Nicole Herbots

Ion-solid interactions during ion beam deposition of 74Ge and 30Si on Si at very low ion energies (0–200 eV range)☆

Atomic collisions in solids in the 40–200 eV energy range have been studied both theoretically and experimentally to determine the feasibility of the ion beam deposition (IBD) of amorphous and/or epitaxial layers. IBD was first modeled by a rate equation including the target sputtering yield and the ion self-sputtering, range and range straggling. To obtain preliminary values of those parameters, Monte Carlo simulations with TRIMSPUT were used. The surface binding energy (SBE) appeared to be an important parameter of the simulation for sputtering yields under 200 eV. By fitting the SBE with available sputtering data for AR on Si below 1 keV, a very good agreement was obtained between simulations and sputtering data of other ion-target combinations. Experimentally, 30Si and 74Ge ions were deposited on Si 〈100〉 at 300 K and 700 K. Cross-section TEM combined with ion scattering and ion channeling showed that IBD can provide very thin (3 nm) though perfectly continuous films with sharp interfaces (<1 nm). IBD damage to the substrate saturates as a function of dose, is negligible below 40 eV, and presents an interesting annihilation/long range diffusion behavior as a function of the temperature during irradiation.

Infrared spectroscopic analysis of an ordered Si/SiO2 interface

Infrared spectroscopy is used to compare the Si/SiO2 interfaces created by thermal oxidation of a standard Si(100) substrate and of an ordered, (1×1) Si(100) substrate. The thermal oxides (approximately 25 A) examined in this study are etched in dilute hydrofluoric acid and the resulting films analyzed spectroscopically. The behavior of the dominant optical phonon modes as a function of film thickness provides strong evidence that the ordered Si(100) substrate provides a template for an Si/SiO2 interface with a higher degree of homogeneity in the Si–O bonding environment of the intervening substoichiometric SiOx layer than does the standard Si(100) substrate.

Low‐temperature epitaxy of Si and Ge by direct ion beam deposition

Amorphous, polycrystalline, and epitaxial thin films of Si and Ge have been grown by ion beam deposition (IBD) under ultrahigh‐vacuum conditions. IBD involves the direct deposition of ions onto single‐crystal substrates from mass‐ and energy‐analyzed beams with energies of 10 to 200 eV. The IBD films were characterized by Rutherford backscattering, ion channeling, cross‐section transmission electron microscopy, and x‐ray diffraction. The effects of substrate temperature, ion energy, and substrate cleaning were studied. Differences in the formation of epitaxial thin films on p‐ and n‐type Si substrates were observed with n− Si showing better epitaxy at low temperatures. Epitaxial overlayers which showed good minimum yields by ion channeling (3%–4%) have been produced at temperatures as low as 375 °C for Ge on Ge(100) and Si on Si(100).

New SiGe dielectrics grown at room temperature by low‐energy ion beam oxidation and nitridation

New dielectric materials based on SiGe have been formed at room temperature by direct ion beam oxidation and nitridation. Si0.8Ge0.2 layers were deposited by molecular beam epitaxy on Si(100) and then exposed to a low‐energy ion beam of 18O+2 to form oxides and 14N+2 to form nitrides. The ion energies investigated ranged from 100 eV to 1 keV. Thin films of SiGe oxide and SiGe nitride were formed at all energies used as evidenced by in situ x‐ray photoelectron spectroscopy analysis. They were found to be insulating by ex situ scanning electron microscopy observations. During the ion beam processing, the Ge content of the alloy layer decreases, due to preferential sputtering of Ge and the Ge compounds. However, as the ion energy is decreased, the concentration of Ge in the alloy remains closer to the original content. The thermal stability of these new SiGe dielectrics was also assessed up to 500 °C.

Shallow-junction diode formation by implantation of arsenic and boron through titanium-silicide films and rapid thermal annealing

The performance of diodes fabricated on n-type and p-type Si substrates by implanting As or B through a low-resistivity titanium-silicide layer is discussed. The effects of varying the implant dose, energy, and postimplant thermal treatment were investigated. After implantation, a rapid thermal anneal was found to remove most of the implant damage and activate the dopants, which resulted in n/sup +/-p and p/sup +/-n junctions under a low-resistivity silicide layer. The n/sup +/-p junctions were as shallow as 1000 AA with reverse leakage currents as low as 5.5 mu A/cm/sup 2/. A conventional furnace anneal resulted in a further reduction of this leakage. Shallow p/sup +/-n junctions could not be formed with boron implantation because of the large projected range of boron ions at the lowest available energy. Ti silicide films thinner than 600 AA exhibited a sharp rise in sheet resistivity after a furnace anneal, whereas thicker films exhibited more stable behavior. This is attributed to coalescence of the films. High-temperature furnace annealing diffused some of the dopants into the silicide film, reducing the surface concentrations at the TiSi/sub 2/-Si interface. >

Low-temperature epitaxial growth of Si and Ge and fabrication of isotopic heterostructures by direct ion beam deposition*

Direct ion beam deposition (IBD) is utilized to deposit isotopic thin films and heterostructures and to achieve high-quality epitaxial growth of 74Ge on Ge(100) and 30Si on Si(100) at temperatures as low as 400°C. Anomalous damage is observed during IBD at 400° and 600°C that results in a band of buried loops at depths 50 times normal and a defect-free region near the original surface. An unexplained doping effect is reported for epitaxial growth of Si on Si at 20-40 eV, 400°C where high-quality epitaxy occurs on n-type Si but amorphous films form on p-type.

Role of ion energy in ion beam oxidation of semiconductors : experimental study and model

Ion beam oxidation (IBO) is a low temperature growth technique where a directional low energy (≤1 keV) ion beam introduces the oxygen into the substrate and athermally activates the chemical reaction leading to the oxide growth. In this work, IBO of Si, Ge, Si1−xGex was investigated experimentally as a function of ion energy from 100 eV to 1 keV. The results show a strong dependence of the materials properties such as phase formation, stoichiometry, and thickness upon the ion energy. To investigate the kinetics of IBO and to account for the observed relationship between ion energy and films properties, three models were successively developed taking progressively into account: (1) ion implantation and sputtering (model IS), (2) replacement and relocation events, i.e., ion beam mixing effects (model ISR) and (3) oxygen diffusion (model ISRD). The simulation results show that the model IS based only on implantation and sputtering cannot explain the oxide thickness dependence upon ion energy observed experim...

COMPARATIVE STUDY ON DRY OXIDATION OF HETEROEPITAXIAL SI1-XGEX AND SI1-X-YGEXCY ON SI(100)+

The goal of this study is to investigate the effect of carbon incorporation upon thermal oxidation of Si1−xGex alloys and its role on strain compensation in Si1−xGex alloys. Si1−xGex and Si1−x−yGexCy alloys on Si(100) are grown by combined ion and molecular beam deposition and are then oxidized at 1000 °C in a dry oxygen ambient for two h. The thickness and the composition of all samples before and after oxidation are measured by Rutherford backscattering spectrometry (RBS) combined with ion channeling at 2.0 MeV and carbon nuclear resonance analysis at 4.3 MeV using 4He++ ions. In agreement with previously reported results of dry oxidation on Si1−xGex thin films, 2.0 MeV RBS analysis shows that a layer of SiO2 is formed on the top surface of both Si1−xGex and Si1−x−yGexCy thin films, while Ge segregates towards the top surface and at the SiO2/Si1−xGex and SiO2/Si1−x−yGexCy interfaces. However, it is observed for the first time that dry oxidation rates of Si1−xGex thin films decrease with increasing Ge fr...

Ion beam deposition in materials research

Abstract Ion beam deposition (IBD) is the direct formation of thin films using a low-energy (tens of eV) mass-analyzed ion beam. The process allows depositions in which the energy, isotopic species, deposition rate, defect production, and many other beam and sample parameters can be accurately controlled. This paper will review recent research at ORNL on the IBD process and the effects of deposition parameters on the materials properties of deposited thin films, epitaxial layers, and isotopic heterostructures. A variety of techniques including ion scattering/channeling, cross-sectional transmission electron microscopy, scanning electron microscopy, and Auger spectroscopy has been used for analysis. The fabrication of isotopic heterostructures of 74 Ge and 30 Si will be discussed, as well as the fabrication of metal and semiconductor overlayers on Si and Ge. The use of IBD for low-temperature epitaxy of 30 Si on Si and 76 Ge on Ge will be presented. The use of self-ion sputter cleaning and in situ reactive ion cleaning as methods for preparing single-crystal substrates for epitaxial deposition will be discussed. Examples of IBD formation of oxides and suicides on Si at low temperatures will also be presented.

The formation of ordered, ultrathin SiO2/Si(1 0 0) interfaces grown on (1 × 1) Si(1 0 0)

Ordering is observed at SiO2/Si(1 0 0) interfaces when 2–40 nm thick SiO2 films are grown on passivated, ordered (1 ×1) Si(1 0 0) surfaces produced by a novel wet chemical cleaning. A mechanism is proposed for the occurrence of this ordering. The thin oxides are grown by a variety of conventional oxidation techniques or by rapid thermal oxidation between 750 and 1100 °C. The evolution of oxygen, carbon, hydrogen and silicon coverages are detected by ion beam analysis (IBA) using a combination of ion channeling, nuclear resonance, elastic recoil detection and time-of-flight secondary ion mass spectrometry. IBA detects Si surface peak areal densities lower than that of a disorder-free, bulk-terminated (1 × 1) Si(1 0 0) crystal calculated by Monte-Carlo methods. This result indicates that Si substrate atoms are shadowed by Si atoms located i na2n mordered region on the oxide side of the interface. Beyond 2 nm, the oxide becomes amorphous. Reflection high-energy electron diffraction (RHEED) at 10 keV confirms the presence of order: a (1 ×1) streaky pattern commensurate with Si(1 0 0) is observed instead of an amorphous surface. Infrared (IR) spectroscopy shows that the ordered SiO2/Si(1 0 0) interfaces exhibit a constant, well-defined frequency of optical absorption across a 1 nm thickness in the interfacial oxide region near Si. This is in contrast to a rapidly changing frequency found for conventional oxides in the same region. Thus, IR supports the presence of a well-defined bond-length and stoichiometry as detected by IBA and RHEED.