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An apparatus is provided for measuring a gas within a semiconductor thin film process. The apparatus includes an optical resonator disposed within an environment of the thin-film process, a tunable laser that excites the optical resonator at a characteristic frequency of the gas and a detector that

An apparatus is provided for measuring a gas within a semiconductor thin film process. The apparatus includes an optical resonator disposed within an environment of the thin-film process, a tunable laser that excites the optical resonator at a characteristic frequency of the gas and a detector that detects an energy within the resonator.

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The invention claimed is: 1. An apparatus for measuring a gas within a semiconductor thin film process, such apparatus comprising: a reactive gas stream of the thin-film process; an optical resonator disposed within the reactive gas stream of the thin-film process; a tunable laser that excites the

The invention claimed is: 1. An apparatus for measuring a gas within a semiconductor thin film process, such apparatus comprising: a reactive gas stream of the thin-film process; an optical resonator disposed within the reactive gas stream of the thin-film process; a tunable laser that excites the optical resonator at a characteristic frequency of the gas; and a detector that detects an energy within the resonator. 2. The apparatus for measuring a gas as in claim 1 further comprising a processor that detects a concentration of the gas based upon a ring down rate of the detected energy. 3. The apparatus for measuring a gas as in claim 2 further comprising a shuttering device disposed between the tunable laser and optical resonator that periodically interrupts optical energy from the optical resonator. 4. The apparatus for measuring the gas as in claim 2 wherein the processor further comprises a curve matching processor that matches the ring down rate of the resonator with a curve of a ring down profile of the gas. 5. The apparatus for measuring the gas as in claim 2 wherein the processor further comprises a lookup table of ring-down rates for the predetermined gas. 6. The apparatus for measuring the gas as in claim 1 wherein the thin film process further comprises a thin film processing chamber. 7. The apparatus for measuring the gas as in claim 6 further comprising an optically transparent window in an exterior wall of the thin-film processing chamber. 8. The apparatus for measuring the gas as in claim 7 further comprising the laser disposed outside the thin-film processing chamber and exciting the resonator through the optically transparent window. 9. The apparatus for measuring the gas as in claim 7 further comprising the detector disposed outside the thin-film processing chamber and receiving an optical signal from the resonator through the optically transparent window. 10. The apparatus for measuring the gas as in claim 9 wherein the resonator further comprises three optical reflectors arranged to reflect a resonating optical signal along a triangular path. 11. The apparatus for measuring the gas as in claim 10 further comprising an optical reflector of the three optical reflectors disposed adjacent the optically transparent window. 12. The apparatus for measuring the gas as in claim 10 further comprising a servo that adjusts a distance between the three optical reflectors to an integral multiple of the characteristic frequency of the gas. 13. An apparatus for measuring a quantity of a predetermined gas within a semiconductor thin film processing chamber, such apparatus comprising: a thin film processing chamber; a reactive gas stream flowing through the thin-film processing chamber; an optical resonator disposed within the reactive gas stream; a tunable laser that excites the optical resonator at an absorption wavelength of the predetermined gas; a detector that detects a ring down rate of the resonator after excitation; and a processor that determines the quantity of the gas within the thin film processing chamber based upon the detected ring down rate of the resonator. 14. The apparatus for measuring the gas as in claim 13 further comprising an optically transparent window in an exterior wall of the thin-film processing chamber. 15. The apparatus for measuring the gas as in claim 14 further comprising the laser disposed outside the thin-film processing chamber and exciting the resonator through the optically transparent window. 16. The apparatus for measuring the gas as in claim 14 further comprising the detector disposed outside the thin-film processing chamber and receiving an optical signal from the resonator through the optically transparent window. 17. The apparatus for measuring the gas as in claim 16 wherein the resonator further comprises three optical reflectors arranged to reflect a resonating optical signal along a triangular path. 18. The apparatus for measuring the gas as in claim 17 further comprising an optical reflector of the three optical reflectors disposed adjacent the optically transparent window. 19. The apparatus for measuring the gas as in claim 18 further comprising the laser coaxial aligned with a first leg of the triangular path through the optically transparent window and the one optical reflector adjacent the optically transparent window. 20. The apparatus for measuring the gas as in claim 18 further comprising the detector coaxial aligned with a second leg of the triangular path through the optically transparent window and the one optical reflector adjacent the optically transparent window. 21. The apparatus for measuring the gas as in claim 13 wherein the processor further comprises a lookup table of ring-down rates for the predetermined gas. 22. The apparatus for measuring the gas as in claim 13 wherein the processor further comprises a curve matching processor that matches the detected ring down rate of the resonator with a curve within a ring down profile of the predetermined gas. 23. An apparatus for measuring a gas within a semiconductor thin film processing chamber, such apparatus comprising: an optically transparent window in an exterior wall of the thin-film processing chamber; a reactive gas stream flowing through the thin-film processing chamber; an optical resonator disposed within the reactive gas stream; a tunable laser disposed outside the thin-film processing chamber that excites the optical resonator through the optically transparent window; a detector disposed outside the thin-film processing chamber that detects a ring-down time; and a lookup table that is used to determine the gas within the thin film processing chamber based upon the ring-down time of the resonator.