Al Film Growth Research Articles

Growth and Characterization of Al (111) Thin Film on Piezoelectric Wafers for SAW Device Fabrication for Space Applications

Surface Acoustic Wave (SAW) filters provide precise frequency filtering in RF and IF range with a tiny footprint. Metallic thin films are the essence of such modern SAW filter technology. However, SAW filters realized using NiCr/Al thin films are limited to power levels of ~5 dBm at RF frequencies. This limitation on power level is due to the acousto-migration phenomenon in thin films at higher power levels. In order to enhance the power durability of SAW filters, the preferred oriented growth of Al along (111) crystallographic direction is one of the methods to reduce acousto-migration. This paper explores the growth and characterization of different metallization schemes (NiCr/Al & Ti/Al) on different piezoelectric wafers to achieve oriented Al (111) film growth. Metallic thin films were deposited using electron beam evaporation technique. High Resolution X-Ray Diffraction (HR-XRD) and Four Point Probe Method were used for crystallographic characterization and Sheet Resistance (SR) measurement, respectively. Atomic Force Microscopy (AFM) and surface profiler were used to characterize the surface morphology of the deposited films. FWHM of 4.12 degree of rocking curve on Al (111) peak has been achieved for Ti/Al metal film deposited on ST-X Quartz piezoelectric wafer along with low sheet resistance of 124 mΩ/sq. A deposition rate of 1 Å/s for Ti and 7 Å/s for Al at a deposition temperature of 100 °C gave the best FWHM value for Al (111) orientation on ST-X Quartz wafer. Space qualification tests were also successfully performed on Ti/Al metalized wafers under extreme environmental conditions. The results obtained in this work demonstrate the suitability of Ti as an under layer to grow preferred oriented Al film along (111) orientation and thus to be used in the fabrication of high-power SAW devices for space applications.

Fabrication of black aluminium thin films by magnetron sputtering.

Black aluminium thin films were prepared by direct current (DC) pulsed magnetron sputtering. The N2 concentration in the Ar–N2 mixture that was used as the deposition atmosphere was varied from 0 to 10%, and its impact on the film growth and optical properties was studied. A strong change in the film growth process was observed as a function of the N2 concentration. At a specific N2 concentration of ∼6%, the Al film growth process favoured the formation of a moth-eye-like antireflective surface. This surface morphology, which was similar to the structure of a cauliflower, is known to trap incident light, resulting in films with a very low reflectivity. A diffuse reflectivity lower than 4% was reached in the ultraviolet-visible-near infrared (UV-VIS-NIR) spectral range that corresponds to a value observed for an ultrahigh absorber. We found that for the preparation of black aluminium, the nitrogen content plays an important role in film formation and the resulting film morphology.

UV Photoactivated Room Temperature CVD of Aluminum on Functionalized Self-Assembled Monolayers Adsorbed on Au

We have investigated the selective photoactivated room temperature chemical vapor deposition (CVD) of aluminum (Al) on functionalized self-assembled monolayers adsorbed on Au. The CVD precursor employed is trimethyl aluminum (TMA). Using a deuterium arc lamp we demonstrate that the rate of the Al film growth is approximately twice that observed for nonphotoactivated Al chemical vapor deposition (CVD) using TMA. At the wavelengths employed, the photolysis of TMA leads to the dissociation of the TMA dimer to its monomer followed by successive release of methyl groups to form (CH(3))(3-x)Al. The photogenerated (CH(3))(3-x)Al species react with -OH- and -COOH-terminated SAMs but not -CH(3)-terminated SAMs. Using these reactions we demonstrate that aluminum can be selectively deposited on -CH(3)/-COOH-patterned SAMs. The possible reaction mechanisms involved in the Al film growth are discussed. These results indicate that photoactivated CVD (laser CVD) processes are suitable for the deposition of stable films of metals and other materials on organic films.

Quantum Confinement Drives Macroscopic Stress Oscillations at the Initial Stage of Thin Film Growth

Functionalization of thin-film heterostructures on the basis of their electrical, optical and magnetic properties, requires precise control of the film stresses that develop during the growth process. By using real-time in situ stress measurements, the present study reveals strikingly that the in-plane film stress oscillates with increasing film thickness at the initial stage of epitaxial Al(111) film growth on a Si(111)-√3×√3-Al surface, with a periodicity of 2 times the Fermi wavelength of bulk Al and a stress variation from maximum to minimum as large as 100 MPa. Such macroscopic stress oscillations are shown to be caused by quantum confinement of the free electrons in the ultrathin epitaxial metal film. The amplitude, period, and phase of the observed stress oscillations are consistent with predictions based on the free electron model and continuum elasticity.

Growth of Al on a W(110) surface

Using low energy electron diffraction and low energy ion scattering spectroscopy, we investigated the growth mode of Al on a W(110) surface at room temperature and at 1000K. We found that Al grew on the W(110) surface in the Frank–van der Merwe mode when the W substrate was kept at room temperature during Al deposition. It was found that at a coverage higher than 2monolayer (ML) in Al grown at room temperature, Al atoms had a well-ordered face centered cubic (fcc) (111) surface. The [11¯0] direction of the Al grown at room temperature on the (111) surface was parallel to the [001] direction of the W(110) substrate surface. When the temperature of the W substrate was kept at 1000K, the adsorbed Al atoms grew in the Volmer–Weber mode. The 1.5ML Al/W(110) surface prepared at 1000K shows two domains of the fcc Al(111) surfaces along with a W(110) surface. We also found that the early stage of Al film growth shows W(110) structure. However as the film becomes thicker (above 3.5–4 layers) the Al face is turned into fcc (111) face.

GaAs Surface Composition Investigation during Al Thin Film Growth Using the CBE Method

GaAs surface composition changes occurring during Al film growth using the CBE method with laser assistance were investigated in situ by means of laser reflectivity. The results were compared with data on precise chemical analyses and X-ray microanalyses carried out after film deposition. It was found that the peculiarity of film formation depended upon the laser power. Physicochemical interactions of the Ga atoms from the GaAs surface, with atoms and molecules from the surrounding media, are determinative reactions at a laser power of 2W. At a power of 0.02W, the laser reflectivity changes were mainly due to reactions with Al. The appearance of “free” Ga and As in the region outside of the laser spot indicated the destruction of GaAs islands weakly connected with the GaAs surface.

Biaxially Textured Al Film Growth on CaF2 Nanostructures toward a Method of Preparing Single-Crystalline Si Film on Glass Substrates

We report the room temperature growth of biaxially textured Al films and further demonstrate the use of these Al films in preparing single-crystalline Si layers on glass substrates. The formation of the biaxial texture in Al film relies on the existence of the CaF(2) buffer layer prepared using oblique angle physical vapor deposition, which consists of single-crystalline nanorods with caps that are in the form of inverted nanopyramids. The single-crystalline Si film was obtained upon crystallization of the amorphous Si film deposited through physical evaporation on the biaxially textured Al film. This method of preparing single-crystalline Si film on glass substrate is potentially attractive for being employed in silicon technology and in fabrication of low-cost electronic devices.

Catalystlike behavior of Si adatoms in the growth of monolayer Al film on Si(111)

The formation mechanism of monolayer Al(111)1x1 film on the Si(111) radical3x radical3-Al substrate was studied by scanning tunneling microscopy and first-principles calculations. We found that the Si adatoms on the radical3x radical3-Al substrate play important roles in the growth process. The growth of Al-1x1 islands is mediated by the formation and decomposition of SiAl(2) clusters. Based on experiments and theoretical simulations we propose a model where free Si atoms exhibit a catalystlike behavior by capturing and releasing Al atoms during the Al film growth.

The conversion of wettability in transparent conducting Al-doped ZnO thin film

We report on the systematic changes of surface wettability in one of the most promising transparent conducting oxide materials, Al-doped ZnO (AZO) thin films. It was revealed that the characteristic surface wettability, which would make a key role in adhesion with other layers of optoelectronic device, can be largely changed by Al concentrations and film growth temperature. Keeping the electrical conductivity constant, the water contact angle (WCA) of a 2 mol% AZO film was changed by about 50 ∘C depending on the surface roughness. In the samples grown at 300 ∘C, the roughness enhancement was large and a hydrophobic surface formed, whereas in the samples grown at 500 ∘C a hydrophilic surface formed. We attributed the variation in surface wettability with growth temperature to changes in surface morphology. This result suggests that 2 mol% Al doping concentration can be considered as a critical concentration in changing of surface morphology of AZO as well as in electrical properties.

Formation of Atomistic Island in Al Film Growth by Kinetic Monte Carlo

Kinetic Monte Carlo (KMC) method realizes the millisecond or second order atomistic thin film growth. Twenty five kinds of events which may occur on Al(111) surface were classified. An attempt frequency and an activation energy of each event were defined using vibration analyses and nudged elastic band (NEB) method by which the minimum energy path (MEP) can be reasonably predicted. Temperature and deposition rate dependences of Al(111) film growth were intensively investigated in the present paper. The higher temperature and the lower rate drive the layer-by-layer film structural change. Two types of islands (fcc and hcp) were seen by modeling without considering the events of diffusion of dimer and trimer, while only fcc islands remain with considering such events. Thus, we find that the primitive events of diffusion of dimer and trimer take important roles in determination of surface morphology.

Atomic-level investigation of Al and Ni thin film growth on Ni(1 1 1) surface: Molecular dynamics simulation

Using molecular dynamics (MD) simulation, the structural characteristics of Al and Ni thin film growth on Ni(1 1 1) substrate according to the incident energy of adatoms were investigated. In case of Al on Ni(1 1 1), Al adatoms were grown basically through the layer-by-layer growth mode. On the other hand, Ni thin films on Ni(1 1 1) surface at low incident energy were shown to favor island growth. The steering effect due to atomic attraction, which results in rougher surface, was significantly observed at low incident energy. The growth mode of Ni film was, however, changed to follow layer-by-layer growth mode for the incident energy of 6 eV. The different aspects of surface morphology between Al and Ni deposition on Ni(1 1 1) surface could be successfully explained by the surface diffusion and impact cascade diffusion.

Formation of Atomistic Island in Al Film Growth by Kinetic Monte Carlo

Kinetic Monte Carlo (KMC) method realizes the millisecond or second order atomistic thin film growth. Twenty five kinds of events which may occur on Al (111) surface were classified. An attempt frequency and an activation energy of each event were defined using vibration analyses and nudged elastic band (NEB) method by which the minimum energy path (MEP) can be reasonably predicted. Temperature and deposition rate dependences of Al (111) film growth were intensively investigated in the present paper. The higher temperature and the lower rate drive the layer-by-layer film structural change. Two types of islands (fcc and hcp) were seen by modeling without considering the events of diffusion of dimer and trimer, while only fcc islands remain with considering such events. Thus, we find that the primitive events of diffusion of dimer and trimer take important roles in determination of surface morphology.

Surface Microrelief Transformation Induced by Laser during Thin Al Film Growth on the (001) GaAs by the CBE Method

In this work microrelief transformation of the (001) GaAs surface due to thin Al film deposition by means of the CBE method has been observed. The growth process was monitored insitu using laser reflectometry. Investigations of samples formed, carried out using TEM-microscopy, show that one of the basic causes of the microrelief transformation is the laser assistance of metal growth. A laser with a low power is used in this work for Al layer composite control in CBE. It was found that, in spite of using a laser having a low power, it is possible to stimulate and guide the complex physical and chemical reactions between deposited Al atoms and the GaAs near-surface layer. It has been found that metal film growth with laser assistance is a non-equilibrium process. The shapes and dimensions of the grown islands depend upon the laser power.

Studies of thin film growth and oxidation processes for conductive Ti–Al diffusion barrier layers via in situ surface sensitive analytical techniques

Conducting diffusion barrier layers play a critical role in high-density memory integration. We recently demonstrated that Ti–Al can be used as a diffusion barrier layer for the integration of ferroelectric capacitors with complementary metal–oxide semiconductor devices for the fabrication of nonvolatile ferroelectric random access memories (NVFRAMs). Here, we discuss results from systematic studies designed to understand Ti–Al film growth and oxidation processes using in situ ion beam sputter deposition in conjunction with complementary in situ atomic layer-resolution mass spectroscopy of recoil ion (MSRI) and surface sensitive x-ray photoelectron spectroscopy (XPS). The concurrent MSRI/XPS analysis revealed that amorphous Ti–Al layers produced by tailored sputter-deposition methods are resistant to oxidation to at least 600 °C, and that oxidation occurs only when the a-Ti–Al layers are exposed to oxygen at >600 °C, via the segregation of Ti species to the surface and TiO2 formation. The a-Ti–Al layers discussed in this letter could be used in the double functionality of a bottom electrode/diffusion barrier for the integration of ferroelectric capacitors with Si substrates for the fabrication of NVFRAMs and other devices.

The interaction of dimethylethylaminealane and ammonia on clean and oxidized Al(111): atomic layer growth of aluminum nitride

The adsorption of dimethylethylaminealane (Me 2EtN·AlH 3 or DMEAA) on clean and oxidized Al(111), its subsequent thermal decomposition, and reaction with ammonia (NH 3) to form aluminum nitride (AIN) was studied using temperature-programmed desorption (TPD), Auger electron spectroscopy (AES), and reactive scattering. DMEAA physisorbs on clean Al(111) at 130 K in ultra-high vacuum and molecular desorption is observed at 190 K. The reactive sticking probability of DMEAA at T<300 K is very low, especially at low surface defect density. At higher substrate temperatures ( T>300 K), the reactive sticking probability of DMEAA is high and elementally pure Al film growth is observed. On oxidized Al(111) at surface temperatures above 400 K, the reactive probability of DMEAA is lower than on the Al(111) surface and, in contrast to the clean Al(111) surface, on the oxidized Al(111) surface DMEAA adsorbs molecularly in a self-limiting manner at 300 K. Consecutive DMEAA and NH 3 exposure cycles result in atomic layer growthof AIN at temperatures as low as 300 K but these films have a high carbon content owing to accumulation of amine groups on the surface. Increasing the substrate temperature from 300 to 600 K results in greatly reduced carbon contamination in the AIN films. During film growth at 600 K, each DMEAA exposure results in the deposition of a new aluminum layer and a subsequent NH 3 dose converts this layer to AIN.

Photochemical vapor deposition of Al thin films on Ti, TiO 2, and Pd surfaces

Al thin films were deposited via photochemical vapor deposition on catalytic layers of Ti, TiO 2, and Pd, using dimethylaluminum hydride. Deposition was carried out at low gas pressures to induce a surface reaction based on adsorption and subsequent decomposition of adsorbates. Of these three layers Ti was so effective as a catalyst that the Al films were thermally deposited even at a low substrate temperature of 60°C with a growth rate of 0.5 nm/min. The UV light generated by a deuterium lamp helped increase the growth rates. On the other hand, Al could be deposited on TiO 2 layers only under irradiation at a substrate temperature of 120°C. It took several minutes to cover the TiO 2 surface with Al and initiate the Al film's growth. An entirely opposite result was observed for Al deposition on Pd layers. Here, the UV light inhibited the Al growth on the surface, whereas the films were deposited thermally. X-ray photoelectron spectroscopy showed the formation of a photolytic production of the adsorbate, which acts presumably as a center that inhibits further Al growth.

Catalytic and Photoinduced Effects of Ti and TiO2 Layers on Al Film Growth by Chemical Vapor Deposition

Catalytic and Photoinduced Effects of Ti and TiO2 Layers on Al Film Growth by Chemical Vapor Deposition

In Situ Real Time Observation of Chemical Vapor Deposition Using an Environmental Transmission Electron Microscope

AbstractMaterial synthesis by chemical vapor deposition (CVD) in a number of material systems has been investigated in real time using an environmental transmission electron microscope (ETEM) with 3.8 Å resolution. Here, we will focus on two metal / insulator systems. Al CVD onto SiO2from trimethyl amine alane and Au CVD from ethyl (trimethylphosphine) gold (I), also onto SiO2. For Al deposition, dendritic growth was observed for all pressure / substrate temperature combinations investigated for growth on untreated SiO2. Subsequent to reaction of the substrate surface with TiC14, almost immediate continuous Al film growth was observed. Growth rates for the Al film could be measured in situ by monitoring the evolution of the growth front at the Al/vacuum interface. In this system, very little enhancement in the metal film growth rate was observed as a consequence of electron beam irradiation for continuous films grown after TiCl4pretreatment.. This dramatically contrasts with the case of Au CVD investigated. In this instance, growth rate enhancements of up to 150 times were observed during electron beam irradiation as compared to purely pyrolytic decomposition of the precursor on the insulator surface. This growth rate enhancement decreased monotonically with substrate temperature. We surmise that this effect is related to the ratio of precursor surface residence time prior to ecomposition to the probability of collision from the impinging electron beam.

Time-resolved spectroscopic studies of the ultraviolet-laser photolysis of aluminum bromide for Al film growth

Time-resolved optical emission spectroscopy, with a resolution of ≂10 ns, was used to investigate the formation of excited photofragments during pulsed ArF excimer-laser irradiation of gaseous aluminum bromide. The solid Al2Br6 source was maintained at 50 °C and Ar used as a carrier gas to provide an aluminum bromide partial pressure of ≂3×10−6 Torr (4×10−4 Pa). The total pressure in the reactor was typically 300 mTorr (40 Pa). Following the laser pulse, emission was observed from the Al 4s 2S1/2→3p 2P1/2 and 4s 2S1/2→3p 2P3/2 transitions at 394 and 396 nm, respectively. The decay of the Al emission intensity IAl was convoluted with the temporal shape of the excitation pulse since the radiative lifetime of the Al 2S state, 6.8 ns, was less than the laser pulse width, ≂20 ns. The rise time of IAl, on the other hand, was &amp;lt;10 ns, indicating that Al was formed photolytically rather than through subsequent collisions involving photofragments. IAl varied with the ArF laser intensity Ihν as IAl∝I2hν for Ihν≲4.5 MW cm−2 and IAl∝Ihν at higher laser fluences. Raising the source gas temperature to increase the AlBr3 to Al2Br6 ratio in the feed gas, at constant total pressure, dramatically increased IAl.

Growth and stability of ultra-thin aluminium films on Ag(110) and Ag(111)

The deposition of Al on Ag(110) and Ag(111) and the stability of the resulting structures have been studied by a variety of techniques. At 300 K the AES, XPS and UPS data show that initial interaction leads to formation of an interfacial compound, probably Ag 2Al. This material gives rise to a characteristic Auger emission at 61 eV, assigned to an Al/Ag cross-transition, a conclusion which is supported by the XPS data. The interfacial alloy is formed with essentially equal facility on both the (110) and (111) surfaces. In the case of the (110) surface Δφ measurements suggest that initial Al adsorption occurs in the troughs. On both (110) and (111) surfaces, subsequent Al film growth proceeds by the Frank-van der Merwe mechanism. Thermal treatment causes rapid inward diffusion of overlayer Al for T ≳ 350 K whereas the interfacial alloy is more stable and does not decompose until T ≳ K.