James R. Ehrstein

Spectroscopic ellipsometry characterization of high-k dielectric HfO2 thin films and the high-temperature annealing effects on their optical properties

The optical properties of a set of high-k dielectric HfO2 films annealed at various high temperatures were determined by spectroscopic ellipsometry. The results show that the characteristics of the dielectric functions of these films are strongly affected by high temperature annealing. For a sample annealed at 600 °C, the film becomes polycrystalline, and its dielectric function displays a distinctive peak at 5.9 eV. On the other hand, the film remains amorphous without the 5.9 eV feature after 500 °C annealing. To model the dielectric functions, the Tauc–Lorentz dispersion was successfully adopted for these amorphous and polycrystalline films. The absorption edge was observed to shift to a higher energy at a high temperature annealing. Defects in the films were shown to relate to the appearance of a band tail above the absorption edge, and they appear to diminish with high temperature annealing.

Structural, electronic, and dielectric properties of ultrathin zirconia films on silicon

As high-permittivity dielectrics approach use in metal-oxide-semiconductor field-effect transistor production, an atomic level understanding of their dielectric properties and the capacitance of structures made from them is being rigorously pursued. We and others have shown that crystal structure of ZrO2 films have considerable effects on permittivity as well as band gap. The as-deposited films reported here appear amorphous below a critical thickness (∼5.4nm) and transform to a predominantly tetragonal phase upon annealing. At much higher thickness the stable monoclinic phase will be favored. These phase changes may have a significant effect on channel mobility.

Interfacial properties of ZrO2 on silicon

The interface of zirconium oxide thin films on silicon is analyzed in detail for their potential applications in the microelectronics. The formation of an interfacial layer of ZrSixOy with graded Zr concentration is observed by the x-ray photoelectron spectroscopy and secondary ion mass spectrometry analysis. The as-deposited ZrO2/ZrSixOy/Si sample is thermally stable up to 880 °C, but is less stable compared to the ZrO2/SiO2/Si samples. Post-deposition annealing in oxygen or ammonia improved the thermal stability of as-deposited ZrO2/ZrSixOy/Si to 925 °C, likely due to the oxidation/nitridation of the interface. The as-deposited film had an equivalent oxide thickness of ∼1.3 nm with a dielectric constant of ∼21 and a leakage current of 3.2×10−3 A/cm2 at −1.5 V. Upon oxygen or ammonia annealing, the formation of SiOx and SiHxNyOz at the interface reduced the overall dielectric constants.

Optical band gaps and composition dependence of hafnium–aluminate thin films grown by atomic layer chemical vapor deposition

We report the optical properties of unannealed hafnium–aluminate (HfAlO) films grown by atomic layer chemical vapor deposition (ALCVD) and correlate them with the aluminum contents in the films. Vacuum ultraviolet spectroscopic ellipsometry (VUV-SE), high-resolution transmission electron microscopy (HRTEM), channeling Rutherford backscattering spectrometry (RBS), and resonant nuclear reaction analysis (NRA) were employed to characterize these films. In the analyses of ellipsometry data, a double Tauc–Lorentz dispersion produces a best fit to the experimental VUV-SE data. As a result, the determined complex pseudodielectric ⟨e⟩ functions of the films clearly exhibit a dependency on the aluminum densities measured by RBS and NRA. We show that the optical fundamental band gap Eg shifts from 5.56±0.05eV for HfO2 to 5.92±0.05eV for HfAlO. The latter was grown by using an equal number of pulses of H2O∕HfCl4 and H2O∕TMA (trimethylaluminum) precursors in each deposition cycle for HfO2 and Al2O3, respectively. The...

Effect of Nitrogen on Band Alignment in HfSiON Gate Dielectrics

Nitridation of HfSiO films improves certain physical and electrical properties—when using gate stack layers—such as their crystallization temperature and their resistance to interdiffusion. We have studied the band alignment of HfSiO and HfSiON films by soft x-ray photoemission, oxygen K-edge x-ray absorption, and spectroscopic ellipsometry. Nitridation of HfSiO reduced the band gap by 1.50eV±0.05eV, and the valence- and conduction-band offsets by 1.2eV±0.1eV and 0.33eV±0.05eV, respectively. Although the band-gap reduction should lead to increased leakage, the barrier heights are still sufficient for proposed near-future complementary metal-oxide-semiconductor applications.

A Comparison of Thickness Values for Very Thin SiO2 Films by Using Ellipsometric, Capacitance-Voltage, and HRTEM Measurements

A comparative study of very thin SiO 2 film thickness values obtained from the three dominant measurement techniques used in the integrated circuit industry, ellipsometry, capacitance-voltage (C-V) measurements, and transmission electron microscopy (TEM) has been completed. This work is directed at evaluating the metrology capabilities that might support the development of thickness reference materials for very thin dielectric films. We used a variety of models to analyze ellipsometry measurements and used three different quantum-mechanical-based algorithms to account for substrate quantized states and depletion effects in the polysilicon electrode to analyze the C-V results. TEM measurements were conducted by both phase contrast high resolution (HRTEM) and atomic number (Z) contrast high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM). We found a range of thickness values with each of the methods, with an overlap of values among the three techniques. HRTEM and STEM values showed less consistency between wafers than did ellipsometry or C-V, and seemed to be influenced more by local variations such as interface nonuniformities. We present sources of variation and estimates of the primary components of uncertainty for the measurements employed and discuss the implications of these results for obtaining consistent and unified film thickness metrology and for possible reference standards.

Determination of densities and mobilities of heavy and light holes in p‐type Si using reduced‐conductivity‐tensor analyses of magnetic‐field‐dependent Hall and resistivity measurements

The densities and mobilities of the individual heavy‐ and light‐hole carriers have been simultaneously determined at various temperatures (40 K to 130 K) in three p‐type, single‐crystal Si samples. The separation of the two‐hole components is achieved by multicarrier analyses of magnetic‐field‐dependent Hall and resistivity measurements within the two‐carrier approximation of the reduced‐conductivity‐tensor scheme. The explicit experimental values for the densities and mobilities of the two‐hole components obtained in this work should be considered as a valuable addition to the existing database for silicon material parameters. They should also be useful to silicon device physics and modeling.

Thickness Evaluation for 2nm SiO2 Films, a Comparison of Ellipsometric, Capacitance‐Voltage and HRTEM Measurements

We have completed a comparison of SiO2 film thicknesses obtained with the three dominant measurement techniques used in the Integrated Circuit industry: ellipsometry, capacitance‐voltage (C‐V) measurements and high resolution transmisission electron microscopy (HRTEM). This work is directed at evaluating metrology capability that might support NIST‐ traceable Reference Materials for very thin dielectric films. Particular care was taken in the design of the sample set to allow redundancy and enable estimates of oxide layer consistency. Ellipsometry measurements were analyzed using a variety of models of the film structure, and C‐V results were analyzed using three different quantum‐mechanical based algorithms to account for quantized states in the substrate and depletion effects in the polysilicon capacitor electrode. HRTEM results were supplemented with Electron Energy‐Loss Spectroscopy. A range of thicknesses was found with each of the methods, but with some overlap of values. HRTEM and STEM values showe...

Assessment of Ultra-Thin SiO2 Film Thickness Measurement Precision by Ellipsometry

The ellipsometric film thickness measurement precision for equivalent oxide thickness as prescribed by the International Technology Roadmap for Semiconductors is quite high. Although short‐term precision on a single ellipsometric instrument can be quite high, deviations of measured film thickness from instrument‐to‐instrument and from lab‐to‐lab for short‐term and long‐term periods of time need to be addressed. Since the derived film thickness is dependent on many factors, each one has to be dealt with in turn. These factors include: ellipsometric instrument precision and accuracy, consistency of film/substrate modeling, optical constants, regression analysis, and film surface contamination. Recommendations for standard models and optical constants are given along with the need to ensure high ellipsometric instrument precision and accuracy and controlled film surfaces and environmental conditions. In this study ultra‐thin refers to oxide films starting at 10 nm and being as thin as the native oxide.

Two-Probe (Spreading Resistance) Measurements for Evaluation of Semiconductor Materials and Devices

Interest in two-probe resistance, (spreading resistance) measurements dates back perhaps 20 years. It arose at a time when the development of a number of techniques for measuring resistivity and resistivity profiles was being pursued, primarily for germanium and silicon technology. In the early days of its use, diffusions were relatively deep and control of epitaxial resistivity was an important problem. The structures of interest have changed noticeably in the interveninng years. Ion implantation has come into regular use and the dimensional scale of diffusions and epitaxy have been considerably reduced.