Photomask CD Correction Using Negative Resist Etch Mask
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Solution Overview
Problem
The existing methods for correcting pattern critical dimensions (CD) in photomasks are hindered by foreign materials adhering to the resist layer, leading to resist residue and bridging defects during the etching process, which degrade the quality of the photomask and cause patterning defects.
Innovation Solution
A method involving the formation of a negative resist pattern with a smaller CD than the light blocking pattern, which is used to correct the CD by etching the light blocking pattern, and subsequently removing the negative resist pattern, thereby preventing foreign material adherence and enhancing CD accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a positive resist layer is used to form a correction mask, then the resist layer can be removed during the development process, but foreign materials may adhere to the resist layer causing resist residue and bridging defects
Solution Approach 1:
The patent inverts the resist type from positive to negative. Instead of using a positive resist layer that is removed during development, a negative resist layer is used that remains after development. This inversion prevents foreign material adherence issues because the negative resist pattern is more resistant to contamination and does not require the same development process that leaves residues.
Solution Approach 2:
The patent employs a disposable negative resist pattern that is formed specifically for the CD correction process and then removed after serving its purpose. This single-use approach eliminates the problem of foreign material accumulation that occurs with reusable positive resist layers, as each new negative resist pattern starts fresh without prior contamination.
2Manufacturing precision
If the CD of the light blocking pattern is corrected by etching with a correction mask, then the CD accuracy is improved, but resist residue remains on the phase shift layer surface causing bridging defects
Solution Approach 1:
The patent inverts the resist type from positive to negative, which fundamentally changes the development process outcome. The negative resist pattern remains after development rather than being removed, preventing resist residue from remaining on the phase shift layer surface. This inversion eliminates the source of bridging defects while maintaining the CD correction functionality.
Solution Approach 2:
The patent extracts the harmful element (resist residue) from the process by changing the resist chemistry. Instead of having residue remain after positive resist development, the negative resist system is designed so that no resist material remains on the phase shift layer after the correction process, completely removing the source of bridging defects.
3Manufacturing precision
If a separate correction mask is formed using a positive resist layer, then the CD correction process can be performed, but the process complexity increases due to additional steps for mask formation and removal
Solution Approach 1:
The patent merges the correction mask formation with the existing photomask fabrication process by using a negative resist pattern that is formed and then removed in-line with the phase shift layer etching process. This integration reduces the number of separate steps compared to using a positive resist system that requires additional removal steps, simplifying the overall process while maintaining CD correction capability.
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 approach effectively corrects the CD of the photomask, reduces bridging defects, and improves the quality of the photomask by ensuring accurate patterning, while also reducing manufacturing costs by minimizing mask discards.
Implementation Method 1
forming a negative resist pattern that has a relatively smaller CD than the CD of the light blocking pattern on the light blocking pattern
Implementation Method 2
correcting the CD of the light blocking pattern by additionally etching the light blocking pattern exposed by the negative resist pattern
Implementation Method 3
forming a phase shift pattern by etching the phase shift layer exposed by the corrected light blocking pattern and the negative resist pattern as an etch mask
Data Source
AI summary
A method of correcting a pattern critical dimension of a photomask includes forming a phase shift layer and a light blocking pattern on a substrate, measuring a critical dimension (CD) of the light blocking pattern, and forming a negative resist pattern that has a relatively smaller CD than the CD of the light blocking pattern on the light blocking pattern, and correcting the CD of the light blocking pattern by etching the light blocking pattern exposed by the negative resist pattern. The method may further include forming a phase shift pattern by etching the phase shift layer exposed by the corrected light blocking pattern and the negative resist pattern as an etch mask, and removing the negative resist pattern and the corrected light blocking pattern.