Photomask Inspection Using Optical Simulation and Contour Comparison
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Solution Overview
Problem
Current mask inspection methods are inadequate for accurately detecting defects in photomasks due to their reliance on indirect verification of printed features on wafers, which can be labor-intensive and time-consuming, and do not effectively distinguish between mask-related and resist-related issues, leading to inefficient process control and reduced yield.
Innovation Solution
A computerized system and method for inspecting photomasks by emulating lithographic tool optics to generate images of mask features, estimating contours, identifying reference contours, and measuring deviations to detect edge displacements and other defects directly on the mask, using actinic or non-actinic inspection tools with optional simulation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If indirect verification of printed features on wafers is used, then defect detection can be performed, but the process becomes labor-intensive and time-consuming
Solution Approach 1:
The patent performs mask inspection before the lithography printing process to detect defects early. By examining the mask directly using optical simulation that mimics the lithographic tool's point spread function, defects are identified in advance, eliminating the need for time-consuming post-printing verification on wafers and enabling early defect detection that prevents multiple defective devices
2Measurement precision
If indirect verification of printed features is used, then defects can be detected, but it is difficult to distinguish between mask-related and resist-related issues
Solution Approach 1:
The patent segments the defect detection process into mask-specific inspection and process-specific analysis. By directly examining the mask with optical simulation and comparing against a simulated perfect mask image, the system isolates mask defects from resist or printing process issues. This segmentation enables precise attribution of defects to the mask itself, separating mask-related problems from resist-related issues
Solution Approach 2:
The patent introduces an optical simulation model as an intermediary that mimics the lithographic tool's point spread function. This simulation creates a reference image of how a perfect mask would appear under the same optical conditions, enabling direct comparison and accurate identification of actual mask defects without contamination from resist or printing process variables
3Measurement precision
If direct mask inspection is performed, then defect detection accuracy improves, but the complexity of the inspection system increases
Solution Approach 1:
The patent creates an optical copy or simulation of the lithographic printing process by modeling the point spread function and generating a simulated mask image. This computational copy allows direct mask inspection with high accuracy by comparing the actual mask image against the simulated perfect mask image, achieving defect detection precision comparable to direct lithographic inspection without requiring the full complexity of a lithographic tool
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Enhances defect detection accuracy and sensitivity, improving process control without affecting throughput, enabling early identification of defects that would otherwise cause multiple defective devices.
Implementation Method 1
obtain a first image representative of at least part of the mask, wherein the first image is acquired by emulating optical configuration of a lithographic tool
Implementation Method 2
emulating optical configuration of a lithographic tool usable for fabrication of the semiconductor specimen
Data Source
AI summary
There is provided a system and method of a method of mask inspection, comprising: obtaining a first image representative of at least part of the mask; applying a printing threshold on the first image to obtain a second image; estimating a contour for each structural element of interest (SEI) of a group of SEIs, and extracting a set of attributes characterizing the contour, giving rise to a group of contours corresponding to the group of SEIs and respective sets of attributes associated therewith; for each given contour, identifying, among the remaining contours in the group of contours, one or more reference contours similar to the given contour, by comparing between the respective sets of attributes associated therewith; and measuring a deviation between the given contour and each reference contour thereof, giving rise to one or more measured deviations indicative of whether a defect is present.