Synthetic Quartz Glass for Immersion Lithography
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Solution Overview
Problem
Optical components made of quartz glass used in immersion lithography face radiation-induced defects, particularly 'compaction,' which leads to inhomogeneous refractive index changes and deteriorated imaging properties under high-energy UV excimer laser radiation, existing solutions such as low defect concentration or annealing being inadequate.
Innovation Solution
The introduction of chemically bound nitrogen in the range of 1-150 wtppm and controlled hydrogen content (5 x 10^15 to 1 x 10^17 molecules/cm^3) in synthetic quartz glass, along with low hydroxyl group content and the use of nitrogen and boron doping, to enhance radiation resistance and reduce compaction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If dehydration treatment is performed in a chlorine-containing atmosphere to remove hydroxyl groups, then the hydroxyl group content is reduced, but chlorine is incorporated into the quartz glass which deteriorates UV radiation resistance
Solution Approach 1:
The patent uses a two-stage dehydration process: first treating in a chlorine-containing atmosphere to efficiently remove hydroxyl groups, then treating in a nitrogen-containing atmosphere to remove incorporated chlorine. The nitrogen treatment acts as an intermediary step that eliminates the harmful side effect of the first treatment without compromising the benefit of hydroxyl removal.
Solution Approach 2:
The patent extracts and removes the harmful chlorine component from the quartz glass after it has served its purpose of removing hydroxyl groups. The nitrogen-containing atmosphere selectively removes chlorine through chemical reactions, separating the useful function (hydroxyl removal) from the harmful effect (chlorine incorporation).
2Productivity
If high-energy UV radiation is transmitted through quartz glass for lithography, then imaging is achieved, but radiation-induced defects and compaction occur which deteriorate imaging properties
Solution Approach 1:
The patent performs preliminary nitrogen doping and controlled dehydration treatments on the quartz glass before it is used for lithography imaging. These pre-treatments modify the glass structure to be more resistant to radiation-induced defects and compaction, preventing deterioration before it occurs during actual use.
Solution Approach 2:
The patent changes the chemical composition parameters of the quartz glass by introducing nitrogen (1-150 wtppm) and controlling hydrogen content. These parameter changes fundamentally alter the material's resistance to radiation damage, enabling it to maintain imaging properties under high-energy UV radiation.
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 approach significantly improves the UV radiation resistance and minimizes compaction, maintaining homogeneous optical properties across the volume of the quartz glass, making it suitable for high-resolution applications in immersion lithography.
Implementation Method 1
a porous SiO2 soot body is produced by flame hydrolysis or oxidation of a silicon-containing start compound
Implementation Method 2
a porous SiO2 soot body is produced by flame hydrolysis or oxidation of a silicon-containing start compound
Implementation Method 3
obtained according to the known VAD (vapor axial deposition) method or the OVD (outside vapor deposition) method
Implementation Method 4
the soot body is subjected to a dehydration treatment in a drying atmosphere for removing hydroxyl groups
Implementation Method 5
the SiO2 soot body is vitrified to obtain a body made from the synthetic quartz glass
Data Source
AI summary
To provide an optical component of quartz glass for use in a projection objective for immersion lithography at an operating wavelength below 250 nm, which component is optimized for use with linearly polarized UV laser radiation and particularly with respect to compaction and birefringence induced by anisotropic density change, it is suggested according to the invention that the quartz glass should contain hydroxyl groups in the range of from 1 wtppm to 60 wtppm and chemically bound nitrogen, and that the mean hydrogen content of the quartz glass should be in the range of 5 x 1015 molecules/cm3 to 1 x 1017 molecules/cm3.