Strained Transistor Fabrication via Selective Amorphization and Recrystallization
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Solution Overview
Problem
Existing transistor structures with strained channels face challenges in efficiently managing mechanical strain to optimize carrier mobility, particularly in creating transistors with uniaxial compression and tensile strain from the same strained semiconducting material.
Innovation Solution
A method involving a mask-based process to selectively amorphize and recrystallize regions of a biaxially strained silicon surface layer, followed by germanium enrichment, to achieve uniaxial compression in one region and maintain tensile strain in another, allowing for the fabrication of P-type and N-type transistors with specific strain orientations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If the same strained semiconducting material is used for both N type and P type transistors, then material uniformity is maintained, but the ability to optimize carrier mobility for both transistor types simultaneously is lost
Solution Approach 1:
The patent maintains material uniformity at the compositional level while introducing local variations in strain state. The silicon surface layer has consistent composition across the substrate, but different regions are subjected to different mechanical strain patterns through selective epitaxial growth conditions, enabling optimized carrier mobility for both NMOS and PMOS transistors.
2Adaptability or versatility
If etching is used to relax strain in certain regions to create different transistor types, then transistor diversity is achieved, but process complexity and potential damage to the strained layer increase
Solution Approach 1:
Instead of etching the strained layer after formation, the patent performs preliminary action by controlling the epitaxial growth conditions during the formation process itself. By adjusting temperature, pressure, and gas composition during selective region growth, the desired strain patterns are created without subsequent etching steps, reducing process complexity and avoiding damage to the strained layer.
Solution Approach 2:
The patent replaces the mechanical etching process with a chemical epitaxial growth process. Instead of physically removing material to relax strain, the patent uses controlled chemical deposition to create regions with different strain characteristics, substituting a less invasive chemical process for a mechanical one.
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 method effectively relaxes strain in one direction while maintaining it in another, enabling the production of transistors with improved performance by controlling strain orientations without etching, thus enhancing carrier mobility and transistor performance.
Implementation Method 1
make at least one ion implantation of the surface layer through openings in the mask, so as to make the second zones amorphous
Implementation Method 2
recrystallise the second zones in the surface layer
Implementation Method 3
enrich the first zone of the surface layer in germanium
Data Source
AI summary
Manufacture of a transistor device with at least one P type transistor with channel structure strained in uniaxial compression strain starting from a silicon layer strained in biaxial tension, by amorphization recrystallization then germanium condensation.