Photomask Evaluation Using Sidewall Angle Data for Lithographic Simulation

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Solution Overview

Problem

Current photomask evaluation methods are inadequate for achieving strict dimensional accuracy in semiconductor manufacturing due to neglecting the influence of sidewall angles in mask patterns, leading to discrepancies between lithographic simulation results and actual wafer exposure outcomes, especially with increasing numerical aperture and complex pattern shapes.

Innovation Solution

A photomask evaluation method that acquires pattern images, generates sidewall angle data, extracts and corrects pattern outlines based on this data, and runs lithographic simulations to accurately calculate exposure margins, incorporating the influence of sidewall angles to improve accuracy.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Ease of manufacture

If uniform outline extraction from SEM image is performed neglecting sidewall angles, then the extraction process is simple, but the lithographic simulation results do not correspond to actual wafer exposure results

Engineering Contradiction:

Improveoutline extraction simplicityVSAvoidlithographic simulation accuracy

Core Design Contradiction:

Ease of manufactureVSMeasurement precision

Solution Approach 1:

The patent changes the parameters used in outline extraction from uniform extraction to variable extraction that accounts for sidewall angles. By introducing sidewall angle as a variable parameter that affects outline position, the extraction process adapts to different pattern geometries, improving simulation accuracy without significantly complicating the overall process.

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent applies local quality by making the outline extraction process location-dependent. Different regions of the mask pattern are extracted with different offset amounts based on their local sidewall angles. This allows the extraction to be simple in regions with uniform sidewalls while being more precise in regions where sidewall variations affect lithographic results.

Inventive Principle:

Principle #3Local quality

2Measurement precision

If sidewall angle consideration is incorporated into outline extraction, then lithographic simulation accuracy improves, but the extraction process becomes more complex

Engineering Contradiction:

Improvelithographic simulation accuracyVSAvoidextraction process complexity

Core Design Contradiction:

Measurement precisionVSDevice complexity

Solution Approach 1:

The patent applies preliminary action by measuring and storing sidewall angle information before performing the outline extraction. This pre-acquired sidewall angle data is then used to determine the appropriate offset for each extracted outline point. By preparing the sidewall angle information in advance, the actual extraction process remains relatively simple while still incorporating the necessary complexity for accurate results.

Inventive Principle:

Principle #10Preliminary action

3Manufacturing precision

If numerical aperture of wafer exposure apparatus is increased, then lithographic resolution improves, but the influence of sidewall angle becomes more significant

Engineering Contradiction:

Improvelithographic resolutionVSAvoidsidewall angle influence

Core Design Contradiction:

Manufacturing precisionVSObject-affected harmful factors

Solution Approach 1:

The patent converts the harmful effect of sidewall angle variations into a beneficial factor by using sidewall angle measurements to correct the outline extraction process. What was previously a source of error (sidewall angle effects becoming more significant with higher NA) is transformed into a correction parameter that improves the accuracy of lithographic simulation, allowing the system to compensate for and even utilize the sidewall angle influence.

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

Data Source

PatentUS8189903B2Photomask evaluation based on lithographic simulation using sidewall angle of photomask pattern

Publication Date: 2012.05.29 KIOXIA CORP

AI summary

According to an aspect of the invention, there is provided a photomask evaluation method including, acquiring a pattern image of a photomask, generating sidewall angle data on the sidewall angle of a pattern from the pattern image, extracting a pattern outline from the pattern image to generate outline data, and running a lithographic simulation on the basis of the outline data and the sidewall angle data to calculate an exposure margin.