Strained Semiconductor-on-Insulator Transfer for Low-Roughness Layers
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Solution Overview
Problem
Conventional methods for fabricating strained semiconductor-on-insulator substrates face challenges in achieving the required uniformity and roughness of the strained semiconductor layer without losing strain effectiveness, particularly due to the limitations of thermal smoothing techniques and compatibility issues with chemical-mechanical polishing.
Innovation Solution
A method involving a donor substrate with multiple layers, where a monocrystalline carrier substrate and an intermediate layer are used, allowing for selective etching to transfer the monocrystalline semiconductor layer to a receiving substrate, avoiding thermal smoothing and achieving the desired uniformity and roughness through epitaxial growth and selective etching processes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If thermal smoothing techniques are used to improve uniformity and reduce roughness of the strained semiconductor layer, then surface uniformity is improved, but strain effectiveness is lost due to germanium diffusion
Solution Approach 1:
A bonding layer is introduced as an intermediary between the strained semiconductor layer and the carrier substrate. This bonding layer acts as a diffusion barrier that prevents germanium from diffusing into the carrier substrate during thermal processing, thereby maintaining strain effectiveness while allowing thermal smoothing to improve surface uniformity
Solution Approach 2:
The method employs a composite structure consisting of multiple layers with different materials properties: a strained semiconductor layer (SiGe), a bonding layer (SiO2 or Si3N4), and a carrier substrate. This composite structure combines the beneficial properties of each material - the strained layer provides high mobility, the bonding layer provides diffusion barrier and mechanical support, and the carrier substrate provides structural stability
2Manufacturing precision
If chemical-mechanical polishing is used to improve surface roughness, then roughness is reduced, but compatibility issues arise with the strained semiconductor layer structure
Solution Approach 1:
Instead of using complex and incompatible chemical-mechanical polishing processes on the strained layer itself, the method uses a sacrificial bonding layer that can be selectively removed or etched. This approach replaces a problematic long-term manufacturing challenge with a simpler, more compatible process that achieves the same surface quality goal
3Manufacturing precision
If the strained semiconductor layer is thinned to achieve desired thickness uniformity, then thickness uniformity is improved, but strain transmission is reduced
Solution Approach 1:
The bonding layer serves as a mediator that decouples the thickness control of the strained semiconductor layer from the strain transmission to the carrier substrate. This allows the strained layer to be thinned to achieve desired thickness uniformity while the bonding layer maintains the strain field integrity for effective strain transmission
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 the fabrication of strained semiconductor-on-insulator substrates with improved uniformity and low roughness without strain loss, as seen in the preservation of germanium content and strain transmission, optimizing the substrate for enhanced charge carrier mobility.
Implementation Method 1
between steps (d) and (e), a first operation of selectively etching the portion of the carrier substrate with respect to the intermediate layer and a second operation of selectively etching the intermediate layer with respect to the monocrystalline semiconductor layer are implemented
Implementation Method 2
the intermediate layer comprises a second material that differs from the first material, the thickness of the intermediate layer being chosen so that the second material retains the lattice parameter of the first material
Implementation Method 3
the donor substrate is formed by epitaxy, on the monocrystalline carrier substrate, of the intermediate layer then of the monocrystalline semiconductor layer
Implementation Method 4
the cutting operation results in the at least partial relaxation of the silicon-germanium and the transmission of at least part of the strain to the transferred silicon layer
Data Source
AI summary
A method for fabricating a strained semiconductor-on-insulator substrate comprises bonding a donor substrate to a receiving substrate with a dielectric layer at the interface. The donor substrate comprises a monocrystalline carrier substrate, an intermediate etch-stop layer, and a monocrystalline semiconductor layer. The monocrystalline semiconductor layer is transferred from the donor substrate to the receiving substrate. Trench isolations are formed to cut a portion from a layer stack including the transferred monocrystalline semiconductor layer, the dielectric layer, and the strained semiconductor material layer. The cutting operation results in relaxation of strain in the strained semiconductor material, and in application of strain to the transferred monocrystalline semiconductor layer. After transferring the monocrystalline semiconductor layer and before the cutting operation, a portion of the carrier substrate is selectively etched with respect to the intermediate layer, and the intermediate layer is selectively etched with respect to the monocrystalline semiconductor layer.