Strained Channel Semiconductor Device Using Lateral Epitaxial Expansion
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
The reduction in channel length of semiconductor devices leads to a short channel effect, decreasing threshold voltage and carrier mobility, while increasing impurity doping to overcome this reduces operation speed and current due to increased impurity scattering. Existing methods to induce strain in channels, such as increasing recess depth or germanium/carbon concentration, compromise layer quality and productivity.
Innovation Solution
A semiconductor device with a strained channel is fabricated by forming recess patterns with side surfaces extending below the gate pattern, allowing an epitaxial layer to increase in volume without increasing recess depth, and adjusting germanium or carbon concentration to enhance strain without compromising layer quality, using protection layers to improve epitaxial layer growth and reduce defects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the depth of the recess pattern is increased to increase the volume of the epitaxial layer, then the strain in the channel is improved, but the growth thickness of the epitaxial layer increases leading to reduced productivity and layer quality
Solution Approach 1:
The patent changes the geometry of the recess pattern from a simple deep cavity to a complex multi-dimensional structure with lateral extensions and varied depth zones. This allows increasing the epitaxial layer volume through lateral expansion rather than vertical depth, avoiding the critical thickness limit while maintaining strain effectiveness.
Solution Approach 2:
The recess pattern is divided into multiple depth zones and regions with different epitaxial growth characteristics. By segmenting the recess structure, the patent enables selective epitaxial growth in different areas, achieving high volume without uniformly increasing depth throughout, thus avoiding defect formation while maintaining productivity.
2Reliability
If the concentration of germanium or carbon in the epitaxial layer is increased to increase the difference in lattice constant, then the strain in the channel is improved, but the critical thickness allowing defect-free growth is reduced leading to reduced layer quality
Solution Approach 1:
The patent applies different germanium or carbon concentrations in different regions of the epitaxial layer rather than using a uniform high concentration throughout. This local quality approach allows achieving sufficient strain in critical areas while maintaining lower concentrations in other regions, thus avoiding defect formation and maintaining overall layer quality.
Solution Approach 2:
The patent optimizes the concentration parameter of germanium or carbon within a specific range (5-50 atomic percent) rather than using maximum concentrations. This parameter optimization achieves effective strain while staying below the critical threshold that would cause defect formation during epitaxial growth.
3Reliability
If the growth thickness of the epitaxial layer is increased to increase the volume, then the strain in the channel is improved, but the layer quality is reduced due to the critical thickness limit for defect-free growth
Solution Approach 1:
The patent transitions from increasing volume through vertical thickness to increasing volume through lateral horizontal expansion. The recess pattern is designed with extended lateral dimensions and multi-level structures, allowing the epitaxial layer to achieve high volume while maintaining thickness within the critical defect-free growth range.
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 carrier mobility and operation speed of semiconductor devices by inducing strain in the channel while maintaining high layer quality and productivity, thereby enhancing device characteristics and yield.
Implementation Method 1
filling the recess pattern with an epitaxial layer formed of a Group IV element having different lattice constant from that of silicon
Implementation Method 2
The epitaxial layers 15 are formed of a material having a different lattice constant from that of the silicon substrate 11, and serve as the source S and the drain D
Data Source
AI summary
A semiconductor device includes: a gate pattern over a substrate; recess patterns provided in the substrate at both sides of the gate pattern, each having a side surface extending below the gate pattern; and a source and a drain filling the recess patterns, and forming a strained channel under the gate pattern.