Ru-Cr Phase Shift Film for EUV Mask Refractive Index Control
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Solution Overview
Problem
Existing phase shift films for EUV lithography have high refractive indices, which complicates the processability and reduces the accuracy of pattern transfer in semiconductor manufacturing.
Innovation Solution
A reflective mask blank is developed with a phase shift film containing a Ru compound, where the melting points of the oxide and fluoride or oxyfluoride of the compound satisfy the formula 0.625MP1 + MP2 ≤ 1000, thereby lowering the refractive index and improving processability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional phase shift film materials are used, then the film can be manufactured with standard processes, but the refractive index remains high which reduces pattern transfer accuracy
Solution Approach 1:
The patent changes the chemical composition parameters of the phase shift film by incorporating Ru compounds with specific melting point characteristics (0.625MP1+MP2≤1000), which fundamentally alters the refractive index from conventional high values to lower values, thereby improving pattern transfer accuracy while maintaining manufacturability
Solution Approach 2:
The patent uses composite Ru compound materials containing multiple elements (Ta, Ru, N) in specific ratios (Ta:Ru = 2:1 or Ta:N:Ru = 2:2:1) to achieve optimal refractive index and etch selectivity properties, combining the benefits of different elements to resolve the contradiction between precision and ease of manufacture
2Manufacturing precision
If the phase shift film refractive index is lowered to improve pattern transfer accuracy, then manufacturing precision improves, but processability may deteriorate
Solution Approach 1:
By carefully selecting Ru compounds with specific melting point parameters (0.625MP1+MP2≤1000), the patent achieves lower refractive index (improving precision) while the specific compound selection ensures good etch selectivity and processability, thus resolving the contradiction between precision and ease of operation
Solution Approach 2:
The patent optimizes the local chemical composition (Ta:Ru ratio, presence of N) in the phase shift film to achieve the desired refractive index and etch selectivity characteristics, allowing different regions of the material property space to be optimized for different functions (optical performance vs. processability)
Data Source
AI summary
A reflective mask blank containing a substrate, a multilayer reflective film that reflects EUV light, and a phase shift film that shifts a phase of the EUV light, the substrate, the multilayer reflective film, and the phase shift film being arranged in this order. The phase shift film contains a compound containing Ru and Cr, an element ratio between Cr and Ru (Cr:Ru) in the phase shift film is 5:95 to 42:58, and a melting point MP1 of an oxide of the compound and a melting point MP2 of a fluoride or an oxyfluoride of the compound satisfy the following relation (1):0.625MP1+MP2≤1000 (1).