# US 8,543,947 B2 · Selection of optimum patterns in a design layout based on diffraction signature analysis

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- Number: US 8,543,947 B2
- Document ID: US8543947B2
- Status: Granted
- Kind: B2
- Application number: 12/914,954
- Filed: 2010-10-28
- Published: 2011-05-05
- Granted: 2013-09-24
- Earliest claimed: 2009-10-28
- Assignees: ASML Netherlands B.V.
- Applicants: Hua-Yu Liu; Luoqi Chen; Hong Chen; Zhi-Pan Li
- Inventors: Hua-Yu Liu; Luoqi Chen; Hong Chen; Zhi-Pan Li
- Web page: https://patentgrep.com/patent/US8543947B2

## CPC

- G06F 30/398: Design verification or optimisation, e.g. using design rule check [DRC], layout versus schematics [LVS] or finite element methods [FEM] (optical proximity correction [OPC] design processes G03F1/36)
- G03F 1/36: Masks having proximity correction features; Preparation thereof, e.g. optical proximity correction [OPC] design processes
- G03F 7/70125: {Use of illumination settings tailored to particular mask patterns (details of setting means G03F7/70091)}
- G03F 7/70425: {Imaging strategies, e.g. for increasing throughput or resolution, printing product fields larger than the image field or compensating lithography- or non-lithography errors, e.g. proximity correction, mix-and-match, stitching or double patterning}
- G03F 7/70441: {Optical proximity correction [OPC]}
- G03F 7/705: {Modelling or simulating from physical phenomena up to complete wafer processes or whole workflow in wafer productions}
- G03F 7/70666: {Aerial image, i.e. measuring the image of the patterned exposure light at the image plane of the projection system}
- G06F 30/00: Computer-aided design [CAD]
- G06F 30/20: Design optimisation, verification or simulation (optimisation, verification or simulation of circuit designs G06F30/30)
- G06F: ELECTRIC DIGITAL DATA PROCESSING (computer systems based on specific computational models G06N)
- 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; (phototypographic composing devices B41B; photosensitive materials or processes for photographic purposes G03C; electrophotography, sensitive layers or processes therefor G03G)

## Abstract

The present invention relates generally to selecting optimum patterns based on diffraction signature analysis, and more particularly to, using the optimum patterns for mask-optimization for lithographic imaging. A respective diffraction map is generated for each of a plurality of target patterns from an initial larger set of target patterns from the design layout. Diffraction signatures are identified from the various diffraction maps. The plurality of target patterns is grouped into various diffraction-signature groups, the target patterns in a specific diffraction-signature group having similar diffraction signature. A subset of target patterns is selected to cover all possible diffraction-signature groups, such that the subset of target patterns represents at least a part of the design layout for the lithographic process. The grouping of the plurality of target patterns may be governed by predefined rules based on similarity of diffraction signature. The predefined rules comprise coverage relationships existing between the various diffraction-signature groups.

## Claims

### Claim 1

A method implemented by a computer, the method being of selecting a subset of target patterns from a design layout configured to be imaged onto a substrate via a lithographic process, the method comprising the steps of:
generating a respective diffraction map for a plurality of target patterns from an initial larger set of target patterns from the design layout;
identifying diffraction signatures from the various diffraction maps of the plurality of target patterns from the initial larger set of target patterns;
grouping the plurality of target patterns from the initial larger set of target patterns into diffraction-signature groups, the target patterns in a specific diffraction-signature group having similar diffraction signature; and
selecting the subset being a representative set of target patterns to cover a predefined number of diffraction-signature groups, such that the representative set of target patterns represents at least a part of the design layout for the lithographic process,
wherein one or more of the above steps are performed by the computer.

### Claim 2 (depends on 1)

The method of claim 1, wherein the grouping of the plurality of target patterns is governed by predefined rules based on similarity of diffraction signature.

### Claim 3 (depends on 2)

The method of claim 2, wherein the predefined rules comprise coverage relationships existing between the various diffraction-signature groups.

### Claim 4 (depends on 1)

The method of claim 1, wherein the method further includes:
using the representative set of target patterns to optimize an illumination source used in the lithographic process.

### Claim 5 (depends on 4)

The method of claim 4, wherein optimizing the illumination source includes tuning polarization distribution of a radiation beam incident on a mask.

### Claim 6 (depends on 4)

The method of claim 4, wherein the method further comprises:
using the optimized illumination source for imaging the part of the design layout represented by the representative set of target patterns.

### Claim 7 (depends on 1)

The method of claim 1, wherein the method further includes:
using the representative set of target patterns to optimize a projection optics system used in the lithographic process.

### Claim 8 (depends on 7)

The method of claim 7, wherein optimizing the projection optics system includes manipulating a wavefront of a radiation beam in a pupil plane after the radiation beam passes through the mask.

### Claim 9 (depends on 7)

The method of claim 7, wherein the method further comprises:
using the optimized projection optics for imaging the part of the design layout represented by the representative set of target patterns.

### Claim 10 (depends on 1)

The method of claim 1, wherein the initial larger set of target patterns is either extracted from the design layout based on one or more predefined image optimization criteria, or, the initial larger set of target patterns is provided a priori based on one or more predefined image optimization criteria at certain known locations in the design layout.

### Claim 11 (depends on 10)

The method of claim 10, wherein the one or more predefined image optimization criteria are based on one or more of the following:
type of the target pattern;
complexity of the target pattern;
location of the target pattern;
lithographic process window performance of the target pattern;
known sensitivity of the target pattern to lithographic process parameter variations;
a dimension of features in the target pattern;
a pitch of the features in the target pattern;
a degree of criticality of the target pattern in the design layout.

### Claim 12 (depends on 1)

The method of claim 1, wherein the step of identifying diffraction signatures further comprises the steps of:
identifying peaks in each of the diffraction maps;
storing one or more characteristic parameters of the identified peaks in each of the diffraction maps; and
analyzing the stored characteristic parameters of the identified peaks to create respective diffraction-signature groups for each of the diffraction maps.

### Claim 13 (depends on 12)

The method of claim 12, wherein, each diffraction-signature group comprises one or more respective basis vectors.

### Claim 14 (depends on 13)

The method of claim 13, wherein a one-dimensional basis vector represents a collinear peak, and two-dimensional basis vectors represent a pair of non-collinear peaks identified in the diffraction map.

### Claim 15 (depends on 12)

The method of claim 12, wherein the characteristic parameters to be stored for the identified peaks include one or more of the following: location of the peak, width of the peak, amplitude of the peak, harmonic index of the peak, and, distance of the peak from one or more neighboring peaks.

### Claim 16 (depends on 1)

The method of claim 1, wherein the diffraction-signature groups are either in spatial domain, or in frequency domain.

### Claim 17 (depends on 1)

The method of claim 1, wherein generating the respective diffraction map comprises:
generating a respective diffraction-order plot corresponding to the target pattern in each of the initial larger set of target patterns; and
removing a zero-eth order peak from each of the diffraction-order plots.

### Claim 18 (depends on 17)

The method of claim 17, wherein the step of analyzing the stored characteristic parameters of the identified peaks includes:
identifying the strongest peak in the diffraction-order plot;
constructing a respective one-dimensional basis vector for each collinear peak including the strongest peak in the diffraction-order plot;
constructing respective two-dimensional basis vectors for each pair of non-collinear peaks in the diffraction-order plot;
ignoring all harmonics present in the diffraction-order plot; and
populating the list of diffraction-signature group by choosing the non-repetitive one dimensional and two-dimensional basis vectors.

### Claim 19 (depends on 18)

The method of claim 18, wherein the predefined rules governing the coverage relationships include one or more of the following:
a peak ‘v’ is considered to overlap with another peak ‘u’ if the distance between ‘v’ and ‘u’ is less than an average width of peaks plus a predefined tolerance;
a one-dimensional diffraction-signature group ‘v1’ is considered to be covered by another one-dimensional diffraction-signature group if and only if there exists an integer ‘n’ such that ‘v1’ overlaps with ‘n*u1’;
a two-dimensional diffraction-signature group (v1, v2) is considered to be covered by another two-dimensional diffraction-signature group (u1, u2), if and only if there exists a pair of integers (n1, n2) such that ‘v1’ overlaps with ‘n1*u1+n2*u2’, and similarly, there exists a pair of integers (m1, m2) such that ‘v2’ overlaps with ‘m1*u1+m2*u2’;
a one-dimensional diffraction-signature group can not cover a two-dimensional diffraction-signature group;
a discrete peak can cover a continuous peak; and
lower-order peaks cover higher-order peaks.

### Claim 20 (depends on 1)

The method of claim 1, wherein the representative set of target patterns includes one or more user-selected clips.

### Claim 21 (depends on 1)

A non-transitory computer program product comprising a computer-readable medium having instructions recorded therein, which when executed, cause the computer to perform the method of selecting the representative set of target patterns according to claim 1.

### Claim 22 (depends on 1)

The method of claim 1, wherein the method of selecting the subset of target patterns from the design layout is independent of the lithographic process.