Photomask CD Mapping for Sectioned Uniformity Inspection
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Solution Overview
Problem
Current mask inspection methods are inadequate for accurately and efficiently monitoring critical dimension (CD) uniformity in photomasks, leading to potential defects in semiconductor devices due to uncorrected CD variations, which can cause device failure and reduced yield.
Innovation Solution
A computerized system and method for inspecting photomasks using a processing and memory circuitry (PMC) to generate a critical dimension (CD) map by dividing images into sections, searching for patterns of interest, applying a printing threshold, and combining CD measurements to assess CD uniformity, enabling defect detection and response.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If indirect inspection method is used (inspecting final printed pattern on wafer), then device performance can be verified, but it is difficult to attribute errors to mask problems and requires extensive inspection time
Solution Approach 1:
The patent applies preliminary action by inspecting the mask before it is used to fabricate semiconductor devices. The system performs CD measurements on the mask itself to detect defects and CD uniformity issues beforehand, preventing defective masks from being used in production. This eliminates the need for time-consuming post-fabrication inspection and attribution analysis, as problems are identified and corrected in advance.
Solution Approach 2:
The patent introduces an intermediary inspection process that measures the mask's CD properties directly as a mediator between mask fabrication and device fabrication. By measuring the mask's transmission characteristics and generating CD maps, the system provides intermediate verification that bridges the gap between mask quality and final device performance, enabling early defect detection without requiring full fabrication cycles.
2Reliability
If mask inspection is performed to detect CD variations, then device yield can be improved, but the inspection process becomes more complex and time-consuming
Solution Approach 1:
The patent applies self-service by designing an automated inspection system that performs CD measurements and generates comprehensive CD maps without requiring complex manual intervention. The system automatically acquires multiple images, processes them through image processing algorithms, calculates CD values, and produces visual CD maps that clearly indicate defects and uniformity issues, enabling rapid mask evaluation with minimal operator involvement.
3Measurement precision
If multiple images are acquired and processed to generate CD map, then measurement precision is improved, but processing time and computational complexity increase
Solution Approach 1:
The patent applies segmentation by dividing the mask inspection process into distinct stages: acquiring multiple images of different mask regions, processing each image to extract CD measurements, and combining results into a comprehensive CD map. This segmented approach allows parallel processing of multiple images and enables efficient computation by breaking down the complex task into manageable segments that can be processed systematically.
Data Source
AI summary
There is provided a system and method for mask inspection, comprising: obtaining a plurality of images, each representative of a respective part of the mask; generating a CD map of the mask comprising a plurality of composite values of a CD measurement of a POI respectively derived from the plurality of images, comprising, for each given image: dividing the given image into a plurality of sections; searching for the POI in the plurality of sections, giving rise to a set of sections, each with presence of at least one of the POI therein; for each section, obtaining a value of the CD measurement using a printing threshold, giving rise to a set of values of the CD measurement corresponding to the set of sections; and combining the set of values to a composite value of the CD measurement corresponding to the given image.