Epitaxial Source-Drain MOS Structure for Channel Stress Transfer
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Solution Overview
Problem
The challenge in semiconductor manufacturing is to prevent crystal defects caused by high concentrations of atoms with a different lattice constant in mixed crystal layers while effectively applying stress to the channel region for enhanced carrier mobility, which existing methods fail to achieve due to counteraction from dummy gate electrodes suppressing the stress applied by mixed crystal layers.
Innovation Solution
A method involving the formation of a dummy gate electrode, recess etching, and epitaxial growth of mixed crystal layers on a silicon substrate, followed by removal of the dummy gate to allow effective stress application to the channel region through the gate insulating film, thereby preventing crystal defects and enhancing carrier mobility.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If dummy gate electrode is formed before epitaxial growth, then source/drain regions can be formed with self-alignment, but the dummy gate electrode suppresses stress application to the channel region
Solution Approach 1:
The patent removes the dummy gate electrode after source/drain region formation is complete. This extraction eliminates the suppressing effect on stress application to the channel region, thereby enabling effective carrier mobility enhancement while having previously utilized the dummy gate for self-alignment during manufacturing
Solution Approach 2:
The dummy gate electrode is formed preliminarily before source/drain region formation to enable self-alignment. After serving its alignment purpose, it is removed to allow stress application. This preliminary action followed by removal resolves the contradiction between needing the dummy gate for alignment and needing its absence for stress enhancement
2Reliability
If high concentration of atoms with different lattice constant is used in mixed crystal layers, then stress application to channel region is enhanced, but crystal defects occur
Solution Approach 1:
The patent applies stress by forming mixed crystal layers (such as SiGe) in the source/drain regions with specific compositional gradients. By controlling the local concentration of atoms with different lattice constants in the source/drain regions rather than uniformly in the channel, effective stress is applied to enhance carrier mobility while avoiding excessive lattice mismatch that would cause crystal defects
Solution Approach 2:
The patent carefully controls the composition parameters of the mixed crystal layers, using gradual changes in atomic concentration (e.g., Ge concentration gradients in SiGe source/drain regions). This parameter control enables sufficient stress application for carrier mobility enhancement while maintaining crystal quality by avoiding abrupt compositional changes that would generate defects
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 strains the channel region, enhancing carrier mobility and preventing crystal defects, leading to improved transistor characteristics such as increased on/off ratio and reduced on-resistance.
Implementation Method 1
epitaxial growth of mixed crystal layers on a silicon substrate
Implementation Method 2
effectively applying stress to the channel region for enhanced carrier mobility
Data Source
AI summary
A semiconductor device in which sufficient stress can be applied to a channel region due to lattice constant differences.