Halftone Phase Shift Photomask Blank for ArF Lithography
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Current halftone phase shift photomasks used in semiconductor lithography face issues with pattern size variation degradation due to ArF excimer laser irradiation, leading to reduced photomask lifetime and accuracy, especially when exposed to high-energy radiation in humid environments, where chemical cleaning can damage the optical films and cause phase shift changes.
Innovation Solution
A method for preparing halftone phase shift photomask blanks using reactive sputtering to deposit a layer containing silicon and nitrogen, with controlled sputtering conditions to achieve in-plane uniformity of optical properties, including a phase shift of 170 to 190° and transmittance of 2 to 15% for ArF excimer laser light, using a silicon target, argon gas, and nitrogen gas, and potentially incorporating a surface oxidized layer for improved chemical resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Duration of action of stationary object
If chemical cleaning is performed to remove haze from the photomask, then the photomask can be reused, but the optical film is damaged and phase shift changes occur
Solution Approach 1:
The patent removes the problematic transition metal element from the optical film composition, extracting the harmful component that reacts with chemical cleaning solutions. This allows the photomask to undergo chemical cleaning without damage to the optical film, resolving the contradiction between reusability and optical property stability.
Solution Approach 2:
The patent changes the chemical composition parameters of the optical film by eliminating transition metals and specifying precise ratios of silicon, nitrogen, and oxygen. This compositional modification makes the film chemically resistant to cleaning solutions while maintaining the required optical properties of 170-190 degree phase shift and 2-15% transmittance.
2Manufacturing precision
If transition metal/silicon base material film is used for halftone phase shift photomask, then the desired optical properties can be achieved, but pattern size variation degradation occurs due to ArF excimer laser irradiation
Solution Approach 1:
The patent extracts and removes the transition metal component from the optical film that causes pattern size variation under laser irradiation. By using only silicon, nitrogen, and oxygen in specific ratios, the film maintains dimensional stability while achieving the required 170-190 degree phase shift and 2-15% transmittance.
Solution Approach 2:
The patent creates a composite material system using silicon nitride oxide (SiNxOy) with precisely controlled stoichiometric ratios. This composite composition provides both the necessary optical properties and resistance to laser-induced pattern size variation, replacing the transition metal/silicon system.
3Manufacturing precision
If ArF excimer laser light of shorter wavelength is used for photolithography, then finer images can be formed, but haze formation and pattern damage occur on the photomask
Solution Approach 1:
The patent removes transition metals from the optical film that are susceptible to damage from high-energy ArF excimer laser irradiation. The resulting silicon-nitrogen-oxygen based film is resistant to laser-induced haze formation and pattern damage, enabling sustained use with 193nm lithography.
Solution Approach 2:
The patent changes the material composition parameters from transition metal-based to silicon-nitrogen-oxygen-based with controlled ratios. This fundamental material parameter change increases laser resistance while maintaining the optical properties needed for fine pattern formation with ArF excimer laser light.
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 results in halftone phase shift photomask blanks with improved in-plane uniformity and chemical resistance, maintaining desired optical properties and extending photomask lifetime by reducing pattern size variation degradation and minimizing damage from chemical cleaning.
Implementation Method 1
a method for preparing a halftone phase shift photomask blank having a halftone phase shift film on a transparent substrate, the method comprising the step of depositing a layer containing silicon and nitrogen on the transparent substrate, as a part or the entirety of the halftone phase shift film, by reactive sputtering
Implementation Method 2
depositing a layer containing silicon and nitrogen on the transparent substrate, as a part or the entirety of the halftone phase shift film, by reactive sputtering
Implementation Method 3
potentially incorporating a surface oxidized layer for improved chemical resistance
Data Source
Figure 1A~1B
Figure 2A~2C
Figure 3
AI summary
A halftone phase shift film is formed on a transparent substrate by reactive sputtering using a silicon target, an inert gas, and a nitrogen-containing reactive gas. A hysteresis curve is drawn by sweeping the flow rate of the reactive gas, and plotting the sputtering voltage or current during the sweep versus the flow rate of the reactive gas. In a transition mode sputtering step of sputtering in a region corresponding to a range from more than the lower limit of reactive gas flow rate providing the hysteresis to less than the upper limit, the target power, the inert gas flow rate and/or the reactive gas flow rate is increased or decreased continuously or stepwise.