Diaphragm Pressure Sensor Etching with 45-Degree Angled Edges
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Solution Overview
Problem
Existing pressure sensor diaphragm etching techniques, such as KOH etching and DRIE, face challenges in achieving precise control over diaphragm thickness and edge orientation, leading to uncertain beveled portions that affect sensor accuracy and yield, particularly in high-sensitivity devices.
Innovation Solution
A hybrid anisotropic etching process is employed, where a silicon wafer with an epitaxial layer is etched using DRIE to form a diaphragm with 45-degree angled edges, followed by KOH etching to create anisotropic edges, optimizing diaphragm thickness and size while minimizing beveled portions in stress/strain areas.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If KOH anisotropic etching is used to form a pressure sensing diaphragm with an epitaxial etch stop, then the diaphragm thickness is controlled, but a relatively larger hole is required in the wafer due to 54.7 degree crystal etch plane, resulting in larger chip size and fewer die per wafer
Solution Approach 1:
The patent changes the crystal orientation parameter of the silicon wafer from the conventional <100> to <110> orientation. This parameter change fundamentally alters the etching behavior, allowing the formation of vertical sidewalls at 90 degrees during DRIE etching, thereby eliminating the need for large 54.7 degree beveled holes while maintaining precise diaphragm thickness control through epitaxial etch stop layers.
Solution Approach 2:
The patent employs a hybrid etching process that combines DRIE (deep reactive ion etching) and KOH (potassium hydroxide) etching techniques. The DRIE process creates the initial vertical cavity structure, while the KOH etching with epitaxial stop layer provides precise thickness control. This composite approach leverages the strengths of both etching methods to achieve both small chip size and precise thickness control.
2Area of stationary object
If DRIE process is used to produce a straight sidewall hole in the silicon wafer, then the chip size is reduced, but the etch depth control is not enough to produce a satisfactory yield for high sensitivity devices
Solution Approach 1:
The patent introduces an epitaxial etch stop layer before the final etching step. This preliminary layer is grown with precise thickness control and serves as a predetermined stopping point for the etching process. The DRIE etching proceeds until it reaches this pre-positioned epitaxial layer, ensuring accurate etch depth control and consistent diaphragm thickness, thereby improving manufacturing yield for high-sensitivity devices.
Solution Approach 2:
The epitaxial etch stop layer acts as an intermediary element between the DRIE etching process and the final diaphragm structure. It mediates the etching process by providing a well-defined termination point, allowing the DRIE process to achieve both the desired depth and precise thickness control that neither process could achieve alone.
3Area of stationary object
If a hybrid process combining DRIE etching with KOH etching and etch stop layer is used, then the die size is reduced by eliminating the 54.7 degree hole, but a variable amount of 54.7 degree bevel is introduced between the diaphragm edge and the etch pit wall, introducing uncertainty in the strain field and leading to inaccurate sensing
Solution Approach 1:
The patent changes the crystal orientation parameter from <100> to <110>, which fundamentally changes the etching geometry. With <110> oriented wafers, the DRIE process produces vertical sidewalls at 90 degrees to the wafer surface, eliminating the formation of 54.7 degree beveled edges. This parameter change ensures that the etch pit walls are perpendicular to the diaphragm plane, creating a well-defined strain field and improving pressure sensing accuracy.
Solution Approach 2:
By changing the crystal orientation to <110>, the patent creates an asymmetric etching response where vertical walls are formed along specific crystal directions while other directions etch at different rates. This asymmetric etching behavior allows for the formation of clean, non-beveled edges in the critical sensing areas, eliminating the uncertainty in the strain field that would otherwise compromise measurement precision.
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 enhances diaphragm structure for pressure sensors by ensuring accurate strain measurement, reducing chip size, and improving manufacturing yield with precise control over diaphragm thickness and edge orientation, resulting in a cost-effective and sensitive sensor design.
Implementation Method 1
A substrate (e.g., a silicon wafer) with an epitaxial layer can be etched utilizing an etching process (e.g., a deep reactive ion etching) in order to form a rectangular diaphragm
Implementation Method 2
The KOH etching, however, requires a relatively larger hole in the wafer due to 54.7 degree crystal etch plane
Implementation Method 3
A substrate (e.g., a silicon wafer) with an epitaxial layer can be etched utilizing an etching process in order to form a rectangular diaphragm
Data Source
AI summary
A method for etching a diaphragm pressure sensor based on a hybrid anisotropic etching process. A substrate with an epitaxial etch stop layer can be etched utilizing an etching process in order to form a diaphragm at a selective portion of the substrate. The diaphragm can be oriented at an angle (e.g., 45 degree) with respect to the substrate in order to avoid an uncertain beveled portion in a stress/strain field of the diaphragm. The diaphragm can be further etched utilizing an etch finishing process to create an anisotropic edge portion on the major areas of the diaphragm and optimize the thickness and size of the diaphragm. Such an approach provides an enhanced diaphragm structure with respect to a wide range of pressure sensor applications.