Heterogeneous Substrate with SiGe-Encapsulated Sacrificial Layer
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Solution Overview
Problem
Current MEMS technologies face limitations in using sacrificial layers for creating monocrystalline mechanical layers, particularly in achieving suitable thicknesses and mechanical properties, and in providing effective protection and integration of three-dimensional structures without inducing stress or increasing component volume and cost.
Innovation Solution
A heterogeneous substrate with a sacrificial layer comprising a stack of monocrystalline Si between two layers of monocrystalline SiGe, allowing for selective etching and epitaxial growth of silicon or other monocrystalline materials, enabling the creation of monocrystalline mechanical layers with improved mechanical properties and three-dimensional structuring.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If polycrystalline silicon is deposited on oxide using PECVD or LPCVD, then the mechanical layer can be formed, but the mechanical properties (stress control, stability) deteriorate and thickness is limited
Solution Approach 1:
The patent changes the material parameter from polycrystalline silicon to monocrystalline silicon, fundamentally altering the crystal structure to improve mechanical properties stability and stress control while maintaining thickness control capabilities
Solution Approach 2:
The patent uses a composite structure with multiple layers including monocrystalline silicon mechanical layer, SiO2 sacrificial layer, and Si3N4 protective layer, where each material contributes specific properties to achieve overall performance
2Reliability
If monocrystalline silicon is used as mechanical layer with SOI-MEMS technology, then mechanical properties and thickness range are improved, but the device complexity increases
Solution Approach 1:
The patent segments the substrate into distinct functional layers (monocrystalline silicon mechanical layer, SiO2 sacrificial layer, Si3N4 protective layer) that can be independently optimized and processed, simplifying the overall fabrication complexity
Solution Approach 2:
The patent introduces SiO2 as a sacrificial intermediary layer that facilitates the formation of monocrystalline silicon mechanical structures through selective etching, simplifying the fabrication process
3Manufacturing precision
If sacrificial layer of oxide is used, then selective etching is excellent, but it is not possible to grow monocrystalline material epitaxially
Solution Approach 1:
The patent extracts the sacrificial layer function to a separate SiO2 layer that is selectively removed through chemical etching, allowing the monocrystalline silicon mechanical layer to be grown epitaxially on a suitable substrate without interference
Solution Approach 2:
The patent performs preliminary epitaxial growth of monocrystalline silicon on the substrate before introducing the SiO2 sacrificial layer, ensuring high-quality monocrystalline structure is established before sacrificial layer removal
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 allows for the fabrication of MEMS with enhanced mechanical properties, selective etching, and integration of multiple thicknesses and materials, including ferroelectric oxides, while reducing stress and component volume, and enabling more complex structural designs.
Implementation Method 1
Selective chemical etching of the sacrificial layer makes it possible to form active structures in the mechanical layer that are locally independent of the support
Implementation Method 2
epitaxial growth of silicon or some other monocrystalline material
Implementation Method 3
selective etching of the silica with HF (in the liquid or the vapor phase)
Data Source
AI summary
The invention relates to a method of making a component from a heterogeneous substrate comprising first and second portions in at least one monocrystalline material, and a sacrificial layer constituted by at least one stack of at least one layer of monocrystalline Si situated between two layers of monocrystalline SiGe, the stack being disposed between said first and second portions of monocrystalline material, wherein the method consists in etching said stack by making:e) at least one opening in the first and/or second portion and the first and/or second layer of SiGe so as to reach the layer of Si; andf) eliminating all or part of the layer of Si.