EUV Reflective Mask Blank Hydrogen Diffusion Barrier
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Solution Overview
Problem
In EUV lithography, the use of hydrogen in the exposure machine environment leads to atomic hydrogen diffusion into the multilayer reflection layer of reflective masks, causing blister formation and a decrease in reflectance due to hydrogen absorption, which existing solutions like metal silicide layers between the reflection and hydrogen absorption layers do not adequately prevent.
Innovation Solution
A reflective mask blank configuration with a Mo/Si multilayer reflection layer, an intermediate silicon nitride layer, a barrier layer containing elements like tantalum or niobium, and a protective layer, all formed using sputtering methods within the same chamber to prevent hydrogen diffusion and maintain reflectance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If hydrogen is used as atmospheric gas in the EUV exposure machine, then absorption of EUV light is reduced, but atomic hydrogen diffuses into the multilayer reflection layer causing blister formation and reflectance decrease
Solution Approach 1:
A barrier layer comprising a metal nitride (such as tantalum nitride, TaN) is introduced between the multilayer reflection layer and the hydrogen absorption layer. This barrier layer acts as an intermediary that prevents atomic hydrogen generated in the hydrogen atmosphere from diffusing into the multilayer reflection layer, thereby resolving the contradiction between using hydrogen as atmosphere gas and maintaining reflection layer integrity.
Solution Approach 2:
The structure is segmented into distinct functional layers: the multilayer reflection layer, the barrier layer (metal nitride), and the hydrogen absorption layer. This segmentation isolates the hydrogen absorption function from the reflection function, allowing hydrogen to be used in the atmosphere without damaging the reflection layer.
2Reliability
If a metal silicide layer is formed between the multilayer reflection layer and hydrogen absorption layer, then hydrogen diffusion is blocked, but mixing between layers decreases reflectance
Solution Approach 1:
The material composition of the barrier layer is changed from metal silicide to metal nitride (such as TaN). This parameter change in material composition provides effective hydrogen diffusion blocking while avoiding the mixing problem that occurs with metal silicide layers, thereby maintaining reflectance.
3Quantity of substance
If atomic hydrogen concentration increases in the multilayer reflection layer, then hydrogen absorption increases, but blister formation and peeling occur
Solution Approach 1:
The barrier layer (metal nitride) serves as an intermediary that captures and retains atomic hydrogen before it can penetrate into the multilayer reflection layer. This prevents hydrogen accumulation within the reflection layer that would lead to blister formation and peeling, while still allowing the system to utilize hydrogen as the exposure atmosphere.
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 proposed configuration effectively prevents blister formation and maintains high reflectance for EUV light by blocking hydrogen diffusion and reducing mixing between the reflection and barrier layers, thereby extending the service life of the reflective mask.
Implementation Method 1
a barrier layer on or above the intermediate layer... blocking hydrogen diffusion
Implementation Method 2
all formed using sputtering methods within the same chamber
Implementation Method 3
a Mo/Si multilayer reflection layer... maintains high reflectance for EUV light
Data Source
AI summary
A reflective mask blank includes: a substrate; a Mo/Si multilayer reflection layer formed by alternately laminating a molybdenum (Mo) layer and a silicon (Si) layer on or above the substrate; an intermediate layer on or above the Mo/Si multilayer reflection layer; a barrier layer on or above the intermediate layer; a protective layer on or above the barrier layer; and an absorption layer on or above the protective layer.