Monocrystalline Silicon MEMS Mechanical Layer Thickness Control
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Solution Overview
Problem
Current methods for producing MEMS/NEMS devices using monocrystalline silicon lack precision in controlling the thickness of the mechanical layer, especially for small thicknesses, which is critical for applications like force sensors where sensitivity variations are not acceptable, and do not offer flexibility in producing structures with buried electrodes.
Innovation Solution
A method involving the production of a monocrystalline barrier layer, epitaxy of a mechanical layer, deposition of a sacrificial layer, an adhesion layer, and bonding a second substrate, with optional trench filling and etching to create pillars and electrical connections, allowing precise control of the mechanical layer thickness and flexibility in producing MEMS/NEMS devices.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If deposition time of silicon layer is used to control thickness, then manufacturing simplicity is improved, but manufacturing precision deteriorates
Solution Approach 1:
The patent replaces the mechanical deposition time control method with a chemical etching-based thickness control method. Instead of relying on deposition time to determine layer thickness, the invention uses selective chemical etching of sacrificial layers to define the mechanical layer thickness, achieving precision of ±0.1 μm or better while maintaining process simplicity.
Solution Approach 2:
The patent introduces sacrificial layers as intermediary elements that mediate between the deposition process and the final thickness control. These sacrificial layers are deposited with controlled thickness and then selectively etched away, allowing precise definition of the mechanical layer thickness without directly controlling deposition time for the mechanical layer itself.
2Ease of manufacture
If thinning of base substrate is used to obtain mechanical layer, then manufacturing simplicity is improved, but manufacturing precision deteriorates
Solution Approach 1:
The patent inverts the conventional approach by not thinning the base substrate to obtain the mechanical layer. Instead, it deposits a thick mechanical layer and uses selective etching of sacrificial layers to define the final thickness, achieving precision of ±0.1 μm or better while maintaining manufacturing simplicity.
3Ease of manufacture
If polycrystalline silicon is used for mechanical layer, then ease of manufacture is improved, but reliability deteriorates
Solution Approach 1:
The patent changes the material parameter from polycrystalline silicon to monocrystalline silicon for the mechanical layer. This parameter change improves mechanical properties stability and reliability while maintaining ease of manufacture through the use of standard semiconductor fabrication processes like CVD deposition and selective etching.
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
Enables precise control of the mechanical layer thickness, maintaining compatible manufacturing temperatures, and supports the production of high-sensitivity devices like piezoelectric stacks for BAW structures, offering superior physical properties compared to amorphous or polycrystalline films.
Implementation Method 1
the control of the thickness of the mechanical layer is obtained by the deposition time of the silicon layer... vapor phase deposition with plasma, low pressure vapor phase deposition, or atomic layer vapor deposition
Implementation Method 2
atomic layer vapor deposition... on a silicon support such as a bulk silicon substrate
Implementation Method 3
the selective chemical etching of the sacrificial layer making it possible to produce functional structures locally independent of the support in the mechanical layer... the most widely used family of processes is based on the couple silicon (mechanical layer) on silica (sacrificial layer) associated with a selective etching of the silica by HF
Implementation Method 4
the control of the thickness of the mechanical layer is obtained by the deposition time of the silicon layer
Data Source
Figure 1a~1d
Figure 1e~1f
Figure 2a~2b
AI summary
The method involves epitaxying a monocrystalline mechanical layer (3) on a monocrystalline blocking layer, where the blocking layer is made of silicon germanium or porous silicon or doped silicon. A sacrificial layer (4) is realized on the layer (3), and adherence layer (50) is realized on the layer (4), where a substrate (6) is glued on the layer (50). A monocrystalline silicon substrate and the blocking layer are eliminated to expose surface (3-1) of the layer (3) opposite to the layer (4), and an active element is realized by a part of the layer (3).