Photomask Absorber Etching via High Cl2:O2 Plasma
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Solution Overview
Problem
The microloading effect in plasma etching leads to variations in etch dimensions between high and low feature density regions, resulting in deformation, line edge roughness, and poor patterned transfer due to insufficient etching selectivity and sidewall passivation in photomask manufacturing, especially at the 45 nanometer technology node and beyond.
Innovation Solution
A method involving specific gas mixtures such as Cl2 and O2 with a ratio greater than 9, or fluorine-containing gases like CHF3 and CF4, is used to etch chromium or tantalum containing layers in a photomask's absorber layer, forming a plasma to improve etching selectivity and control the etching process in plasma processing chambers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional plasma etching is used to etch absorber layers in photomask fabrication, then the etching process can be completed, but microloading effects cause variations in etch dimensions between high and low feature density regions resulting in deformation and poor pattern transfer
Solution Approach 1:
The patent applies parameter changes by optimizing the gas mixture composition (Cl2:O2 ratio greater than 9:1) and controlling process parameters such as pressure, power, and gas flow rates to achieve uniform etching across different feature density regions, thereby resolving the microloading effect and improving both etch dimension uniformity and pattern transfer quality
Solution Approach 2:
The patent uses a composite gas mixture of chlorine (Cl2) and oxygen (O2) in a specific ratio greater than 9:1. This composite gas system provides both reactive species for etching and oxygen for sidewall passivation, enabling simultaneous control of etch rate and profile uniformity across high and low density regions
2Manufacturing precision
If higher etching selectivity is achieved to improve pattern transfer, then pattern fidelity improves, but etching rate decreases leading to longer process times
Solution Approach 1:
The patent optimizes multiple parameters simultaneously including gas composition (Cl2:O2 > 9:1), pressure, power, and flow rates to achieve a balanced state where high etching selectivity and adequate etching rate coexist, resolving the trade-off between pattern transfer fidelity and productivity
Solution Approach 2:
Oxygen acts as an intermediary substance in the gas mixture, providing sidewall passivation that protects against lateral etching while allowing vertical etching to proceed at an acceptable rate, thus maintaining both pattern fidelity and reasonable etching speed
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
This approach enhances etching selectivity and uniformity, reducing microloading effects, and enables precise transfer of patterns in EUV and binary photomask fabrication, ensuring accurate critical dimension maintenance and improved pattern quality.
Implementation Method 1
supplying a RF source power to form a plasma from the etching gas mixture, and etching the chromium containing layer through the patterned photoresist layer in the presence of the plasma
Data Source
AI summary
Embodiments of the present invention provides methods to etching a mask layer, e.g., an absorber layer, disposed in a film stack for manufacturing a photomask in EUV applications and phase shift and binary photomask applications. In one embodiment, a method of etching an absorber layer disposed on a photomask includes transferring a film stack into an etching chamber, the film stack having a chromium containing layer partially exposed through a patterned photoresist layer, providing an etching gas mixture including Cl2, O2 and at least one hydrocarbon gas in to a processing chamber, wherein the Cl2 and O2 is supplied at a Cl2:O2 ratio greater than about 9, supplying a RF source power to form a plasma from the etching gas mixture, and etching the chromium containing layer through the patterned photoresist layer in the presence of the plasma.