Replacement Source/Drain Structure for Nanosheet FET Current Loss
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Solution Overview
Problem
The challenge in semiconductor manufacturing is the degradation of transistor current due to epitaxial damage during source/drain formation in nanosheet FETs, leading to increased strain on the channel and higher source/drain contact resistance.
Innovation Solution
The use of a SiB layer and lower Ge concentration SiGe layer is followed by growing a high Ge concentration layer to reduce strain on the channel, and subsequently replacing the SiGe sacrificial source/drain with pure Ge or high Ge concentration source/drain, increasing lattice constant and lowering contact resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If epitaxial source/drain formation is used in nanosheet FETs, then source/drain structure is formed, but transistor current degrades due to epitaxial damage and increased strain on channel
Solution Approach 1:
The source/drain structure is divided into two distinct parts: a sacrificial source/drain formed during epitaxial growth and a replacement source/drain formed later. This segmentation allows the sacrificial structure to serve its structural purpose during fabrication while the replacement structure provides the optimal electrical properties, thereby resolving the contradiction between forming a source/drain structure and avoiding epitaxial damage that degrades transistor current.
Solution Approach 2:
The harmful epitaxial damage is extracted from the final source/drain structure by using a sacrificial source/drain that is subsequently removed and replaced. The sacrificial structure is formed during epitaxial growth but is then taken out and replaced with a non-epitaxial replacement source/drain, eliminating the negative effects of epitaxial damage while maintaining the benefits of having a defined source/drain structure during fabrication.
2Reliability
If SiGe sacrificial source/drain is replaced with pure Ge or high Ge concentration source/drain, then contact resistance decreases, but manufacturing process complexity increases
Solution Approach 1:
The sacrificial source/drain is formed in advance during the epitaxial growth process, establishing the basic source/drain structure and positioning before the replacement source/drain is formed. This preliminary action allows subsequent replacement with pure Ge or high Ge concentration material to achieve low contact resistance, while the preliminary structure guides the replacement process to maintain manufacturability despite the additional steps.
Solution Approach 2:
The SiGe sacrificial source/drain acts as an intermediary structure that facilitates the formation of the final replacement source/drain. It provides a template and structural framework during fabrication, enabling controlled replacement with pure Ge or high Ge concentration material. This intermediary approach reduces contact resistance while keeping the manufacturing process manageable by providing clear process steps and material transitions.
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 drive current and reduces source/drain contact resistance, improving the performance of nanosheet FETs by increasing strain on the channel and boosting current output.
Implementation Method 1
forming a sacrificial source/drain in the source/drain opening, the sacrificial source/drain including a SiB layer and a lower Ge concentration SiGe layer
Implementation Method 2
growing a high Ge concentration layer to reduce strain on the channel, and subsequently replacing the SiGe sacrificial source/drain with pure Ge or high Ge concentration source/drain, increasing lattice constant
Data Source
AI summary
A device and method of forming a device are provided. The method includes forming a stack of nanostructure channels over a substrate by forming a source/drain opening. The method also includes forming a sacrificial source/drain in the source/drain opening. The method further includes increasing tensile strain of the stack of nanostructure channels by replacing the sacrificial source/drain with a replacement source/drain having germanium concentration that exceeds that of the sacrificial source/drain.