Formation and Properties of Thin Tunnelable SiO2 Films Using a Vaporized  O 2 Source at Liquid  N 2 Temperature

Abstract

A high temperature (700~176 oxidation process for the formation of thin tunnelable SiO2 (20-70A) is described. This oxidation process uses liquid 02 at liquid N2 temperature as a source of oxidant and oxygen is vaporized just before the furnace tube to supply a water-free oxidant ambient. The activation energy (20.2 keal/mole) of oxidation rate differs from that previous (43.9 kcal/mole) which has been evaluated for thin oxide growth using the 02/N2 partial pressure method. By the use of this technique we can control thickness to ~_0.5~ accuracy. The rate of oxidation has been found to be governed by the inverse-logarithmic growth law, i.e., Mott-Cabrera's fieldassisted diffusion law. Electrical characteristics, such as dynamic conductance, capacitance, and tunnel current, are measured and discussed. The increment of the oxidation temperature is found to result in the decrease of surfacestate density at the Si-SiO2 interface. The process described enables the way for wider application of thin oxide devices.There has been a good deal of recent interest in thin oxide nonvolatile memory devices such as metalnitride-oxide silicon (MNOS) devices. This is because of the proposed use of MNOS devices in electrically alterable read-only memories as well as for various other applications (1). In these devices, a thin tunnelable oxide plays a very important role in governing several properties of the memory actions, such as switching speed, retention characteristics, and degradation phenomena. Although there is a considerable amount of information available about the kinetics and electrical properties of relatively thick (0.02-1 #m) SiO2 layers (2-4), there has been comparatively little published on thin (<200A) SiO2 films (5-7). Most importantly, there is little information on the reproducibility of the formation and quality control of thin tunnelable oxides.This paper presents a study of the growth of thin tunnelable oxides (20-80A) on freshly etched Si at 700~176 in dry oxygen. It describes the successful development of a technique for reproducibly ~abricat-ing thin tunnelable SiO2 films (on Si) and for improving the Si-SiO2 interface properties. Experimental ProceduresSample preparation.--Most of the single crystal silicon wafers in this study were 8-12 ~2-cm p-type with a chemmechanically polished (100) face. Conductance measurements were carried out using sample wafers of 0.002 ~2-cm p+ +-type or 0.009 l~-cm n + +-type (111) face. The wafers were cleaned by a standard ammoniacal peroxide process as a preoxidation wafer treatment after the field oxide was etched off to expose the gate region. Wafers for studying the rate of formation of thin tunnelable SiO2 films did not have a field oxide, so only the cleaning sequence was carried out.All thickness measurements were made ellipsometrically. The films formed in air during 7-10 min measurement time on freshly etched Si wafers were measured to be about 6.0A (assuming that the films were SiO2 films). In this study, the refractive indexes of nsio2 = 1.47 and nsi = 4.08-0.02...

Low Temperature Oxidation of Silicon in a Microwave‐Discharged Oxygen Plasma

“…However, Fehlner (22) reported that the Cabrera-Mott model (23) (CM model) is valid for explaining the oxidation under low temperature or low pressure conditions. Kamigaki et al (24) and Horiuchi et al (25) reported that the CM model rather than the DG model was adequate for explaining the kinetics of thermal oxidation under low partial pressures, in which diluted oxygen is used to grow very thin oxide films of less than 10 nm for MNOS nonvolatile memory devices. Furthermore, Yamasaki et al…”

“…[3] rather than Eq. [5], since the oxide thickness is much larger than the results obtained from Kamigaki et al (24) and Horiuchi et al (25). The oxidation rate, i.e., dx/dt at an arbitrary oxide thickness, can be estimated by differentiating Eq.…”

On the Oxidation Kinetics of Silicon: The Role of Water

“…There is, however, a maximum thickness at which the Mott-Cabrera mechanism stops being effective. Horiuchi (20) shows that this thickness is about 60-70A which is much less than the 200-800A oxide thickness where the rapid initial growth is found (19).…”

“…It was shown by Horiuchi et al (20) that for extremely dry oxygen ambients an inverse logarithmic growth regime is found which is characteristic for the field-assisted growth (also called Mott-Cabrera mechanism). There is, however, a maximum thickness at which the Mott-Cabrera mechanism stops being effective.…”

Generalized linear-parabolic law: a mathematical model for thermal oxidation of silicon

“…It was found that all the growth curves can be fitted reasonably well by the linear-parabolic equation. In the case of low oxygen partial pressure [14] and pyrogenic steam oxidation at high temperature [ 151, the linear rate constant may take a negative value. Fig.…”