Metal Shell Hard Masks for 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 low selectivity and stress issues, leading to distorted sidewalls and inadequate pattern integrity.
Innovation Solution
A method using a metal shell hard mask comprising multiple refractory metal layers with low stress amorphous carbon or silicon layers, employing anisotropic etching to form recesses with varying aspect ratios, providing high selectivity and minimal stress.
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 etch selectivity is inadequate leading to poor pattern integrity
Solution Approach 1:
The patent divides the mask structure into multiple segments: a base hard mask layer, intermediate metal layers (TiN, TaN), and a top photoresist layer. Each layer serves a specific function - the base layer provides structural support and initial pattern definition, the intermediate metal layers provide high etch selectivity for deep trenches, and the top photoresist layer enables final pattern transfer. This segmented approach resolves the contradiction by combining the simplicity of photoresist patterning with the selectivity of metal hard masks.
Solution Approach 2:
The patent employs a composite mask structure combining organic photoresist with inorganic metal layers (TiN, TaN, W). The photoresist provides ease of patterning while the metal layers provide high etch selectivity and structural stability. This composite material approach allows the system to simultaneously achieve pattern integrity through metal selectivity and manufacturing simplicity through photoresist processing.
2Manufacturing precision
If conventional hard masks are used for deep etching, then etch selectivity improves, but stress issues cause distorted sidewalls
Solution Approach 1:
The patent changes the material parameters of the mask structure by introducing low-stress metal layers (TiN, TaN, W) with controlled stress characteristics. These materials are selected to have low intrinsic stress and appropriate stress signs to counteract etching-induced compressive stresses. By adjusting the thickness and stress parameters of each layer, the system maintains high etch selectivity while preventing sidewall distortion through stress compensation.
Solution Approach 2:
The patent applies beforehand cushioning by incorporating low-stress metal layers that pre-compensate for the compressive stresses that will develop during deep etching. These layers are designed with specific stress characteristics that counteract the etching-induced stresses before they cause sidewall distortion. The stress buffering capacity is built into the mask structure in advance, preventing sidewall bowing and maintaining pattern fidelity throughout the etching process.
3Device complexity
If single-layer hard masks are used, then the structure is simple, but mask erosion occurs during extended etching
Solution Approach 1:
The patent segments the mask into multiple functional layers with different erosion resistances. The base hard mask layer provides initial pattern definition, while overlying metal layers (TiN, TaN, W) with higher etch selectivity protect the underlying layers during extended etching. This segmentation allows each layer to be optimized for its specific function, with the top layers sacrificing themselves to protect the critical pattern definition layers below.
Solution Approach 2:
The patent employs a disposable sacrificial metal layer strategy where the top metal layers are designed to erode preferentially during extended etching, protecting the underlying pattern-critical layers. These sacrificial layers are intentionally made erodible so they can be consumed during the etching process, serving as a protective buffer that maintains pattern integrity while the actual etching of deep trenches occurs.
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
Enables the etching of high aspect ratio features with improved pattern fidelity and depth, reducing sidewall distortion and mask erosion, allowing deeper and more precise semiconductor fabrication.
Implementation Method 1
employing anisotropic etching to form recesses with varying aspect ratios
Implementation Method 2
forming a first metal layer on top of an amorphous mask layer disposed over a substrate
Data Source
AI summary
A method for forming a semiconductor device is disclosed. The method includes forming a first metal layer on top of an amorphous mask layer disposed over a substrate. The method includes forming a second metal layer that extends along vertical sidewalls of an opening in the amorphous mask layer. The method includes forming a first recess partially extending into the substrate using the first metal layer and the second metal layer as a first etch mask. The method includes forming a third metal layer that extends along vertical sidewalls of the first recess. The method includes forming a second recess below the first recess using the first to third metal layers as a second etch mask.