R. Tonini

Infrared study of Si-rich silicon oxide films deposited by plasma-enhanced chemical vapor deposition

A single chamber system for plasma-enhanced chemical vapor deposition was employed to deposit different films of SiOx:N,H with 0.85⩽x⩽1.91, which are studied here by Fourier transform infrared transmission spectroscopy. The sample composition was determined by Rutherford backscattering spectrometry, nuclear reaction, and elastic recoil detection analysis. Moreover, physical properties such as thickness uniformity, deposition rate, density, wet and dry etch rates, and stress are determined. A quantitative study of Si–OH, N–H, and Si–H bonds was performed and interpreted on the basis of the random bonding model; in addition, the presence of NH2, Si–O–Si, H2SiO2, and Si–N groups was detected. The effect of sample annealing at 600 and 900 °C was studied and two species of Si–H bonds were identified, one more stable and the other one easily releasable. A reordering effect of annealing was also detected as a reduction of the amorphous network stress and as the increase of the bond angle in the Si–O–Si groups up...

HELIUM-IMPLANTED SILICON : A STUDY OF BUBBLE PRECURSORS

The interaction of helium atoms with the radiation damage imparted to (100) silicon single crystal by He+ implantation at 5×1015 cm−2, 20 keV, and liquid–nitrogen temperature is investigated by means of various complementary techniques during and after thermal treatments. Thermal programmed desorption was used to study the dissociation kinetics of helium from the defects and to plan suitable heat treatments for the other techniques. The helium profiles were determined by 8 MeV 15N2+ elastic recoil detection, quantitative data on damage were obtained by channeling Rutherford backscattering spectrometry, double crystal x-ray diffraction, and positron annihilation spectroscopy. Isothermal treatments at 250 °C produce first helium redistribution and trapping in vacancy-like defects, rather than helium desorption from traps. The process is thermally activated with an effective activation energy, dispersed in a band from 1.1 to about 1.7 eV. For higher temperature treatments (2 h at 500 °C) the traps are almost...

HIGH-DOSE HELIUM-IMPLANTED SINGLE-CRYSTAL SILICON : ANNEALING BEHAVIOR

The modifications induced in single-crystal silicon by implanted helium have been investigated by ion beam techniques. The damage has been detected by 2 MeV 4He+ backscattering in channeling conditions and the helium in-depth distribution by 7 and 8 MeV 15N++ elastic recoil scattering. The samples prepared by implanting 2×1016 cm−2 helium ions at 20 keV in silicon wafers held either at 77 K (LNT sample) or at 300 K (RT sample) have been heat treated for 2 h in the 100–800 °C temperature range. In the as-implanted LNT sample the damage maximum is at 130±20 nm and shifts in-depth to 180±10 nm after annealing at 200 °C, in the as-implanted RT sample, the damage maximum is already located at 180±10 nm. In the 250–500 °C temperature range, the LNT and RT samples follow the same annealing path with only slight differences in the temperature values; in both cases, the dechanneling signal increases and reaches a maximum value of nonregistered silicon atoms of 2.2–2.5×1022 at/cm3. In the same temperature range, th...

A fast technique for the quantitative analysis of channeling RBS spectra

Abstract A straightforward method for the analysis of channeling RBS spectra is developed and validated. This method needs a minimum of computational complexity and does not require the a priori knowledge of the location of the scattering centres and of their dechanneling cross section. The method is applied to channeling RBS spectra obtained along the 〈100〉 direction in a hydrogen-implanted (100) silicon crystal to verify that the evaluated displaced-atom depth distribution is independent of the probe energy.

Ultradense gas bubbles in hydrogen- or helium-implanted (or coimplanted) silicon

Abstract Both hydrogen (as H2) and helium are dissolved endothermically in crystalline silicon. Once implanted into silicon, they have therefore a tendency to segregate in the vacancy clusters produced by the implantation itself, possibly transforming them in more or less stable cavities. Since the amount of vacancies generated in silicon by the implantation of hydrogen or helium at low energy, and surviving the spontaneous recovery of the radiation damage, may be lower than the amount of the implanted species, the atomic density attained after the cluster-to-cavity transformation may exceed the silicon one, with the formation of ultradense gas bubbles. The major difference between hydrogen and helium is that the pristine state of hydrogen in as-implanted silicon is not the molecular one, so that the formation of cavities requires preliminarily the transformation of hydrogen-involving species in H2. This paper highlights the mechanisms of cavity formation by helium or hydrogen implantation and sketches analogies and differences between these processes; coimplantation is discussed too.

Structural evolution in Ar+ implanted Si-rich silicon oxide

Silicon-rich silicon oxide films were deposited by plasma-enhanced chemical vapor deposition. Energy was released into the film by ion bombardment, with the aim of promoting formation of Si nanoclusters and reordering the oxide matrix. The effect of the initial stoichiometry, as well as the evolution of the oxide films due to the ion bombardment and to subsequent thermal treatments, has been studied by depth-resolved positron annihilation Doppler spectroscopy, Raman scattering and Fourier transform infrared spectroscopy. As-deposited films were found to contain an open volume fraction in the form of subnanometric cavities that are positively correlated with oxygen deficiency. No Si aggregates were observed. The ion bombardment was found to promote the formation of amorphous Si nanoclusters, together with a reduction of the open volume in the matrix and a substantial release of hydrogen. It also leaves electrically active sites in the oxide and produces gas-filled vacancy defects in the substrate, with the...

Growth kinetics of a displacement field in hydrogen implanted single crystalline silicon

The growth of a displacement field in single crystal silicon resulting from high dose hydrogen implantation and subsequent heat treatments has been investigated by MeV 4He+ Rutherford backscattering in channeling conditions, double crystal x-ray diffraction, and transmission electron microscopy. The results obtained in samples annealed for various times in the temperature range 220–350 °C have been explained in terms of a kinetic model which assumes the formation of clusters of hydrogen molecules. The growth of the displacement field is thermally activated with an activation energy of 0.50±0.05 eV, suggesting that the limiting process could be the release of hydrogen atoms bounded to defects created by ion implantation.

Visible photoluminescence from He‐implanted silicon

Visible photoluminescence has been observed at cryogenic temperatures from crystalline Si bombarded with He and exposed to H either as plasma or gas in the 250–450 °C temperature range. The experimental results are consistent with the formation of Si nanoparticles produced by He segregation, which is responsible for exciton localization, and H passivation of the nonradiative recombination centers.

Visible luminescence from silicon by hydrogen implantation and annealing treatments

Luminescence at an energy higher than the Si band‐gap energy has been observed following H implantation and annealing treatments of Si samples. This phenomenon is discussed considering the damage caused by the H implantation and its evolution with thermal treatments. No definitive answer on the origin of the luminescence is given but various possible models are proposed.

Helium/deuterium coimplanted silicon: A thermal desorption spectrometry investigation

Thermal desorption spectrometry has been applied to investigate the blistering and exfoliation phenomena which occur at the surface of a p-type (100) silicon wafer coimplanted with helium and deuterium. During the heat treatments in linear temperature ramp, an explosive emission of both gases occurs. The phenomenon is kinetically controlled with an effective activation energy of 1.3±0.2 eV. In addition, the desorption spectra present a second contribution, attributed to deuterium emission from buried cavities. Also in this case, the process is kinetically controlled with an effective activation energy of 1.9±0.3 eV. Thermal desorption spectrometry is a suitable technique to have information about various phenomena which occur during blistering and exfoliation.