Phase Shift Film Layered Structure for ArF Lithography Thermal Stability
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Solution Overview
Problem
Phase shift masks used in semiconductor manufacturing face challenges in preventing thermal expansion and pattern displacement due to ArF exposure light absorption, which is difficult to address with existing designs that require high transmittance and phase difference while maintaining low absorptivity and back surface reflectance.
Innovation Solution
A mask blank with a phase shift film composed of non-metallic elements and silicon, featuring a stacked structure of multiple layers with specific refractive indices and extinction coefficients, designed to transmit ArF exposure light with 15% or more transmittance and generate a phase difference of 150-200 degrees, while minimizing thermal expansion by optimizing the refractive and extinction coefficients of each layer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a phase shift film is designed to transmit ArF exposure light with high transmittance (15% or more) and generate a phase difference of 150-200 degrees, then the photolithography performance is improved, but thermal expansion and pattern displacement occur due to absorbed light energy transforming into heat
Solution Approach 1:
The patent changes the optical parameters (refractive index and extinction coefficient) of the phase shift film materials to optimize the balance between transmittance and heat absorption. By selecting specific materials and their optical properties, the film achieves the required phase difference while minimizing thermal expansion that causes pattern displacement.
Solution Approach 2:
The patent employs composite material structures for the phase shift film, combining multiple layers with different material properties. This composite approach allows simultaneous optimization of transmittance, phase difference, and thermal stability to prevent pattern displacement during ArF exposure.
2Temperature
If the back surface reflectance is increased to reduce heat generation from absorbed light, then thermal expansion is suppressed, but the overall light transmission and phase difference generation are compromised
Solution Approach 1:
The patent applies different optical properties to different regions of the phase shift film. The front surface is designed with specific refractive index and extinction coefficient to maximize phase difference generation, while the back surface is optimized for reflectance to minimize heat absorption. This local differentiation resolves the contradiction between phase difference and thermal stability.
Solution Approach 2:
The phase shift film is divided into multiple layers with distinct functional characteristics. Some layers are optimized for phase difference generation (high refractive index), while others are optimized for thermal management (high reflectance). This segmentation allows independent optimization of each function without compromise.
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 effectively suppresses thermal expansion and pattern displacement, ensuring high precision in semiconductor device manufacturing by maintaining low absorptivity and adequate back surface reflectance, thus enhancing the accuracy of the phase shift mask.
Implementation Method 1
generate a phase difference of 150 degrees or more and 200 degrees or less between the exposure light transmitted through the phase shift film and the exposure light transmitted through air for a same distance as a thickness of the phase shift film
Implementation Method 2
ArF exposure light absorbed within the pattern of the phase shift film transforming into thermal energy
Implementation Method 3
the heat is transmitted to the transparent substrate to cause thermal expansion
Data Source
AI summary
Provided is a mask blank including a phase shift film. The phase shift film is made of a material containing a non-metallic element and silicon and includes first, second, and third layers; refractive indexes n1, n2, and n3 of the first, second, and third layers, respectively, at the wavelength of an exposure light satisfy the relations of n1<n2 and n2>n3; and extinction coefficients k1, k2, and k3 of the first, second, and third layers, respectively, at the wavelength of an exposure light satisfy the relation of k1>k2>k3.