The electron trapping behavior of SiO2 has been measured as a function of thickness at 295 and 77 °K. The devices used were metal‐oxide‐semiconductor devices with the SiO2 grown thermally. The results indicate bulk traps are dominant at 295 °K and traps associated with the Si‐SiO2 interface are dominant at 77 °K. The effect of processing conditions was also studied and the optimum conditions are different for the two temperatures used for the measurements. These observations have been verified using a photo I‐V technique. The generation of donor states in the SiO2 near the Si‐SiO2 interface was observed as a result of the electron current through the SiO2.

Electron trapping in SiO2 at 295 and 77 °K

Auger electron spectroscopy has been used in conjunction with argon ion sputtering in a study of the chemical structure of the interface region between thermally grown SiO2 and the Si substrate. The distorting effects of the electron and ion beams are dealt with in detail, and we show how the beam parameters can be chosen to minimize instrumental artifacts in the Auger spectra and the chemical depth profiles of the SiO2‐Si interface. We discuss the SiO2‐Si interface in terms of a morphology model which includes a natural interface roughness and inclusions of silicon in the oxide close to the interface. The width of the interface of a 1000‐A oxide grown at 1200 °C in dry O2 on Si (100) is approximately 35 A.

An Auger analysis of the SiO2‐Si interface

An experiment using the effect of optically induced hot‐electron injection in MOS transistor structures to study electron traps in SiO2 films is described. By simultaneously monitoring the gate current and the surface channel conductance shift, information on the trapping efficiency, the capture cross sections, and the trap concentrations could be obtained. Trap centers with capture cross sections differing by more than two orders of magnitude could probably be separated and their cross sections determined depending on their concentrations. Experimental results are presented for electron traps using n ‐channel silicon‐gate structures, with SiO2 layers thermally grown in dry oxygen. Two electron‐capture cross sections of 3.3 × 10−13 and 2.4 × 10−19 cm2 were measured. Although there was evidence indicating the presence of other electron traps their capture cross sections could not be unambiguously determined. The injection current can be described by Schottky‐emission processes at an effective electron temp...

Optically induced injection of hot electrons into SiO2

Water was diffused into very dry thermal SiO2 films under conditions such that the penetration of water related electron trapping centers was of the order of the oxide thickness. In both dry oxides and water diffused oxides, production of negative bulk oxide charge Qot and positive interface charge Qit by an avalanche‐injected electron flux was observed. The efficiencies of both processes were enhanced by water indiffusion. Analysis of the kinetics of charge generation indicated that production of trapped electron centers (Qot ) was required for subsequent production of interface states and charge (Qit ). Models for both processes are discussed. We suggest that inelastic collisions of conduction electrons with the trapped electron centers releases mobile hydrogen atoms or excitons. The mobile species migrate to the Si–SiO2 interface and form states and fixed charge.

The effects of water on oxide and interface trapped charge generation in thermal SiO2 films

A new rapid technique for determining the density and centroid of trapped space charge in MOS structures is described. Photocurrent‐voltage characteristics for both the metal‐oxide and Si‐oxide interfaces are used to determine the internal fields due to bulk trapped charge and, hence, its density and centroid. An experimental example of this technique is shown for a MOWOS (metal‐SiO2‐W‐SiO2‐Si) structure where a layer of approximately 1014 W atoms/cm2 deposited 80 or 42 A from the Si‐SiO2 interface and charged by internal photoemission is investigated. This technique is compared to others in terms of its direct, rapid, minimally perturbing, low‐current and low‐field characteristics.

Determination of insulator bulk trapped charge densities and centroids from photocurrent‐voltage charactersitcs of MOS structures

Determination of the nature and distribution of oxide charge in MOS structures is important to an understanding of oxide charging phenomena. In addition to their relevance to device failure mechanisms, it appears that charging phenomena may be used to advantage in memory device applications. The physical mechanism dominating the voltage dependence of photoinjected currents in SiO2 is the scattering of electrons in the region of the oxide between the injecting electrode and the image force potential maximum. Since the spatial position of the potential maximum depends on the electric field resulting from space charge in the oxide as well as the field due to the applied voltage, analysis of the V‐I characteristics of photoinjected currents can provide information about the spatial location of oxide charge. Presented in this paper are the results of an analysis of the effects of oxide space charge on the voltage dependence of photoinjected currents. It is shown that effective charge distributions in SiO2 can ...

R. J. Powell

Papers

Photoinjection Studies of Charge Distributions in Oxides of MOS Structures