Exposure Apparatus Focus Calibration via Positional Shift Feedback
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Solution Overview
Problem
Conventional exposure apparatuses face challenges in accurately determining focus positions due to positional shifts and telecentricity errors during the photolithography process, leading to measurement deviations in focus calibration.
Innovation Solution
The exposure apparatus incorporates a projection optical system, a substrate stage capable of movement in multiple directions, and a controller that measures light amounts through reference marks to determine focus positions by accounting for positional shifts and telecentricity, allowing for precise focus calibration even in the presence of these errors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If focus calibration is performed using conventional TTL method, then focus position measurement is achieved, but measurement precision deteriorates due to positional shift and telecentricity errors
Solution Approach 1:
The system measures the actual projection position of the mask-side reference mark on the substrate-side reference mark, detects the positional shift, and feeds back this information to correct the focus position calculation. The controller adjusts the focus determination based on the measured positional shift, creating a closed-loop feedback system that compensates for measurement errors caused by positional shifts and telecentricity.
Solution Approach 2:
The substrate-side reference mark serves as an intermediary element that enables the measurement of both the focus position and the projection position. By projecting the mask-side reference mark onto this intermediary reference mark, the system can detect positional shifts and use this information to correct focus measurements, effectively using the intermediary to bridge the measurement of two different parameters.
2Measurement precision
If substrate stage is driven in Z direction for focus measurement, then focus position is determined, but positional shift in X and Y directions causes measurement deviation
Solution Approach 1:
Before determining the focus position, the system preliminarily measures the projection position of the mask-side reference mark on the substrate-side reference mark. This preliminary measurement of the projection position is used to calculate the positional shift, which then serves as a correction factor for the subsequent focus position determination, ensuring that focus accuracy is maintained despite positional shifts.
Solution Approach 2:
The system changes the measurement approach by not only measuring light intensity variations with Z-position (conventional method) but also measuring the lateral projection position on the substrate-side reference mark. This additional parameter measurement (projection position in X and Y directions) is used to correct the focus position calculation, transforming a single-parameter measurement into a multi-parameter measurement system.
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 accurate focus position determination and correction, ensuring precise projection of mask patterns onto substrates, thereby improving the quality of microdevice manufacturing processes.
Implementation Method 1
a projection optical system configured to project, on a substrate (5), a pattern of a mask (2) held by a mask stage (3)
Implementation Method 2
measuring a light amount that is transmitted through a mask-side reference mark, the projection optical system, and a substrate-side reference mark
Data Source
AI summary
An exposure apparatus obtains information on a relationship between a moving amount of a substrate stage in the first direction and an amount of a positional shift in an image of a mask-side reference mark projected on a substrate-side reference mark by a projection optical system in the second direction perpendicular to an optical axis of the projection optical system with respect to the substrate-side reference mark. A controller determines a focus position based on the measurement result by causing the measurement device to measure the light amount while, together with driving the substrate stage in the first direction and the second direction based on the information.