R. T. Kuehn

Thickness and effective electron mass measurements for thin silicon dioxide films using tunneling current oscillations

A novel method is presented for measuring the thicknesses of thin (<60 A) silicon dioxide (SiO2) films using the oscillations in the Fowler‐Nordheim tunneling currents. An important feature of the proposed method is that the accuracy of this method increases with decreasing oxide thickness and thicknesses changes of ∼1 A can be detected. The oscillations are also used for measuring the average effective electron mass in the conduction band of SiO2.

Measurement of the refractive index of thin SiO2 films using tunneling current oscillations and ellipsometry

We use Fowler–Nordheim tunneling current oscillations to accurately determine the thicknesses of ultrathin SiO2 films, and with the thicknesses as input, we employ precision single wavelength ellipsometry to determine the real part of the refractive index for thin SiO2 films in the range of 4–6 nm. An average value for this refractive index was found to be 1.894±0.110. This value is shown to yield SiO2 thicknesses to an accuracy of ±0.1 nm. A SiO2 thickness‐refractive index interpolation formula for the thin film regime is given.

Rapid thermal chemical vapor deposition of thin silicon oxide films using silane and nitrous oxide

Thin (80–200 A) silicon dioxide (SiO2) films have been deposited by low pressure rapid thermal chemical vapor deposition (RTCVD), using silane (SiH4) and nitrous oxide (N2O) as the reactive gases for the first time. A deposition rate of 55 A/min has been achieved at 800 °C with a SiH4/N2O flow rate ratio of 2%. Auger electron spectroscopy (AES) and Rutherford back scattering spectroscopy (RBS) have shown a uniform and stoichiometric composition throughout the deposited oxide films. Electrical characterization of the films have shown an average catastrophic breakdown field of 13 MV/cm and a midgap interface trap density (Dit) of equal to or less than 5×1010 eV−1 cm−2. The results suggest that the deposited RTCVD SiO2 films using SiH4‐N2O gas system may have the potential to be used as the gate dielectric in future low‐temperature metal oxide semiconductor (MOS) device processes for ultralarge scale integration (ULSI).

Influence of dry and wet cleaning on the properties of rapid thermal grown and deposited gate dielectrics

Various silicon surface cleaning processes for rapid thermal in-situ polysilicon/ oxide/silicon stacked gate structures have been evaluated. Metal-oxide-semiconductor capacitors were fabricated to assess the effects of cleaning on the quality of gate oxide structures produced by both rapid thermal oxidation (RTO) and rapid thermal chemical vapor deposition (RTCVD). Excellent electrical properties have been achieved for both RTO and RTCVD gate oxides formed on silicon wafers using either an ultraviole/zone (UV/O3) treatment or a modified RCA clean. On the contrary, poor electrical properties have been observed for RTO and RTCVD gate oxides formed on silicon wafers using a high temperature bake in Ar, H2, or high vacuum ambient. It has also been found that the electrical properties of the RTCVD gate oxides exhibit less dependence upon cleaning conditions than those of RTO gate oxides. This work demonstrates that initial surface condition prior to gate oxide formation plays an important role in determining the quality of RTO and RTCVD gate oxides.

High quality gate dielectrics formed by rapid thermal chemical vapor deposition of silane and nitrous oxide

In the present study, we have performed electrical characterization of oxides deposited via rapid thermal chemical vapor deposition using SiH4 and N2O. We have investigated the effect of temperature, pressure, and SiH4 to N2O ratio on the electrical and material properties of as-deposited films. We have found that as-deposited oxides deposited at low temperatures, low pressures, and with a low silane to nitrous oxide ratio of ∼0.5% give good material and electrical properties. The as-deposited films are stoichiometric in nature and have high deposition rates. As-deposited films had very low Dit values, high breakdown fields, and excellent subthreshold swing. The leakage currents and metal oxide semiconductor field effect transistor current drive, although lower than thermal oxides, were found to be quite acceptable. We have also investigated the thickness dependence of the films and found that as the film thickness is reduced below 50Å, the reliability improves for all oxides including the silicon-rich deposited oxides.

Rapid thermal chemical vapor deposition of in situ boron-doped polycrystalline silicon-germanium films on silicon dioxide for complimentary-metal-oxide-semiconductor applications

In situ boron-doped polycrystalline Si1−xGex (x>0.4) films have been formed on the thermally grown oxides in a rapid thermal chemical vapor deposition processor using SiH4-GeH4-B2H6-H2 gas system. Our results showed that in situ boron-doped Si1−xGex films can be directly deposited on the oxide surface, in contrast to the rapid thermal deposition of undoped silicon-germanium (Si1−xGex) films on oxides which is a partially selective process and requires a thin silicon film pre-deposition to form a continuous film. For the in situ boron-doped Si1−xGex films, we observed that with the increase of the germane percentage in the gas source, the Ge content and the deposition rate of the film are increased, while its resistivity is decreased down to 0.66 mΩ cm for a Ge content of 73%. Capacitance-voltage characteristics of p-type metal-oxide-semiconductor capacitors with p+-Si1−xGex gates showed negligible polydepletion effect for a 75 A gate oxide, indicating that a high doping level of boron at the poly-Si1−xGex...

Rapid Thermal Chemical Vapor Deposition of Polycrystalline Silicon-Germanium Films on SiO 2 and Their Properties

In this work, polycrystalline SiGe has been viewed as an alternative gate material to polysilicon in single wafer processing for the deep submicrometer VLSI applications. We studied deposition of the silicon-germanium (SiGe) films with different germanium concentrations (up to 85%) on SiO 2 in a rapid thermal chemical vapor deposition reactor using GeH 4 and SiH 4 /H 2 gas mixture with the temperature ranging from 550°C to 625°C. Since the SiGe RTCVD process is selective toward oxide and does not form nucleation sites on the oxide easily, an in-situ polysilicon flash technique is used to provide the necessary nucleation sites for the deposition of SiGe films with high germanium content. It was observed that with the in-situ polysilicon flash as a pre-nucleation seed, the SiGe deposited on SiO 2 forms a continuous polycrystalline layer. Polycrystalline SiGe films of about 2000A in thickness have a columnar grain structure with a grain size of approximately 1000A. Compositional analyses from Auger Electron Spectroscopy (AES) and Rutherford backscattering (RBS) show that the high germanium incorporation in the SiGe films has a weak dependence on the deposition temperature. It is also noted that the germanium content across the film thickness is fairly constant which is a critical factor for the application of SiGe films as the gate material. Lastly, we found that the surface morphology of SiGe films become smoother at lower deposition temperature.

Low-thermal-budget MOS gate stack formation using a cluster tool rapid-thermal-processing module

Low thermal budget deposition of thin MOS gate stacks has been performed using a cluster tool rapid thermal processing module. This paper introduces the operational characteristics of the module, and the deposition conditions for gate oxide, nitride, and poly, in addition to spacer oxides. The different processing sequences for gate stacks are described, and finally the electrical characterization results of both rapid thermal chemical vapor deposition and conventional thermal MOS devices are compared.

A Comparison of Mos Devices with In-Situ Boron Doped Polysilicon and Poly Sige Gates Deposited in an Rtcvd System Using S12H6 and B2H6 Gas Mixture

In this work, in-situ doped polysilicon and poly-SiGe films have been used as the gate material for the fabrication of MOS devices to evaluate their respective performances. These films were deposited in an RTCVD system using a Si 2 H 6 and GeH 4 gas mixture. MOS capacitors with 45 A thick gate oxides and polysilicon/poly-SiGe gates were subjected to different anneals to study boron penetration. SIMS analysis and flat band voltage measurements showed much lower boron penetration for devices with poly-SiGe gates than for devices with polysilicon gates. In addition, C-V measurements showed no poly depletion effects for poly-SiGe gates while polysilicon gates had a depletion effect of about 8%. A comparison of resistivities of these films showed a low resistivity of 1 mΩ-cm for poly-SiGe films versus 3 mΩ-cm for polysilicon films after an anneal at 950 °C for 30 seconds.