Transistor Spacer Isolation for Controlled Oxidation Removal
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Solution Overview
Problem
The existing 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
Treatment of spacer material with oxygen or nitrogen radicals using a microwave plasma to oxidize or nitridize the spacer material, allowing for controlled removal and preventing oxidation of SiGe and Si layers, thereby maintaining a co-planar surface topography and reducing material loss.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If traditional oxidation process is used to oxidize spacer material, then spacer material is successfully oxidized for removal, but SiGe and Si nano-sheet or nano-wire layers undergo undesirable oxidation leading to material loss and process variability
Solution Approach 1:
The patent applies local quality by creating a non-uniform oxygen concentration distribution within the spacer layer through atomic layer deposition (ALD). The oxygen concentration is highest at the outer surface and decreases toward the inner surface, enabling selective oxidation removal of the outer spacer material while protecting the inner SiGe and Si layers from oxidation. This gradient structure allows different regions of the spacer layer to have different oxidation resistance properties.
Solution Approach 2:
The patent implements preliminary action by pre-forming the oxygen concentration gradient in the spacer layer before the oxidation removal process. The ALD process deposits oxygen-containing species that create a controlled concentration profile in advance, so that when oxidation is applied, the desired selective removal pattern is achieved without directly exposing the SiGe and Si layers to harsh oxidation conditions.
2Productivity
If oxidation process is applied to remove spacer material, then spacer material is removed effectively, but surface topography becomes non-co-planar and transistor performance varies
Solution Approach 1:
The oxygen concentration gradient creates local quality differences where the outer regions of the spacer layer are more susceptible to oxidation and removal, while inner regions maintain structural integrity. This results in a controlled removal pattern that preserves co-planar surface topography across the transistor structure, ensuring uniform electrical characteristics.
Solution Approach 2:
The ALD process creates a replicated oxygen concentration profile throughout the spacer layer thickness, with each layer depositing oxygen species that contribute to the overall gradient. This copying mechanism ensures consistent oxidation behavior across the entire spacer structure, leading to uniform surface topography after removal.
3Ease of manufacture
If conventional oxidation methods are used, then process is simple and fast, but oxidation penetrates deeply into SiGe and Si layers causing material loss
Solution Approach 1:
The patent changes the parameter of oxygen concentration distribution from uniform to gradient-based. By controlling the oxygen concentration to decrease from outer to inner regions of the spacer layer, the oxidation process becomes selective and stops before penetrating deeply into the SiGe and Si layers, thus preventing material loss while maintaining process feasibility.
Solution Approach 2:
The spacer layer functions as a composite structure with varying oxygen concentration zones. The outer high-oxygen region facilitates easy removal, while the inner low-oxygen region acts as a protective barrier, creating a multi-functional composite that combines ease of manufacture with material protection.
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 improves oxidation control, reduces surface topography, and maintains the integrity of Si and SiGe layers, enhancing the transistor's performance by minimizing material loss and process variability.
Implementation Method 1
Treatment of spacer material with oxygen or nitrogen radicals using a microwave plasma to oxidize or nitridize the spacer material
Implementation Method 2
oxidize or nitridize the spacer material
Implementation Method 3
oxidize or nitridize the spacer material
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.