Epitaxial Cap Layer Structure for FinFET Surface Evenness
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Solution Overview
Problem
Existing methods for fabricating semiconductor devices with epitaxial layers struggle to achieve an even surface, which affects the performance of non-planar metal-oxide semiconductor (MOS) transistors like fin field effect transistors (FinFETs).
Innovation Solution
A method involving the formation of a gate structure on a substrate, followed by the growth of an epitaxial layer and a first cap layer with a V-shape profile and planar surfaces, which helps in achieving a more even surface and reducing defects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If selective epitaxial growth technique is used to form epitaxial layer, then carrier mobility is improved through stress application, but surface evenness deteriorates affecting device performance
Solution Approach 1:
The epitaxial layer formation process is segmented into multiple stages: first forming a stress-inducing epitaxial layer (SiGe for PMOS or SiC for NMOS) to provide carrier mobility enhancement, then forming a separate cap layer with different material composition and controlled thickness to restore surface evenness. This segmentation allows each layer to fulfill its specific function without compromising the other.
Solution Approach 2:
The patent employs composite material structure consisting of epitaxial layer and cap layer with different material compositions. The epitaxial layer uses SiGe or SiC to induce stress, while the cap layer uses materials with different lattice constants to compensate for surface irregularities. This composite approach enables simultaneous achievement of stress-induced carrier mobility improvement and surface evenness restoration.
2Reliability
If epitaxial layer is formed to induce stress in gate channel, then carrier mobility increases, but surface irregularities are introduced
Solution Approach 1:
The cap layer acts as an intermediary element between the stress-inducing epitaxial layer and the subsequent processing layers. It mediates the surface irregularities by providing a planarizing effect, allowing the stress benefits of the epitaxial layer to be retained while eliminating the harmful surface shape deviations for subsequent device fabrication 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 proposed method improves the surface evenness of epitaxial layers, enhances the performance of semiconductor devices by reducing defects and voids, and maintains the structural integrity of the semiconductor device.
Implementation Method 1
selective epitaxial growth (SEG) technique to form epitaxial structure such as silicon germanium (SiGe) epitaxial layer in a silicon substrate
Implementation Method 2
forming a first cap layer on the epitaxial layer
Data Source
AI summary
A method for fabricating a semiconductor device includes the steps of forming a gate structure on a substrate, forming an epitaxial layer adjacent to the gate structure, and then forming a first cap layer on the epitaxial layer. Preferably, a top surface of the first cap layer includes a curve concave upward and a bottom surface of the first cap layer includes a planar surface higher than a top surface of the substrate.