Height Detection Optical Path Correction for Charged Particle Beam Focusing
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Solution Overview
Problem
Conventional optical height detection apparatuses struggle to accurately detect the height of samples with deep holes or grooves in semiconductor wafers due to limitations in the magnetic field's ability to focus a charged particle beam, making it difficult to adjust the sample height when the focal position changes.
Innovation Solution
A height detection apparatus that projects a pattern onto a sample using a projection optical system and detects the reflected pattern with an imaging element, incorporating an optical path length correction member to equalize the optical paths of spatially separated light beams, allowing for relative height detection from multiple reference positions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the energy of the charged particle beam is increased to increase the resolution of the image, then the resolution is improved, but the focal position changes due to limitation of the magnetic field for condensing the charged particle beam
Solution Approach 1:
The patent introduces a new dimension by adding optical path length correction members to compensate for focal position changes. Instead of trying to maintain a single fixed focal position, the system creates multiple reference positions (first reference position and second reference position) along the optical axis and provides correction mechanisms for each, allowing the system to adapt to energy changes in the charged particle beam.
Solution Approach 2:
The patent changes the parameter of optical path length by introducing correction members with specific thicknesses designed to compensate for focal position shifts. The thickness of each optical path length correction member is calculated based on the difference in optical path lengths, allowing the system to maintain accurate height detection despite changes in beam energy and focal position.
2Device complexity
If a conventional optical height detection apparatus with a single reference position is used, then the device complexity is low, but it cannot detect height accurately when the focal position changes
Solution Approach 1:
The patent makes the height detection apparatus universal by enabling it to detect heights at multiple reference positions along the optical axis. The projection optical system and imaging element work together with multiple optical path length correction members to provide height detection functionality at both the first and second reference positions, allowing the same apparatus to handle different focal positions without requiring separate detection systems.
3Adaptability or versatility
If multiple reference positions are added to detect height from different focal positions, then the adaptability increases, but the device complexity increases due to multiple optical paths
Solution Approach 1:
The patent applies local quality by placing optical path length correction members at specific locations within the optical system. Each correction member is positioned in a corresponding optical path to compensate for path length differences locally, rather than attempting to redesign the entire optical system. This allows for targeted correction in each optical path while maintaining the overall structure.
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
Enables easy detection of sample height from multiple reference positions, facilitating accurate adjustment of the sample height even when the focal position changes, thereby improving the ability to focus a charged particle beam on deep features without degrading resolution.
Implementation Method 1
detecting the pattern reflected from the sample
Implementation Method 2
an optical path length correction member disposed on an optical path different from an optical path having a shortest optical path length among a plurality of optical paths corresponding to the plurality of light beams
Data Source
AI summary
A height detection apparatus is configured to project a pattern on a sample arranged at any of a plurality of reference positions and configured to detect a height of the sample. The apparatus includes: a projection optical system that generates a plurality of spatially separated light beams each having the pattern and projects the generated spatially separated light beams onto the sample; an imaging element that images the pattern reflected from the sample; a detection optical system that guides the pattern reflected from the sample to the imaging element; and at least one optical path length correction member disposed on an optical path different from an optical path having a shortest optical path length among a plurality of optical paths corresponding to the plurality of light beams at a position where the plurality of light beams is spatially separated.