Photomask Cleaning Method for Haze Prevention
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional wet cleaning methods fail to completely remove haze formed on photomasks during photolithography processes at shorter wavelengths, leading to optical property changes and phase shift issues.
Innovation Solution
A multi-step cleaning process involving acid and base treatments, followed by heat treatments in specific gas atmospheres, to remove residual ions and prevent haze formation, utilizing a device with cleaning units, a robot arm, and heat treating units like electric heating furnaces or convection ovens.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional wet cleaning methods are used to clean the photomask, then the cleaning process is simple and quick, but haze cannot be completely removed from the photomask surface
Solution Approach 1:
The cleaning process is divided into multiple distinct stages: acid cleaning to remove polymers, base cleaning to remove metal ions, heat treatment to vaporize residual ions, and rinsing. Each stage targets specific contaminants, achieving complete haze removal through segmented action rather than a single complex process
Solution Approach 2:
The patent changes chemical parameters by alternating between acidic and basic cleaning solutions, and changes physical parameters by introducing heat treatment at elevated temperatures. These parameter changes enable the removal of different types of contaminants that cannot be removed by a single cleaning method
2Reliability
If heat treatment is added to the cleaning process to remove residual ions, then haze is prevented and optical properties are improved, but the process time and energy consumption increase
Solution Approach 1:
Heat treatment is performed as a preliminary step after chemical cleaning to activate and vaporize residual ions before the photomask is used. This preliminary action prevents haze formation during subsequent photolithography processes, ensuring optical property stability
Solution Approach 2:
Heat treatment causes residual ions to undergo phase transition from adsorbed state to vaporized state. The thermal energy enables ions to desorb from the photomask surface and be removed, effectively eliminating haze without requiring additional chemical cleaners
3Manufacturing precision
If multiple cleaning steps with acids and bases are used, then residual ions are effectively removed, but the complexity of the cleaning device increases
Solution Approach 1:
The cleaning device is segmented into separate functional units: acid cleaning unit, base cleaning unit, heat treatment unit, and rinsing unit. Each unit performs a specific function, making the overall system more manageable and easier to operate despite the multiple steps involved
Solution Approach 2:
Rinsing with deionized water serves as an intermediary step between acid and base cleaning, removing residual chemicals and preparing the surface for heat treatment. This intermediary action ensures that each cleaning step works effectively without interfering with the others
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
Effectively removes residual ions, prevents haze formation, and reduces optical property changes by activating and vaporizing ions, thereby ensuring stable photomask performance during exposure.
Implementation Method 1
a heat treating unit for heat treating the photomask cleaned using the acids and bases
Implementation Method 2
basic residual ions are vaporized, and the surface of the mask is oxidized in step (f)
Implementation Method 3
a first cleaning unit for cleaning the photomask using acids to remove a polymer formed on the photomask
Implementation Method 4
the surface of the mask is oxidized in step (c)
Implementation Method 5
a cooling unit for cooling the heat treated high temperature photomask
Data Source
AI summary
Disclosed herein is a method of cleaning a photomask, which prevents haze from being generated on a surface of the photomask during a photolithography process. The photomask is heat treated to remove residual ions on a surface thereof and to induce curing and oxidation of Cr and MoSiON layers, thereby preventing diffusion of the ions. Etching of Cr and MoSiON layers due to a cleaning process is suppressed in order to significantly reduce a change in phase and transmissivity of optical properties of Cr and MoSiON.