Reflective Mask Blank Buffer Layer Edge Thickness Control
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Solution Overview
Problem
Conventional reflective mask blanks are prone to electrostatic breakdown during the manufacturing process due to the formation of isolated island-shaped protective films, which can lead to defects in the substrate peripheral edge portion, affecting the accuracy and reliability of the reflective mask.
Innovation Solution
Incorporating a buffer layer and absorption layer with specific thickness and material compositions, such as tantalum (Ta), silicon (Si), chromium (Cr), and ruthenium (Ru), to ensure the protective film and buffer layer thickness is maintained even after edge rinse, preventing the formation of isolated island-shaped protective films and electrostatic breakdown.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the protective film is formed on the multilayer reflective film, then the multilayer reflective film is protected from damage, but isolated island-shaped protective films are formed in the peripheral edge portion leading to electrostatic breakdown
Solution Approach 1:
An absorber film is introduced as an intermediary layer between the protective film and the multilayer reflective film. This absorber film absorbs electrostatic charge that accumulates on the protective film, preventing electrostatic breakdown while maintaining the protective function. The absorber film acts as a charge dissipation pathway without compromising the physical protection barrier.
Solution Approach 2:
The film thickness of the absorber film is controlled to be 1 nm to 10 nm, which is sufficiently thin to not interfere with the protective function but thick enough to effectively absorb electrostatic charge. This parameter optimization resolves the contradiction between providing protection and preventing electrostatic accumulation.
2Reliability
If the absorber film is formed in a film forming region larger than the multilayer reflective film, then the protective film is protected from edge effects, but the absorber film extends beyond the required area
Solution Approach 1:
The absorber film is formed with different thickness characteristics in different regions: in the peripheral edge portion, the absorber film thickness is controlled to be 1 nm to 10 nm to provide electrostatic discharge pathways without excessive extension, while in the central region, the absorber film provides full coverage protection. This local differentiation optimizes both protection and area utilization.
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 prevents electrostatic breakdown and ensures the integrity of the reflective mask blank, enhancing the manufacturing process by maintaining the protective film coverage and reducing defects in the peripheral edge portion.
Implementation Method 1
a multilayer film in which elements having different refractive indices are periodically layered is used
Implementation Method 2
a Mo/Si periodic layered film in which a Mo film and a Si film are alternately layered for about 40 periods
Implementation Method 3
an absorber film that absorbs EUV light
Implementation Method 4
a protective film for protecting the multilayer reflective film
Implementation Method 5
a resist film for electron beam drawing is formed on a surface of the reflective mask blank. Next, a desired pattern is drawn on the resist film with an electron beam
Data Source
AI summary
Provided are a reflective mask blank, a reflective mask, a method for manufacturing a reflective mask, and a method for manufacturing a semiconductor device, capable of preventing occurrence of electrostatic breakdown in a substrate peripheral edge portion.The reflective mask blank comprises a substrate, a multilayer reflective film on the substrate, a protective film on the multilayer reflective film, and an absorber film on the protective film. The absorber film comprises a buffer layer and an absorption layer formed on the buffer layer. When a distance from a center of the substrate to an outer peripheral end of the protective film is denoted by Lcap, and a distance from the center of the substrate to an outer peripheral end of the buffer layer is denoted by Lbuf, Lcap≤Lbuf is satisfied. There is at least one location where a total film thickness of the protective film and the buffer layer is 4.5 nm or more in a range of 0.5 mm or less from a side surface of the substrate 10 toward the center of the substrate.