater than the first preset difference and less than the second preset difference, set N=4; when the line width difference is greater than the second preset difference, set N=5.
[0018] Further, the centermost square alone constitutes a correction subzone; each of the correction subzones covers at least one cross pattern, and the side length of the centermost square is equal to the center distance between adjacent cross patterns, and the side length difference between adjacent concentric squares is equal to 2 times the side length of the centermost square.
[0019] Further, the S3 specifically includes:
[0020] S31, alternatively select multiple mask substrates from the same batch of mask substrates as mask experimental pieces, and expose the multiple mask experimental pieces with different exposure amounts respectively, calculate the pattern line width increment corresponding to different exposure amounts, and obtain an exposure increment-line width increment sequence;
[0021] S32, based on the exposure increment-line width increment sequence, linear fitting is performed to construct a conversion formula of exposure increment and line width increment:
[0022] ;
[0023] Wherein, P represents the exposure increment; C represents the line width increment; k represents the conversion coefficient obtained by fitting;
[0024] S33, the difference between the average line width of the cross pattern in each correction subzone of the mask test piece and the maximum line width of the cross pattern on the entire mask test piece is taken as the line width increment of the corresponding correction subzone, and the corresponding exposure increment of each correction subzone is calculated through the conversion formula, that is, the secondary exposure amount;
[0025] S34, according to the secondary exposure amount corresponding to each subzone, set the exposure correction file of the exposure machine.
[0026] Further, in the S31, exposure amounts that increase sequentially are set, and the multiple mask experimental pieces are exposed using exposure amounts that increase sequentially, and the pattern line width increment of each mask experimental piece is calculated sequentially.
[0027] According to the present application, the radiation type line width difference decreases from the center to the edge, the correction subzones are set from the center to the outside, the secondary exposure amount of the corresponding subzone is set according to the difference between the maximum pattern line width and the average pattern line width of different correction subzones, and the mask substrate is exposed twice, so that the secondary exposure amount is superimposed on the basis of the preset exposure amount, the pattern line width of the correction subzone with the superimposed secondary exposure amount is increased, thereby compensating for the line width difference caused by different developing and etching rates, and the mask reticle obtained finally is greatly improved in the mean value of the radiation type line width difference compared with the mask test piece, the radiation type line width difference of the mask reticle is significantly reduced, and the quality of the mask reticle is improved. BRIEF DESCRIPTION OF DRAWINGS
[0028] Figure 1 It is a flowchart of the mask radiation type line width difference improvement method embodiment of the present application;
[0029] Figure 2 It is a schematic diagram of a related technical chemical spraying mask substrate;
[0030] Figure 3 It is a related technical line width difference schematic diagram;
[0031] Figure 4A schematic diagram of a design pattern corresponding to a photomask test piece;
[0032] Figure 5 This is a schematic diagram of the setting of the exposure correction file;
[0033] Figure 6 This is a comparison chart of the difference in radiation line width between the mask test piece and the mask;
[0034] Figure 7 Schematic diagram of line width difference after improvement.
[0035] The purpose, features and advantages of the present invention will be further described with reference to the accompanying drawings and in conjunction with the embodiments. DETAILED DESCRIPTION
[0036] It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.
[0037] The inventive concept of the present application is further described below with reference to some specific embodiments and implementation methods.
[0038] Reference Figure 1 The embodiment of the present invention provides a method for improving the difference in the line width of the radiation type of the mask, the method comprising the following steps:
[0039] Step S1: randomly selecting a photomask substrate from a batch of photomask substrates, sequentially subjecting the photomask substrate to exposure with a preset exposure amount, development, etching, and photoresist removal to obtain a photomask test piece having an etched cross pattern array on the photomask test piece.
[0040] As an example, Figure 4 As shown, Figure 4 The design pattern corresponding to the mask test piece is an 11×11 cross pattern array. The design spacing between each cross pattern is 13mm, and the design line width of the cross pattern is 1μm. The exposure machine exposes a 6-inch mask substrate with a preset exposure amount (that is, the exposure amount used in related technologies, such as 7μC / cm²) according to the design pattern. That is, the exposure machine projects the cross pattern in the design pattern onto the mask substrate through the light source. After the exposed mask substrate is developed, etched, and photoresist removed, a mask test piece with a cross pattern array is obtained, that is, Figure 4 Due to the difference in radial line width, the actual line width of the cross pattern on the mask test piece is as follows: Figure 6 As shown, line width differences appear from the center of the mask test piece outward, that is, the closer to the center, the smaller the line width of the cross pattern. Therefore, the difference in line width between the cross image at the outermost edge of the mask test piece and the center will be very large.
[0041] Step S2: measuring the line width of each cross pattern in the cross pattern array on the test mask, dividing N concentric squares from the geometric center of the test mask, and each modified partition is formed by the non-overlapping area of two adjacent concentric squares.
[0042] measuring the line width of each cross pattern in the cross pattern array on the test mask, dividing N (N is 3-5) concentric squares from the geometric center of the test mask according to the line width difference between the cross pattern at the center of the test mask and the cross pattern at the edge of the test mask, so as to divide the test mask into N modified partitions, that is, each modified partition is formed by the non-overlapping area of two adjacent concentric squares, and the centermost square constitutes a modified partition; each of the modified partitions covers at least one cross pattern, the side length of the centermost square is equal to the center distance between adjacent cross patterns, and the side length difference between adjacent concentric squares is equal to 2 times the side length of the centermost square.
[0043] It is worth mentioning that the number of modified partitions affects the final improvement effect and implementation cost. The more the modified partitions, the better the improvement effect, but the implementation cost will also increase. Therefore, in the specific setting of the number of modified partitions, the line width difference between the cross pattern at the center of the test mask and the cross pattern at the edge of the test mask is compared with a first preset difference value and a second preset difference value (the first preset difference value < the second preset difference value), if the line width difference is less than the first preset difference value, 3 modified partitions are set; if the line width difference is greater than the first preset difference value and less than the second preset difference value, 4 modified partitions are set; if the line width difference is greater than the second preset difference value, 5 modified partitions are set.
[0044] As shown in Figure 5 , the present embodiment divides 4 modified partitions (N=4), the centermost square is a modified partition, the side length of which is 13mm, the side length difference between adjacent concentric squares is 26mm, and the width of each modified partition in the radial direction is 13mm.
[0045] In the process of step S2, the plurality of modified partitions are set based on the geometric center of the test mask, and the width of adjacent modified partitions in the radial direction is the same, so that the distribution of the modified partitions is more consistent with the distribution of the radiation type line width difference, thereby more accurately compensating the radiation type line width difference.
[0046] Step S3: calculating the secondary exposure amount of each modified partition according to the difference between the maximum line width of the pattern on the test mask and the average line width of the pattern on each modified partition, and setting the exposure correction file of the exposure machine based on the secondary exposure amount of each modified partition; the secondary exposure amount is less than the preset exposure amount.
[0047] The step S3 specifically includes the following steps:
[0048] Step S31: Selecting multiple mask substrates as mask experimental pieces from the same batch of mask substrates, and exposing the M mask experimental pieces with different exposure amounts respectively, calculating the pattern line width increment corresponding to different exposure amounts, and obtaining the exposure increment-line width increment sequence.
[0049] Selecting M mask substrates as mask experimental pieces from the same batch of mask substrates, and exposing the M mask experimental pieces with different exposure amounts respectively by using an exposure machine, and then measuring the line width of the patterns after development and etching, calculating the line width increment between patterns corresponding to different exposure amounts, and obtaining the exposure increment-line width increment sequence. The different exposure amounts for each mask experimental piece refer to the exposure amounts obtained by increasing the exposure amount on the basis of the preset exposure amount.
[0050] It is worth mentioning that after increasing the exposure amount on the basis of the preset exposure amount, the reaction degree of the photoresist in the exposure area is strengthened, causing the solubility of the photoresist to change, and then affecting the final line width of the patterns after development and etching. For positive photoresist: the photoresist in the exposure area of the positive photoresist becomes more easily dissolved, and with the increase of the exposure amount, the photoresist in the exposure area is more strongly "weakened", the part removed in the development process increases, and a wider pattern is formed. For negative photoresist: the photoresist in the exposure area of the negative photoresist becomes more solid, and with the increase of the exposure amount, the photoresist in the unexposed area will be removed more, and finally a pattern with wider line width is formed.
[0051] As an example, the preset exposure amount of a certain mask substrate is 7 μC / cm², and the exposure amount will be developed when it exceeds about 5 μC / cm². After multiple tests, it is found that based on 7 μC / cm², every 1% increase in exposure amount will increase the line width by 1.5 nm.
[0052] As an example, assuming that the preset exposure amount is 7 μC / cm2, step S31 selects 10 mask experimental pieces (M=10), and after using different exposure amounts to expose the 10 mask experimental pieces respectively, the line width of the pattern in each mask experimental piece will change, usually increase. In detail, if an arithmetic progression is formed in the manner that the exposure amount of each time is 1% of the preset exposure amount, it can be understood that: the exposure amount of 7x(1+1%) μC / cm2 is used to expose the first mask experimental piece, to obtain the line width increment of the pattern in the mask experimental piece; the exposure amount of 7x(1+2%) μC / cm2 is used to expose the second mask experimental piece, and so on, finally the exposure amount of 7x(1+10%) μC / cm2 is used to expose the tenth mask experimental piece. Thus, 10 groups of exposure increments relative to the preset exposure amount and the line width increment of the pattern under each group of exposure increments can be obtained, and after linear fitting, the "exposure increment-line width increment sequence" can be obtained. It should be noted that this example is only for the convenience of understanding the linear fitting process, and in fact, the setting of different exposure amounts and the number of mask experimental pieces selected are not limited by the present scheme.
[0053] Step S32: Linear fitting is performed based on the exposure increment-line width increment sequence to construct a conversion formula of exposure increment and line width increment:
[0054] ;
[0055] Wherein, P represents the exposure increment; C represents the line width increment; k represents the conversion coefficient obtained by fitting, and the range of k is 0.4-1.5.
[0056] Step S33: The difference between the average line width of the cross pattern in each correction subzone of the mask test piece and the maximum line width of the cross pattern on the entire mask test piece is taken as the line width increment of the corresponding correction subzone, and the exposure increment corresponding to each correction subzone is calculated through the conversion formula, that is, the secondary exposure amount.
[0057] Step S34: The exposure correction file of the exposure machine is set according to the secondary exposure amount corresponding to each subzone.
[0058] As shown in Figure 5 , a total of 4 correction subzones are divided, the secondary exposure amount of the central correction subzone is 16% of the preset exposure amount, and the secondary exposure amounts of the remaining correction subzones from inside to outside are 12% of the preset exposure amount, 8% of the preset exposure amount and 4% of the preset exposure amount, respectively. The exposure correction file of the exposure machine is set based on the secondary exposure amounts of all correction subzones.
[0059] During the whole step S3, since the photoresist used by the mask substrates in the same batch is the same, the mask manufacturing process is the same, and thus the radiation type line width difference and its distribution are also basically the same. According to the secondary exposure amount of each correction zone set according to the mask test piece and the mask experimental piece selected from the same batch, the compensation of the radiation type line width difference of all the remaining mask substrates in the batch can be met, and the compensation efficiency is greatly improved.
[0060] Step S4: for the remaining other mask substrates in the same batch, after one-time exposure with a preset exposure amount, secondary exposure is performed through the exposure correction file, and then development, etching and photoresist removal are sequentially performed to obtain a mask mask plate.
[0061] As shown in Figure 6 and Figure 7 , the pattern line widths of the mask test piece and the mask mask plate are measured respectively, and the average of the radiation type line width difference of the mask test piece is calculated to be 42.4 nm, and the average of the radiation type line width difference of the mask mask plate is calculated to be 22.7 nm. As can be seen, after the line width difference of the mask mask plate is improved according to the present scheme, the radiation type line width difference is reduced compared with the unimproved mask test piece, and great improvement is obtained.
[0062] In the present embodiment, according to the distribution of the radiation type line width difference decreasing from the center to the edge, the correction zones are set from the center to the outside, the secondary exposure amount of the corresponding correction zone is set according to the difference between the maximum line width of the pattern and the average line width of the different correction zones, and the secondary exposure amount is superimposed on the basis of the preset exposure amount. After the mask substrate is subjected to secondary exposure, the pattern line width of the correction zone superimposed with the secondary exposure amount is increased, so that the line width difference caused by the different development and etching rates can be compensated, and the line width difference of the finally obtained mask mask plate is greatly improved, the radiation type line width difference of the mask mask plate is significantly reduced, and the quality of the mask mask plate is improved.
[0063] The above-mentioned embodiment numbers of the present application are only for description, and do not represent the advantages and disadvantages of the embodiments.
[0064] The above is only the preferred embodiment of the present application, and does not limit the patent scope of the present application, and any equivalent structure or equivalent flow transformation according to the content of the specification and drawings of the present application, or direct or indirect application in other related technical fields, are also included in the patent protection scope of the present application.
Claims
1. A method for improving the difference in radiation line width of a mask, characterized in that: The following steps are involved: S1, randomly selecting a photomask substrate from a batch of photomask substrates, sequentially subjecting the photomask substrate to exposure with a preset exposure amount, development, etching, and photoresist removal to obtain a photomask test piece; the photomask test piece has a cross pattern array obtained by etching; S2, measuring the line width of each cross pattern in the cross pattern array on the mask test piece, dividing the mask test piece into N concentric squares outward from the geometric center, and the area where two adjacent concentric squares do not overlap constitutes a correction partition; S3, calculating a secondary exposure amount of each correction zone according to a difference between a maximum line width of a pattern on the test mask and an average line width of a pattern on each correction zone, and setting an exposure correction level of an exposure machine based on the secondary exposure amount of each correction zone; wherein the secondary exposure amount is less than a preset exposure amount; S4, after exposing the remaining photomask substrates in the same batch to a preset exposure amount, performing a second exposure using an exposure correction file, and then performing development, etching, and photoresist removal in sequence to obtain a photomask mask.
2. The method for improving the line width variation of the mask radiation pattern according to claim 1, wherein: The preset exposure range is 5μC / cm² to 30μC / cm².
3. The method for improving the line width variation of the mask radiation pattern according to claim 1, wherein: The range of N is 3 to 5.
4. The method for improving the line width variation of the mask radiation pattern according to claim 1, wherein: Set a first preset difference and a second preset difference, and the first preset difference < the second preset difference; Measuring the line width of each cross pattern in the cross pattern array on the mask test piece, and calculating the line width difference between the cross pattern at the center and the cross pattern at the outermost edge of the mask test piece; When the line width difference is less than the first preset difference, set N=3; When the line width difference is greater than the first preset difference and less than the second preset difference, set N=4; when the line width difference is greater than the second preset difference, set N=5.
5. The method for improving the line width variation of the mask radiation pattern according to claim 1, wherein: The centralmost square alone constitutes a correction partition; each of the correction partitions covers at least one cross figure, the side length of the centralmost square is equal to the center distance between adjacent cross figures, and the difference in side lengths of adjacent concentric squares is equal to twice the side length of the centralmost square.
6. The method for improving the line width variation of the mask radiation pattern according to claim 1, wherein: The S3 specifically includes: S31, selecting multiple mask substrates from the same batch of mask substrates as mask test pieces, exposing the multiple mask test pieces at different exposure amounts, calculating pattern line width increments corresponding to the different exposure amounts, and obtaining an exposure increment-line width increment sequence; S32, based on the exposure increment-line width increment sequence, linear fitting is performed to construct the conversion formula between exposure increment and line width increment: ； Where P represents the exposure increment; C represents the line width increment; k represents the conversion coefficient obtained by fitting, and the range of k is 0.4~1.5; S33, taking the difference between the average line width of the cross pattern in each correction zone of the test mask and the maximum line width of the cross pattern on the entire test mask as the line width increment of the corresponding correction zone, and calculating the exposure increment corresponding to each correction zone using a conversion formula, i.e., the secondary exposure amount; S34, setting the exposure correction gear of the exposure machine according to the secondary exposure amount corresponding to each partition.
7. The method for improving the line width variation of the mask radiation pattern according to claim 6, wherein: In the above S31 , successively increasing exposure amounts are set, and a plurality of photomask test pieces are exposed respectively using the successively increasing exposure amounts, and the pattern line width increment in each photomask test piece is calculated in sequence.