Carbon-Containing Cap Epitaxial Layers for Sharper Doping Profiles
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Solution Overview
Problem
High phosphorous doping in semiconductor devices leads to dopant diffusion, making it challenging to control the doping profile and achieve low contact resistance in source/drain regions of n-type metal-oxide semiconductor (MOS) devices.
Innovation Solution
A semiconductor structure and method involving a stack of alternating doped semiconductor epitaxial layers and cap epitaxial layers, where the doped layers include silicon with carrier dopants and the cap layers include silicon and carbon, un-doped with carrier dopants, are formed using cyclic deposition and etch processes to prevent dopant diffusion and enhance epitaxial growth, resulting in a sharper doping profile and improved electron mobility.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If high phosphorous doping is used to reduce contact resistance, then contact resistance decreases, but dopant diffusion increases making doping profile control difficult
Solution Approach 1:
The patent divides the doped semiconductor layer into multiple thin epitaxial layers separated by undoped cap layers. This segmentation allows high phosphorous doping concentration in each doped layer while the cap layers act as barriers to prevent dopant diffusion between layers, thus maintaining both low contact resistance and precise doping profile control.
Solution Approach 2:
The undoped cap layers serve as intermediary barriers between the phosphorous-doped epitaxial layers. These cap layers prevent direct diffusion of phosphorous dopants between adjacent doped layers, enabling high doping concentrations without losing control over the doping profile.
2Manufacturing precision
If multiple deposition and etch cycles are performed to form alternating doped and cap layers, then doping profile precision improves, but process complexity increases
Solution Approach 1:
The patent employs periodic cycles of deposition and etch processes to form the alternating stack of doped epitaxial layers and cap layers. Each cycle deposits a doped layer followed by a cap layer, then selectively etches portions. This periodic repetition enables precise control of the doping profile through multiple thin layers while using standardized process modules.
Solution Approach 2:
The patent changes process parameters including deposition thickness, etch selectivity, and cycle repetition to achieve the desired multi-layer structure. By adjusting these parameters, precise control over the doping profile is achieved while managing process complexity through parameter optimization rather than fundamentally different process 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
The solution effectively prevents dopant diffusion, enabling a sharper doping profile and enhanced electron mobility, leading to higher conductivity in semiconductor devices.
Implementation Method 1
The cap epitaxial layer includes silicon and carbon and is not doped with carrier dopants. The cap epitaxial layer prevents migration of carrier dopants from the doped semiconductor epitaxial layer.
Implementation Method 2
Due to tensile strain induced in the cap epitaxial layer, an electron mobility can be enhanced, thus leading to high conductivity in its device application.
Data Source
AI summary
A semiconductor structure includes a stack of alternating doped semiconductor epitaxial layers and cap epitaxial layers formed on a substrate. Each doped semiconductor epitaxial layer includes silicon having carrier dopants, and each cap epitaxial layer includes silicon and carbon un-doped with carrier dopants.