Microscope Oblique Illumination Focus Control
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Solution Overview
Problem
Existing microscope systems face challenges in accurately focusing on sample surfaces due to variations in sample height, leading to misalignment and reduced throughput, especially when dealing with samples without patterns like bare wafers, and require expensive hardware for height measurement.
Innovation Solution
A microscope system with an irradiation optical system that irradiates the sample from an oblique direction, an observation optical system to form images of scattered light, and a computer system to control the optical systems and calculate the sample height change based on spot pattern changes, allowing for precise focus adjustments.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a plurality of images are captured and processed to calculate focus height, then focusing accuracy is improved, but processing time increases and throughput decreases
Solution Approach 1:
The patent extracts only the necessary information (spot pattern position) from the captured images rather than processing complete images. By isolating and tracking the position of the spot pattern caused by oblique illumination, the system calculates focus height without the need for complex multi-image processing, thereby reducing computation time while maintaining focusing accuracy.
Solution Approach 2:
The patent uses a virtual focus map created from spot pattern positions as a simplified copy of the actual sample surface topology. This virtual representation allows rapid focus height calculation without repeatedly capturing and processing multiple images of the sample, significantly reducing processing time while preserving focusing precision.
2Speed
If a focus map is created in advance to determine focus height, then focusing speed is improved, but the system cannot adapt to changes in sample height over time and requires periodic updates
Solution Approach 1:
The system performs self-updating of the focus map by automatically detecting spot pattern positions during normal operation. The focus map is continuously refreshed using real-time spot position data without requiring external intervention or periodic manual updates, enabling the system to adapt to sample height changes autonomously while maintaining fast focusing performance.
Solution Approach 2:
The patent implements a feedback mechanism where spot pattern position measurements are continuously fed back to update the focus map. This closed-loop approach ensures the focus map remains current with sample height variations, combining the speed of pre-created maps with the adaptability to change over time.
3Measurement precision
If dedicated hardware for height measurement is added to the microscope system, then measurement precision is improved, but apparatus cost and size increase
Solution Approach 1:
The patent introduces a spot pattern as an intermediary element that enables height measurement without direct hardware measurement. The spot pattern, created by oblique illumination, serves as a visual mediator that encodes height information in its position, allowing the existing imaging system to measure height precisely without adding dedicated measurement hardware.
Solution Approach 2:
The patent replaces potential mechanical or dedicated optical height measurement systems with an optical imaging-based method. By using the position of the spot pattern in captured images to infer height information, the system substitutes complex measurement hardware with a software-based calculation approach using existing imaging components.
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 rapid and accurate focusing on sample surfaces without the need for dedicated height measurement hardware, improving throughput and allowing for effective observation of both patterned and unpatterned samples.
Implementation Method 1
an observation optical system configured to form an image of scattered light from the surface of the sample
Data Source
AI summary
Regarding a microscope system, a technique capable of suitably achieving a focusing on a surface of a sample is provided. The microscope system includes an irradiation optical system (laser light source 101 or the like) that irradiates a surface of a sample 3 on a stage 104 with light from an oblique direction, an observation optical system (camera 112 or the like) that forms an image of scattered light from the surface of the sample 3, a focus mechanism (piezo stage 106 or the like) that changes a height position of focus with respect to the surface of the sample 3, and a computer system 100 that acquires an image from the observation optical system. Regarding the sample 3, the computer system acquires a first image in a first focus state and a second image in a second focus state, in which the first image and the second image have different focus heights, calculates an amount of change between a position of a first spot pattern in the first image and a position of a second spot pattern in the second image, calculates an amount of change in height of the sample 3 based on an incident angle in the oblique direction and the amount of change in position of spot pattern, and adjusts the height position of the focus by using the amount of change in sample height so as to focus on the surface of the sample 3.