F. Roozeboom

High-Speed Spatial Atomic-Layer Deposition of Aluminum Oxide Layers for Solar Cell Passivation

In this Communication we show that with spatially separated ALD of Al2O3 growth rates of 1.2 nm s-1 can be achievd, showing excellent surface passivation (surface recombination velocities of <2 cm s-1). This implies a revolutionary breakthrough in industrial throughput ALD of Al2O3 passivation of silicon solar cells.

Spatial atomic layer deposition: A route towards further industrialization of atomic layer deposition

Atomic layer deposition (ALD) is a technique capable of producing ultrathin conformal films with atomic level control over thickness. A major drawback of ALD is its low deposition rate, making ALD less attractive for applications that require high throughput processing. An approach to overcome this drawback is spatial ALD, i.e., an ALD mode where the half-reactions are separated spatially instead of through the use of purge steps. This allows for high deposition rate and high throughput ALD without compromising the typical ALD assets. This paper gives a perspective of past and current developments in spatial ALD. The technology is discussed and the main players are identified. Furthermore, this overview highlights current as well as new applications for spatial ALD, with a focus on photovoltaics and flexible electronics. 2012 American Vacuum Society.

Plasma and Thermal ALD of Al2O3 in a Commercial 200 mm ALD Reactor

The deposition of Al 2 O 3 by remote plasma atomic layer deposition (ALD) in the Oxford Instruments FlexAL reactor was studied and compared with results from thermal ALD in the same reactor. Trimethylaluminum [Al(CH 3 ) 3 ] was used as the metal precursor and O 2 plasma and H 2 O were used as oxidizing agents for the plasma and thermal processes, respectively. For remote plasma ALD with a total cycle time of 4 s, the growth per cycle decreased monotonically with substrate temperature, from 1.7 A/cycle at 25°C to 1.0 A/cycle at 300°C. This growth per cycle was consistently higher than that obtained for thermal ALD. For the latter a maximum growth per cycle of ∼ 1.0 A/cycle was found at 200°C. The film properties investigated were nearly independent of oxidant source for temperatures between 100 and 300°C, with a slightly higher mass density for the remote plasma ALD Al 2 O 3 films. Films deposited at 200 and 300°C were stoichiometric with a mass density of 3.0 g/cm 3 and low C (< 1 atom %) and H (<3 atom %) contents. At lower substrate temperatures, oxygen-rich films were obtained with a lower mass density and higher H-content. Remote plasma ALD produced uniform Al 2 O 3 films with nonuniformities of less than ±2% over 200 mm diam substrates. Excellent conformality was obtained for films deposited in macropores with an aspect ratio of ∼8 (2.0-2.5 μm diam). Preliminary results on electrical properties of remote plasma deposited films showed high dielectric constants of 7.8 and 8.9 for as-deposited and forming gas annealed Al 2 O 3 , respectively.

Rapid thermal processing systems: A review with emphasis on temperature control

This paper highlights the basic principles of rapid thermal processing (RTP) systems and the important areas of concern. The basic system characteristics, the fundamental physics involved, and the techniques for temperature measurement and control are extensively reviewed. We summarize the options currently available for 15 RTP equipment manufacturers and point out the latest developments in RTP system design and temperature measurement. Some novel options for temperature control (optical, fiber optical, and photoacoustic) are included.

Ultrahigh Capacitance Density for Multiple ALD-Grown MIM Capacitor Stacks in 3-D Silicon

ldquoTrenchrdquo capacitors containing multiple metal-insulator-metal (MIM) layer stacks are realized by atomic-layer deposition (ALD), yielding an ultrahigh capacitance density of 440 at a breakdown voltage VDB > 6 V. This capacitance density on silicon is at least 10times higher than the values reported by other research groups. On a silicon substrate containing high-aspect-ratio macropore arrays, alternating MIM layer stacks comprising high-k Al2O3dielectrics and TiN electrodes are deposited using optimized ALD processing such that the conductivity of the TiN layers is not attacked. Ozone annealing subsequent to each Al2O3 deposition step yields significant improvement of the dielectric isolation and breakdown properties.

Vanadium oxide monolayer catalysts: The vapor-phase oxidation of methanol

The oxidation of methanol over vanadium oxide, unsupported and applied as a monolayer on γ-Al2O3, CeO2, TiO2, and ZrO2, was studied between 100 and 400 °C in a continuous-flow reactor. At temperatures from 150 to about 250 °C two main reactions take place, (a) dehydration of methanol to dimethyl ether and (b) partial oxidation to formaldehyde. A very slight direct oxidation to CO2 proceeds simultaneously. At higher temperatures two further reactions take place, i.e., (c) consecutive oxidation of the ether and/or formaldehyde to CO and (d) consecutive oxidation of CO to CO2. Selectivity to formaldehyde increased with decreasing reducibility of the catalyst, which in turn was a function of the catalyst-support interactions. Since the reducibility of V(V) has been shown to be related to the charge/radius ratio of the cation of the carrier, the selectivity to formaldehyde is also determined by this ratio.

Ferromagnetic resonance and eddy currents in high-permeable thin films

The effect of eddy currents and ferromagnetic resonance (FMR) on the frequency dependence of the permeability of FeTaN thin films is studied. An equation is given that describes the combination of these two effects. The agreement between the theoretical calculations and the experimental data is excellent. Already at 1 MHz the imaginary part of the permeability is significantly changed by FMR. Above 10 MHz the real part of the permeability is decreased by FMR. The combined effect is best observed in extremely high permeable, 1 μm thick films. A value for the ferromagnetic damping constant is obtained.

Deposition of TiN and HfO2 in a commercial 200mm remote plasma atomic layer deposition reactor

The authors describe a remote plasma atomic layer deposition reactor (Oxford Instruments FlexAL™) that includes an inductively coupled plasma source and a load lock capable of handling substrates up to 200mm in diameter. The deposition of titanium nitride (TiN) and hafnium oxide (HfO2) is described for the combination of the metal-halide precursor TiCl4 and H2–N2 plasma and the combination of the metallorganic precursor Hf[N(CH3)(C2H5)]4 and O2 plasma, respectively. The influence of the plasma exposure time and substrate temperature has been studied and compositional, structural, and electrical properties are reported. TiN films with a low Cl impurity content were obtained at 350°C at a growth rate of 0.35A∕cycle with an electrical resistivity as low as 150μΩcm. Carbon-free (detection limit <2at.%) HfO2 films were obtained at a growth rate of 1.0A∕cycle at 290°C. The thickness and resisitivity nonuniformity was <5% for the TiN and the thickness uniformality was <2% for the HfO2 films as determined over 200mm wafers.The authors describe a remote plasma atomic layer deposition reactor (Oxford Instruments FlexAL™) that includes an inductively coupled plasma source and a load lock capable of handling substrates up to 200mm in diameter. The deposition of titanium nitride (TiN) and hafnium oxide (HfO2) is described for the combination of the metal-halide precursor TiCl4 and H2–N2 plasma and the combination of the metallorganic precursor Hf[N(CH3)(C2H5)]4 and O2 plasma, respectively. The influence of the plasma exposure time and substrate temperature has been studied and compositional, structural, and electrical properties are reported. TiN films with a low Cl impurity content were obtained at 350°C at a growth rate of 0.35A∕cycle with an electrical resistivity as low as 150μΩcm. Carbon-free (detection limit <2at.%) HfO2 films were obtained at a growth rate of 1.0A∕cycle at 290°C. The thickness and resisitivity nonuniformity was <5% for the TiN and the thickness uniformality was <2% for the HfO2 films as determined over 20...

Thermally assisted reversal of exchange biasing in NiO and FeMn based systems

The stability of the exchange bias field Heb has been studied for magnetron sputtered NiO/Ni66Co18Fe16 and Ni66Co18Fe16/FeMn bilayers. A forced antiparallel alignment of the ferromagnetic magnetization to Heb results in a gradual decrease of Heb as a function of time for NiO as well as FeMn based samples. The observed decrease of Heb increases with temperature and is interpreted as a thermally assisted reversal of magnetic domains in the antiferromagnetic layer.

Very low surface recombination velocities on p- and n-type c-Si by ultrafast spatial atomic layer deposition of aluminum oxide

Using aluminum oxide (Al2 O3) films deposited by high-rate spatial atomic layer deposition (ALD), we achieve very low surface recombination velocities of 6.5 cm/s on p -type and 8.1 cm/s on n -type crystalline silicon wafers. Using spatially separated reaction zones instead of the conventional time-sequenced precursor dosing enables growth rates up to 70 nm/min, whereas conventional ALD limits the growth rate to <2 nm/min. The excellent passivation level is predominantly assigned to a high negative fixed charge density of Qf =- (4±1) × 1012 cm-2 in the Al2 O3 films. We demonstrate an excellent thermal stability of the passivation quality.