Strained Heterojunction Release via Sacrificial Etching
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Solution Overview
Problem
Current methods for forming high-quality strained heterojunction semiconductor structures face challenges in controlling strain and reducing dislocation defects in SiGe films, leading to poor carrier mobility and thermal conductivity, and are limited by the difficulty in achieving compliant substrates and maintaining strain states in adjacent devices.
Innovation Solution
A method involving the growth of multilayer films on a crystalline template layer supported by a sacrificial layer, allowing for controlled strain relaxation and release of the multilayer structure, which can be mounted on various substrates to form devices with improved carrier mobility and strain distribution.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If thick graded SiGe films are grown to achieve strain relaxation, then strain control is improved, but dislocation density increases and thermal conductivity deteriorates
Solution Approach 1:
The patent segments the continuous graded SiGe buffer into multiple discrete SiGe layers with different Ge compositions (e.g., 0%, 5%, 10%, 15% Ge). Each layer is thin enough to remain strain-free while collectively providing the desired strain profile. This segmentation prevents dislocation formation that would occur in thick continuous graded layers, thus resolving the contradiction between strain control and dislocation density.
Solution Approach 2:
The patent performs preliminary strain engineering by growing thin SiGe layers with controlled Ge content before growing the final strained Si channel. The SiGe layers are prepared in advance with compositions that induce the desired tensile strain in the Si channel, eliminating the need for thick graded buffers and associated dislocations.
2Manufacturing precision
If thick graded SiGe films are grown to achieve strain relaxation, then strain control is improved, but film thickness increases making adjacent devices difficult to form
Solution Approach 1:
The patent replaces thick continuous graded buffers with multiple thin discrete SiGe layers. Each layer is only tens of nanometers thick, yet collectively they provide the same strain control function as a micrometer-thick graded buffer. This dramatically reduces the vertical space required, enabling adjacent devices to be formed in the same wafer.
3Manufacturing precision
If dislocation-driven relaxation is used, then strain relaxation is achieved, but threading dislocations extend through the strained-Si layer degrading carrier mobility
Solution Approach 1:
The patent performs preliminary strain engineering by growing thin SiGe layers with controlled Ge content before growing the final strained Si channel. The SiGe layers are prepared in advance with compositions that induce the desired tensile strain in the Si channel, eliminating the need for thick continuous graded buffers and associated dislocations.
Solution Approach 2:
The patent changes the composition parameter of SiGe layers from continuous grading to discrete steps (0%, 5%, 10%, 15% Ge). Each layer has a specific Ge content that provides controlled strain without exceeding the critical thickness for dislocation formation. This parameter change enables strain relaxation without threading dislocations penetrating the Si channel.
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 enables precise control of strain in semiconductor layers, reducing dislocation defects and enhancing carrier mobility, facilitating the fabrication of high-performance devices such as modulation-doped field-effect transistors and imaging devices with increased speed.
Implementation Method 1
the final strain state is achieved by elastic strain sharing between the films
Implementation Method 2
The sacrificial layer is then preferentially etched at the exposed areas thereof to release the multilayer structure
Data Source
AI summary
Growth of multilayer films is carried out in a manner which allows close control of the strain in the grown layers and complete release of the grown films to allow mounting of the released multilayer structures on selected substrates. A layer of material, such as silicon-germanium, is grown onto a template layer, such as silicon, of a substrate having a sacrificial layer on which the template layer is formed. The grown layer has a lattice mismatch with the template layer so that it is strained as deposited. A top layer of crystalline material, such as silicon, is grown on the alloy layer to form a multilayer structure with the grown layer and the template layer. The sacrificial layer is preferentially etched away to release the multilayer structure from the sacrificial layer, relaxing the grown layer and straining the crystalline layers interfaced with it.