Metal Shell Hard Masks for Deep High-Aspect-Ratio Etching
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Solution Overview
Problem
Existing hard masks used for etching high aspect ratio features in semiconductor manufacturing suffer from inadequate selectivity and stress issues, leading to distorted sidewalls and limited depth of etched features.
Innovation Solution
The use of a metal shell hard mask comprising a low stress amorphous mask layer covered by thin metal layers provides high selectivity and minimal stress, allowing for deeper and more precise etching of high aspect ratio trenches and holes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If photoresist patterns are used as etch masks for high aspect ratio features, then the process is simple, but the mask to substrate etch selectivity is inadequate
Solution Approach 1:
The patent uses a composite hard mask structure consisting of multiple layers including photoresist, amorphous carbon, and metal layers (tungsten, titanium nitride). This composite structure combines the advantages of each material: photoresist for pattern definition, amorphous carbon for stress management, and metal layers for high etch selectivity. The multi-layer composite enables both high aspect ratio etching and maintained pattern integrity.
2Length of stationary object
If thick hard mask layers are used to increase etch depth, then the etching depth increases, but stress in the mask layer increases causing sidewall distortion
Solution Approach 1:
The hard mask is segmented into multiple thin layers rather than one thick layer. The structure includes photoresist (50-100 nm), amorphous carbon (50-150 nm), and metal layers (20-50 nm each). This segmentation allows each layer to be thin enough to minimize stress while collectively providing sufficient thickness for deep etching. The stress is distributed across layers rather than concentrated in a single thick layer.
Solution Approach 2:
The patent changes the material parameters of the mask layers by introducing amorphous carbon and thin metal layers with specific stress characteristics. The amorphous carbon layer has low intrinsic stress compared to traditional single-material masks, and the thin metal layers provide high etch selectivity without adding excessive stress. This parameter optimization enables deeper etching while maintaining sidewall straightness.
3Device complexity
If single material hard masks are used, then the structure is simple, but the etch selectivity and stress control are insufficient
Solution Approach 1:
The patent employs a composite hard mask structure with photoresist, amorphous carbon, and metal layers (tungsten, titanium nitride). Each material contributes specific properties: photoresist for UV lithography compatibility, amorphous carbon for low stress and good etch resistance, and metal layers for high etch selectivity. This composite approach achieves superior etch selectivity and stress control compared to single-material masks.
Solution Approach 2:
Different layers of the hard mask have different local qualities optimized for specific functions. The photoresist layer is optimized for pattern definition, the amorphous carbon layer for stress management and lateral protection, and the metal layers for vertical etch selectivity. Each layer's thickness and material properties are locally optimized to fulfill its specific role in the etching process.
Data Source
AI summary
A method for forming a semiconductor device includes forming a first metal layer on top of an amorphous mask layer disposed over a substrate, forming a second metal layer that covers vertical sidewalls of openings in the amorphous mask layer, and etching a pattern in the substrate using the first metal layer and the second metal layer as an etch mask.