Thermal Annealing In Vacuum Research Articles

Mechanism for the bulk-assisted reoxidation of ion sputtered TiO 2 surfaces: diffusion of oxygen to the surface or titanium to the bulk?

The reoxidation of Ar + sputtered TiO 2 surfaces by thermal annealing in vacuum is shown to result primarily from the diffusion of titanium cations, presumably in reduced oxidation states, from the damaged surface into the bulk, and not from the diffusion of bulk oxygen anions to the surface. Temperature programmed static secondary ion mass spectrometry (SSIMS) measurements indicate that the ratios of O to Ti in the Ar + sputtered surfaces of TiO 2(110) and TiO 2(100) increase significantly as the temperature exceeds 700 K. With oxygen-18 incorporated into the Ar + sputtered surfaces, the ratios of 16O to 18O remain constant during this reoxidation process. However, for both surfaces, the ratios of 16O to Ti and 18O to Ti increase during the reoxidation process. These ratios increase primarily as a result of a decrease in the surface Ti concentration which is ascribed to the diffusion of reduced Ti cations into the bulk of the oxide.

The effect of rapid thermal annealing in vacuum on the properties of thin SiO2 films

The influence of rapid thermal annealing in vacuum on the properties of thermally grown SiO2 has been investigated by means of high-field Fowler-Nordheim tunnelling injection and breakdown field techniques. The results indicate that the rapid thermal annealing process anneals the original electron traps in the oxide but at the same time introduces a positive charge. These two mechanisms are a strong function of the technological history of the samples and of the oxide quality. Rapid thermal annealing in vacuum improves the properties of the as-grown oxides without conventional post-oxidation annealing in N2 but degrades the oxides that are preliminarily annealed in N2. The extent of the improvement (degradation) depends on the temperature of rapid annealing (1073-1473 K).

Creation of variable concentrations of defects on TiO 2(110) using low-density electron beams

Low density (~ μA cm 2 ) 0.48 and 1.0 keV electron beams have been used to create surface defects on a TiO 2(110) surface. These electron-beam induced defects were examined primarily by X-ray photoelectron spectroscopy (XPS) with supporting ultraviolet photoemission spectroscopy (UPS). Glancing and normal emission XPS spectra of nearly defect-free surfaces revealed that Ti atoms on the surface were similar to the bulk Ti, while some surface oxygen atoms were different from the bulk oxygen. XPS of Ti 2p 3 2 was used to quantify the defect concentration and to examine the defect electronic structure. Based on our calculation of defect concentrations and the comparison of our results with results and models from the literature, we conclude that oxygen vacancies induced by electron beams in the current study are mostly from the bridging oxygen sites, in agreement with the previous work. A range of defect concentrations with similar electronic structure, mainly composed of Ti 3+, have been induced by low-density electron beams. Beam energy and exposure were the experimental variables. The rates of defect formation at low beam exposure were beam-energy dependent, with a faster growth rate at 0.48 keV than at 1.0 keV. These defects were similar to those by thermal annealing in vacuum, but a higher concentration of defects could be obtained with longer beam exposure. However, the e-beam induced defects were different from those produced by Ar + ion bombardment since both this and previous studies have found defects produced by Ar + ion bombardment to be complex, with a variety of different local environments where oxygen and titanium surface atoms coexist.

Electrical and optical properties and structural changes of diamondlike carbon films during thermal annealing.

Diamondlike carbon films, prepared by the dual-ion-beam sputtering method on a glass substrate, were thermally annealed in vacuum for 30 min at 300 \ifmmode^\circ\else\textdegree\fi{}C, 400 \ifmmode^\circ\else\textdegree\fi{}C, 500 \ifmmode^\circ\else\textdegree\fi{}C and 600 \ifmmode^\circ\else\textdegree\fi{}C, respectively. Electrical resistivity, infrared transmittance, and Raman spectroscopy were used to characterize the films before and after annealing. The results showed that the vacuum thermal annealing caused a decrease and even the removal of bond-angle disorder, and an increase of the ${\mathit{sp}}^{2}$ C-C-bond-dominated crystallite size and/or number in the films. This then led to decreases in both film resistivity and optical transmittance of the specimens. Meanwhile, we found that the most substantial changes in structure and in electrical and optical properties occurred at a temperature higher than 400 \ifmmode^\circ\else\textdegree\fi{}C. It was concluded that the annealing effects of diamondlike carbon films in vacuum are nearly the same as those in hydrogen or in nitrogen atmospheres.

Radiative transitions in crystals of sillenite-type structure

The complicated spectrum of radiative transitions in sillenite-type crystals is investigated. It is shown that the luminescence excitation spectra (LES) of crystals studied can be divided into three groups: a) the excitation in the fundamental absorption band leading to a generation of electron–hole pairs (330 nm); b) exciton excitation resulting in their autolocalization (370 nm); c) activation excitation leading to a generation of free electrons (470 and 640 nm). The temperature dependences of the photoluminescence (PL) intensity are investigated and the activation energies are determined. The irradiation by electrons and thermal annealing in vacuum are shown to result in an interrelated change of PL and luminescence excitation spectra. A new (red) band of PL (1040 nm) attributed to oxygen vacancies in the crystals considered is found. The PL kinetics at excitation of sillenites by nanosecond pulses is studied. It is shown that the PL is quenched exponentially with temperature and the values of the PL quenching constants are determined.

Strain relief of metastable GeSi layers on Si(100)

Highly metastable pseudomorphic Ge0.3Si0.7 layers 570 nm thick were grown on Si(100) at ∼300 °C by molecular-beam epitaxy. The relief of strain in such metastable layers upon ex situ thermal annealing in vacuum is investigated by double-crystal x-ray diffractometry and MeV 4He channeling spectrometry. Upon isochronal annealing of 30 min, the strain relieves sharply at (375±25) °C, and reaches the thermal equilibrium value above 400 °C. Under isothermal annealing between 300 and 400 °C, the time evolution of the strain relief has the characteristics of a nucleation and growth transformation. The strain relief is very slow initially, increases approximately linearly as the strain is partially relieved, and saturates upon approaching equilibrium strain state. Two important results are drawn from the experimental data. First, a deformation-mechanism map is constructed from which the strain relief rate of a metastable GeSi/Si can be extrapolated for given stress state and temperature. Second, the rate of the strain relief when the strain is partially relieved increases with rising temperature, and follows an Arrhenius behavior as a function of the inverse temperature with a slope of 2.1±0.2 eV. This value coincides with the activation energy for dislocation glide in Ge0.3Si0.7. Furthermore, the strain-relief equation of a plastic flow model is solved and fits well the experimental strain-time dependence. One of the two fitting parameters, the time constant, has an Arrhenius temperature dependence. The slope, 1.9±0.2 eV, is assumed to be the activation energy for dislocation motion, and agrees with the previous value extracted from the simple rate-temperature dependence. In addition, as the strain is relieved, the x-ray-diffraction peak from the layer broadens and the channeling yield increases, confirming that the generation of misfit dislocations associated with the strain relief is accompanied by the generation of threading dislocations in the layer.

X-ray photoelectron spectroscopy of thermally treated TiO 2 thin films

Thin polycrystalline films of TiO 2 obtained by the chemical vapour deposition method have been examined by X-ray photoelectron spectroscopy (XPS) before and after thermal annealing in vacuum at temperatures from 300 to 900°C. In the temperature range from 25 to 800°C we have found carbon to be the dominant impurity at the surface of the films.

Strain in porous Si with and without capping layers

The strain of porous Si formed on p+-Si wafers without and with GeSi or CoSi2 capping layers were analyzed by double crystal x-ray diffractometry, MeV 4He backscattering spectrometry, and Auger electron spectroscopy. The parallel strain is zero for all the samples. The perpendicular strain of uncapped porous Si is positive, and decreases from ∼0.3% to ∼−0.6% upon vacuum annealing at 600 °C for 30 min. That of GeSi-capped porous Si is negative (∼−0.1%) and remains unchanged upon the same annealing. The perpendicular strain of CoSi2-capped porous Si also decreases due to the pinholes in the CoSi2 layer. We propose that the decrease of strain upon thermal annealing in vacuum is a result of the desorption of physisorbed gas molecules from the native oxide of the pore walls in the porous Si layer. The strain of annealed uncapped-porous Si increases again when stored in ambient air at room temperature, with a time constant on the order of days, while no change was detected for the annealed GeSi-capped porous Si. A little increase was observed for the annealed CoSi2-capped porous Si due to the existence of the pinholes. We attribute the increase of strain to adsorption of gas molecules (H2O in particular) from air.

In-Situ Studies of the Formation Sequence of Silicides During Vacuum (10-7 TORR)Thermal Annealing of TI/Polysilicon Bilayers

ABSTRACTThe formation of suicides during the thermal reaction of Ti/polysilicon bilayers has been investigated using both in-stu four point sheet resistance measurements and ex-situ measurements including X-ray diffraction, cross-sectional transmission electron microscopy and Auger electron spectroscopy. For a series of samples annealed at a ramp rate of 10°C/min the following sequence of changes in the bilayers occurred. At temperatures exceeding 350°C and prior to the silicidation oxygen from the vacuum system diffuses into the Ti film forming a solid solution of Ti(O) with O levels up to 20 %. An amorphous TixSiy layer is the first major suicide reaction observed at temperatures near 440°C. The first major crystalline phase is observed at 500°C and identified as C49 TiSi2. This phase was found to coexist at these temperatures with the partially consumed Ti(O) and the amorphous TixSiy layers. Further annealing above 700 °C results in the final structural transformation from C49 TiSi2 to C54 TiSi2.

Heat-induced redistribution of surface oxide in uranium

The redistribution of oxygen and uranium metal at the vicinity of the metal-oxide interface of native and grown oxides due to vacuum thermal annealing was studied for uranium and uranium-chromium alloy using Auger depth profiling and metallographic techniques. It was found that uranium metal is segregating out through the uranium oxide layer for annealing temperatures above 450°C. At the same time the oxide is redistributed in the metal below the oxide-metal interface in a diffusion like process. By applying a diffusion equation of a finite source, the diffusion coefficients for the process were obtained from the oxygen depth profiles measured for different annealing times. An Arrhenius like behavior was found for the diffusion coefficient between 400 and 800°C. The activation energy obtained was E a = 15.4 ± 1.9 kcal/mole and the pre-exponential factor, D 0 = 1.1 × 10 −8 cm 2/ s. An internal oxidation mechanism is proposed to explain the results.

Dissociation kinetics of hydrogen-passivated (111) Si-SiO2interface defects

This paper is concerned with the chemical kinetics of the transformation of hydrogen-passivated interface defects (H${\mathit{P}}_{\mathit{b}}$ centers) into paramagnetic ${\mathit{P}}_{\mathit{b}}$ centers (\ensuremath{\cdot}Si?${\mathrm{Si}}_{3}$) at the (111) Si-${\mathrm{SiO}}_{2}$ interface under vacuum thermal annealing. Float-zone (111) silicon substrates were oxidized in dry oxygen at 750 \ifmmode^\circ\else\textdegree\fi{}C to a thickness of 500 \AA{}, passivated with ${\mathrm{H}}_{2}$ (${\mathrm{D}}_{2}$) at 300 \ifmmode^\circ\else\textdegree\fi{}C for 3 h (4 h), and then vacuum thermal annealed at temperatures ranging from 500 to 595 \ifmmode^\circ\else\textdegree\fi{}C. The results of this analysis indicate that the kinetic process is described by a first-order rate equation d[H${\mathit{P}}_{\mathit{b}}$]/dt=-${\mathit{k}}_{\mathit{d}}$[H${\mathit{P}}_{\mathit{b}}$] where ${\mathit{k}}_{\mathit{d}}$=${\mathit{k}}_{\mathit{d}0}$exp(-${\mathit{E}}_{\mathit{d}}$/kT). An activation energy of 2.56\ifmmode\pm\else\textpm\fi{}0.06 eV with a preexponential factor ${\mathit{k}}_{\mathit{d}0}$ of approximately 1.2\ifmmode\times\else\texttimes\fi{}${10}^{12}$ ${\mathrm{sec}}^{\mathrm{\ensuremath{-}}1}$ was obtained. The reaction rate is reduced if the samples are passivated with deuterium instead of hydrogen. These results suggest that the chemical process is due to the thermal decomposition of the H${\mathit{P}}_{\mathit{b}}$ center into ${\mathit{P}}_{\mathit{b}}$ centers and atomic hydrogen. Although the activation energy for the diffusion of interstitial oxygen in silicon is also 2.56 eV, a rate-limiting step involving this mechanism is inconsistent with the hydrogen isotope effect as well as other considerations. Comparison of the activation energies for the ${\mathrm{H}}_{2}$ passivation of the ${\mathit{P}}_{\mathit{b}}$ center and dissociation of the H${\mathit{P}}_{\mathit{b}}$ center are shown to be chemically and energetically equivalent to the dissociation of the ${\mathrm{H}}_{2}$ molecule as originally indicated by Myers and Richards. Thus, the reverse passivation reaction, H+H${\mathit{P}}_{\mathit{b}}$\ensuremath{\rightarrow}${\mathit{P}}_{\mathit{b}}$+${\mathrm{H}}_{2}$, and the reverse dissociation reaction, H+${\mathit{P}}_{\mathit{b}}$\ensuremath{\rightarrow}H${\mathit{P}}_{\mathit{b}}$, are exo- thermic reactions that proceed with very little thermal activation in the presence of atomic hydrogen.

Structural distortions of sputtered niobium nitride films

The structural properties of NbN thin films have been investigated as a function of vacuum and rapid thermal annealing at temperatures to 1200 °C. X-ray diffraction data were analyzed using a least-squares fit to the cubic and monoclinic structures. Vacuum annealing resulted in a multiphase material with a reduced transition temperature for annealing temperatures above 900 °C. The rapid-thermal-annealed films showed improved electrical characteristics and reduced compressive stress inferred from the monoclinic distortion for all annealing temperatures. NbN thin films sputtered with a methane/nitrogen reactive gas ratio of approximately 0.3 exhibited a slightly distorted cubic lattice and low compressive stress compared to other films sputtered in different reactive gas mixtures. The higher-temperature rapid-thermal-annealed films have structural and electrical characteristics desirable for device fabrication.

Comparison of the GaAs Layers Grown on Porous Si and on Si by Molecular Beam Epitaxy

AbstractGaAs layers have been successfully grown on tilted (100) Si as well as porous Si substrates by molecular beam epitaxy(MBE). Rapid thermal annealing and vacuum thermal annealing have been used to further improve the quality of the epitaxial layers. We observed that the dislocation density near the interface of the heterostructure is higher for GaAs on Si substrate. Both annealing processes are proven to be useful in improving layer quality, while the vacuum thermal annealing seemed to be more effective in minimizing the residual stress.

Cosputtered W 75C 25 thin film diffusion barriers

The performance of cosputtered W 75C 25 thin films as diffusion barriers between an Si〈111〉 substrate and metallic overlayers of silver, gold or aluminum is investigated. Backscattering spectrometry and X-ray diffraction are used to detect metallurgical interactions, and four-point probe measurement of resistance is used to monitor the electrical stability of the metallization schemes upon thermal annealing in vacuum for 30 min at temperatures ranging from 500 to 700 °C. It is found that the W 75C 25 layer prevents metallurgical interdiffusion and reaction between gold or silver overlayers and the Si〈111〉 substrate up to 700 °C, and between an aluminum overlayer and the Si〈111〉 substrate up to 450 °C. In addition, the W 75C 25 film as a diffusion barrier on GaAs was also investigated and found to be very effective metallurgically between silver overlayers and GaAs substrates for annealing up to 700 °C.

Self‐Aligned Titanium Silicided Junctions Formed by Rapid Thermal Annealing in Vacuum

New self‐aligned silicided junctions have been developed by rapid thermal annealing in vacuum for applications to VLSI technology. These silicided junctions were investigated in regard to sheet resistance, junction depth, junction leakage current, and impurity depth profiles. After Ti film (35 nm) was deposited by dc magnetron sputtering, Si+ was implanted for interface mixing and rapid thermal annealing (RTA) in vacuum (∼10−1 Pa) were performed in temperature range of 550°–750°C. In these temperature ranges, the lateral growth of titanium silicide was prevented. After Si+ implantation through the titanium silicide layer to amorphize the Si substrate, As+ and B+ ions were implanted for n+/p junction, and p+/n junction, respectively. Finally furnace annealing (900°C, 30 min) was performed with a cap CVD oxide. We have successfully fabricated the silicided junctions with the junction depth of 0.12 μm, and the leakage current of (at reverse bias of 5.0V) for n+/p junction and of 0.14 μm, and of for p+/n junction.

Density of states and photoconductivity in hydrogenated amorphous silicon

Changes in the electron structure of a-Si:H films subjected to thermal annealing in vacuum has been investigated by ultrasoft X-ray emission spectroscopy. It is shown that the density of localized states (DOLS) in various regions of the pseudogap varies differently with the annealing temperature. Two maxima in the DOLS were detected at a distance of ~1 eV and ~1.4 eV from the top of the valence band.

Epitaxial growth of C40 structure silicides on (111)Si

C40-type, hexagonal VSi 2 , MoSi 2 and WSi 2 have been grown epitaxially on (111)Si. V, Mo or W thin films, 250–300 rA in thickness, were electron gun deposited on (111)Si. Epitaxial growth of metal disilicides were induced by thermal annealing in vacuum. For VSi 2 on (111)Si, epitaxial regions, 1–2 μm in size, were found to grow in samples 400–1000°C two-step annealed. MoSi 2 grains, 0.2–2 μm in size, were observed to grow epitaxially on (111)Si following 1100°C annealing. WSi 2 epitaxy, 0.4–1.2 μm in size, on (111)Si was obtained in samples annealed at 1050–1100°C. The orientation relationships between these metal silicides MSi 2 and substrate Si were determined to be (0001) MSi 2 (111) Si , (22 4 0) MSi 2 (22 4 ) Si and (20 2 0) MSi 2 (20 2 ) Si . Regular interfacial dislocation networks were observed at silicides/Si interfaces. The dislocations were identified to be of edge type with 6 1 〈112〉 Burgers vectors. The average spacings of dislocations are 250, 100 and 40 Å for VSi 2 /Si, MoSi 2 /Si and WSi 2 /Si systems, respectively. The disparities in dislocation spacings are attributed to the differences in lattice mismatches and thermal expansion coefficients among these silicide/Si systems. The discovery of a number of new epitaxial silicides presents the exciting possibilities that novel devices with desirable characteristics may be realized.

Epitaxial growth of C40 structure silicides on (111)Si

C40-type, hexagonal VSi 2, MoSi 2 and WSi 2 have been grown epitaxially on (111)Si. V, Mo or W thin films, 250–300 rA in thickness, were electron gun deposited on (111)Si. Epitaxial growth of metal disilicides were induced by thermal annealing in vacuum. For VSi 2 on (111)Si, epitaxial regions, 1–2 μm in size, were found to grow in samples 400–1000°C two-step annealed. MoSi 2 grains, 0.2–2 μm in size, were observed to grow epitaxially on (111)Si following 1100°C annealing. WSi 2 epitaxy, 0.4–1.2 μm in size, on (111)Si was obtained in samples annealed at 1050–1100°C. The orientation relationships between these metal silicides MSi 2 and substrate Si were determined to be (0001) MSi 2(111) Si, (22 40) MSi 2(22 4) Si and (20 20) MSi 2(20 2) Si . Regular interfacial dislocation networks were observed at silicides/Si interfaces. The dislocations were identified to be of edge type with 6 1〈112〉 Burgers vectors. The average spacings of dislocations are 250, 100 and 40 Å for VSi 2/Si, MoSi 2/Si and WSi 2/Si systems, respectively. The disparities in dislocation spacings are attributed to the differences in lattice mismatches and thermal expansion coefficients among these silicide/Si systems. The discovery of a number of new epitaxial silicides presents the exciting possibilities that novel devices with desirable characteristics may be realized.

Electron beam induced effects at silicon-transition metal silicide interfaces

Transition metal silicides were made by the vacuum thermal annealing of 20 nm metal layers on silicon substrates. The samples were then argon sputtered at 2 keV in a UHV Auger system till the silicide-silicon interface was reached. The interface was irradiated with electrons and the Auger spectrum recorded at regular time intervals. Metal atoms which had diffused into the silicon were found to be moving towards the surface under electron bombardment. A surface silicide layer 1–2 nm thick was formed by these migrating metal atoms. Pd, Pt and Cr silicides on (100) and (111) silicon surfaces were observed. The electron induced migration was much stronger for the Pd 2SiSi interface than for either the Pt 2SiSi or CrSi 2Si interface.

Deep Level Spectra of Ion-Implantation Defects and Slip Dislocations Introduced by CO2 Laser

ABSTRACTThe CW CO2 laser annealing is an effective method for removing deep level defects induced by ion-implantation. The available laser density range is 350˜600 W/cm2, which is consistent with that needed to fully activate implanted impurities. At high power density (>600W/cm2 ) slip dislocations can be induced. The energy spectra of dislocations were measured with DLTS technique. One peak at Ev + 0.33eV in p-Si and two at peaks at Ec −0.37eV and Ec −0.50eV in n-Si have been found. These peaks are stable during thermal annealing at high temperature. But they can be passivated with hydrogen plasma annealing and reactivated by subsequent thermal annealing in vacuum. The dislocation core is reconstructed.