Dual-Layer EUV Mask Absorption Films for Pattern Accuracy
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Solution Overview
Problem
Existing reflective masks for EUV lithography face challenges in forming fine mask patterns using difficult-to-etch materials like Pt or Ir, which are hard to etch by chemical dry etching, leading to dimension errors and reduced yield due to shadowing effects.
Innovation Solution
A reflective mask blank with a dual-layer absorption structure, where a first easy-to-etch film (e.g., Ru or Ta) and a second difficult-to-etch film (e.g., Pt or Ir) are used, allowing for efficient and accurate dry etching by sputtering followed by chemical dry etching, maintaining a refractive index of 0.95 or less and a total thickness of 60 nm or less, and achieving a phase difference of 150° to 270° for improved pattern contrast.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a difficult-to-etch material (Pt or Ir) is used for the absorption layer, then the refractive index is low and reflectance can be controlled, but the material cannot be efficiently etched by chemical dry etching, making it difficult to form fine mask patterns
Solution Approach 1:
The absorption layer is divided into two distinct films: a first absorption film made of easy-to-etch material (Ru, Ta, or W) and a second absorption film made of difficult-to-etch material (Pt or Ir). This segmentation allows each film to serve its specific function - the first film enables efficient etching by chemical dry etching to form fine patterns, while the second film provides the desired low refractive index and controlled reflectance for EUV light
Solution Approach 2:
The absorption layer uses a composite structure combining two different materials with complementary properties. The first film (Ru/Ta/W) provides etchability, while the second film (Pt/Ir) provides optical properties. This composite approach resolves the contradiction between etchability and optical performance by integrating the advantages of both material types
2Manufacturing precision
If the absorption layer is thick, then the reflectance can be controlled, but dimension error occurs due to shadowing from oblique incident EUV light
Solution Approach 1:
The invention optimizes the thickness parameter of the absorption layer to 60 nm or less, which is sufficiently thin to prevent shadowing effects from oblique EUV light while still maintaining the desired optical properties through the composite structure. The total thickness is controlled by adjusting the individual thicknesses of the first and second films
3Adaptability or versatility
If an alloy of Ta and Nb is used to achieve wide reflectance, then the composition ratio can be controlled, but the refractive index is relatively large requiring thicker film formation
Solution Approach 1:
Instead of using a Ta-Nb alloy with relatively high refractive index, the invention employs a composite of Ru (or Ta/W) and Pt/Ir. This composite structure achieves the desired wide reflectance control and low refractive index (0.95 or less) while maintaining a thin total thickness of 60 nm or less, avoiding the need for thicker film formation
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
This approach enables the efficient and accurate formation of mask patterns with reduced surface roughness and residues, improving the yield and pattern accuracy by effectively etching difficult-to-etch materials while controlling reflectance and phase difference for EUV lithography.
Implementation Method 1
a multilayer reflective film configured to reflect EUV light
Implementation Method 2
a phase shift mask which absorbs EUV light and improves contrast of a transfer pattern by an absorption layer which reflects (preferably inverted) light in a different phase
Implementation Method 3
an absorption layer configured to absorb EUV light
Implementation Method 4
the formation of the mask pattern is performed by subjecting the absorption layer to a sputtering etching treatment
Implementation Method 5
chemical dry etching, which is plasma etching generally applied at the time of mask pattern formation
Data Source
AI summary
A reflective mask blank for EUV lithography, the reflective mask blank including: a substrate; a multilayer reflective film configured to reflect EUV light; and an absorption layer configured to absorb EUV light, in this order from a substrate side, in which the absorption layer includes a first absorption film and a second absorption film in this order from the substrate side, the absorption layer has a refractive index for EUV light having a wavelength of 13.5 nm of 0.95 or less, and the first absorption film is more easily chemically dry etched than the second absorption film.