EUV Mask Blank Low Reflective Layer Etching
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Solution Overview
Problem
EUV mask blanks with conventional low reflective layers face challenges such as low etching rates when using chlorine-type gases, contamination issues during two-step etching processes, and adhesion problems with resist patterns, particularly for fine features below 100 nm.
Innovation Solution
A stacked low reflective layer structure comprising a SiN film and a TaN or TaON film, with specific atomic percentages and layer thicknesses, is used to enhance etching rates with chlorine-type gases and improve adhesion with resist layers, allowing for single-step etching and reduced contamination.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a low reflective layer is formed to reduce reflectance at inspection light wavelength (190-260 nm), then detection sensitivity of mask pattern defects is improved, but etching rate decreases when using chlorine-type gases
Solution Approach 1:
The low reflective layer is divided into multiple layers with different material compositions and functions. The first layer (TaON or TaBNO) provides low reflectance for inspection light, while the second layer (SiN) provides high etching rate with chlorine-type gases. This segmentation allows each layer to optimize its specific function without compromising the other.
Solution Approach 2:
The invention uses composite material structure combining different materials (TaON/TaBNO and SiN) in a stacked configuration. Each material contributes its unique properties: TaON/TaBNO for optical performance (low reflectance) and SiN for etching performance (high etching rate with chlorine gases). The composite structure achieves overall performance that neither single material could provide alone.
2Manufacturing precision
If a two-step etching process is used to etch the low reflective layer and absorber layer separately, then etching precision is improved, but process complexity and contamination increase
Solution Approach 1:
The low reflective layer is segmented into two distinct layers with different material compositions optimized for different etching rates. This allows both layers to be etched simultaneously at appropriate rates using a single chlorine-type gas etching process, achieving precise pattern transfer without requiring multiple etching steps.
Solution Approach 2:
By changing the material composition parameters of the low reflective layer (using TaON or TaBNO instead of single-material structures), the etching characteristics are modified to enable simultaneous etching of both the low reflective layer and absorber layer with chlorine-type gases, simplifying the process while maintaining precision.
3Measurement precision
If the low reflective layer is made with certain materials to achieve low reflectance, then detection sensitivity is improved, but adhesion to resist patterns deteriorates for fine features below 100 nm
Solution Approach 1:
The low reflective layer is segmented into two functional layers: the first layer (TaON or TaBNO) optimized for optical properties (low reflectance) and the second layer (SiN) optimized for adhesion properties. This segmentation allows the second layer to provide reliable adhesion to resist patterns for fine features while the first layer maintains the low reflectance characteristic.
Solution Approach 2:
The composite structure combines TaON/TaBNO material (providing low reflectance) with SiN material (providing good adhesion to resist). The SiN layer specifically addresses the adhesion problem for fine-pitch patterns while the TaON/TaBNO layer maintains the optical performance, creating a composite structure that satisfies both requirements.
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 configuration achieves higher etching rates and improved resist pattern adhesion, enabling finer patterning and simplifying the etching process while reducing contamination and adhesion issues.
Implementation Method 1
a reflective layer to reflect EUV light... it is common to use a multilayer reflective film having a high refractive index layer and a low refractive index layer alternately stacked to have the light reflectance improved
Implementation Method 2
an absorber layer to absorb EUV light... a material having a high absorption coefficient to EUV light
Implementation Method 3
a low reflective layer to an inspection light... to increase the sensitivity of the detection of mask pattern, the contrast is required to be increased
Data Source
AI summary
To provide an EUV mask blank provided with a low reflective layer, which has excellent properties as an EUV mask blank. A reflective mask blank for EUV lithography comprising a substrate, and a reflective layer for reflecting EUV light, an absorber layer for absorbing EUV light and a low reflective layer to an inspection light (wavelength: 190 to 260 nm) for a mask pattern, formed in this order on the substrate, wherein the low reflective layer has a stacked structure having a first layer containing at least 95 at % in total of silicon (Si) and nitrogen (N), and a second layer containing at least 95 at % in total of tantalum (Ta), oxygen (O) and nitrogen (N) or a second layer containing at least 95 at % in total of tantalum (Ta) and nitrogen (N), stacked in this order from the absorber layer side.