Chromium Target Silver Content Control for Photomask Defect Reduction
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Solution Overview
Problem
Current photomask blank preparation methods using a halftone phase shift film and chromium-containing light-shielding film result in defects due to metal impurities, particularly silver, which affect pattern accuracy and reliability during repeated exposure processes.
Innovation Solution
A method involving a metallic chromium target with minimized silver content (up to 1 ppm) is used for sputtering a chromium-containing film contiguous to a silicon-containing film or transparent substrate, ensuring reduced defect formation by controlling the silver impurity level, thereby enhancing the quality of photomask blanks and minimizing defects during pattern exposure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a chromium-containing light-shielding film is deposited using a conventional chromium target, then the photomask blank can be manufactured, but metal impurities (particularly silver) are introduced causing defects during repeated exposure processes
Solution Approach 1:
The invention changes the purity parameter of the chromium target material, specifying that the target must have a silver content of 1 ppm or less. This parameter change in the raw material directly prevents the introduction of harmful metal impurities that cause defects during repeated photomask exposure processes.
2Ease of manufacture
If a chromium-containing film is deposited without controlling silver content, then manufacturing is simpler, but defects form on silicon-containing films and transparent substrates during repeated exposures
Solution Approach 1:
The invention imposes a specific parameter constraint on the chromium target (silver content ≤ 1 ppm) to prevent defect formation during repeated exposures, thereby maintaining high pattern accuracy while still allowing for straightforward sputtering deposition processes.
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 approach significantly reduces defect formation on silicon-containing films and transparent substrates, improving pattern accuracy and reliability during repeated exposures to ArF excimer laser radiation, ensuring higher quality photomask performance.
Implementation Method 1
depositing the chromium-containing film by sputtering the metallic chromium target
Data Source
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AI summary
A method for preparing a photomask blank comprising a transparent substrate and a chromium-containing film contiguous thereto involves the step of depositing the chromium-containing film by sputtering a metallic chromium target having an Ag content of up to 1 ppm. When a photomask prepared from the photomask blank is repeatedly used in patternwise exposure to ArF excimer laser radiation, the number of defects formed on the photomask is minimized.