B. Agius

Low-pressure oxidation of silicon stimulated by low-energy electron bombardment

Abstract The mechanisms of silicon oxide growth stimulated by electronic bombardment have been studied. Silicon single crystals, after cleaning by ion bombardment in UHV, were submitted to a low-energy (<100eV) electron irradiation (∼ 1 mA cm−2), under low oxygen pressure (10−4 Torr) in the temperature range 25–700°C. Oxide thicknesses less than 10 nm were thereby achieved. There is a strong increase of the initial growth rate when the electron energy decreases to 10eV. The oxidation kinetics can be fitted by a direct logarithmic law: X = X 0 log [(t/τ) + 1] where X is the thickness of oxide grown during time t and U = X 0/τ is the initial growth rate. Using the results of 18O tracing experiments, the growth mechanism is explained by a step-by-step motion of charged oxygen species under a constant electric field.

Radio‐frequency bias effects on SiO2 films deposited by distributed electron cyclotron resonance plasma enhanced chemical vapor deposition

The effects of radio‐frequency (rf) bias on the chemical, physical and electrical properties of SiO2 films deposited by distributed electron cyclotron resonance plasma enhanced chemical vapor deposition have been investigated. The rf bias power densities used here are relatively low (≤0.3 W/cm2) compared to that used by other researchers, but their influences on deposition processes and on film properties are apparent: the deposition rate decreases with increasing rf bias; the in situ relaxation process of the oxide and the observed surface polish effects have been found to be caused by ion bombardment. The most important effects of the rf bias are on the electrical properties of the deposited films. In particular, a SiO2 film without net fixed charges may be deposited with a low rf bias. It is also shown that the increase in interface trap density with rf bias power is not caused by ion bombardment but to the electron injection from the Si substrate towards the Si/SiO2 interface.

Highly stable sputtered NiInW refractory ohmic contact to n‐type GaAs

Thermally stable low specific resistivity ohmic contact on n‐type GaAs is required to fabricate high‐speed GaAs integrated circuits. The Nix‐In1−x/W (x being either 0.95 or 0.9) contact prepared by magnetron cathodic sputtering is attractive because this contact is expected to be ohmic and thermally stable after rapid thermal annealing. Moreover, the sputter deposition is well suited for refractory metals. The specific resistivity measurements and microstructural analysis were carried out to establish a simple fabrication process which forms an ohmic contact with low specific resistivity. This last parameter was found to be sensitive to the deposition sequence, and the annealing time and temperature. Low specific resistivity of 10−6 Ω cm2 was obtained for Nix‐In1−x/W contact annealing at 850 °C for 10 s. This rapid thermal annealing is interesting because simultaneous annealing for contact formation and activation of implanted dopants is possible. The formation of phases during heat treatment stimulates t...

Investigation of ion‐beam‐sputtered Nb‐Ti thin films by complementary use of backscattering and nuclear‐reaction microanalysis

The composition of superconducting Nb‐Ti films deposited by ion‐beam sputtering has been studied. Both MeV 4He backscattering and direct observation of nuclear reactions on nitrogen and oxygen were used to determine the composition of the deposits. The films appear to have a uniform composition with depth. The stoichiometry of the Nb‐Ti alloy is independent of beam intensity and is equal to that of the target. The oxygen and nitrogen content decrease with the background pressure inside the sputtering chamber and with deposition rate; oxygen contents as low as 0.6 at.% have been obtained. Irrespective of deposition conditions, the argon inclusion was very low. The various mechanisms of incorporation of argon and of the reactive species into ion‐beam‐sputtered films are discussed taking these results into account.

Langmuir probe analysis of distributed electron cyclotron resonance silicon nitride deposition plasma

Single and double Langmuir probe analyses have been realized in the wafer region of an electron cyclotron resonance reactor in its distributed configuration. Results in nitrogen gas have shown unambiguously that two electron populations exist in this region: one with low temperature (about 1–2eV) and high density and the second with higher temperature (about 8 eV) and lower density. Measurements in silicon nitride deposition plasma (nitrogen and silane gases) have been successfully realized and have shown that these two populations are also present. Finally, we try to correlate the plasma parameters (electron temperatures and densities and ions’ energy) to the deposited film parameters (deposition rate and refractive index).

Thermally stable low resistance ohmic contacts to n‐type gallium arsenide: Magnetron cathodic sputter‐deposited NiInW contacts

W/Ni0.9‐In0.1 refractory ohmic contacts presenting low specific resistivity have been formed on n‐type GaAs by magnetron cathodic sputtering and subsequently annealed by rapid thermal processing at 850 °C for 10 s. The increase of Ni‐In film thickness (with a W layer of 80 nm) stimulated the Schottky‐to‐ohmic behavior conversion with a minimum specific resistivity value of 10−5 Ω cm2. By increasing the W layer thickness to 160 nm, the specific resistivity was dropped to a minimum value of 10−6 Ω cm2. Such a low value was attributed to the presence of InGaAs phase. The W/Ni0.9‐In0.1 contact showed excellent thermal stability at 400 °C and during 100 h.

EPITAXIAL GROWTH OF (PB, LA)TIO3 THIN FILMS ON (0001) AL2O3 AND (001)SRTIO3 SUBSTRATES BY RF MAGNETRON SPUTTERING

Abstract Ferroelectric lead lathanum titanate (PLT) thin films were grown by rf magnetron sputtering on (0001) A12O3 and (001) SrTiO3 substrates, from a ceramic Pb0.9La0.1TiO3 target, in a reactive Ar/O2, atmosphere. The surface morphology was examined by atomic force microscopy (AFM); rms roughness of 2 to 4 nm was achieved on these films. Thin film interfaces were characterized by grazing X-ray reflectometry : they were found to be relatively smooth, and no interdiffusion layer was found between the film and the substrate. The structural properties of the films were investigated by X-ray diffraction (XRD). Perovskite single phase has been achieved with a temperature of 650°C. Pole figures and asymmetric scans show the epitaxial nature of the films.

Physicochemical and Microstructural Characterization of Rf Sputtering Magnetron Pb(ZrTi)O 3 Thin Films

Lead zirconate titanate thin films were deposited on Pt/TiN/BPSG/Si structures by sputtering an oxide target of nominal composition (Pb(Zr 0.55 ,Ti 0.45 )O 3 or PZT) in argon plasma. The PZT films were deposited at different pressures and different substrate temperatures ranging from floating temperature to 400°; the thicknesses of the sputtered films were in the 15-720 nm range. The absolute and relative cation and oxygen compositions of the thin films were determined by a new method based on the simultaneous use of Rutherford Backscattering Spectroscopy (RBS) and Nuclear Reaction Analysis (NRA) induced by a deuteron beam. The total deposition rate and atomic ones are observed as a function of the substrate temperature and pressure. Therefore the dependence of fil composition on pressure and substrate temperature is discussed. Post-deposition annealing studies and ferroelectric properties are presented. The values of the remanent polarization, Pr, were in the range 5-7 µC/cm 2 , the coercitive field, Ec, between 15 and 25 kV/cm and the dielectric constant, µ r , evaluated from capacitance measurements around 1200, depending on the process parameters.

Optical and Electrical Characterizations of Pzt Films With Different O/Pb Stoichiometry

Thin films were deposited by radio frequency (rf) magnetron sputtering on Pt/TiN/Ti/SiO 2 /Si substrates starting from a ceramic Pb(Zr 0.4 Ti 0.6 )O 3 or metallic Pb 1.1 (Zr 0.4 Ti 0.6 ) target. To promote the ferroelectric properties, films were successively processed by rapid thermal annealing (RTA). Before and after the RTA process, the film optical constants, in terms of refractive index and. extinction coefficient, were measured by spectroscopic ellipsometry and spectrophotometry and their values were related to the film composition determined by nuclear microanalysis with a precision better than ±2%. By adjusting the sputtering conditions, it was possible to grow different films with oxygen stoichiometry (O/Pb) in the range of 2.5-4.5. The electrical P-E characterization revealed a strong relation between the optical properties (film composition) before annealing and the hysteresis loop after annealing. This was mainly attributed to changes in the film oxidation during RTA and indicates that ferroelectric properties can be optimized adjusting the O/Pb ratio in the film.