GAA Inner Spacer Formation With Plasma Oxidation Control
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Solution Overview
Problem
The existing methods for forming gate-all-around (GAA) field effect transistors (FETs) face challenges with undesirable oxidation of silicon-germanium (SiGe) and silicon (Si) nano-sheet or nano-wire layers during the spacer material oxidation process, leading to material loss and process variability, which affects the transistor's effective channel length and performance.
Innovation Solution
The use of oxygen or nitrogen radicals in a microwave plasma treatment to convert portions of the spacer material into an oxide or nitride, allowing for selective removal and controlling the oxidation process at a lower temperature, thereby preventing unwanted oxidation of SiGe and Si layers and improving surface topography.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If steam anneal or plasma oxidation processes are used to oxidize spacer material, then the spacer material is successfully converted into oxide for selective removal, but unwanted oxidation of SiGe and Si nano-sheet or nano-wire layers occurs, leading to material loss and process variability
Solution Approach 1:
A sacrificial oxide layer is introduced as an intermediary between the spacer material and the SiGe/Si nano-sheet or nano-wire layers. This sacrificial oxide layer selectively protects the SiGe and Si layers from unwanted oxidation during the spacer material oxidation process, while allowing the spacer material to be oxidized and removed. The sacrificial oxide layer acts as a mediator that enables selective oxidation of the spacer material without damaging the underlying semiconductor layers.
Solution Approach 2:
The oxidation process parameters are changed by using atomic layer deposition (ALD) at controlled temperatures and oxygen exposure conditions to form the sacrificial oxide layer with specific properties. The ALD process parameters (temperature, oxygen partial pressure, deposition rate) are optimized to create an oxide layer that is selectively removable and provides appropriate protection to the SiGe and Si layers during subsequent oxidation steps.
2Shape
If conventional oxidation processes are used, then spacer material oxidation proceeds, but surface topography becomes non-co-planar and parasitic capacitance increases
Solution Approach 1:
The sacrificial oxide layer is formed in advance before the spacer material oxidation process. This preliminary formation of the protective oxide layer ensures that when the spacer material is subsequently oxidized and removed, the underlying SiGe and Si layers maintain their original surface topography. The pre-formed sacrificial oxide layer prevents surface non-co-planarity and minimizes parasitic capacitance by protecting the semiconductor layers from oxidation-induced surface irregularities.
3Productivity
If higher temperature oxidation is used to accelerate spacer material conversion, then oxidation rate increases, but unwanted oxidation of SiGe and Si layers increases and material loss worsens
Solution Approach 1:
The sacrificial oxide layer serves as a protective intermediary that enables the use of higher temperature oxidation processes without causing material loss. By introducing this intermediary layer, the system can tolerate higher oxidation temperatures and rates because the sacrificial oxide layer absorbs the oxidative attack, protecting the SiGe and Si layers from damage while allowing faster spacer material removal.
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 oxidation control, reduces material loss, and maintains a co-planar surface topography, leading to improved transistor performance by minimizing parasitic capacitance and ensuring precise channel length, thus addressing the limitations of steam anneal or plasma oxidation processes.
Implementation Method 1
oxygen or nitrogen radicals in a microwave plasma treatment to convert portions of the spacer material into an oxide or nitride
Implementation Method 2
oxygen or nitrogen radicals in a microwave plasma treatment
Data Source
AI summary
The present disclosure is directed to method for the fabrication of spacer structures between source/drain epitaxial structures and metal gate structures in nanostructure transistors. The method includes forming a fin structure with alternating first and second nanostructure elements on a substrate. The method also includes etching edge portions of the first nanostructure elements in the fin structure to form spacer cavities, and depositing a spacer layer on the fin structure to fill the spacer cavities. Further, treating the spacer layer with a microwave-generated plasma to form an oxygen concentration gradient within the spacer layer outside the spacer cavities and removing, with an etching process, the treated portion of the spacer layer. During the etching process, a removal rate of the etching process for the treated portion of the spacer layer is based on an oxygen concentration within the oxygen concentration gradient.