SiGe Source/Drain Lattice Change Layer for Leakage Control
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Solution Overview
Problem
In the embedded SiGe technology for FETs, the growth of SiGe epitaxy in un-tuck structures is hindered by crystal orientation selectivity, leading to insufficient thickness of SiGe seed and bulk layers, which results in poor contact with metal silicide, causing leakage and increased resistance due to Ni infiltration.
Innovation Solution
A structure and method that includes a semiconductor substrate with recesses for epitaxially growing a SiGe seed and bulk layer, followed by a crystal plane treatment using mixed gases (SiH4, SiH2Cl2, HCl, H2, B2H6, and GeH4) to enhance the SiGe bulk layer growth, and a lattice change layer with a cap layer to improve morphology and prevent NiSi infiltration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If epitaxial growth is performed on SiGe bulk layer, then SiGe seed layer and SiGe bulk layer are formed, but the thickness is insufficient due to crystal orientation selectivity restraining growth
Solution Approach 1:
A lattice change layer is epitaxially grown on the SiGe bulk layer before growing the cap layer. This preliminary action changes the crystal plane from the restrictive <100> orientation to <110> orientation, enabling subsequent cap layer growth without restriction. The lattice change layer serves as an intermediate structure that resolves the crystal orientation conflict.
Solution Approach 2:
The lattice change layer acts as an intermediary between the SiGe bulk layer and the cap layer. It has a different crystal plane (<110> vs <100>) that mediates the transition, allowing the cap layer to grow properly while maintaining the underlying SiGe structure. This intermediary layer eliminates the direct conflict between the SiGe bulk layer's crystal orientation and the cap layer's growth requirements.
2Manufacturing precision
If cap layer is grown on SiGe bulk layer with restricted growth, then morphology becomes uneven and thickness is insufficient, but growing thicker requires overcoming crystal orientation barriers
Solution Approach 1:
The lattice change layer is grown as a preliminary step before the cap layer to prepare the surface morphology and crystal orientation. This preliminary action ensures that when the cap layer is grown, it does so on a favorable <110> crystal plane, resulting in uniform morphology and adequate thickness without requiring excessive cap layer thickness.
Solution Approach 2:
The crystal plane parameter is changed from <100> in the SiGe bulk layer to <110> in the lattice change layer. This parameter change fundamentally alters the growth characteristics, enabling the cap layer to grow with uniform morphology and sufficient thickness. The parameter change is achieved through selective epitaxial growth conditions.
3Reliability
If Ni metal silicide reaction is performed, then Ni atom infiltrates into substrate causing active area leakage, but preventing infiltration requires adequate cap layer thickness which is insufficient due to growth restrictions
Solution Approach 1:
The lattice change layer is grown preliminarily to enable adequate cap layer growth. With the lattice change layer providing a favorable crystal plane, the cap layer can achieve sufficient thickness to act as an effective barrier against Ni atom infiltration during the metal silicide reaction, thereby preventing active area leakage.
Solution Approach 2:
The lattice change layer serves as an intermediary that enables the cap layer to achieve adequate thickness. By changing the crystal orientation, it allows the cap layer to grow thick enough to prevent Ni infiltration, thus mediating between the requirement for thin structure and the requirement for thick protective cap layer.
4Reliability
If SiGe epitaxy with high germanium concentration is used, then contact formation is poor causing increased resistance, but reducing germanium concentration reduces the strain effect on channel
Solution Approach 1:
Different regions of the SiGe structure have different germanium concentrations optimized for their specific functions. The SiGe bulk layer has high germanium concentration to provide strong compressive strain for high carrier mobility in the channel. The lattice change layer and cap layer have lower germanium concentrations to ensure good contact formation and low resistance, while still maintaining adequate strain effect.
Solution Approach 2:
The germanium concentration parameter is varied across different layers of the SiGe structure. The SiGe bulk layer uses high Ge concentration (e.g., 50-70%) for maximum strain effect, while the lattice change layer and cap layer use progressively lower Ge concentrations to optimize contact properties. This parameter gradient resolves the contradiction between strain effect and contact quality.
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 approach improves the morphology and thickness of the SiGe epitaxy, preventing active area leakage and enhancing the formation of metal silicide, thus addressing issues of abnormal resistance and uncontrolled resistance.
Implementation Method 1
the crystal plane treatment comprises simultaneous etching of the SiGe bulk layer surface and growth of a new SiGe bulk layer
Implementation Method 2
a lattice change layer, epitaxially grown on the top of the treated SiGe bulk layer
Data Source
AI summary
A structure of SiGe source/drain and a preparation method thereof are disclosed in the present invention. Firstly, providing a semiconductor single crystal silicon substrate. Secondly, etching the semiconductor single crystal silicon substrate to form recesses on both sides of the gate. Thirdly, epitaxially growing a SiGe seed layer and a SiGe bulk layer in the recesses in turn. Fourthly, subjecting the SiGe bulk layer to a crystal plane treatment with a mixed-gases. Fifthly, epitaxially growing a lattice change layer on the SiGe bulk layer. Finally, epitaxially growing a cap layer on the lattice change layer. The preparation method of the present invention can greatly improve the morphology of the SiGe epitaxy in the incomplete Un-tuck structure, and promote the formation of the subsequent metal silicide (NiSi), so that problems such as abnormal resistance and leakage of active area (AA leakage) can be effectively prevented.