In Situ Fiber Optical Sensor for the Measurement of Thin Films

Yifei HE  Brian W. SHELDON  Theodore F. MORSE  

IEICE TRANSACTIONS on Electronics   Vol.E83-C   No.3   pp.315-325
Publication Date: 2000/03/25
Online ISSN: 
Print ISSN: 0916-8516
Type of Manuscript: Special Section PAPER (Special Issue on Optical Fiber Sensors)
Category: Physical and Mechanical Sensors
optical fiber sensor,  in situ measurement,  refractive index,  surface roughness,  film thickness,  

Full Text: PDF>>
Buy this Article

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.