CdU correction method

Abstract

This invention discloses a CDU correction method, comprising: Step 1, identifying multiple weak points within a die chip, forming measurement regions within the die chip centered on each weak point; measuring the critical dimensions of the patterns within each measurement region to obtain multiple CD measurement values. Step 2, subtracting the CD target value from the CD measurement value corresponding to each pattern within each measurement region to obtain CD offset values. The distribution of CD offset values ​​within the die chip is obtained based on the distribution of patterns corresponding to each CD offset value. Step 3, correcting the CDU menu based on the distribution of CD offset values ​​in each measurement region to obtain a CDU correction menu. Step 4, inputting the CDU correction menu into a lithography machine, which performs exposure using the CDU correction menu to achieve CDU correction. This invention directly uses the measurement of device patterns within the die chip to achieve CDU correction, eliminating the need for CDU marking and improving the CDU correction effect.

Description

Technical Field

[0001] This invention relates to a method for manufacturing semiconductor integrated circuits, and more particularly to a method for correcting critical dimension uniformity (CDU). Background Technology

[0002] like Figure 1 The diagram shows a flowchart of an existing CDU correction method; the existing CDU correction method includes the following steps:

[0003] The wafer 201 is exposed using a lithography machine 101.

[0004] Then, an etching machine is used to etch wafer 201; before CDU correction, the obtained CDU data will be poor after etching.

[0005] Next, marking 104, critical dimension (CD) measurements are performed, and a CD map is generated. The figure marked 202 represents the CD map. Each coordinate on the map corresponds one-to-one with each coordinate on the wafer, and the CD map displays the CD value at each coordinate position on the map.

[0006] like Figure 2 The diagram shown is a distribution of CDU marks 205 in the exposure area 204 in the existing CDU correction method. In the existing method, CD measurement is achieved by measuring the CDU marks 205 placed on the cutting path. By placing more CDU marks 205, the entire exposure area 204 of the product is covered to achieve CDU correction.

[0007] like Figure 3A The diagram shown is a structural schematic of the CDU mark 205 in the existing CDU correction method; the CDU mark 205 is basically a one-dimensional dense line pattern 206 or a dense trench pattern.

[0008] like Figure 3B As shown, is Figure 3A SEM image of CDU marker 205; line 206a is Figure 3A SEM image of line 206 in the middle, through Figure 3B The line 206a in the diagram can be used to obtain the corresponding CD value.

[0009] Back Figure 1 As shown, CDU optimization 105 is performed. Typically, CDU optimization 105 is achieved through IMO software processing of the lithography machine.

[0010] After CDU optimization 105, a revised recipe is obtained, which typically includes an exposure dose sub-recipe 106. Map 203 shows the control diagram of exposure dose by exposure dose sub-recipe 106, that is, a map diagram for setting the exposure dose at various locations on the wafer.

[0011] When the wafer is subsequently exposed again, it will include correction information from the correction menu, which will correct the CDU.

[0012] Existing methods achieve CDU correction through mark dose control. However, due to the use of CDU labeling, these methods are limited by the CDU labeling and have the following drawbacks:

[0013] 1. When the chip pattern is different, different CDU markings need to be used.

[0014] 2. It is limited by the layout. For example, large die products cannot use CDU markers for CDU correction well because there cannot be a sufficient number of CDU markers in large die products.

[0015] 3. Limited CDU marker distribution can lead to insufficient intrafield dose control within the exposure area.

[0016] 4. Due to the limited number of CDU markers, the amount of CD data obtained from the measurement is limited, and measurement noise cannot be avoided. Only simple marker designs can be used, mostly 1D. Summary of the Invention

[0017] The technical problem to be solved by the present invention is to provide a CDU correction method that directly uses the measurement of the device pattern in the die to achieve CDU correction, thereby improving the CDU correction effect.

[0018] To solve the above-mentioned technical problems, the CDU correction method provided by the present invention includes the following steps:

[0019] Step 1: Locate multiple weaknesses within the die chip, and form a measurement region within the die chip centered on each weakness; measure the key dimensions of the pattern within each measurement region to obtain multiple CD measurement values.

[0020] Step 2: Subtract the corresponding CD target value from the CD measurement value corresponding to each of the graphics in each of the measurement areas to obtain the corresponding CD offset value.

[0021] The distribution of the CD offset values ​​within the die chip is obtained based on the distribution of the patterns corresponding to each CD offset value.

[0022] Step 3: Correct the CDU menu according to the distribution of the CD offset values ​​in each measurement area to obtain the CDU correction menu.

[0023] Step 4: Input the CDU correction menu into the lithography machine, and the lithography machine performs exposure using the CDU correction menu to achieve CDU correction.

[0024] A further improvement is to use OPC software to find the aforementioned weaknesses.

[0025] A further improvement is to use SEM measurements to obtain the CD measurement values.

[0026] A further improvement is that the field of view (FOV) of the SEM is greater than 2 micrometers * 2 micrometers.

[0027] A further improvement is that the graphics in each of the measurement areas are the same or different.

[0028] A further improvement is that step two also includes:

[0029] The virtual CD value corresponding to each measurement area is obtained by averaging the CD measurement values ​​in each measurement area.

[0030] Step three also includes modifying the CDU menu using the virtual CD value.

[0031] A further improvement is that step two also includes:

[0032] The average CD offset is obtained by averaging the CD offset values ​​in each of the measurement areas.

[0033] In step three, the average CD offset is used as a common correction value for various graphics in each of the measurement areas, and the CDU menu is corrected using the correction value.

[0034] A further improvement is that the CD target value is provided by OPC software.

[0035] A further improvement is that the CDU menu includes an exposure dose control sub-recipe for controlling the exposure dose; the modification of the CDU menu includes the modification of the exposure dose control sub-recipe.

[0036] A further improvement is that, in step one, key dimensions are measured for the graphics in all directions within each measurement area.

[0037] A further improvement is that no CDU markings are set on the dicing track of the die chip.

[0038] A further improvement is that, in step one, the wafer corresponding to the chip completes the photolithography process controlled by the CDU menu before the correction in step three, as well as the etching process, in the photolithography machine.

[0039] A further improvement is that, after step four is completed, the CDU correction menu is used as the CDU menu for the lithography machine in implementing subsequent lithography processes.

[0040] A further improvement is to cycle steps one through four more times to ensure that the CDU meets the process requirements.

[0041] Compared with the existing technology that requires the use of CDU markers to achieve CDU correction, the present invention directly uses the measurement of the device pattern within the die to achieve CDU correction, without the need for CDU markers. Therefore, the CDU correction effect of the present invention is not limited by CDU markers, such as the number and arrangement of CDU markers, which enables the present invention to achieve better CDU correction effect.

[0042] Compared with existing methods using CDU marking, the improvement in CDU correction effect of this invention is further reflected in:

[0043] Since this invention directly uses the device pattern within the die chip to achieve CDU correction, changes to the device pattern within the die chip will not affect the CDU correction effect of this invention. In contrast, in existing methods, when CDU markings are applied to different device patterns within different die chips, the CDU correction effect often varies and often fails to achieve the desired CDU correction effect.

[0044] Since this invention does not require setting CDU markers, it is not limited by the die chip layout and is applicable to all products. In contrast, existing methods require setting CDU markers in the layout, which often results in insufficient CDU markers for products with large dies, thus preventing CDU correction for large dies.

[0045] In this invention, the device patterns within the die chip used for CDU correction are densely and uniformly distributed, which effectively increases the control of the exposure dose in the exposure area, thereby improving the CDU correction effect within the exposure area. In contrast, existing methods have a limited distribution of CDU markers, which leads to insufficient control of the exposure dose within the exposure area, thus limiting the CDU correction effect.

[0046] The device patterns within the die chip of this invention can provide massive amounts of data, as well as metrology settings based on Graphic Data System (GDS) files, enabling the application of complex two-dimensional graphic patterns. In contrast, existing methods, due to the limited amount of data provided by CDU markers, cannot avoid metrological noise, and CDU markers can only use simple marker designs, mostly 1D. Attached Figure Description

[0047] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments:

[0048] Figure 1 This is a flowchart of an existing CDU correction method;

[0049] Figure 2 This is a distribution map of CDU markers in the exposure area in existing CDU correction methods;

[0050] Figure 3A This is a schematic diagram of the structure of the CDU marker in existing CDU correction methods;

[0051] Figure 3B yes Figure 3A SEM images with CDU tags;

[0052] Figure 4 This is a flowchart of the CDU correction method according to an embodiment of the present invention;

[0053] Figure 5 This is a distribution map of weak points, i.e. hot spots (HS), in the exposure area of ​​the CDU correction method in this embodiment of the invention;

[0054] Figure 6 This is a photograph of a measurement area during the critical dimension measurement process in the CDU correction method of this invention embodiment;

[0055] Figure 7 This is a comparison chart showing the improvement of CDU by the CDU correction method of the present invention and existing CDU correction methods. Detailed Implementation

[0056] like Figure 4 The diagram shown is a flowchart of the CDU correction method according to an embodiment of the present invention; as shown Figure 5 The image shown is a distribution diagram of weak points 302 within the exposure area in the CDU correction method of this embodiment of the invention; as shown... Figure 6 The image shown is a photograph of a measurement area during the critical dimension measurement process in the CDU correction method of this embodiment of the invention. The CDU correction method of this embodiment of the invention includes the following steps:

[0057] Step 1, such as Figure 5 As shown, multiple weaknesses 302 within the die chip are identified.

[0058] Figure 5 The image shows the range of an exposure area, which typically includes more than one die chip.

[0059] In this embodiment of the invention, OPC software is used to find each of the aforementioned weaknesses 302.

[0060] In some embodiments, the number of weaknesses 302 is one or more. When the number of weaknesses 302 is large, multiple more important weaknesses 302 can be selected according to their importance.

[0061] A measurement region is formed within the die chip with each of the aforementioned weaknesses 302 as the center; the key dimensions of the pattern within each measurement region are measured to obtain multiple CD measurement values.

[0062] In this embodiment of the invention, the CD measurement values ​​are obtained by SEM measurement.

[0063] The measurement area is determined based on the field of view (FOV) of the SEM, and typically the largest possible FOV is used for measurement. In some embodiments, the FOV of the SEM is greater than 2 micrometers * 2 micrometers.

[0064] The graphics within each measurement area may be the same or different. For example... Figure 6 As shown, photo 303 is a SEM image of one of the measurement areas. Photo 303 displays multiple patterns 304, which may be identical or different. In this embodiment of the invention, key dimensions are measured for all directions of the patterns within each measurement area. This corresponds to existing methods. Figure 3A The difference lies in the fact that only the key dimensions of the graphic 206 corresponding to the CDU mark in one direction are measured.

[0065] In this embodiment of the invention, no CDU markings are provided on the dicing track of the die chip. Therefore, in this embodiment of the invention, CDU correction can be achieved without using CDU markings, thereby overcoming various defects caused by using CDU markings for CDU correction.

[0066] The wafer corresponding to the chip has undergone photolithography and etching processes in the photolithography machine, controlled by the CDU menu before the correction in step three.

[0067] Step 2: Subtract the corresponding CD target value from the CD measurement value corresponding to each of the graphics in each of the measurement areas to obtain the corresponding CD offset value.

[0068] The formula for calculating the CD offset value is:

[0069] CD_bias=CD_measure-CD_target (1);

[0070] In formula (1), CD_bias represents the CD offset value, CD_measure represents the CD measurement value, and CD_target represents the CD target value.

[0071] The distribution of the CD offset values ​​within the die chip is obtained based on the distribution of the graphics corresponding to each CD offset value, i.e., a map of the CD offset values ​​is obtained. The map represents a one-to-one mapping between the coordinates on the map and the corresponding coordinates on the actual wafer, and the CD offset values ​​are displayed at the corresponding coordinates on the map.

[0072] In this embodiment of the invention, the CD target value is provided by OPC software.

[0073] In this embodiment of the invention, it further includes:

[0074] The virtual CD value corresponding to each measurement area is obtained by averaging the CD measurement values ​​in each measurement area.

[0075] The formula for calculating the virtual CD value is:

[0076]

[0077] In formula (2), CD_virtual represents the virtual CD value, k represents the sequence number of the graphic in the measurement area, n represents the total number of graphics in the measurement area, and CD_measure k This represents the CD measurement value of the k-th graphic in the measurement area.

[0078] In this embodiment of the invention, it further includes:

[0079] The average CD offset is obtained by averaging the CD offset values ​​in each of the measurement areas.

[0080] The formula for calculating the average CD offset is:

[0081]

[0082] In formula (3), bias_mean represents the average CD offset, and CD_bias k This represents the CD offset value of the k-th graphic in the measurement area.

[0083] Step 3: Correct the CDU menu according to the distribution of the CD offset values ​​in each measurement area to obtain the CDU correction menu.

[0084] In this embodiment of the invention, the method further includes: modifying the CDU menu using the virtual CD value.

[0085] In this embodiment of the invention, the method further includes: using the average CD offset as a common correction value for various graphics in each of the measurement areas, and using the correction value to correct the CDU menu.

[0086] In this embodiment of the invention, the R value of the correction is the average of the R values ​​of all patterns within all measurement areas. The R value represents the correction ratio, that is, the correction ratio of the exposure dose. In some embodiments, the specific magnitude of the R value can be obtained through OPC simulation.

[0087] The upper and lower limits of the correction value are adopted from the edge limit (EL) values ​​verified by the process window of the same type of product. In some embodiments, the specific size of the EL value can be obtained by OPC simulation.

[0088] In this embodiment of the invention, the CDU menu includes an exposure dose control submenu for controlling the exposure dose; the modification of the CDU menu includes the modification of the exposure dose control submenu.

[0089] Step 4: Input the CDU correction menu into the lithography machine, and the lithography machine performs exposure using the CDU correction menu to achieve CDU correction.

[0090] After step four is completed, the CDU correction menu is used as the CDU menu for the lithography machine in implementing subsequent lithography processes.

[0091] In some embodiments, steps one through four are repeated more than once to make the CDU meet process requirements.

[0092] Compared with the existing technology that requires the use of CDU markers to achieve CDU correction, the embodiments of the present invention directly use the measurement of the device pattern within the die to achieve CDU correction, without the need for CDU markers. Therefore, the CDU correction effect of the embodiments of the present invention is not limited by CDU markers, such as the number and arrangement of CDU markers, so that the embodiments of the present invention can achieve better CDU correction effect.

[0093] Compared with existing methods that use CDU marking, the improved CDU correction effect of the embodiments of the present invention is further reflected in:

[0094] Since the embodiments of the present invention directly use the device pattern within the die chip to achieve CDU correction, changes to the device pattern within the die chip will not affect the CDU correction effect of the embodiments of the present invention; while in existing methods, when the CDU mark is applied to different device patterns within different die chips, the CDU correction effect is often different and often fails to achieve the required CDU correction effect.

[0095] Since the embodiments of the present invention do not require setting CDU markers, they are not limited by the layout of the die chip and are applicable to all products. In contrast, existing methods require setting CDU markers in the layout, which often results in insufficient CDU markers for products with large die chips, thus preventing CDU correction for large die chips.

[0096] In this embodiment of the invention, the device patterns within the die chip used for CDU correction are densely and uniformly distributed, which effectively increases the control of the exposure dose in the exposure area, thereby improving the CDU correction effect in the exposure area. In contrast, in existing methods, the distribution of CDU markers is limited, which leads to insufficient control of the exposure dose in the exposure area, thus limiting the CDU correction effect.

[0097] The device patterns within the die chip of this invention can provide massive amounts of data, as well as metrology settings based on GDS files, enabling the application of complex two-dimensional graphic patterns. In contrast, existing methods, due to the limited amount of data provided by CDU markers and the inability to avoid metrological noise, can only use simple marker designs, mostly 1D.

[0098] Experimental verification shows that before CDU correction using the method of this embodiment, the 3σ of the CD distribution is 1.87 nm; while after CDU correction using the method of this embodiment, the 3σ of the CD distribution can be reduced to 0.81 nm.

[0099] Compared with existing methods that use CDU markers for CDU correction, the method of this invention can achieve better CDU correction results, such as... Figure 7 The figure shown is a comparison chart of the CDU correction method of the present invention and the existing CDU correction method in terms of CDU improvement. Figure 7 Taking the 28HK product as an example, Figure 7 This includes:

[0100] The dashed box 401a contains the comparison data of IMO hard mask (HM) full wafer CDU. IMO refers to the software of the lithography machine, i.e., IMO software. CDU correction is achieved through IMO software.

[0101] The area within the dashed box 401b contains comparative data for full wafer CDUs with exposure dose mapper (DOMA). CDU correction is achieved through DOMA.

[0102] The area within the dashed box 402a contains the comparison data for inter-CDU exposure regions of the IMO HM.

[0103] The area within the dashed box 402b contains comparison data for CDUs between DOMA exposure regions (inter).

[0104] The data within the dashed box 403a represents the comparison data of the intra-CDU within the IMO HM exposure area.

[0105] The area within the dashed box 403b contains comparison data for intra CDUs between DOMA exposure regions.

[0106] In the two sets of comparison data above, each set includes:

[0107] The CDU map diagram in the dashed box 401a is represented by label 501.

[0108] The bar chart of CDU, the bar chart of CDU in the dashed box 401a is represented by label 502.

[0109] In the CDU histogram, the left bar represents the CDU value after CDU correction using the method of this embodiment, and the right bar represents the CDU value after CDU correction using the existing method. Within the dashed box 401a, the value of the left bar is 0.98, and the value of the right bar is 0.66. The CDU value obtained by the method of this embodiment is 33% higher than that obtained by the existing method.

[0110] Similarly, in dashed box 401b, the value of the left bar is 1.28 and the value of the right bar is 1.19. The CDU value of the method in this embodiment of the invention is 7% higher than that of the existing method.

[0111] In the dashed box 402a, the value of the left bar is 0.64 and the value of the right bar is 0.42. The CDU value of the method in this embodiment of the invention is 34% higher than that of the existing method.

[0112] In the dashed box 402b, the value of the left bar is 0.9 and the value of the right bar is 0.83. The CDU value of the method in this embodiment of the invention is 8% higher than that of the existing method.

[0113] In the dashed box 403a, the value of the left bar is 0.71 and the value of the right bar is 0.51. The CDU value of the method in this embodiment of the invention is 28% higher than that of the existing method.

[0114] In the dashed box 403b, the value of the left bar is 0.88 and the value of the right bar is 0.86. The CDU value of the method in this embodiment of the invention is 2% higher than that of the existing method.

[0115] Therefore, by Figure 7 As can be seen from the figure, compared with the existing methods, the method of the present invention can improve CDU.

[0116] The present invention has been described in detail above through specific embodiments, but these are not intended to limit the invention. Many modifications and improvements can be made by those skilled in the art without departing from the principles of the invention, and these should also be considered within the scope of protection of the present invention.

Claims

1. A CDU correction method, characterized in that, Includes the following steps: Step 1: Locate multiple weak points within the die chip, and form a measurement area within the die chip centered on each of the weak points; measure the key dimensions of the patterns within each measurement area to obtain multiple CD measurement values; Step 2: Subtract the corresponding CD target value from the CD measurement value corresponding to each of the graphics in each of the measurement areas to obtain the corresponding CD offset value; The distribution of the CD offset values ​​within the die chip is obtained based on the distribution of the patterns corresponding to each CD offset value; Step 3: Correct the CDU menu according to the distribution of the CD offset values ​​in each measurement area to obtain the CDU correction menu; Step 4: Input the CDU correction menu into the lithography machine.

2. The CDU correction method as described in claim 1, characterized in that: OPC software was used to find the weaknesses mentioned above.

3. The CDU correction method as described in claim 1, characterized in that: The CD values ​​were obtained using SEM measurements.

4. The CDU correction method as described in claim 3, characterized in that: The SEM has a field of view (FOV) greater than 2 micrometers * 2 micrometers.

5. The CDU correction method as described in claim 1, characterized in that: The graphics in each of the measurement areas may be the same or different.

6. The CDU correction method as described in claim 5, characterized in that: Step two also includes: The virtual CD value corresponding to each measurement area is obtained by averaging the CD measurement values ​​of each measurement area. Step three also includes modifying the CDU menu using the virtual CD value.

7. The CDU correction method as described in claim 6, characterized in that: Step two also includes: The average CD offset is obtained by averaging the CD offset values ​​in each of the measurement areas. In step three, the average CD offset is used as a common correction value for various graphics in each of the measurement areas, and the CDU menu is corrected using the correction value.

8. The CDU correction method as described in claim 1, characterized in that: The CD target value is provided by OPC software.

9. The CDU correction method as described in claim 1, characterized in that: The CDU menu includes an exposure dose control submenu for controlling the exposure dose; modifications to the CDU menu include modifications to the exposure dose control submenu.

10. The CDU correction method as described in claim 3, characterized in that: In step one, key dimensions are measured for the graphics in all directions within each measurement area.

11. The CDU correction method as described in claim 1, characterized in that: The die chip does not have a CDU mark on the dicing path.

12. The CDU correction method as described in claim 1, characterized in that: In step one, the wafer corresponding to the chip completes the photolithography process controlled by the CDU menu before the correction in step three, and also completes the etching process in the photolithography machine.

13. The CDU correction method as described in claim 12, characterized in that: After step four is completed, the CDU correction menu is used as the CDU menu for the lithography machine in implementing subsequent lithography processes.

14. The CDU correction method as described in claim 13, characterized in that: Repeat steps one through four more times to ensure that the CDU meets the process requirements.

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