Advanced process technologies : plasma, direct-wire, atmospheric pressure, and roll-to-roll ALD

As applications of atomic layer deposition (ALD) in emerging areas such as nanoelectronics, photovoltaics, and flexible electronics expand beyond single-wafer semiconductor processing, there is a growing need for novel approaches to integrate new process designs, substrate materials, and substrate delivery methods. An overview is given of new means to extend the capabilities of ALD and to improve the speed and simplicity of ALD coatings using new reactor designs. These include energy-enhanced and spatial ALD schemes involving plasma, direct-write, atmospheric pressure, and roll-to-roll processing. The long-term goal of this work is to integrate viable high-throughput capabilities with ALD processes

De kunst van het maken

Nanotechnologie wordt gezien als dé grote belofte voor de toekomst, ook op het gebied van nieuwe elektronica en zonnecellen. Het bijbehorende onderzoek is echter nog vooral veel ‘nano’ en weinig ‘technologie’. In deze intreerede zal ik laten zien dat het mogelijk is om nieuwe technieken, materialen en toepassingen te ontwikkelen door fabricageprocessen op atomaire schaal te begrijpen en te beheersen. Ik zal duiden hoe zo de kloof tussen onderzoek in het lab en industriële productie overbrugd kan worden

Impact of Film Thickness and Thermal Treatment on the Excellent Surface Passivation of c-Si by ALD Al2O3 for Solar Cell Applications

The surface passivation of c-Si by atomic layer deposited (ALD) Al2O3 has recently gained considerable interest after extremely low surface recombination velocities (<10 cm/s) have been reported for low resistivity n- and p-type c-Si wafers [1]. The incorporation of an Al2O3 film for boron doped emitter passivation led to enhanced efficiencies of 23.2% for n-type c-Si solar cells [2]. From the cumulative research, various questions related to the thermal stability and other processing aspects of the Al2O3 films appeared. In this contribution we will show that a decrease of film thickness down to ~5 nm does not compromise the passivation quality, enabling a straightforward reduction of deposition time and providing freedom in the design of optimal front passivation/antireflection schemes. To activate the Al2O3 surface passivation a post-deposition anneal is required, but also the thermal budget during the plasma enhanced chemical vapor deposition of an a-SiNx:H capping layer was found sufficient to activate the passivation. Although an anneal effect can be observed in a large temperature range (~350 - ~600oC) the optimal post-deposition anneal temperature window was found to be much smaller. Within the optimum temperature range, the largest anneal effect was observed to take place during the first minutes of the process. For the successful implementation of Al2O3 in conventional screen printed solar cells, thermal stability is required. In this paper we demonstrate the relative stability of Al2O3 and Al2O3/a-SiNx:H passivation/antireflection stacks against an industrial "firing" process reaching temperatures > 800oC. Although the minority carrier lifetime was found to decrease during the firing process, values in excess of 1 ms were obtained on 2 O cm n-Si wafers after firing. These lifetimes suggest that surface recombination will not likely be the efficiency limiting step for solar cells that combine Al2O3 passivation and screen printed metallization as recombination in the metalized area will be dominant. The findings in this paper demonstrate the suitability of thin ALD-synthesised Al2O3 passivation films for large scale photovoltaic applications. [1] B. Hoex, J. Schmidt, P. Pohl, M. C. M. van de Sanden, and W. M. M. Kessels, J. Appl. Phys. 104, 044903 2008 [2] J. Bennick, B. Hoex, M.C.M. van de Sanden, W.M.M. Kessels, O. Schultz, S. Glunz, Appl. Phys. Lett. 92, 253504 (2008

Molecular dynamics simulations of AR+ bombardment of Si with comparison to experiment

The authors present molecular dynamics (MD) simulations of energetic Ar+ ions (20–200 eV) interacting with initially crystalline silicon, with quantitative comparison to experiment. Ar+ bombardment creates a damaged or amorphous region at the surface, which reaches a steady-state thickness that is a function of the impacting ion energy. Real-time spectroscopic ellipsometry data of the same phenomenon match the MD simulation well, as do analogous SRIM simulations. They define positional order parameters that detect a sharp interface between the amorphous and crystalline regions. They discuss the formation of this interesting feature in the simulation, and show that it provides insight into some assumptions made in the analysis of experimental data obtained by interface-sensitive surface spectroscopy techniques

Workshop ALD FUNdamentals : hot topics in ALD

Breng 101 onderzoekers, promovendi en specialisten uit de industrie met praktische kennis van atoomlaagdepositie (ALD) bij elkaar en stimuleer de discussie over de belangrijkste vragen waar iedereen mee worstelt. Dan gaan deze specialisten met nog meer vragen naar huis en hebben ze inspiratie opgedaan voor het schrijven van nieuwe onderzoeksvoorstellen en weten ze wie er in staat is om in samenwerking antwoorden te vinden voor het verleggen van de huidige ALD-grenzen. Dat is in het kort het idee achter de workshop Nanomanufacuring: ALD FUNdamentals, die op 8 en 9 juni georganiseerd werd door de groep van Erwin Kessels aan de Technische Universiteit Eindhoven

Surface-diffusion-controlled incorporation of nanosized voids during hydrogenated amorphous silicon film growth

The incorporation of nanosized voids during hydrogenated amorphous silicon film growth is studied by measurements of the film mass density and the hydrogen present at the void surfaces. The observed dependence of the density of nanosized voids on the growth flux and substrate temperature is explained in terms of a surface-diffusion-controlled void incorporation model. From this analysis, an activation energy for surface diffusion in the range of 0.77–1.05 eV has been found, a value which is in agreement with the activation energy obtained from the analysis of the surface roughness evolution during growth in a previous study

Crystallization study by transmission electron microscopy of SrTiO3 thin films prepared by plasma-assisted ALD

The crystallization behavior of thin strontium titanate (SrTiO3, STO) films with ~15 nm thickness was studied by Transmission Electron Microscopy (TEM). Amorphous STO films with [Sr]/([Sr]+[Ti]) ratio ranging from 0.50 to 0.63 were deposited at 350°C by plasma-assisted ALD and subsequently treated by rapid thermal annealing in flowing N2 for crystallization. Different temperatures and annealing durations were employed to fully characterize the crystallization process. TEM analysis showed that transrotational crystals were formed and evidenced the influence of the STO composition and of the thermal budget applied on the grain size, crack and void formation. In particular, Sr-rich layers ([Sr]/([Sr]+[Ti] = 0.59) showed a finer crystalline structure which was imputed to a higher nucleation probability at the onset of the crystallization process. Crystallization into the perovskite structure was confirmed for all the film compositions studied. By tuning the STO composition and the thermal budget of the annealing step it was demonstrated that it is possible to control the microstructure of the crystallized film as a further step in optimizing the STO film properties