Phase Shift Mask Blank with Chromium-Silicon Lower Layer
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Solution Overview
Problem
In phase shift masks with MoSi-based films, etching processes using fluorine-based gases lead to inaccurate phase control and pattern defects due to substrate etching, and chromium films etched with chlorine-based gases suffer from side etching and pattern fall issues, especially with increased oxygen and nitrogen content for higher transmittance.
Innovation Solution
A phase shift mask blank with a transparent substrate and a phase shift film comprising a lower chromium layer and an upper transition metal layer, where the lower layer contains 3-15% silicon and less than 1.7% oxygen, and the upper layer has a transition metal content of 20% or less, providing etching selectivity of 10 or more in fluorine-based dry etching, and a light shielding film with chromium for controlled etching.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If fluorine-based gas etching is used to pattern the phase shift film, then the phase shift film can be etched, but the substrate is also slightly etched leading to inaccurate phase control
Solution Approach 1:
The patent introduces a lower layer containing chromium as an intermediary between the transparent substrate and the upper phase shift film layer. This lower layer serves as a protective barrier that prevents fluorine-based etching gas from attacking the substrate while still allowing the upper layer to be etched for phase shift pattern formation. The chromium-containing lower layer thus mediates between the etching process and the substrate protection requirement.
Solution Approach 2:
The phase shift film is structured as a composite with two distinct layers: an upper layer containing transition metal and silicon for phase shift functionality, and a lower layer containing chromium for substrate protection during etching. This composite structure allows each layer to perform its specific function - the upper layer provides the required phase shift while the lower layer protects the substrate from fluorine-based etching damage.
2Illumination intensity
If chromium film is etched with chlorine-based gas to increase transmittance, then transmittance improves, but side etching and pattern fall occur
Solution Approach 1:
The patent applies local quality by creating a chromium-containing lower layer with specific composition characteristics (3-15 at% silicon content) that differs from conventional chromium films. This localized modification of the chromium layer's composition provides resistance to side etching during chlorine-based gas etching, while still maintaining the required light transmittance properties for the overall phase shift film structure.
Solution Approach 2:
The patent changes the compositional parameters of the chromium-containing lower layer by controlling silicon content at 3-15 at%, which fundamentally alters the etching characteristics of the chromium film. This parameter change makes the chromium layer resistant to side etching by chlorine-based gas while preserving the necessary optical transmittance, thereby resolving the contradiction between transmittance and pattern shape accuracy.
3Illumination intensity
If oxygen and nitrogen content in chromium film is increased to improve transmittance, then transmittance increases, but side etching during etching increases
Solution Approach 1:
The patent changes the compositional parameters of the chromium-containing lower layer by precisely controlling silicon content at 3-15 at%, which fundamentally alters the etching characteristics of the chromium film. This parameter change makes the chromium layer resistant to side etching by chlorine-based gas while preserving the necessary optical transmittance, thereby resolving the contradiction between transmittance and pattern shape accuracy.
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 configuration enables precise phase control and excellent pattern shape during etching, suppressing substrate digging and side etching, while maintaining high transmittance and etching selectivity, thus improving the manufacturing of phase shift masks.
Implementation Method 1
The phase shift method is a contrast enhancing method by utilizing interference of light caused by a phase shift film pattern formed on a photomask substrate that is transparent to exposure light. The phase shift film pattern has a phase difference of approximately 180° between a light through the phase shift film and an exposure light through a portion where the phase shift film is not formed
Implementation Method 2
etching selectivity of the upper layer is 10 or more compared to the lower layer in fluorine-based dry etching
Implementation Method 3
the chromium film on the substrate side exposed by etching the silicon containing film is etched by chlorine-based gas containing chlorine gas and oxygen gas
Data Source
Figure 1~3
Figure 4
AI summary
Provided is a phase shift mask blank having a transparent substrate and a phase shift film formed on the transparent substrate, comprising, the phase shift film has a phase difference of 160 to 200°and a transmittance of 3 to 15% at exposure wavelength of 200 nm or less, the phase shift film includes a lower layer and an upper layer in order from the transparent substrate side, the upper layer contains transition metal, silicon, nitrogen and/or oxygen, or silicon, nitrogen and/or oxygen, the lower layer contains chromium, silicon, nitrogen and/or oxygen, and the content of silicon is 3% or more to less than 15% for the sum of chromium and silicon in the lower layer, and the ratio of oxygen content to the total content of chromium and silicon is less than 1.7, and etching selectivity of the upper layer is 10 or more compared to the lower layer in fluorine-based dry etching.