Photomask Surface Modification for Irradiation Durability
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Solution Overview
Problem
Photomasks used in semiconductor manufacturing experience degradation due to repeated exposure to short-wavelength light sources like ArF excimer lasers, leading to changes in transmittance, phase difference, and line width, which affect transfer accuracy and resolution, particularly in phase shift masks with transition metal silicide-based films.
Innovation Solution
A method of manufacturing photomasks that involves modifying the surface and side walls of thin film patterns with a layer containing silicon and oxygen, either through heat treatment or oxygen plasma treatment, to suppress oxidation and formation of modified layers, thereby enhancing irradiation durability and preventing changes in transfer characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a photomask is repeatedly used with short-wavelength exposure light, then productivity increases, but the thin film undergoes oxidation and modified layer formation causing degradation in transmittance, phase difference, and line width
Solution Approach 1:
The patent applies preliminary oxidation treatment to the thin film before the photomask is actually used for exposure. This pre-oxidation creates a stable oxide layer that prevents further oxidation during repeated use with short-wavelength light, thereby maintaining transfer characteristics (transmittance, phase difference, line width) stable over extended usage periods
Solution Approach 2:
The patent changes the oxidation state parameter of the thin film by performing controlled oxidation treatment. This parameter change transforms the thin film surface to a more stable oxidized state that is resistant to further oxidation during exposure, thus resolving the contradiction between repeated use and characteristic stability
2Manufacturing precision
If the wavelength of exposure light is shortened for miniaturization, then pattern resolution improves, but mask degradation due to cumulative irradiation becomes more severe
Solution Approach 1:
The patent converts the harmful effect of light irradiation (which causes oxidation) into a beneficial pre-controlled oxidation process. By deliberately oxidizing the thin film before use, the patent creates a stable layer that is actually protected against further harmful oxidation during exposure to short-wavelength light, thus allowing high-resolution patterning without severe mask degradation
3Manufacturing precision
If a light-semitransmissive film made of transition metal silicide is used for phase shift mask, then phase difference and transmittance control improve, but oxidation resistance deteriorates under short-wavelength irradiation
Solution Approach 1:
The patent performs preliminary oxidation on the transition metal silicide film before the photomask is put into service. This pre-oxidation creates a stable oxide protective layer on the film surface that maintains the desired phase difference and transmittance characteristics while preventing composition changes during repeated exposure to short-wavelength light
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 method significantly improves the irradiation durability of photomasks to short-wavelength light, reducing changes in transmittance, phase difference, and line width, thereby extending the photomask's lifetime and maintaining performance even after repeated use with high-energy exposure light.
Implementation Method 1
performing a treatment to modify a main surface and side walls of the formed thin film pattern in advance... either through heat treatment or oxygen plasma treatment
Implementation Method 2
forming a layer containing silicon and oxygen... to suppress oxidation and formation of modified layers
Implementation Method 3
either through heat treatment or oxygen plasma treatment
Data Source
AI summary
A thin film composed of a material containing a metal and silicon is formed on a transparent substrate, and a thin film pattern is formed by patterning the thin film. Then, the main surface and the side walls of the thin film pattern are previously modified so as to prevent the transfer characteristics of the thin film pattern from changing more than predetermined even in the case where exposure light with a wavelength of 200 nm or less is cumulatively applied onto the thin film pattern which has been formed. The main surface and the side walls are modified by, for instance, performing heat treatment to the main surface and the side walls at 450-900° C. in the atmosphere containing oxygen.