Exposure Mask Distortion Correction for Lithography Overlay
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Solution Overview
Problem
In semiconductor device fabrication, the lithography process faces challenges in accurately controlling overlay margins due to pattern distortion caused by off-axis illumination systems, which can degrade overlay accuracy and reduce fabrication yield.
Innovation Solution
A method is introduced to control exposure process distortion by aligning an exposure mask with a wafer, forming test patterns, extracting distortion values, and correcting the exposure mask using these values, which includes specific image patterns and marks to improve alignment accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If off-axis illumination systems are used in lithography, then imaging capability is improved, but pattern distortion occurs causing overlay accuracy to deteriorate
Solution Approach 1:
The patent applies preliminary action by pre-correcting the exposure mask with opposite distortion patterns before actual lithography. The mask is intentionally fabricated with distorted patterns that will compensate for the distortion introduced by the off-axis illumination system during exposure, thereby achieving accurate overlay without requiring real-time correction of the illumination system
Solution Approach 2:
The patent changes the parameters of the exposure mask by introducing specific distortion correction patterns and overlay marks with known geometric relationships. By modifying the mask parameters (pattern positions, orientations, and shapes) to account for anticipated illumination-induced distortion, the system maintains overlay accuracy despite using off-axis illumination
2Reliability
If overlay margin control is tightened for highly integrated devices, then fabrication yield is improved, but process complexity increases
Solution Approach 1:
The patent implements self-service by incorporating overlay marks and test patterns directly into the exposure mask that automatically provide distortion measurement and correction data. The mask itself serves as both the patterning tool and the measurement reference, eliminating the need for separate alignment marks or additional measurement equipment, thereby tightening overlay control without proportionally increasing process complexity
Solution Approach 2:
The exposure mask is designed with multi-functionality, serving simultaneously as the patterning element, the alignment reference, and the distortion measurement tool. The inclusion of overlay marks and test patterns within the mask structure allows it to perform multiple functions that would otherwise require separate components, simplifying the overall process while maintaining tight overlay control
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 effectively corrects distortion in the exposure process, enhancing overlay margin control and improving the reliability and yield of semiconductor device fabrication by stabilizing subsequent exposure processes.
Implementation Method 1
selectively exposing portions of the photoresist layer to a light passing through the reticle loaded into an exposure equipment
Implementation Method 2
performing a second exposure process with the exposure mask and a second illumination system to form a second test pattern overlapping with the first test pattern
Data Source
AI summary
A method of controlling distortion of an exposure process is provided. The method includes aligning an exposure mask with a wafer, forming a first test pattern on the wafer by performing a first exposure with the exposure mask and a first illumination system, forming a photoresist layer on an entire surface of the wafer including the first test pattern, performing a second exposure with the exposure mask and a second illumination system to form a second test pattern overlapping with the first test pattern, extracting a distortion value between the first test pattern and the second test pattern, and correcting the exposure mask or fabricating a corrected exposure mask using the distortion value.