Hf-O-N and HfO2 barrier layers for Hf-Ti-O gate dielectric thin films

Hf-O-N and HfO₂ thin films were evaluated as barrier layers for Hf-Ti-O metal oxide semiconductor capacitor structures. The films were processed by sequential pulsed laser deposition at 300 °C and ultra-violet ozone oxidation process at 500 °C. The as-deposited Hf-Ti-O films were polycrystalline in nature after oxidation at 500 °C and a fully crystallized (o)-HfTiO₄ phase was formed upon high temperature annealing at 900 °C. The Hf-Ti-O films deposited on Hf-O-N barrier layer exhibited a higher dielectric constant than the films deposited on the HfO₂ barrier layer. Leakage current densities lower than 5 × 10 A/cm² were achieved with both barrier layers at a sub 20 Å equivalent oxide thickness.     

High performance TaYOx-based MIM capacitors

TaYO_x-based metal-insulator-metal (MIM) capacitors with excellent electrical properties have been fabricated. Ultra-thin TaYO_x films in the thickness range of 15-30 nm (EOT ∼ 2.4-4.7 nm) were deposited on Au/SiO₂ (100 nm)/Si (100) structures by rf-magnetron co-sputtering of Ta₂O₅ and Y₂O₃ targets. TaYO_x layers were characterized by X-ray photoelectron spectroscopy (XPS), energy dispersive X-ray (EDX) and X-ray diffraction (XRD) to examine the composition and crystallinity. An atomic percentage of Ta:Y = 58.32:41.67 was confirmed from the EDX analysis while XRD revealed an amorphous phase (up to 500 °C) during rapid thermal annealing. Besides, a high capacitance density of ∼3.7-5.4 fF/μm² at 10 kHz (ε_r ∼ 21), a low value of VCC (voltage coefficients of capacitance, α and β) have been achieved. Also, a highly stable temperature coefficient of capacitance, TCC has been obtained. Capacitance degradation phenomena in TaYO_x-based MIM capacitors under constant current stressing (CCS at 20 nA) have been studied. It is observed that degradation depends strongly on the dielectric thickness and a dielectric breakdown voltage of 3-5 MV/cm was found for TaYO_x films. The maximum energy storage density was estimated to be ∼5.69 J/cm³. Post deposition annealing (PDA) in O₂ ambient at 400 °C has been performed and further improvement in device reliability and electrical performances has been achieved.     

Atomic layer deposition of tantalum oxide thin films for their use as diffusion barriers in microelectronic devices

Atomic Layer Deposition (ALD) was used for the deposition of tantalum oxide thin films in order to be integrated in microelectronic devices as barrier to copper diffusion. The influence of deposition temperature, number of cycles and precursor pulse time on the film growth was discussed. The conformity of thinnest deposited films was shown. Copper diffusion through ALD Ta₂O₅ thin films, 20 nm in thickness, was investigated, for three temperatures from 600 to 800 °C, using X-ray Photoelectron Spectroscopy. The failure of such films was detected after a thermal treatment at 700 °C.     

Infrared spectroscopy and X-ray diffraction studies on the crystallographic evolution of La2O3 films upon annealing

Rare earth oxides (REOs) have lately received extensive attention in relation to the continuous scaling down of non-volatile memories (NVMs). In particular, La₂O₃ films are promising for integration into future NVMs because they are expected to crystallize above 400 °C in the hexagonal phase (h-La₂O₃) which has a higher κ value than the cubic phase (c-La₂O₃) in which most of REOs crystallize. In this work, La₂O₃ films are grown on Si by atomic layer deposition using La(C₅H₅)₃ and H₂O. Within the framework of the h-La₂O₃ formation, we systematically study the crystallographic evolution of La₂O₃ films versus annealing temperature (200-600 °C) by Fourier transform infrared spectroscopy (FTIR) and grazing incidence X-ray diffraction (GIXRD). As-grown films are chemically unstable in air since a rapid transformation into monoclinic LaO(OH) and hexagonal La(OH)₃ occurs. Vacuum annealing of sufficiently thick (>100 nm) La(OH)₃ layers induces clear changes in FTIR and GIXRD spectra: c-La₂O₃ gradually forms in the 300-500 °C range while annealing at 600 °C generates h-La₂O₃ which exhibits, as inferred from our electrical data, a desirable κ ∼ 27. A quick transformation from h-La₂O₃ into La(OH)₃ occurs due to H₂O absorption, indicating that the annealed films are chemically unstable. This study extends our recent work on the h-La₂O₃ formation.     

Fabrication of quasi-one dimension silicon carbide nanorods prepared by RF sputtering

Anodic aluminum oxide (AAO) template was prepared by a two-step anodization method at low temperature (1 °C) and silicon carbide was deposited on the templates by non-reactive radio frequency sputtering method. Well-aligned quasi-one dimension silicon carbide nanorods with the average diameter about 80-90 nm and a mean length of 400 nm were obtained perpendicular to the substrate and observed by AFM and SEM after the aluminum substrates were striped off. Then some samples were annealing at flowing N₂ at 400, 500 and 600 °C and FTIR was performed on these samples to obtain the information of structure.     

ALD of LaHfOx nano-laminates for high-κ gate dielectric applications

Electrical properties and thermal stability of LaHfO_x nano-laminate films deposited on Si substrates by atomic layer deposition (ALD) have been investigated for future high-κ gate dielectric applications. A novel La precursor, tris(N,N′-diisopropylformamidinato) lanthanum [La(ⁱPrfAMD)₃], was employed in conjunction with conventional tetrakis-(ethylmethyl)amido Hf (TEMA Hf) and water (H₂O). The capacitance-voltage curves of the metal oxide semiconductor capacitors (MOSCAPs) showed negligible hysteresis and frequency dispersion, indicating minimal deterioration of the interface and bulk properties. A systematic shift in the flat-band voltage (V_fb) was observed with respect to the change in structure of nano-laminate stacks as well as La₂O₃ to HfO₂ content in the films. The EOTs obtained were in the range of ∼1.23-1.5 nm with leakage current densities of ∼1.3 × 10⁻⁸ A/cm² to 1.3 × 10⁻⁵ A/cm² at V_fb − 1 V. In addition, the films with a higher content of La₂O₃ remained amorphous up to 950 °C indicating very good thermal stability, whereas the HfO₂ rich films crystallized at lower temperatures.     

Plasma-assisted chemical vapor deposited silicon oxynitride as an alternative material for gate dielectric in MOS devices

Silicon oxynitride films have been deposited on Si substrates at 200 °C by a remote-plasma-assisted process in a RF-plasma CVD reactor using Si(OC₂H₅)₄ (TEOS) as a precursor and nitrogen as gas ambient. During deposition the Si substrates were biased with negative voltages of −120 and −600 V or were under no DC bias and the influence of this voltage on the film properties has been considered. Film parameters, such as density, chemical bonds, refractive index, composition, oxide and interface charge densities of the deposited dielectric films have been estimated by analysis of the results from the infrared (IR) spectroscopy, spectral ellipsometry (SE) and capacitance-voltage (C-V) measurements. The IR and SE results have proven the films are oxynitrides of silicon with predominantly oxide network. The analysis of the capacitance-voltage characteristics has shown that the dielectric charge densities increase with increasing DC bias but they remain considerably low in comparison to that for a standard SiO₂/Si structure before any annealing steps.     

Metal-insulator phase transition in vanadium oxides films

Vanadium oxide films (VO₂) are of a typical phase transition ranging between metal phase to a semi-conducting phase. The theoretical metamorphose temperature of VO₂ is around 340 K (67 °C). This transition temperature is mostly governed by the deposition method in which the film was made, and the film's composition. Optical and electrical properties of VO₂ films are dramatically changed during this phase transition, thus making it useful in many microelectronics and optoelectronics applications. In this work we evaluate several deposition methods of VO₂ and their relations to the electro-optics properties of such films. The examined VO₂ films consisted of various phases of the material. Best films to demonstrate a metal-insulator transition were made in vacuum evaporation of V powder in a tungsten boat, treated in argon-oxygen flow (10:1), at 400 °C. The temperature range of phase transitions was found at 16-80 °C. Resistivity changes and colors of the films were studied as well.     

Microstructure and stress in high-k Hf-Y-O thin films

We investigated the microstructure and the stress of high-k Hf-Y-O thin films deposited by atomic layer deposition (ALD). These hafnium oxide based films with a thickness of 5-60 nm stabilized in crystal structure with yttrium oxide by alternating the Hf- or Y-containing metal precursor during deposition. The microstructure was investigated by XRD and TEM in dependence of substrate and deposition temperature. The film stress was monitored during thermal cycles up to 500 °C using the substrate curvature method on (1 0 0)-Si wafer material with or without 10 nm TiN bottom electrode as well as on fused silica. It was observed that crystallinity and phases are depending on deposition temperature and film thickness. During thermal treatment the films crystallize depending on deposition temperature, yttrium content and substrate material at different temperatures. Crystallization of the films depends strongly on yttrium content. The highest reduction of 720 MPa was observed for films deposited with a Hf:Y cycle ratio of 10:1 where 6.2% of all metal atoms are replaced by yttrium. These Hf-Y-O films also show the highest k-value of 29 and have the smallest thermal expansion coefficient mismatch to TiN electrodes. Therefore we conclude that Hf-Y-O films are candidates for application in next generations of microelectronic MIM-capacitor devices or metal gate transistor technology.     

Investigation of RF sputtered PSG films for MEMS and semiconductor devices

In this work, we report the preparation of phospho-silicate-glass (PSG) films using RF magnetron sputtering process and its application as a sacrificial layer in surface micromachining technology. For this purpose, a 76 mm diameter target of phosphorus-doped silicon dioxide was prepared by conventional solid-state reaction route using P₂O₅ and SiO₂ powders. The PSG films were deposited in a RF (13.56 MHz) magnetron sputtering system at 200-300 W RF power, 10-20 mTorr pressure and 45 mm target-to-substrate spacing without external substrate heating. To confirm the presence of phosphorus in the deposited films, hot-probe test and sheet resistance measurements were performed on silicon wafers following deposition of PSG film and a drive-in step. As a final confirmatory test, a p-n diode was fabricated in a p-type Si wafer using the deposited film as a source of phosphorus diffusion. The phosphorus concentration in the target and the deposited film were analyzed using energy dispersive X-rays (EDAX) tool. The etch rate of the PSG film in buffered HF was measured to be about 30 times higher as compared to that of thermally grown SiO₂ films. The application of RF sputtered PSG film as sacrificial layer in surface micromachining technology has been explored. To demonstrate the compatibility with MEMS process, micro-cantilevers and micro-bridges of silicon nitride were fabricated using RF sputtered PSG as a sacrificial layer in surface micromachining. It is envisaged that the lower deposition temperature in RF sputtering (<150 °C) compared to CVD process for PSG film preparation is advantageous, particularly for making MEMS on temperature sensitive substrates.     

Effects of annealing schedule on orientations of Bi3.2Nd0.8Ti3O12 ferroelectric films prepared by metalorganic solution deposition

Fatigue-free Bi_3.2Nd_0.8Ti₃O₁₂ ferroelectric thin films were successfully prepared on p-Si(1 1 1) substrate using metalorganic solution deposition process. The orientation and formation of thin film under different annealing schedules were studied using XRD and AFM. XRD analysis indicated that (2 0 0)-oriented films with degree of orientation of I₍₂₀₀₎/I₍₁₁₇₎ = 2.097 and 0.466 were obtained by preannealing the film at 400 °C for 10 min followed by rapid thermal annealing at 700 °C for 3 min, 10 min and 20 min, respectively, (0 0 8)-oriented film with degree of orientation of I₍₀₀₈₎/I₍₁₁₇₎ = 1.706 were obtained by rapid thermal annealing the film at 700 °C for 3 min without preannealing, and (0 0 8)-oriented film with degree of orientation of I₍₀₀₈₎/I₍₁₁₇₎ = 0.719 were obtained by preheating the film from room temperature to 700 °C at 20 °C/min followed by annealing for 10 min. The a-axis and c-axis orientation decreased as increase in annealing time due to effects of (1 1 1)-oriented substrate. AFM analysis further indicated that preannealing at 400 °C for 10 min followed by rapid thermal annealing at 700 °C for 3 min resulted in formation of platelike crystallite parallel to substrate surface, however rapid thermal annealing at 700 °C for 3 min without preannealing resulted in columnar crystallite perpendicular to substrate surface.     

A novel thermally-stable zirconium amidinate ALD precursor for ZrO2 thin films

ZrO₂ thin films were deposited by the atomic layer deposition process on Si substrates using tetrakis(N,N′-dimethylacetamidinate) zirconium (Zr-AMD) as a Zr precursor and H₂O as an oxidizing agent. Tetrakis (ethylmethylamino) zirconium (TEMA-Zr) was also evaluated for a comparative study. Physical properties of ALD-derived ZrO₂ thin films were studied using ellipsometry, grazing incidence XRD (GI-XRD), high resolution TEM (HRTEM), and atomic force microscopy (AFM). The ZrO₂ deposited using Zr-AMD showed a better thermal stability at high substrate temperature (>300 °C) compared to that using TEMA-Zr. GI-XRD analysis reveals that after 700 °C anneal both ZrO₂ films enter tetragonal phase. The electrical properties of N₂-annealed ZrO₂ film using Zr-AMD exhibit an EOT of 1.2 nm with leakage current density as low as 2 × 10⁻³ A/cm² (@V_fb−1 V). The new Zr amidinate is a promising ALD precursor for high-k dielectric applications.     

Anomalous thermal oxidation of gadolinium thin films deposited on silicon by high pressure sputtering

Thin gadolinium metallic layers were deposited by high-pressure sputtering in pure Ar atmosphere. Subsequently, in situ thermal oxidation was performed at temperatures ranging from 150 to 750 °C. At an oxidation temperature of 500 °C the films show a transition from monoclinic structure to a mixture of monoclinic and cubic. Regrowth of interfacial SiO_x is observed as temperature is increased, up to 1.6 nm for 750 °C. This temperature yields the lowest interface trap density, 4 × 10¹⁰ eV⁻¹ cm⁻², but the effective permittivity of the resulting dielectric is only 7.4. The reason of this low value is found on the oxidation mechanism, which yields a surface with located bumps. These bumps increase the average thickness, thus reducing the capacitance and therefore the calculated permittivity.     

Top injection reactor tool with in situ spectroscopic ellipsometry for growth and characterization of ALD thin films

Ta-N based thin films were grown by thermal atomic layer deposition (ALD) with an alternating supply of the reactant source TBTDET (tert-butylimidotris(diethylamido)tantalum) and NH₃ (ammonia). The films were deposited using a newly designed and constructed atomic layer deposition prototype tool combined with several in situ metrology. It was observed that thin films were successfully deposited on a 300 mm Wafer with a saturated growth rate of approximately 0.55 Å/cycle at 270 °C. The as deposited films resulted in the formation of Ta(C)N consisting of 38 at% Ta, 32 at% N and 10 at% C. With in situ spectroscopic ellipsometry (SE) the growing behaviour of the film was investigated and compared to atomic force microscopy (AFM) images.     

Effect of substrate temperature on vapor-phase self-assembly of n-octylphosphonic acid monolayer for low-voltage organic thin-film transistors

N-octylphosphonic acid (C₈PA) monolayer was self-assembled on aluminum oxide (AlO_x) from vapor in vacuum, while the substrate temperature was varied between 25 and 150 °C. The capacitance, water contact angle measurement, Fourier transform infrared (FTIR) spectroscopy, and atomic force microscopy (AFM) confirmed the presence of C₈PA on AlO_x for all growth temperatures. However, the structural and electrical properties of such monolayers depend on their growth temperature. The minimum surface roughness of 0.36 nm, the maximum water contact angle of 113.5° ± 1.4°, the lowest leakage current density of ∼10⁻⁷ A/cm² at 3 V, and the capacitance of 0.43 μF/cm² were obtained for AlO_x/C₈PA bi-layers with C₈PA deposited at 25 °C. The elevated temperature led to increased surface roughness, decreased water contact angle, increased leakage current, inferior molecular ordering, and lower molecular coverage; while the effect on the chemisorption of the phosphonate was minimal. Methyl and methylene FTIR vibrations associated with C₈PA aliphatic tails exhibited similar centre-peak wavenumbers to those observed for C₈PA monolayers assembled from solutions, presenting a viable ‘dry’ alternative to the existing solution process.     

Improved properties of Al-doped ZnO film by electron beam evaporation technique

High-quality Al-doped ZnO (AZO) thin films have been fabricated by electron beam evaporation technique. The effect of the growth temperature on the optical and electrical properties of the electron-beam (e-beam) evaporated AZO film is investigated. X-ray diffraction measurements have shown that e-beam evaporated films are highly c-axis oriented at appropriate growth temperature. Transmittance measurement showed that the best optical and structural quality of the e-beam evaporated AZO film occurred at 200 °C. The scanning electron microscope images have shown that the surfaces of the e-beam evaporated AZO became smoother for the growth temperature at and above 200 °C. Finally, the maximum electrical resistivity of 2.5×10⁻⁴ Ω cm and optical transmittance of more than 85% has been found at 200 °C growth temperature, which explains its relation with the crystal quality of the film.     

Effect of pressure on efficiency of UV curing of CVD-derived low-k material at different wavelengths

Low-k dielectrics prepared by CVD in the form of 200 nm thick layers on Si wafers were thermally treated at 410 °C and irradiated using UV lamps emitting photons of different wavelengths around 172 nm, 185 nm, and 222 nm. The treatment was performed in high vacuum and under a nitrogen atmosphere at various pressures ranging from 0.1 mbar up to 700 mbar. Subsequently, the samples were investigated using FTIR transmission spectroscopy, contact angle measurement, X-ray photoelectron spectrometry (XPS), time-of-flight secondary ion mass spectrometry (TOF-SIMS), X-ray reflectometry (XRR), surface acoustic wave spectrometry (SAW), and purged UV spectroscopic ellipsometry (PUVSE). It was found that for all UV wavelengths applied for curing the depth profiles of the chemical composition were homogeneous. For all properties evaluated, irradiation at wavelengths below 200 nm resulted in more pronounced changes than at longer wavelengths. Generally, a decrease in residual porogen content, conversion of the Si-O-Si bonds from cage to network/suboxide, degradation of Si-CH₃ bonds, formation of H-SiO bonds, increase in surface energy, changes of element concentrations and of density, increase in Young’s modulus, and changes in dielectric constant were observed. These findings were confirmed by quantum-chemical calculations. With increasing nitrogen pressure the effects were more considerable. An attempt was undertaken to explain the effect of nitrogen pressure in course of the role of nitrogen molecules as collision partners.     

Evaluation of a novel unfluorinated copper precursor for chemical vapor deposition

A kinetics of the chemical vapor deposition (CVD) of copper using novel unfluorinated precursor, copper(I)(N(1(dimethylvinylsiloxy)-1-methylethano)-2-imino-4-pentanoate), namely Cu-KI5, was studied. Since its great thermal stability, Cu-KI5 allowed high source temperature to provide high vapor pressure, for example Cu-KI5 has a vapor pressure of 0.2-2.2 Torr at the temperature range of 100-140 °C. Furthermore, copper could be deposited by direct reduction from Cu-KI5 instead of disproportionation. By using formic acid (HCOOH) as a reducing agent, copper films were deposited on ruthenium substrate at temperature range of 150-350 °C. The activation energy was 48.9 kJ/mol in surface reaction limited region (<210 °C) and 1.9 kJ/mol in diffusion limited region (>210 °C) at the total pressure of 5 Torr. Secondary ion mass spectroscopy (SIMS) analysis showed that CVD copper film of high purity (>99.99%) was deposited at 250 °C. The as-deposited copper films grown at 150-300 °C exhibited strong 〈111〉 preferred orientation. The minimum resistivity of the copper film was 1.77 μΩ cm obtained at the deposition temperature of 250 °C. In the surface reaction limited region, kinetic data extracted from experiments enabled 2-D computational simulation to predict copper deposition into trench structures. Simulation results showed excellent step coverage, which was larger than 90% for aspect ratio of 10:1. Cu-KI5 is a promising Cu-CVD precursor for the fabrication of ultra large scale integration (ULSI) or through silicon via (TSV) copper interconnects.     

Effect of post deposition heat treatment on microstructure parameters,optical constants and composition of thermally evaporated CdTe thin films

Thin film microstructure and its properties can be effectively altered with post deposition heat treatments. In this respect, CdTe thin films were deposited on glass substrates at a substrate temperature of 200 °C using thermal evaporation technique, followed by air annealing at different temperatures from 200 to 500 °C. Structural analysis reveals that CdTe thin films have a cubic zincblend structure with two oxide phases related to CdTe₂O₅ and CdTeO₃ at annealing temperature of 400 and 500 °C respectively. Regardless of the annealing temperature, the plane (111) was found to be the preferred orientation for all films. The crystallite size was observed to increase with annealing temperature. All films were found to display higher lattice parameters than the standard, and hence found to carry a compressive stress. Optical measurements suggest high uniformity of films both before and after post deposition heat treatment. Films annealed at 400 °C displayed superior optical properties due to its high refractive index, optical conductivity, relative density and low disorder. Furthermore, according to the compositional measurements, CdTe thin films were found to exhibit Te rich and Cd rich nature at regions near the substrate and center of the film respectively, for all annealing temperatures. However, composition of the regions near the substrate was found to become more Te rich with increasing annealing temperature. The study suggests that changing the annealing temperature as a post deposition treatment affects structural and optical properties of CdTe thin film as well as its composition. According to the observations, films annealed at 400 °C can be concluded to be the best films for photovoltaic applications due to its superior optical and structural properties.     

Raman scattering of polycrystalline 3C-SiC film deposited on AlN buffer layer by using CVD with HMDS

This paper presents the Raman scattering characteristics of poly (polycrystalline) 3C-SiC thin films deposited on AlN buffer layer by atmospheric pressure chemical vapor deposition (APCVD) using hexamethyldisilane (MHDS) and carrier gases (Ar+H₂). The Raman spectra of SiC films deposited on AlN layer of before and after annealing were investigated according to the growth temperature of 3C-SiC. Two strong Raman peaks, which mean that poly 3C-SiC admixed with nanoparticle graphite, were measured in them. The biaxial stress of poly 3C-SiC/AlN was calculated as 896 MPa from the Raman shifts of 3C-SiC deposited at 1180 °C on AlN of after annealing.