E. A. Irene

Electron trapping in SiO2 at 295 and 77 °K

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.

A Viscous Flow Model to Explain the Appearance of High Density Thermal SiO2 at Low Oxidation Temperatures

Higher density results from the thermal oxidation of Si in dry at lower oxidation temperatures. More than 3% higher density is observed for grown at 600°C as compared with 1150°C. A consistent model for the formation of this material is deduced based on the following: the temperature dependence of the density, the annealing behavior of the higher density , and on the literature and new measurements of the intrinsic stress in films. The model considers viscous flow of a Maxwell solid and hinges on the attainment of the necessary free volume for oxidation at lower oxidation temperatures.

Applications of spectroscopic ellipsometry to microelectronics

Abstract Ellipsometry has been applied to problems in the microelectronics industry since the 1960s. Recently, spectroscopic ellipsometry has been introduced. In situ during-process ellipsometry offers great promise for monitoring and control of a wide variety of microelectronics processes. This review covers some applications in silicon technology such as oxidation, chemical vapor deposition, etching, interfaces, and new processing techniques such as plasma, ion beam and rapid thermal processing, in an effort to demonstrate the kinds of crucial microelectronics information and processes that modern ellipsometry can access. The conclusion is that single wavelength ellipsometry alone is not sufficient; spectroscopic ellipsometry is required to establish the optimum ellipsometry measurement conditions. The future of ellipsometry in microelectronics is assessed.

Visible light emission from thin films containing Si, O, N, and H

We report the fabrication, chemical, optical, and photoluminescence characterization of amorphous silicon‐rich oxynitride (SiOxNy:H) thin films by plasma‐enhanced chemical‐vapor deposition. The film compositions were followed by changes in the refractive index. X‐ray photoelectron and Fourier transform infrared spectroscopy indicate that the chemical composition is dominated by silicon suboxide bonding with N present as a significant impurity. A broad tunable photoluminescence (PL) emission is visible at room temperature with a quantum efficiency of 0.011% at peak energies to 3.15 eV. The radiative lifetimes are less than 10 ns, and there is nearly no temperature dependence of the PL intensity down to 80 K. Ex situ annealing at temperatures above 850 °C results in an increase in PL efficiency by nearly three orders of magnitude, and the PL intensity is independent of the annealing ambient. The PL results are remarkably similar to literature results in oxidized porous silicon and oxidized nanocrystalline S...

Silicon oxidation studies: A revised model for thermal oxidation

A number of recent experimental silicon oxidation studies has suggested that the present form of the linear‐parabolic oxidation model is inadequate in explaining the results. However, the best available oxidation data are linear‐parabolic in shape. The present study relieves this dilemma by revising the linear‐parabolic model. The revisions are essentially twofold: a new transport flux, viz., transport in micropores is invoked and the viscoelastic properties of SiO2 are utilized. A revised linear‐parabolic model is obtained which better explains high and low temperature oxidation behavior, the formation higher density SiO2, and the initial oxidation regime.

Magnesium oxide as a candidate high-κ gate dielectric

Magnesium oxide (MgO) thin films with sharp interfaces were deposited by sputtering of a Mg target on Si. The film stack was characterized using spectroscopic ellipsometry and transmission electron microscopy and the film static dielectric constant (κ) and interface traps were determined. An amorphous SiO2 layer was found at the MgO∕Si interface as a result of subcutaneous Si oxidation. κ for the MgO films was found to be about twice that of SiO2, and the interface trap densities of MgO∕Si were found to be comparable with SiO2∕Si, rendering MgO competitive with all presently considered high-κ dielectrics.

Silicon Oxidation Studies: Silicon Orientation Effects on Thermal Oxidation

Abstract : The initial stage of the thermal oxidation of various crystallographic orientations of silicon reveals a complex rate behavior. This behavior is not understood within the conventional linear - parabolic model. A recently revised model which explicitly contains the areal density of Si atoms and mechanical stress effects is shown to provide both a qualitative and somewhat quantitative explanation of the complex substrate orientation effects. The purpose of this study is to analyze the crossover effect in terms of a recently proposed viscous flow model for Si oxidation. This model utilizes the notion of mechanical stress and viscous relaxation in Si02 which occur as a result of the oxidation process on a Si substrate in addition to the other assumptions in the L-P model such as a steady state between the interface reaction and the transport of oxidant through the oxide. It is reported herein that the new viscous flow model provides a reasonable qualitative explanation for the crossover effect and in some instances a quantitative correlation of the effect.

Hybrid titanium–aluminum oxide layer as alternative high-k gate dielectric for the next generation of complementary metal–oxide–semiconductor devices

Research is focused on finding reliable high-dielectric constant (k) oxides with high capacitance and all critical properties required for the next generation of complementary metal–oxide–semiconductor (CMOS) gates. A trade-off between dielectric constant and band-offset height is generally observed on gate oxides. Combining TiO2 and Al2O3, with the two extremes of high permittivity (k) and high band offset, we produced a TixAl1−xOy (TAO) oxide layer with k=∼30 and low dielectric leakage for a next generation of high-k dielectric gates. We developed a low temperature oxidation process, following room temperature sputter-deposition of TiAl layers, to produce ultrathin TAO layers on Si with subatomic or no SiO2 or silicide interface formation. We demonstrated TAO layers with <0.5nm equivalent oxide thickness on Si and thermal stability under rapid thermal annealing up to about 950°C. The data presented here provide insights into fundamental physics and materials science of the TAO layer and its potential ap...

Oxidation of silicide thin films: TiSi2

The oxidation of TiSi2 thin films on polysilicon illustrates extreme examples of behavior. At 700 °C in wet O2, one observes the formation of titanium oxide and the simultaneous rejection of silicon towards greater depths, away from the oxidized surface layer. At 1100 °C with the same type of sample, one observes the growth of a metal‐free layer of SiO2, the formation of which required not only the use of the whole available polysilicon, but the reduction of the initial disilicide to a lower silicide, mostly TiSi. These observations are discussed in terms of previous results obtained either with TiSi2 or with other silicides, and in terms of what is known about the thermodynamics of the system titanium oxide‐silicon oxide.

Residual stress in silicon nitride films

The mechanical stress caused by Si3N4 films on (111) oriented Si wafers was studied as a function of the Si3N4 film thickness, deposition rate, deposition temperature and film composition. The Si3N4 films were prepared by the reaction of gaseous SiH4 and NH3 in the temperature range 700–1000°C. The curvature of the Si substrates caused by the Si3N4. films is related to the film stress; the substrate curvature was measured by an optical interference technique. The measured Si3N4. film stress was found to be highly tensile with a magnitude of about 1010 dynes/cm2. For the thickness range of 2000–5000Å, there was no change in the measured stress. The total film stress was observed to decrease for decreasing deposition rate and increasing deposition temperature. A large change in film stress was observed for films containing excess Si; the stress decreased with increasing Si content. Based on published values for the thermal expansion coefficients for Si and Si3N4, a published value for Young’s Modulus for Si3N4, and the measured total stress values, a consistent argument is developed in which the total stress consists of a compressive component due to thermal expansion coefficient mismatch and a larger tensile intrinsic stress component. Both the thermal and intrinsic stress components vary with film deposition temperature in directions which decrease the total room temperature stress for higher deposition temperatures.