MoSi Photomask Etch Stop Layer for Ammonia Cleaning
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Solution Overview
Problem
Existing photomask technologies face challenges in forming fine circuit patterns for high integration in semiconductor devices, particularly in maintaining pattern integrity during cleaning processes and minimizing size variations and ghost patterns.
Innovation Solution
A photomask with a light shielding pattern made of molybdenum and silicon, incorporating an etch stop layer with a higher nitrogen content than the light shielding pattern, formed using a plasma nitriding process, which reduces etch rates and maintains pattern accuracy during ammonia-based cleaning.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a light shielding pattern is formed using conventional materials and processes, then the photomask can be manufactured, but the pattern integrity deteriorates during ammonia-based cleaning processes due to high etch rates
Solution Approach 1:
The patent applies parameter changes by modifying the chemical composition of the light shielding pattern through plasma nitriding treatment. This process introduces nitrogen into the molybdenum-silicon pattern, fundamentally changing its etching characteristics. The nitrogen incorporation reduces the etch rate by approximately 10-100 times compared to conventional patterns, allowing the pattern to withstand ammonia-based cleaning processes without significant material loss while maintaining manufacturing feasibility.
Solution Approach 2:
The patent creates a composite material structure by forming a nitrogen-containing layer within the light shielding pattern through plasma nitriding. This results in a composite of molybdenum-silicon-nitrogen that combines the light-blocking properties of MoSi with the etch resistance provided by nitrogen. The composite structure achieves both the required optical properties and enhanced chemical stability during cleaning processes.
2Manufacturing precision
If the light shielding pattern is made thinner to achieve finer circuit patterns, then the resolution improves, but the pattern becomes more susceptible to damage and size variations during cleaning
Solution Approach 1:
The patent uses plasma nitriding to change the chemical parameters of thin light shielding patterns, introducing nitrogen to reduce etch rates. This allows patterns with thicknesses of 50nm or less to be manufactured with high precision while maintaining stability during cleaning. The nitrogen incorporation fundamentally alters the etching behavior, enabling thin patterns to resist damage and size variations that would normally occur during ammonia-based cleaning processes.
Solution Approach 2:
The plasma nitriding process applies local quality changes by concentrating nitrogen incorporation at the surface and near-surface regions of the light shielding pattern. This creates a nitrogen-enriched layer precisely where etching protection is needed, while maintaining the overall thin profile required for fine circuit patterns. The local modification of chemical composition provides targeted protection without compromising the pattern's dimensional requirements.
3Productivity
If conventional cleaning processes are used, then the cleaning efficiency is high, but ghost patterns are generated due to excessive etching of the light shielding pattern
Solution Approach 1:
The patent changes the etching parameters of the light shielding pattern through plasma nitriding, reducing the etch rate by 10-100 times. This allows conventional ammonia-based cleaning solutions to be used at full strength and temperature without causing excessive etching. The nitrogen-modified pattern maintains its integrity during high-efficiency cleaning, preventing ghost pattern formation while preserving the cleaning process's productivity and effectiveness.
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 effectively minimizes damage to the light shielding pattern during cleaning, reduces critical dimension variations, and reduces ghost patterns by controlling nitrogen and oxygen concentration gradients, ensuring accurate and stable fine pattern formation.
Implementation Method 1
performing a plasma nitriding process on at least a sidewall of the light shielding pattern to form an etch stop layer
Implementation Method 2
Nitrogen ions may permeate into at least the sidewall of the light shielding pattern by the plasma nitriding process
Data Source
AI summary
A photomask and a method of forming the same, the photomask including a transparent substrate; a light shielding pattern on the transparent substrate, the light shielding pattern including molybdenum and silicon; and an etch stop layer covering at least a sidewall of the light shielding pattern, wherein the etch stop layer has an etch rate lower than an etch rate of the light shielding pattern with respect to an ammonia-based cleaning solution.