Low-Resistivity Contact Formation via Selective TiSiN Etching
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Solution Overview
Problem
Traditional contact formation processes in semiconductor devices result in high resistivity due to the use of titanium silicon nitride (TiSiN) layers, which are challenging to deposit uniformly and require costly processes, leading to poor connections between front-end-of-the-line (FEOL) and back-end-of-the-line (BEOL) structures.
Innovation Solution
A method involving selective etching processes to remove the TiSiN layer and deposit a low-resistivity metal cap, followed by a metal gap fill material, using chemical vapor deposition (CVD) and plasma-enhanced techniques to form low-resistivity contacts.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conformal titanium silicide (TiSi) layer is formed and nitrided to form titanium silicon nitride (TiSiN) to prevent oxidation, then oxidation protection is improved, but contact resistivity increases to approximately 300μ ohms-cm
Solution Approach 1:
The patent removes the TiSiN layer from the contact region using selective etching processes. The gradient etch process selectively removes TiSiN from contact regions while preserving it in field regions, eliminating the high resistivity barrier in the contact path while maintaining oxidation protection in non-contact areas.
Solution Approach 2:
The patent applies different treatments to different regions: TiSiN is removed from contact regions to achieve low resistivity, while TiSiN is retained in field regions to provide oxidation protection. This local differentiation resolves the contradiction between needing oxidation protection and avoiding high contact resistance.
2Reliability
If a bilayer of TiSi and TiSiN is formed over field, sidewalls and contact regions, then oxidation protection is improved, but the complexity of the process increases due to pull-back requirements
Solution Approach 1:
The patent segments the TiSiN removal process into two distinct stages: a gradient etch process that selectively removes TiSiN from contact regions, and a subsequent pull-back process that removes remaining TiSiN from field regions. This segmentation allows precise control over where TiSiN is removed, simplifying the overall process by eliminating the need for complex masking and re-deposition steps.
Solution Approach 2:
The gradient etch process is performed as a preliminary step before the pull-back process, pre-positioning the TiSiN layer for selective removal from contact regions. This preliminary action reduces the workload for the subsequent pull-back process and simplifies the integration flow by preparing the structure in advance.
3Reliability
If PVD tungsten is deposited to form a capping layer, then oxidation protection is improved, but uniform deposition on high sloped areas is difficult due to PVD technology limitations
Solution Approach 1:
The patent replaces the PVD mechanical deposition system with a chemical vapor deposition (CVD) system for forming the TiSiN layer. CVD provides superior conformal coverage on high sloped areas and complex three-dimensional structures, achieving uniform deposition where PVD fails due to line-of-sight limitations.
4Reliability
If thick TiN/PVD W is used for contact formation, then oxidation protection is improved, but the cost increases due to expensive ALD deposition and pull-back processes
Solution Approach 1:
The patent uses a thinner TiSiN layer that is selectively removed from contact regions, replacing the need for thick TiN/PVD W combinations. This approach uses less material and eliminates expensive pull-back processes, reducing manufacturing cost while maintaining adequate oxidation protection in field regions where TiSiN is retained.
Solution Approach 2:
The patent changes the thickness parameter of the TiSiN layer from thick (in traditional processes) to thin, and changes the deposition method from ALD/PVD to CVD. These parameter changes reduce material consumption and processing costs while achieving the same functional outcomes through selective removal strategies.
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
The method reduces contact resistance and simplifies the process, ensuring reliable connections between FEOL and BEOL structures by maintaining selectivity towards the capping layer, thereby improving semiconductor device performance.
Implementation Method 1
exposing the first metal containing layer and the second metal containing layer to an etchant gas containing plasma to remove at least a portion of the first metal containing layer and the second metal containing layer from the sidewalls
Implementation Method 2
The deposition operation including forming a carbon-containing passivation layer over the first metal containing layer and the second metal containing layer
Implementation Method 3
exposing at least the carbon-containing passivation layer and the second metal containing layer to a hydrogen plasma so that a portion of the carbon-containing passivation layer and a portion of the second metal containing layer is etched away
Implementation Method 4
exposing the first metal containing layer and the carbon-containing passivation layer with hydrogen plasma to remove at least a portion of the carbon-containing passivation layer
Data Source
AI summary
The present disclosure generally provides methods of forming contact structures on semiconductor substrates. The methods include forming a first metal containing layer on a surface of the contact structure and forming a second metal containing layer over the first metal containing layer. Performing a gradient etch process including exposing the first metal containing layer and the second metal containing layer to an etchant gas containing plasma to remove at least a portion of the first metal containing layer and the second metal containing layer from the sidewalls. Performing a selective etch process including a deposition operation, an etch operation and a trim operation. Performing a post etch treatment process including exposing the first metal containing layer and a carbon-containing passivation layer with a hydrogen plasma to remove at least a portion of the carbon-containing passivation layer.