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Ultralow-power gas sensing devices need to operate without an energy consuming heater element. This requires the design of sensing devices that are so efficient that they can operate at room temperature (RT). Here, we report on the RT sensing performance of atomic layer deposition (ALD) prepared i-ZnO and Al-doped ZnO sensing devices. The sensitivity of these devices has been catalytically enhanced with ALD Pt nanoparticles (NPs). It was shown that the size distribution of the Pt NPs can be controlled by the number of Pt-ALD cycles. The Pt-enhanced sensing devices showed a reversible, proportional change in current response at RT upon exposure to O2 and CO. O2 could be detected, diluted in N2, down to 0.5%. CO could be detected, diluted in N2 in the presence of O2 and H2O, down to 20 ppm. Reference devices without Pt NPs showed no response, indicating the importance of the Pt NPs for the sensing mechanism.

Deep anisotropic silicon etching with the expanding thermal plasma (ETP) technique using fluorine-based chemistries was demonstrated. The ETP technique makes use of a remote high-d. plasma source and it has a good control of the downstream plasma chem. Both a cryogenic etching process and a time-multiplexed etching process were developed. Etch rates up to 12 micro m min-1 and selectivities higher than 300 were obtained while feature profiles were comparable to those obtained with the widely used inductively coupled plasma reactors. Therefore, this deep anisotropic silicon etching technique is an attractive alternative for the fabrication of microstructures with high-aspect-ratio features. [on SciFinder (R)]

Remote plasmas, which are subjected to a radio-frequency (RF) biased surface, have been investigated theoretically and experimentally for decades. The relation between the complex power (DC) voltage characteristics, the ion energy distribution and control losses of the ion bombardment are of increasing interest. Therefore, in this present investigation, a simple sinusoidal voltage is applied to a single electrode posed in a semi-infinite, ideal pure Argon discharge with a given electron density ne and temperature Te, to rule the ion energy of the ions when they hit the surface. A linear relation is found between the (DC) potential and the dissipated power, as observed experimentally under high ne conditions. The equations of Poisson and momentum for ions moving in the sheath are solved at a fixed dissipated power when they strike the surface, resulting in the well-known bimodal ion energy distribution. These results will be compared with those obtained from experiments using expanding thermal plasmas with additional (RF) biasing to control ion energy.

This paper reports on the use of ion energy and ion flux during the deposition of thin amorphous AIDx , SiO, and ZnO using expanding thermal plasma (ETP) CVD. This plasma deposition method enables a good control of both ion flux by changing the deposition chemistry and arc plasma settings as well as the ion energy by an additional RF biasing or a so called tailored ion biasing technique based on the work by Wendt et al.l1] In the latter case an almost mono-cnergetic ion energy distribution resulls with a typical width below 5 eV. Due to the low electron temperature in the ETP (Te

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A review. Fundamental studies which are relevant for the successful industrial implementation of the expanding thermal plasma set up, a novel plasma source characterized by high deposition rates (1-100 nm/s), are discussed. The plasma chem. in Ar/O2/hexamethyldisiloxane and Ar/O2/octamethylcyclosiloxane-fed expanding thermal plasma setup and the influence of an addnl. ion bombardment during high rate Si3N4 deposition from Ar/N2/SiH4 and Ar/NH3/SiH4 mixt. is reviewed. The versatile control of parameters in the ETP setup (i.e., arc current, gas flow rates and working pressure) enable specific tuning of the film properties (i.e., chem. compn., optical and mech. properties). In addn. an example of a fundamental study of the gas phase and surface loss rates of Si and SiH3 radicals during plasma deposition of hydrogenated amorphous silicon as obtained from time-resolved cavity ringdown absorption measurements are demonstrated.

This thesis deals with the dry etching of deep anisotropic microstructures in monocrystalline silicon by high-density plasmas. High aspect ratio trenches are necessary in the fabrication of sensitive inertial devices such as accellerometers and gyroscopes. The etching of silicon in fluorine-based plasmas is isotropic. To obtain anisotropy the addition of sidewall passivation is necessary. This is achieved with both oxygen passivation at low temperatures and fluorocarbon passivation at room temperature. A quantitative approach was pursued to explain the etching mechanism. The etch results were analysed using the measured plasma species fluxes and the surface composition. Moreover, the transport of the plasma species in narrow anisotropic structures is a fundamental factor determining the etch rate and the profile evolution. The experimental methods such as the etching equipment, plasma diagnostics, surface analysis and sample preparation are described in chapter 2. Three etching processes were investigated: the cryogenic etching process with oxygen passivation at low temperatures, the Bosch process with fluorocarbon passivation at room temperature and the novel triple pulse process that was developed in our laboratory. The polymer deposition mechanism and the characteristic role of the ions are also explained. The cryogenic etching process is discussed in chapter 3. Fluorine radicals, oxygen radicals and ion bombardment are responsible for the three main sub-processes, that is, etching, sidewall passivation and depassivation of the trench bottom, respectively. Etching experiments with an extremely low ion-to-radical flux ratio were used to reveal the etching mechanism. Crystal orientation dependent etching leading to Si(111) crystal facets is observed in a surface kinetics controlled regime. By varying the plasma conditions it is possible to adjust the etching mechanism from fluorine-limited to ion-limited. Controlled etching is obtained because the etching is tuned from aspect ratio dependent in the fluorine-limited domain to aspect ratio independent in the ion-limited domain. The transport of radicals in high aspect ratio trenches is an important limiting factor and was investigated with special structures. The etch results are described by an analytic model that is based on the surface site balance of fluorine and oxygen radicals. The results are further explained with a Monte Carlo simulation model. The Bosch process is clarified in chapter 4. The anisotropy of the etched structures is controlled by balancing the etching and passivation pulse. However, the maximal obtainable aspect ratio is limited by convergence of the trench sidewalls due to excessive passivation. The maximal obtainable aspect ratio increases if the ion-to-radical flux ratio increases. The transport of ions is an important limiting factor in the depassivation of the bottom of the trench. Divergence of the ion beam leads to a reduction of the ion flux, so that the fluorocarbon passivation is insufficiently removed near the base of the sidewalls. The average ion angle was measured and correlated to the maximal obtainable aspect ratio. The Bosch process was improved at the depassivation side with the triple pulse process and at the passivation side with preferential sidewall deposition. The triple pulse process that is described in chapter 5 has the aim to improve the depassivation in deep trenches. The three main sub-processes are decoupled using a separate depassivation pulse directly after the etching and passivation pulses. The fluorocarbon passivation is efficiently removed with low-pressure, high-density, oxygen-based plasmas. The investigated plasma chemistries include O2, CO2 and SO2. The triple pulse process leads to better profile control with a straight trench bottom. However, the maximal obtainable aspect ratio is comparable to the Bosch process because a larger etch depth and a small lateral etch cancel out. The polymer deposition mechanism is treated in chapter 6 with the aim to understand the fluorocarbon passivation in deep trenches. The deposition on plane surfaces and on special structures was investigated to distinguish between the radical-induced and ion-enhanced components. A simple analytical model, which explains the main deposition characteristics, was developed. Preferential sidewall deposition is obtained for higher ion fluxes and higher bias voltages where sputtering plays an important role. In this case no fluorocarbon passivation has to be removed from the bottom of the trench. The trench profile was optimised in the Bosch process by tuning the bias voltage during etching and passivation independently. It resulted in perfectly anisotropic trenches but the maximal obtainable aspect ratio was still limited by a small lateral etch. The characteristic role of the ions in the etching mechanism is explained in chapter 7. Ion-induced etching of both SiC in a SF6-O2 plasma and Si in a Cl2 plasma were investigated. The impact of the ions on the profile evolution can be examined more explicitly because spontaneous chemical reactions are absent for these plasma-material systems. The etching mechanism varies from fluorine-limited to ion-limited depending on the radical-to-ion flux ratio. Microtrenches are observed for an ion-limited etching mechanism. Fluorine-limited SiC etching is aspect ratio dependent in contrast to ion-limited SiC etching, which is aspect ratio independent. The etching of high aspect ratio SiC structures is limited by the positive sidewall taper. This is presumably caused by insufficient removal of the thin fluorocarbon layer on the surface. Si etching in a Cl2 plasma is always aspect ratio independent in contrast to SiC etching because of the low reaction probability. The conclusions and recommendations of this thesis are given in chapter 8.

In a method and device for treating a substrate by means of a plasma, the plasma is generated and accelerated at substantially sub-atmospheric pressure between a cathode and an anode of a plasma source (1) in a channel of system of at least one conductive cascaded plate between said cathode and anode. Said plasma is released from said plasma source to a treatment chamber (2) in which said substrate (9) is exposed to said plasma. The treatment chamber is sustained at a reduced, near vacuum pressure during operation. An alternating bias voltage is applied between said substrate and said plasma during said exposure

In a method and device for etching a substrate by a plasma, the plasma is generated and accelerated at substantially sub-atm. pressure between a cathode and an anode of a plasma source in a channel of system of at least one conductive cascaded plate between said cathode and anode. Said plasma is released from said plasma source to a treatment chamber in which said substrate is exposed to said plasma. The treatment chamber is sustained at a reduced, near vacuum pressure during operation. An alternating bias voltage is applied between said substrate and said plasma during said exposure. [on SciFinder (R)]