SPECTROSCOPIC ELLIPSOMETRY STUDIES OF VERY THIN THERMALLY GROWN SIO2-FILMS - INFLUENCE OF OXIDATION PROCEDURE ON OXIDE QUALITY AND STRESS

The qualitative and structural modifications of very thin SiO2 films w ith thicknesses between 80 and 500 Angstrom, caused by the oxidation p rocedure, were studied with spectroscopic ellipsometry (SE), Analysis of the experimental dielectric function obtained by SE provides the st ructural characteristics and the thickness of the oxide in fairly good agreement with electron microscopy results in cross-sectional. geomet ry. The calculated voids volume fraction was found to drop below 3% (2 %) for oxides thicker than 250 (400) Angstrom grown at 900 (1000) degr ees C. The densification of thermal oxides grown at low oxidation temp erature predicted by Fourier transform infrared is discussed and compa red to the SE results, whereas a relation between the final oxidation time and the viscoelastic relaxation time was found. Furthermore, it i s shown that in situ SE can be used to monitor the process of oxide re moval with very low-energy Ar+ ions and to control the conditions in o rder to avoid oxide and Si substrate damage. It is found that Ar+ ions with energy of about 10 eV are required to avoid oxide damage and Si substrate amorphization at a depth below 6 Angstrom. The latter findin g is also corroborated by atomic force microscopy images obtained from Si substrates after oxide etching. Finally, the influence of oxide th ickness and the oxidation procedure on the E(1) structure of c-Si was studied and from the results the stress applied by the oxide on the Si substrate was determined. From this study it was found that the stres s depends strongly on the oxidation duration as well as on the oxidati on procedure and the type of Si substrate and is minimized at an oxida tion temperature 900 degrees C for oxidation duration longer than 70 m in. (C) 1995 American Institute of Physics.