Photomask Blank Crystal Matching for Thermal-Stable Pattern Resolution
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Solution Overview
Problem
The miniaturization of semiconductor device circuit patterns requires advanced lithography techniques, but existing photomasks, such as Binary and Phase shift masks, face challenges in forming precise patterns due to light diffraction and thermal variations, especially with exposure lights of shorter wavelengths like ArF excimer laser.
Innovation Solution
A blank mask comprising a transparent substrate, a phase shift film, and a light shielding film, with controlled crystal characteristics and optical properties, is designed to minimize thermal variations and improve pattern resolution through precise XRD analysis and sputtering processes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of moving object
If a Binary mask is used with shortened wavelength exposure light, then miniaturized circuit patterns can be formed, but light diffraction at the edge of transmissive portions causes problems in pattern development
Solution Approach 1:
The patent employs a composite mask structure combining transparent substrate, phase shift film, and light shielding film. The phase shift film (e.g., MoSiN) with specific optical properties creates phase differences in transmitted light, while the light shielding film (e.g., Cr, W) blocks light in pattern areas. This composite approach enables both miniaturization and precise pattern formation by counteracting diffraction effects through phase modulation.
Solution Approach 2:
The patent optimizes specific parameters including phase shift film thickness (30-100 nm), light shielding film thickness (5-50 nm), and material composition (MoSiN with controlled stoichiometry). By precisely controlling these parameters, the mask achieves optimal phase shift effects that eliminate diffraction-related patterning issues while maintaining miniaturized circuit features.
2Manufacturing precision
If a Phase shift mask is used to counteract diffraction light, then refined minute patterns can be formed, but thermal variations during exposure processes cause optical distortions
Solution Approach 1:
The patent applies different material properties to different regions of the mask structure. The phase shift film has specific thermal expansion characteristics tailored to match the transparent substrate, while the light shielding film has different properties optimized for light blocking. This local differentiation of material qualities enables precise pattern formation while compensating for thermal effects in each specific region.
Solution Approach 2:
The patent selects materials with matched thermal expansion coefficients, particularly between the phase shift film and transparent substrate. This thermal expansion matching minimizes relative dimensional changes and optical path variations during exposure, reducing thermal-induced distortions while maintaining high pattern resolution.
3Length of moving object
If advanced lithography techniques are used for miniaturization, then smaller circuit patterns can be achieved, but existing photomasks face challenges in forming precise patterns
Solution Approach 1:
The patent incorporates a phase shift film that pre-modulates the optical phase of transmitted light before it reaches the resist. This preliminary phase adjustment creates constructive and destructive interference patterns that enhance contrast and ensure reliable pattern formation at miniaturized dimensions, overcoming limitations of conventional masks.
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 enhances pattern resolution and reduces optical distortions by aligning the crystal characteristics of the phase shift film with the transparent substrate, maintaining consistent performance under temperature changes during exposure processes.
Implementation Method 1
The attenuated exposure light is allowed to have a phase difference compared to exposure light which has transmitted the transmissive portion. Accordingly, diffraction light occurring at the edge of the transmissive portion is counteracted by the exposure light which has transmitted the semi-transmissive portion
Implementation Method 2
a light shielding portion including a light shielding pattern film shields exposure light to transfer a pattern on a resist film of the surface of a wafer
Implementation Method 3
a transmissive portion not including a light shielding pattern film allows exposure light to be transmitted
Data Source
AI summary
A blank mask including a transparent substrate, a phase shift film disposed on the transparent substrate, and a light shielding film disposed on the phase shift film. The phase shift film has XRD maximum peak at 2θ of 15° to 30° when normal mode XRD analysis is performed on an upper surface of the phase shift film. The transparent substrate has XRD maximum peak at 2θ of 15° to 30° when performing normal mode XRD analysis on a lower surface of the transparent substrate. AI1 value of the blank mask expressed by below Equation is 0.9 to 1.1.AI1=XM1XQ1XM1 is the maximum value of the measured X-ray intensity when the normal mode XRD analysis is performed on upper surface of the phase shift film. XQ1 is the maximum value of the measured X-ray intensity when the normal mode XRD analysis is performed on the lower surface of the transparent substrate.