Mask Inspection Using Dual-Resolution Optical Imaging
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Solution Overview
Problem
In the manufacturing of semiconductor devices, it is challenging to accurately distinguish between true defects and fault defects on masks, particularly due to the miniaturization of patterns, which complicates the comparison of reference image data with optical image data, and simulation methods require ambiguous threshold settings and can vary based on pattern type and quality.
Innovation Solution
An inspection method and apparatus that acquire both high-resolution and low-resolution optical image data of a mask pattern, generate reference image data based on corrected design data, and compare these images to detect defects, with the low-resolution data simulating the exposure apparatus's optical system to evaluate the transferability of defects to a wafer, thereby reducing fault defects through accurate inspection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If simulation methods are used to determine defect transferability, then defect evaluation can be performed, but threshold settings become ambiguous and results vary based on pattern type and quality
Solution Approach 1:
The patent creates a reference image that copies the optical characteristics of the exposure apparatus by simulating its optical system. This reference image serves as a standardized template for comparing defect transferability, eliminating the need for ambiguous threshold settings in traditional simulation methods. The reference image encapsulates the optical system's behavior across different pattern types and qualities.
Solution Approach 2:
The patent changes the approach from using multiple simulation parameters with ambiguous thresholds to using a single reference image that inherently contains all necessary optical characteristics. By transforming the simulation output into a visual reference format, the system eliminates parameter-setting complexity while maintaining evaluation accuracy.
2Measurement precision
If only high-resolution optical image data is used for inspection, then fine pattern defects can be detected, but fault defects cannot be distinguished from true defects
Solution Approach 1:
The patent merges high-resolution optical image data with simulated reference image data into a composite evaluation process. The high-resolution data provides detailed defect information, while the reference image provides transferability context. By combining these data sources, the system achieves both fine pattern detection and fault defect discrimination.
Solution Approach 2:
The reference image acts as an intermediary between the optical image data and defect evaluation. It mediates the comparison by providing a standardized template that indicates which defects are transferable, allowing the system to distinguish fault defects from true defects without losing transferability information.
3Reliability
If the inspection threshold is set to detect all potential defects, then true defects are identified, but fault defects increase due to false positives
Solution Approach 1:
The patent implements feedback through the reference image comparison process. The reference image provides feedback on which detected defects are actually transferable, allowing the system to adjust defect classification based on optical system characteristics rather than relying solely on fixed thresholds. This feedback mechanism reduces false positives while maintaining detection reliability.
Solution Approach 2:
The patent introduces dynamic defect evaluation by comparing optical image data against a reference image that represents the optical system's actual behavior. This dynamic approach allows the inspection criteria to adapt to different pattern types and optical conditions, reducing false positives without compromising detection reliability.
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
This approach enables accurate inspection by minimizing fault defects and improving the distinction between true and fault defects, ensuring higher yield rates in semiconductor manufacturing by accurately determining defect transferability to the wafer.
Implementation Method 1
acquiring first optical image data of a pattern arranged on a mask by irradiating the mask with light emitted by a light source via a first optical system and directing the light transmitted through or reflected by the mask to be incident on an imaging device
Implementation Method 2
acquiring second optical image data of the pattern by irradiating the mask with light emitted by the light source via a second optical system and directing the light transmitted through or reflected by the mask to be incident on the imaging device, wherein the second optical system has a resolution lower than the first optical system and simulates an optical system of an exposure apparatus
Data Source
AI summary
A high resolution optical image is acquired by irradiating a mask with light emitted by a light source via a high resolution optical system. A low resolution optical image is acquired by irradiating the same mask with the light via a low resolution optical system. The design data of the mask pattern is corrected in light of shapes and dimensions determined according to at least one of a manufacturing process of the mask and a manufacturing process of a semiconductor device to be manufactured by transferring the mask pattern to a semiconductor wafer. Reference image data are generated corresponding to the high resolution optical image and the low resolution optical image. Whether the defect detected in the high resolution optical image is true or false is determined according to information of the defect detected in the low resolution optical image.