Measurement method of mask positioning accuracy
By introducing translation steps in the mask lithography process, forming a superimposed exposure unit and comparing it with the reference exposure unit, the problem of inaccurate measurement of the mask positioning accuracy in the prior art is solved, and the mask is realized in the actual circuit Accurate measurement of transistor positioning accuracy and improvement of lithography accuracy.
Patent Information
- Application Number
- CN202210127084.X
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- Filing Date
- 2022-02-11
- Publication Date
- 2025-02-07
- Estimated Expiration
- 2042-02-11
AI Technical Summary
The prior art cannot accurately measure the positioning accuracy of individual transistors in actual circuits of masks, resulting in insufficient lithography erection accuracy.
By exposing the light-measuring sheet to be metered using a mask plate, a first exposure unit is formed, and then the mask plate is translated to a certain distance, and the light-measuring sheet is exposed again to form a second exposure unit. The key size of the second exposure unit is measured and compared with the key size of the reference exposure unit to determine the positioning accuracy of the mask plate.
This method can accurately reflect the positioning accuracy of the mask plate during the actual lithography overprinting process, and improve the accuracy of the lithography process.
Smart Images
Figure CN114488710B_ABST
Abstract
Description
Technical Field
[0001] The present application relates to the technical field of semiconductor integrated circuit manufacturing, and in particular to a method for measuring mask positioning accuracy. Background Art
[0002] As the size of semiconductor devices becomes smaller and smaller, the requirements for photolithography accuracy are getting higher and higher, and the impact of mask accuracy on the photolithography process is becoming increasingly greater.
[0003] Mask manufacturers usually use the DTD (Die to database) method to measure the positioning accuracy of the mask. That is, first measure the actual position of a specific measurement pattern on the mask, and determine the preset position of the specific measurement pattern in the layout database, and then compare the actual position of the specific measurement pattern with the preset position to determine the error, and use the error to characterize the positioning accuracy of the mask.
[0004] Semiconductor manufacturers usually do not have the ability to measure the positioning accuracy of the above-mentioned mask, and can only rely on the test report provided by the mask manufacturer. However, the test report provided by the mask manufacturer can only reflect the positioning accuracy of a limited number of specific test patterns of the mask relative to the layout database, and characterize the overall macro positioning accuracy through a limited number of sampling statistics, and cannot accurately reflect the actual positioning accuracy of specific individual transistors in the actual circuit of the mask. Summary of the invention
[0005] The present application provides a method for measuring the positioning accuracy of a mask, which can solve the problem in the related art that the actual positioning accuracy of specific individual transistors in the actual circuit in the mask cannot be accurately reflected.
[0006] In order to solve the technical problem described in the background technology, the present application provides a method for measuring the positioning accuracy of a mask, and the method for measuring the positioning accuracy of a mask comprises the following steps performed in sequence:
[0007] The first step: using the mask to expose the photosensitive sheet to form a first exposure unit;
[0008] Step 2: The mask is translated by a first distance, and the photosensitive sheet is exposed again through a different position of the mask, so that the first exposure unit is superimposed and exposed to form a second exposure unit;
[0009] Step 3: Measure the critical dimension of the second exposure unit; the critical dimension may be the critical dimension of a specific transistor of concern in design or manufacturing, selected at any position and in any number among all transistors.
[0010] Step 4: Determine the positioning accuracy of the mask based on the comparison result of the critical dimension of the second exposure unit with the critical dimension of the corresponding test structure in the reference exposure unit;
[0011] The reference exposure unit is an exposure unit formed by performing an exposure operation on a light sheet using the mask.
[0012] Optionally, before the first step of using the mask to expose the photosensitive sheet to form a first exposure unit, the following preliminary steps are also performed:
[0013] Obtain preliminary light films;
[0014] Using a mask to expose the preliminary light sheet to form a preliminary exposure unit, and obtaining a critical dimension of the preliminary exposure unit;
[0015] The preliminary exposure unit is used as the reference exposure unit, and the critical dimension of the preliminary exposure unit is used as the critical dimension of the reference exposure unit.
[0016] Optionally, the method for measuring the positioning accuracy of the mask further includes the following steps performed in sequence:
[0017] Using the mask to expose the photosensitive sheet to form a third exposure unit;
[0018] The mask is translated by a second distance, and the photosensitive sheet is exposed again through a different position of the mask, so that the third exposure unit is superimposed and exposed to form a fourth exposure unit;
[0019] measuring the critical dimension of the fourth exposure unit; taking the fourth exposure unit as the reference exposure unit, and taking the critical dimension of the fourth exposure unit as the critical dimension of the reference exposure unit;
[0020] The second distance is different from the first distance.
[0021] Optionally, the fourth step: determining the positioning accuracy of the mask based on a comparison result of the critical dimension of the second exposure unit with the critical dimension of the reference exposure unit, comprises:
[0022] comparing a statistical distribution difference between a critical dimension of the second exposure unit and a critical dimension of the reference exposure unit;
[0023] The positioning differences between different positions of the mask are determined based on the statistical distribution differences.
[0024] Optionally, the second distance includes m chip areas, where m is an integer.
[0025] Optionally, the preliminary exposure unit, the first exposure unit and the second exposure unit each include a plurality of chip regions formed by exposing different mask regions of the mask.
[0026] Optionally, the patterns of different mask areas of the mask are the same.
[0027] Optionally, the first distance includes n chip areas, where n is an integer.
[0028] Optionally, the chip area includes an exposure pattern;
[0029] The third step: the step of measuring the critical dimension of the second exposure unit, comprises the following steps performed in sequence:
[0030] Determine any number of chip regions at any position in the second exposure unit;
[0031] The critical dimension of the exposure pattern of the chip area is measured as the critical dimension of the second exposure unit.
[0032] Optionally, the fourth step: determining the positioning accuracy of the mask based on a comparison result of the critical dimension of the second exposure unit with the critical dimension of the reference exposure unit, comprises:
[0033] The positioning accuracy of the mask is determined based on the comparison result of the critical dimensions of the chip area exposure patterns at any position and any number in the second exposure unit with the critical dimensions of the test chip area exposure patterns corresponding to the chip area in the reference exposure unit.
[0034] The technical solution of the present application includes at least the following advantages: through the translation of the mask, the finally formed exposure unit is formed by two superimposed exposures at different positions of the mask, and the difference between the critical dimensions of the exposure unit formed by the superimposed exposure and the critical dimensions of the reference exposure unit is compared to determine the positioning accuracy of the mask, thereby being able to accurately reflect the actual positioning accuracy of the mask in the actual lithography overlay process. BRIEF DESCRIPTION OF THE DRAWINGS
[0035] In order to more clearly illustrate the specific implementation methods of the present application or the technical solutions in the prior art, the drawings required for use in the specific implementation methods or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some implementation methods of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.
[0036] Figure 1 A flow chart of a method for measuring mask positioning accuracy provided by an embodiment of the present application is shown;
[0037] Figure 2a A schematic diagram of the local structure of the mask in the first step is shown;
[0038] Figure 2b A schematic diagram of a first exposure unit formed after the first step is completed is shown;
[0039] Figure 2c A schematic diagram showing the second step of an embodiment of the present application is shown;
[0040] Figure 2d Shows Figure 2c Schematic diagram of the position of the projection area of the middle mask during the second step;
[0041] Figure 2e A schematic diagram showing the comparison between the critical dimensions of the second exposure unit and the critical dimensions of the reference exposure unit is shown;
[0042] Figure 3 A flow chart of the steps for obtaining a reference exposure unit is shown. DETAILED DESCRIPTION
[0043] The following will be combined with the accompanying drawings to clearly and completely describe the technical solutions in this application. Obviously, the described embodiments are part of the embodiments of this application, rather than all of the embodiments. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of this application.
[0044] In the description of the present application, it should be noted that the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", etc., indicating the orientation or positional relationship, are based on the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the present application and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as limiting the present application. In addition, the terms "first", "second", and "third" are used for descriptive purposes only, and cannot be understood as indicating or implying relative importance.
[0045] In the description of this application, it should be noted that, unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, it can also be the internal connection of two components, it can be a wireless connection, or it can be a wired connection. For ordinary technicians in this field, the specific meanings of the above terms in this application can be understood according to specific circumstances.
[0046] In addition, the technical features involved in the different embodiments of the present application described below can be combined with each other as long as they do not conflict with each other.
[0047] Figure 1 The flowchart of the method for measuring the positioning accuracy of the mask provided by an embodiment of the present application is shown. Figure 1 It can be seen that the method for measuring the positioning accuracy of the mask plate includes the following steps:
[0048] The first step: using the mask to expose the photosensitive sheet to form a first exposure unit.
[0049] Reference Figure 2a , which shows a schematic diagram of the local structure of the mask in the first step, from Figure 2a It can be seen that the mask 200 includes multiple projection areas (shot), one projection area is the area corresponding to one projection exposure operation (shot), each projection area includes multiple mask areas (chips), and the patterns of different mask areas of the mask 200 are the same.
[0050] Taking the mask projection area 210 as an example, the mask projection area 210 includes a plurality of mask areas (chips), for example, Figure 2a The first mask area 211 at the lower left corner of the mask projection area 210 is shown, and the Figure 2a The second mask area 212 is shown at the upper right corner of the mask projection area 210 .
[0051] Reference Figure 2b , which shows a schematic diagram of the first exposure unit formed after the first step is completed. Figure 2b As can be seen from FIG. 1 , the first exposure unit 220 includes a plurality of chip regions, for example, Figure 2b The first chip area 221 at the lower left corner of the first exposure unit 220 is shown, and the Figure 2b The second chip region 222 at the upper right corner of the first exposure unit 220 is shown.
[0052] For example, when using Figure 2a The mask 200 shown in the figure is used to expose the photosensitive film to be tested, and the mask projection area 210 forms Figure 2b The first exposure unit 220 , for example, exposes the first mask region 211 of the mask projection region 210 to form a first chip region 221 of the first exposure unit 220 , and exposes the second mask region 212 to form a second chip region 222 .
[0053] Step 2: The mask is translated by a first distance, and the photosensitive sheet is exposed again through a different position of the mask, so that the first exposure unit is superimposed and exposed to form a second exposure unit.
[0054] The first distance includes n chip areas, where n is an integer.
[0055] Reference Figure 2c , which shows a schematic diagram of the second step of the embodiment of the present application. Figure 2c As can be seen from the figure, when the second step is performed, the mask 210 is shifted along the direction D by n chip regions from the position after the first step is completed. After exposure again, different positions of the mask 200 are Figure 2c The first exposure unit 220 at the position corresponding to the dotted line frame performs exposure again, so that the first exposure unit is superimposed and exposed to form a second exposure unit.
[0056] Reference Figure 2d , which shows Figure 2c Figure 2 is a schematic diagram of the position of the mask projection area 210 during the second step. Figure 2d As can be seen, the mask projection area 210 at the lower left is the starting position before the second step, at which the mask projection area 210 is exposed to form Figure 2b The first exposure unit 220 shown in the figure; the mask projection area 210 on the upper right is the position after the second step is completed, so that the first exposure unit is superimposed and exposed to form the second exposure unit. For example, after the second step is completed, the second chip area 222 of the first exposure unit 220 is superimposed and exposed by the second mask area 212 of the mask projection area 210.
[0057] Step 3: Measure the critical dimension of the second exposure unit.
[0058] The critical dimension of the second exposure unit in the third step can be used to linearly determine chip areas at any position and in any number in the second exposure unit; and then measure the critical dimension of the exposure pattern of the chip area as the critical dimension of the second exposure unit.
[0059] Step 4: Based on the comparison result of the critical dimension of the second exposure unit and the critical dimension of the reference exposure unit, the positioning accuracy of the mask is determined.
[0060] The reference exposure unit is an exposure unit formed by performing an exposure operation on a light sheet using the mask.
[0061] The fourth step can determine the positioning accuracy of the mask based on the comparison result of the critical dimensions of the chip area exposure pattern at any position and any number of chip areas in the second exposure unit and the critical dimensions of the test chip area exposure pattern corresponding to the chip area in the reference exposure unit.
[0062] Reference Figure 2e, which shows a schematic diagram of the comparison between the critical dimensions of the second exposure unit and the critical dimensions of the reference exposure unit. Figure 2e It can be seen that the critical dimension CD2 of the second exposure unit and the critical dimension CD1 of the reference exposure unit are measured, and the positioning accuracy of the mask is determined by comparing the difference between the critical dimension CD2 of the second exposure unit and the critical dimension CD1 of the reference exposure unit. When the difference between the critical dimension CD2 of the second exposure unit and the critical dimension CD1 of the reference exposure unit is small, it is determined that the positioning accuracy of the mask is high, otherwise the positioning accuracy of the mask is low.
[0063] The reference exposure unit in the fourth step can be obtained through the following steps, wherein the following steps of obtaining the reference exposure unit can be completed before the first step in the above embodiment is performed.
[0064] Reference Figure 3 , which shows a flowchart of the steps of obtaining a reference exposure unit, from Figure 3 It can be seen that the step of obtaining the reference exposure unit includes the following steps performed in sequence:
[0065] S31: Obtain a preliminary light sheet.
[0066] S32: using a mask to expose the preliminary light sheet to form a preliminary exposure unit, and obtaining a critical dimension of the preliminary exposure unit.
[0067] S33: making the preliminary exposure unit serve as the reference exposure unit, and the critical dimension of the preliminary exposure unit serve as the critical dimension of the reference exposure unit.
[0068] The present application also provides another embodiment of a method for measuring the positioning accuracy of a mask. Figure 1 Based on the embodiment shown, the following steps are also included:
[0069] S41: using the mask to expose the photosensitive sheet to form a third exposure unit.
[0070] S42: the mask is translated by a second distance, and the photosensitive sheet is exposed again through a different position of the mask, so that the third exposure unit is superimposed and exposed to form a fourth exposure unit.
[0071] S43: measuring the critical dimension of the fourth exposure unit; taking the fourth exposure unit as the reference exposure unit, and taking the critical dimension of the fourth exposure unit as the critical dimension of the reference exposure unit.
[0072] The second distance is different from the first distance. The second distance includes m chip areas, where m is an integer.
[0073] Then, the critical dimension of the fourth exposure unit measured in step S43 is compared with the critical dimension of the second exposure unit measured in the first embodiment, and the positioning accuracy of the mask is determined according to the comparison result.
[0074] For the above two embodiments, the fourth step: determining the positioning accuracy of the mask based on the comparison result of the critical dimension of the second exposure unit with the critical dimension of the reference exposure unit, comprises the following steps:
[0075] S51: comparing the statistical distribution difference between the critical dimension of the second exposure unit and the critical dimension of the reference exposure unit;
[0076] S52: Determine positioning differences between different positions of the mask based on the statistical distribution differences.
[0077] By translating the mask, the final exposure unit is formed by two superimposed exposures at different positions of the mask. The positioning accuracy of the mask is determined by comparing the difference between the critical dimensions of the exposure unit formed by the superimposed exposure and the critical dimensions of the reference exposure unit, thereby accurately reflecting the actual positioning accuracy of the mask in the actual lithography overlay process.
[0078] Obviously, the above embodiments are merely examples for the purpose of clear explanation, and are not intended to limit the implementation methods. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the implementation methods here. The obvious changes or modifications derived therefrom are still within the scope of protection created by this application.
Claims
1. A method for measuring mask positioning accuracy, characterized in that: The method for measuring the positioning accuracy of the mask plate comprises the following steps performed in sequence: Step 1: using the mask to expose the photosensitive sheet to form a first exposure unit; the mask includes a plurality of projection areas, the mask projection area includes a plurality of mask areas, and the patterns of different mask areas are the same; the mask projection area is exposed once to form the first exposure unit, the first exposure unit includes a plurality of chip areas, and the chip areas are formed by exposing the mask areas; Step 2: The mask is translated by a first distance, and the photosensitive sheet is exposed again through a different position of the mask, so that the first exposure unit is superimposed and exposed to form a second exposure unit; the first distance includes n chip areas, where n is an integer; Step 3: measuring the critical dimension of the second exposure unit; Step 4: Determine the positioning accuracy of the mask based on the comparison result of the critical dimension of the second exposure unit with the critical dimension of the reference exposure unit; The reference exposure unit is an exposure unit formed by performing an exposure operation on a light sheet using the mask.
2. The method for measuring the positioning accuracy of a mask according to claim 1, characterized in that: Before the first step of using the mask to expose the photosensitive sheet to form the first exposure unit, the following preliminary steps are also performed: Obtain preliminary light films; Using a mask to expose the preliminary light sheet to form a preliminary exposure unit, and obtaining a critical dimension of the preliminary exposure unit; The preliminary exposure unit is used as the reference exposure unit, and the critical dimension of the preliminary exposure unit is used as the critical dimension of the reference exposure unit.
3. The method for measuring the positioning accuracy of a mask according to claim 1, characterized in that: The method for measuring the positioning accuracy of the mask also includes the following steps performed in sequence: Using the mask to expose the photosensitive sheet to form a third exposure unit; The mask is translated by a second distance, and the photosensitive sheet is exposed again through a different position of the mask, so that the third exposure unit is superimposed and exposed to form a fourth exposure unit; measuring a critical dimension of the fourth exposure unit; Taking the fourth exposure unit as the reference exposure unit, and taking the critical dimension of the fourth exposure unit as the critical dimension of the reference exposure unit; The second distance is different from the first distance.
4. The method for measuring the positioning accuracy of a mask according to any one of claims 1 to 3, characterized in that: The fourth step: determining the positioning accuracy of the mask based on the comparison result of the critical dimension of the second exposure unit with the critical dimension of the reference exposure unit, comprises: comparing a statistical distribution difference between a critical dimension of the second exposure unit and a critical dimension of the reference exposure unit; The positioning differences between different positions of the mask are determined based on the statistical distribution differences.
5. The method for measuring the positioning accuracy of a mask according to claim 3, characterized in that: The second distance includes m chip regions, where m is an integer.
6. The method for measuring the positioning accuracy of a mask according to claim 2, characterized in that: The preliminary exposure unit, the first exposure unit and the second exposure unit each include a plurality of chip regions formed by exposing different mask regions of the mask.
7. The method for measuring the positioning accuracy of a mask according to claim 6, characterized in that: The patterns of different mask areas of the mask are the same.
8. The method for measuring mask positioning accuracy according to claim 6, characterized in that: The first distance includes n chip areas, where n is an integer.
9. The method for measuring the positioning accuracy of a mask according to claim 6, characterized in that: The chip region includes an exposure pattern; The third step: the step of measuring the critical dimension of the second exposure unit, comprises the following steps performed in sequence: Determine any number of chip regions at any position in the second exposure unit; The critical dimension of the exposure pattern of the chip area is measured as the critical dimension of the second exposure unit.
10. The method for measuring mask positioning accuracy according to claim 9, characterized in that: The fourth step: determining the positioning accuracy of the mask based on the comparison result of the critical dimension of the second exposure unit with the critical dimension of the reference exposure unit, comprises: The positioning accuracy of the mask is determined based on the comparison result of the critical dimensions of the chip area exposure patterns at any position and any number in the second exposure unit with the critical dimensions of the test chip area exposure patterns corresponding to the chip area in the reference exposure unit.
Citation Information
Patent Citations
Determining position accuracy of double exposure lithography using optical metrology
US20080016487A1