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In situ spectroscopic ellipsometry for advanced process control in vertical furnaces

In situ-Spektralellipsometrie für moderne Prozeßkontrolle in Vertikalöfen

Collins, R.W.:
Spectroscopic ellipsometry. Proceedings of the 2nd International Conference on Spectroscopic Ellipsometry 1997
Amsterdam: Elsevier, 1998 (Thin solid films 313-314)
International Conference on Spectroscopic Ellipsometry (ICSE) <2, 1997, Charleston/SC>
Conference Paper
Fraunhofer IIS B ( IISB) ()
high-temperature ellipsomtry; in situ ellipsometry; optical high-temperature data; spectroscopic ellipsometry

For the first time, a spectroscopic ellipsometer (SE) has been integrated into a vertical furnace to use it as an in situ layer thickness sensor. An SE was selected because of its high accuracy and versatility. In the vertical furnace, the SE can be used for in situ sensing of the layer growth as well as for post process control of the batch. The adaptation of the SE to the furnace was performed with minor modifications of the furnace geometry. The light beam of the SE is guided through the base plate into the furnace tube and directed onto the wafer by quartz glass prisms operating in total internal reflection mode. This arrangement introduces an additional phase shift in the polarization state of the light which can be determined and subtracted from the measured phase shift. For in situ spectroscopic ellipsometry at high-temperature process steps the exact knowledge of the spectral refractice indices of the measured substrate and layer materials is of crucial importance. As there is still a lack of optical data as a function of temperature reported in the literature, these optical data of some relevant materials have been determined at high temperatures to make in situ measurement possible. The determination of this refractive indices was done with the in situ SE in the vertical furnace that ensures accurate temperature control and temperature homogeneity on the wafer up to 9000C. With the knowledge of this refractive indices the SE can be used for in situ end point detection during layer growth. As the arrangement of the in situ SE enables also post process measurements on selected wafers of the batch during the unloading sequence, in situ and post process data can be used by an integrated novel furnace control system for immediate and automated correction of the parameter settings. The advantage of this integrated in situ SE such as time reduction for process optimization, avoidance of monitor wafers, and a better control of integrated multilayer processing can be beneficial for future thermal processing.