A novel optical technique for the measurement of temperature is proposed. This is accomplished by depositing alternating 1/4 wave layers of silicon nitride and silicon-rich silicon nitride at the end of an optical fiber. These layers of alternating refractive index form the equivalent of a Bragg grating of a high temperature material. When the fiber and the Bragg grating are heated, the Bragg stack expands, and there is a change in the reflective peak wavelength of this wave stack. Thus, the wavelength of peak reflectivity is a function of temperature. Currently, the 15 nm spectral width of the Bragg stacks is achieved in our laboratory, which is conveniently monitored with a CCD solid state spectrometer and the temperature sensor probes can be also multiplexed at separated specific reflection wavelength. In the experiment, the temperatures in excess of 1,100 centigrade have been measured with a resolution of less than 3 centigrade degree.

A novel technique has been developed for in situ sensing of thin film growth. In this method, a fiber optic probe is placed at an appropriate position in a deposition chamber, and the thin film builds up on the end of the fiber. This film is either the same as on the wafer where deposition occurs, or it bears a fixed relationship to the film on the wafer. By an analysis of the intensity of the light reflected from the film and guided by the fiber, information on the film may be obtained. With interference causing maxima, minima and a point of inflection as the film grows, it is possible to obtain near real time information on the following quantities: the real and imaginary parts of the refractive index of the film, a Gaussian parameter characterizing surface roughness, and the film thickness itself. To demonstrate this technique, we have studied the deposition of silicon nitride films in a CVD reactor and how reactor temperature and reactant flow rates influence film growth. This technique may be applied to measure in situ reflectivity of multi layer films, so that reflectance as a function of temperature and time may be obtained. Because the measurement is simple and direct and the information is optical, we believe that this technique has the potential to supplant quartz oscillators in the measurement of thin film growth.