EUV Reflective Mask Blank Surface Roughness Control
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Solution Overview
Problem
Highly sensitive defect inspection apparatuses in EUV lithography detect excessive pseudo defects due to surface roughness, obscuring critical defects and leading to unnecessary labor and economic losses in semiconductor device production.
Innovation Solution
A reflective mask blank with a multilayer film structure, where the relationship between bearing area and bearing depth, as measured by an atomic force microscope, is optimized to inhibit pseudo defect detection, and the absorber film is composed of tantalum and nitrogen with controlled thickness and phase shift function to enhance defect visibility.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If highly sensitive defect inspection apparatuses are used to detect defects in reflective mask blanks, then critical defects can be detected, but excessive pseudo defects due to surface roughness are detected, obscuring critical defects
Solution Approach 1:
The patent applies parameter changes by optimizing the surface roughness parameters of the reflective mask blank. Specifically, it controls the root mean square roughness (Rms) to be 0.2 nm or less and the maximum height (Rmax) to be 4.5 nm or less. By changing these surface roughness parameters to specific ranges, the inspection apparatus can distinguish between actual defects and pseudo defects caused by surface irregularities, thereby resolving the contradiction between detection sensitivity and pseudo defect generation.
Solution Approach 2:
The patent converts the harmful effect of surface roughness into a beneficial control parameter. Instead of simply trying to eliminate all surface irregularities, it establishes specific quantitative ranges for roughness parameters (Rms ≤ 0.2 nm, Rmax ≤ 4.5 nm) that actually improve defect detection. By converting the previously harmful surface roughness into a controlled parameter within optimal ranges, the system achieves both high sensitivity detection and reduced pseudo defects.
2Reliability
If surface roughness is reduced to improve optical properties and defect quality, then critical defects become more visible, but manufacturing complexity increases
Solution Approach 1:
The patent applies parameter changes by establishing specific quantitative thresholds for surface roughness parameters. It defines Rms (root mean square roughness) should be 0.2 nm or less and Rmax (maximum height) should be 4.5 nm or less. These parameter specifications provide clear manufacturing targets that balance defect quality improvement with manufacturing feasibility, avoiding overly stringent requirements that would make production impractical.
Solution Approach 2:
The patent replaces complex mechanical polishing processes with controlled deposition techniques. By using atomic layer deposition (ALD) or chemical vapor deposition (CVD) to form the reflective multilayer film, the surface roughness is inherently controlled during the deposition process itself, eliminating the need for additional mechanical polishing steps and reducing overall manufacturing complexity while achieving the required surface quality.
3Manufacturing precision
If ion beam sputtering is used to deposit multilayer reflective film at large angles, then surface smoothness is improved, but deposition time and process complexity increase
Solution Approach 1:
The patent applies dynamics by making the substrate rotation speed variable during the ion beam sputtering process. It specifies that the substrate rotation speed should be in the range of 1-100 rpm, allowing optimization between surface smoothness and deposition efficiency. This dynamic control enables the system to achieve adequate surface quality while maintaining reasonable deposition rates, resolving the contradiction between precision and productivity.
Solution Approach 2:
The patent changes the incident angle parameter of the ion beam sputtering process to be in the range of 45-75 degrees relative to the substrate normal. This parameter optimization achieves a balance point where sufficient surface smoothness is obtained without requiring excessively large angles that would dramatically reduce deposition efficiency. The parameter change resolves the contradiction by finding the optimal operating point.
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 reduces the detection of pseudo defects, making critical defects more conspicuous, thereby improving the reliability of defect inspections and reducing unnecessary labor and economic losses in semiconductor production.
Implementation Method 1
the relationship between bearing area (%) and bearing depth (nm), as measured by an atomic force microscope
Implementation Method 2
an absorber film formed in a pattern on the multilayer reflective film that absorbs exposure light
Implementation Method 3
a multilayer reflective film that reflects exposure light formed on a substrate
Implementation Method 4
Multilayer reflective films are formed by alternately laminating layers that have a high refractive index with layers that have a low refractive index on the surface of a mask blank substrate. Each layer is typically formed by sputtering using sputtering targets composed of the materials that form these layers.
Data Source
AI summary
A reflective mask blank capable of facilitating the discovery of contaminants, scratches and other critical defects by inhibiting the detection of pseudo defects attributable to surface roughness of a substrate or film in a defect inspection using a highly sensitive defect inspection apparatus. The reflective mask blank has a mask blank multilayer film comprising a multilayer reflective film, obtained by alternately laminating a high refractive index layer and a low refractive index layer, and an absorber film on a main surface of a mask blank substrate, wherein, in the relationship between bearing area (%) and bearing depth (nm) as measured with an atomic force microscope for a 1 μm×1 μm region of the surface of the reflective mask blank on which the mask blank multilayer film is formed, the surface of the reflective mask blank satisfies the relationship of (BA70−BA30)/(BD70−BD30)≧60(%/nm) and maximum height (Rmax)≦4.5 nm.