Reflective Phase-Edge EUV Mask Without Absorber Heat Loss
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Solution Overview
Problem
EUV lithography masks face challenges in precise patterning of absorbers, leading to EUV energy loss, heat generation, and reduced throughput due to the use of patterned absorbers, which necessitate offline cooling and lower wafer per hour (WPH) throughput.
Innovation Solution
A Fully Reflective Phase-Edge Mask (FR-PEM) is developed, where the reflective multilayer is patterned to create phase edges for imaging contrast, eliminating the need for a patterned absorber, and is covered with a thin capping layer for protection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If a patterned absorber is used in EUV masks, then imaging contrast is achieved, but EUV energy loss increases and heat generation occurs
Solution Approach 1:
The invention extracts and removes the absorber layer from the mask structure, transitioning from a binary mask with absorber to a fully reflective mask. This eliminates the source of EUV energy absorption and heat generation while maintaining imaging contrast through phase edges created by the reflective multilayer pattern alone.
Solution Approach 2:
Instead of using an absorptive mechanism to create contrast, the invention inverts the approach by using a purely reflective mechanism. The phase edges are created by variations in the reflective multilayer structure rather than by absorption, fundamentally changing from absorptive to reflective contrast generation.
2Illumination intensity
If a patterned absorber is used in EUV masks, then imaging contrast is achieved, but heat generation increases requiring offline cooling
Solution Approach 1:
The absorber layer is completely removed from the mask structure, eliminating the source of heat generation. The fully reflective mask structure allows EUV radiation to pass through or be reflected without significant absorption, preventing mask heating and eliminating the need for offline cooling cycles.
Solution Approach 2:
The invention converts the harmful effect of absorption (heat generation) into a beneficial fully reflective structure. By making the mask completely reflective, the previously harmful absorbed energy is now reflected or transmitted, turning the heat generation problem into continuous operational capability.
3Illumination intensity
If a patterned absorber is used in EUV masks, then imaging contrast is achieved, but wafer per hour throughput decreases
Solution Approach 1:
By removing the absorber layer and eliminating the need for offline cooling cycles, the fully reflective mask enables continuous mask operation. This increases productivity by allowing more wafers to be processed per hour without interruption for mask cooling, while maintaining imaging contrast through phase edges.
Solution Approach 2:
The fully reflective mask enables continuous operation without interruption for cooling, as the mask does not heat up significantly. This continuous useful action (mask exposure) directly increases wafer per hour throughput compared to binary masks that require periodic offline cooling.
4Manufacturing precision
If absorber patterning is performed, then pattern definition is achieved, but manufacturing precision requirements increase due to stringent etching selectivity and sidewall profile requirements
Solution Approach 1:
The absorber layer and its associated complex patterning processes are completely removed. The pattern definition is achieved directly through reflective multilayer patterning, which has less stringent requirements for etching selectivity and sidewall profile control compared to absorber patterning.
Solution Approach 2:
The invention changes the fundamental parameter of contrast generation from absorption to reflection. This parameter change simplifies the manufacturing process by eliminating the need for precise absorber etching and sidewall control, as the reflective multilayer can be patterned with more relaxed tolerances.
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 FR-PEM achieves higher WPH throughput and equivalent imaging performance compared to binary EUV masks, with reduced EUV energy absorption and heat generation, enabling concurrent optimization of throughput and imaging quality.
Implementation Method 1
the ML reflects EUV light, thereby creating a patterned EUV radiation
Implementation Method 2
the reflective multilayer is patterned to create phase edges for imaging contrast
Data Source
AI summary
A EUV lithography mask includes a substrate of a low thermal expansion material, a first reflective multilayer over the substrate, and a patterned reflective multilayer over the first reflective multilayer. The patterned reflective multilayer includes trenches through the patterned reflective multilayer. Each of the first reflective multilayer and the patterned reflective multilayer includes a stack of film pairs.