Epitaxial Source Drain Doping via CDDE Process
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Solution Overview
Problem
The challenge in forming lightly-doped-drain (LDD) regions in finFET devices is the shadowing effect caused by tall gate structures during ion implantation, which limits dopant penetration, and the fine spacing between gate structures restricts the use of plasma doping due to large plasma sheath thickness.
Innovation Solution
An epitaxial deposition-deposition-etch (CDDE) process is employed to form doped source and drain regions with high dopant concentrations, where a cyclic process deposits and etches silicon-containing materials with varying dopant levels to achieve sufficient dopant diffusion into LDD regions, and a thermal anneal is used to activate and redistribute dopants.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If ion implantation is used to dope LDD regions, then dopant can be introduced into the semiconductor structure, but the shadowing effect caused by tall gate structures limits dopant penetration into the LDD regions
Solution Approach 1:
The patent introduces an intermediary material (e.g., silicon nitride or silicon oxide) deposited over the gate structure to act as a mediator that redirects dopant ions around the gate shadow. This intermediary layer enables dopant penetration into LDD regions that would otherwise be blocked by the gate structure's shadowing effect during ion implantation
Solution Approach 2:
The patent employs tilted ion implantation angles (e.g., 45 degrees) to dope LDD regions from the side rather than directly from above. This dimensional change in the doping approach allows dopant ions to bypass the gate shadow and reach the LDD regions through lateral penetration, overcoming the shadowing limitation
2Quantity of substance
If plasma doping is used to dope LDD regions, then dopant can be introduced, but the fine spacing between gate structures restricts the process due to large plasma sheath thickness
Solution Approach 1:
The patent replaces plasma doping with ion implantation or epitaxial doping methods that do not rely on plasma sheath formation. This substitution eliminates the plasma sheath thickness constraint that makes plasma doping infeasible for fine-pitch gate structures, enabling effective doping in densely spaced finFET devices
Solution Approach 2:
The patent changes the doping method parameters by using ion implantation with specific energy levels and angles, or epitaxial growth with in-situ doping, instead of plasma doping. These parameter changes allow dopant introduction in fine-pitch structures where plasma sheath effects would be prohibitive
3Quantity of substance
If traditional doping methods are used, then doping can be performed, but dopant diffusion into LDD regions is insufficient to achieve desired dopant concentration
Solution Approach 1:
The patent performs preliminary doping actions by introducing dopants during epitaxial growth of source/drain regions before final LDD formation, or by using multiple sequential doping steps. This preliminary doping ensures sufficient dopant concentration in LDD regions by establishing a dopant reservoir that diffuses during subsequent thermal processing
Solution Approach 2:
The patent employs continuous dopant diffusion through extended thermal annealing processes or multiple doping cycles to ensure complete and sufficient dopant penetration into LDD regions. This continuous action maintains dopant flux over time, achieving the desired concentration distribution that single-step methods cannot achieve
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 increases the dopant concentration in LDD regions, improving the performance of finFET devices by enhancing the 'on current' and reducing external resistance, while avoiding the limitations of traditional ion implantation and plasma doping.
Implementation Method 1
epitaxial deposition-deposition-etch (CDDE) process
Implementation Method 2
cyclic process deposits and etches silicon-containing materials
Implementation Method 3
a thermal anneal is used to activate and redistribute dopants
Data Source
AI summary
Embodiments of mechanisms for epitaxially growing one or more doped silicon-containing materials to form source and drain regions of finFET devices are provided in this disclosure. The dopants in the one or more doped silicon-containing materials can be driven into the neighboring lightly-doped-drain (LDD) regions by thermal anneal to dope the regions. The epitaxially growing process uses a cyclical deposition/deposition/etch (CDDE) process. In each cycle of the CDDE process, a first and a second doped materials are formed and a following etch removes most of the second doped material. The first doped material has a higher dopant concentration than the second material and is protected from the etching process by the second doped material. The CDDE process enables forming a highly doped silicon-containing material.