Projection Optical System Evaluation Method for Semiconductor Exposure
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Solution Overview
Problem
Existing exposure apparatuses in semiconductor manufacturing face challenges in accurately transferring patterns due to fluctuations in optical characteristics of the projection optical system caused by heat absorption, leading to inaccuracies in predicting and controlling these fluctuations.
Innovation Solution
An evaluation method that uses a dedicated pattern with multiple marks arranged in a matrix on the object plane to determine a prediction formula for optical characteristic fluctuations, allowing for accurate prediction and control of these fluctuations by selecting specific marks within the illuminated region and using them to calculate and correct the predicted values.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a mark on the original having a circuit pattern is used to measure the fluctuation amount of optical characteristics, then the measurement can be performed, but it is impossible to detect an image of the mark in the region where the circuit pattern is projected, resulting in inadequate determination of the prediction formula
Solution Approach 1:
The original is divided into two distinct types: a first original containing only marks for measuring optical characteristics, and a second original containing both circuit patterns and marks. This segmentation allows the marks to be measured in the illuminated region without interference from circuit patterns, enabling accurate detection of optical characteristic fluctuations.
Solution Approach 2:
The first original acts as an intermediary tool specifically for measuring optical characteristics. By using a separate original with only marks (no circuit patterns), the measurement process can detect mark images in the illuminated region accurately, serving as a mediator between the optical system and the measurement apparatus.
2Measurement precision
If the prediction formula is determined using marks outside the illuminated region, then the marks can be detected, but the prediction accuracy of optical characteristic fluctuations deteriorates
Solution Approach 1:
Different regions of the original are assigned different functions: marks in the illuminated region are specifically positioned to be detected by the measurement apparatus, while marks outside the illuminated region serve as references. This local quality differentiation ensures that the measurement marks are detectable while maintaining prediction accuracy through proper selection of marks within the illuminated region.
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 method reduces errors in predicting optical characteristic fluctuations, enabling more accurate pattern transfer and improving the precision of semiconductor manufacturing processes.
Implementation Method 1
a part of exposure light is absorbed in a projection optical system, and thus optical characteristics of the projection optical system may fluctuate under the influence of heat generated by the absorption
Implementation Method 2
there is an exposure apparatus which transfers a pattern of an original to a shot region on a substrate
Data Source
AI summary
The present invention provides an evaluation method of evaluating optical characteristics of a projection optical system by obtaining, by a prediction formula, a predicted value for a fluctuation amount of the optical characteristics relative to an exposure period of a substrate via the projection optical system, the method comprising determining the prediction formula by using a dedicated pattern in which a plurality of marks are arranged in a matrix on an object plane of the projection optical system, wherein the determining includes selecting, from the plurality of marks, at least two marks located in an illuminated region to be formed on the object plane when exposing the substrate, and obtaining the prediction formula based on positions of images of the at least two marks formed on an image plane of the projection optical system.