US5470797A
Expired / Lapsed
US
⏱️ 0.0 years remaining
Method for producing a silicon-on-insulator capacitive surface micromachined absolute pressure sensor
Assignee: University of Michigan-Ann Arbor
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Filing: 1994-10-31
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Granted: 1995-11-28
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Expires: 2014-10-31
Abstract
Abstract A method and structure for forming a capacitive transducer having a deformable single crystal diaphragm. A first well region is formed within a semiconductor substrate in an SOI wafer having a sacrificial layer of known thickness and a top single-crystal silicon layer thereon. Next, a silicon, epitaxial layer is deposited on the top silicon layer for forming a flexible single crystal membrane. The epitaxial layer and the sacrificial layer are masked and etched to define the flexible diaphragm. An electrical insulating conformal support layer is deposited on the substrate and attached to the diaphragm so as to seal the sacrificial layer therebetween. An access opening is etched through the diaphragm, and then a wet etchant is inserted through the access opening for removing the sacrificial layer, thereby defining a diaphragm cavity between the remaining epitaxial layer and the substrate. Conductive ions are diffused into facing sections of the diaphragm and the first well of the substrate so as to define fixed and deformable electrodes of the sensing capacitor. Next, a plug is selectively deposited within and for sealing the access opening without substantially reducing the volume of the diaphragm cavity.
Inventors
- 👤 Carlos H. Mastrangelo
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-11-03 19:11
CPC Classifications
G; G01; G01L; G01L9/00; G01L9/0041; G01L9/0042; G01L9/0072; G01L9/0073
Claims Analysis
Total Claims: 10
Claim 1
Independent Claim
261 words
A method for producing a capacitive transducer, comprising the steps of: (a) selectively forming a first well within the substrate of an SOI wafer having a top silicon layer and a sacrificial layer of known thickness therebetween, (b) depositing an epitaxial layer of silicon on said top silicon layer, said epitaxial silicon layer combining with said top silicon layer to form a single crystal silicon layer supported by said sacrificial layer, (c) masking and etching said epitaxial layer and said sacrificial layer down to said substrate so as to define a diaphragm from said epitaxial layer, (d) depositing an electrically insulating conformal support layer for coupling to and supporting said diaphragm above said substrate so as to seal said sacrificial layer therebetween, (e) selectively etching an access opening through said diaphragm, (f) selectively etching, through said access opening, and removing said sacrificial layer from between said diaphragm and said substrate so as to form a diaphragm cavity therebetween, said diaphragm cavity having a thickness substantially equal to said known thickness of said sacrificial layer, and (g) diffusing conductive ions through said diaphragm cavity and into opposing sections of said flexible diaphragm and said substrate for defining deformable and fixed conductive electrodes of the capacitive transducer, (h) selectively depositing a plug within and for sealing said access opening without significantly reducing the volume of said diaphragm cavity, wherein the deflection of said flexible diaphragm responsive to variations between the ambient pressure and the pressure sealed within said diaphragm cavity causes a corresponding change in the capacitance between said fixed and deformable electrodes.
Claim 2
Independent Claim
261 words
A method for producing a capacitive transducer, comprising the steps of: (a) selectively forming a first well within the substrate of an SOI wafer having a top silicon layer and a sacrificial layer of known thickness therebetween, (b) depositing an epitaxial layer of silicon on said top silicon layer, said epitaxial silicon layer combining with said top silicon layer to form a single crystal silicon layer supported by said sacrificial layer, (c) masking and etching said epitaxial layer and said sacrificial layer down to said substrate so as to define a diaphragm from said epitaxial layer, (d) depositing an electrically insulating conformal support layer for coupling to and supporting said diaphragm above said substrate so as to seal said sacrificial layer therebetween, (e) selectively etching an access opening through said diaphragm, (f) selectively etching, through said access opening, and removing said sacrificial layer from between said diaphragm and said substrate so as to form a diaphragm cavity therebetween, said diaphragm cavity having a thickness substantially equal to said known thickness of said sacrificial layer, and (g) diffusing conductive ions through said diaphragm cavity and into opposing sections of said flexible diaphragm and said substrate for defining deformable and fixed conductive electrodes of the capacitive transducer, (h) selectively depositing a plug within and for sealing said access opening without significantly reducing the volume of said diaphragm cavity, wherein the deflection of said flexible diaphragm responsive to variations between the ambient pressure and the pressure sealed within said diaphragm cavity causes a corresponding change in the capacitance between said fixed and deformable electrodes.
Claim 3
Dependent Claim
60 words
The method as described in claim 1 wherein step (a) includes the preliminary step of forming said SOI wafer by depositing said sacrificial layer of SiO 2 having said known thickness onto a silicon substrate, and then growing an epitaxial layer of single crystal silicon, having a thickness smaller than the thickness of said flexible diaphragm, on said sacrificial layer.
Claim 4
Dependent Claim
23 words
The method as described in claim 2 wherein said sacrificial layer is deposited to a known thickness of between 0.2 and 1.0 micrometers.
Claim 5
Dependent Claim
109 words
The method as described in claim 1 wherein: step (c) further includes the step of etching through said epitaxial layer and said sacrificial layer to expose said substrate, and wherein step (d) further includes the step of depositing a conformal layer of LTO so as to form a base section coupled to said substrate and encircling the perimeter of said sacrificial layer, and so as to form a lip section coupled over and fixed to at least a portion of said epitaxial layer for providing support thereto, whereby said diaphragm will be supported above and spaced from said substrate by said known thickness after said sacrificial layer is removed.
Claim 6
Dependent Claim
22 words
The method as described in claim 4 wherein step (d) further includes the step of sealing said substrate to said epitaxial layer.
Claim 7
Dependent Claim
76 words
The method as described in claim 1 wherein step (f) further includes the substeps of: inserting a wet etching solution through said access opening for removing said sacrificial layer, removing said wet etching solution from within said diaphragm cavity with a rinsing solution, freeze-drying said wet solutions within said diaphragm cavity in order to prevent the capillary deflection of said diaphragm as said solutions are removed, removing said frozen solution from said diaphragm cavity by sublimation.
Claim 8
Dependent Claim
42 words
The method as described in claim 1 further including the steps of inserting an insulating material through said access opening so as to deposit an insulating layer onto the surfaces or said epitaxial layer and said substrate that define said diaphragm cavity.
Claim 9
Dependent Claim
37 words
The method as described in claim 1 wherein step (g) also includes the step of diffusing conductive n+ carriers into said epitaxial and said substrate layers for forming diffused structures for said fixed and said conductive electrodes.
Claim 10
Dependent Claim
105 words
The method as described in claim 1 wherein: step (h) includes the step of: identifying generally adjacent pairs of commonly processed capacitive transducers on said substrate and identifying one transducer as a reference transducer and one transducer as a pressure transducer, and further including the additional steps of: (i) selectively etching a reference access hole in said diaphragm of said reference transducer, and (j) selectively depositing a gas permeable plug within said reference access hole without coating or substantially reducing the volume of said diaphragm cavity, said permeable plug being capable of passing gases into said diaphragm cavity while excluding the passage of solids therethrough.
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USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1998-11-27 | 1999-05-29 | 1999-11-28 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 2002-11-27 | 2003-05-29 | 2003-11-28 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 2006-11-27 | 2007-05-29 | 2007-11-28 | $7700.00 | Window Closed / Lapsed |