Mask Blank Etching Stopper Film for Transfer Masks
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Solution Overview
Problem
The existing methods for manufacturing transfer masks face challenges in achieving high accuracy for fine pattern formation in the light-semitransmissive film while minimizing damage to the surface layer during the removal of the light-shielding film, due to differences in etching characteristics and oxidation issues with materials like tantalum-hafnium alloys.
Innovation Solution
A mask blank structure is developed with a light-semitransmissive film capable of dry etching with fluorine-based gases, a light-shielding film made of tantalum and hafnium with no oxygen except in surface layers, and an etching stopper film of chromium with low oxygen content, along with a specific etching process to maintain etching selectivity and prevent surface damage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a light-shielding film made of tantalum-hafnium alloy is used to achieve high optical density, then the optical density requirement is satisfied, but the surface layer is damaged during etching due to oxidation
Solution Approach 1:
A protective film made of silicon oxide or silicon nitride is introduced as an intermediary layer between the tantalum-hafnium alloy light-shielding film and the etching environment. This protective film acts as a mediator that prevents direct contact between oxygen-containing etching gases and the light-shielding film surface, thereby preventing oxidation and surface damage while allowing the underlying fine pattern to be formed with high precision
Solution Approach 2:
The protective film is formed in advance before the etching process to preemptively shield the light-shielding film surface from oxidation. By performing this protective action beforehand, the surface layer is preserved from damage that would otherwise occur during subsequent etching operations, ensuring both high optical density and surface integrity
2Productivity
If dry etching with oxygen-containing gases is used to remove the light-shielding film, then the etching process is effective, but oxidation of the surface layer occurs causing damage
Solution Approach 1:
The protective film serves as a protective intermediary that allows oxygen-containing etching gases to effectively remove the light-shielding film through the protective film without directly oxidizing the underlying surface layer. The protective film consumes the oxidizing action, preserving the surface layer while maintaining etching efficiency
Solution Approach 2:
The protective film transforms the potentially harmful oxidizing action of the etching gases into a beneficial selective removal process. The oxygen-containing gases are directed to etch the protective film and light-shielding film while the surface layer remains protected, converting what would be damage into a controlled manufacturing step
3Object-affected harmful factors
If chromium-based etching stopper film is used to prevent surface damage, then surface protection is achieved, but the film loses etching stopper function due to high oxygen content
Solution Approach 1:
The oxygen content parameter of the chromium-based protective film is precisely controlled to be 20 at% or less. This parameter change maintains the film's etching stopper function by preserving its resistance to oxygen-containing etching gases, while still providing sufficient protection to the underlying surface layer from oxidation damage
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 allows for accurate formation of fine patterns in the light-semitransmissive film with reduced risk of surface damage during light-shielding film removal, enhancing the overall precision and reliability of the transfer mask manufacturing process.
Implementation Method 1
a light-semitransmissive film (halftone phase shift film) has a function of transmitting light therethrough with an intensity that does not substantially contribute to exposure, and further has a function of providing the light transmitted therethrough with a predetermined phase difference relative to light transmitted in air for the same distance, thereby producing a so-called phase shift effect
Implementation Method 2
an etching stopper film provided between the light-semitransmissive film and the light-shielding film, and made of a material that contains chromium and has an oxygen content of 20 at % or less
Data Source
AI summary
In a mask blank having a structure in which a light-semitransmissive film and a light-shielding film are laminated on a main surface of a transparent substrate, the light-semitransmissive film is made of a material that can be dry-etched with an etching gas containing a fluorine-based gas, the light-shielding film is made of a material that contains tantalum and one or more elements selected from hafnium and zirconium and contains no oxygen except in a surface layer thereof, an etching stopper film is provided between the light-semitransmissive film and the light-shielding film, and the etching stopper film is made of a material that contains chromium with an oxygen content of 20 at % or less.