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A gas detector and process for detecting a fluorine-containing species in a gas containing same, e.g., an effluent of a semiconductor processing tool undergoing etch cleaning with HF, NF 3, etc. The detector in a preferred structural arrangement employs a microelectromechanical system (MEMS)-based d

A gas detector and process for detecting a fluorine-containing species in a gas containing same, e.g., an effluent of a semiconductor processing tool undergoing etch cleaning with HF, NF 3, etc. The detector in a preferred structural arrangement employs a microelectromechanical system (MEMS)-based device structure and/or a free-standing metal element that functions as a sensing component and optionally as a heat source when elevated temperature sensing is required. The free-standing metal element can be fabricated directly onto a standard chip carrier/device package so that the package becomes a platform of the detector.

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What is claimed is: 1. A gas sensor assembly for sensing fluoro species, the assembly comprising a gas sensing element coupled to a substrate defining a recess, wherein the gas sensing element is fabricated directly on the substrate, and spans across the recess and bounds a portion of the recess to

What is claimed is: 1. A gas sensor assembly for sensing fluoro species, the assembly comprising a gas sensing element coupled to a substrate defining a recess, wherein the gas sensing element is fabricated directly on the substrate, and spans across the recess and bounds a portion of the recess to define an air-gap, thereby forming a free standing gas sensing element in sensory communication with the air-gap; wherein the substrate is communicatively connected to means for monitoring a change in at least one property of the gas sensing element upon contact thereof with a fluoro species and responsively generating an output signal; and wherein the gas sensing element is formed of a noble metal or transition metal material that exhibits a monitorable change when reacting with the fluoro species. 2. The gas sensor assembly of claim 1, wherein the material of which the free-standing gas sensing element is formed comprises a metal selected from the group consisting of Ti, V, Cr, Mn, Nb, Mo, Ru, Pd, Ag, Ir, Ni, Al, Cu and Pt, and alloys and combinations thereof. 3. The gas sensor assembly of claim 1, wherein the material of which the free-standing gas sensing element is formed comprises Ni. 4. The gas sensor assembly of claim 1, wherein the fluoro species comprises a fluoro species selected from the group consisting of NF3, SiF4, C2F6, HF, F2, COF2, CIF3, IF3, and activated species thereof. 5. The gas sensor assembly of claim 4, wherein the material of which the free-standing gas sensing element is formed comprises Ni, and wherein the fluoro species comprises a fluoro species selected from the group consisting of NF3, SiF4, C2F 6, HF, F2, COF2, and activated species thereof. 6. The gas sensor assembly of claim 1, wherein the free-standing gas sensing element has a conformation selected from the group consisting of foils, films, filaments, needles, powders, metal-doped conductive threads, electrodeposited metals, and vapor-deposited metals. 7. The gas sensor assembly of claim 1, wherein the free-standing gas sensing element has a critical dimension less than 100 μm. 8. The gas sensor assembly of claim 1, wherein the free-standing gas sensing element has a critical dimension less than 50 μm. 9. The gas sensor assembly of claim 1, wherein the free-standing gas sensing element has a critical dimension less than 25 μm. 10. The gas sensor assembly of claim 1, wherein the free-standing gas sensing element has a critical dimension less than 10 μm. 11. The gas sensor assembly of claim 1, wherein the free-standing gas sensing element has a critical dimension in a range of from about 0.1 μm to about 0.5 μm. 12. The gas sensor assembly of claim 1, wherein the free-standing gas sensing element comprises a foil or film having a thickness in a range of from about 0.1 μm to about 100 μm. 13. The gas sensor assembly of claim 12, wherein the lateral dimensions of the foil or film, in each of the x and y directions, are less than about 10 mm. 14. The gas sensor assembly of claim 12, wherein the lateral dimensions of the foil or film, in each of the x and y directions, are less than about 1 mm. 15. The gas sensor assembly of claim 12, wherein the lateral dimensions of the foil or film, in each of the x and y directions, are less than about 100 μm. 16. The gas sensor assembly of claim 12, wherein the lateral dimensions of the foil or film, in each of the x and y directions, are in a range of from about 20 μm to about 5 mm. 17. The gas sensor assembly of claim 1, wherein the free-standing gas sensing element comprises a filament having a diameter of less than 150 μm. 18. The gas sensor assembly of claim 1, wherein the free-standing gas sensing element comprises a filament having a diameter of less than 50 μm. 19. The gas sensor assembly of claim 1, wherein the free-standing gas sensing element comprises a filament having a diameter of less than 25 μm. 20. The gas sensor assembly of claim 1, wherein the free-standing gas sensing element comprises a filament having a diameter of less than 10 μm. 21. The gas sensor assembly of claim 1, wherein the free-standing gas sensing element comprises a filament having a diameter in a range of from about 0.1 μm to about 0.5 μm. 22. The gas sensor assembly of claim 1, wherein said means for monitoring a change in at least one property of the gas sensing element upon contact thereof with a fluoro species and responsively generating an output signal, comprise electrical circuitry responsively generating said output signal, and wherein said change in at least one property of the gas sensing element, comprises a change in electrical resistivity of the gas sensing element. 23. The gas sensor assembly of claim 1, wherein said means for monitoring a change in at least one property of the gas sensing element upon contact thereof with a fluoro species and responsively generating an output signal, generates an output signal that is used to monitor a process or control a process that generates the fluoro species. 24. The gas sensor assembly of claim 1, wherein the substrate comprises a chip carrier/device package and electrical contact to the gas sensing element is effected from the backside of the chip carrier/device package by through-vias or pins disposed in the chip carrier/device package. 25. The gas sensor assembly of claim 1, wherein contacting of the fluoro species with the gas sensing element effects a temperature-sensitive reaction of the fluoro species and the gas sensing element, and wherein the assembly is constructed and arranged for passing current through the gas sensing element for heating thereof to temperature facilitating the temperature-sensitive reaction. 26. The gas sensor assembly of claim 1, comprising a multiplicity of said gas sensing elements defining an array. 27. The gas sensor assembly of claim 26, wherein the array is constructed and arranged to monitor different fluoro species, and/or to operate in different operating modes in different elements of the array. 28. The gas sensor assembly of claim 26, wherein the array is constructed and arranged to monitor the same fluoro species at different process conditions. 29. A solid state sensor coupled in gas sensing relationship to a process chamber and arranged to withstand a corrosive condition within said process chamber, wherein said solid state sensor comprises a non-silicon containing gas sensing element arranged for contacting said corrosive environment and responsive to said contacting by change of at least one monitorable property of the gas sensing element, wherein the gas sensing element is connected to a non-silicon containing substrate and positioned directly over an air gap thereby forming a free standing gas sensing element; and a signal generator arranged to output a signal indicative of said change in said at least one property of the gas sensing element. 30. The solid state sensor of claim 29, wherein the process chamber comprises a semiconductor process chamber. 31. The solid state sensor of claim 29, wherein said free-standing gas sensing element comprises a wire or metal film. 32. A gas sensor assembly arranged to monitor an effluent from a semiconductor manufacturing plant or a fluid derived from said effluent, wherein said effluent or fluid derived therefrom is susceptible to the presence of a target fluoro species, wherein said gas sensor assembly comprises a gas sensing element coupled on a substrate, wherein the substrate is a chip carrier/device package and the gas sensing element is fabricated directly thereon and positioned over an air-gap thereby forming a free standing gas sensing element, and the substrate is communicatively connected to means for monitoring a change in at least one property of the gas sensing element upon contact thereof with the target fluoro species in said effluent or a fluid derived from said effluent, and responsively generating an output signal, wherein the gas sensing element is formed of a noble metal or transition metal material that exhibits a monitorable change when reacting with the target fluoro species. 33. The gas sensor assembly of claim 32, arranged to monitor an effluent from a semiconductor processing chamber that is arranged for periodic cleaning with NF3, wherein silicon and/or silicon-containing material present in said semiconductor processing chamber is susceptible of reacting with the NF3 to form SiF4, and wherein SiF4 is the target fluoro species. 34. The gas sensor assembly of claim 32, wherein the gas sensing element is formed of nickel. 35. A method of monitoring a fluid locus for the presence or change in concentration of a target fluoro species therein, said method comprising: (a) exposing fluid from said fluid locus to a non-silicon containing gas sensing element formed of a transition metal or noble metal material exhibiting a change in at least one property thereof upon contact with the target fluoro species, wherein the gas sensing element is coupled to a non-silicon containing substrate and positioned directly over an air gap to form a free-standing gas sensing element; (b) monitoring said at least one property of the gas sensing element during step (a); and (c) responsively generating an output signal when the gas sensing element exhibits said change in at least one property of the gas sensing element, indicating the presence of the target fluoro species in the fluid locus. 36. The method of claim 35, wherein the fluid locus comprises an ambient gas environment of a manufacturing process. 37. The method of claim 35, wherein the fluid locus comprises a fluid stream in a semiconductor processing plant. 38. The method of claim 35, wherein the free-standing gas sensing element material comprises a metal selected from the group consisting of Ti, V, Cr, Mn, Nb, Mo, Ru, Pd, Ag, Ir, Ni, Al, Cu, Pt, and alloys and combinations thereof. 39. The method of claim 35, wherein the free-standing gas sensing element material comprises Ni. 40. The method of claim 35, wherein the fluoro species comprises a fluoro species selected from the group consisting of NF 3, SiF4, C2F6, HF, F2, COF 2, CIF3, IF3 and activated species thereof. 41. The method of claim 35, wherein the free-standing gas sensing element material comprises Ni, and wherein the fluoro species comprises a fluoro species selected from the group consisting of NF 3, SiF4, C2F6, HF, and activated species thereof. 42. The method of claim 35, wherein the free-standing gas sensing element has a conformation selected from the group consisting of foils, films, filaments, needles, powders, metal-doped conductive threads, and deposited metals. 43. The method of claim 35, wherein the free-standing gas sensing element has a critical dimension less than 150 μm. 44. The method of claim 35, wherein the free-standing gas sensing element has a critical dimension less than 50 μm. 45. The method of claim 35, wherein the free-standing gas sensing element has a critical dimension less than 25 μm. 46. The method of claim 35, wherein the free-standing gas sensing element has a critical dimension less than 10 μm. 47. The method of claim 35, wherein the free-standing gas sensing element has a critical dimension in a range of from about 0.1 μ m to about 0.5 μm. 48. The method of claim 35, wherein the free-standing gas sensing element comprises a foil or film having a thickness in a range of from about 0.1 μm to about 50 μm. 49. The method of claim 48, wherein the lateral dimensions of the foil or film, in each of the x and y directions, are less than about 10 mm. 50. The method of claim 48, wherein the lateral dimensions of the foil or film, in each of the x and y directions, are less than about 1 mm. 51. The method of claim 48, wherein the lateral dimensions of the foil or film, in each of the x and y directions, are less than about 100 μm. 52. The method of claim 48, wherein the lateral dimensions of the foil or film, in each of the x and y directions, are in a range of from about 20 μm to about 5 mm. 53. The method of claim 35, wherein the free-standing gas sensing element comprises a filament having a diameter of less than 100 μm. 54. The method of claim 35, wherein the free-standing gas sensing element comprises a filament having a diameter of less than 50 μm. 55. The method of claim 35, wherein the free-standing gas sensing element comprises a filament having a diameter of less than 25 μm. 56. The method of claim 35, wherein the free-standing gas sensing element comprises a filament having a diameter of less than 10 μm. 57. The method of claim 35, wherein the free-standing gas sensing element comprises a filament having a diameter in a range of from about 0.1 μm to about 0.5 μm. 58. The method of claim 35, wherein the output signal generated in step (c) is employed to control a process in which the target fluoro species is generated. 59. The method of claim 58, wherein the process comprises a semiconductor manufacturing process. 60. The method of claim 35, wherein the output signal generated in step (c) is employed to actuate an alarm. 61. The method of claim 35, wherein the output signal generated in step (c) is employed to actuate one or more valves. 62. The method of claim 35, wherein the output signal generated in step (c) is employed to effect an operational change in a process having the target fluoro species generated as a chemical reaction product. 63. The method of claim 62, wherein the target fluoro species comprises at least one of the species selected from the group consisting of SiF4, F2 and F•. 64. A gas sensor assembly for sensing fluoro species, the assembly comprising a substrate having deposited thereon a barrier layer for protection of the substrate from attack during gas sensing, and a layer deposited on said barrier layer of a sensing material fabricated from a transition metal or noble metal to act as a sensing layer and a resistive heating device and producing in exposure to a fluoro species containing gas to be sensed a change in at least one property or response characteristic of the sensing material layer, wherein the barrier layer is disposed between the sensing layer and the substrate, and the substrate defines a cavity on a back side thereof, said cavity being bounded in part by and terminating at a back face of the sensing layer. 65. The gas sensor assembly of claim 64, wherein the substrate is formed of silicon. 66. The gas sensor assembly of claim 64, wherein the barrier layer is formed of an inorganic dielectric material. 67. The gas sensor assembly of claim 66, wherein the inorganic dielectric material comprises a material selected from the group consisting of silicon carbide and diamond-like carbon. 68. The gas sensor assembly of claim 64, wherein the barrier layer is formed of an organic material. 69. The gas sensor assembly of claim 68, wherein said inorganic dielectric material comprises polyimide. 70. The gas sensor assembly of claim 64, wherein the sensing material layer comprises a metal selected from the group consisting of platinum, copper, aluminum and nickel. 71. The gas sensor assembly of claim 64, wherein the sensing material layer is formed of nickel. 72. The gas sensor assembly of claim 64, wherein the sensing material layer is patterned by a patterning technique selected from the group consisting of pattern etching and patterning through a shadow mask. 73. The gas sensor assembly of claim 64, wherein the cavity comprises an etch cavity. 74. The gas sensor assembly of claim 64, further comprising an electrical contact to the sensing layer. 75. The gas sensor assembly of claim 74, wherein the electrical contact is formed by top wirebonding. 76. The gas sensor assembly of claim 74, wherein the electrical contact is formed through the barrier layer by buried contact and through via structure. 77. The gas sensor assembly of claim 64, as mounted in a sealed package. 78. The gas sensor assembly of claim 64, as mounted on the front side of a flange member. 79. The gas sensing assembly according to claim 1, wherein said free-standing gas sensing element comprises a composite filament including a filament core having a fluoro species-sensitive material coated thereon, wherein said core material has a higher resistivity than said fluoro species-responsive material. 80. The gas sensing assembly of claim 79, wherein the filament core comprises Monel. 81. The gas sensing assembly of claim 80, wherein the fluoro species-responsive material comprises nickel.