CN117289555A - Near-field calculation method and system for extreme ultraviolet lithography mask - Google Patents

Near-field calculation method and system for extreme ultraviolet lithography mask Download PDF

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Publication number
CN117289555A
CN117289555A CN202311161823.8A CN202311161823A CN117289555A CN 117289555 A CN117289555 A CN 117289555A CN 202311161823 A CN202311161823 A CN 202311161823A CN 117289555 A CN117289555 A CN 117289555A
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light source
mask
source point
absorber
electric field
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刘世元
谷洪刚
何玭炫
江浩
刘佳敏
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Huazhong University of Science and Technology
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Huazhong University of Science and Technology
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    • G—PHYSICS
    • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
    • G03F—PHOTOMECHANICAL PRODUCTION OF TEXTURED OR PATTERNED SURFACES, e.g. FOR PRINTING, FOR PROCESSING OF SEMICONDUCTOR DEVICES; MATERIALS THEREFOR; ORIGINALS THEREFOR; APPARATUS SPECIALLY ADAPTED THEREFOR
    • G03F7/00—Photomechanical, e.g. photolithographic, production of textured or patterned surfaces, e.g. printing surfaces; Materials therefor, e.g. comprising photoresists; Apparatus specially adapted therefor
    • G03F7/20—Exposure; Apparatus therefor
    • G03F7/2002—Exposure; Apparatus therefor with visible light or UV light, through an original having an opaque pattern on a transparent support, e.g. film printing, projection printing; by reflection of visible or UV light from an original such as a printed image
    • G03F7/2004—Exposure; Apparatus therefor with visible light or UV light, through an original having an opaque pattern on a transparent support, e.g. film printing, projection printing; by reflection of visible or UV light from an original such as a printed image characterised by the use of a particular light source, e.g. fluorescent lamps or deep UV light
    • G—PHYSICS
    • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
    • G03F—PHOTOMECHANICAL PRODUCTION OF TEXTURED OR PATTERNED SURFACES, e.g. FOR PRINTING, FOR PROCESSING OF SEMICONDUCTOR DEVICES; MATERIALS THEREFOR; ORIGINALS THEREFOR; APPARATUS SPECIALLY ADAPTED THEREFOR
    • G03F1/00—Originals for photomechanical production of textured or patterned surfaces, e.g., masks, photo-masks, reticles; Mask blanks or pellicles therefor; Containers specially adapted therefor; Preparation thereof
    • G03F1/36—Masks having proximity correction features; Preparation thereof, e.g. optical proximity correction [OPC] design processes
    • G—PHYSICS
    • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
    • G03F—PHOTOMECHANICAL PRODUCTION OF TEXTURED OR PATTERNED SURFACES, e.g. FOR PRINTING, FOR PROCESSING OF SEMICONDUCTOR DEVICES; MATERIALS THEREFOR; ORIGINALS THEREFOR; APPARATUS SPECIALLY ADAPTED THEREFOR
    • G03F7/00—Photomechanical, e.g. photolithographic, production of textured or patterned surfaces, e.g. printing surfaces; Materials therefor, e.g. comprising photoresists; Apparatus specially adapted therefor
    • G03F7/70—Microphotolithographic exposure; Apparatus therefor
    • G03F7/70483—Information management; Active and passive control; Testing; Wafer monitoring, e.g. pattern monitoring
    • G03F7/70491—Information management, e.g. software; Active and passive control, e.g. details of controlling exposure processes or exposure tool monitoring processes
    • G—PHYSICS
    • G06—COMPUTING; CALCULATING OR COUNTING
    • G06F—ELECTRIC DIGITAL DATA PROCESSING
    • G06F17/00—Digital computing or data processing equipment or methods, specially adapted for specific functions
    • G06F17/10—Complex mathematical operations
    • G—PHYSICS
    • G06—COMPUTING; CALCULATING OR COUNTING
    • G06F—ELECTRIC DIGITAL DATA PROCESSING
    • G06F17/00—Digital computing or data processing equipment or methods, specially adapted for specific functions
    • G06F17/10—Complex mathematical operations
    • G06F17/14—Fourier, Walsh or analogous domain transformations, e.g. Laplace, Hilbert, Karhunen-Loeve, transforms
    • G06F17/141—Discrete Fourier transforms
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation

Abstract

The invention provides a near-field calculation method and a near-field calculation system for an extreme ultraviolet lithography mask, comprising the following steps: generating an incident field corresponding to each light source point based on the incident angle and the polarization type of each light source point in the partially coherent illumination; generating a mask absorber based on the mask pattern and the absorber layer; calculating a scattering potential corresponding to the mask absorber based on the refractive index of the mask absorber; based on the scattering potential corresponding to the mask absorber, the incident field corresponding to each light source point and the initial value of the electric field distribution corresponding to each light source point, calculating the electric field distribution of each light source point in the mask absorber by adopting a modified born series method so as to determine the mask near field of each light source point; for the first calculated light source point, the initial value of the electric field distribution is preset, and for other light source points, the initial value of the electric field distribution is the electric field distribution corresponding to the light source point close to the other light source points. The invention realizes the acceleration of near-field calculation of the extreme ultraviolet lithography mask of the partially coherent light source, and saves calculation time and calculation resources.

Description

Near-field calculation method and system for extreme ultraviolet lithography mask
Technical Field
The invention belongs to the technical field of scattering near fields, and particularly relates to a near field calculation method and a near field calculation system for an extreme ultraviolet lithography mask.
Background
Integrated circuits are a vital component in modern technological and industrial fields. As technology evolves, feature sizes on photolithographic wafers in advanced nodes of integrated circuits have been much smaller than wavelengths. In this case, the optical proximity effect becomes more pronounced due to diffraction-limited characteristics of the projection system and optical diffraction phenomena in lithography, and it is necessary to improve the lithography quality using a computational lithography technique such as optical proximity correction. In Extreme Ultraviolet (EUV) computing lithography, however, mask near field computation under partially coherent illumination is a crucial step.
When the partial coherent illumination is strictly considered, the near field generated by thousands of point light source illuminations needs to be calculated, and the calculation needs to be repeated for a plurality of times in the mask pattern optimization, so that the existing method for calculating the scattering near field of the mask, such as a time domain finite difference method and a strictly coupled wave method, needs a long calculation time and huge calculation resources for the near field calculation of the extreme ultraviolet lithography mask for the partial coherent illumination.
Disclosure of Invention
Aiming at the defects of the prior art, the invention aims to provide an extreme ultraviolet lithography mask near-field computing method and system, and aims to solve the problems that the existing mask scattering near-field computing method needs a long computing time and huge computing resources for partial coherent illumination extreme ultraviolet lithography mask near-field computing.
To achieve the above object, in a first aspect, the present invention provides a near-field computing method for an euv lithography mask, comprising the steps of:
step S101, generating an incident field corresponding to each light source point based on the incident angle and the polarization type of each light source point in the partially coherent illumination;
step S102, generating a mask absorber based on the mask pattern and the absorber layer;
step S103, calculating scattering potential corresponding to the mask absorber based on the refractive index of the mask absorber;
step S104, calculating the electric field distribution of each light source point in the mask absorber by adopting a modified Bonn series method based on the scattering potential corresponding to the mask absorber, the incident field corresponding to each light source point and the initial value of the electric field distribution corresponding to each light source point; for the first calculated light source point, the initial value of the corresponding electric field distribution is preset, and for other light source points, the initial value of the corresponding electric field distribution is the electric field distribution corresponding to the light source point close to the other light source points;
step S105, determining a mask near field of each light source point based on the electric field distribution of each light source point in the mask absorber.
In an alternative example, step S103 specifically includes:
calculating a wave vector of the mask absorber based on the refractive index of the mask absorber and the wave vector in vacuum;
based on the wave vector of the mask absorber and the wave vector in vacuum, the scattering potential corresponding to the mask absorber is calculated.
In an optional example, for each light source point, the iterative convergence condition of the modified born series method is that the amplitude variation of the electric field distribution of each light source point before and after iteration is smaller than a preset threshold; the preset threshold is determined based on the amplitude of the incident field of each light source point.
In an alternative example, in the case where the mask pattern is changed, step S104 further includes:
generating a varying mask absorber based on the varying mask pattern;
based on the scattering potential corresponding to the changed mask absorber, the incident field corresponding to each light source point, and the electric field distribution of each light source point in the mask absorber, the electric field distribution of each light source point in the changed mask absorber is calculated to determine the mask near field of the changed mask pattern corresponding to each light source point.
In a second aspect, the present invention provides an extreme ultraviolet photomask near field computing system comprising:
the incident field calculation module is used for generating an incident field corresponding to each light source point based on the incident angle and the polarization type of each light source point in the partially coherent illumination;
a mask absorber build module for generating a mask absorber based on the mask pattern and the absorber layer;
a scattering potential calculation module for calculating a scattering potential corresponding to the mask absorber based on the refractive index of the mask absorber;
the electric field distribution calculation module is used for calculating the electric field distribution of each light source point in the mask absorber by adopting a modified born series method based on the scattering potential corresponding to the mask absorber, the incident field corresponding to each light source point and the initial value of the electric field distribution corresponding to each light source point; for the first calculated light source point, the initial value of the corresponding electric field distribution is preset, and for other light source points, the initial value of the corresponding electric field distribution is the electric field distribution corresponding to the light source point close to the other light source points;
and the mask near field calculation module is used for determining the mask near field of each light source point based on the electric field distribution of each light source point in the mask absorber.
In an alternative example, the scattering potential calculation module is specifically configured to:
calculating a wave vector of the mask absorber based on the refractive index of the mask absorber and the wave vector in vacuum;
based on the wave vector of the mask absorber and the wave vector in vacuum, the scattering potential corresponding to the mask absorber is calculated.
In an optional example, for each light source point in the electric field distribution calculation module, the iterative convergence condition of the modified born series method is that the amplitude variation of the electric field distribution of each light source point before and after iteration is smaller than a preset threshold; the preset threshold is determined based on the amplitude of the incident field of each light source point.
In an alternative example, in case that the mask pattern is changed, the system further includes a mask pattern changing module for:
generating a varying mask absorber based on the varying mask pattern;
based on the scattering potential corresponding to the changed mask absorber, the incident field corresponding to each light source point, and the electric field distribution of each light source point in the mask absorber, the electric field distribution of each light source point in the changed mask absorber is calculated to determine the mask near field of the changed mask pattern corresponding to each light source point.
In general, the above technical solutions conceived by the present invention have the following beneficial effects compared with the prior art:
the invention provides an extreme ultraviolet lithography mask near-field calculation method and system, which provide an initial value without extra calculation amount for calculating mask electric field distribution corresponding to other light source points by utilizing the calculation of mask electric field distribution of adjacent light source points in extreme ultraviolet lithography facing a partially coherent light source, thereby realizing the acceleration of the correction of the born series method, determining the mask near-field of each light source point after calculating the mask electric field distribution corresponding to each light source point, further realizing the acceleration of the extreme ultraviolet lithography mask near-field calculation facing the partially coherent light source, shortening the calculation time and saving the calculation resources.
Drawings
FIG. 1 is a schematic flow chart of a near-field calculation method for an EUV lithography mask according to an embodiment of the present invention;
FIG. 2 is a second flowchart of a near-field calculation method for an EUV lithography mask according to an embodiment of the present invention;
FIG. 3 is an exemplary diagram of an EUV lithography mask pattern provided by an embodiment of the present invention;
FIG. 4 is a graph showing the comparison of the effects of the method provided by the embodiment of the present invention and the modified born series method without optimizing the initial value;
FIG. 5 is a third flowchart of a near-field computing method for an EUV lithography mask according to an embodiment of the present invention;
FIG. 6 is an exemplary graph of a changed mask pattern and a computational effect comparison graph provided by an embodiment of the present invention;
fig. 7 is a schematic diagram of an euv mask near-field computing system according to an embodiment of the present invention.
Detailed Description
The present invention will be described in further detail with reference to the drawings and examples, in order to make the objects, technical solutions and advantages of the present invention more apparent. It should be understood that the specific embodiments described herein are for purposes of illustration only and are not intended to limit the scope of the invention.
In the calculation method of the EUV mask near field, the near field solution based on the modified born series method (modified Born series) can calculate the mask near field rapidly while maintaining higher calculation accuracy. The modified born series method is a numerical method for strictly solving a diffraction field based on fixed point iteration, and is different from other methods for solving the diffraction field, such as a time domain finite difference method and the like, and the calculation time of the method is highly related to an initial value. If the iteration can be started from an initial value close to the true value, the calculation efficiency can be greatly improved, and the calculation time can be reduced.
In the prior art, each light source point acts on a mask to generate a near field; considering partially coherent illumination requires consideration of thousands of light source points. In addition, since the diffraction fields generated by the adjacent light source points are similar in the partial coherent illumination, the diffraction fields generated by the adjacent light source points can be used as the initial value of the near-field calculation of the next light source point, so that the mask near-field calculation time of the partial coherent illumination is greatly shortened.
In this regard, the present invention provides a near-field computing method for an euv lithography mask. Fig. 1 is a schematic flow chart of a near-field calculation method for an euv lithography mask according to an embodiment of the present invention, as shown in fig. 1, the method includes the following steps:
step S101, generating an incident field corresponding to each light source point based on the incident angle and the polarization type of each light source point in the partially coherent illumination;
step S102, generating a mask absorber based on the mask pattern and the absorber layer;
step S103, calculating scattering potential corresponding to the mask absorber based on the refractive index of the mask absorber;
step S104, calculating the electric field distribution of each light source point in the mask absorber by adopting a modified Bonn series method based on the scattering potential corresponding to the mask absorber, the incident field corresponding to each light source point and the initial value of the electric field distribution corresponding to each light source point; for the first calculated light source point, the initial value of the corresponding electric field distribution is preset, and for other light source points, the initial value of the corresponding electric field distribution is the electric field distribution corresponding to the light source point close to the other light source points;
step S105, determining a mask near field of each light source point based on the electric field distribution of each light source point in the mask absorber.
Specifically, after generating an euv illumination pupil, i.e., a partially coherent illumination, to be calculated using corresponding pupil parameters, the position of a light source point in the illumination pupil determines an incident angle, and an electric field component of an incident field needs to be determined by a polarization type of the partially coherent illumination, common polarization types include: TE polarization, TM polarization, X polarization, Y polarization. The incident field corresponding to each light source point can be generated according to the incident angle and the polarization type of the light source point.
A three-dimensional calculation region, namely a mask absorber, is generated according to the mask pattern and the absorber layer, and a scattering potential corresponding to the mask absorber is calculated according to the refractive index of the mask absorber. And calculating the electric field distribution of each light source point in the mask absorber by adopting a modified Bonn series method according to the scattering potential corresponding to the mask absorber, the incident field corresponding to each light source point and the initial value of the electric field distribution corresponding to each light source point. The electric field distribution of each light source point in the mask absorber is three-dimensional electric field distribution, namely diffraction field, and a slice of the diffraction field (three-dimensional array) in the upper surface direction (z direction) of the mask absorber is mask near field (two-dimensional array). The near field of the mask for each light source point in the partially coherent illumination may provide data support for joint optimization of the light source mask.
It should be noted that, the partially coherent illumination includes thousands of light source points, if each light source point samples a preset initial value to perform iterative computation, it will consume too much iterative convergence time, but in the embodiment of the present invention, only the first computed light source point corresponds to the initial value of the electric field distribution, and for other light source points, the initial value of the electric field distribution adopts the electric field distribution corresponding to the light source point close to the initial value of the electric field distribution. Here, the first calculated light source point may, for example, select the light source point of the edge, and the adjacent light source points may be specifically determined according to the mutual distance between the light source points on the illumination pupil, or the difference of the incident angles of the light source points.
For example, in the specific implementation process, after one light source point is calculated, it may be determined whether the mutual distance between the other light source points which are not calculated and the light source point is smaller than a preset range, if there are a plurality of light source points which are smaller than the preset range, the electric field distributions of the light source points may be synchronously calculated, and the electric field distributions of the light source points are all adopted as initial values, so as to further accelerate near-field calculation of the euv lithography mask. Repeating the steps until the calculation of all the light source points is completed.
According to the method provided by the embodiment of the invention, by utilizing the calculation of the mask electric field distribution of the adjacent light source points in the extreme ultraviolet lithography facing the partially coherent light source, an initial value without additional calculation amount is provided for calculating the mask electric field distribution corresponding to other light source points by the correction of the born series method, the acceleration of the correction of the born series method is realized, and after the mask electric field distribution corresponding to each light source point is calculated, the mask near field of each light source point can be determined, so that the acceleration of the extreme ultraviolet lithography mask near field calculation facing the partially coherent light source is realized, the calculation time is shortened, and the calculation resources are saved.
Based on the above embodiment, step S103 specifically includes:
calculating a wave vector of the mask absorber based on the refractive index of the mask absorber and the wave vector in vacuum;
based on the wave vector of the mask absorber and the wave vector in vacuum, the scattering potential corresponding to the mask absorber is calculated.
Specifically, the corresponding scattering potential V is calculated from the refractive index n (r) in the mask absorber. The scattering potential V is expressed as follows:
wherein r is a space coordinate vector; k (k) 0 Is a wave vector in vacuum; k (r) is the wave vector at any position r in the mask absorber, k (r) =k 0 n (r); epsilon is an iteration convergence auxiliary constant; i is an imaginary unit.
Based on any one of the embodiments, for each light source point, the iterative convergence condition of the modified born series method is that the amplitude variation of the electric field distribution of each light source point before and after iteration is smaller than a preset threshold value; the preset threshold is determined based on the amplitude of the incident field of each light source point.
Specifically, the iterative calculation form of the modified born series method is as follows:
E＝ME 0 +γGS
M＝γGV-γ+1
wherein E is electric field distribution; e (E) 0 Is the initial value of the electric field distribution; s is an incident electric field; gamma=iv/epsilon, i is an imaginary unit, epsilon is a constant; g is a convolution operator, V is a scattering potential corresponding to the mask absorber, and V (r) is used for forming the mask absorber.
The expression of the convolution operator G is as follows:
wherein,and->For fourier and inverse fourier transforms, p is the frequency domain coordinate vector. According to the calculation accuracy requirement, a termination condition, that is, an iteration convergence condition, is set for the iteration, for example, an incident field amplitude in which the maximum amplitude change of the electric field before and after the iteration is less than 5% may be set. The diffraction field obtained by calculation is the distribution of the electric field in the three-dimensional space and is a three-dimensional array. The near field of the mask at the incident field is the corresponding two-dimensional slice in the three-dimensional array.
Based on any of the above embodiments, in the prior art, each light source point acts on a mask to generate a near field, and thousands of light source points need to be considered for partial coherent illumination. In mask optimization, the pattern of the mask is slowly changed until the pattern on the wafer meets certain conditions. After the mask is changed, the near fields corresponding to all the light source points need to be recalculated, if the existing methods such as a time domain finite difference method, a strict coupled wave method and the like are adopted, a large amount of calculation time is consumed, and particularly, the methods consume calculation time and calculation resources when calculating the mask pattern with a large size.
The corresponding electric field diffraction results are similar, considering that the required mask pattern is slowly varying. The electric field result obtained by calculation can be used as the initial value of the calculation of the next similar pattern, thereby greatly improving the calculation efficiency.
Therefore, in the case where the mask pattern is changed, the embodiment of the present invention further includes, after step S104:
generating a varying mask absorber based on the varying mask pattern;
based on the scattering potential corresponding to the changed mask absorber, the incident field corresponding to each light source point, and the electric field distribution of each light source point in the mask absorber, the electric field distribution of each light source point in the changed mask absorber is calculated to determine the mask near field of the changed mask pattern corresponding to each light source point.
It will be appreciated that after a mask pattern has been changed, the mask absorber needs to be regenerated, and the refractive index of the resulting changed mask absorber will also change, so that the scattering potential corresponding to the changed mask absorber needs to be regenerated.
Further, in order to correct the line segment end shortening caused by the photoresist shrinkage, the changed mask pattern can be generated by adding auxiliary squares to four corners of a rectangle in the original mask pattern, so that the efficiency of the joint optimization of the light source masks can be improved.
According to the embodiment of the invention, the diffraction field of the mask is calculated by using the modified born series method, and when the diffraction field of another mask with similar patterns is calculated after the diffraction field of the mask is calculated once, the calculated diffraction field is used as an initial value for iteration of the modified born series method, so that the calculation efficiency of the modified born series method is improved. According to the invention, the diffraction field of the similar pattern mask in the photoetching is calculated, no additional calculation amount is needed, a high-quality initial value is provided for the correction of the born series method, and the acceleration of the correction of the born series method is realized.
Based on any of the above embodiments, the illumination modes of the partially coherent illumination include conventional illumination, annular illumination, dipole illumination, quadrupole illumination, etc., and the method of the present invention is applicable to all illumination modes. The pupil parameters required for generating an illumination pupil are correspondingly different for different illumination modes, for example, a conventional illumination pupil has only one pupil parameter, namely a partial coherence factor; the annular illumination is determined by the inner and outer partial coherence factors.
Based on any of the above embodiments, in order to address the above defects or improvements of the prior art, the present invention provides a near-field calculation acceleration method for an euv lithography mask, which aims to achieve acceleration of near-field calculation for an euv lithography mask by providing an approximation of a diffraction electric field distribution as an iteration initial value.
In order to achieve the above objective, the present invention provides a near-field computing acceleration method for an euv lithography mask, and fig. 2 is a second flowchart of the near-field computing method for an euv lithography mask according to an embodiment of the present invention, as shown in fig. 2, the method includes the following steps:
s1: generating an illumination pupil according to the pupil parameters, and generating an incident field corresponding to each light source point;
the illumination pupil is in the form of conventional illumination, annular illumination, dipole illumination, quadrupole illumination, etc. Wherein the conventional illumination pupil has only one pupil parameter, namely a partial coherence factor; the annular illumination is determined by the inner and outer partial coherence factors. After the illumination pupil to be calculated is generated by using the corresponding pupil parameters, the position of the light source point in the illumination pupil determines the incident angle, and the electric field component of the incident field needs to be determined by the polarization type of the partially coherent illumination, and common polarization types include: TE polarization, TM polarization, X polarization, Y polarization. The corresponding incident field may be generated according to the incident angle and the polarization type of the light source point.
S2: generating a three-dimensional calculation region, namely a mask absorber, according to the mask pattern;
determining the size of the discrete grid according to the required discrete precision, converting the mask pattern into a corresponding two-dimensional array, determining the longitudinal discrete grid span according to the height of the mask absorber, generating a three-dimensional array, adding an absorption layer for simulating the aperiodic situation in the longitudinal direction, and finally obtaining the mask absorber. The corresponding scattering potential V is calculated from the refractive index n (r) in the absorber of the mask. The scattering potential V is expressed as follows:
wherein r is a space coordinate vector; k (k) 0 Is a wave vector in vacuum; k (r) is the wave vector at any position r in the mask absorber, k (r) =k 0 n (r); epsilon is an iteration convergence auxiliary constant; i is an imaginary unit;
s3: iteratively solving a diffraction field and a near field by using a modified born series method;
the iterative calculation form of the modified born series method is as follows:
E＝ME 0 +γGS
M＝γGV-γ+1
wherein E is electric field distribution; s is an incident electric field; γ=iv/epsilon; g is a convolution operator.
The expression of the convolution operator G is as follows:
wherein,and->For fourier and inverse fourier transforms, p is the frequency domain coordinate vector. Setting termination for iterations according to computational accuracy requirementsConditions. The diffraction field obtained by calculation is the distribution of the electric field in the three-dimensional space and is a three-dimensional array. The near field of the mask at the incident field is the corresponding two-dimensional slice in the three-dimensional array.
S4: selecting the next light source point to be calculated, judging whether the light source point is the adjacent light source point, and taking the diffraction field obtained in the step S3 as an initial value;
selecting one light source point from the light source points to be calculated, judging the similarity degree of the light source point and the last calculated light source point, thereby determining whether to take the diffraction field obtained by calculating the last light source point as the initial value of the diffraction field corresponding to the next light source point, and then carrying out near-field calculation of the next light source point according to the diffraction field corresponding to the next light source point obtained by calculation.
S5: repeating the steps S3-S4 to solve the near field of the adjacent light source points until the calculation of all the light source points is completed;
according to the method, the diffraction near field of the mask is calculated by using the modified born series method, after the diffraction near field corresponding to one light source point of the partial coherent light source is calculated, when the diffraction near field of the other adjacent light source point is calculated, the three-dimensional diffraction field obtained in the calculation of the last light source point is used as the diffraction field initial value of the modified born series method, and the calculation efficiency of the modified born series method is improved. According to the invention, a three-dimensional diffraction field generated by near-field calculation of similar light source points in the partially coherent light source is utilized, a good initial value is provided for correcting the born series method under the condition that additional calculation is not needed, and the acceleration of near-field calculation of the extreme ultraviolet lithography mask is realized.
Examples: taking a series of continuous light source points in the traditional illumination pupil corresponding near field calculation as an example, a near field calculation acceleration method for mask by using extreme ultraviolet lithography is described in detail:
s1: generating an illumination pupil according to the pupil parameters, and generating an incident field corresponding to each light source point;
the first calculated source point was a TE polarized 6 ° oblique plane incident wave, with the corresponding electric field component being only the Y component other than 0. The incident angle of the remaining light source points varies from 0.01 ° to 0.1 ° with respect to 6 °. This example demonstrates the acceleration effect of the method at different angle of incidence variation values.
S2: generating a three-dimensional calculation region, namely a mask absorber, according to the mask pattern;
the EUV lithography mask pattern provided in the embodiment of the present invention is shown in fig. 3, the size of the discrete grid is 8 dots per wavelength, the height of the mask absorber is 50nm, and the thickness of the longitudinal absorption layer is 4 wavelengths per side.
S3: iteratively solving a diffraction field and a near field by using a modified born series method;
the iterative convergence criterion is set to an incident field amplitude where the maximum amplitude of the electric field varies by less than 5%.
S4: selecting the next light source point to be calculated, judging whether the light source point is the adjacent light source point, and taking the diffraction field obtained in the step S3 as an initial value;
in this embodiment, the diffraction field obtained by calculating the light source point with the angle of incidence of 6 ° is used as the initial value, and the near field corresponding to the light source point with other angles of incidence is calculated.
S5: repeating the steps S3-S4 to solve the near field of the adjacent light source points until the calculation of all the light source points is completed;
fig. 4 is a graph comparing the effects of the method provided by the embodiment of the invention and the modified born series method without optimizing the initial value, as shown in fig. 4, the horizontal axis is the difference of the incident angles between two adjacent light source points, the vertical axis is the iteration number required for calculating the near field corresponding to the new light source point, and the calculation efficiency of the modified born series method is represented. Compared with the number of iterations required without acceleration by the method in fig. 4, when the change of the incident angle is small (dtheta=0.01°), the method can save 71.8% of calculation time, and greatly improve the calculation efficiency. While the angle of incidence varies greatly (dTheta >0.05 deg.), the method can still provide a considerable acceleration effect.
It will be appreciated that the angle of incidence is different between different light source points. The position of the source point in the illumination pupil determines the angle of incidence. The smaller the change in angle of incidence, the closer the initial value is to the true value. The characteristic of the modified born series method is that the closer the initial value is to the true value, the higher the calculation efficiency is.
Based on any of the above embodiments, the embodiment of the present invention uses line segment length correction in optical proximity correction as an example, and describes a near-field computing acceleration method using an euv mask in detail.
Fig. 5 is a third flowchart of a near-field calculation method for an euv lithography mask according to an embodiment of the present invention, as shown in fig. 5, which includes the following steps:
d1: generating a three-dimensional calculation region, namely a mask absorber, according to the mask pattern;
fig. 6 is an exemplary diagram of a modified mask pattern and a calculation result diagram provided by an embodiment of the present invention, the original mask pattern is shown in fig. 6 (a), and a partial enlarged view is shown in fig. 6 (b).
D2: generating an initial value of the diffraction field;
the array size of the initial values needs to be consistent with the absorber model established by step S1, and an array of zeros of corresponding size may be used in general. The initial value is marked as E 0 。
D3: d2, starting from the initial value generated in the step D, iteratively solving a diffraction field by using a modified Boen series method;
d4: saving the result of the diffraction field;
the diffraction field to be stored is usually a three-dimensional array, the data volume is large, and the diffraction field can be directly stored in the memory of a computer in consideration of the influence of time consuming for reading a hard disk on the calculation time.
D5: repeating step D1 to generate an absorber model of another mask of similar pattern;
as shown in fig. 6 (d), the modification of the pattern in this embodiment simulates the modification of the optical proximity correction to the shortening of the line segment ends, and the modification of the line segment shortening due to the photoresist shrinkage is performed by adding auxiliary squares to the rectangular corners of the pattern.
D6: and D4, taking the diffraction field saved in the step D as an initial value, and iteratively solving the diffraction field by using a modified Bohn series method.
The calculation effect of the modified born series method of the present invention and the modified born series method not optimizing the initial value is as shown in fig. 6 (c), the horizontal axis represents the side length (W) added with the auxiliary square, the variation with the previous pattern is represented, the vertical axis represents the iteration number required for calculating the near field of the new pattern, and the calculation efficiency of the modified born series method is represented. Compared with the number of iterations required in fig. 6 (c) which is not accelerated by the method, when the variation of the pattern is small (w=5 nm), the method can save 50% of calculation time, and greatly improve the calculation efficiency. While this method can still provide a considerable acceleration effect when the variation of the pattern is large (W >20 nm).
The near-field computing acceleration method for the extreme ultraviolet lithography mask provided by the invention utilizes the diffraction field of the similar pattern mask in the computing lithography, provides an initial value without additional calculated amount for the correction of the born series method, and realizes the acceleration of the correction of the born series method.
Based on any one of the above embodiments, the present invention provides an euv lithography mask near-field computing system. Fig. 7 is a schematic diagram of an euv mask near-field computing system according to an embodiment of the present invention, as shown in fig. 7, the system includes:
an incident field calculation module 710, configured to generate an incident field corresponding to each light source point based on an incident angle and a polarization type of each light source point in the partially coherent illumination;
a mask absorber construction module 720 for generating a mask absorber based on the mask pattern and the absorber layer;
a scattering potential calculation module 730, configured to calculate a scattering potential corresponding to the mask absorber based on the refractive index of the mask absorber;
the electric field distribution calculation module 740 is configured to calculate, based on the scattering potential corresponding to the mask absorber, the incident field corresponding to each light source point, and the initial value of the electric field distribution corresponding to each light source point, the electric field distribution of each light source point in the mask absorber by using a modified born series method; for the first calculated light source point, the initial value of the corresponding electric field distribution is preset, and for other light source points, the initial value of the corresponding electric field distribution is the electric field distribution corresponding to the light source point close to the other light source points;
the mask near field calculation module 750 is configured to determine a mask near field of each light source point based on an electric field distribution of each light source point in the mask absorber.
It can be understood that the detailed functional implementation of each module may be referred to the description in the foregoing method embodiment, and will not be repeated herein.
In addition, an embodiment of the present invention provides another near field computing device for an euv mask, which includes: a memory and a processor;
the memory is used for storing a computer program;
the processor is configured to implement the method in the above-described embodiments when executing the computer program.
Furthermore, the present invention provides a computer-readable storage medium having stored thereon a computer program which, when executed by a processor, implements the method in the above embodiments.
Based on the method in the above embodiments, an embodiment of the present invention provides a computer program product, which when run on a processor causes the processor to perform the method in the above embodiments.
It will be readily appreciated by those skilled in the art that the foregoing description is merely a preferred embodiment of the invention and is not intended to limit the invention, but any modifications, equivalents, improvements or alternatives falling within the spirit and principles of the invention are intended to be included within the scope of the invention.

Claims (8)

1. The near-field calculation method for the extreme ultraviolet lithography mask is characterized by comprising the following steps of:
step S101, generating an incident field corresponding to each light source point based on the incident angle and the polarization type of each light source point in the partially coherent illumination;
step S102, generating a mask absorber based on the mask pattern and the absorber layer;
step S103, calculating scattering potential corresponding to the mask absorber based on the refractive index of the mask absorber;
step S104, calculating the electric field distribution of each light source point in the mask absorber by adopting a modified Bonn series method based on the scattering potential corresponding to the mask absorber, the incident field corresponding to each light source point and the initial value of the electric field distribution corresponding to each light source point; for the first calculated light source point, the initial value of the corresponding electric field distribution is preset, and for other light source points, the initial value of the corresponding electric field distribution is the electric field distribution corresponding to the light source point close to the other light source points;
step S105, determining a mask near field of each light source point based on the electric field distribution of each light source point in the mask absorber.
2. The method according to claim 1, wherein step S103 specifically comprises:
calculating a wave vector of the mask absorber based on the refractive index of the mask absorber and the wave vector in vacuum;
based on the wave vector of the mask absorber and the wave vector in vacuum, the scattering potential corresponding to the mask absorber is calculated.
3. The method according to claim 1, wherein for each light source point, the iterative convergence condition of the modified born series method is that the amplitude variation of the electric field distribution of each light source point before and after iteration is smaller than a preset threshold; the preset threshold is determined based on the amplitude of the incident field of each light source point.
4. The method according to claim 1, wherein in case of a change of the mask pattern, step S104 further comprises:
generating a varying mask absorber based on the varying mask pattern;
based on the scattering potential corresponding to the changed mask absorber, the incident field corresponding to each light source point, and the electric field distribution of each light source point in the mask absorber, the electric field distribution of each light source point in the changed mask absorber is calculated to determine the mask near field of the changed mask pattern corresponding to each light source point.
5. An extreme ultraviolet lithography mask near field computing system, comprising:
the incident field calculation module is used for generating an incident field corresponding to each light source point based on the incident angle and the polarization type of each light source point in the partially coherent illumination;
a mask absorber build module for generating a mask absorber based on the mask pattern and the absorber layer;
a scattering potential calculation module for calculating a scattering potential corresponding to the mask absorber based on the refractive index of the mask absorber;
the electric field distribution calculation module is used for calculating the electric field distribution of each light source point in the mask absorber by adopting a modified born series method based on the scattering potential corresponding to the mask absorber, the incident field corresponding to each light source point and the initial value of the electric field distribution corresponding to each light source point; for the first calculated light source point, the initial value of the corresponding electric field distribution is preset, and for other light source points, the initial value of the corresponding electric field distribution is the electric field distribution corresponding to the light source point close to the other light source points;
and the mask near field calculation module is used for determining the mask near field of each light source point based on the electric field distribution of each light source point in the mask absorber.
6. The system of claim 5, wherein the scattering potential calculation module is specifically configured to:
calculating a wave vector of the mask absorber based on the refractive index of the mask absorber and the wave vector in vacuum;
based on the wave vector of the mask absorber and the wave vector in vacuum, the scattering potential corresponding to the mask absorber is calculated.
7. The system of claim 5, wherein for each light source point in the electric field distribution calculation module, the iterative convergence condition of the modified born series method is that the change of the amplitude of the electric field distribution of each light source point before and after iteration is smaller than a preset threshold; the preset threshold is determined based on the amplitude of the incident field of each light source point.
8. The system of claim 5, wherein in the event of a mask pattern change, the system further comprises a mask pattern change module to:
generating a varying mask absorber based on the varying mask pattern;
based on the scattering potential corresponding to the changed mask absorber, the incident field corresponding to each light source point, and the electric field distribution of each light source point in the mask absorber, the electric field distribution of each light source point in the changed mask absorber is calculated to determine the mask near field of the changed mask pattern corresponding to each light source point.
CN202311161823.8A 2023-09-08 2023-09-08 Near-field calculation method and system for extreme ultraviolet lithography mask Pending CN117289555A (en)

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