Laminated Layer Structure Gradient Composition Strained Silicon
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Solution Overview
Problem
Conventional strained silicon substrates suffer from high surface roughness and dislocation density due to lattice parameter differences in layered structures, limiting their crystalline quality and applicability in microelectronic devices.
Innovation Solution
A laminated layer structure is developed with a stack of layers having a gradient composition of compounds A and B, where the composition parameter of B increases gradually, followed by layers with a constant composition, allowing for controlled stress reduction and dislocation elimination, thereby improving surface roughness and dislocation density.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If alternating layers of silicon germanium gradient composition and constant composition are provided, then surface roughness is reduced, but dislocation density remains high
Solution Approach 1:
The patent applies parameter changes by systematically varying the germanium composition ratio across multiple layers in a specific sequence. The composition parameter (1-x) increases from the substrate interface toward the surface, with each subsequent layer having a higher germanium content than the previous one. This gradual parameter change allows the lattice structure to adapt progressively, reducing both surface roughness and dislocation density simultaneously by minimizing sudden lattice mismatches between layers.
2Strength
If silicon is deposited on a SixGe1-x layer with larger lattice constant, then strained silicon is achieved, but crystalline defaults like dislocations and high surface roughness are created
Solution Approach 1:
The patent segments the buffer layer into multiple thin alternating layers of gradient composition and constant composition, rather than using a single thick layer. This segmentation allows the strain to be distributed progressively across many interfaces, each with a small composition step. The gradient layers transition composition gradually, while constant composition layers provide stable platforms, together achieving the necessary strain for high-speed devices while maintaining excellent crystalline quality with reduced dislocations and surface roughness.
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 significantly reduced dislocation density and improved surface roughness, achieving crystalline quality superior to existing technologies, with surface roughness less than 15 Å RMS and dislocation density of less than 10^4 cm^-2, enabling the production of high-quality strained silicon substrates for advanced microelectronic applications.
Implementation Method 1
at least a part of the layers of the stack has a grading composition AxgB(1-xg), with x being a composition parameter within the range of 0 and 1 and with the composition parameter (1-xg) increasing gradually, in particular linearly, over the thickness of the corresponding layer
Implementation Method 2
compound A has a lattice parameter being sufficient to allow a homo- or heteroepitaxial growth of compound A on the substrate
Data Source
AI summary
The invention relates to a laminated layer structure that includes a substrate and a stack of a plurality of layers of a material that includes at least two compounds A and B, wherein compound A has a crystalline structure being sufficient to allow a homo- or heteroepitaxial growth of compound A on the substrate, and wherein at least a part of the layers of the stack have a gradient composition AxB(1-xg), with x being a composition parameter within the range of 0 and 1 and with the composition parameter (1-xg) increasing gradually, in particular linearly, over the thickness of the corresponding layer. In order to improve the quality of the laminated layer structure with respect to the surface roughness and dislocation density, the composition parameter at the interface between the layer in the stack with the gradient composition and the subsequent layer in the stack is chosen to be smaller than the composition parameter (1-xg) of the layer with a gradient composition. The invention also relates to a method to fabricate such a laminated layer structure.