Gas Manifold Flow Control for Lithographic Optical Element Thermal Stability
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Solution Overview
Problem
In lithographic apparatuses, the small size and increased density of integrated circuits lead to non-uniform heating of optical elements due to radiation absorption, causing refractive index changes and deformations that result in distorted aerial images, particularly with illumination modes like dipole and quadrupole where radiation traverses small poles, leading to heat transfer issues between optical elements.
Innovation Solution
A gas manifold is designed to stabilize the gas flow between two parallel plates of an optical component, comprising an inlet, diffuser, flow straightener, contractor, and outlet, which helps in reducing heat transfer perpendicular to the radiation beam and allows for two-sided temperature control by using a gas at a lower temperature than ambient, thereby minimizing refractive index changes and deformations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If off-axis illumination with small poles (dipole/quadrupole modes) is used to improve resolution, then resolution and process latitude are improved, but non-uniform heating of optical elements occurs causing refractive index changes and image distortion
Solution Approach 1:
The patent applies local quality by implementing region-specific temperature control within the optical element. Different zones of the optical element are independently heated or cooled to compensate for non-uniform temperature distribution caused by off-axis illumination. This allows maintaining the beneficial small pole illumination mode while correcting local thermal distortions that would otherwise degrade image quality.
Solution Approach 2:
The patent changes the temperature parameter locally within the optical element to compensate for heating effects. By dynamically adjusting the temperature in specific regions using integrated heating/cooling mechanisms, the system maintains optimal refractive index uniformity despite the non-uniform energy distribution from dipole or quadrupole illumination modes.
2Stability of the object's composition
If gas flow is provided between parallel plates to reduce heat transfer, then temperature stability is improved, but device complexity increases due to additional gas manifold components
Solution Approach 1:
The patent merges multiple functions into the gas manifold structure. The same gas manifold system performs both cooling/heating of the optical element and stabilization of the gap between parallel plates. By combining these functions into a single integrated system rather than separate mechanisms, the patent reduces overall device complexity while achieving both temperature stability and mechanical stability.
Solution Approach 2:
The gas flowing through the manifold serves multiple purposes: it acts as a thermal management medium to control optical element temperature, as a mechanical support to maintain plate spacing, and as a protective atmosphere. This multi-functionality reduces the need for separate systems and simplifies the overall device architecture.
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 gas manifold effectively reduces temperature variations and optical path length fluctuations, improving the stability of the optical component and preventing distortion in the aerial image projected onto the resist layer, enhancing the lithographic apparatus's resolution and process latitude.
Implementation Method 1
a diffuser downstream of the inlet to provide a pressure drop in the gas flow
Implementation Method 2
a flow straightener, downstream of the inlet, to straighten the flow of gas out of the diffuser
Implementation Method 3
a contractor, downstream of the flow straightener, to reduce the cross sectional area through which the gas flow flows
Implementation Method 4
providing a gas through a diffuser, a flow straightener, a contractor and between the two plates... reducing heat transfer perpendicular to the radiation beam
Implementation Method 5
The optical component comprises a first plate with an individually addressable electrical heating device configured locally to heat the optical element
Implementation Method 6
A flow of gas is provided between the two parallel plates. This reduces the transfer of heat within the optical member in a direction perpendicular to the radiation beam
Data Source
AI summary
A gas manifold to direct a gas flow between two plates of an optical component of a lithographic apparatus, the gas manifold having an inlet, a diffuser downstream of the inlet, a flow straightener downstream of the inlet, a contractor downstream of the flow straightener, and an outlet downstream of the contractor.