Wafer bonding is used in industry for manufacturing silicon-oninsulator (SOI) materials and sensors. In most cases the bonding procedure involves high annealing temperatures around 1000ЊC, while in many applications high-temperature steps are unacceptable. This may be the case when dissimilar materials are to be bonded or in sensor manufacturing when metal wires are already present on the structures to be bonded. Hence, there is a clear need of low-temperature, preferably room temperature, bonding techniques.Plasma-assisted wafer bonding has recently attracted attention as a room temperature bonding method. [1][2][3][4] The bonded interfaces exhibit very high surface energies, comparable to what can be achieved with annealing steps in the range of 600-800ЊC using normal wet chemical activation before bonding.When designing SOI materials and sensors it is of great importance to know how the plasma-assisted bonding technique affects the properties of the component to be manufactured. However, the bonding mechanism and the features of the bonded interface are still unclear. Therefore, this paper is aimed at finding a mechanism for the plasma activation, the driving forces for the speculated formation of covalent bonds at room temperature, and the electrical characteristics for future electronic devices.

The influence of interface states and charges on the properties of Si/Si and Si/Si0 2 interfaces prepared by wafer bonding, using the direct bonding technique, has been investigated. Surface potentials of Si/Si. interfaces with all combinations of doping type (n-n,p-p,p-n) are dependent on surface and heat treatments in the bonding procedure and on wafer dopant concentration. In earlier reported works, hydrophilic wafer surface properties have been reported as necessary for a good mechanical bonding. We find that wafer treatment in HF giving hydrophobic surfaces not only gives good mechanical properties, but also better electronic properties as well. For all combinations of doping type, lower magnitudes in surface potential were measured in samples prepared from wafers pretreated in HF in order to etch off the native oxi.de layer, normally present on silicon surfaces, If a native oxide is present when the bonded interface is prepared, the current through the interface will be influenced by an energy barrier due to the presence of charged interface states. The amount of charge trapped at the interface has been found to be dependent on the applied bias. A theoretical description is made for the Si/Si interfaces, and predictions are compared to results obtained from electrical measurements_ Based on this theory, using data from the current-voltage characteristic, an interface state density in the region 5 X 1010_10 12 cm--2 eV--1 at the bonded interface has been deduced for different samples. Bonded Si/SiO z interfaces with interface state densities of about 1011 em --2 eV--1 and low flat-band voltages have been achieved. No influence of different chemical pretreatments, used in this paper, on properties of bonded SiiSiO z interfaces, as seen in fiat-band voltage and interface state density, was found, although the bonding process is critical in the preparation of the Si/SiO z interfaces.

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A series of alpha-amino acid esters of substituted phenethyl alcohols was prepared and tested as inhibitors of the neuronal reuptake of noradrenaline and 5-hydroxytryptamine. Some of the compounds are potent and very selective in blocking the 5-hydroxytryptamine uptake, as evidenced by biochemical data and behavioral tests. The most promising agent, alaproclate [2-(4-chlorophenyl)-1,1-dimethylethyl 2-aminopropanoate hydrochloride (I, IV)], was selected for further studies as a potential antidepressant agent. A discussion on structure--activity relationships (SAR) is given. In an attempt to explain the selective action on the mechanism of 5-hydroxytryptamine uptake by the new inhibitors, their structures are compared with those of the two neurotransmitters. From the tentative pharmacophore and conformations of transmitter (5-HT) and inhibitor (alaproclate) derived from SAR, a hypothetic carrier site for 5-HT uptake is deduced in terms of geometry and electronic properties.

The effects of oxygen plasma treatment on silicon surface topography and the properties of bonded interfaces formed using the oxygen plasma pretreatment were investigated. Bonded samples of silicon or oxidized silicon wafers using oxygen plasma pretreatment in reactive ion etchers with and without inductively coupled plasma were characterized in terms of surface energies obtained at room temperature. Annealing experiments at 1000°C were made to study the origin of thermally generated voids. Atomic force microscopy was used to study how the surface roughness of plasma-treated silicon wafers evolved over time. Furthermore, the influence of water dipping on the roughness of plasma-treated silicon surfaces was investigated. The results showed that plasma treatment of one wafer results in a surface energy of approximately 1 J m Ϫ2 at room temperature. The role of water in the increase of surface energy was found to be crucial. From annealing experiments it is concluded that water present at the wafer surfaces before bonding has a pronounced influence on void generation upon annealing. A dramatic change in the topography of silicon surfaces treated in oxygen plasma was observed during storage at room temperature, while water dipping the wafers after plasma treatment appeared to stabilize the surface topography.

The electrical and optical properties of wafer bonded unipolar silicon-silicon junctions were investigated. The interfaces, both n-n type and p-p type, were prepared using wafers with hydrophilic surfaces. The current versus voltage characteristics, the current transients following stepwise changes in the applied bias, and the capacitance versus voltage characteristics as well as the temperature dependence of the current and capacitance were experimentally obtained and theoretically modeled. The proposed model assumes two distributions of interface states, one of acceptors and one of donors, causing a potential barrier at the bonded interface. It is argued that the origins of the interface states are impurities and crystallographic defects in the interfacial region. The capacitance of the bonded structures includes contributions from the depletion regions as well as from minority carriers. When bonded n-n type samples were illuminated with light of photon energies larger than the silicon band gap the current across the junction increased. This is caused by the photogenerated increase in the minority carrier concentration in the interfacial region, which results in a lowering of the potential barrier. Illumination of n-n type structures with light of photon energies lower than the band gap caused a considerable photocurrent at low temperatures. In this case the observed behavior cannot be explained by interaction with the interface states. Instead, the mechanism is the change in the occupancy of deep electron traps caused by the illumination. These traps are located in the silicon in a small volume around the bonded interface with energies close to the center of the band gap and with a peak concentration of about 1013 cm−3. Impurities present on the silicon surfaces before bonding and impurities gettered to the bonded interface are possible reasons for the increased concentration of deep electron traps in the vicinity of the bonded interface.

One important requirement for future applications of carbon nanotube electronic devices is the ability to controllably grow carbon nanotubes on metal electrodes. Here we show that it is possible to grow small diameter (<10 nm) vertically aligned carbon nanotubes on different metal underlayers using plasma-enhanced chemical vapour deposition. A crucial component is the insertion of a thin silicon layer between the metal and the catalyst particle. The electrical integrity of the metal electrode layer after plasma treatment and the quality of the metals as interconnects are also investigated.

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