Oxide Charge Distribution Research Articles

Radiation-Induced Oxide Charge Distributions in Simox Buried Oxides

AbstractIn ionizing-radiation environments, oxide charge buildup in the buried oxide of SIMOX SOI material causes an increase in the back-channel leakage current, resulting in an instability in electronic circuits formed on SIMOX wafers. We report the measured distributions of radiation-induced oxide charge density in buried oxides formed by oxygen implantation. These are obtained by etch-back experiments including C-V measurements using a mercury probe and ellipsometer measurements. The results show a region of higher charge density about 1500A from the top interface with a lower density region within a few hundred angstroms of the top interface. The results also show that the oxide charge density decreases with annealing temperature. Some unusual optical properties of SIMOX oxide observed in ellipsometer measurements are discussed comparatively with thermal oxide.

Comments on ’’Effects of spatially inhomogeneous oxide charge distribution on the MOS capacitance-voltage characteristics’’

Clarifying distinctions are made concerning the models employed to describe the spatial oxide charge inhomogeneity in MOS capacitors.

Effects of spatially inhomogeneous oxide charge distribution on the MOS capacitance-voltage characteristics

The commonly assumed linear model of surface potential fluctuation using a Gaussian distribution is shown to be invalid. A macrocapacitor model previously proposed by us is used to analyze the effects of spatially inhomogeneous oxide charge distribution on the MOS C-V characteristics at various rms oxide charge deviations and temperatures. It is shown that a Gaussian oxide charge distribution of rms value of as low as 1011 electrons/cm2 gives rise to a doubly peaked probability distribution of the surface potential fluctuation. Substantial errors in fast surface state density occur using either the low-frequency capacitance (Berglund), the high-frequency capacitance (Terman), or the temperature dependence (Gray-Brown) analysis of the fast surface states from C-V curves. A major source of error is in the value of the average surface potential which is changed substantially from the ideal case by the presence of inhomogeneous oxide charge distributions.

Photoinjection Studies of Charge Distributions in Oxides 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 be nondestructively profiled over a range from about ten to several hundred angstroms from the injecting electrode. Since photoinjection V-I characteristics depend on electric field at the potential maximum in the oxide, whereas C-V characteristics depend on the field just inside the semiconductor, analysis of both characteristics permits distinction between charge in the oxide a distance greater than about 10 Å and charge located at the interface. The results of experiments on Au–SiO2–Si structures in which charge has been purposely introduced into the oxide are presented, and it is shown that the interface fixed charge and the charge associated with fast surface states extend no further than about 20 Å into the oxide from the Si–SiO2 interface.

The Use of Photoinjection to Determine Oxide Charge Distributions and Interface Properties in MOS Structures-Invited Paper

Determination of the distribution of oxide charge and interface properties is important to an understanding of oxide charging phenomena such as that produced by irradiation. 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 charge distribution in SiO2 can be nondestructively profiled over a range from about ten to several hundred angstroms from the injecting electrode. Since photoinjection V-I characteristics depend on electric field at the potential maximum in the oxide, whereas C-V characteristics depend on the field just inside the semiconductor, analysis of both characteristics permits distinction between charge in t e oxide a distance greater than about 10 A and charge located at the interface.

The kinetics of oxide growth during thermal oxidation of silicon†

A model of the Si/Si O2 interface, based on the oxidation kinetics during growth, is presented. The distribution of oxide charge within the oxide is determined. This distribution is similar to that, predicted by the model, for incompletely reacted silicon. In order to aid quantitative application of this model, results, which indicate that molecular oxygen is the diffusing species during growth, arc presented.

Iprrdiation Damage of MOS-FETS Operating in the Common Source Mode

Thirty-three MOS-FETS were operated at various bias points under 60Co gamma irradiation up to a total dose of approximately 107 R. The n-channel depletion, n-channel enhancement, and p-channel enhancement devices were operated at constant drain voltage in the common source mode. The results demonstrate effects of lateral oxide charge distributions along the channel between source and drain terminals. A tendency for the n-channel devices to gradually turn off is observed in addition to the threshold voltage shifts previously reported. A factor of ten improvement in radiation resistance can be obtained by using optimum device types (n-channel) at gate voltages which minimize threshold voltage shift (approximately zero volts).