Mask Blank Substrate Surface Roughness Control for Defect Inspection
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Solution Overview
Problem
Conventional mask blank substrates suffer from false defects in defect inspection due to surface roughness, leading to the masking of critical defects such as foreign matters and scratches, which can result in failures in semiconductor device production.
Innovation Solution
A mask blank substrate with a multilayer reflective film is configured to have a specific surface roughness characterized by a relational equation of (BA70−BA30)/(BD70−BD30)≥350(%/nm) and a maximum height (Rmax)≤1.2 nm, ensuring high alignment and smoothness, and optionally treated with catalyst-referred etching to enhance defect detection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional mask blank substrates are used, then manufacturing is simpler, but false defects are detected in defect inspection due to surface roughness
Solution Approach 1:
The patent applies parameter changes by precisely controlling surface roughness parameters (Rmax ≤ 1.2 nm and bearing curve relationship) to transform the substrate surface from a rough state that generates false defects to an ultra-smooth state that enables accurate defect detection. This quantitative control of surface parameters directly resolves the contradiction between measurement precision and harmful factors.
Solution Approach 2:
The patent implements preliminary action by performing surface treatment (such as catalyst-referred etching) on the mask blank substrate before defect inspection to pre-establish the required surface smoothness. This advance preparation eliminates surface roughness-induced false defects before the inspection process, ensuring accurate detection of critical defects without interference from manufacturing imperfections.
2Object-generated harmful factors
If surface roughness is reduced to improve defect detection, then false defects are suppressed, but manufacturing precision requirements increase
Solution Approach 1:
The patent transforms the manufacturing challenge by establishing specific parameter thresholds (Rmax ≤ 1.2 nm and bearing curve relationship) that define the boundary between acceptable and unacceptable surface quality. This quantified approach converts an ambiguous manufacturing precision requirement into a measurable target, enabling consistent achievement of ultra-smooth surfaces through controlled surface treatment processes.
Solution Approach 2:
The patent replaces conventional mechanical polishing methods with catalyst-referred etching, a chemical process that achieves superior surface smoothness by selectively removing material at the atomic level. This substitution of chemical etching for mechanical polishing enables attainment of Rmax ≤ 1.2 nm with better controllability and reduced surface damage, resolving the manufacturing precision challenge.
3Reliability
If high-sensitivity defect inspection is performed, then critical defects can be detected, but false defects from surface roughness mask them
Solution Approach 1:
The patent converts the harmful effect of surface roughness into a benefit by using catalyst-referred etching to create an ultra-smooth surface (Rmax ≤ 1.2 nm) with controlled bearing curve characteristics. This transformed surface quality reduces false defects to minimal levels, allowing high-sensitivity defect inspection to operate in a high signal-to-noise ratio environment where critical defects are clearly distinguishable from surface imperfections.
Solution Approach 2:
The patent changes the surface parameter regime from conventional roughness (Rmax > 1.2 nm) to ultra-smooth conditions (Rmax ≤ 1.2 nm with specific bearing curve relationship). This parameter transformation suppresses false defect generation to such an extent that high-sensitivity inspection can reliably detect critical defects without being overwhelmed by noise from surface irregularities.
Data Source
AI summary
Disclosed is a mask blank substrate for use in lithography, wherein a main surface of the substrate satisfies a relational equation of (BA70−BA30)/(BD70−BD30)≥350(%/nm), and has a maximum height (Rmax)≤1.2 nm in a relation between a bearing area (%) and a bearing depth (nm) obtained by measuring, with an atomic force microscope, an area of 1 μm×1 μm in the main surface on the side of the substrate where a transfer pattern is formed, wherein BA30 is defined as a bearing area of 30%, BA70 is defined as a bearing area of 70%, and BD70 and BD30 are defined to respectively represent bearing depths for the bearing area of 30% and the bearing area of 70%.