Lithographic Apparatus Optical Element Sputtering Protection
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Solution Overview
Problem
Lithographic apparatuses operating in extreme ultraviolet radiation ranges face issues with ionization of background gases leading to sputtering and etching of optical elements, which reduces their lifetime and causes transmission and homogeneity losses.
Innovation Solution
Incorporating a support structure with materials having low sputtering yield, high sputter threshold energy, or high ion implantation yield, and applying a conductive coating with low secondary electron emission to reduce the impact of ions and plasma breakdown, thereby protecting optical elements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Duration of action of stationary object
If electrical fields are applied to protect mirrors from sputtering and etching, then mirror lifetime is improved, but lens structure becomes damaged by accelerated ions
Solution Approach 1:
A plasma-generating gas is introduced as an intermediary substance between the ion source and the optical elements. The gas absorbs ionizing radiation and generates plasma that acts as a buffer, reducing direct ion impact on mirrors and lenses while maintaining protective electrical fields
Solution Approach 2:
The patent changes the physical and chemical parameters of the environment by introducing specific gases with controlled pressure and composition. This modifies the plasma characteristics and ion behavior, allowing protection of optical elements without causing damage to other components
2Object-affected harmful factors
If background gas is introduced to protect optical elements, then sputtering and etching effects are reduced, but plasma formation causes new damage mechanisms
Solution Approach 1:
Inert gases such as nitrogen or noble gases are introduced to create an inert atmosphere that reduces sputtering and etching of optical elements. The inert nature of these gases minimizes chemical reactions while still allowing plasma formation for protection
Solution Approach 2:
The patent uses composite approaches by combining multiple gases with different properties, or combining gas protection with coating materials on optical elements, to achieve synergistic protection against plasma-induced damage while maintaining the benefits of background gas introduction
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 solution significantly reduces the effects of sputtering and etching on optical elements, extending their lifetime and maintaining optical performance by minimizing plasma-induced degradation.
Implementation Method 1
The radiation, for example, EUV radiation, but also other radiation, for example, 157 nm, 193 nm and a particle beam, generated by the radiation source may be partially absorbed by the background gas. The radiation may also ionize the background gas, on-setting the creation of a plasma.
Implementation Method 2
Accelerated ions in such potential drop may impact on surfaces in the lithographic apparatus, including optical elements such as mirrors and lenses, resulting in processes, such as etching and sputtering.
Data Source
AI summary
The invention relates to a lithographic apparatus that includes a system configured to condition a radiation beam or project a patterned radiation beam onto a target portion of a substrate. The system includes an optically active device configured to direct the radiation beam or the patterned radiation beam, respectively, and a support structure configured to support the optically active device. The apparatus further includes a gas supply for providing a background gas into the system. The radiation beam or patterned radiation beam react with the background gas to form a plasma that includes a plurality of ions. The support structure includes an element that includes a material that has a low sputtering yield, a high sputter threshold energy, or a high ion implantation yield, to reduce sputtering and the creation of sputtering products.