Ge-Based Multi-Gate Transistor Source/Drain Diffusion Control
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Solution Overview
Problem
The scaling down of integrated circuits to smaller technology nodes poses challenges with germanium-based multi-gate transistors due to higher dielectric constants leading to worse short channel effects and increased leakage, requiring an abrupt junction dopant profile and high dopant concentrations in source/drain features while preventing dopant diffusion into the channel member.
Innovation Solution
The implementation of a semiconductor device with a source/drain feature that includes an outer epitaxial layer acting as a diffusion retardation layer, formed of germanium doped with boron, and an inner epitaxial feature doped with gallium, which are spaced apart from the channel member, to control short channel effects and reduce parasitic resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If germanium is used to form channel members of MBC transistor, then hole mobility is improved, but dielectric constant increases leading to worse short channel effects and increased leakage
Solution Approach 1:
A silicon germanium sacrificial layer is introduced as an intermediary material between the germanium channel members and the source/drain regions. This sacrificial layer acts as a mediator that prevents direct contact and dopant diffusion from the silicon doped source/drain regions into the germanium channel, thereby resolving the short channel control issue while maintaining the high hole mobility benefit of germanium.
Solution Approach 2:
The problematic direct interface between silicon doped source/drain regions and germanium channel members is extracted/removed by introducing the silicon germanium sacrificial layer. This separation extracts the harmful dopant diffusion pathway while preserving the beneficial electrical properties of the germanium channel.
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 configuration achieves good short channel control and reduced parasitic resistance by preventing dopant diffusion into the channel member, thereby improving the performance of germanium-based multi-gate transistors.
Implementation Method 1
Each of the source/drain features includes an outer epitaxial layer that interfaces the channel member and an inner epitaxial feature spaced apart from the channel member. The outer epitaxial layer serves as a diffusion barrier to prevent diffusion of dopants from the inner epitaxial feature into the channel member.
Implementation Method 2
Each of the source/drain features includes an outer epitaxial layer that interfaces the channel member and an inner epitaxial feature spaced apart from the channel member
Data Source
AI summary
A semiconductor device according to the present disclosure includes a first source/drain epitaxial feature and a second source/drain epitaxial feature each having an outer liner layer and an inner filler layer, a plurality of channel members extending between the first source/drain epitaxial feature and the second source/drain epitaxial feature along a first direction, and a gate structure disposed over and around the plurality of channel members. The plurality of channel members are in contact with the outer liner layer and are spaced apart from the inner filler layer. The outer liner layer comprises germanium and boron and the inner filler layer comprises germanium and gallium.