Photomask Blank Warpage Reduction via Heat Treatment
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Solution Overview
Problem
The challenge in manufacturing photomask blanks is the warpage-induced loss of flatness during the photomask manufacturing process, which affects the resolution and accuracy of pattern exposure, particularly due to stress in functional transparent films like phase shift films, making it difficult to achieve the required high degree of flatness and superposition accuracy.
Innovation Solution
A method involving a heat treatment and flash irradiation treatment is performed on a laminated body including a functional transparent film, such as a halftone phase shift film, after depositing the film or after forming a different functional film, to effectively release stress and reduce warpage, with specific conditions including temperatures between 260°C to 320°C for four hours and flash irradiation times of one second or less.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a functional transparent film is deposited on the substrate to form a photomask blank, then the photomask blank can be used for pattern formation, but stress accumulates in the film causing warpage and loss of flatness
Solution Approach 1:
A heat treatment is performed before the actual photomask manufacturing process to preemptively reduce stress and warpage in the functional transparent film. This preliminary stress relief action prevents flatness degradation during subsequent manufacturing steps, ensuring the required precision is maintained throughout the process.
2Manufacturing precision
If the photomask blank is used for high-resolution patterning, then finer circuit patterns can be formed, but the required flatness and superposition accuracy become difficult to maintain due to warpage
Solution Approach 1:
The heat treatment is conducted in advance to stabilize the flatness of the photomask blank before high-resolution patterning begins. This preliminary stabilization ensures that the stringent flatness requirements for fine pattern formation are met and maintained throughout the exposure process.
Solution Approach 2:
The heat treatment process changes the thermal parameters (temperature and time) of the functional transparent film to alter its stress state. By controlling these parameters within specific ranges, the film's internal stress is reduced, warpage is minimized, and flatness is improved to the level required for high-resolution patterning.
3Manufacturing precision
If heat treatment is applied to reduce stress in the functional transparent film, then warpage is reduced and flatness is improved, but the treatment must be precisely controlled within specific temperature and time ranges
Solution Approach 1:
The heat treatment process defines specific parameter ranges (260°C to 320°C for four hours or more) to optimize stress relief while avoiding excessive treatment. These parameter specifications provide clear control guidelines that balance effectiveness with process simplicity, ensuring flatness improvement without requiring overly complex control systems.
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 significantly reduces the warpage change in the photomask blank to within ±0.05 µm, enhancing the flatness and superposition accuracy, thereby improving the resolution and accuracy of pattern formation during the photomask manufacturing process.
Implementation Method 1
a heat treatment is performed on the laminated body at least one time after any one of: a step of depositing the functional transparent film; a step of performing a flash irradiation treatment at least one time after deposition of the functional transparent film; and a step of forming a layer of a functional film that is different to the functional transparent film thereon to form the laminated body
Implementation Method 2
a flash irradiation treatment is performed on a laminated body including a functional transparent film, such as a halftone phase shift film, after depositing the film or after forming a different functional film
Data Source
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AI summary
An object of this invention is to provide a photomask blank in which there is little warpage and is which an amount of warpage change after a photomask manufacturing process ends is also small. First, a phase shift film is deposited (S101), next, the phase shift film is subjected to a heat treatment within a temperature range of 260°C to 320°C for four hours or more (S102), and thereafter a flash irradiation treatment is performed thereon (S103). A light-shielding film is deposited on the phase shift film after the aforementioned treatments (S104), to thereby obtain a photomask blank (S105).