Method for Detecting and Verifying Optical-Assisted Grating Optical Imaging

Abstract

The present invention provides a method for detecting and verifying optical-assisted grating optical imaging. A wafer is provided, and a photoresist layer is formed on the wafer. The photoresist layer is exposed using a mask plate including a receptor pattern and an optical-assisted grating; at least one physical variable of the optical-assisted grating is sequentially changed for each selected shot in each row, and then the developed result of the photoresist layer is obtained. Imaging patterns with different imaging degrees of the optical-assisted grating are obtained according to the developed result; the imaging patterns are optically simulated to establish an OPC model; the parameters of the OPC model in which the optical-assisted grating does not form an image during optical simulation exposure are used as the design criteria for the optical-assisted grating. The method of the present invention can detect patterns with high risks of optical-assisted grating imaging using a normal model. The OPC script person in charge can adjust and modify the script for each optical-assisted grating imaging parameter according to the severity of imaging to improve the imaging of the optical-assisted grating. The physical quantities of optical-assisted grating imaging are defined at the initial stage of modeling, reducing the verification time.

Description

Technical Field

[0001] The present invention relates to the field of semiconductor technology, and particularly to a method for detecting and verifying optical imaging of an optical assist grating. Background Art

[0002] Source Mask Optimization (SMO) simultaneously considers the light source illumination mode and the mask pattern. Compared with the traditional resolution enhancement technology (OPC), SMO has greater degrees of freedom and is one of the key technologies for further improving the lithography resolution and process window.

[0003] The basic principle of the simulation calculation of Source Mask Optimization (SMO) is similar to that of model-based proximity effect correction. Move the edges of the mask pattern and calculate the deviation from the target pattern on the wafer, that is, the edge placement error. During optimization, perturbations of the exposure dose, focus, and pattern size on the mask are deliberately introduced into the model, and the edge placement errors of the images on the wafer caused by these perturbations are calculated. The evaluation function and optimization are both realized based on the edge placement error. The result calculated by Source Mask Optimization not only includes a pixelated light source but also includes the proximity effect correction made to the input design. Since the illumination parameters and the patterns on the mask can vary simultaneously, the result of the optimization calculation may not be unique.

[0004] Although the optical assist grating can improve the lithography process window effect, it sometimes also has the risk of causing imaging. If the etching cannot remove these patterns that should not originally exist, it will cause pattern loss and thus affect the product yield.

[0005] Generally, when determining the conditions of the optical assist grating, an optical simulation software such as Pro_litho or S_litho is first used to find the poor lithography process window and the appropriate environment for adding the optical assist grating. When establishing the OPC model, if the optical assist grating imaging is not encountered, the results of the software optical simulation conditions are followed instead of confirming according to the actual severity of the optical assist grating imaging on the chip. When the OPC verifies AF printing, it is known from the model simulation imaging results. If the OPC model is less sensitive to AF, misjudgment may occur.

[0006] When establishing the OPC model, due to the main imaging, the receptor is interfered and the CD value of the receptor cannot be simulated because the simulated value includes the CD (critical dimension) of the AF (main body) imaging. After the OPC model is corrected by S-litho, the imaging is correctly and completely predicted. Figure 1 For the SEM pattern of the chip AF101 imaging under normal exposure conditions, the measured CD value is the CD of the receptor. Figure 2 For the actual measurement and simulation difference values of each pattern receptor, a deviation value of 40 nanometers is caused by the influence of the main imaging.

[0007] To solve the above problems, a new method for detecting and verifying optical-assisted grating optical imaging needs to be proposed. Summary of the Invention

[0008] In view of the above-mentioned disadvantages of the prior art, the purpose of the present invention is to provide a method for detecting and verifying optical-assisted grating optical imaging, which is used to solve the problems in the prior art that although the optical-assisted grating can improve the lithography process window effect, there is sometimes a risk of imaging. If the etching cannot remove these patterns that should not originally exist, it will cause pattern loss and thus affect the product yield. If the OPC model has poor sensitivity to AF, misjudgment will occur.

[0009] To achieve the above purpose and other related purposes, the present invention provides a method for detecting and verifying optical-assisted grating optical imaging, including:

[0010] Step 1: Provide a wafer, form a photoresist layer on the wafer, use a mask plate including a receptor pattern and an optical-assisted grating to expose the photoresist layer, selectively add a fixed offset to N shots, and upload it to a lithography machine;

[0011] One shot is an exposure unit, N is an integer greater than 1, the number of shots included on the wafer is greater than N, the shots with the fixed offset added are defined as selected shots, and the shots without the fixed offset added are defined as unselected shots;

[0012] Step 2: Sequentially change at least one physical variable of the optical-assisted grating for each of the selected shots in each row, then obtain the result after development of the photoresist layer, and obtain imaging patterns with different imaging degrees of the optical-assisted grating according to the result after development;

[0013] Step 3: Perform optical simulation on the imaging patterns to establish an OPC model;

[0014] Step 4: Use the parameters of the OPC model in which the optical-assisted grating does not form an image in optical simulation exposure as the design standard of the optical-assisted grating.

[0015] Preferably, the exposure conditions of each of the selected shots in Step 1 are different: one part is the energy step of each column of the shots, and the other part is the focal length step of each row of the shots, finally forming a matrix of focal length and energy.

[0016] Preferably, in Step 1, a subroutine is used to selectively add the fixed offset to the N selected shots and upload it to the lithography machine.

[0017] Preferably, the fixed offset in step one includes an X-direction fixed offset value and a Y-direction fixed offset value.

[0018] Preferably, the X-direction fixed offset values among the selected shots in step one are equal, and the Y-direction fixed offset values among the selected shots are equal.

[0019] Preferably, the physical variables in step two include the line width of the optical assist grating, the distance between the optical assist gratings, the distance between the optical assist gratings, the optical assist grating and the pattern density, and the individual imaging result of the optical assist grating.

[0020] Preferably, in step two, an electron microscope is used to obtain the result after development of the photoresist layer.

[0021] Preferably, the method of performing optical simulation on the imaging pattern and establishing an OPC model in step three includes: marking all the optical assist gratings between weak imaging and non-imaging in the same row, and then performing optical simulation based on them to establish the OPC model.

[0022] Preferably, in step three, an S-Litho simulation software is used to generate the OPC model.

[0023] Preferably, the method is used for source-mask co-optimization simulation of technology nodes of 28 nanometers and below.

[0024] As described above, the method for detecting and verifying the optical imaging of the optical assist grating of the present invention has the following beneficial effects:

[0025] The method of the present invention can detect patterns with high risk of optical assist grating imaging with a normal model. The OPC script responsible person can adjust and modify the script of each optical assist grating imaging parameter according to the severity of imaging to improve the optical assist grating imaging. The physical quantities of optical assist grating imaging are defined at the initial stage of modeling, reducing the verification time. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 Schematic diagram of the SEM graph of the optical assist grating imaging of the chip under normal exposure conditions shown as the prior art;

[0027] Figure 2 Schematic diagram of the actual measurement and simulation difference values of each pattern receptor shown as the prior art;

[0028] Figure 3 Schematic diagram of the method for detecting and verifying the optical imaging of the optical assist grating of the present invention;

[0029] Figure 4 Schematic diagram of the imaging of a main pattern of the present invention in an isolated space;

[0030] Figure 5 Shown is a schematic diagram of an optical simulation graph of the master receptor of the present invention;

[0031] Figure 6 Shown is a schematic diagram of the original pattern of the master receptor of the present invention;

[0032] Figure 7 Shown is a schematic diagram of an optical-assisted grating imaging graph obtained by the present invention. Detailed implementation manners

[0033] The following uses specific examples to illustrate the implementation manners of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific implementation manners. Various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention.

[0034] Please refer to Figure 3 , the present invention provides a method for detecting and verifying optical-assisted grating optical imaging, including:

[0035] Step 1: Provide a wafer, form a photoresist layer on the wafer, use a mask plate including a receptor pattern and an optical-assisted grating to expose the photoresist layer, selectively add a fixed offset to N shots, and upload it to a lithography machine;

[0036] One shot is an exposure unit, N is an integer greater than 1, the number of shots included on the wafer is greater than N. Let the shots with the fixed offset added be selected shots, and the shots without the fixed offset added be unselected shots;

[0037] In the implementation manner of the present invention, the exposure conditions of each selected shot in Step 1 are different: one part is the energy step of each column of shots, and the other part is the focal length step of each row of shots, finally forming a matrix of focal length and energy.

[0038] In the implementation manner of the present invention, in Step 1, a subroutine is used to selectively add a fixed offset to N selected shots and upload it to a lithography machine.

[0039] In the implementation manner of the present invention, the fixed offset in Step 1 includes a fixed offset value in the X direction and a fixed offset value in the Y direction.

[0040] In the implementation manner of the present invention, the fixed offset value in the X direction between the selected shots is equal, and the fixed offset value in the Y direction between the selected shots is equal.

[0041] Step 2: Sequentially change at least one physical variable of the light-assisted grating for the selected shots in each row, and then obtain the result after development of the photoresist layer. Based on the result after development, obtain imaging patterns with different imaging degrees of the light-assisted grating, that is, control one or more physical variables to sequentially increase or decrease the parameter values on the same row of shots, while keeping the remaining physical variables unchanged, and step the energy of the shots in each column in sequence. In the matrix composed of several shots, the influence of the physical variables on the imaging of the light-assisted grating can be marked by controlling the variables;

[0042] In an embodiment of the present invention, the physical variables in Step 2 include the line width of the light-assisted grating, the distance between the light-assisted gratings, the distance between the light-assisted gratings, the light-assisted grating and the pattern density, and the individual imaging result of the light-assisted grating.

[0043] Specifically, please refer to Figure 4 which shows an imaging of a main pattern in an isolated space 102; please refer to Figure 5 which shows an optical simulation pattern of a main receptor 103, where the main body is the light-assisted grating and the receptor is the pattern assisted by the light-assisted grating; please refer to Figure 6 which shows the original pattern 104 of the main receptor.

[0044] In an embodiment of the present invention, in Step 2, an electron microscope is used to obtain the result after development of the photoresist layer. Specifically, that is, a photoresist layer is spin-coated on the wafer, exposed on the photoresist layer using a mask plate including the main pattern and the light-assisted grating, and then steps such as development, standing film, and baking are performed to transfer the main pattern and the light-assisted grating pattern to the photoresist layer. An electron microscope is used to obtain an image of the developed photoresist layer, and key dimension data is obtained by analyzing the image.

[0045] Step 3: Perform optical simulation on the imaging pattern to establish an OPC model;

[0046] In an embodiment of the present invention, the method for performing optical simulation on the imaging pattern and establishing an OPC model in Step 3 includes: marking all the light-assisted gratings between weak imaging and non-imaging in the same row, and then performing optical simulation based on this to establish an OPC model.

[0047] In an embodiment of the present invention, the S-Litho simulation software is used to generate the OPC model in Step 3.

[0048] Specifically, please refer to Figure 7, first find the (slight) light-assisted grating imaging at the center deviation in the matrix of focal length and energy, and then obtain the light-assisted grating imaging patterns corresponding to two shots on the left and right sides of the (slight) light-assisted grating imaging, that is, the exposure patterns (105 to 109) of the first to fifth shots. Import these light-assisted grating patterns into S-Litho for simulation, so that the variation trend of light-assisted grating imaging with exposure dose and focus approaches that of the actual chip.

[0049] Step 4: Use the parameters of the OPC model where the light-assisted grating does not form an image in optical simulation exposure as the design standard for the light-assisted grating. That is, according to the actual situation of the light-assisted grating addition, use S-Litho to simulate and find the situation closest to these under the change of optical energy, assist the grating imaging, verify according to the actual chip, and make appropriate adjustments to the simulation conditions. Calibrate the actual OPC light-assisted grating imaging model to find the S-Litho model that meets the standard.

[0050] In the embodiments of the present invention, any of the above methods is used for the simulation of source mask co-optimization at technology nodes of 28 nanometers and below.

[0051] It should be noted that the diagrams provided in this embodiment only illustrate the basic concept of the present invention in a schematic manner. Therefore, only the components related to the present invention are shown in the diagrams, rather than being drawn according to the number, shape, and size of the components in actual implementation. The type, quantity, and ratio of each component in actual implementation can be arbitrarily changed, and the component layout type may also be more complex.

[0052] In summary, the method of the present invention can detect patterns with high risk of light-assisted grating imaging with a normal model. The OPC script person in charge can adjust and modify the script according to the severity of the imaging to improve the light-assisted grating imaging. The physical quantity of light-assisted grating imaging is defined at the initial stage of modeling, reducing the verification time. Therefore, the present invention effectively overcomes various disadvantages in the prior art and has high industrial utilization value.

[0053] The above embodiments only illustrate the principle and its effects of the present invention by way of example, rather than limiting the present invention. Any person familiar with this technology can make modifications or changes to the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or changes completed by those with ordinary knowledge in the technical field without departing from the spirit and technical idea disclosed by the present invention should still be covered by the claims of the present invention.

Claims

1. A method for detecting and verifying the optical imaging of an optical assist grating, characterized in that, it at least includes: Step 1: Provide a wafer, form a photoresist layer on the wafer, use a mask plate including a receptor pattern and an optical assist grating to expose the photoresist layer, selectively add a fixed offset to N shots, and upload it to a lithography machine; One shot is an exposure unit, N is an integer greater than 1, the number of shots included on the wafer is greater than N, the shots with the fixed offset added are defined as selected shots, and the shots without the fixed offset added are defined as unselected shots; Step 2: Sequentially change at least one physical variable of the optical assist grating for each selected shot in each row, then obtain the result after development of the photoresist layer, and obtain imaging patterns with different imaging degrees of the optical assist grating according to the result after development; Step 3: Perform optical simulation on the imaging patterns, mark all the optical assist gratings between weak imaging and non-imaging in the same row, and then perform optical simulation according to them to establish an OPC model; Step 4: Use the parameters of the OPC model in which the optical assist grating does not form an image in optical simulation exposure as the design standard of the optical assist grating to avoid the optical assist grating from imaging itself in subsequent designs.

2. The method for detecting and verifying the optical imaging of an optical assist grating according to claim 1, characterized in that: The exposure conditions of each selected shot in Step 1 are different: one part is the energy step of the shots in each column, and the other part is the focal length step of the shots in each row, finally forming a matrix of focal length and energy.

3. The method for detecting and verifying the optical imaging of an optical assist grating according to claim 2, characterized in that: In Step 1, a subroutine is used to selectively add the fixed offset to N selected shots and upload it to the lithography machine.

4. The method for detecting and verifying the optical imaging of an optical assist grating according to claim 3, characterized in that: The fixed offset in Step 1 includes a fixed offset value in the X direction and a fixed offset value in the Y direction.

5. The method for detecting and verifying the optical imaging of an optical assist grating according to claim 4, characterized in that: The fixed offset value in the X direction between the selected shots is equal, and the fixed offset value in the Y direction between the selected shots is equal.

6. The method for detecting and verifying the optical imaging of an optical assist grating according to claim 1, characterized in that: The physical variables in Step 2 include the line width of the optical assist grating, the distance between the optical assist grating and the optical assist grating, the distance between the optical assist gratings, the optical assist grating and the pattern density, and the separate imaging result of the optical assist grating.

7. The method for detecting and verifying the optical imaging of an optical assist grating according to claim 1, characterized in that: In Step 2, an electron microscope is used to obtain the result after development of the photoresist layer.

8. The method for detecting and verifying the optical imaging of an optical assist grating according to claim 1, characterized in that: In Step 3, S-Litho simulation software is used to generate the OPC model.

9. The method for detecting and verifying optical assist grating optical imaging according to claim 1, wherein: the method is used for source mask co-optimization simulation of 28 nm and below technology nodes.

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