Real time, in situ measurement of film thickness with reflexion supported pyrometric interferometry (RSPI)

Real time, in situ measurement of film thickness is of crucial importance for many manufacturing processes of high-end electronic and opto-electronic devices. Most in situ process control strategies depend heavily on large data bases of process and material parameters. With RSPI film thickness and temperature are evaluated together with optical material parameters in real time using the measured data only. Material and process parameters need not to be known for evaluation. In this paper we concentrate on real time, in situ determination of film thickness and optical constants by RSPI. Temperature measurements by RSPI are discussed elsewhere. As far as the physical measurement principle for film thickness is concerned, RSPI is identical to similar intensity based monochromatic interferometric methods like Dynamical Optical Reflectivity (DOR), etc. The main progress made by RSPI compared to similar inteferometric methods concerns the evaluation algorithms, which made RSPI the only intensity based measurement approach so far suitable for in situ film thickness monitoring of multi-layer stacks and real time in situ evaluation of composition (via determination of optical constants). RSPI has been proven to be a suitable method for in situ monitoring of growth in silicon processing. Data from Si_(1-x) Ge_x Rapid Thermal Chemical Vapour Deposition (RTCVD) growth on Si wafers as well as poly-Si on a Si wafer coated with 200 nm of Si₃N₄ are presented. Further experiments have been carried out during wet silicon oxidation. In most cases thickness resolution has been better than 0.5 nm. The in situ determination of optical constants by RSPI agrees within 1% with literature values