EP0319871A1
Expired / Lapsed
EP
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Thin film orthogonal microsensor for air flow and method for its fabrication
Assignee: Honeywell Inc
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Filing: 1988-12-03
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Granted: —
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Expires: 2008-12-03
Abstract
Abstract A microbridge air flow sensor which has a sealed etched cavity (23) beneath the silicon nitride diaphragm (14, 16) so that the cavity is not susceptible to contamination from residual films or other material accumulating within the cavity. The cavity thermally isolates the heater (24) and detectors (31, 30) which are encapsulated in the diaphragm (14, 16). The cavity is fabricated by front side etching of the silicon wafer (11). Narrow slots (40-47; 50-57; 60-65) are made through the silicon nitride diaphragm (14, 16) to expose a thin film (400 angstrom) rectangle of aluminum (13). A first etch removes the aluminum leaving a 400 angstrom very shallow cavity under the diaphragm. Anisotropic etch is then introduced into the shallow cavity to etch the silicon pit (23).
Inventors
- 👤 Robert E Higashi
- 👤 Steven D. James
- 👤 Jeffrey A. Ridley
- 👤 James O. Holmen
- 👤 Robert G. Johnson
Bibliographic Details
Application Number
—
Jurisdiction
EP
Data Source
google_patents
Last Synchronized
2026-11-01 01:06
CPC Classifications
G; G01; G01F; G01F1/00; G01F1/68; G01F1/684; G01F1/6845; H; H10; H10P; H10P50/00; H10P50/69; H10P50/691; H01; H01H; H01H1/00; H01H1/0036; H01H2001/0089; Y; Y10; Y10T; Y10T428/00; Y10T428/12; Y10T428/12493; Y10T428/12528
Claims Analysis
Total Claims: 18
Claim 1
Independent Claim
262 words
A process for fabricating a thin film microsensor for air flow, characterized by the steps of: a) providing a single crystal (100) silicon wafer (11) having a planar surface (12), and having a <110> direction; b) depositing and delineating a rectangular area of a thin film layer (13) of sacrificial selectively etchable material on the silicon surface (12); c) depositing a thin film (14) of silicon nitride on the selectively etchable material (13) and the rest of the silicon surface (12), the film being thicker than the thickness of the sacrificial material; c) depositing and delineating a thin film (15) of electrically resistive material on the silicon nitride (14) to form desired circuit elements such as detector resistors (20, 21), circuit resistors (R A , R B ) and a heater resistor (24), said heater resistor (24) and detector resistors (21) being located over said sacrificial material area (13); e) depositing a thin film (16) of silicon nitride over the resistive material and the previous silicon nitride (14); f) cutting narrow slots (40 to 47; 50 to 57; 60 to 65) through the silicon nitride (14, 16) to the sacrificial material layer (13), the slots being near the sacrificial material layer edges; g) introducing selective etch through the slots to etch out the sacrificial material layer (13) leaving a thin cavity in its place; h) introducing an anisotropic etch through the slots and cavity to anisotropically etch a thermal isolation pit (23) in the silicon wafer (11); and i) applying and delineating polyimide film (27) over slots to close off the slots.
Claim 2
Dependent Claim
262 words
A process for fabricating a thin film microsensor for air flow, characterized by the steps of: a) providing a single crystal (100) silicon wafer (11) having a planar surface (12), and having a <110> direction; b) depositing and delineating a rectangular area of a thin film layer (13) of sacrificial selectively etchable material on the silicon surface (12); c) depositing a thin film (14) of silicon nitride on the selectively etchable material (13) and the rest of the silicon surface (12), the film being thicker than the thickness of the sacrificial material; c) depositing and delineating a thin film (15) of electrically resistive material on the silicon nitride (14) to form desired circuit elements such as detector resistors (20, 21), circuit resistors (R A , R B ) and a heater resistor (24), said heater resistor (24) and detector resistors (21) being located over said sacrificial material area (13); e) depositing a thin film (16) of silicon nitride over the resistive material and the previous silicon nitride (14); f) cutting narrow slots (40 to 47; 50 to 57; 60 to 65) through the silicon nitride (14, 16) to the sacrificial material layer (13), the slots being near the sacrificial material layer edges; g) introducing selective etch through the slots to etch out the sacrificial material layer (13) leaving a thin cavity in its place; h) introducing an anisotropic etch through the slots and cavity to anisotropically etch a thermal isolation pit (23) in the silicon wafer (11); and i) applying and delineating polyimide film (27) over slots to close off the slots.
Claim 3
Dependent Claim
24 words
The process according to claim 1, characterized in that the thin film layer of sacrificial selectively etchable material (13) is a selectively etchable metal.
Claim 4
Dependent Claim
19 words
The process according to claim 2, characterized in that the thin film of selectively etchable metal (13) is aluminum.
Claim 5
Dependent Claim
26 words
The process according to one of the preceding claims, characterized in that the thin film (15) of resistive material is a resistive metal, preferably is platinum.
Claim 6
Dependent Claim
251 words
A process for fabricating a thin film microsensor for airflow, characterized by the steps of: a) providing a single crystal (100) silicon wafer (11) having a planar surface (12), and having a <110> direction; b) sputter depositing and delineating a 400 angstrom thick layer (13) of sacrificial aluminum on the silicon surface, the critical edge of the aluminum delineation being oriented orthogonally to the <110> direction; c) sputter depositing about 5000 angstroms of silicon nitride (14) on the aluminum (13) and the rest of the silicon surface (12); d) depositing and delineating about 800 angstroms of platinum (15) on the silicon nitride (14) to form desired circuit elements such as detector resistors (20, 21), circuit resistors (R A , R B ) and a heater resistor (24), said heater resistor (24) and detector resistors (21) being located over said aluminum (13); e) sputter depositing about 5000 angstroms of silicon nitride (16) over the platinum and the previous silicon nitride (14); f) cutting narrow slots (40 to 47; 50 to 57; 60 to 65) through the silicon nitride (14, 16) to the aluminum layer (13), the slots being near but spaced from the aluminum edges; g) introducing acid etch through the slots to etch out the sacrificial aluminum leaving a 400 angstrom high cavity; h) introducing KOH anisotropic etch through the slots and cavity to anisotropically etch a thermal isolation pit (23) in the silicon wafer (11); and i) applying and delineating polyimide film (27) over slots to close off the slots.
Claim 7
Dependent Claim
251 words
A process for fabricating a thin film microsensor for airflow, characterized by the steps of: a) providing a single crystal (100) silicon wafer (11) having a planar surface (12), and having a <110> direction; b) sputter depositing and delineating a 400 angstrom thick layer (13) of sacrificial aluminum on the silicon surface, the critical edge of the aluminum delineation being oriented orthogonally to the <110> direction; c) sputter depositing about 5000 angstroms of silicon nitride (14) on the aluminum (13) and the rest of the silicon surface (12); d) depositing and delineating about 800 angstroms of platinum (15) on the silicon nitride (14) to form desired circuit elements such as detector resistors (20, 21), circuit resistors (R A , R B ) and a heater resistor (24), said heater resistor (24) and detector resistors (21) being located over said aluminum (13); e) sputter depositing about 5000 angstroms of silicon nitride (16) over the platinum and the previous silicon nitride (14); f) cutting narrow slots (40 to 47; 50 to 57; 60 to 65) through the silicon nitride (14, 16) to the aluminum layer (13), the slots being near but spaced from the aluminum edges; g) introducing acid etch through the slots to etch out the sacrificial aluminum leaving a 400 angstrom high cavity; h) introducing KOH anisotropic etch through the slots and cavity to anisotropically etch a thermal isolation pit (23) in the silicon wafer (11); and i) applying and delineating polyimide film (27) over slots to close off the slots.
Claim 8
Dependent Claim
34 words
The process according to one of the preceding claims, characterized in that the delineated rectangular area of a thin film layer of sacrificial selectively etchable material (13) is about 325 microns on a side.
Claim 9
Dependent Claim
23 words
The process according to one of the preceding claims, characterized in that the narrow slots (40-47; 50-57; 60-65) are about 2-4 microns wide.
Claim 10
Dependent Claim
22 words
The process according to one of the preceding claims, characterized in that the polyimide selected to close the slots is Probimide 285.
Claim 11
Dependent Claim
29 words
The process according to one of the preceding claims, characterized in that the critical edge of the selectively etchable material (13) delineation is oriented orthogonally to the <110> direction.
Claim 12
Dependent Claim
229 words
An intermediate structure formed in the fabrication process of a thin film microsensor for airflow, characterized by : a) a single crystal (100) silicon wafer (11) having a planar surface (12) and having a <110> direction; b) a sacrificial thin film layer (13) of aluminum on said planar surface (12), said aluminum having a thickness of about 400 angstroms, said aluminum being delineated so that the critical edges of the aluminum delineation are oriented orthogonally to the <110> direction; c) a thin film layer (14) of silicon nitride on the aluminum (13) and the remainder of the silicon surface (12); d) a thin film resistive heater element (24) on said silicon nitride layer (14) and centered over said aluminum layer (13); e) first (30) and second (33) thin film resistive flow detector elements on said silicon nitride layer (14), one on each side of said heater element (24), said detector elements being located over said aluminum layer (13); f) another thin film layer (16) of silicon nitride over said heater (24) and detector (30, 33) elements and the earlier mentioned silicon nitride layer (14); g) a plurality of narrow slots (40-47; 50-57; 60-65) formed through said silicon nitride (14, 16) to said aluminum (13), said slots being positioned to be near but spaced from the critical edges of the aluminum and also positioned away from said heater element (24).
Claim 13
Dependent Claim
229 words
An intermediate structure formed in the fabrication process of a thin film microsensor for airflow, characterized by : a) a single crystal (100) silicon wafer (11) having a planar surface (12) and having a <110> direction; b) a sacrificial thin film layer (13) of aluminum on said planar surface (12), said aluminum having a thickness of about 400 angstroms, said aluminum being delineated so that the critical edges of the aluminum delineation are oriented orthogonally to the <110> direction; c) a thin film layer (14) of silicon nitride on the aluminum (13) and the remainder of the silicon surface (12); d) a thin film resistive heater element (24) on said silicon nitride layer (14) and centered over said aluminum layer (13); e) first (30) and second (33) thin film resistive flow detector elements on said silicon nitride layer (14), one on each side of said heater element (24), said detector elements being located over said aluminum layer (13); f) another thin film layer (16) of silicon nitride over said heater (24) and detector (30, 33) elements and the earlier mentioned silicon nitride layer (14); g) a plurality of narrow slots (40-47; 50-57; 60-65) formed through said silicon nitride (14, 16) to said aluminum (13), said slots being positioned to be near but spaced from the critical edges of the aluminum and also positioned away from said heater element (24).
Claim 14
Dependent Claim
26 words
The structure according to claim 10, characterized in that the delineated aluminum (13) is in the shape of a square about 325 microns on a side.
Claim 15
Dependent Claim
26 words
The structure according to claim 10, characterized in that each of the silicon nitride layers (14, 16) is in the range of 2000-7000 angstroms in thickness.
Claim 16
Dependent Claim
23 words
The structure according to claim 12, characterized in that each of the silicon nitride layers (14, 16) is about 5000 angstroms in thickness.
Claim 17
Dependent Claim
28 words
The structure according to one of the claims 10 to 13, characterized in that said narrow slots (40-47; 50-57; 60-65) are in the range of 2-4 microns wide.
Claim 18
Dependent Claim
26 words
The structure according to one of the claims 10 to 14, characterized in that said aluminum (13) is on the order of 400 angstroms in thickness.
References Cited (Backward Citations)
EP0176996A2
Cited
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