Fused Silica Low OH OD Concentration Halogen-Free Drying
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Solution Overview
Problem
Fused silica optical components used in the semiconductor field, particularly in photolithography, are susceptible to laser damage due to high concentrations of hydroxyl (OH) and deuteroxyl (OD) groups, which affect their dynamic and static properties, and existing methods struggle to control the distribution of these groups in a halogen-free environment.
Innovation Solution
A method of forming fused silica articles with low concentrations of OH and OD groups by drying a soot blank in a halogen-free atmosphere comprising carbon monoxide, followed by oxidation and sintering, to achieve a combined concentration of less than 10 parts per million (ppm), with optional doping to improve homogeneity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If hydroxyl groups are present in the silica to increase resistance to optical deterioration, then reliability is improved, but manufacturing precision deteriorates because it becomes difficult to control the distribution of chlorine and OH within the fused silica
Solution Approach 1:
The patent extracts the harmful chlorine from the system by using a halogen-free drying atmosphere, while separately controlling the hydroxyl content through precise water vapor management. This separates the control of chlorine removal from OH management, allowing independent optimization of both parameters.
Solution Approach 2:
The patent changes the drying atmosphere parameters by using carbon monoxide instead of traditional halogen-containing atmospheres, and carefully controls water vapor partial pressure to achieve the desired OH concentration range. This parameter change enables simultaneous achievement of low chlorine and controlled OH levels.
2Stability of the object's composition
If the soot is doped with water and heated for a very long time to achieve homogenous OH distribution, then homogeneity is improved, but productivity deteriorates due to the very long heating time required
Solution Approach 1:
The patent changes the heating parameters by using a controlled water vapor partial pressure in the drying atmosphere and optimizing the temperature profile. This allows achieving homogeneous OH distribution in a shorter time by maintaining optimal vapor pressure conditions throughout the heating process.
Solution Approach 2:
The patent implements continuous doping with water vapor during the heating process by maintaining a controlled water vapor partial pressure in the drying atmosphere. This continuous action ensures homogeneous OH distribution without requiring excessively long heating times.
3Reliability
If the soot is processed to simultaneously contain low levels of water and chlorine, then reliability is improved, but manufacturing precision deteriorates because the distribution of chlorine and OH within the fused silica is difficult to control
Solution Approach 1:
The patent extracts chlorine using a halogen-free drying atmosphere and separately manages water content through controlled water vapor partial pressure. This separate extraction and control approach allows independent optimization of both chlorine and water levels, achieving low concentrations of both while maintaining distribution control.
Solution Approach 2:
The patent uses carbon monoxide as an intermediary drying atmosphere that is free from both chlorine and excessive water vapor. This intermediary atmosphere enables simultaneous removal of chlorine and control of water content, achieving low levels of both contaminants while maintaining homogeneous 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
The method effectively reduces the combined concentration of OH and OD groups to less than 10 ppm, enhancing the homogeneity and reducing laser-induced damage in fused silica optical components, thereby improving their performance in ultraviolet applications.
Implementation Method 1
drying the soot blank in a halogen-free atmosphere comprising carbon monoxide... heating the soot blank at a temperature in a range from about 1150° C. up to about 1300° C.
Implementation Method 2
The dried soot blank is then oxidized and sintered to form the article
Implementation Method 3
sintering the blank to form the fused silica article
Data Source
AI summary
A fused silica article having a combined concentration of hydroxyl (OH) and deuteroxyl (OD) concentration of less than 10 parts per million (ppm) and, in one embodiment, less than 1 ppm. The fused silica article is formed by drying a soot blank in a halogen-free atmosphere comprising carbon monoxide. The dried soot blank may optionally be doped to reach target levels of OH and OD concentrations and improve homogeneity within the fused silica article. The dried soot blank is then oxidized and, sintered to form the article. A method of reducing the combined concentration of OH and OD to less than 10 ppm is also described.