EUVL Mask Border Reflectivity Reduction via Phase Shift Grating
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Solution Overview
Problem
Extreme Ultraviolet Lithography (EUVL) masks experience unwanted reflections from the border region, leading to critical dimension errors and penumbra effects due to the reflective nature of the absorber material, which affects pattern accuracy and dimensional precision.
Innovation Solution
A sub-resolution phase shift grating is integrated into the multilayer reflective film beneath the border region of the EUVL mask, reducing reflectivity by creating destructive interference and scattering light out of the lens, thus minimizing black border reflections.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a border region of absorber material is used to isolate individual patterns on the wafer surface, then pattern isolation is improved, but unwanted reflections from the border region increase and contribute to neighboring exposure dies
Solution Approach 1:
The patent applies a sub-resolution phase shift grating structure specifically to the border region of the mask, creating a localized modification that reduces reflectivity in that specific area without affecting other regions. This local quality change allows the border region to maintain its isolation function while reducing harmful reflections to neighboring dies.
Solution Approach 2:
The patent converts the harmful reflective property of the border region into a beneficial low-reflection property by introducing the sub-resolution phase shift grating. The grating structure causes destructive interference of reflected light, transforming the border region from a source of harmful reflections to a region that actively suppresses reflections through optical interference.
2Manufacturing precision
If the thickness of absorber material is reduced to provide desired pattern dimensional accuracy, then pattern precision is improved, but reflectivity of the absorber material increases
Solution Approach 1:
The patent introduces a sub-resolution phase shift grating as an intermediary structure between the absorber material and the incident light. This grating acts as a mediator that modifies the optical interaction by creating destructive interference of reflected light, thereby reducing the effective reflectivity without requiring changes to the absorber material thickness that would compromise pattern precision.
3Illumination intensity
If REMA blades are placed in front of the mask to confine light to the active area, then light confinement is improved, but black border reflection with penumbra spatial signature increases due to standoff distance
Solution Approach 1:
The patent applies the sub-resolution phase shift grating to the border region in advance, before the light interaction occurs. This preliminary modification of the border region's optical properties prevents the generation of harmful reflections and penumbra effects at their source, rather than attempting to address them after they are created by the REMA blade standoff distance.
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 implementation significantly decreases black border reflection, improving critical dimension accuracy and reducing unwanted intensity on neighboring exposure dies, thereby enhancing pattern precision and spatial dimensioning in EUVL systems.
Implementation Method 1
The sub-resolution phase shift grating reduces a reflectivity of the border region of the mask
Implementation Method 2
The sub-resolution phase shift grating reduces a reflectivity of the border region of the mask
Implementation Method 3
Some of the incident light is reflected by the reflective film
Data Source
AI summary
Extreme ultraviolet lithography (EUVL) masks and methods of manufacturing are provided. A method includes forming a sub-resolution phase shift grating in a multilayer reflective film beneath a border region of an absorber layer of an extreme ultraviolet lithography (EUVL) mask. The sub-resolution phase shift grating reduces a reflectivity of the border region of the mask.