Composite Hardmask Structure for High-Aspect-Ratio Etching
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Solution Overview
Problem
The challenge of scaling down semiconductor devices is exacerbated by the use of traditional hardmasks, which can cause wafer bowing and lateral etching of sidewalls, leading to handling issues and reduced device density due to reentrant cavities.
Innovation Solution
A hardmask layer comprising alternating compressive and tensile sub-layers, such as tungsten-containing and silicon nitride layers, is used to mitigate wafer bowing and protect sidewalls during high aspect ratio etches, ensuring precise etching without reentrant cavities.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a reduced thickness hardmask is employed to improve selectivity, then etching selectivity is improved, but lateral etching of sidewalls occurs
Solution Approach 1:
The hardmask layer is constructed as a composite structure with alternating compressive and tensile sub-layers. This composite design provides both the thin profile needed for etching selectivity and the mechanical strength to prevent sidewall collapse during high aspect ratio etching processes.
2Object-affected harmful factors
If the thickness of the hardmask is increased to protect sidewalls, then sidewall protection is improved, but wafer stress increases causing bowing
Solution Approach 1:
The hardmask structure uses alternating compressive and tensile sub-layers that act as counterbalancing forces. The tensile sub-layers compensate for the compressive stress in the compressive sub-layers, resulting in a net-zero stress state that prevents wafer bowing while maintaining sufficient thickness for sidewall protection.
Solution Approach 2:
The invention changes the stress parameter distribution within the hardmask layer by introducing alternating compressive and tensile sub-layers. This parameter modification allows the hardmask to maintain a controlled thickness that provides sidewall protection without inducing excessive wafer stress or bowing.
3Ease of manufacture
If traditional hardmasks are used, then fabrication process is simple, but wafer bowing and handling issues occur
Solution Approach 1:
The alternating compressive and tensile sub-layer structure creates a self-balancing stress system that eliminates wafer bowing. This composite hardmask design maintains compatibility with existing fabrication processes while dramatically improving wafer handling characteristics during high aspect ratio etching.
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 approach enhances device density and reduces wafer stress by maintaining vertical etching profiles, preventing sidewall damage, and allowing for efficient fabrication of memory devices like NAND flash and DRAM.
Implementation Method 1
a deposition of an oppositely stressed (e.g., tensile) material such as a nitride between alternating compressive hardmask layers can increase a thickness of the hardmask to avoid bowing
Implementation Method 2
High aspect ratio (HAR) etches can extend through the various layers of to form connections to or therebetween. The etchants can be substantially anisotropic
Data Source
AI summary
A method for fabricating semiconductor devices is disclosed. The method includes forming a stack over a substrate. The method includes forming a hardmask layer over the stack, the hardmask layer comprising a first tungsten containing sub-layer, and at least one compressive sub-layer and at least one tensile sub-layer. The method includes forming a patternable layer over the hardmask layer. The method includes etching the hardmask layer according to the patternable layer.