Several samples of thin-film silicon grown on oxidized Si, both oxidized and unoxidized, have been examined using spectroscopie ellipsometry (SE) and constant angle reflection interference spectroscopy (CARIS). The SE data was fit to 5- or 6- layer models of the sample near-surface region, using the optical functions of thin-film silicon determined from a previous work. Reasonable fits were obtained from samples containing amorphous Si (a-Si) or large-grain poly-crystalline Si (p-Si), but fits to samples containing small-grain, undoped p-Si were poor unless a 8–15 nm surface roughness layer is included. Furthermore, the optical functions of p-Si:ud are not consistent from sample to sample. The optical functions determined from SE measurements were then used to interpret CARIS measurements, extracting the thicknesses of the films, which are then compared with the thicknesses obtained from SE.
Amorphous silicon has been used extensively in electro-optical applications. Its use as a gate electrode material for advanced CMOS devices is currently being developed, as it offers certain desirable characteristics compared to the commonly used polycrystalline silicon. The properties of amorphous silicon, including optical and electronic, are highly variable depending on process conditions, i.e. deposition temperature, etching conditions, and chemistry. The variable optical properties present a challenge for broad-band reflected intensity optical thickness measurement techniques. This is because the constant angle reflection interference spectroscopy (CARTS) technique requires the knowledge of a film's dispersion (the change in refractive index with wavelength) before the film thickness can be determined'. An updated feature in Prometrix CARIS-based spectrophotometers allows the user to easily determine or verify dispersion for both transparent and absorbing films.As a demonstration of this technique, we have studied a series of amorphous silicon films deposited at varying temperatures. The deposition temperature ranged from 54(Y C to 570' C. The nominal thickness was approximately 1575A to 3170A. Due to the differences in deposition temperature, one would expect the optical properties to vary slightly. Using software that allows analysis of the spectral information, the dispersion was examined for each sample. With this knowledge, the film thicknesses could be reliably measured.
The design of the world's first production worthy broadband ultra-violet and visible small spot spectroscopic ellipsometer is described. The instrument, called the Prometrix® UV-125OSE, was developed by the Prometrix division of Tencor Instruments in cooperation with SOPRA S.A., a pioneer in the field of spectroscopic ellipsometry. It has the ability to measure both the thickness and refractive index of different layers on a wide variety of materials in multiple layer film stacks. In this paper the optical system will be reviewed and spot size data presented. We will further discuss some of the design considerations such as the angle of incidence and allowed spread of the collection beam. Data characterizing the precision and stability of the instrument is presented for a variety of films including SiO on silicon, and Si3N4 on silicon, and a multiple layer stack of SiO I poly-Si I SiO on silicon.
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