Aperture Filter Optical Microscope for High-Contrast Wafer Imaging

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Solution Overview

Problem

Conventional optical microscopes struggle to achieve sufficient contrast for pattern recognition in samples with small pattern heights, leading to alignment failures, especially when using bright-field observation, due to reduced contrast and increased noise or low illumination efficiency in dark-field observation.

Innovation Solution

The implementation of an optical microscope device with an objective lens and aperture filters that attenuate bright-field observation components, allowing for stable pattern image capture with sufficient contrast by combining bright-field and dark-field light components.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Illumination intensity

If bright-field observation is used for pattern recognition, then the illumination efficiency is high and the captured image is bright, but the contrast of patterns with small pattern heights is insufficient

Engineering Contradiction:

Improvebrightness of captured imageVSAvoidpattern contrast

Core Design Contradiction:

Illumination intensityVSMeasurement precision

Solution Approach 1:

The patent segments the light field into different angular components using an aperture filter. The filter divides the illumination into a first light field (small angles, passes through) and a second light field (large angles, blocked). This segmentation allows selective observation of scattered light from patterns while maintaining adequate illumination, resolving the contradiction between brightness and contrast.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The patent applies local quality by creating different observation conditions for different spatial frequencies. The aperture filter allows low-angle light (background) to pass while blocking high-angle scattered light (pattern signal), effectively enhancing local contrast for small pattern heights while maintaining overall image brightness through the transmitted low-angle components.

Inventive Principle:

Principle #3Local quality

2Measurement precision

If dark-field observation is used to enhance pattern contrast, then the contrast of patterns is improved, but the brightness of the captured image is insufficient and the throughput decreases

Engineering Contradiction:

Improvepattern contrastVSAvoidbrightness of captured image

Core Design Contradiction:

Measurement precisionVSIllumination intensity

Solution Approach 1:

The patent applies partial action by using an aperture filter that blocks only the excessive large-angle scattered light components while allowing the necessary small-angle light components to pass. This partial blocking provides sufficient contrast enhancement without completely eliminating the background illumination, thus maintaining adequate image brightness and throughput compared to full dark-field observation.

Inventive Principle:

Principle #16Partial or excessive action

3Measurement precision

If dark-field observation is used to enhance pattern contrast, then the contrast of patterns is improved, but the apparatus size increases due to the need for a thick objective lens

Engineering Contradiction:

Improvepattern contrastVSAvoidapparatus size

Core Design Contradiction:

Measurement precisionVSVolume of moving object

Solution Approach 1:

The patent introduces an aperture filter as an intermediary element in the optical path. This mediator performs the function of angular selectivity that would otherwise require a thick objective lens with specific numerical aperture characteristics. By placing the aperture filter at the intermediate image plane or pupil plane, the system achieves dark-field-like contrast enhancement without needing to increase the objective lens thickness, thus maintaining compact apparatus size.

Inventive Principle:

Principle #24Intermediary (Mediator)

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 stable and sufficient contrast image capture of samples with small pattern heights, improving pattern recognition and alignment accuracy without increasing the size or complexity of the inspection apparatus.

Implementation Method 1

an aperture filter is arranged on an imaging optics side so that an image is captured while light of bright-field observation components is significantly attenuated

Methodology Applied

Scientific EffectLight blocking/attenuation: Absorption (EM radiation)

Data Source

PatentUS9851548B2Optical microscope device and testing apparatus comprising same

Publication Date: 2017.12.26 HITACHI HIGH TECH CORP

AI summary

The present invention allows observation or capturing of a high-contrast image of a sample for which sufficient contrast cannot be obtained in bright-field observation, such as a wafer having a pattern with a small pattern height. According to the present invention, a sample is illuminated through an objective lens used for capturing an image, and an imaging optics are provided with an aperture filter so that an image is captured while light of bright-field observation components is significantly attenuated.