Photomask Silicon-Based Coating for Sub-Pellicle Defect Reduction
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Solution Overview
Problem
Defect growth during photomask exposure in semiconductor fabrication is a concern due to surface contaminants, outgassing, and airborne impurities, which conventional methods fail to adequately address, especially for sub-pellicle defects that can print on semiconductor wafers and backside haze that affects light transmission.
Innovation Solution
A method involving a thin film of silicon-based compounds such as siloxane, silane, silicon oxide, silicon dioxide, or silicon nitride is applied to both sides of the photomask to create a diffusion barrier or hydrophobic surface, reducing nucleation sites and preventing defect formation by immobilizing contaminants.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional methods (fluorocarbon films or aqueous solutions) are applied to reduce mask surface contamination, then large crystal formation is prevented, but backside haze is not prevented and sub-pellicle defects still occur
Solution Approach 1:
The patent uses a composite coating system comprising multiple layers: a first coating of fluorocarbon polymer on the frontside, a second coating of inorganic material (silicon oxide, silicon nitride, or silicon oxycarbonide) on the frontside, and a third coating of inorganic material on the backside. This multi-layer composite structure combines the benefits of fluorocarbon (preventing large crystal formation) with inorganic materials (preventing backside haze and sub-pellicle defects), thereby resolving the contradiction between preventing large crystals and preventing backside haze.
Solution Approach 2:
The patent applies different coating materials and thicknesses to different locations on the photomask: the frontside receives both fluorocarbon and inorganic coatings to address sub-pellicle defects, while the backside receives inorganic coatings specifically to prevent haze. This localized application of different coating qualities resolves the contradiction by tailoring the protective properties to the specific needs of each mask surface.
2Reliability
If no protective coating is applied, then optical characteristics are maintained, but defect growth occurs from surface contaminants and airborne impurities
Solution Approach 1:
The patent carefully controls the thickness parameters of the protective coatings to maintain optical transparency. The fluorocarbon coating is applied at 5-50 nm thickness and the inorganic coatings at 50-200 nm thickness, ensuring these thin layers provide defect protection while remaining optically transparent at the 193 nm wavelength, thus resolving the contradiction between defect prevention and optical characteristic maintenance.
Solution Approach 2:
The protective coatings act as intermediary barrier layers between the photomask substrate and the external environment (airborne contaminants, moisture). These intermediary layers prevent harmful substances from reaching and reacting with the mask surface, thereby preventing defect growth while maintaining optical properties, as the coatings are designed to be optically transparent at the operating wavelength.
3Reliability
If thick protective coatings are applied to prevent defects, then defect occurrence is reduced, but optical transmission is affected
Solution Approach 1:
The patent optimizes the thickness parameters of the protective coatings to achieve the right balance: the fluorocarbon coating is kept thin (5-50 nm) and the inorganic coatings are kept thin (50-200 nm). These controlled thicknesses provide sufficient defect protection while maintaining optical transparency at the 193 nm wavelength, resolving the contradiction between defect reduction and light transmission.
Solution Approach 2:
The patent employs thin film technology to create protective layers that are sufficiently thin to be optically transparent yet thick enough to provide defect protection. The use of thin films (total coating thickness typically less than 500 nm) allows the protective function to be achieved without significantly impacting light transmission, as the films are thin enough to be transparent at the operating wavelength.
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 silicon-based coatings significantly reduce defect occurrence on photomasks without affecting their optical characteristics, creating a pristine surface and minimizing haze, thus enhancing the quality of semiconductor fabrication.
Implementation Method 1
A method involving a thin film of silicon-based compounds such as siloxane, silane, silicon oxide, silicon dioxide, or silicon nitride is applied to both sides of the photomask to create a diffusion barrier
Implementation Method 2
A method involving a thin film of silicon-based compounds such as siloxane, silane, silicon oxide, silicon dioxide, or silicon nitride is applied to both sides of the photomask to create a diffusion barrier or hydrophobic surface, reducing nucleation sites and preventing defect formation by immobilizing contaminants
Data Source
AI summary
In one embodiment, the invention is a method and apparatus for sub-pellicle defect reduction on photomasks. One embodiment of a photomask for use in photolithography includes a substrate on which a pattern is formed, the substrate having a frontside and an opposite backside, and a protective coating formed on at least one of the frontside and the backside, the protective coating comprising silicon-based compound.