EUV Mask Blank Flatness via Selective Layer Heating
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Solution Overview
Problem
Extreme ultraviolet (EUV) mask blanks in lithography systems face challenges in achieving the required flatness specifications due to stress-induced distortion, which affects image placement and overlay errors, and conventional annealing processes compromise reflectance while attempting to relieve stress.
Innovation Solution
A method and apparatus for selectively heating EUV mask blanks by directing light to heat only a portion of the reflective layer pairs adjacent to the substrate to a first temperature, while maintaining the remaining layers at a lower temperature, to relieve stress without reducing reflectance, thereby improving flatness and meeting stringent EUV mask blank specifications.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Shape
If conventional annealing processes are used to relieve stress in EUV mask blanks, then stress-induced distortion is reduced, but reflectance is compromised
Solution Approach 1:
The patent applies local quality by selectively heating only the lower portion of the multilayer stack (near the substrate) to relieve stress, while maintaining the upper portions at lower temperatures to preserve reflectance. This localized thermal treatment allows different regions of the mask blank to have different thermal histories, achieving both flatness improvement and reflectance preservation
Solution Approach 2:
The heating process is segmented into distinct zones: a heated lower portion for stress relief and a cooler upper portion for reflectance preservation. The multilayer stack is effectively divided into temperature zones during processing, with the substrate and lower layers experiencing higher temperatures while upper layers remain cooler
2Shape
If the entire multilayer stack is heated uniformly to relieve stress, then flatness is improved, but energy consumption increases and reflectance deteriorates
Solution Approach 1:
Energy is applied locally rather than uniformly across the entire mask blank. The heating is concentrated in the lower portion of the multilayer stack where stress relief is most needed, reducing overall energy consumption while achieving the desired flatness improvement
Solution Approach 2:
Instead of heating the entire stack, only a partial portion (the lower layers near the substrate) is heated to the stress-relief temperature. This partial action is sufficient to achieve the desired flatness improvement without the excessive energy consumption and reflectance deterioration that would result from heating the entire stack
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 selective heating process effectively reduces distortion and maintains high reflectance, achieving the necessary flatness and reflectivity for EUV mask blanks, addressing the limitations of conventional annealing methods.
Implementation Method 1
directing light to heat only a portion of the reflective layer pairs adjacent to the substrate to a first temperature, while maintaining the remaining layers at a lower temperature
Implementation Method 2
selectively heating a number Y reflective layer pairs adjacent to the substrate to a first temperature... to relieve stress without reducing reflectance, thereby improving flatness
Data Source
AI summary
Apparatus and methods for improving flatness of extreme ultraviolet (EUV) mask blanks are disclosed. The apparatus and methods may utilize one or more of heating the backside and/or the front side of the EUV mask blank and a cooling system. Interfacial layers of the EUV mask blank are selectively heated, resulting in improved flatness of the EUV mask blanks.