Micromechanical Membrane Rear Access via Epitaxial Segmentation
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Solution Overview
Problem
Existing methods for producing micromechanical membrane structures with rear-side access in semiconductor components face challenges in maintaining precise production tolerances and design flexibility, especially when dealing with harsh environments for absolute pressure sensors.
Innovation Solution
The method involves creating an opening in the n-doped lattice structure that remains accessible during epitaxial growth, forming an oxide layer on the cavern wall as an etch stop, and removing it to create a rear-side access, allowing for reliable protection and precise control of the membrane structure production.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the n-doped lattice structure openings are closed by the epitaxial layer to form a complete membrane, then the membrane structure integrity is improved, but access to the cavern for rear-side processing is lost
Solution Approach 1:
The lattice structure openings are segmented into two categories: those closed by the epitaxial layer to maintain membrane integrity, and one or more access openings that remain open to provide rear-side access to the cavern. This segmentation allows simultaneous achievement of membrane integrity and processing access.
Solution Approach 2:
The oxide layer is deposited on the cavern wall before removing the sacrificial porous silicon. This preliminary action creates an etch stop layer that protects the cavern wall during subsequent etching processes to create the rear-side access opening.
2Ease of operation
If the porous silicon is removed early to create the cavern, then access to the cavern is improved, but the cavern wall lacks protection during subsequent epitaxial growth
Solution Approach 1:
The oxide layer is deposited on the cavern wall in advance, before the porous silicon removal and epitaxial growth steps. This preliminary protective layer prevents unwanted silicon deposition on the cavern wall during epitaxy while still allowing access to the cavern space.
Solution Approach 2:
The oxide layer acts as an intermediary etch stop layer between the cavern wall and the epitaxial silicon growth process. It mediates the interaction by providing a protective barrier that is resistant to the epitaxial deposition process.
3Productivity
If standard etching methods are used from the rear side, then productivity is improved, but the membrane structure may be damaged by etching attack
Solution Approach 1:
The oxide layer on the cavern wall serves as an intermediary etch stop layer during rear-side processing. It allows standard etching methods to be used efficiently while protecting the membrane structure above the cavern from etching attack.
Solution Approach 2:
The oxide layer provides localized protection specifically at the cavern wall interface, allowing aggressive etching conditions to be used in the bulk substrate while the membrane structure remains protected where it interfaces with the cavern.
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 cost-effective and precise production of micromechanical membrane structures with defined dimensions and high long-term stability, suitable for various applications, including pressure sensors and microphone elements, while maintaining CMOS compatibility.
Implementation Method 1
an oxide layer is produced on the cavern wall; a rear side access to the cavity is produced, with the oxide layer on the cavity wall serving as an etching stop layer
Implementation Method 2
growth of a monocrystalline silicon epitaxial layer on the n-doped lattice structure
Implementation Method 3
the porous silicon is rearranged during the epitaxial process and a further annealing step in such a way that a cavern is formed below the n-doped lattice structure and the grown epitaxial layer
Implementation Method 4
the cavern wall - insofar as it exists before the epitaxy - is protected by a thermal oxide against the growth of silicon material during the epitaxy process
Data Source
Figure 1a~1b
Figure 1c~1d
Figure 1e~1f
AI summary
The invention proposes a particularly simple, cost-effective method for producing a micromechanical membrane structure with access from the rear of the substrate. Said method is based on a p-doped Si substrate (1) and comprises the following process steps: n-doping of at least one continuous lattice-type region (2) of the substrate surface; porous etching of a substrate region (5) below the n-doped lattice structure (2); creation of a cavity (7) in said substrate region (5) below the n-doped lattice structure (2); growing of a first monocrystalline silicon epitaxial layer (8) on the n-doped lattice structure (2). The invention is characterised in that at least one opening (6) in the n-doped lattice structure (2) is dimensioned in such a way that it is not closed by the growing first epitaxial layer (8) and instead forms an access opening (9) to the cavity (7); an oxide layer (10) is created on the cavity wall; A rear face access (13) to the cavity (7) is created, the oxide layer (10) acting as an etch stop layer; and the oxide layer (10) is removed in the region of the cavity (7) producing a rear face access (13) to the membrane structure (14) lying above the cavity (7).