Phase Shift Film Composition for High Transmittance and Thin Thickness
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Solution Overview
Problem
Existing phase shift films in photomasks face challenges in achieving high transmittance while maintaining a thin thickness, as higher oxygen content reduces the refractive index and requires thicker films to achieve necessary phase shift, which is undesirable for finer patterning and reduced three-dimensional effects in photolithography.
Innovation Solution
A phase shift film composed of transition metal, silicon, and oxygen with a specific atomic ratio of transition metal to silicon, allowing for a thickness of 150 nm or less, achieving a phase shift of 150 to 250° and transmittance of 60 to 80% for exposure light with a wavelength of 200 nm or less, using a single or multiple layers with a chromium-containing second layer for improved patterning.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If higher oxygen content is used to increase transmittance, then transmittance is improved, but refractive index decreases requiring thicker film
Solution Approach 1:
The patent changes the chemical composition parameters of the phase shift film by incorporating nitrogen along with oxygen, creating a SiON system. This compositional parameter change allows simultaneous optimization of transmittance and refractive index, enabling thin film thickness (150 nm or less) while achieving high transmittance (60-80%) and sufficient phase shift (150-250°).
Solution Approach 2:
The patent uses a composite material system consisting of silicon, oxygen, and nitrogen (SiON) rather than simple silicon oxide. This composite approach combines the high transmittance benefit of oxygen-rich materials with the high refractive index benefit of nitrogen-containing materials, resolving the contradiction between transmittance and film thickness.
2Manufacturing precision
If thinner film is used for finer patterning, then three-dimensional effects are reduced, but achieving necessary phase shift becomes difficult
Solution Approach 1:
The patent modifies the optical parameters of the film by introducing nitrogen into the silicon oxide matrix, creating SiON compounds with enhanced refractive index. This parameter change allows thin films (150 nm or less) to achieve the required phase shift (150-250°) that would normally require much thicker films, thereby maintaining patterning precision while reducing three-dimensional effects.
Solution Approach 2:
The patent optimizes the local chemical composition of the phase shift film by controlling the ratios of silicon, oxygen, and nitrogen. This local compositional optimization creates regions with specific optical properties that enable thin film thickness to simultaneously achieve both sufficient phase shift and high transmittance for fine patterning applications.
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 solution enables a thinner phase shift film that satisfies both phase shift and high transmittance requirements, enhancing patterning precision and miniaturization capabilities in photolithography, allowing for finer patterns and reduced three-dimensional effects.
Implementation Method 1
The phase shift method is a contrast enhancing method utilizing interference of light caused by a film pattern, capable of inverting phase approximately 180°
Data Source
Figure 1A~1B
Figure 2A~2C
AI summary
Provided is a phase shift-type photomask blank that includes a transparent substrate, and a phase shift film thereon, the phase shift film consisting of a single layer or multiple layers, the single layer or multiple layers including at least one layer selected from the group consisting of a layer composed of transition metal, silicon, nitrogen and oxygen, and a layer composed of silicon, nitrogen and oxygen, the phase shift film having a phase shift of 150 to 250°, and a transmittance of 60 to 80%, with respect to light having a wavelength of up to 200 nm, the phase shift film having a thickness of up to 150 nm, and the layer composed of transition metal, silicon, nitrogen and oxygen having a content (atomic ratio) of up to 0.03, as a ratio of the transition metal to a total content of the transition metal and silicon.