Effect of different sputtering gas mixtures on the structural,electrical, and optical properties of p-type NiO thin films

We investigated how mixtures of Ar and O₂ or N₂ gases affect the structural, electrical and optical properties of RF-magnetron-sputtered NiO films. It is shown that the addition of O₂ gas to Ar ambient (namely, Ar:O₂=2:1 to 1:2) slightly reduces the (2 0 0) texturing of the NiO films. The introduction of N₂ gas (from 0 to 2 sccm) to Ar:O₂ (2:1) mixture enhances the (2 0 0) texturing, while the addition of N₂ gas (from 0 to 2 sccm) to Ar ambient slightly weakens the (1 1 1) texturing. The deposition rate is reduced from 6.1 to 1.5 nm/min when O₂ gas is added to Ar ambient. The addition of N₂ gas to the Ar:O₂ (2:1) mixture slightly increases the deposition rate from 1.8 to 2.6 nm/min, whereas adding N₂ gas to Ar only ambient somewhat reduces the rate from 6.1 to 4.4 nm/min. The carrier concentration of the films is increased and the mobility is decreased as the O₂ flow rate in the Ar:O₂ mixture is increased. The addition of N₂ gas to the Ar:O₂ (2:1) mixture increases the resistivity of the films, while adding N₂ gas to Ar ambient decreases the resistivity. The transmittance and optical bandgap of the films are reduced (from 58.4 to 45.5% at 550 nm and from 3.5 to 3.3 eV, respectively) with increasing O₂ flow to Ar ambient. When N₂ gas is added to the Ar:O₂ (2:1) mixture, the transmittance in the visible wavelength range increases from 58.4 to 71.3% and the optical bandgap increases from 3.5 to 3.6 eV. However, adding N₂ gas to the Ar only ambient results in decrease in the transmittance in the visible wavelength region (from 69.3 to 56%) and the optical bandgap (from 3.7 to 3.5 eV).     

Synthesis and characterization of phosphorus-doped ZnO and (Zn,Mg)O thin films via pulsed laser deposition

The transport and optical properties of phosphorus-doped (Zn,Mg)O thin films grown via pulsed laser deposition (PLD) are studied. The carrier type of as-deposited (Zn,Mg)O:P films converts from n-type to p-type with increasing oxygen partial pressure. All the films exhibit good crystallinity with c-axis orientation. This result indicates the importance of oxidation conditions in realizing p-type (Zn,Mg)O:P films. The as-deposited ZnO:P film properties show a strong dependence on the deposition ambient at different growth temperatures. The resistivity of the samples deposited in O₃/O₂ mixture is two orders of magnitude higher than the films grown in oxygen and O₂/Ar/H₂ mixture. The room-temperature photoluminescence (PL) of the as-deposited films has been shown that growing in the O₂/Ar/H₂ mixture ambient significantly increases the band edge emission while inhibiting the visible emission. The enhanced ultraviolet (UV) emission in the films grown in O₂/Ar/H₂ mixture may result from hydrogen passivation of the deep level emission centers. The annealed ZnO:P films are n-type with nonlinear dependence of resistivity on annealing temperature. The resistivity increases in the films with annealing at 800°C while decreasing with further increasing annealing temperature. Strong visible light emission is observed from the ZnO:P films annealed in oxygen.     

Effects of annealing on the characteristics of ZnO films deposited in various O2/(O2+Ar) ratios

C-axis oriented ZnO films are deposited on polished diamond substrates in various O₂/(O₂+Ar) ratios using the radio frequency (RF) magnetron sputtering technique and are subsequently annealed in oxygen ambience under the same conditions. Structural, morphologic and electrical properties of ZnO films are characterized by X-ray diffraction (XRD), high-resistance instrument, energy dispersive X-ray spectroscopy (EDS) and scanning electronic microscopy (SEM). As the O₂/(O₂+Ar) ratio increasing from 1/12 to 5/12, the crystallinity of the as grown ZnO films becomes better and the electrical resistivity increases slowly. After annealing, the ZnO films deposited in O₂/(O₂+Ar) =1/12 and 3/12 are improved greatly in crystallinity, and their electrical resistivity is enhanced by two orders of magnitude, while those deposited in O₂/(O₂+Ar) =5/12 are scarcely changed in crystallinity, and their resistivity is only increased by one order. In addition, the ZnO films deposited in O₂/(O₂+Ar) =3/12 and annealed in oxygen are with the best crystal quality and the highest resistivity.     

Low-temperature metal-organic chemical vapor deposition (LTMOCVD) of device-quality copper films for microelectronic applications

Copper films for potential use in multilevel metallization in ULSIC’s were produced by low temperature (250–350° C) metal-organic chemical vapor deposition (LTMOCVD) in atmospheres of pure H₂ or mixture Ar/H₂ from the β-diketonate precursor bis(1,1,1,5,5,5-hexafluoroacetylacetonato) copper(ll), Cu(hfa)₂. The films were analyzed by x-ray diffraction (XRD), Rutherford backscattering (RBS), Auger electron spectroscopy (AES), scanning electron microscopy (SEM), and energy-dispersive x-ray spectroscopy (EDXS). The results of these studies showed that the films were uniform, continuous, adherent and highly pure—oxygen and carbon contents were below the detection limits of AES. Four point resistivity measurements showed that the copper films had very low resistivity, as low as 1.9 μΩcm for the films deposited in pure hydrogen atmosphere. Our preliminary results seem to indicate that LTMOCVD is a very attractive technique for copper multilevel metallizations.     

Synthesis and Characterization of Magnesium-Alloyed Hematite Thin Films

We have synthesized pure and Mg-alloyed hematite thin films on F-doped, SnO₂-coated glass substrates by radiofrequency magnetron cosputtering of iron oxide with and without MgO sources in mixed Ar/O₂ and mixed N₂/O₂ ambient. We found that hematite films deposited in N₂/O₂ ambient exhibited much poorer crystallinity than those deposited in Ar/O₂ ambient. We determined that Mg alloying led to increased crystallinity and bandgap. Furthermore, we found that Mg alloying inverted the type of conductivity of the thin films: pure hematite thin films exhibited n-type conductivity, whereas Mg-alloyed hematite thin films exhibited p-type conductivity.     

TaCN growth with PDMAT and H2/Ar plasma by plasma enhanced atomic layer deposition

TaCN films were deposited using atomic layer deposition (ALD) using PDMAT and H₂/Ar plasma. Calculations based on density functional theory (DFT) indicate a high energy barrier and a low reaction energy for reducing the +5 Ta oxidation state in the PDMAT precursor by using pure H radicals. Through the assistance of Ar radicals, low resistivity of TaCN films of 230 μΩ cm could be deposited by using H₂/Ar plasma. By employing in situ X-ray diffraction during annealing, the activation energy for Cu diffusion through the TaCN barrier was evaluated at 1.6 eV.     

Nitridation of hafnium oxide by reactive sputtering

Hafnium oxide films were RF sputtered from HfO₂ target in Ar/O₂ or Ar/N₂ ambient on silicon substrates. The composition of the deposited films was analyzed by X-ray photoelectron spectroscopy (XPS). For samples sputtered in Ar/N₂, it was observed that nitrogen was incorporated in the bulk of hafnium oxide films in the form of HfON, and SiON layer was formed at the silicon-insulator interface. After annealing the hafnium oxide films at 600-700 °C, MOS structures were fabricated and used for electrical characterization. The effects of nitridation of hafnium oxide on both the capacitance-voltage and current-voltage characteristics of the MOS capacitors were discussed.     

The CVD growth of Cu films using H2 as carrier gas

Copper chemical vapor deposition from Cu(hexafluoroacetylacetonate)trimethylvinylsilane (Cu(hfac)TMVS) was studied using a low pressure chemical vapor deposition system of a cold wall vertical reactor. The Cu films deposited using H₂ as a carrier gas revealed no impurities in the films within the detection limits of Auger electron spectroscopy and x-ray photoelectron spectroscopy. Using hydrogen as a carrier gas, the hydrogen not only acts as a reducing agent, but also reacts with the residual fragment of precursor. As a result, using H₂ as a carrier gas for Cu(hfac)TMVS resulted in Cu films of lower resistivity, denser microstructure and faster deposition rate than using Ar or N₂ as the carrier gas. Moreover, we found that N₂ plasma treatment on the substrate surface prior to Cu deposition increased the deposition rate of Cu films.     

The effects of carrier gas and substrate temperature on ZnO films prepared by ultrasonic spray pyrolysis

ZnO films were deposited on glass substrates in the temperature range of 350–470 °C under an atmosphere of compressed air or nitrogen (N₂) by using ultrasonic spray pyrolysis technique. Structural, electrical and optical properties of the ZnO films were investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM), electrical two-probe and optical transmittance measurements. The ZnO films deposited in the range of 350–430 °C were polycrystalline with the wurtzite hexagonal structure having preferred orientation depending on the substrate temperature. The ZnO films deposited below 400 °C had a preferred (100) orientation while those deposited above 400 °C mostly had a preferred (002) orientation. The resistivity values of ZnO films depended on the types of carrier gas. The ZnO thin films deposited under N₂ atmosphere in the range of 370–410 °C showed dense surface morphologies and resistivity values of 0.6–1.1 Ω-cm, a few orders of magnitude lower than those deposited under compressed air. Hydrogen substition in ZnO possibly contributed to decreasing resistivity in ZnO thin films deposited under N₂ gas. The Hall measurements showed that the behavior of ZnO films deposited at 410 °C under the N₂ atmosphere was n-type with a carrier density of 8.9–9.2×10¹⁶ cm^-3 and mobility of ～70 cm²/Vs. ZnO thin films showed transmission values at 550 nm wavelength in a range of 70–80%. The values of band gaps extrapolated from the transmission results showed bandgap shrinkage in an order of milli electron volts in ZnO films deposited under N₂ compared to those deposited under compressed air. The calculation showed that the bandgap reduction was possibly a result of carrier–carrier interactions.     

Optimization of N2/Ar gas flow ratio for the realization of nitrogen-doped p-type ZnCdO thin films synthesized by RF magnetron sputtering

Nitrogen doped ZnCdO films [ZCO:N] have been grown on quartz substrates by radio frequency (RF) reactive magnetron sputtering technique, and the effect of the ratio of nitrogen to argon gas flow [N₂:Ar] on their electrical, microstructure and optical properties were investigated by Hall effect, energy dispersive X-ray spectroscopy (EDX), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), transmission electron microscope (TEM), optical absorbance and photoluminescence (PL) measurements. The results indicate that all the ZCO:N films are of hexagonal wurtzite structure with highly (002) preferential orientation. As the N₂:Ar increases from 0:1 to 4:1, the absorption edge for the samples exhibits blue shift. Hall effect measurement results indicate that the N₂:Ar exerts an immense influence on the p-type conduction conversion for ZCO:N film. It is found that ZCO:N film deposited at the N₂:Ar of 1:2 shows the optimal p-type behavior, which has a carrier concentration of 1.10×10¹⁷ cm⁻³, a mobility of 3.28 cm²V⁻¹s⁻¹ and a resistivity of 17.3 Ω cm. Compared with the other samples, ZCO:N film fabricated at the relatively lower N₂:Ar possesses the superior crystal quality, luminescent and electrical properties. Additionally, a possible mechanism of p-type conduction for ZCO:N film was discussed in this work.     

Deposition characteristics of Ti−Si−N films reactively sputtered from various targets in a N2/Ar gas mixture

The deposition characteristics of Ti−Si−N films obtained by using RF reactive sputtering of various targets in N₂/Ar gas mixtures have been investigated. The dependence of film growth rate and stoichiometry on both the Ti/Si ratio of the target and the N₂ flow rate were found to be due to the different intridation rates of Ti and Si, resulting in, different sputter yields of titanium and silicon nitrides. XPS results showed that an increase in nitrogen content of the Ti−Si−N films leads to the formation of amorphous Si₃N₄ bonding, which produces an in crease in resistivity. Lowering the Si content in the deposited Ti−Si−N films favors the formation of crystalline TiN, even at low N₂ flow rates, and leads to a lower resistivity. A film growth mechanism, expressed in terms of the nitrogen surface coverage on the target, was proposed.     

Field Emission and Electric Discharge of Nanocrystalline Diamond Films

Nanocrystalline diamond (NCD) films were produced by microwave plasma-enhanced chemical vapor deposition (MPECVD) using gas mixtures of Ar, H₂, and CH₄. The structural properties, electron emission, and electric discharge behaviors of the NCD films varied with H₂ flow rates during MPECVD. The turn-on field for electron emission at a pressure of 2.66 × 10⁻⁴ Pa increased from 4.2 V μm⁻¹ for the NCD films that were deposited using a H₂ flow rate of 10 cm³ min⁻¹ to 7 V μm⁻¹ for films deposited at a H₂ flow rate of 20 cm³ min⁻¹. The NCD film with a low turn-on field also induced low breakdown voltages in N₂. The grain size and roughness of the NCD films may influence both the electron emission and the electric discharge behaviors of the NCD cathodes.     

The effects of process conditions and substrate on copper MOCVD using liquid injection of (hfac)Cu(vtmos)

Copper MOCVD (metalorganic chemical vapor deposition) using liquid injection for effective delivery of the (hfac)Cu(vtmos) [1,1,1,5,5,5-hexafluoro-2,4-pentadionato(vinyltrimethoxysilane) copper(I)] precursor has been performed to clarify growth behavior of copper films onto TiN, <100> Si, and Si₃N₄ substrates. Especially, we have studied the influences of process conditions and the substrate on growth rates, impurities, microstructures, and electrical characteristics of copper films. As the reactor pressure was increased, the growth rate was governed by a pick-up rate of (hfac)Cu(vtmos) in the vaporizer. The apparent activation energy for copper growth over the surface-reaction controlled regime from 155°C to 225°C was in the range 12.7–32.5 kcal/mol depending upon the substrate type. It revealed that H₂ addition at 225°C substrate temperature brought about a maximum increase of about 25% in the growth rate compared to pure Ar as the carrier gas. At moderate deposition temperatures, the degree of a <111> preferred orientation for the deposit was higher on the sequence of <Cu/Si<Cu/TiN<Cu/Si₃N₄. The relative impurity content within the deposit was in the range 1.1 to 1.8 at.%. The electrical resistivity for the Cu films on TiN illustrated three regions of the variation according to the substrate temperature, so the deposit at 165°C had the optimum resistivity value. However, the coarsened microstructures of Cu on TiN prepared above 275°C gave rise to higher electrical resistivities compared to those on Si and Si₃N₄ substrates.     

Study of electrical and optical properties of CNx thin films deposited by reactive magnetron sputtering

The study concerns the CN_x thin films deposited by Low Pressure Hot Target Reactive Magnetron Sputtering (LP-HTRMS). The thin film resistance changes with relative humidity (RH) and optical properties have been studied in the range of 300-653 K. The temperature coefficients of resistivity changes were −2.5%/K at 300 K and −0.5%/K at 500 K. The activation energy of conductivity E_ρ was found to be 0.21 eV in the case of unannealed sample and 0.44 eV when the sample was annealed at 653 K. The CN_x thin films fastness to light was tested in the range of 200-2500 nm by measuring their transmittance. The calculations of absorption carrying out with Tauc formula proved the dominance of indirect optical transitions with Eg energy of 1.04 eV and direct transitions of Eg 2.05 eV. The UV radiation was fully absorbed and light transmission was ca. 90% in the range from visible radiation to far infrared of 1000-2500 nm. The CN_x thin films showed the high resistance sensitivity to RH changes. At T = 300 K resistance changed from 882 M Ω for 36% RH to 386 k Ω for 85% RH. The CN_x thin films susceptibility to humidity was observed in case of both DC and AC current (100 Hz to 10 kHz) measurements. The Si₃N₄ or SiC buffer adhesive layer was incorporated between CN_x film and substrate and its influence on CN_x electrical properties was observed.     

Thermal conductivity of AlN thin films deposited by RF magnetron sputtering

Aluminum nitride (AlN) film, which is being investigated as a possible passivation layer in inkjet printheads, was deposited on a Si (1 0 0) substrate at 400 °C by radio frequency (RF) magnetron sputtering using an AlN ceramic target. Dependence on various reactive gas compositions (Ar, Ar:H₂, Ar:N₂) during sputtering was investigated to determine thermal conductivity. The crystallinity, grain size, and Al–N bonding changes by the gas compositions were examined and are discussed in relation to thermal conductivity. Using an Ar and 4% H₂, the deposited AlN films were crystalline with larger grains. Using a higher nitrogen concentration of 10%, a near amorphous phase, finer morphology, and an enhanced Al–N bonding ratio were achieved. A high thermal conductivity of 134 W/mk, which is nine times higher than that of the conventional Si₃N₄ passivation film, was obtained with a 10% N₂ reactive gas mixture. A high Al–N bonding ratio in AlN film is considered the most important factor for higher thermal conductivity.     

Effects of thermal annealing on the structural properties of sputtered W–Si–N diffusion barriers

W–Si–N thin films were deposited via rf-magnetron sputtering from a W₅Si₃ target in Ar/N₂ reactive gas mixtures over a large range of compositions, obtained by varying the partial flow of nitrogen within the reaction chamber. The samples of each set were then thermally annealed in vacuum at different temperatures up to 980 °C.Film composition was determined by Rutherford backscattering spectrometry (RBS), surface film morphology by scanning electron microscopy (SEM), micro-structure by transmission electron microscopy (TEM), vibrational properties by FT-IR absorption and Raman scattering spectroscopy, and electrical resistivity by four-point probe measurements.Independently of the deposition conditions, all the as-deposited films have an amorphous structure, while their composition varies, showing an increase of Si/W ratio from 0.1 up to 0.55 when the nitrogen concentration in the films increases from 0 to 60 at%. Thermal treatments in vacuum induce an important loss of nitrogen in the nitrogen-rich samples, especially at temperatures higher than 600 °C. Samples with high nitrogen content preserve their amorphous structure even at the highest annealing temperature, despite the chemical bonding ordering observed by means of FT-IR measurements. Raman spectroscopy of as-deposited films rich in nitrogen suggests the presence of an important amorphous silicon nitride component, but fails to detect any structural rearrangement either within the composite matrix of film or within silicon nitride component. Segregation of metallic tungsten was detected by TEM in the annealed sample with lowest nitrogen content (W₅₈Si₂₁N₂₁). Finally, the resistivity of the films increases with the N content, while the loss of nitrogen accompanies the decrease of resistivity especially of samples with high nitrogen content.     

Effects of post-thermal treatment on the properties of rf reactive sputtered ITO films

Indium tin oxide (ITO) thin film prepared by rf sputtering at various Ar-O₂ mixtures, were annealed at several temperatures. The electrical, optical and structural properties of the film were systematically investigated before and after post-thermal treatment. The influence of a reactive gas (O₂) on the sputtering rate of a metallic (indium/tin) alloy target was also investigated. The films were characterized by X-ray diffraction (XRD) measurement, scanning electron microscopy, and transmittance as a function of wavelength. The resistivity of 8.3×10⁻⁴ Ω cm has been achieved for the film thickness of 250 nm, deposited in pure Ar at room temperature (RT).     

Formation of thin-film HfO<Subscript>2</Subscript>/Si(100) structures by high-frequency magnetron sputtering

The results of X-ray structural investigations and current-voltage measurements of the HfO₂/Si(100) structures are presented. The HfO₂ films of 50 nm thickness were deposited in a Si substrate by high-frequency magnetron sputtering in argon plasma and subjected to rapid thermal annealing at 500, 700, and/or 800°C in the Ar or O₂ ambient. It is shown that the HfO₂ films become polycrystalline after annealing. The presence of various crystalline phases in them and the form of the I–V characteristics of the Al/HfO₂/Si(100) test structures strongly depend on the growth conditions and the gas ambient during the rapid thermal annealing. It is established that the HfO₂ films deposited at a high-frequency bias at a substrate of −7 V during the growth and then passed through rapid thermal treatment in the O₂ ambient at 700°C have the highest breakdown voltages.     

Study on the Thermoelectric Properties of CVD SiC Deposited with Inert Gases

We deposited silicon carbide (SiC) by the chemical vapor deposition (CVD) method using the inert gases Ar and He. It was confirmed that SiC deposited with inert gases had a porous microstructure and high carbon content. We also studied the thermoelectric properties. SiC deposited with He gas had lower electrical and thermal conductivity compared with SiC deposited with Ar gas. Both samples using Ar and He exhibited a negative Seebeck coefficient, indicating n-type semiconductor behavior. The calculated figure of merit (Z) of SiC deposited with inert gases was improved compared with SiC deposited with H₂ or N₂ gas. The value for SiC deposited with He was higher than that for SiC deposited with Ar. The thermoelectric properties of porous silicon carbide deposited with inert gases were also compared with those of silicon carbide deposited with hydrogen or nitrogen gas.     

Effect of si—h and n—h bonds on electrical properties of plasma deposited silicon nitride and oxynitride films

Strong correlations were observed between the improvement in the metal-insulator-semiconductor (MIS) (aluminum-nitride-semiconductor) electrical properties of plasma deposited silicon nitride and oxynitride films and their (Si—H/N—H) bonding ratios in the film bulk. Total hydrogen concentration and spin density of all deposited films decreased with post-deposition annealing. Films with more Si—H bonds and stable (Si—H/ N—H) ratios generally have lowerV _fb shift, less positive trap charge and higher breakdown dielectric strength. Silicon oxynitride films with refractive indices of 1.75-1.80, as-deposited and after annealing in forming gas (10% H₂ + 90% N₂) at various temperatures, were found to have stable (Si—H/N—H) bonding ratios, lower silicon dangling bond density, and better MIS electrical properties compared to other plasma deposited nitride and oxynitride films.