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.     

Influence of growth conditions on the structural,optical, and electrical properties of ZnSe films

ZnSe films were grown by chemical vapour deposition on GaAs substrates. The influence of the source temperature (between 820 and 900° C) and the substrate temperature (between 620 and 790° C) on the film properties were investigated by Hall measurements, X-ray diffraction, and photoluminescence. With respect to blue luminescent devices the ratio of excitonic to deep level transitions was found to be optimum at low growth rates when the source temperatures were kept below 840° C. P-type conduction up to a net carrier concentration of 8×10¹⁸ cm^–3 could be obtained by substrate temperatures above 700° C. Lattice contraction versus substrate temperature pointed to a reduced incorporation of donors at higher growth temperatures.     

The influence of substrate temperature on the morphology, optical and electrical properties of thermal-evaporated ZnTe Thin Films

The structural, morphological, optical and electrical properties of ZnTe films deposited by evaporation were investigated as a function of substrate temperature (at −123 and 27 °C) and post-deposition annealing temperature (at 200, 300 and 400 °C). It was determined that films deposited at both substrate temperatures were polycrystalline in nature with zinc-blende structure and a strong (1 1 1) texture. A small Te peak was detected in XRD spectra for both substrate temperatures, indicating that as-deposited ZnTe films were slightly rich in Te. Larger grains and a tighter grain size distribution were obtained with increased substrate temperature. Scanning electron microscopy (SEM) studies showed that the microstructures of the as-deposited films agreed well with the expectations from structure zone model. Post-deposition annealing induced further grain growth and tightened the grain size distribution. Annealing at 400 °C resulted in randomization in the texture of films deposited at both substrate temperatures. Optical spectroscopy results of the films indicated that the optical band gap value increased from 2.13 to 2.16 eV with increased substrate temperature. Increasing the annealing temperature sharpened the band-edge. Resistivity measurements showed that the resistivity of films deposited at substrate temperatures of −123 and 27 °C were 32 Ω cm, and 1.0 × 10⁴ Ω cm, respectively with corresponding carrier concentrations of 8.9 × 10¹⁵ cm⁻³ and 1.5 × 10¹⁴ cm⁻³. Annealing caused opposite changes in the film resistivity between the samples prepared at substrate temperatures of −123 and 27 °C.     

Deposition of copper oxide (Cu2O,CuO) thin films at high temperatures by plasma-enhanced CVD

Copper-oxide films are deposited by plasma-enhanced CVD using copper acetylacetonate as a precursor. The influence of various experimental parameters on deposition rate, film composition and resistivity have been studied. The substrate temperature and the bias are the parameters which affect these properties the most. An increase of the substrate temperature changes the phases of the deposit from Cu₂O-CuO over Cu₂O to Cu. At temperatures 500° C the deposition rates are high but the films consist mainly of metallic Cu. A negative bias enhances the deposition rate only slightly but has a strong effect on the film composition and can completely balance the oxygen deficiency. At a bias of –120 V the films consist of pure CuO even at temperatures 500° C.     

Development of conductive transparent indium tin oxide (ITO) thin films deposited by direct current (DC) magnetron sputtering for photon-STM applications

Highly conductive and transparent indium tin oxide (ITO) thin films, each with a thickness of 100 nm, were deposited on glass and Si(100) by direct current (DC) magnetron sputtering under an argon (Ar) atmosphere using an ITO target composed of 95% indium oxide and 5% tin oxide for photon-STM use. X-ray diffraction, STM observations, resistivity and transmission measurements were carried out to study the formation of the films at substrate temperatures between 40 and 400 °C and the effects of thermal annealing in air between 200 and 400 °C for between1 and 5 h. The film properties were highly dependent on deposition conditions and on post-deposition film treatment. The films deposited under an Ar atmosphere pressure of ∼1.7×10^-3 Torr by DC power sputtering (100 W) at substrate temperatures between 40 and 400 °C exhibited resistivities in the range 3.0–5.7×10^-5 Ω m and transmissions in the range 71–79%. After deposition and annealing in air at 300 °C for 1 h, the films showed resistivities in the range 2.9–4.0×10^-5 Ω m and transmissions in the range 78–81%. Resistivity and transmission measurements showed that in order to improve conductive and transparent properties, 2 h annealing in air at 300 °C was necessary. X-ray diffraction data supported the experimental measurements of resistivity and transmission on the studies of annealing time. The surface roughness and film uniformity improve with increasing substrate temperature. STM observations found the ITO films deposited at a substrate temperature of 325 °C, and up to 400 °C, had domains with crystalline structures. After deposition and annealing in air at 300 °C for 1 h the films still exhibited similar domains. However, after deposition at substrate temperatures from 40 °C to 300 °C, and annealing in air at 300 °C for 1 h, the films were shown to be amorphous. More importantly, the STM studies found that the ITO film surfaces were most likely to break after deposition at a substrate temperature of 325 °C and annealing in air at 300 °C for 2 or 3 h. Such findings give some inspiration to us in interpreting the effects of annealing on the improvement of conductive and transparent properties and on the transition of phases. In addition, correlations between the conductive/transparent properties and the phase transition, the annealing time and the phase transition, and the conductive/transparent properties and the annealing time have been investigated. Received: 10 July 2000 / Accepted: 27 October 2000 / Published online: 9 February 2001     

Formation of palladium silicide by rapid thermal annealing

The formation of palladium silicide Pd₂Si by rapid thermal annealing of Pd layers on silicon has been studied as a function of annealing time (1–60s) in the temperature range 350–500 °C. It is shown that the results found for conventional furnace annealing (long duration, low temperature) can be extrapolated for rapid thermal annealing (shorter time, higher temperature) when taking into account the exact time dependence of the short temperature cycle. The growth rate is essentially diffusion limited and the activation energy is close to 1.1±0.1 eV. Silicide resistivity of about 30–40 cm was obtained for 200–400 nm thick Pd₂Si layers formed at 400 °C for a few seconds.     

Thermal stability of Ag films in air prepared by thermal evaporation

The thermal stability of silver films in air has been studied. Pure Ag films, 250 nm in thickness, were prepared on glass substrates by thermal evaporation process, and subsequently annealed in air for 1 h at temperatures between 200 and 400 °C. The structure and morphology of the samples were investigated by X-ray diffraction, Raman spectra and atomic force microscopy. It is found that the crystallization enhances for the annealed films, and film surface becomes oxidized when annealing temperature is higher than 350 °C. The electrical and optical properties of the films were studied by van der Pauw method and spectrophotometer, respectively. Reflectance drops sharply as Ag films are annealed at temperatures above 250 °C. Film annealed at 250 °C has the maximum surface roughness and the minimum reflectance at 600 nm optical wavelength. Film annealed at 200 °C has the minimum resistivity, and resistivity increases with the increasing of the annealing temperature when temperature is above 200 °C. The results show that both oxidization on film surface and agglomeration of silver film result in infinite of electrical resistivity as the annealing temperature is above 350 °C.     

Annealing of chemically vapor deposited nanoscale Ti-Si islands on Si

Small islands of Ti-Si were formed by chemical vapor deposition onto a Si substrate and subsequently annealed. The islands were deposited in the 610–730 °C temperature range by the H₂ reduction of TiCl₄, either without or with a Si-containing gas added during deposition. Subsequent annealing above 800 °C decreases the island density significantly, and the islands take characteristic shapes. After annealing, the island size depends only weakly on the amount of Ti deposited while the island density varies more significantly and depends on the addition of a Si-containing gas during deposition. Three different dominant island shapes are seen on Si(001), and different shapes are found on Si(111). PACS 68.60.Dv; 68.65.Hb; 68.35.Fx     

Formation of thermally stable low-resistance Ti/W/Au ohmic contacts on n-type GaN

A Ti(12 nm)/W(20 nm)/Au(50 nm) metallization scheme has been investigated for obtaining thermally stable low-resistance ohmic contacts to n-type GaN (4.0×10¹⁸ cm^-3). It is shown that the current–voltage (I–V) characteristics of the samples are abnormally dependent on the annealing temperature. For example, the samples that were annealed at temperatures below 750 °C for 1 min in a N₂ ambient show rectifying behavior. However, annealing the samples at temperatures in excess of 850 °C results in linear I–V characteristics. The contact produces a specific contact resistance as low as 8.4×10^-6 Ω cm² when annealed at 900 °C. It is further shown that the contacts are fairly thermally stable even after annealing at 900 °C; annealing the samples at 900 °C for 30 min causes insignificant degradation of the electrical and structural properties. Based on glancing angle X-ray diffraction and Auger electron microscopy results, the abnormal temperature dependence of the ohmic behavior is described and discussed. PACS 72.80.Ey; 73.40.Cg; 73.20.At; 79.60Bm; 73.40.Gk     

Spray pyrolytic synthesis of samarium doped ceria (Ce0.8Sm0.2O1.9) films for solid oxide fuel cell applications

Uniform, adherent, single phase samarium doped ceria films have been successfully deposited by spray pyrolysis technique for their application in solid oxide fuel cell. These films have been deposited at different substrate temperatures on glass substrate and subsequently heat treated in tube furnace. Effect of substrate temperature and annealing temperature on phase formation was studied with thermo-gravimetric analysis and differential temperature analysis, X-ray diffraction, scanning electron microscope, and energy dispersive X-ray analysis techniques. These studies showed the formation of single phase Ce_0.8Sm_0.2O_1.9 films, at substrate temperature 400 °C and annealing temperature 550 °C. Electrical resistivity of the films, at room temperature was of the order of 10⁷ Ω cm while at 400 °C it is found to be of the order of 10¹ Ω cm. This reveals the use of these films for making low temperature solid oxide fuel cells.     

Bulk and near-surface annealing behavior of the 0.8 eV luminescence in semi-insulating gallium arsenide

An annealing study of the 0.8 eV photoluminescence band in LEC GaAs has been performed, using a combination of 10 min annealing steps over a temperature range of 800–1100° C and one hour furnace annealing steps at 500–700° C. Results show that the defect responsible for the luminescence is stable in bulk material under all annealing conditions that have been investigated. In combination with earlier results, this demonstrates a stability of the defect to temperatures in excess of 900° C and indicates a parallel with the annealing behavior of the 0.67 eV band in semi-insulating GaAs. The observed annealing behavior is very different in the near-surface region, indicating an important role of As out-diffusion.     

Influence of substrate temperature and post-treatment on the properties of ZnO:Al thin films prepared by pulsed laser deposition

Highly transparent conductive Al₂O₃ doped zinc oxide (AZO) thin films have been deposited on the glass substrate by pulsed laser deposition technique. The effects of substrate temperature and post-deposition annealing treatment on structural, electrical and optical properties of AZO thin films were investigated. The experimental results show that the electrical resistivity of films deposited at 240 °C is 6.1 × 10⁻⁴ Ω cm, which can be further reduced to as low as 4.7 × 10⁻⁴ Ω cm by post-deposition annealing at 400 °C for 2 h in argon. The average transmission of AZO films in the visible range is 90%. The optical direct band gap of films was dependent on the substrate temperature and the annealing treatment in argon. The optical direct band gap value of AZO films increased with increasing annealing temperature.     

Role of columnar grain size in magnetization of La0.8MnO3 thin films grown by pulsed laser deposition

La_0.8MnO₃ thin films have been deposited on (100) SrTiO₃ substrates at different substrate temperatures by a pulsed laser deposition method. Electronic transport measurements show that a higher substrate temperature results in lower resistivity and higher insulator–metal transition temperature. Transmission electron microscope studies reveal that all the films exhibit a feature of columnar structure with the grain size decreasing with substrate temperature. We argue that the columnar grain size strongly affects the ferromagnetic transition temperature and, in turn, dominates the resistivity behavior. Based on this point, other effects, such as of annealing and film thickness, on the electronic properties are also discussed. PACS 68.55.Jk; 71.30.+h; 75.70.Ak; 75.70.Pa     

Effect of bulk resistivity,annealing temperature and illumination on oxygen sorption on CdSe surfaces

The bulk resistivity, annealing temperature and photo-illumination were found to have large effects on the oxygen sorption of the Cd (0001) surfaces of CdSe. For the higher resistivity surfaces, annealing at temperatures below ~ 400°C, no oxygen adsorption was detected. However, if the surfaces were annealed at temperatures above ~ 500°C, a significant amount of oxygen adsorption was subsequently detected at room temperature in darkness. This adsorbed oxygen could be partially desorbed by visible light and almost completely desorbed by UV light. On the other hand, surfaces of very low resistivities were so much more reactive to oxygen that appreciable oxygen adsorption in darkness was detected. This oxygen adsorption was always enhanced by illumination with UV or visible light. Annealing at ~ 550 °C had no significant effect on this photo-adsorptive behaviour. However, annealing at temperatures ~ 500–550°C decreased the diffraction intensity. Based on mass spectrometer analysis, the decrease in diffraction intensity was interpreted as due to diffusion of excess Cd to the surface. The oxygen sorption behaviours of all the surfaces investigated were adequately explained by the existing theories based on charge transfer between the surfaces and the adsorbed oxygen.     

Effect of composition and deposition temperature on the characteristics of Ga doped ZnO thin films

ZnO films doped with Ga (GZO) of varying composition were prepared on Corning glass substrate by radio frequency magnetron sputtering at various deposition temperatures of room temperature, 150, 250 and 400 °C, and their temperature dependent photoelectric and structural properties were correlated with Ga composition. With increasing deposition temperature, the Ga content, at which the lowest electrical resistivity and the best crystallinity were observed, decreased. Films with optimal electrical resistivity of 2-3 × 10⁻⁴ Ω cm and with good crystallinity were obtained in the substrate temperature range from 150 to 250 °C, and the corresponding C_Ga/(C_Ga + C_Zn) atomic ratio was about 0.049. GZO films grown at room temperature had coarse columnar structure and low optical transmittance, while films deposited at 400 °C yielded the highest figure of merit (FOM) due to very low optical absorption despite rather moderate electrical resistivity slightly higher than 4 × 10⁻⁴ Ω cm. The optimum Ga content at which the maximum figure of merit was obtained decreased with increasing deposition temperature.     

Characterization of the interfacial reaction between sputter-deposited Ni film and Si substrate

In the present work, we report the interfacial reaction characteristics between sputter-deposited Ni film and a single crystalline Si substrate. The effect of substrate bias during the deposition process on the interfacial reaction is also discussed. It was found that sputter deposition with a substrate bias can promote the interfacial reaction between Ni film and Si substrate. Under our experimental conditions, Ni₂Si (orthorhombic) with good crystallinity formed in the film when it was deposited at 200 °C and with a -80 V substrate bias. Such films had relatively low resistivity. Upon thermal annealing at 500 °C, NiSi formed through further reaction, however there is almost no change in resistivity. PACS 67.57.Np; 68.55.-a; 68.35.Fx     

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.     

Comparison of annealing effects on Zn-doped GaMnAs and undoped GaMnAs epilayers

To compare the annealing effects on GaMnAs-doped with Zn (GaMnAs:Zn) and undoped GaMnAs (u-GaMnAs) epilayers, we grew GaMnAs thin films at 200 °C by molecular beam epitaxy (MBE) on GaAs substrates, and they were annealed at temperatures ranging from 220 °C to 380 °C for 100 min in air. These epilayers were characterized by high-resolution X-ray diffraction (XRD), electrical, and magnetic measurements. A maximum resistivity at temperatures T_m close to the Curie temperatures T_c was observed from the measurement of the temperature-dependent resistivity ρ(T) for both the GaMnAs:Zn and the u-GaMnAs samples. We found, however, that the maximum temperature T_m observed for GaMnAs:Zn epilayers increased with increasing annealing temperature, which was different from the result with the u-GaMnAs epilayers. The formation of GaAs:Zn and MnAs or Mn-Zn-As complexes with increasing annealing temperature is most likely responsible for the differences in appearance.     

Influence of annealing temperature on structural,electrical and optical properties of WSi2

WSi₂ polycrystalline films of different thicknesses were prepared by low pressure chemical vapor deposition on silicon wafers, and their crystallization properties were studied as a function of the annealing temperature. Structural measurements were performed by X-ray diffraction, detailing for the first time the phase transition from the amorphous to the hexagonal structure at an annealing temperature 380° C and from hexagonal to tetragonal above 700° C. The electrical sheet resistance showed the same transition temperatures.Optical characterization was performed by spectroscopic ellipsometry, and the real and imaginary part of the complex refractive index were obtained as a function of the annealing temperature in the 0.25–0.9 m wavelength range. A broad optical band was found for samples annealed up to 700° C, while for higher annealing temperatures a transparency region for wavelengths greater than 0.5 m and some significant structures appear. A corresponding behavior was observed in the infrared reflectance spectra. Furthermore, it was shown that the determination of the thickness of SiO₂ grown on WSi₂ requires a multilayer model, taking into account the transparency of tetragonal WSi₂.     

Influence of annealing temperature on structural and optical properties of ZnO: In thin films prepared by ultrasonic spray technique

Transparent conducting indium doped zinc oxide was deposited on glass substrate by ultrasonic spray method. The In doped ZnO samples with indium concentration of 3 wt.% were deposited at 300, 350 and 400 °C with 2 min of deposition time. The effects of substrate temperature and annealing temperature on the structural, electrical and optical properties were examined. The DRX analyses indicated that In doped ZnO films have polycrystalline nature and hexagonal wurtzite structure with (0 0 2) preferential orientation and the maximum average crystallite size of ZnO: In before and annealed at 500 °C were 45.78 and 55.47 nm at a substrate temperature of 350 °C. The crystallinity of the thin films increased by increasing the substrate temperature up 350 °C, the crystallinity improved after annealing temperature at 500 °C. The film annealed at 500 °C and deposited at 350 °C show lower absorption within the visible wavelength region. The band gap energy increased from E_g = 3.25 to 3.36 eV for without annealing and annealed films at 500 °C, respectively, indicating that the increase in the transition tail width. This is due to the increase in the electrical conductivity of the films after annealing temperature.