Patterned Si/SiGe Superlattice Buffer for Low-Dislocation Thin Films
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Solution Overview
Problem
Existing methods for growing silicon germanium thin films on silicon substrates result in materials with poor flatness and high threading dislocation density, which reduce carrier mobility and device performance.
Innovation Solution
A patterned silicon substrate-silicon germanium thin film composite structure is created by alternately growing silicon germanium and silicon layers, with a silicon germanium buffer layer and a silicon germanium thin film layer, using molecular beam epitaxy, to achieve high quality and flatness, and a method involving patterned substrate preparation and epitaxial growth.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If graded composition method is used to grow silicon germanium thin film, then stress from lattice mismatch is relieved, but threading dislocation density increases and carrier mobility decreases
Solution Approach 1:
The continuous graded layer is segmented into alternating thin layers of silicon germanium and silicon, each with thickness of several nanometers. This segmentation allows stress management while preventing threading dislocation propagation that occurs in continuous graded structures.
Solution Approach 2:
A composite structure is created by combining silicon germanium and silicon in alternating layers within the buffer region. This composite approach leverages the beneficial properties of both materials to achieve stress relief without the harmful effects of high dislocation density.
2Length of moving object
If conventional CVD or MBE methods are used to grow silicon germanium thin film, then film thickness can be controlled, but surface flatness deteriorates and additional CMP process is required
Solution Approach 1:
The buffer layer is segmented into multiple thin alternating layers of silicon germanium and silicon, each several nanometers thick. This fine segmentation enables precise thickness control while maintaining excellent surface flatness throughout the growth process.
Solution Approach 2:
The invention changes the compositional parameters by alternating between silicon germanium and silicon layers, and controls the thickness parameter of each layer to be several nanometers. These parameter changes enable simultaneous achievement of thickness control and surface flatness without requiring CMP processing.
3Stability of the object's composition
If graded layer with several microns thickness is grown to relieve stress, then stress relief is achieved, but device fabrication complexity increases and additional CMP process is needed
Solution Approach 1:
Instead of growing a single thick graded layer of several microns, the invention segments the buffer into many thin alternating layers of silicon germanium and silicon, each only several nanometers thick. This segmentation achieves stress relief while eliminating the need for additional CMP processing steps.
Solution Approach 2:
The buffer region is designed as a composite structure with alternating silicon germanium and silicon layers. This composite approach provides stress relief inherent to the layered structure, simplifying the overall fabrication process by eliminating separate CMP steps required in conventional approaches.
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
The approach results in low threading dislocation density and surface roughness, improving carrier mobility and device performance by reducing defect scattering in strained silicon devices.
Implementation Method 1
using molecular beam epitaxy, to achieve high quality and flatness
Data Source
AI summary
The present invention provides a patterned silicon substrate-silicon germanium thin film composite structure comprising a silicon substrate having a patterned structure, a silicon germanium buffer layer positioned on the silicon substrate, a silicon germanium/silicon superlattice layer positioned on the silicon germanium buffer layer and a silicon germanium thin film layer positioned on the silicon germanium/silicon superlattice layer, wherein the silicon germanium/silicon superlattice layer comprises silicon germanium layers and silicon layers which are grown alternately. The present invention also provides a preparation method of the patterned silicon substrate-silicon germanium thin film composite structure of the present invention. The present invention also provides an application of the patterned silicon substrate-silicon germanium thin film composite structure of the present invention in strained silicon devices. The patterned silicon substrate-silicon germanium thin film composite structure provided by the present invention has low threading dislocation density and low surface roughness. A strained silicon device fabricated based on the silicon germanium thin film layer can effectively reduce the scattering of defects to carriers, thereby improving carrier mobility.