Pattern Inspection Apparatus with Multi-Height Scale Detectors
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Solution Overview
Problem
Current pattern inspection apparatuses face challenges in achieving high accuracy due to stage tilting and air flow fluctuations, which affect position measurement and lead to errors in detecting minute pattern defects on semiconductor masks and wafers.
Innovation Solution
A pattern inspection apparatus with a stage capable of two-dimensional movement, equipped with multiple detectors of a two-dimensional scale at different heights, and a sensor to acquire optical images, along with calculation and comparison processing circuitry to correct image acquiring positions and compare images pixel-by-pixel.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If laser length measuring method is used to detect stage position, then position measurement can be performed, but measurement accuracy deteriorates due to air flow fluctuations and stage tilting
Solution Approach 1:
The patent introduces a reflection board as an intermediary element. The reflection board is fixed to the stage, and a laser beam is reflected from it to a detector. This intermediary setup allows position measurement without direct exposure to air flow fluctuations and stage tilting, as the reflection board maintains a stable reference frame relative to the stage movement.
Solution Approach 2:
The patent replaces the traditional laser interferometer-based mechanical measurement system with an optical reflection-based system. Instead of directly measuring stage position through mechanical means that are susceptible to air flow and tilting, the system uses optical reflection from a fixed board to infer position, thereby eliminating the harmful effects of air flow and stage tilting on measurement accuracy.
2Ease of operation
If stage tilting occurs during movement, then two-dimensional movement can be achieved, but image acquiring position deviates from actual position
Solution Approach 1:
The patent implements a feedback mechanism where the position detected by the detector (which accounts for stage tilting) is fed back to the control unit. The control unit then calculates the actual stage position by compensating for the tilting effect, ensuring that the image acquiring position accurately reflects the true position despite stage movement and tilting.
Solution Approach 2:
The patent performs preliminary position detection using the reflection board and detector before image acquisition. By measuring the position of the reflection board in advance and using this information to calculate the actual stage position, the system prepares compensation data that ensures accurate image acquiring position even when stage tilting occurs during movement.
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 solution enables highly accurate position measurement and defect detection even when the stage tilts, improving inspection precision and reducing errors caused by stage posture changes.
Implementation Method 1
a sensor configured to acquire an optical image of the pattern formed on the substrate
Implementation Method 2
a plurality of detectors of a two-dimensional scale configured to perform measurement and arranged at positions on the stage different from a position of the substrate
Data Source
AI summary
A pattern inspection apparatus includes a stage to mount thereon a substrate with patterns formed thereon and be able to move two-dimensionally, plural detectors of a two-dimensional scale, whose height positions are mutually different and arranged at positions on the stage different from the substrate position, to perform measurement, the body of the two-dimensional scale arranged fixed to a position facing the plural detectors, a sensor to acquire an optical image of the pattern on the substrate, in a state where the stage with the substrate is moving in one direction on a surface for the two-dimensional movement, a calculation circuitry to calculate an image acquiring position of the optical image by using position information measured by the two-dimensional scale, and a comparison circuitry to compare, using a reference image corresponding to the image acquiring position of the optical image, the optical image with the reference image for each pixel.