Rapid thermal annealing and titanium silicide formation

Titanium silcides have been formed on monocrystalline (111) silicon substrates by rapid thermal annealing (RTA) of Ti layers deposited on Si at 700–800 °C for 1 to 240 s. The phase composition is dependent on the annealing temperature and time: at 700° and 750 °C for short annealing, TiSi and TiSi₂ are observed. At 800 °C and by increasing the exposure time at 700 ° and 750 °C, only TiSi₂ is detected. The growth of the total silicide thickness is found to be faster for RTA than for conventional furnace annealing and governed by two different mechanisms depending on the phases formed: in the range 700–750 °C, and 750–800 °C, activation-energy values of 2.6 ± 0.2 and 1.5 ±0.2 eV are found, respectively.For a thin deposited Ti layer (< 100 nm), the whole Ti is finally transformed into TiSi₂ with 20@ cm resistivity. For thicker Ti thicknesses, titanium oxide stops the reaction.     

Dielectric properties of SrZrO3 thin films prepared by pulsed laser deposition

SrZrO₃ (SZO) thin films have been prepared on Pt-coated silicon substrates and directly on Si substrates by pulsed laser deposition (PLD) using a ZrSrO target at a substrate temperature of 400 °C in 20 Pa oxygen ambient. X-ray –2 scans showed that the as-deposited films remain amorphous at a substrate temperature of 400 °C. The dielectric constant of SZO has been determined to be in the range 24–27 for the Pt/SZO/Pt structure. Capacitance–voltage (C–V) characteristics of a metal-oxide-semiconductor (MOS) structure for SZO films deposited in 20 Pa oxygen ambient and 20 Pa nitrogen ambient (SZON) indicated that incorporation of nitrogen during the substrate heating and film deposition can suppress the formation of an interfacial SiO₂ layer, and the SZON films have a lower equivalent oxide thickness (EOT) than that of the SZO films. However, the leakage current of the SZON films is larger than that of the SZO films. The EOT is about 1.2 nm for a 5-nm SZON film deposited at 400 °C. The leakage-current characteristics of as-deposited SZON films and SZON films post-annealed in oxygen ambient by rapid thermal annealing (RTA) have been studied comparatively. The films post-annealed with RTA have a lower leakage current than the as-deposited SZON films. Optical transmittance measurements showed that the band gap of the films is about 5.7 eV. It is proposed that SrZrO₃ films prepared at 400 °C are potential materials for alternative high-k gate-dielectric applications. PACS 77.84.Bw; 77.84.-s; 77.55.+f     

Growth of Ni2Si by rapid thermal annealing: Kinetics and moving species

The growth kinetics is characterized and the moving species is identified for the formation of Ni₂Si by Rapid Thermal Annealing (RTA) of sequentially deposited Si and Ni films on a 100 Si substrate. The interfacial Ni₂Si layer grows as the square root of time, indicating that the suicide growth process is diffusion-limited. The activation energy is 1.25±0.2 eV in the RTA temperature range of 350–450° C. The results extend those of conventional steady-state furnace annealing quite fittingly, and a common activation energy of 1.3±0.2 eV is deduced from 225° to 450° C. The marker experiment shows that Ni is the dominant moving species during Ni₂Si formation by RTA, as is the case for furnace annealing. It is concluded that the two annealing techniques induce the same growth mechanisms in Ni₂Si formation.     

Optical Properties and Structure of Electroluminescent SiOx:Tb Films

Using nondestructive optical methods (measurement of transmission spectra in the visible and IR regions and multiangular ellipsometry), we have studied the structural changes in SiO _x :Tb films subjected to high–temperature annealing in air, which are responsible for the appearance of electroluminescence in light–emitting structures based on them. It has been established that the appearance of green electroluminescence in such a film (upon annealing of the film in air at temperatures of 600–800°C) is due to the structural changes in its matrix, leading to partial disproportionation of the thermally deposited SiO _x :Tb film (as a result, the film represents a mixture of several phases – Si, SiO_x, and SiO₂). Films showing blue electroluminescence (annealing temperature 1000°C) are characterized by a higher content of oxygen, a better compactness, and a better macroscopic homogeneity in comparison with films showing green electroluminescence. It is also shown that the thermal cycling accompanying the annealing leads to the appearance of birefringence and scattering in SiO _x O:Tb films. It is anticipated that the annealing–stimulated structural changes taking place at both the micro– and the macrolevel should cause changes in the local surroundings of the luminescence center and in the conditions for heating the charge carriers exciting the luminescence centers.     

Tantalum and cobalt suicides: Temperature sensor applications

Ion bombardment induced mixing of Ta-Si films has been studied using 400 keV argon ions. Doses varied from 7×10¹⁴ to 1×10¹⁷ Ar⁺ cm^–2 with post-bombardment anneals of 180–900 s at temperatures in the range 600–860 °C using radiant heating. Silicide uniformity and stoichiometry were determined using alpha backscattering spectrometry. Optimum fabrication parameters were determined with regard to subsequent material sheet resistivity, temperature coefficient of resistance and application as a temperature sensing material. Similar measurements were made on CoSi₂ layers prepared by annealing ion bombarded samples and comparison with silicide films arising from purely thermal annealing was made.CoSi₂ was found to be the more suitable material for temperature-sensor applications, showing a positive linear variation in sheet resistivity in the range 0–400 °C for samples which could be prepared simply and reproducibly.     

Highly reproducible ideal SiC Schottky rectifiers: effects of surface preparation and thermal annealing on the Ni/6H-SiC barrier height

In this work, the effects of surface preparation and thermal annealing on the Ni/6H-SiC Schottky barrier height were studied by monitoring the forward I–V characteristics of Schottky diodes. The ideality factor n and the barrier height _B were found to be strongly dependent on the impurity species present at the metal/SiC interface. The physical mechanism which rules the Schottky barrier formation is discussed by considering the nature of the impurities left from the different surface preparation methods prior to metal deposition. In contrast, nickel silicide/SiC rectifiers (Ni₂Si/6H-SiC), formed by thermal reaction of Ni/6H-SiC above 600 °C, have an almost ideal I–V curve, independent of the surface preparation. Further improvement in the barrier height distribution can be obtained by increasing the annealing temperature to 950 °C. This behaviour is discussed in terms of the silicide phases and the consumption of a SiC layer during the thermal reaction. PACS 73.30.+y; 81.65.Cf; 81.05.Je     

Simultaneous formation of contacts and diffusion barriers for VLSI by rapid thermal silicidation of TiW

The formation of (Ti_xW_1–x)Si₂/(Ti_xW_1–x)N, by rapid thermal processing of Ti_xW_1–x on Si in an N₂ ambient is investigated. An activation energy of 1.7 eV is obtained for silicide formation. A distinct snow-ploughing of As atoms is observed during silicide formation whereas the interfacial B concentration decreases with increasing silicide formation temperature. The diffusion barrier properties of the (Ti_xW_1–x)Si₂/(Ti_xWi_1–x)N stack in contact with Al is investigated upon post-metal annealing. No interaction between the layers is found for temperatures as high as 475°C after 60 min. The improved thermal stability of the (Ti_xW_1–x)N layer in contact with Al is attributed to nitrogen blocking of the grain boundaries.     

Correlation between impurities in Fe-Si amorphous layers synthesized by Fe implantation and photoluminescence property of β-FeSi2 precipitates in Si

Completely amorphous Fe-Si layers are formed by Fe implantation into Si substrate at a dosage of 5×10¹⁵ cm⁻² using a metal vapor vacuum arc (MEVVA) ion source under 80 kV extraction voltage and cryogenic temperature. After thermal annealing, β-FeSi₂ precipitates are formed in Si matrix. The influence of impurities in these amorphous Fe-Si layers on the photoluminescence (PL) from β-FeSi₂ precipitates is investigated. PL is found to be significantly enhanced by optimizing the impurity concentration and annealing scheme. After 60 s of rapid thermal annealing (RTA) at 900 °C, β-FeSi₂ precipitates in medium boron-doped Si substrate give the strongest PL intensity without boron out-diffusion from them.     

Thermal stability and electrical properties of Zr silicate films for high-k gate-dielectric applications, as prepared by pulsed laser deposition

Zirconium silicate films with high thermal stability and good electrical properties have been prepared on n-Si(100) substrates and commercially available Pt-coated Si substrates to fabricate metal–insulator–metal (MIM) structures by the pulsed laser deposition (PLD) technique using a Zr_0.69Si_0.31O_2- ceramic target. Rapid thermal annealing (RTA) in N₂ was performed. X-ray diffraction indicated that the films annealed at 800 °C remained amorphous. Differential thermal analysis revealed that amorphous Zr silicate crystallized at 830 °C. X-ray photoelectron spectroscopy showed that RTA annealing of Zr silicate films at 900 °C led to phase separation. The dielectric constant has been determined to be about 18.6 at 1 MHz by measuring the Pt/Zr silicate/Pt MIM structure. The equivalent oxide thicknesses (EOTs) and the leakage-current densities of films with 6-nm physical thickness deposited in O₂ and N₂ ambient were investigated. An EOT of 1.65 nm and a leakage current of 31.4 mA/cm² at 1-V gate voltage for the films prepared in N₂ and RTA annealed in N₂ at 800 °C were obtained. An amorphous Zr-rich Zr silicate film fabricated by PLD looks to be a promising candidate for future high-k gate-dielectric applications. PACS 77.55.+f; 81.15.Fg; 73.40.Qv     

Rapid growth of ultra thin SiO2 films by a large-area electron beam

Rapid growth of ultra thin oxide films (40–180Å) of silicon using a low-energy large-area electron beam has been performed with a pressure ratio of 31 (O₂/He) and a total pressure of 0.5–0.7 Torr. A higher oxidation rate of about 625Ų/s is found for shorter irradiation time of the e-beam in the e-beam dose range 0.75–3 Coulomb/cm² and at lower substrate temperature 540–740°C. AES and XPS demonstrated a rapid electron-stimulated oxidation process of the Si surface. For the grown ultra thin oxide films, C-V characteristics, dielectric strength, uniformity of the film over the entire Si wafer and its thickness as a function of the processing time of the e-beam are also presented.     

Dissociation of PtSi,NiSi and PdGe in presence of Pt,Ni and Pd films,respectively

⁴He⁺ ions backscattering spectrometry and x-ray diffractometry were used to study interactions between PtSi and Pt, NiSi and Ni, PdGe and Pd. Due to the dissociation of the compound the formation of a phase richer in metal was observed to grow at the original compound/metal interface in the temperature range considered, 280–325°C for Pt₂Si, 325°C for Ni₂Si and 180–260°C for Pd₂Ge. The growth kinetics of these new phases (Pt₂Si and Pd₂Ge) follow a parabolic relation between thickness and annealing time. At a given temperature the growth rate of Pt₂Si and Pd₂Ge in compound-metal structure is a factor higher than in the usual semiconductor-metal structure. Partially supported by Consiglio nazionale delle Ricerche (Italy) and by Commission of the European Communities.     

Effect of magnetic field on tempering processes in silicon iron

The effect of magnetic fied on the annealing of silicon iron (3% Si) was studied in the temperature range 480–680°C. The imposition of a magnetic field at 480°C leads to more complete tempering by comparison with similar annealing without field. The effect of the magnetic field on the primary recrystallization texture of the silicon iron is shown: this is expressed in the enhanced scattering of deformation type orientations in the annealing texture.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 1, pp. 82–87, January, 1973.     

Charge-storage effects in a metal-insulator-semi-conductor structure containing germanium nano-crystals formed by rapid thermal annealing of an electron-beam evaporated germanium layer

Charge-storage effects in a metal-insulator-semi-conductor device containing germanium (Ge) nano-crystals were investigated. The Ge nano-crystals were formed by rapid thermal annealing (RTA) of an evaporated, ultra-thin Ge layer at 1000 °C in argon. Capacitance–voltage measurements shows that the amount of electrical charge which can be stored in the device varies with the duration of the RTA treatment. The charge shows a maximum value for 200 s RTA treatment, and then decreases with longer annealing time up to 400 s. Atomic force microscopy analysis indicates that there is a correlation between the density of Ge nano-crystals in the devices, and the amount of electrical charge stored. For an RTA treatment of 300 s, capacitance–time measurements show a time dependence, which indicates a dispersive carrier relaxation. The retention time is dependent on the applied bias, and a maximum retention time of 115 s was observed at -7 V. The value of the stored electrical charges in the device decreases with increasing ambient temperature. A possible charging/discharging mechanism for the device was discussed to explain the capacitance–time measurements and the temperature stored charge results. PACS 81.07.Ta; 81.15.Jj; 73.63.Kv; 85.35.Be; 81.40.Ef     

Rapid thermal processing of lithium tantalite thin films prepared by a diol-based sol–gel process

Lithium tantalite (LiTaO₃) thin films have been deposited on Pt(111)/SiO₂/Si(100) substrates by means of sol–gel spin-coating technology. Using a diol-based precursor solution and rapid thermal processing (RTP), highly c-axis oriented LiTaO₃ thin films are obtained and the degree of orientation is increased with an increase of the heating rate. By changing the heating rate (600–3000 °C/min) and heating temperature (500–800 °C), the effects of various processing parameters on the growth of films are investigated. With the increase of heating rate, the grain size of LiTaO₃ thin films decreases markedly, and the relative dielectric constant (_r) increases from 28 up to 45.6. It was found that the dielectric loss factor (cos) decreased, and the ferroelectric properties were improved by the increase of heating rate. The figures of merit (F_v and F_m) indicate that the LiTaO₃ thin film with a heating rate of 1800 °C/min is suitable for application as a high-performance pyroelectric thin-film detector. PACS 81.20.Fw; 81.40.-z; 61.10.Eq; 77.84.-s     

Microstructure and magnetic properties of FePt:Ag nanocomposite films on SiO2/Si(1 0 0)

FePt:Ag nanocomposite films were prepared by pulsed filtered vacuum arc deposition system and subsequent rapid thermal annealing on SiO₂/Si(1 0 0) substrates. The microstructure and magnetic properties were investigated. A strong dependence of coercivity and ordering of the face-central tetragonal structure on both Ag concentration and annealing temperature was observed. With Ag concentration of 22% in atomic ratio, the coercivity got to 6.0 kOe with a grain size of 6.7 nm when annealing temperature was 400 °C.     

Microstructure and thermal stability of Fe,Ti, and Ag implanted yttria-stabilized zirconia

Yttria-stabilized zirconia (YSZ) was implanted with 15 keV Fe or Ti ions up to a dose of 8×10¹⁶ at cm^–2. The resulting dopant concentrations exceeded the concentrations corresponding to the equilibrium solid solubility of Fe₂O₃ or TiO₂ in YSZ. During oxidation in air at 400° C, the Fe and Ti concentration in the outermost surface layer increased even further until a surface layer was formed of mainly Fe₂O₃ and TiO₂, as shown by XPS and ISS measurements. From the time dependence of the Fe and Ti depth profiles during anneal treatments, diffusion coefficients were calculated. From those values it was estimated that the maximum temperature at which the Fe- and Ti-implanted layers can be operated without changes in the dopant concentration profiles was 700 and 800° C, respectively. The high-dose implanted layer was completely amorphous even after annealing up to 1100° C, as shown by scanning transmission electron microscopy. Preliminary measurements on 50 keV Ag implanted YSZ indicate that in this case the amorphous layer recrystallizes into fine grained cubic YSZ at a temperature of about 1000° C. The average grain diameter was estimated at 20 nm, whereas the original grain size of YSZ before implantation was 400 nm. This result implies that the grain size in the surface of a ceramic material can be decreased by ion beam amorphisation and subsequent recrystallisation at elevated temperatures.     

MOS transistors with epitaxial Si,laterally grown over SiO2 by liquid phase epitaxy

We describe the first MOS transistors fabricated in silicon-on-insulator layers, obtained by liquid phase epitaxial lateral overgrowth of Si over SiO₂. Growth is performed around 930°–920° C using indium as a solvent. The layers are therefore p-type and have a doping of 4·10¹⁶ cm^–3. Electron mobilities of 540 cm²/Vs are obtained in the inversion channel; the threshold voltage of transistors with a gate length of 14.1 m is 510 mV. Our data demonstrate the applicability of liquid-phase epitaxial Si grown over oxidized Si for future use in three-dimensional integrated-device processing.     

Study of quasicrystalline thin films based on Al–Pd–Mn and Al–Cu–Fe prepared by PLD

Thin films of Al₇₀Pd₂₀Mn₁₀ Al₆₃Cu₂₅Fe₁₂ Al₇₀Pd₂₀Mn₁₀ and Al₆₃Cu₂₅Fe₁₂ were grown by laser ablation on fused silica at set of deposition temperature –196°C, room temperature 165°C and 350°C. Structure, morphology, resistivity and refractive index of prepared layers were studied.     

Preparation and electrical properties of Bi<Subscript>3.25</Subscript>Pr<Subscript>0.75</Subscript>Ti<Subscript>3</Subscript>O<Subscript>12</Subscript> ferroelectric thin films

Bi_3.25Pr_0.75Ti₃O₁₂ (BPT) ferroelectric thin films have been prepared by chemical solution deposition on platinized Si substrates. Well-crystallized BPT films can be achieved by 600 °C rapid thermal annealing. The film surface is smooth and crack-free, composed of uniform spherical grains around 90–100 nm in diameter. The electrical properties of Pt/BPT/Pt thin film capacitors were characterized by hysteresis and impedance measurements. The remanent polarization of 700 °C annealed BPT films is around 20 C/cm² at 120-kV/cm stimulus field. The dielectric constant is around 380 at 10 kHz, 100-mV amplitude. The remanent polarization of BPT film showed a slight reduction, 10% of its original value, after 2.8×10⁹ cycles, while a 30% reduction of non-volatile polarization was observed. PACS 81.15.-z; 77.55.+f; 77.22.Gm