In situ fiber optical sensor for the measurement of thin films

A novel technique has been developed for in situ sensing of thin film growt h. 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 fib er. This film is either the same as on the wafer where deposition occurs, o r 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 firm may be obtained. With interference causing maxima , minima and a point of inflection as the film grows, it is possible to obt ain near real time information on the following quantities: the real and im aginary parts of the refractive index of the firm, a Gaussian parameter cha racterizing surface roughness, and the film thickness itself. To demonstrat e this technique, we have studied the deposition of silicon nitride films i n a CVD reactor and how reactor temperature and reactant flow rates influen ce film growth. This technique may be applied to measure in situ reflectivi ty of multi layer films, so that reflectance as a function of temperature a nd time may be obtained. Because the measurement is simple and direct and t he information is optical, we believe that this technique has the potential to supplant quartz oscillators in the measurement of thin film growth.