Epitaxial Structure With Graded Ge Concentration For Strain
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Solution Overview
Problem
Conventional epitaxial semiconductor structures with silicon germanium (SiGe) bulk structures fail to achieve high enough germanium concentration in the Ge region, which is not adequately close to the channel region, limiting the strain effect and device performance.
Innovation Solution
The epitaxial structure involves forming a recess in a substrate, followed by sequential epitaxial layers with increasing germanium concentration, where a cave is etched to accommodate a third epitaxial layer with a high Ge concentration, allowing it to fill and extend close to the channel region, enhancing strain effect.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If SiGe bulk structure is formed with conventional epitaxial growth, then the structure is simple to manufacture, but the Ge concentration in Ge region is not high enough and the Ge region is not close enough to channel region
Solution Approach 1:
The epitaxial structure is divided into multiple distinct layers with different Ge concentrations: a first epitaxial layer with lower Ge concentration, a second epitaxial layer with intermediate Ge concentration, and a third epitaxial layer with high Ge concentration. This segmentation allows precise control over Ge distribution to maximize strain effect while maintaining manufacturability.
Solution Approach 2:
Different regions of the epitaxial structure are assigned different Ge concentrations according to their functional requirements. The third epitaxial layer with high Ge concentration is positioned adjacent to the channel region where maximum strain effect is needed, while lower Ge concentration layers are positioned elsewhere. This local optimization of material composition directly addresses the contradiction between Ge concentration and structural complexity.
2Reliability
If Ge concentration is increased to enhance strain effect, then device performance is improved, but the fabrication process becomes more complex
Solution Approach 1:
The recess structure is formed in the substrate before epitaxial growth begins, pre-positioning the high Ge concentration third epitaxial layer adjacent to the channel region. This preliminary structural preparation ensures that when the high Ge concentration layer is grown, it is already in the optimal position to maximize strain effect on the channel, achieving high device performance without requiring complex post-growth processing.
Solution Approach 2:
The Ge concentration parameter is systematically varied across different epitaxial layers and positions. The third epitaxial layer is grown with high Ge concentration (e.g., 30-50% or higher) specifically in the region adjacent to the channel, while other layers have lower Ge concentrations. This parameter optimization enhances strain effect and device performance while the systematic approach keeps the fabrication process manageable.
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 improves the strain effect by ensuring the high Ge concentration layer has a large top area adjacent to the channel region, enhancing device performance while maintaining a simple fabrication process.
Implementation Method 1
silicon germanium (SiGe) may be epitaxially grown to form source and drain features
Implementation Method 2
performing an etching back process to remove a portion of the second epitaxial layer to form a cave in the recess
Data Source
AI summary
An epitaxial structure of semiconductor device includes a substrate, a recess, a first epitaxial layer, a second epitaxial layer, and a third epitaxial layer. The recess is formed in the substrate and disposed near a surface of the substrate, wherein the recess has a recess depth. The first epitaxial layer is disposed on surfaces of a sidewall and a bottom of the recess. The second epitaxial layer is disposed on the surface of the first epitaxial layer, wherein the Ge concentration of the second epitaxial layer is greater than the Ge concentration of the first epitaxial layer. The third epitaxial layer is disposed on the surface of the second epitaxial layer, wherein the Ge concentration of the third epitaxial layer is greater than the Ge concentration of the second epitaxial layer, and the depth of the third epitaxial layer is about ½ to about ¾ of the recess depth.