Transition Metal Silicide Photomask Light-Shielding Film
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Solution Overview
Problem
The increasing demand for smaller geometries in semiconductor integrated circuits and the need for higher accuracy in photomask production pose challenges in achieving precise circuit patterns, as existing technologies struggle with the transfer of resist patterns due to light interference and the limitations of chromium-based light-shielding films, which lack chemical stability and etch resistance at lower resist film thicknesses.
Innovation Solution
A photomask blank with a light-shielding film composed of transition metal silicides having a silicon content of less than 80% and incorporating nitrogen, which enhances chemical stability and electrical conductivity, allowing for high-resolution and high-accuracy pattern transfer, is developed. This film, combined with a chrome-based material, enables mutual selective etching and reduces the risk of charge-up during e-beam lithography.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If chromium-based light-shielding films are used, then etching processes are well-established and extensive knowledge exists, but chemical stability and etch resistance deteriorate at lower resist film thicknesses
Solution Approach 1:
The patent employs a composite light-shielding film structure consisting of a first light-shielding film layer (chromium-based material) and a second light-shielding film layer (material containing silicon, oxygen, and nitrogen). This composite structure combines the etching advantages of chromium-based materials with the chemical stability and etch resistance of the silicon-oxygen-nitrogen-containing material, thereby resolving the contradiction between ease of manufacture and reliability.
2Length of moving object
If resist film thickness is reduced to achieve smaller feature sizes, then minimum feature size decreases, but resist pattern shape degrades and pattern transfer accuracy worsens
Solution Approach 1:
The composite light-shielding film structure provides enhanced chemical stability and etch resistance, enabling the use of thinner resist films without compromising pattern transfer accuracy. The second layer (silicon, oxygen, nitrogen-containing material) specifically addresses the degradation issues associated with thin resist films by providing a stable foundation that maintains pattern integrity during etching processes.
Solution Approach 2:
The patent changes the compositional parameters of the light-shielding film by introducing a second layer containing silicon, oxygen, and nitrogen. This parameter change (adding specific elements in controlled amounts) improves the film's chemical stability and etch resistance, allowing thinner resist films to be used while maintaining manufacturing precision.
3Reliability
If transition metal silicides with high silicon content are used, then chemical stability improves, but electrical conductivity decreases increasing charge-up risk
Solution Approach 1:
The patent optimizes the compositional parameters of the second light-shielding film layer by controlling the silicon content to be 10-70 atomic%, oxygen content to be 10-70 atomic%, and nitrogen content to be 10-70 atomic%. This parameter optimization achieves a balance between chemical stability and electrical conductivity, preventing charge-up while maintaining chemical stability.
Solution Approach 2:
The composite structure allows the first chromium-based layer to provide electrical conductivity while the second silicon-oxygen-nitrogen-containing layer provides chemical stability. The combination of these two materials with different properties resolves the contradiction between chemical stability and electrical conductivity.
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 use of transition metal silicides with nitrogen improves chemical stability and etch resistance, enabling the production of photomasks with smaller feature sizes and higher accuracy, while preventing charge-up and maintaining optical density, thus addressing the limitations of chromium-based materials.
Implementation Method 1
transition metal silicides having a silicon content of less than 80% and incorporating nitrogen, which enhances chemical stability and electrical conductivity
Implementation Method 2
a light-shielding film composed of transition metal silicides... regions substantially opaque to an exposure light
Implementation Method 3
photomask pattern bearing a circuit shape that has been enlarged four-fold is used, owing to such effects as the light interference that arises during actual photolithography
Data Source
Figure 1A~1B
Figure 2A~2H
Figure 3A~3J
AI summary
A photomask blank has a light-shielding film (3) composed of a single layer of a material containing a transition metal, silicon and nitrogen or a plurality of layers that include at least one layer made of a material containing a transition metal, silicon and nitrogen, and has one or more chrome-based material film. The high transition metal content ensures electrical conductivity, preventing charge-up in the photomask production process, and also provides sufficient chemical stability to cleaning in photomask production. The light-shielding film has a good resistance to dry etching of the chrome-based material film in the presence of chlorine and oxygen, thus ensuring a high processing accuracy.