Dennis M. Maher

Evidence of aluminum silicate formation during chemical vapor deposition of amorphous Al2O3 thin films on Si(100)

Using narrow nuclear reaction resonance profiling, aluminum profiles are obtained in ∼3.5 nm Al2O3 films deposited by low temperature (<400 °C) chemical vapor deposition on Si(100). Narrow nuclear resonance and Auger depth profiles show similar Al profiles for thicker (∼18 nm) films. The Al profile obtained on the thin film is consistent with a thin aluminum silicate layer, consisting of Al–O–Si bond units, between the silicon and Al2O3 layer. Transmission electron microscopy shows evidence for a two-layer structure in Si/Al2O3/Al stacks, and x-ray photoelectron spectroscopy shows a peak in the Si 2p region near 102 eV, consistent with Al–O–Si units. The silicate layer is speculated to result from reactions between silicon and hydroxyl groups formed on the surface during oxidation of the adsorbed precursor.

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...

Formation of titanium and cobalt germanides on Si (100) using rapid thermal processing

Titanium and cobalt germanides have been formed on Si (100) substrates using rapid thermal processing. Germanium was deposited by rapid thermal chemical vapor deposition prior to metal evaporation. Solid phase reactions were then performed using rapid thermal annealing in either Ar or N2 ambients. Germanide formation has been found to occur in a manner similar to the formation of corresponding silicides. The sheet resistance was found to be dependent on annealing ambient (Ar or N2) for titanium germanide formation, but not for cobalt germanide formation. The resistivities of titanium and cobalt germanides were found to be 20 µΩ-cm and 35.3µΩ-cm, corresponding to TiGe2 and Co2Ge, respectively. During solid phase reactions of Ti with Ge, we have found that the Ti6Ge5 phase forms prior to TiGe2. The TiGe2 phase was found to form approximately at 800° C. Cobalt germanide formation was found to occur at relatively low temperatures (425° C); however, the stability of the material is poor at elevated temperatures.

Phase transitions during solid‐state formation of cobalt germanide by rapid thermal annealing

Phase transitions that involve solid‐state reactions between cobalt and thin films of germanium have been investigated. Germanides are formed by reacting Co (300 A thick) with thin layers of Ge (∼2000 A thick) deposited on silicon substrates. Germanium was deposited on Si by rapid thermal chemical‐vapor deposition and cobalt was deposited onto Ge by evaporation. The Co/Ge/Si stacked structure samples were then rapid thermally annealed at atmospheric pressure in an inert ambient consisting of Ar. Using x‐ray‐diffraction spectroscopy, Co5Ge7 and CoGe2 are identified as the phases which form at 300 and 425 °C respectively. The sheet resistance was found to be a strong function of the annealing temperature and a minimum resistivity of approximately 35 μΩ cm is obtained after annealing at 425 °C. The minimum resistivity material corresponds to the CoGe2 phase with an orthorhombic crystal structure. Above 600 °C, the resistivity increases due to an instability of the solid‐phase reaction between Co and thin Ge ...

Oxygen gettering and precipitation at MeV Si+ ion implantation induced damage in silicon

The interaction of intrinsic oxygen in Czhochralski silicon with implantation damage induced by 2.0 MeV Si+ ions has been investigated as a function of annealing temperature and time. Four distinct regions of oxygen localization are revealed by secondary ion mass spectrometry following sample annealing. The different regions are correlated with either a near surface vacancy‐rich region or the buried layer of extended defects near the projected range. The relative concentration of oxygen in each region depends on the competition between oxygen gettering in each region and out‐diffusion to the surface. It has been established, using quasikinematical and dynamical contrast transmission electron microscopy imaging techniques, that the oxygen in regions containing extended dislocations is in the form of fine precipitates. The precipitates decorate both the dislocations and, for faulted loops, the stacking fault planes.

Real time investigation of nucleation and growth of silicon on silicon dioxide using silane and disilane in a rapid thermal processing system

The kinetics of the nucleation and growth of Si films on amorphous SiO2‐covered Si using rapid thermal chemical vapor deposition from SiH4 and Si2H6 (5% in He) were compared at temperatures between 600 and 800 °C and reactant gas pressures between 1 and 25 mTorr. Quantitative assessment of the nucleation parameters and the structures of the deposited Si films have been determined using in situ real time single wavelength and spectroscopic ellipsometry. In addition to ellipsometry, atomic force microscopy, scanning electron microscopy, and cross‐sectional transmission electron microscopy were used ex situ to observe the nucleation stage and the microstructures of the films. This study compares the initial growth parameters for SiH4: nuclei density (6×108 cm−2), nuclei size (94 nm), incubation time (4.2 min), and degree of selectivity (42 nm) with those for Si2H6: 1.3×1010 cm−2, 31 nm, 0.4 min, and 10 nm, respectively. The incubation times for SiH4 and Si2H6 are different, as is the degree of selectivity, b...

Low temperature selective silicon epitaxy by ultra high vacuum rapid thermal chemical vapor deposition using Si2H6, H2 and Cl2

We present the use of the Si2H6/H2/CL2 chemistry for selective silicon epitaxy by rapid thermal chemical vapor deposition (RTCVD). The experiments were carried out in an ultrahigh vacuum rapid thermal chemical vapor deposition reactor. Epitaxial layers were grown selectively with growth rates above 150 nm/min at 800 °C and 24 mTorr using 10% Si2H6 and H2 and Cl2 with a minimum Si:Cl ratio of 1. Excellent selectivity with respect to SiO2 and Si3N4 was obtained indicating that very low Cl2 partial pressures are sufficient to preserve selectivity. In situ doping results with B2H6 show that sharp doping transitions and a wide range of B concentrations can be obtained with a slight B incorporation rate reduction with Cl2 addition. Our results indicate that UHV‐RTCVD with the Si2H6/H2/Cl2 chemistry yields highly selective Si epitaxy with growth rates well within the practical throughput limits of single wafer manufacturing and with a potential to reduce the Cl content below the levels used in conventional SiH2C...

On the Role of Chlorine in Selective Silicon Epitaxy by Chemical Vapor Deposition

Si thermal etching studies have been performed using pure Cl 2 in an ultrahigh vacuum rapid thermal chemical vapor deposition reactor in the temperature range of 650-850°C and the flow rate range of 1-10 sccm which corresponds to a pressure range of 0.5-3.5 mTorr. The effects of temperature and Cl 2 flow were investigated with thermodynamic equilibrium calculations performed to determine possible reaction pathways. The effect of a ding H 2 , up to 500 sccm. on Si etch rates at 800 and 850°C was also obtained experimentally. Thermodynamic equilibrium calculations were used to support the experimental results and determine the reaction by-products. It is proposed that SiCl 2 equilibrium partial pressure can be used as a means to compare the etching ability, thus the selectivity, of different selective Si processes. The results from the etching studies were used to explain the be avior of Si epitaxy growth rate from the Si 2 H 6 , H 2 , and Cl 2 system in the 650-850°C, 22-24 mTorr processing regime. The implications of the etching studies for selective silicon epitaxy with the Si 2 H 6 and Cl 2 chemistry are discussed and then extended to the SiH 2 Cl 2 based chemistry.

Deposition and characterization of polysilicon films deposited by rapid thermal processing

Low‐pressure chemical vapor deposition (LPCVD) of polycrystalline silicon in a cold‐wall, lamp‐heated, rapid‐thermal processor was investigated. Blanket polysilicon films were obtained by the pyrolysis of a 10% silane–argon gas mixture onto (100) Si wafers which were capped with a thermal SiO2 layer. The depositions were performed at a total pressure ranging from 1 to 5 Torr and in a temperature range from 575 to 850 °C. It was found that the deposition of films was controlled by a surface limited reaction at temperatures below ∼780 °C, and an activation energy of 39±2 kcal/mol was measured for this reaction. Above 780 °C, a decrease in activation energy was observed. To meet the throughput requirement of single wafer processing, deposition temperatures higher than 700 °C are needed. In this temperature range, deposition rates exceed 1000 A/min as compared to 20–300 A/min in conventional LPCVD furnaces. The structural characteristics of the films were assessed by ultraviolet surface reflectance, Raman spe...

Characterization of structure/dopant behavior by electron microscopy

Transmission electron microscopy analyses that result in a quantitative characterization of structure/dopant behavior at the nanometer scale are the focus of this research activity. Of particular concern is the quantitative characterization of sequential changes in process‐dependent material features, which impact on structure/dopant behavior for silicon‐based material systems. In order to illustrate the situation, the determination of the vertical and lateral donor distribution is addressed, and the case of diffusion into a 〈100〉 silicon substrate from a patterned structure of arsenic implanted and rapid thermally annealed polysilicon is discussed. The so‐called chemical etching technique is used to delineate arsenic by local variations in the crystal thickness. It is demonstrated that a two‐dimensional isoconcentration contour that maps the arsenic distribution can be quantitatively characterized at the nanometer scale from cross‐sectional transmission electron microscopy data, which are recorded under ...