Mask Blank Birefringence Control for Lithography
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Solution Overview
Problem
In semiconductor device production, photomask substrates for immersion exposure and polarized illumination techniques face challenges with high birefringence due to residual strain in synthetic quartz glass and stress from light-shielding films, affecting image resolution and polarization integrity at shorter exposure wavelengths.
Innovation Solution
A mask blank comprising a synthetic quartz glass substrate with a light-shielding film, where the birefringence is reduced to 1 nm or less per substrate thickness at 193 nm wavelength, and the light-shielding film has a film stress of 800 MPa or lower, ensuring minimal warpage and optimal performance in immersion exposure and polarized illumination techniques.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If a light-shielding film is laminated on the photomask substrate, then light-shielding function is improved, but film stress causes warpage and increases birefringence
Solution Approach 1:
The patent changes the physical and chemical parameters of the light-shielding film by controlling the sputtering conditions (gas pressure, power, temperature) to achieve a film stress of 800 MPa or lower and birefringence of 1 nm/cm or less, resolving the contradiction between light-shielding function and manufacturing precision
Solution Approach 2:
The patent uses composite material structure with specific composition ratios (Cr: 80-95 at%, Mo: 5-20 at%) to create a light-shielding film that simultaneously provides effective light-shielding function while maintaining low stress and low birefringence properties
2Measurement precision
If exposure light wavelength is shortened to improve resolution, then image resolution is improved, but birefringence effects are intensified
Solution Approach 1:
The patent changes the optical parameters of the photomask substrate by controlling the synthesis conditions of synthetic quartz glass (temperature, pressure, composition) to achieve extremely low birefringence of 1 nm/cm or less, which allows short-wavelength exposure light to pass through without being distorted by birefringence effects, thereby maintaining high image resolution
3Manufacturing precision
If film stress is reduced to minimize warpage, then substrate flatness is improved, but light-shielding performance may be compromised
Solution Approach 1:
The patent uses composite material composition (Cr-Mo alloy system with specific ratios) where Mo addition reduces film stress to 800 MPa or lower while Cr provides sufficient light-shielding performance, thus achieving both substrate flatness and light-shielding performance simultaneously
Solution Approach 2:
The patent optimizes the deposition parameters including gas pressure (0.5-5 Pa), power (50-500 W), and temperature (20-200°C) during sputtering to control film stress and composition, achieving the balance between substrate flatness and light-shielding performance
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
The solution provides mask blanks with low birefringence and controlled film stress, enhancing image resolution and polarization integrity, making them suitable for advanced semiconductor lithography techniques.
Implementation Method 1
a light-shielding film laminated on a surface of the substrate
Implementation Method 2
the birefringence of which, when measured at a wavelength of 193 nm, is 1 nm or less per substrate thickness
Data Source
AI summary
The present invention provides a mask blank which comprises a substrate made of a synthetic quartz glass and a light-shielding film laminated on a surface of the substrate and is for use in a semiconductor device production technique employing an exposure light wavelength of 200 nm or shorter, wherein the mask blank has a birefringence, as measured at a wavelength of 193 nm, of 1 nm or less per substrate thickness. According to the present invention, mask blanks suitable for use in the immersion exposure technique and the polarized illumination technique are provided.