Investigation of reactive ion etching of dielectrics and Si in CHF₃/O₂ or CHF₃/Ar for photovoltaic applications

Using a combination of etch rate, photoconductance, and deep level transient spectroscopy(DLTS) measurements, the authors have investigated the use of reactive ion etching (RIE) of dielectrics and Si in CHF₃∕O₂ and CHF₃∕Arplasmas for photovoltaic applications. The radio frequency power (rf-power) and gas flow rate dependencies have shown that the addition of either O₂ or Ar to CHF₃ can be used effectively to change the etch selectivity between SiO₂ and Si₃N₄. The effective carrier lifetime of samples degraded upon exposure to a CHF₃-based plasma, reflecting the introduction of recombination centers in the near-surface region. The extent of minority carrier lifetime degradation was similar in both types of plasmas, suggesting that the same defects were responsible for the increased recombination. However, the rf-power dependence of lifetime degradation in n- and p-type Si was different. Moreover, the lifetime degradation did not exhibit a linear rf-power dependence, suggesting that primary defects were not the dominant recombination centers responsible for the decrease in lifetime. Indeed, DLTS measurements have shown that secondary defects were formed in samples exposed to the plasma after annealing at 400°C, the temperature at which a SiN:H layer is deposited on samples to passivate their surfaces. The minority carrier lifetime degradation in RIE processed samples could be partially avoided using post-RIE chemical treatments.The authors would like to thank the Australian Research Council for financial support

Trifluoroiodomethane as an environmentally friendly gas for water patterning by plasma etching process

Trifluoroiodomethane (CF3I), a non-global warming gas, has been investigated with study as a substitute for typical CFC etchants, such as CF4 and C2F6, used in wafer pattering technology. This investigation was carried out by exposing dielectric films of silicon oxide (SiO2) and silicon nitride (Si3N4) in CF3I and C2F6/O2 (used as a reference) plasma environments. The etch rate of these films was ascertained as function of applied rf power, etchant gas flow rate, reaction chamber operating pressure, and O2 to CF3I ratio. Upon increasing power, the etch rates of SiO2 and Si3N4 by both CF3I and C2F6/O2 were increased. The study of flow rate showed various results depending on types of etchants and dielectric film materials. According to the processing conditions, there were two limits in etching with CF3I. First, at the pressure higher than 50 mTorr, etching of\u27 Si3N4 can produce polymer film on sample surface. Secondly, at O2/CF3I ratio higher than 0.17, etching of both dielectric films can result in generating reddish particles all over the sample and the reaction chamber side wall

Plasma Nanoscience: from Nano-Solids in Plasmas to Nano-Plasmas in Solids

The unique plasma-specific features and physical phenomena in the organization of nanoscale solid-state systems in a broad range of elemental composition, structure, and dimensionality are critically reviewed. These effects lead to the possibility to localize and control energy and matter at nanoscales and to produce self-organized nano-solids with highly unusual and superior properties. A unifying conceptual framework based on the control of production, transport, and self-organization of precursor species is introduced and a variety of plasma-specific non-equilibrium and kinetics-driven phenomena across the many temporal and spatial scales is explained. When the plasma is localized to micrometer and nanometer dimensions, new emergent phenomena arise. The examples range from semiconducting quantum dots and nanowires, chirality control of single-walled carbon nanotubes, ultra-fine manipulation of graphenes, nano-diamond, and organic matter, to nano-plasma effects and nano-plasmas of different states of matter.Comment: This is an essential interdisciplinary reference which can be used by both advanced and early career researchers as well as in undergraduate teaching and postgraduate research trainin

Low temperature remote plasma sputtering of indium tin oxide for flexible display applications

Tin doped indium oxide (ITO) has been directly deposited onto a variety of flexible materials by a reactive sputtering technique that utilises a remotely generated, high density plasma. This technique, known as high target utilisation sputtering (HiTUS), allows for the high rate deposition of good quality ITO films onto polymeric materials with no substrate heating or post deposition annealing. Coatings with a resistivity of 3.8 ×10−4 Ωcm and an average visible transmission of greater than 90% have been deposited onto PEN and PET substrate materials at a deposition rate of 70 nm/min. The electrical and optical properties are retained when the coatings are flexed through a 1.0 cm bend radius, making them of interest for flexible display applications

Shining a light on silicon etching

Surprisingly little is known about the statistical nature of the shape of a free surface above turbulence and about how this shape depends on the properties of the turbulence. The main focus of this thesis is on experiments in which the statistical properties of both the surface and the turbulence are measured with a number of di??erent techniques. The experiments are done in a free-surface water-channel, in which turbulence is generated with an active grid. This active grid consists of an array of horizontal and vertical rods through the channel, with small wings attached to them. The rods are individually driven by electric motors, according to a certain forcing protocol, thereby adding energy to the turbulence. A major advantage of an active grid is that, by changing this protocol, the properties, such as the intensity and the isotropy, of the generated turbulence can be changed. These properties were measured by means of Laser-Doppler Velocimetry. The turbulence behind the active grid is much more intense than turbulence generated by a more common static grid. The maximum Taylorbased Reynolds number reached with the active grid (at 40 times the mesh size behind the grid) was Re?? = 256, compared to Re?? = 70 with a similarly dimensioned static grid. Consequently, the active-grid-generated turbulence shows clear Kolmogorov scaling behaviour over a relatively wide range of scales. The stronger turbulence also leads to stronger surface deformations. In order to characterise the shape of the surface, it is essential to measure the surface shape with a high resolution both in space and time. In order to achieve this, a novel technique has been developed, based on refraction of a laser beam that shines through the surface. The de ection of the beam due to the local surface slope is measured by means of an optical position sensing device. The beam is swept along a line by means of a rapidly oscillating mirror (with a frequency of close to 2 kHz). This allows measurements of the surface slope at multiple points along the line as a function of time. This surface scanning technique can be combined with Particle Image Velocimetry (PIV), which provides snapshots of the velocity ??eld and the vertical component of vorticity in horizontal planes just below the surface. This combination allows us to simultaneously measure the velocity ??eld and the surface deformations above it. PIV is based on the cross-correlation of the intensity distributions in images of particles suspended in the ow, that are illuminated by a thin laser light sheet. When applying PIV to turbulence, it is important to realise that the velocity ??eld that can be obtained with PIV is a spatially averaged representation of the actual velocity ??eld. The e??ect this averaging has on measured turbulence properties is investigated by means of kinematic simulations, in which realistic turbulent velocity ??elds, with a prescribed energy spectrum, are generated. Synthetic particle images derived from these ??elds are evaluated by means of a PIV algorithm and the velocity spectrum is calculated. Comparing this to the prescribed spectrum clearly shows the averaging, and allows us to predict its in uence on other measured turbulence properties. The turbulence generated by our grid is not strong enough to lead to very large deformations of the surface. The measured changes in elevation are less than 1 mm. In that case, somewhat naively, one would expect the surface deformations to be primarily associated with sub-surface vortices. In the core of a vortex the magnitude of the vorticity is high, while the pressure is low. This low pressure causes a dimple in the surface above the vortex. This e??ect can, for instance, be seen when stirring a cup of tea or in the wake behind bridge pillars in a river. Consequently, in simultaneous measurements of the surface shape and the sub-surface velocity ??eld one would expect to ??nd a relatively large correlation between the vertical component of vorticity and the surface elevation. Indeed, our measurements show that relatively strong vortices in the turbulence do deform the surface. However, the measured correlation coe??cients are low (<0:1). Spectra of the surface slope in space and time show that, instead of being connected directly to sub-surface structures, much of the surface actually consists of gravity-capillary waves, i.e. regular surface waves. For surface waves, there is a clear relation between their wavelength and their frequency. This relation can be identi??ed in our spectra. The presence of these waves is somewhat surprising, since resonant wave growth can only be expected to occur if the uctuation velocities in the turbulence are larger than the minimum phase velocity of the waves (?? 0:23 m/s), while the measured uctuation velocities in our turbulence are an order of magnitude smaller. A remarkable feature of the waves above the turbulence is that they travel in all directions across the surface. In fact, provided that the turbulence far below the surface is isotropic, the surface shape itself is isotropic as well. In other words, statistically, the waves on the surface are the same in every direction. We can change this by changing the forcing protocol of the active grid such that the turbulence becomes anisotropic. In that case the surface shape becomes anisotropic as well. This is a clear indication that the surface waves are excited locally by the turbulence. We have found evidence to suggest that the waves are excited by the largest structures in the turbulence. As a consequence of this, the surface shape does not re ect the wide range of scales in the sub-surface turbulence, but instead exhibits waves primarily with wavelenghts close to the integral scale of the turbulence

Roughening of ion-eroded surfaces

Recent experimental studies focusing on the morphological properties of surfaces eroded by ion-bombardment report the observation of self-affine fractal surfaces, while others provide evidence about the development of a periodic ripple structure. To explain these discrepancies we derive a stochastic growth equation that describes the evolution of surfaces eroded by ion bombardment. The coefficients appearing in the equation can be calculated explicitly in terms of the physical parameters characterizing the sputtering process. Exploring the connection between the ion-sputtering problem and the Kardar-Parisi-Zhang and Kuramoto-Sivashinsky equations, we find that morphological transitions may take place when experimental parameters, such as the angle of incidence of the incoming ions or their average penetration depth, are varied. Furthermore, the discussed methods allow us to calculate analytically the ion-induced surface diffusion coefficient, that can be compared with experiments. Finally, we use numerical simulations of a one dimensional sputtering model to investigate certain aspects of the ripple formation and roughening.Comment: 20 pages, LaTeX, 5 ps figures, contribution to the 4th CTP Workshop on Statistical Physics "Dynamics of Fluctuating Interfaces and Related Phenomena", Seoul National University, Seoul, Korea, January 27-31, 199