Optical Inspecting Apparatus for Photomask Defect Detection
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Solution Overview
Problem
Current optical inspecting apparatuses for photomasks struggle to accurately detect defects, especially in shadow areas, due to the design where the photomask's bottom surface contacts the stage, leading to reduced detection performance and inspection speed.
Innovation Solution
An optical inspecting apparatus with a confocal microscope setup that includes multiple light sources with different wavelengths and polarization directions, a beam splitter, and pinhole plates, allowing light to be focused on the photomask's top surface while avoiding shadow areas by positioning the photomask on a horizontal stage with edge supports, enabling comprehensive inspection without direct contact and enhancing defect detection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the photomask bottom surface contacts the stage for support, then the photomask is stable and easy to position, but shadow areas are created that reduce defect detection accuracy
Solution Approach 1:
The photomask is rotated 90 degrees so that the previously horizontal bottom surface becomes vertical, allowing light to illuminate the top surface without obstruction from stage contact. This dimensional change eliminates shadow areas while maintaining stable positioning through vertical supports.
Solution Approach 2:
Instead of illuminating the photomask from the bottom surface (conventional approach), the system illuminates from the top surface. This inversion of the illumination direction eliminates shadow areas created by stage contact while still enabling stable positioning.
2Measurement precision
If multiple light sources with different wavelengths and polarization directions are used, then defect detection accuracy and inspection speed are improved, but device complexity increases
Solution Approach 1:
Multiple light sources with different wavelengths and polarization directions are employed to detect various types of defects that may be invisible to single-wavelength or single-polarization illumination. This multi-functional approach enables comprehensive inspection while the confocal microscope design integrates these diverse light sources into a unified system.
Solution Approach 2:
The patent combines multiple light sources, beam splitters, and pinhole plates into an integrated confocal microscope system. By merging these components, the system achieves enhanced defect detection capability while managing complexity through systematic integration rather than separate independent systems.
3Measurement precision
If the photomask is positioned with edge supports on a horizontal stage, then shadow areas are eliminated and inspection coverage is improved, but the positioning and support mechanism becomes more complex
Solution Approach 1:
The photomask is rotated 90 degrees so that edge supports on a horizontal stage support the previously vertical edges, allowing the top surface to be fully illuminated without shadow areas. This dimensional change enables complete inspection coverage while using a relatively simple horizontal stage mechanism.
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 configuration improves defect detection accuracy and speed by providing clearer images and increased inspection power, capable of detecting defects as small as 100 nm, surpassing human vision and reducing the need for manual inspection.
Implementation Method 1
The beam splitter transmits or reflects the first light beam
Implementation Method 2
The first lens provides the first light beam to transmit through a transparent substrate of a photomask and forms a first focusing spot on a first surface of the transparent substrate
Implementation Method 3
The pinhole plates are disposed in front of the first light detector to filter noise in the reflection light beam
Implementation Method 4
The first light detector detects a first reflection light beam generated by reflecting the first light beam by the first surface of the transparent substrate or the top surface of a photomask pattern
Data Source
AI summary
An optical inspecting apparatus includes a first light source, a beam splitter, a first lens, a first light detector, and pinhole plates. The first light source emits a first light beam. The beam splitter transmits or reflects the first light beam. The first lens provides the first light beam to transmit through a transparent substrate of a photomask and forms a first focusing spot on a first surface of the transparent substrate or a top surface of a photomask pattern formed on the transparent substrate. The first light detector detects a first reflection light beam generated by reflecting the first light beam from the first surface of the transparent substrate or the top surface of the photomask pattern. The pinhole plates are disposed in front of the first light detector to filter noise in the reflection light beam.