F. Corni

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...

Porosity in low dielectric constant SiOCH films depth profiled by positron annihilation spectroscopy

The 3γ annihilation of orthopositronium and the Doppler broadening of the positron annihilation line have been measured by implanting low energy positrons in low dielectric constant (low-k) SiOCH films. The evolution and stability of film porosity with thermal treatments in the 400–900 °C temperature range has been studied. The films have been produced by plasma enhanced chemical vapor deposition and after annealing in N2 atmospheres at 480 °C have been treated in N2+He plasma. The minimum free volume of the pores in the as-produced samples has been estimated to correspond to that of a sphere with radius r=0.6 nm. The treatment in the N2 plasma was found to seal the pores up to 45 nm depth. Both the composition of the films (as obtained by Rutherford backscattering spectroscopy and elastic recoil detection analysis) and the chemical environment of the pores probed by positrons were found to be very stable up to 600 °C thermal treatment. Above such a temperature a reduction of the hydrogen content accompan...

Solid‐phase epitaxial growth of Ge‐Si alloys made by ion implantation

Solid‐phase epitaxial growth was studied in germanium‐implanted 〈100〉 silicon wafers as a function of germanium fluence, annealing temperature, and time. MeV He Rutherford backscattering in channeling conditions, cross‐sectional transmission electron microscopy, double‐crystal x‐ray diffraction, and secondary‐ion mass spectroscopy techniques were used to characterize the samples. At low fluences, up to 1×1015 cm−2 at 130 keV, the crystallization kinetics is similar to that measured on self‐amorphized silicon. In the high‐dose samples, prepared by multiple implants with a total dose of 3.12×1016 cm−2, the growth rate at fixed temperatures decreases. A comparison with literature data, obtained by similar experiments performed on amorphized uniform GexSi100−x films prepared by molecular‐beam epitaxy or chemical‐vapor deposition, reveals that the concentration gradient, unavoidable in implanted samples mainly at the end of the ion range region, is strictly connected with the observed decrease.

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...

Dilute NiPt alloy interactions with Si

Abstract The reaction between a dilute Ni 95 Pt 5 alloy and Si has been investigated as a function of the annealing temperature and time, and the film thickness. Contrary to the concentrate alloys the first phase formed is Ni 2 Si and the growth kinetics in the initial steps are similar to the case of pure Ni. Pt segregates in the alloy and its presence slows down the silicide growth rate suggesting that a new mechanism, namely the release of Ni from the alloy, is competing with the diffusion process in the silicide. In all the cases here considered NiSi starts to form only when all the Ni is reacted, indicating that the Pt never reaches high enough concentrations to inhibit the Ni 2 Si growth. The further evolution of the system is similar to the ones reported for bilayers and non-dilute alloys. The I–V characteristics measured after annealing give a barrier height of 0.70 ± 0.01 eV.

He-implantation induced defects in Si studied by slow positron annihilation spectroscopy

Open volume defect profiles have been obtained by performing Doppler broadening measurements with a slow positron beam on p-type Si samples implanted near liquid nitrogen temperature with He ions at 20 keV and at 5×1015 and 2×1016 cm−2 fluence. The evolution of the defect profiles was studied as a function of isothermal annealing at 250 °C. The fraction of released He was measured by thermal programmed desorption. The defects could be identified as a coexistence of monovacancies stabilized by He-related defects and divacancies. The number of defects decreases for annealing time of a few minutes, then increases at longer annealing times. The mean depth of the defect profiles in the as-implanted samples was found to be very near the surface. After annealing, the mean depth increases to less than one half of the projected He range. This complex dynamics has been interpreted as due to passivation of vacancies by He during the implantation process and the first annealing step when no appreciable He is lost, an...

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.

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.