Showing papers by "James W. Mayer published in 1995"

Silicon tip field emission cathodes

Abstract: A micrometer scale emitter tip or array is disclosed having precisely located tips and surrounding gates. A silicide on the tips reduces tip work function.

Wet oxidation of amorphous and crystalline Si1-x-yGexCy alloys grown on (100)Si substrates

Abstract: The oxidation of amorphous Si0.65Ge0.27C0.08 and single‐crystal Si0.63Ge0.36C0.01 in wet ambient at 700 and 900 °C has been studied using Rutherford backscattering spectrometry and transmission electron microscopy. A reference sample of Si0.63Ge0.37 was also oxidized in order to determine the influence of carbon on the oxidation behavior. The low C content alloy behaved similar to the SiGe alloy: uniform Si1‐xGexO2 was obtained at 700 °C whereas SiO2 was formed at 900 °C, and Ge piled up underneath the oxide. In both cases, carbon was not detected in the oxide layer. The amorphous Si0.65Ge0.27C0.08 alloy behaved significantly different at both oxidation temperatures in comparison with the crystalline Si0.63Ge0.36C0.01 and Si0.65Ge0.37. Negligible oxidation occurred at 700 °C whereas SiO2 was obtained at 900 °C and the rejected Ge distributed uniformly throughout the SiGeC alloy. It is proposed that fast Ge diffusion during oxidation at 900 °C resulted from diffusion at grain boundaries, since crystallizat...

Quantification of carbon in Si1−x−yGexCy with uniform profiles

Abstract: Methods to quantify the carbon concentration of CVD grown Si1−x−yGexCy (0.25 < x < 0.37 and 0.01 < y < 0.12) layers on (100) Si with uniform composition profiles were investigated. Two analysis techniques were used: Rutherford backscattering spectrometry (RBS) using a 4.295 MeV He+2 incident ion and elastic recoil detection (ERD) using a 24 MeV Si+5 incident ion. For the RBS measurements the 12C(α,α)12C elastic resonance reaction near 4.265 MeV was used to enhance the scattering cross section of carbon. These carbon concentrations were calculated by either integrating the resonant scattering cross section across the energy width of the layer or by using a Lorentzian fit to estimate the area. The backscattering data were additionally analyzed with the program RUMP. These different analysis techniques resulted in a large scatter in the RBS predictions for the carbon concentrations depending on how the resonant cross sectional area was calculated. The appropriateness of each technique was judged by comparing the predicted concentrations to those obtained by ERD. The divergence between the carbon concentration predicted by using the Lorentzian approximation and the ERD values was great enough to deem this method as inappropriate. The values obtained by RUMP were systematically greater than the ERD concentrations, however the percent difference was never more than 20. The predicted carbon concentration that had the closest correlation to ERD was found by integrating an appropriate scattering cross section across the energy width of the layer.

Dealloying Kinetics of Cu1 − x Ti x on SiO2 Using In Situ X‐Ray Diffraction

Abstract: We study the dealloying of Ti from Cu 1-x Ti x (x∼10 atom percent) alloy films on oxidized Si substrates in the temperature range of 375 to 490 o C and an estimated O 2 partial pressure of ∼10 -6 to 10 -5 Torr. Reaction products were determined to be TiO and Ti 2 O 3 and possibly TiO 2 at the free surface, and TiO at the SiO 2 interface, according to Rutherford backscattering spectrometry and Auger electron spectroscopy. We found that the Cu lattice parameter varies linearly with Ti concentration, and this variation is independent of temperature in this composition range. As a consequence, we were able to study the dealloying kinetics using in situ x-ray diffraction by monitoring the time dependence of the Cu lattice parameter. We observe that the reaction kinetics obey a parabolic rate law, i.e., X 2 Ti,reacted =kt, with a single activation energy of 1.6±0.1 eV, suggesting that one process governs dealloying kinetics over this temperature range. In addition, we note a pronounced composition dependence, in that the reaction rate increases sharply with increasing Ti concentration. These observations suggest that Ti diffusion in Cu is the rate-limiting kinetic process for the dealloying reactions in this temperature regime. We model the dealloying reaction and in so doing estimate the diffusion coefficient for Ti in these alloy films

In situ ion-beam analysis and modification of sol-gel zirconia thin films

Abstract: We report the investigation of ion-beam-induced densification of sol-gel zirconia thin films via in situ ion backscattering spectrometry. We have irradiated three regions of a sample with neon, argon, and krypton ions. For each ion species, a series of irradiation and analysis steps were performed using an interconnected 3 MV tandem accelerator. The technique offers the advantages of minimizing the variation of experimental parameters and sequentially monitoring the densification phenomenon with increasing ion dose.

Inversion of dose rate effects in ion implanted gallium arsenide in the low dose regime

Abstract: Control of threshold voltage during gallium arsenide (GaAs) Metal Semiconductor Field Effect Transistor (MESFET) processing is critical. Variation in the dose rate during ion implantation has previously been demonstrated to affect sheet resistance and peak damage fraction for doses of 5 × 1013 ions/cm2 and higher. In this high dose regime, sheet resistance and damage increase as the dose rate increases. This paper describes dose rate effects in the low dose regime, where traditional channel implants are done, i.e., for 29Si+ in the low 1012 ions/cm2 range. 29Si+ was implanted at 3 × 1012 ions/cm2 followed by a co-implant of 9Be+ at 1 × 1012 ions/cm2 into GaAs substrates. The silicon dose rate was varied from 3 nA/cm2 to 44 nA/cm2. The FET channel resistance varied by 4.0%, and was a direct function of the implanted beam current. Sheet resistance decreased as the beam current increased, which is in sharp contrast to results previously published for the high dose regime. Damage has been characterized and correlated to the electrical properties in the low dose regime. The results are compared to those for the high dose regime in order to more clearly define the differences associated with the inversion of the dose rate dependence between the low dose and high dose regimes.

A novel technique for characterizing the surface coverage of thin-film chemical vapor deposition in ultra-high-aspect-ratio microstructures

Abstract: A simple technique is introduced for accurately characterizing the surface coverage of chemical vapor deposition (CVD) processes in microstructures with very high aspect ratios. Conventional microfabrication processes are used to produce a planar array of capillary‐like silicon structures with entrance dimensions as small as 2 μm and aspect ratios ranging from 10:1 to 200:1. Dielectric or semiconductor films are then deposited on the inner and outer surfaces of the capillary by low pressure chemical vapor deposition (LPCVD). After deposition, the inner surface of the capillary is exposed and the thickness of the CVD film deposited on the interior of the capillary is measured by thin‐film spectrophotometry. Thickness measurements are taken along the entire length of the capillary, thus providing a deposition profile for the CVD process under investigation. Deposition profiles were measured in these structures for LPCVD silicon nitride (SiH2Cl2/NH3 precursors), polysilicon (SiH4 precursor), and silicon diox...

Energetic ion beams in semiconductor processing: Summary of a DOE panel study

Abstract: The trend toward smaller dimensions in integrated circuit technology presents severe physical and engineering challenges for ion implantation. These challenges, together with the need for physically-based models at exceedingly small dimensions, are leading to a new level of understanding of fundamental defect science in silicon. Recently the DOE Council on Materials requested that our panel examine the current status and future research opportunities in the area of ion beams in semiconductor processing. Particularly interesting are the emerging approaches to defect and dopant distribution modeling, transient enhanced diffusion, high energy implantation and defect accumulation, and metal impurity gettering. These topics were explored both from the perspective of emerging science issues and technology challenges.

Heteroepitaxial Si1-x-yGex Cy Layer Growth on (100)Si by Atmospheric Pressure Chemical Vapor Deposition

Abstract: Thin heteroepitaxial films of Si1-x-yGexCy have been grown on (100)Si substrates using atmospheric pressure chemical vapor deposition at 550 and 700°C. The crystallinity, composition and microstructure of the SiGeC films were characterized using Rutherford backscattering spectrometry (ion channeling), secondary-ion-mass-spectrometry and cross-sectional transmission electron microscopy. SiGeC films with up to 2% C were grown at 700°C with good crystallinity and very few interracial defects, while misfit dislocations at the SiGe/Si interface were observed for SiGe films grown under the same conditions. This difference indicates that the presence of carbon in the SiGe matrix increases the critical thickness of the grown layers. SiGeC thin films (>110 nm) with up to 3.5% C were grown at 550°C with good crystallinity. The crystallinity of the films grown at lower temperature (550°C) was less sensitive to the flow rate of the C source (C2H4), which enabled growth of single crystal SiGeC films with higher C content.

A Forward Recoil Energy Spectrometry (Fres) Test of Hydrogen Reduction as a Strategy for Firing of Chinese Ceramics

Abstract: We have investigated successfully the hydrogen concentration of samples of modern roof tile from the Shanghai Roof Tile and Brick Works. The intent of the investigation is to determine the applicability of ion beam analysis in the form of Forward Recoil Energy Spectrometry (FRES) to the analysis of the hydrogen content of the samples. We can measure hydrogen introduced during firing in modern bricks that we know were fired using hydrogen reduction. Completion of this feasilibity test allows us to propose sampling and testing ancient Chinese ceramics and to use the modern roof tile samples as a baseline for comparison.