Growth and structure of rapid thermal silicon oxides and nitroxides studied by spectroellipsometry and Auger electron spectroscopy

Abstract

Rapid thermal oxidation of Czochralski-grown silicon in either O2 or N2O atmospheres have been studied using spectroellipsometry and Auger electron spectroscopy. Multiwavelength ellipsometric data were processed in order to separately derive the thicknesses and refractive indexes of rapid thermal dielectrics. Results revealed a significant increase of the mean refractive index as the film thickness falls below 20 nm for both O2 or N2O oxidant species. A multilayer structure including an about 0.3-nm-thick interfacial region of either SiOx or nitroxide in the case of O2 and N2O growth, respectively, followed by a densified SiO2 layer, was found to accurately fit the experimental data. The interfacial region together with the densified state of SiO2 close to the interface suggest a dielectric structure in agreement with the continuous random network model proposed for classical thermal oxides. Auger electron spectroscopy analysis confirmed the presence of noncrystalline Si—Si bonds in the interfacial region, mostly in the case of thin oxides grown in O2. It was speculated that the initial fast growth regime was due to a transient oxygen supersaturation in the interfacial region. Besides, the self-limiting growth in N2O was confirmed and explained in agreement with several recently published data, by the early formation of a very thin nitride or oxynitride membrane in the highly densified oxide beneath the interface. The beneficial effect of direct nitrogen incorporation by rapid thermal oxidation in N2O instead of O2 for the electrical behavior of metal-oxide-semiconductor capacitors is likely a better SiO2/Si lattice accommodation through the reduction of stresses and Si—Si bonds in the interfacial region of the dielectric.

Light nitrogen implant for preparing thin-gate oxides

“…Similar reservations have been recently raised in a study on the sensitivity of the measured oxide thickness on ellipsometry parameters [6]. In [4], it was suggested that 0741-3106/97$10.00 © 1997 IEEE the refraction index could change from 1.4 for thick oxides to 1.7 for oxides thinner than 100Å. Based on our data, 1.458 is still valid for thin oxides down to 25Å.…”

“…The averaged values from ellipsometry (TEM) are 25 (26), 38 (38), 76 (79), 96 (97), 123 (123), and 144Å (146Å). This indicates that previous suggestions of substantial changes in the oxide index of refraction [4] should be reexamined. Similar reservations have been recently raised in a study on the sensitivity of the measured oxide thickness on ellipsometry parameters [6].…”

“…We also found that, with a fixed index of refraction at 1.458, ellipsometry measurement gave identical oxide thickness as high-resolution TEM's for oxides between 25 and 144Å. Previously, index of refraction close to 1.7 has been suggested for oxides thinner than 100Å [4].…”

Measurement of N in nitrided oxides using spectroscopic immersion ellipsometry

“…Another way to view this situation is that the measured changes are optically dominated by the overlayer. It is interesting to consider a recent article 27 where SE and Auger spectroscopy were used to characterize nitrided oxides. The SE measurements were done in air and nitrided oxides were prepared by rapid thermal oxidation in N 2 O at temperatures up to 1200°C.…”

Structure of silicon/oxide and nitride/oxide interfaces

“…µÏÇÐßÛÇÐËÇ ÕÑÎÜËÐÞ ÑÕ 8 AEÑ 2 ÐÏ ÔÑÒÓÑÄÑÉAEÂÇÕÔâ ÖÄÇÎËÚÇÐËÇÏ ÒÑÍÂÊÂÕÇÎâ ÒÓÇÎÑÏÎÇÐËâ ÑÕ 1,52 AEÑ 2,0. ±ÑAEÑÃÐÞÌ à××ÇÍÕ ÐÂÃÎá-AEÂÎÔâ ÓÂÐÇÇ ¤ÑÐÑÐÑÏ Ô ÔÑÂÄÕÑÓÂÏË [13].¯Â ÓËÔÖÐÍÇ 2 6 ÊÄÇÐßÇÄ, n 1,57 [18,19] ²ËÔ. 14.…”