Refractory Metal Source/Drain Cap for Low-Resistance Contacts
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Solution Overview
Problem
During the fabrication of transistors, especially p-type transistors, the etching process can damage the source and drain regions and surrounding layers, leading to higher contact resistance, which hampers the performance of the transistor.
Innovation Solution
The use of thermally-stable refractory metals, such as tungsten or molybdenum, as a protective cap over the source and drain regions, particularly after epitaxial growth of silicon germanium with high germanium and boron concentrations, to shield these regions from damage during subsequent processing steps.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If etching process is used to form source/drain contacts, then contact openings can be formed, but the source and drain regions and surrounding layers are damaged leading to higher contact resistance
Solution Approach 1:
A refractory metal cap layer is deposited over the source and drain regions before the etching process. This preliminary protective action prevents damage to the underlying layers during subsequent etching steps, thereby maintaining low contact resistance while enabling contact opening formation.
Solution Approach 2:
The refractory metal cap layer acts as an intermediary protective barrier between the etching process and the source/drain regions. This intermediate layer absorbs the harmful effects of etching, protecting the underlying sensitive layers while allowing the etch to proceed for contact opening formation.
2Reliability
If refractory metal cap is added to protect source and drain regions, then contact resistance is reduced, but device structure becomes more complex
Solution Approach 1:
The refractory metal cap layer serves multiple functions simultaneously: it protects the source and drain regions from etching damage, provides a diffusion barrier, and can serve as part of the contact structure itself. This multi-functionality reduces the need for additional separate protective layers, thereby limiting the increase in device complexity.
3Reliability
If high germanium and boron concentrations are used in capping layer, then contact resistance is reduced, but thermal stability during processing is compromised
Solution Approach 1:
The solution employs a composite capping structure combining a high germanium/boron layer (for low contact resistance) with an overlying refractory metal layer (for thermal stability). This composite structure allows the high-performance semiconductor layer to maintain its beneficial electrical properties while being protected from thermal degradation during subsequent processing steps.
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 effectively reduces source and drain contact resistance by preserving the high germanium/boron capping layer, enhancing the transistor's switching speed and maintaining a larger metal contact area, thus improving overall transistor performance.
Implementation Method 1
a refractory metal cap layer 310 that protects the source and drain regions 306 from damage during etching and cleaning processes
Implementation Method 2
after epitaxial growth of silicon germanium with high germanium and boron concentrations
Data Source
AI summary
Semiconductor structures having a source and/or drain with a refractory metal cap, and methods of forming the same, are described herein. In one example, a semiconductor structure includes a channel, a gate, a source, and a drain. The source and drain contain silicon and germanium, and one or both of the source and drain are capped with a semiconductor cap and a refractory metal cap. The semiconductor cap is on the source and/or drain and contains germanium and boron. The refractory metal cap is on the semiconductor cap and contains a refractory metal.