EUV Reflective Mask Blank Conductive Underlayer
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Solution Overview
Problem
EUV lithography reflective masks face challenges with charge-up during electron beam inspections, phase defects due to surface irregularities, and out-of-band light reflections, which affect pattern precision and yield in semiconductor manufacturing.
Innovation Solution
A reflective mask blank with a conductive underlying film made of tantalum or ruthenium-based materials, having a thickness of 1-10 nm, is used to prevent charge-up and reduce phase defects, and a multilayer reflective film with alternately layered silicon and molybdenum layers is employed to minimize out-of-band light reflections.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a multilayer reflective film-etched light-shielding band is used in EUV reflective masks, then light-shielding performance is improved, but charge-up occurs during electron beam inspections
Solution Approach 1:
A conductive underlying film is introduced as an intermediary layer between the substrate and the multilayer reflective film. This conductive film serves as a mediator that provides electrical grounding during electron beam inspections, preventing charge-up while not interfering with the light-shielding function of the etched multilayer reflective film bands.
Solution Approach 2:
The mask structure is segmented into distinct functional layers: the substrate, the conductive underlying film, the multilayer reflective film, and the absorber film. This segmentation allows the conductive underlying film to independently handle electrical grounding without compromising the optical functions of other layers.
2Ease of manufacture
If the surface of the underlying film is not sufficiently smooth, then manufacturing is easier, but phase defects occur due to surface irregularities
Solution Approach 1:
The conductive underlying film is formed with high surface smoothness as a preliminary step before depositing the multilayer reflective film. This preliminary action ensures that the foundation is properly prepared, preventing phase defects in the subsequent reflective film without requiring excessive complexity in the manufacturing process.
3Productivity
If the multilayer reflective film is used to reflect EUV light, then pattern transfer is enabled, but out-of-band light reflections occur
Solution Approach 1:
The optical parameters of the multilayer reflective film are optimized to achieve high reflectivity at the EUV wavelength (13.5 nm) while minimizing reflection at other wavelengths. By carefully controlling the thickness and material composition of alternating high and low refractive index layers, the film reflects EUV light effectively for pattern transfer while suppressing out-of-band light reflections that could cause defects.
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 enables high-sensitivity defect inspections, reduces phase defects, and minimizes out-of-band light reflections, resulting in improved pattern transfer precision and increased yield in semiconductor device manufacturing.
Implementation Method 1
a conductive underlying film which is formed on a substrate and which is adjacent to a multilayer reflective film
Implementation Method 2
a multilayer reflective film which reflects exposure light and which is layered on the conductive underlying film
Implementation Method 3
an absorber film which absorbs exposure light and which is layered on the multilayer reflective film
Data Source
AI summary
The present invention aims to provide a reflective mask blank and a reflective mask which have a highly smooth multilayer reflective film as well as a low number of defects, and methods of manufacturing the same, and aims to prevent charge-up during a mask defect inspection using electron beams.The present invention provides a reflective mask blank for EUV lithography in which a conductive underlying film, a multilayer reflective film that reflects exposure light, and an absorber film that absorbs exposure light are layered on a substrate, wherein the conductive underlying film is a single-layer film made of a tantalum-based material or a ruthenium-based material with a film thickness of greater than or equal to 1 nm and less than or equal to 10 nm that is formed adjacent to the multilayer reflective film, or the conductive underlying film is a multilayer film including a layer of a tantalum-based material with a film thickness of greater than or equal to 1 nm and less than or equal to 10 nm that is formed adjacent to the multilayer reflective film and a layer of a conductive material that is formed between the layer of the tantalum-based material and the substrate. The present invention also provides a reflective mask manufactured using the reflective mask blank. Furthermore, a semiconductor device is manufactured using the reflective mask.