# US 9,518,935 B2 · Monitoring changes in photomask defectivity

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- Number: US 9,518,935 B2
- Document ID: US9518935B2
- Status: Granted
- Kind: B2
- Application number: 14/278,277
- Filed: 2014-05-15
- Published: 2015-01-29
- Granted: 2016-12-13
- Earliest claimed: 2013-07-29
- Assignees: KLA-Tencor Corporation
- Applicants: KLA-Tencor Corporation
- Inventors: Chun Guan; Yalin Xiong; Joseph M. Blecher; Robert A. Comstock; Mark J. Wihl
- Web page: https://patentgrep.com/patent/US9518935B2

## CPC

- G06T 7/0006: {using a design-rule based approach}
- G01N 21/956: Inspecting patterns on the surface of objects {(contactless testing of electronic circuits G01R31/308; testing currency G07D; manufacturing processes per se of semiconductor devices implementing a measuring step H10P74/20)}
- G01N 21/95607: {using a comparative method}
- G01N 2021/95676: {Masks, reticles, shadow masks}
- G06T 2207/30148: Semiconductor; IC; Wafer
- G06T: IMAGE DATA PROCESSING OR GENERATION, IN GENERAL
- G01N: INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES (measuring or testing apparatus or processes other than immunoassay, involving enzymes or microorganisms C12M, C12Q)

## Abstract

A reticle that is within specifications is inspected so as to generate a baseline event indicating a location and a size value for each unusual reticle feature. After using the reticle in photolithography, the reticle is inspected so as to generate a current event indicating a location and a size value for each unusual reticle feature. An inspection report of candidate defects and their images is generated so that these candidate defects include a first subset of the current events and their corresponding candidate defect images and exclude a second subset of the current events and their corresponding excluded images. Each of the first included events has a location and size value that fails to match any baseline event's location and size value, and each of the excluded second events has a location and size value that matches a baseline event's location and size value.

## Claims

### Claim 1

A method of inspecting a photolithographic reticle, the method comprising:
performing a first single-die inspection of a reticle that has been identified as being within specifications so as to generate a plurality of baseline events corresponding to a plurality of unusual baseline features of the reticle, wherein each baseline event indicates a location and a size value for a corresponding unusual baseline feature;
after using the reticle in one or more photolithography processes, performing via a reticle inspection tool a second single-die inspection of the reticle so as to generate a plurality of current events corresponding to a plurality of current unusual features of the reticle, wherein each current event indicates a location and a size value for a corresponding current unusual feature; and
generating an inspection report of a plurality of candidate reticle defects and their images, wherein the candidate defects include a first subset of the current events and their corresponding plurality of candidate defect images and exclude a second subset of the current events and their corresponding plurality of excluded images, wherein each of the first subset of events included in the inspection report has a location and size value that fails to match any baseline event's location and size value by a predefined amount, and each of the second subset of events excluded from the inspection report has a location and size value that matches any baseline event's location and size value by the predefined amount.

### Claim 2 (depends on 1)

The method of claim 1, wherein at least some of the baseline events correspond to a plurality of reticle features that were designed to be identical prior to an optical proximity correction (OPC) process being implemented on such reticle features to add OPC decorations so that such reticle features are no longer identical.

### Claim 3 (depends on 1)

The method of claim 1, wherein at least some of the baseline events correspond to reticle features that were not part of an original design for such reticle and were determined to not limit wafer yield using such reticle.

### Claim 4 (depends on 1)

The method of claim 1, wherein at least some of the baseline events correspond to reticle features that have been determined to not print onto a wafer during a photolithography process using the reticle.

### Claim 5 (depends on 1)

The method of claim 1, wherein at least some of the baseline events correspond to repair features for correcting defects on the reticle.

### Claim 6 (depends on 1)

The method of claim 1, wherein the first and second single-die inspections determine which features of the reticle are atypical based on the context of such features.

### Claim 7 (depends on 6)

The method of claim 6, wherein the first and second single-die inspections include template matching.

### Claim 8 (depends on 1)

The method of claim 1, further comprising discarding a plurality of baseline images for the baseline events and discarding the second subset of candidate events' corresponding images.

### Claim 9 (depends on 1)

The method of claim 1, wherein each baseline event further indicates a channel and each of the second subset of events excluded from the inspection report has a channel and a location and size value that matches any baseline event's channel and location and size value by a predefined amount.

### Claim 10 (depends on 1)

The method of claim 1, wherein generating the inspection report of the candidate defects and their images comprises:
for each current event that has a location and size value that fails to match any baseline event's location and size value by a predefined amount, determining whether such current event is a candidate defect by performing a third single-die inspection that has a less stringent threshold or algorithm than the second single-die inspection.

### Claim 11 (depends on 1)

The method of claim 1, wherein the candidate defect images and the excluded images include one or more combinations of reflected images, transmitted images, or combined reflected and transmitted images.

### Claim 12 (depends on 1)

The method of claim 1, wherein the candidate defects further include a third subset of current events that each has a location and size value that matches any baseline event's location and size value by a predefined amount and is identified as a repair location.

### Claim 13 (depends on 1)

The method of claim 1, wherein the first single-die inspection is performed using a reticle inspection tool.

### Claim 14 (depends on 1)

The method of claim 1, wherein the first single-die inspection is performed on an reticle image that was generated from design database.

### Claim 15 (depends on 1)

The method of claim 1, wherein matches between the current unusual events and baseline current events are found by:
finding reference images for a subset of the current and baseline unusual events and their corresponding test images;
for the subset of current and baseline unusual events, finding current and baseline candidate defects based on a comparison between reference images and their corresponding test images; and
determining whether there is a match between any current candidate defects and baseline candidate defects and only performing further processing for one or more candidate defects that do not have matches, wherein at least a portion of the reference images are baseline images for baseline unusual events for which corresponding reference images were not found.

### Claim 16

An inspection system for inspecting a photolithographic reticle, the system comprising at least one memory and at least one processor that are configured to perform the following operations:
in a first single-die inspection of a reticle that has been identified as being within specifications, generating a plurality of baseline events corresponding to a plurality of unusual baseline features of the reticle, wherein each baseline event indicates a location and a size value for a corresponding unusual baseline feature;
after using the reticle in one or more photolithography processes, performing a second single-die inspection of the reticle so as to generate a plurality of current events corresponding to a plurality of current unusual features of the reticle, wherein each current event indicates a location and a size value for a corresponding current unusual feature; and
generating an inspection report of a plurality of candidate reticle defects and their images, wherein the candidate defects include a first subset of the current events and their corresponding plurality of candidate defect images and exclude a second subset of the current events and their corresponding plurality of excluded images, wherein each of the first subset of events included in the inspection report has a location and size value that fails to match any baseline event's location and size value by a predefined amount, and each of the second subset of events excluded from the inspection report has a location and size value that matches any baseline event's location and size value by the predefined amount.

### Claim 17 (depends on 16)

The system of claim 16, wherein at least some of the baseline events correspond to a plurality of reticle features that were designed to be identical prior to an optical proximity correction (OPC) process being implemented on such reticle features to add OPC decorations so that such reticle features are no longer identical.

### Claim 18 (depends on 16)

The system of claim 16, wherein at least some of the baseline events correspond to reticle features that were not part of an original design for such reticle and were determined to not limit wafer yield using such reticle.

### Claim 19 (depends on 16)

The system of claim 16, wherein at least some of the baseline events correspond to reticle features that have been determined to not print onto a wafer during a photolithography process using the reticle.

### Claim 20 (depends on 16)

The system of claim 16, wherein at least some of the baseline events correspond to repair features for correcting defects on the reticle.

### Claim 21 (depends on 16)

The system of claim 16, wherein the first and second single-die inspections determine which features of the reticle are atypical based on the context of such features.

### Claim 22 (depends on 21)

The system of claim 21, wherein the first and second single-die inspections include template matching.

### Claim 23 (depends on 16)

The system of claim 16, wherein the at least one memory and at least one processor are further configured for discarding a plurality of baseline images for the baseline events and discarding the second subset of candidate events' corresponding images.

### Claim 24 (depends on 16)

The system of claim 16, wherein each baseline event further indicates a channel and each of the second subset of events excluded from the inspection report has a channel and a location and size value that matches any baseline event's channel and location and size value by a predefined amount.

### Claim 25 (depends on 16)

The system of claim 16, wherein generating the inspection report of the candidate defects and their images comprises:
for each current event that has a location and size value that fails to match any baseline event's location and size value by a predefined amount, determining whether such current event is a candidate defect by performing a third single-die inspection that has a less stringent threshold or algorithm than the second single-die inspection.

### Claim 26 (depends on 16)

The system of claim 16, wherein the candidate defect images and the excluded images include one or more combinations of reflected images, transmitted images, or combined reflected and transmitted images.

### Claim 27 (depends on 16)

The system of claim 16, wherein the candidate defects further include a third subset of current events that each has a location and size value that matches any baseline event's location and size value by a predefined amount and is identified as a repair location.

### Claim 28

A non-transitory computer readable medium having instruction stored thereon for performing the following operations:
performing a first single-die inspection of a reticle that has been identified as being within specifications so as to generate a plurality of baseline events corresponding to a plurality of unusual baseline features of the reticle, wherein each baseline event indicates a location and a size value for a corresponding unusual baseline feature;
after using the reticle in one or more photolithography processes, performing via an optical reticle inspection tool a second single-die inspection of the reticle so as to generate a plurality of current events corresponding to a plurality of current unusual features of the reticle, wherein each current event indicates a location and a size value for a corresponding current unusual feature; and
generating an inspection report of a plurality of candidate reticle defects and their images, wherein the candidate defects include a first subset of the current events and their corresponding plurality of candidate defect images and exclude a second subset of the current events and their corresponding plurality of excluded images, wherein each of the first subset of events included in the inspection report has a location and size value that fails to match any baseline event's location and size value by a predefined amount, and each of the second subset of events excluded from the inspection report has a location and size value that matches any baseline event's location and size value by the predefined amount.