Reflective Mask Blank Convex Backside for EUV Lithography
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Solution Overview
Problem
The semiconductor industry faces challenges with adsorption failure in fixing reflective masks using electrostatic chucks due to substrate warping caused by high compressive stress in multilayer reflective films, leading to pattern distortion and reduced throughput in EUV lithography processes.
Innovation Solution
A reflective mask blank with a convex surface shape on the side opposite to the transfer pattern forming surface, combined with a stress correction film made of tantalum and boron, ensures accurate adsorption by an electrostatic chuck, maintaining flatness and reducing pattern distortion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If a multilayer reflective film with high film density is formed to obtain high reflectance, then the reflectance of EUV light is improved, but the compressive stress in the film increases causing substrate warping and adsorption failure
Solution Approach 1:
A stress correction film is introduced as an intermediary layer between the substrate and the multilayer reflective film. This stress correction film acts as a mediator to counterbalance the compressive stress generated by the high-density multilayer reflective film, preventing substrate warping while allowing the reflective film to maintain its high film density and reflectance.
Solution Approach 2:
The stress correction film provides a counterbalancing stress that opposes the compressive stress of the multilayer reflective film. By forming this counterweight stress in the opposite direction, the net stress on the substrate is reduced to near-zero, preventing warping and adsorption failure while maintaining high reflectance.
2Shape
If the compressive stress of the multilayer reflective film is reduced to improve flatness, then substrate warping is decreased, but the film density decreases causing reduction in reflectance
Solution Approach 1:
The stress correction film serves as an intermediary that decouples the relationship between film density and substrate flatness. It allows the multilayer reflective film to maintain high film density for high reflectance while the stress correction film independently manages the stress balance to achieve substrate flatness.
Solution Approach 2:
The film structure is segmented into two independent functional layers: the multilayer reflective film responsible for high reflectance through high film density, and the stress correction film responsible for stress management and flatness control. This segmentation allows each layer to optimize its specific function without compromising the other.
3Shape
If a stress correction film is formed to correct warping, then substrate flatness is improved, but in-plane stress distribution and film thickness distribution cannot be completely corrected leading to adsorption failure
Solution Approach 1:
The stress correction film utilizes parameter changes in material composition and stress characteristics to achieve effective stress correction. By carefully selecting materials with appropriate stress properties and controlling film formation parameters, the system achieves comprehensive correction of both out-of-plane warping and in-plane stress distribution, enabling successful adsorption.
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 allows for high-accuracy pattern transfer with no pattern distortion, improving the adsorption process and reducing the effective area required for mask flattening, thereby enhancing the overall efficiency of EUV lithography.
Implementation Method 1
a multilayer reflective film 101 having a multilayer film structure is formed on a substrate 100... Exposure light such as a soft X-ray incident on the reflective mask for exposure is reflected at a portion where the multilayer reflective film 101 is exposed
Implementation Method 2
an absorbent layer 103 is formed on the etching stopper layer 102... is not reflected but is absorbed at a portion where the pattern 103a of the absorbent layer is formed
Implementation Method 3
the mask substrate is brought into contact therewith from its outer side and the adsorption spreads toward its inner side... the principle is such that adsorption spreads from a contact point
Data Source
AI summary
To provide a reflective mask blank for exposure that can solve a problem of adsorption failure in fixing a reflective mask using an electrostatic chuck and thus can flatten the surface of the mask using the electrostatic chuck, thereby realizing high-accuracy pattern transfer. In a reflective mask blank for exposure having a multilayer reflective film formed on a board and adapted to reflect exposure light and an absorbent layer formed on the multilayer reflective film and adapted to absorb the exposure light, the shape of a surface of the mask blank on its side opposite to its transfer pattern forming surface is a shape having a convex surface.