EUV Reflective Mirror with Position-Dependent Multilayer Film Thickness
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Solution Overview
Problem
Multilayer-film reflective mirrors in EUV exposure apparatuses face a decrease in reflectance with varying incident angles, leading to potential exposure defects and defective device manufacturing due to insufficient light intensity.
Innovation Solution
A reflective mirror design featuring a multilayer film with alternating first and second layers of different thicknesses, positioned rotationally symmetrically about the optical axis, to maintain high reflectance across varying incident angles.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional multilayer film with uniform thickness is used, then the structure is simple and easy to manufacture, but the reflectance decreases when the incident angle varies, leading to exposure defects
Solution Approach 1:
The patent applies local quality by making the multilayer film thickness position-dependent. Specifically, the thickness of the multilayer film varies in the radial direction from the optical axis, with different thickness values at different radial positions. This local variation in thickness compensates for the incident angle variations across the optical field, maintaining high reflectance consistency despite the increased structural complexity.
2Reliability
If the multilayer film thickness is increased to maintain reflectance, then reflectance is improved, but the manufacturing precision requirements increase due to rotational symmetry constraints
Solution Approach 1:
The patent employs asymmetry in a controlled manner by introducing intentional thickness variation in the multilayer film. Rather than using a symmetric uniform thickness design, the film thickness is deliberately made asymmetric with respect to the radial position from the optical axis. This controlled asymmetry allows the reflectance to be maintained across different incident angles while the manufacturing precision is managed through the specific functional form of the thickness distribution.
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
This design suppresses the generation of exposure defects and improves the throughput of both the exposure apparatus and device manufacturing by maintaining high reflectance and consistent light intensity across different incident angles.
Implementation Method 1
a multilayer film configured to reflect at least a portion of the incident light
Implementation Method 2
a multilayer film having a first layer and second layer that are laminated alternately on the base
Data Source
AI summary
A reflective mirror is provided with a base and a multilayer film including a first layer and a second layer laminated alternately on the base and capable of reflecting at least a portion of incident light. The multilayer film is provided with a first portion having a first thickness, and with a second portion having a second thickness that is different from the first thickness, and which is provided at a position rotationally symmetric to that of the first portion about an optical axis of the reflective mirror.