Many reported atomic layer deposition (ALD) processes are carried out at elevated temperatures (>150°C), which can be problematic for temperature-sensitive substrates. Plasma-enhanced ALD routes may provide a solution, as the ALD temperature window can, in theory, be extended to lower deposition temperatures due to the reactive nature of the plasma. As such, the plasma-enhanced ALD of Al 2 O 3 , TiO 2 , and Ta 2 O 5 has been investigated at 25-400°C using [Al(CH 3 ) 3 ], [Ti(O i Pr) 4 ], [Ti(Cp Me )(O i Pr) 3 ], [TiCp*(OMe) 3 ], and [Ta(NMe 2 ) 5 ] as precursors. An O 2 plasma was employed as the oxygen source in each case. We have demonstrated metal oxide thin-film deposition at temperatures as low as room temperature and compared the results with corresponding thermal ALD routes to the same materials. The composition of the films was determined by Rutherford backscattering spectroscopy. Analysis of the growth per cycle data and the metal atoms deposited per cycle revealed that the growth per cycle is strongly dependent on the film density at low deposition temperatures. Comparison of these data for Al 2 O 3 ALD processes in particular, showed that the number of Al atoms deposited per cycle was consistently high down to room temperature for the plasma-enhanced process but dropped for the thermal process at substrate temperatures lower than 250°C.

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Low temperature plasma-enhanced atomic layer deposition of metal oxide thin films

An intensive study has been performed to understand and tune deep reactive ion etch (DRIE) processes for optimum results with respect to the silicon etch rate, etch profile and mask etch selectivity (in order of priority) using state-of-the-art dual power source DRIE equipment. The
research compares pulsed-mode DRIE processes (e.g. Bosch technique) and mixed-mode DRIE processes (e.g. cryostat technique). In both techniques, an inhibitor is added to
fluorine-based plasma to achieve directional etching, which is formed out of an oxide-forming (O2) or a fluorocarbon (FC) gas (C4F8 or CHF3). The inhibitor can be introduced together with the etch gas, which is named a mixed-mode DRIE process, or the inhibitor can be added in a
time-multiplexed manner, which will be termed a pulsed-mode DRIE process. Next, the most convenient mode of operation found in this study is highlighted including some remarks to
ensure proper etching (i.e. step synchronization in pulsed-mode operation and heat control of the wafer). First of all, for the fabrication ......
 Enjoy reading . Henri Jansen 18 June 2008

https://iopscience.iop.org/article/10.1088/0960-1317/19/3/033001/pdf

Black silicon method X: a review on high speed and selective plasma etching of silicon with profile control: an in-depth comparison between Bosch and cryostat DRIE processes as a roadmap to next generation equipment

https://tandfonline.com/doi/pdf/10.1080/14686996.2019.1599694

New development of atomic layer deposition: processes, methods and applications.

Surface passivation of crystalline silicon solar cells: Present and future

Low-temperature atomic layer deposition of Al2O3 thin coatings for corrosion protection of steel: Surface and electrochemical analysis

Processing at the atomic scale is becoming increasingly critical for state-of-the-art electronic devices for computing and data storage, but also for emerging technologies such as related to the internet-of-things, artificial intelligence, and quantum computing. To this end, strong interest in improving nanoscale fabrication techniques such as atomic layer deposition (ALD) has been present. New ALD processes are being sought continuously and particularly plasma-assisted processes are considered an enabler for a wide range of applications because of their enhanced reactivity. This review provides an update on the status and prospects of plasma-assisted ALD with a focus on the developments since the publication of the review by Profijt et al. [J. Vac. Sci. Technol. A 29, 050801 (2011)]. In the past few years, plasma ALD has obtained a prominent position in the field of ALD with (i) a strong application base as demonstrated by the breakthrough in high-volume manufacturing; (ii) a large number of established processes, out of which several are being enabled by the plasma step; and (iii) a wide range of plasma ALD reactor designs, demonstrating many methods by which plasma species can be applied in ALD processes. In addition, new fundamental insights have been obtained, for instance, with respect to plasma damage, on the effect of ions on the material properties and on the so-called redeposition effect. Regarding new and emerging developments, plasma ALD is expected to take a prominent position in the atomic-scale processing toolbox and will contribute to ongoing developments in area-selective deposition, controlled growth of 2D materials, and atomic layer etching.

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Status and prospects of plasma-assisted atomic layer deposition

Low-temperature atomic layer deposition (ALD) offers significant merits in terms of processing uniform, conformal and pinhole-free thin films, with sub-nanometer thickness control. In this work, plasma-assisted atomic layer deposition (ALD) of nickel oxide (NiO) is carried out by adopting bis-methylcyclopentadienyl-nickel (Ni(MeCp)2) as precursor and O2 plasma as co-reactant, over a wide table temperature range of 50–300 °C. A growth rate of 0.32 A per cycle is obtained for films deposited at 150 °C with an excellent thickness uniformity on a 4 inch silicon wafer. Bulk characteristics of the NiO film together with its interfacial properties with a triple cation hybrid perovskite absorber layer are comprehensively investigated, with the aim of integrating NiO as hole transport layer (HTL) in a p–i–n perovskite solar cell (PSC) architecture. It is concluded that “key” to efficient solar cell performance is the post-annealing treatment of the ALD NiO films in air, prior to perovskite synthesis. Post-annealing leads to better wettability of the perovskite layer and increased conductivity and mobility of the NiO films, delivering an increase in short-circuit current density (Jsc) and fill factor (FF) in the fabricated devices. Overall, a superior 17.07% PCE is achieved in the post-annealed NiO-based PSC when compared to the 13.98% PCE derived from the one with pristine NiO.

/pdf/plasma-assisted-atomic-layer-deposition-of-nickel-oxide-as-5d4qdep0p6.pdf

Plasma-assisted atomic layer deposition of nickel oxide as hole transport layer for hybrid perovskite solar cells

Area-selective atomic layer deposition (ALD) of ZnO was achieved on SiO2 seed layer patterns on Hterminated silicon substrates, using diethylzinc (DEZ) as the zinc precursor and H2O as the coreactant. The selectivity of the ALD process was studied using in situ spectroscopic ellipsometry and scanning electron microscopy, revealing improved selectivity for increasing deposition temperatures from 100 to 300 °C. The selectivity was also investigated using transmission electron microscopy and energy-dispersive X-ray spectroscopy. Density functional theory (DFT) calculations were performed to corroborate the experimental results obtained and to provide an atomic-level understanding of the underlying surface chemistry. A kinetically hindered proton transfer reaction from the H-terminated Si was conceived to underpin the selectivity exhibited by the ALD process. By combining the experimental and DFT results, we suggest that the trend in selectivity with temperature may be due to a strong DEZ or H2O physisorption on the H-terminated Si that hampers high selectivity at low deposition temperature. This work highlights the deposition temperature as an extra process parameter to improve the selectivity.

/pdf/area-selective-atomic-layer-deposition-of-zno-by-area-1emkc1tyrg.pdf

Area-selective atomic layer deposition of ZnO by area activation using electron beam-induced deposition

This paper reviews the options of using Atomic Layer Deposition (ALD) in passive and heterogeneous integration. The miniaturization intended by both integration schemes aim at Si-based integration for the former and at die stacking in a compact System-in-Package for the latter. In future Si-based integrated passives a next miniaturization step in trench capacitors requires the use of multiple ‘classical’ MOS layer stacks and the use of so-called high-k dielectrics (based on HfO2, etc.) and novel conductive layers like TiN, etc. to compose MIS and MIM stacks in ‘trench’ and ‘pore’ capacitors with capacitance densities exceeding 200 nF/mm 2 . One of the major challenges in realizing ultrahigh-density trench capacitors is to find an attractive pore lining and filling fabrication technology at reasonable cost and reaction rate as well as low temperature (for back-end processing freedom). As the deposition for the dielectric and conductive layers should be highly uniform, step-conformal and lowtemperature (≤ 400 °C), ALD is an enabling technology here, by virtue of the self-limiting mechanism of this layer-by-layer deposition technique. This article discusses first a few examples of LPCVD deposition of conventional MOS layers with ONO-dielectrics and in situ doped polycrystalline silicon, both as single layers and multilayer stacks. In addition, a few options for ALD deposition of thin dielectric and conductive layers (e.g. HfO2- and TiN-based) will be discussed. The silicon substrates that were used contained high aspect ratio (≥ 20) features with cross-section and spacing of the order of 1 µm.

/pdf/ald-options-for-si-integrated-ultrahigh-density-decoupling-2ymx1sm2xt.pdf

ALD Options for Si-integrated Ultrahigh-density Decoupling Capacitors in Pore and Trench Designs

In order to increase the efficiency of silicon-wafer-based solar cells in production well above 20%, it is indispensable to improve the currently applied level of surface passivation at the front as well as at the rear of the cells. This paper focuses on two main challenges: (i) the low-temperature passivation of lowly doped p-type silicon surfaces at the cell rear and (ii) the passivation of highly boron-doped p + emitter surfaces as used at the front of solar cells on high-lifetime n-type silicon wafers. In the past, low surface recombination velocities (< 20 cm/s) have been achieved on low-resistivity (~1 Ωcm) p-type silicon using plasma-enhanced chemical-vapour-deposited (PECVD) silicon nitride (SiNx) as well as amorphous silicon (a-Si). However, the high density of fixed positive charges within the PECVD-SiNx layer induces an inversion layer at the rear of p-type Si cells, producing a detrimental parasitic shunting, which reduces the short-circuit current density by up to 3 mA/cm 2 . The passivation quality of a-Si on the other hand is very temperature sensitive. More recently it has been shown that atomic-layer-deposited (ALD) alumin- ium oxide (Al2O3) provides an outstanding level of surface passivation, which can be attributed to its extremely high negative fixed charge density in combination with the very gentle deposition technique ALD, leading to low inter- face state densities. The application of these ALD-Al2O3 layers to the rear of p-type solar cells shows that this new passivation scheme is indeed suitable for high efficiencies and that due to the large negative fixed charge density no parasitic shunting occurs. We also demonstrate that ALD-Al2O3 seems to be the ideal passivation layer for boron- doped p + emitter surfaces. In a direct comparison with other passivation schemes, it is found that Al2O3 even outper- forms optimized thermally grown SiO2 and opens the possibility of achieving very large open-circuit voltages up to Voc = 740 mV.

/pdf/progress-in-the-surface-passivation-of-silicon-solar-cells-wpt72on3ik.pdf

Erwin Kessels

Papers

Status and prospects of plasma-assisted atomic layer deposition

Plasma-assisted atomic layer deposition of nickel oxide as hole transport layer for hybrid perovskite solar cells

Area-selective atomic layer deposition of ZnO by area activation using electron beam-induced deposition

ALD Options for Si-integrated Ultrahigh-density Decoupling Capacitors in Pore and Trench Designs

Progress in the surface passivation of silicon solar cells