Pattern Inspection Apparatus with Switchable Numerical Aperture
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Solution Overview
Problem
Current pattern inspection apparatuses for semiconductor manufacturing are unable to accurately inspect minute defects on photomasks due to their high resolution settings, which are higher than those of exposure apparatuses, making it difficult to reproduce the pattern image for transfer printing and leading to unnecessary defect corrections, thereby increasing manufacturing time and costs.
Innovation Solution
A pattern inspection apparatus with a movable stage, adjustable numerical aperture, and a polarizing element that switches between high and low numerical aperture modes to capture transmitted and reflected light images, allowing for defect inspection and simulation comparison to match the exposure apparatus's resolution, enabling the detection of minute defects without requiring defect correction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the inspection apparatus uses high numerical aperture settings to detect minute defects, then measurement precision is improved, but the ability to reproduce the exposure apparatus's pattern image deteriorates
Solution Approach 1:
The patent implements dynamic switching between high NA and low NA modes. The system can change the numerical aperture of the objective lens based on the inspection requirements, allowing it to operate in high NA mode for detecting minute defects and switch to low NA mode for reproducing exposure pattern images that match the exposure apparatus characteristics.
Solution Approach 2:
The patent changes the numerical aperture parameter of the optical system. By adjusting the NA value, the system can optimize between two conflicting requirements: high NA for superior defect detection precision and low NA for accurate reproduction of exposure pattern images. This parameter adjustment allows the same apparatus to perform both functions effectively.
2Measurement precision
If the inspection apparatus detects all minute defects with high precision, then measurement precision is improved, but manufacturing time increases due to unnecessary defect corrections
Solution Approach 1:
The patent creates a simulated exposure pattern image that replicates how the exposure apparatus would actually form the pattern. By comparing the actual inspection results with this simulation, the system can determine whether detected defects will actually affect the final exposure outcome. This allows differentiation between critical defects requiring correction and non-critical variations that would not impact manufacturing.
Solution Approach 2:
The patent implements a feedback mechanism where the inspection results are compared against the simulated exposure pattern. This comparison provides feedback on whether detected minute defects will actually manifest as problems in the final exposure, allowing the system to avoid unnecessary defect corrections and optimize manufacturing time.
3Measurement precision
If the inspection apparatus uses high numerical aperture to inspect patterns, then measurement precision is improved, but the device complexity increases due to additional optical components
Solution Approach 1:
The patent designs a universal optical system that can perform multiple functions: high NA inspection, low NA exposure pattern reproduction, and simulated exposure imaging. By making the same optical system multi-functional through NA switching and simulation capabilities, the patent avoids the need for separate dedicated systems for each function, thereby managing complexity while maintaining high measurement precision.
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
The apparatus effectively detects minute defects on photomasks, reducing unnecessary corrections and shortening manufacturing time by reproducing the pattern image suitable for exposure and transfer, thus improving yield and efficiency in semiconductor production.
Implementation Method 1
a transmitted illumination optical system configured to illuminate the mask substrate with a first inspection light
Implementation Method 2
a reflected illumination optical system configured to include an objective lens and a polarizing element, illuminate the mask substrate with a second inspection light by using the objective lens and the polarizing element, and let a reflected light from the mask substrate pass through the reflected illumination optical system
Implementation Method 3
a reflected illumination optical system configured to include an objective lens and a polarizing element, illuminate the mask substrate with a second inspection light by using the objective lens and the polarizing element
Implementation Method 4
an aperture stop placed between the mask substrate and the sensor, and configured to adjust a light flux diameter of the transmitted light so that the transmitted light reaching the sensor can be switched between a transmitted light corresponding to a state of high numerical aperture (NA) and a transmitted light corresponding to a state of low numerical aperture
Implementation Method 5
an image forming optical system configured to receive the transmitted light through the objective lens, and focus a received transmitted light to form an image on the sensor
Data Source
AI summary
A pattern inspection apparatus includes a transmitted illumination optical system to illuminate change the shape of a first inspection light, a reflected illumination optical system to illuminate a mask substrate with a second inspection light by using an objective lens and a polarizing element, and let a reflected light from the mask substrate pass therethrough, a drive mechanism to enable the polarizing element to be moved from/to outside/inside an optical path, a sensor to receive a transmitted light from the mask substrate illuminated with the first inspection light during stage moving, and an aperture stop, between the mask substrate and the sensor, to adjust a light flux diameter of the transmitted light so that the transmitted light reaching the sensor can be switched between high and low numerical aperture (NA) states with which the transmitted light from the mask substrate can enter the objective lens.