Jan Musschoot

Growth Kinetics and Crystallization Behavior of TiO2 Films Prepared by Plasma Enhanced Atomic Layer Deposition

cSCK-CEN, Boeretang 200, B-2400 Mol, Belgium Atomic layer deposition ALD of TiO2 films from tetrakisdimethylamido titanium TDMAT or titanium tetraisopropoxide TTIP precursors was investigated. The growth kinetics, chemical composition, and crystallization behavior of the TiO2 films were compared for combinations of the two precursors with three different sources of oxygen thermal ALD using H2O and plasma-enhanced ALD PEALD using H2 Oo r O 2 plasma. For TDMAT, the growth rate per cycle GPC decreased with increasing temperature; while for TTIP with either water plasma or O2 plasma, a relatively constant growth rate per cycle was observed as a function of substrate temperature. It was found that the crystallization temperature of the TiO2 films depends both on film thickness and on the deposition conditions. A correlation was observed between the TiO2 crystallization temperature and the C impurity concentration in the film. The TiO2 films grown using a H2O plasma exhibit the lowest crystallization temperature and have no detectable C impurities. In situ X-ray diffraction measurements were used to test the diffusion barrier properties of the TiO2 layers and proved that all TiO2 films grown using either H2 Oo r O2 plasma are dense and continuous.

Modeling the Conformality of Atomic Layer Deposition: The Effect of Sticking Probability

The key advantage of atomic layer deposition (ALD) is undoubtedly the excellent step coverage, which allows for conformal deposition of thin films in high-aspect-ratio structures. In this paper, a model is proposed to predict the deposited film thickness as a function of depth inside a hole. The main model parameters are the gas pressure, the deposition temperature, and the initial sticking probability of the precursor molecules. Earlier work by Gordon et al. assumed a sticking probability of 0/100% for molecules hitting a covered/uncovered section of the wall of the hole, thus resulting in a stepwise film-thickness profile. In this work, the sticking probability is related to the surface coverage θ by Langmuirs equation s(θ) = s 0 (1 - θ), whereby the initial sticking probability s 0 is now an adjustable model parameter. For s 0 ≅ 100%, the model predicts a steplike profile, in agreement with Gordon et al., while for smaller values of s 0 , a gradual decreasing coverage profile is predicted. Furthermore, experiments were performed to quantify the conformality for the trimethylaluminum (TMA)/H 2 O ALD process using macroscopic test structures. It is shown that the experimental data and the simulation results follow the same trends.

Conformality of Al2O3 and AlN Deposited by Plasma-Enhanced Atomic Layer Deposition

This paper focuses on the conformality of the plasma-enhanced atomic layer deposition (PE-ALD) of Al2O3 using trimethylaluminum [Al(CH3)(3); (TMA)] as a precursor and O-2 plasma as an oxidant source. The conformality was quantified by measuring the deposited film thickness as a function of depth into macroscopic test structures with aspect ratios of similar to 5, 10, and 22. A comparison with the thermal TMA/H2O process indicates that the conformality of the plasma based process is more limited due to the surface recombination of radicals during the plasma step. The conformality can slightly be improved by raising the gas pressure or the radio-frequency power. Prolonging the plasma exposure time results in further improvement of the conformality. Furthermore, there are indications that the H2O produced during the plasma step in the PE-ALD process for Al2O3 contributes to the observed conformality through a secondary thermal ALD reaction. The conformality of Al2O3 is also compared to the conformality of AlN deposited by PE-ALD from TMA and NH3 plasma. For the same exposure, O-2 plasma results in better conformality compared to NH3 plasma, suggesting a faster recombination of the radicals in the NH3 plasma.

Microencapsulation of Moisture-Sensitive CaS : Eu2 + Particles with Aluminum Oxide

Single-crystal, submicrometer-sized CaS:Eu luminescent particles were synthesized via a solvothermal route, and these moisture-sensitive particles were coated with aluminum oxide using atomic layer deposition (ALD). Photoluminescence (PL) spectra of coated and uncoated particles were compared. They both showed a broad-band PL emission with a maximum of 650 nm. Microencapsulation by aluminum oxide layers did not have a pronounced effect on the intensity of the emission. In situ luminescence measurements during the accelerated aging (80 degrees C, 80% relative humidity) of coated and uncoated CaS: Eu particles were performed. While the uncoated phosphor was largely degraded within 30 h of aging, it was observed that a 20 nm thick aluminum oxide coating dramatically increased the resistance of the luminescent material against moisture, showing the conformity of the Al2O3 coating by the ALD process. Upon degradation, CaCO3 was formed, leading to Eu3+ emission as observed in cathodoluminescence. Finally, the use of these coated particles as a wavelength conversion material in light-emitting diodes was evaluated.

Comparison of Thermal and Plasma-Enhanced ALD/CVD of Vanadium Pentoxide

Vanadium pentoxide was deposited by atomic layer deposition (ALD) from vanadyl-tri-isopropoxide (VTIP). Water or oxygen was used as a reactive gas in thermal and plasma-enhanced (PE) processes. For PE ALD, there was a wide ALD temperature window from 50 to 200°C. Above 200°C, VTIP decomposed thermally, resulting in the chemical vapor deposition (CVD) of vanadium pentoxide. The PE ALD reactions saturated much faster than during thermal ALD, leading to a growth rate of approximately 0.7 A/cycle during PE ALD using H 2 O or O 2 . Optical emission spectroscopy showed combustion-like reactions during the plasma step. X-ray diffraction was performed to determine the crystallinity of the films after deposition and after postannealing under He or O 2 atmosphere. Films grown with CVD at 300°C and PE O 2 ALD at 150°C were (001)-oriented V 2 O 5 as deposited, while thermal and PE H 2 O ALD films grown at 150°C were amorphous as deposited. The crystallinity of the PE O 2 ALD could be correlated to its high purity, while the other films had significant carbon contamination, as shown by X-ray photoelectron spectroscopy. Annealing under He led to oxygen-deficient films, while all samples eventually crystallized into V 2 O 5 under O 2 .

Ultrathin GeOxNy interlayer formed by in situ NH3 plasma pretreatment for passivation of germanium metal-oxide-semiconductor devices

In situ NH3 plasma surface-nitridation treatments at 250 °C on both p- and n-type Ge(100) wafers were investigated. An ultrathin high quality GeOxNy interlayer was formed and exhibited dielectric breakdown for electric fields greater than 15 MV/cm. Well behaved capacitance-voltage characteristics were obtained for the complementary metal-oxide-semiconductor capacitors (CMOSCAPs) with HfO2(3 nm)/GeOxNy(1 nm) gate stacks. Gate leakage current density was below 5×10−7 A/cm2 at VFB±1 V for both MOSCAPs with an equivalent oxide thickness of 1.1 nm. Promising electrical properties of the CMOSCAPs indicate effective passivation of the Ge interface with GeOxNy interlayer formed by in situ NH3 plasma treatment.

Influence of the geometrical configuration on the plasma ionization distribution and erosion profile of a rotating cylindrical magnetron: a Monte Carlo simulation

The ionization distribution of a small scale rotating cylindrical magnetron discharge is simulated by a Monte Carlo based program. The simulation describes the high energy electron trajectories and the interaction between these electrons and the sputtering gas, which finally leads to the ionization distribution. By radial projection of the ionization positions on the target surface, the erosion track dimensions can be correctly simulated. The discrepancy between the simulation and the experiments shows the need to modify the experimental design and to control the alignment between the central axis of the target tube and the magnet configuration in a better way.

Thermal Versus Plasma-Enhanced ALD: Growth Kinetics and Conformality

Film purity, growth kinetics and conformality were compared for thermal and plasma-enhanced atomic layer deposition (PE-ALD) of Al2O3, AlN and TiN. The use of a plasma to enhance the activity of the reactant gas results in a significant improvement of the growth rate and film purity. However, based on experiments with an ammonia plasma for the growth AlN, the conformality of PE-ALD appears to be quite limited.

Investigation of the sustaining mechanisms of dc magnetron discharges and consequences for I–V characteristics

The influence of the starting conditions and sheath thickness on the magnetron discharge is investigated using a Monte Carlo program. The average number of ionizations caused by an electron emitted from the cathode is calculated. It is shown that the sheath thickness plays a crucial role in the generation of ions and the sustainment of the discharge. An analytical formula is obtained which relates discharge voltage, sheath thickness and ion-induced secondary electron coefficient. From it, a natural explanation for the very steep current-voltage (I-V) characteristic in magnetron discharges follows. Comparison with experiment suggests an anomalous diffusion of electrons across the sheath. The simulations were done for a rotatable cylindrical magnetron, but the results should be valid for planar magnetrons as well.

TiO2/HfO2 Bi-Layer Gate Stacks Grown by Atomic Layer Deposition for Germanium-Based Metal-Oxide-Semiconductor Devices Using GeOxNy Passivation Layer

Material and electrical properties of TiO2/HfO2 bi-layer gate stacks were investigated for germanium (Ge) based metal-oxidesemiconductor devices. In situ NH3 plasma treatment was employed to passivate the Ge surface and promising performance including low capacitance-voltage hysteresis and interface trap density was achieved. It shows a superior dielectric breakdown voltage (4.2–3.4 V) for the TiO2/HfO2 bi-layer stacks than HfO2 single layer stack at a similar capacitance equivalent thickness (CET) of 1.6 nm. A minimum CET of 1.4 nm was obtained for capacitors on both p and n-type Ge (100) with a gate leakage current density< 4 10 7 A/cm at VFB 6 1 V. VC 2011 The Electrochemical Society. [DOI: 10.1149/1.3559770] All rights reserved.