Nm Of Deposition Research Articles

Initial Growth and Crystallization Onset of Plasma Enhanced-Atomic Layer Deposited ZnO

Direct plasma enhanced-atomic layer deposition (PE-ALD) is adopted for the growth of ZnO on c-Si with native oxide at room temperature. The initial stages of growth both in terms of thickness evolution and crystallization onset are followed ex-situ by a combination of spectroscopic ellipsometry and X-ray based techniques (diffraction, reflectivity, and fluorescence). Differently from the growth mode usually reported for thermal ALD ZnO (i.e., substrate-inhibited island growth), the effect of plasma surface activation resulted in a substrate-enhanced island growth. A transient region of accelerated island formation was found within the first 2 nm of deposition, resulting in the growth of amorphous ZnO as witnessed with grazing incidence X-ray diffraction. After the islands coalesced and a continuous layer formed, the first crystallites were found to grow, starting the layer-by-layer growth mode. High-temperature ALD ZnO layers were also investigated in terms of crystallization onset, showing that layers are amorphous up to a thickness of 3 nm, irrespective of the deposition temperature and growth orientation.

Highly selective atomic layer deposition of MoSiOx using inherently substrate-dependent processes

A resistive MoSiOx film was deposited with high selectivity on Si in preference to SiO2 and SiN using MoF6, Si2H6 and O2 as reactants. Two different approaches were demonstrated via thermal atomic layer deposition (ALD). First, ALD of MoSiOx by sequential dosing of MoF6, Si2H6 and O2 (ABC-type) at 200 °C followed by an ex-situ post-deposition anneal (PDA) in O2 at 350 °C was performed. The growth of the film using the ABC-type deposition was limited to ~5.25 ± 0.5 nm because the insulating film inhibits the MoF6 and Si2H6 ALD reaction. The second method was to grow MoSix at 120 °C and employ a post-deposition anneal in O2/He at 350 °C (AB + C-type) to form MoSiOx. The selectivity of this process on Si versus SiO2 was perfect for 10 nm of deposition on Si, as there were no nuclei or particle formation observed on the SiO2 surface by atomic force microscopy (AFM). The high selectivity can be obtained due to the inherent inability of MoF6 to react SiO2 and SiN surfaces. Transmission electron microscopy (TEM) of a nanoscale-patterned sample demonstrated that the highly selective MoSiOx can be achieved and be integrated into three-dimensional nanoscale structures.

Reactive metal-organic interfaces studied with hard x-ray photoelectron spectroscopy: controlled formation of metalloporphyrin interphase layers during metal vapor deposition onto porphyrin films

Interfaces between organic semiconductors and metallic layers are ubiquitous in organic (opto-) electronic devices and can significantly influence their functionality. Here, we studied in situ prepared metal-organic interfaces, which were obtained by vapor deposition of metals (Co, Fe) onto organic semiconductor films (2H-tetraphenylporphyrin), with hard x-ray photoelectron spectroscopy. In these systems, the interphase zones, which are formed by diffusion and reaction of the metal in the organic material, can be clearly distinguished spectroscopically from the unreacted organic bulk, since they comprise the corresponding metalloporphyrins, CoTPP and FeTPP. In order to gain control over the thickness of the interphase layers, we varied process parameters such as sample temperature and metal-atom flux during interface preparation. We found that the temperature of the organic film during metal deposition was the only parameter that significantly influenced the formation of the interphase layers: their thicknesses were typically ~0.5 nm for deposition at 90 K, compared to ~1 nm at 300 K, irrespective of metal atom flux and chemical nature of the metal atom (Fe versus Co). Notably, these values are significantly smaller than the thicknesses of other metal/organics interphase regions reported in the literature.

Determination of optical constants of tantalum oxide thin film deposited by electron beam evaporation

Tantalum oxide is a widely used material as a high index layer in multilayer interference filters for UV, visible and IR filters, laser mirror coatings as well as polarizer and beam splitter applications. In the present study, a single layer of Ta2O5 was deposited on BK7 glass substrate using electron beam evaporation technique in an oxygenated reactive environment. The film was characterized using spectrophotometer and variable angle spectroscopic ellipsometry at angles of 65°, 70° and 75° to extract and estimate its optical constants as well as thickness. The refractive index of the film was found to be 2.0419 at 550 nm for deposition without ion assistance on a heated substrate at 250° C.

Optimization of Ion Assist Beam Deposition of Magnesium Oxide Template Films During Initial Nucleation and Growth

AbstractRecent efforts in investigating the mechanism of ion beam assisted deposition (IBAD) of biaxially textured thin films of magnesium oxide (MgO) template layers have shown that the texture develops suddenly during the initial 2 nm of deposition. To help understand and tune the behavior during this initial stage, we pre-deposited thin layers of MgO with no ion assist prior to IBAD growth of MgO. We found that biaxial texture develops for pre-deposited thicknesses < 2 nm, and that the thinnest layer tested, at 1 nm, resulted in the best qualitative RHEED image, indicative of good biaxial texture development. The texture developed during IBAD growth on the 1.5 nm pre-deposited layer is slightly worse and IBAD growth on the 2 nm pre-deposited layer produces a fiber texture. Application of these layers on an Al2O3 starting surface, which has been shown to impede texture development, improves the overall quality of the IBAD MgO and has some of the characteristics of a biaxially texture RHEED pattern. It is suggested that the use of thin (<2 nm) pre-deposited layers may eliminate the need for bed layers like Si3N4 and Y2O3 that are currently thought to be required for proper biaxial texture development in IBAD MgO.

Initial growth of chemical-vapor-deposited SiO2

Amorphous SiO2 was deposited on three single-crystalline substrates: alumina, CaF2, and hydrogen-terminated silicon, by chemical vapor deposition (CVD) using tetraethoxysilane (TEOS) and ozone (O3). The deposited layers were then examined by using atomic force microscopy (AFM). For deposition times of 3, 8, 15, and 180 s, the film thickness ranged from less than 2.4 to 150 nm, respectively. Comparison of the surface roughness with the film thickness, as determined independently by ellipsometry, indicated that the thinnest film formed on the silicon surface (2.4 nm) was continuous. During film formation, for all three substrates, the surface roughness increased initially, reached a maximum, and then decreased. Surprisingly, the surface became smooth (within the resolution of 0.2 nm of our AFM). For the silicon substrate, this smoothing occurred between 3 and 8 s, which corresponds to 2.4 and 6.4 nm of deposition, respectively. Furthermore, just before the smoothing started, the surface of the deposited film contained protuberances, 1.6 nm high and 16 nm×16 nm in area. This indicates that smooth film of a few tens angstroms in thickness can form on the silicon. The smoothing of the protuberances occurred between 3 and 8 s for the CaF2 substrate, and between 15 to 180 s for the alumina substrate. The initial formation of a rough surface followed by smoothing is likely to be inherent in TEOS/O3 CVD systems, irrespective of substrate type. Surface-tension-induced flows of the surface, which has liquidlike properties, is a plausible mechanism.

Low Temperature Epitaxy on H-Passivated Si(100) by Sputter Deposition

ABSTRACTConventional preparation of Si for epitaxy involves high-temperature heating to remove surface oxide or to remove H passivation left by HF cleaning. Attempted MBE on H-passivated Si(100) has resulted in amorphous films below 640 K. We show that the use of ion beam sputtered Si allows the growth of thick (300 nm) epitaxial layers on H-passivated Si(100) at high rate (0.65 nm/s) and at 483 K, well below the H desorption temperature. This is because the sputtered Si has translational kinetic energy of tens of eV, well above the Si-H bond strength of a few eV, so that the passivating H does not block the epitaxial bonding sites as it does in MBE. The ability to grow epitaxially on H-passivated Si not only reduces the maximum Si processing temperature required, but also keeps the substrate passivated against contamination until the onset of deposition.During deposition, the LEED pattern changes gradually from the 1 × 1 of the H-passivated Si to the 2 × 1 reconstruction of bare or partially hydrogenated Si(1 00), yet SIMS shows that little of the disappearing H accumulates at the substrate interface or in the bulk of the film. Thermal desorption spectra show that its bonding remains similar to that on the substrate surface. Thus, it appears to float to the surface of the depositing film and become gradually knocked off of the surface over the course of a few hundred nm of deposition. Cross-sectional TEM lattice imaging shows near-perfect ordering of the epilayer and a barely distinguishable substrate interface.

Demonstration of laser-assisted epitaxial deposition of GexSi1−x alloys on single-crystal Si

We report initial results of a novel technique for epitaxial growth of GexSi1−x alloys on single-crystal Si. During electron beam deposition of amorphous GexSi1−x, an incident XeCl excimer laser, operating at 308 nm with a 30 ns pulse duration, melts and crystallizes the amorphous layer in situ after each ≊5 nm of deposition. This laser-induced melt extends approximately 20 nm and provides epitaxy from the underlying substrate (or previous layers) at each stage of deposition. This melt/solidification process can be repeated continuously until the final desired alloy thickness is achieved. For layers up to 260 nm with Ge concentrations of 1.5–3 at. %, MeV ion channeling and cross-sectional transmission electron microscopy confirm epitaxial growth.

The microstructure of aluminium thin films on amorphous SiO 2

The microstructure of aluminium thin films deposited onto amorphous SiO 2 by tungsten filament evaporation was studied by transmission and scanning electron microscopy and grazing-incidence X-ray diffraction. The early stages of film growth were characterized by an island or connected-network structure and a random grain orientation. The thickness at which complete coverage occurred ranged from 15 nm at 295 K to 100 nm at 625 K, and above this thickness a 〈111〉 fibre texture became apparent. The grain size distribution of films 1 μm thick was log-normal and the average grain size ranged from 500 nm for deposition at 295 K to 4 μm for deposition at 675 K. “Growth hillocks” were observed on the surface of films deposited at 295 K but were absent when higher substrate temperatures were used. Annealing caused grain growth and the formation of “annealing hillocks” which were of different structure from the growth hillocks. Examination of a small number of electron-beam-deposited aluminium films showed these to have similar microstructures to the filament-evaporated films, whereas sputter-deposited films were characterized by a smaller grain size and random orientation.