Self-Aligned Contact Etch Selective Layer Polishing Control
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Solution Overview
Problem
The existing self-aligned contact process for semiconductor devices faces challenges in controlling the thickness of the nitride capping layer due to poor etch selectivity, leading to under- or over-polishing, which can result in electrical shorts or opens, affecting yield and performance.
Innovation Solution
Incorporating a sacrificial etch selective layer, comprising a liner and a fill layer, such as cobalt or ruthenium, to provide precise polishing control of the nitride capping layer, ensuring accurate thickness and preventing under- or over-polishing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a polishing step is used to remove the nitride capping layer overburden and expose adjacent trench locations, then the nitride capping layer thickness is reduced to expose ILD oxide, but poor etch selectivity between the nitride capping layer and ILD oxide results in under- or over-polishing
Solution Approach 1:
An etch selectivity enhancement layer is introduced as an intermediary between the nitride capping layer and the ILD oxide. This layer has superior etch selectivity differences from both the nitride capping layer and ILD oxide, enabling precise polishing control. The enhancement layer acts as a mediator that facilitates selective removal of the nitride capping layer while protecting the ILD oxide from being etched, thereby resolving the poor etch selectivity issue.
Solution Approach 2:
The etch selectivity enhancement layer is formed in advance before the polishing step. This preliminary action prepares the structure with a layer that will guide the polishing process, ensuring that the nitride capping layer is removed to the correct depth while preventing over- or under-polishing. The enhancement layer is strategically deposited on the ILD oxide surface before subsequent processing steps.
2Manufacturing precision
If under-polishing occurs, then nitride material remains over the ILD oxide blocking etching, resulting in incomplete source/drain contact, but if over-polishing occurs, then insufficient nitride material remains over the gate structure causing electrical short
Solution Approach 1:
The etch selectivity enhancement layer serves as a mediator that provides a clear etching boundary. During the polishing step, this layer enables selective removal of the nitride capping layer while stopping before etching the ILD oxide. The enhancement layer's superior etch selectivity creates a well-defined interface that guides the polishing process to the precise desired depth, preventing both under- and over-polishing conditions.
Solution Approach 2:
The invention changes the etching parameters by introducing a layer with different etch selectivity characteristics. The etch selectivity enhancement layer has been specifically chosen or engineered to exhibit significantly different etch rates compared to both the nitride capping layer and ILD oxide. This parameter change transforms the polishing process from one with poor selectivity to one with precise control, allowing reliable source/drain contact formation.
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 the robustness of the self-aligned contact process by allowing selective etching and polishing, thereby improving the formation of source/drain contacts and reducing the risk of electrical failures.
Implementation Method 1
a polishing step is used to remove the dielectric layer overburden and expose the etch stop layer
Data Source
AI summary
In a self-aligned contact (SAC) process, a sacrificial etch stop layer is embedded over source/drain regions, i.e., directly over an interlayer dielectric (IDL) disposed over source/drain regions to enable polishing of a nitride capping layer with respect to the interlayer dielectric. The sacrificial etch stop layer may comprise cobalt metal, and is adapted to be removed and replaced with additional ILD material after controlled polishing of the nitride capping layer.