Reflective Mask Blank Charge Dissipation for EUV Lithography
Solution Overview
Problem
Reflective mask blanks for EUV lithography experience high processing errors during charged particle beam processing due to charging issues caused by insulating layers, particularly the etching mask layer.
Innovation Solution
The reflective mask blank is designed with a configuration where the internal electrical resistance between the outermost layer and the protective film is kept at 100 kΩ or lower, and any layer between the outermost layer and the protective film is an insulating layer with a sheet resistance of 1.0×10^3 Ω/sq. or higher, ensuring easy charge transfer and minimizing processing errors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If an insulating layer (etching mask layer) is provided on the outermost side of the reflective mask blank, then the layer provides protective or functional benefits, but charging occurs during charged particle beam processing causing large processing errors
Solution Approach 1:
A conductive layer is introduced as an intermediary between the insulating outermost layer and the substrate. This conductive layer mediates charge dissipation by providing a pathway for accumulated charges to be discharged to the grounded substrate, thereby preventing charging artifacts during charged particle beam processing while preserving the protective function of the insulating outermost layer.
Solution Approach 2:
The electrical conductivity parameter of the outermost layer structure is changed by adding the conductive layer. The overall electrical resistance of the outermost layer is reduced from insulating to conductive state, enabling charge dissipation during processing while maintaining the structural and protective integrity of the original insulating layer.
2Reliability
If the outermost layer is made insulating to prevent charging, then charging is suppressed, but processing errors increase due to charge accumulation
Solution Approach 1:
The conductive layer serves as a mediator that allows controlled charge dissipation. It enables the insulating outermost layer to maintain its charge-stable properties during normal operation while providing a discharge pathway through the conductive layer to the grounded substrate, preventing charge accumulation that causes processing errors.
3Use of energy by moving object
If a multilayer structure is used to improve EUV light reflection, then optical performance is enhanced, but processing complexity increases during patterning
Solution Approach 1:
The multilayer reflective film is segmented into alternating high-refractive-index and low-refractive-index layers with specific thicknesses. This segmentation creates a periodic structure that constructively interferes to enhance EUV light reflection while maintaining manageable processing complexity through standardized deposition techniques for each layer.
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 significantly reduces processing errors in charged particle beam processing by preventing charging of the outermost layer, thereby ensuring accurate patterning of the absorber film.
Implementation Method 1
a multilayer reflective film for reflecting EUV light
Implementation Method 2
a phase shift film that causes a phase shift in EUV light passing therethrough and lowers the EUV light reflectance by interference of the phase-shifted EUV lights
Implementation Method 3
an absorber film formed on the multilayer reflective film to absorb EUV light
Implementation Method 4
a conductive layer formed on the absorber film and having a sheet resistance of lower than 1.0×103 Ω/sq.
Data Source
AI summary
Provided is a reflective mask blank that is small in processing error in charged particle beam processing. A reflective mask blank (10a) includes a substrate (11), a multilayer reflective film (12) for reflecting EUV light, a protective film (13) and an absorber film (14) having a single-layer structure or a multilayer structure, wherein: any layer between the protective film (13) and the outermost layer located on the outermost side of the reflective mask blank (10a) opposite from the substrate (11) is an insulating layer having a sheet resistance of 1.0×103 Ω/sq. or higher; and an internal electrical resistance between a surface of the outermost layer opposite from the substrate (11) and the protective film (13) is 100 kΩ or lower.