Collimated deposition

Aluminum, the most common material used for contacts, is easy to use, has low resistivity, and reduces surface Si02 to form interfacial metal-oxide bonds that promote adhesion to the substrate. However, as designs reach submicrometer dimensions, aluminum, Al, has been found to be a poor choice for metallization of contacts and via holes. Al has relatively poor step coverage, which is nonuniform layer thickness when deposited over right-angled geometric features. This leads to keyhole void formation when spaces between features are smaller than 0.7 p.m. New collimated sputtering techniques can extend the lower limit of Al use to 0.5-p.m appHcations. 

Volunteers smoked the labelled cigarettes. The activity deposited in the mouth, and the activity removed to the GI tract in the 15-min interval between smoking and measurement, were measured with collimated detectors. The clearance of activity from the lung was followed for 2 d to allow the deposit to be fractionated into TB and P components. Comparative tests were also done with subjects inhaling 2.5-jum polystyrene particles, which were also labelled with 123I. 

Fig. 10.18. Schematic illustration of steps for nanotransfer printing. Depositing a layer of metal using a collimated flux normal to the surface of the stamp yields a thin discontinuous coating on the raised and recessed regions of the stamp but not on its side-walls. Contacting this coated stamp to a substrate that supports suitable surface...

The first step was to spin-coat an electron-sensitive polymer (polymethylmethacrylate (PMMA)) onto an oxidized Si(l 00) wafer (which serves as a Si02 support). The desired pattern is subsequently written into the polymer layer by a highly collimated electron beam, followed by the selective dissolution of the polymer damaged by the electron exposure. A thin film of platinum is then deposited on this mask, and after the remaining polymer resist is removed completely by dissolution, metal particles remain on the substrate and are located at the positions of the prior electron irradiation, typically forming an ordered array of nanoparticles. 

For the FEM experiments described below, the cluster beam was directed through a small collimation capillary into a separately pumped deposition chamber, which is kept at 1 x 10 8 Torr. A transfer cell equipped with a 2 1/s ion pump enabled a tungsten FEM tip to be 1. inserted into the deposition chamber and positioned with its apex in the cluster beam, 2. withdrawn and transported at 2 x 10 7 Torr to a UHV field emission microscope, and 3. inserted into the field emission apparatus and positioned properly for field emission measurements (6). 

A systematic view of the relevant elements is depicted in Figure 17.10. The deposited clusters can be exposed to different reactant gases by two kinds of valves. First, they can be exposed isotropically to e.g. O2 by a commercial, ultra-high vacuum (UHV) compatible, variable leak valve. Second, reactant molecules (e.g. CO) can be introduced via a pulsed molecular beam produced by a piezo-electric driven, pulsed valve. This pulsed valve has a high pulse-to-pulse stability (time profile), and allows the study of catalytic processes on supported clusters at relatively high pressures (up to 10 mbar). Furthermore, a stainless steel tube is attached to the pulsed nozzle in order to collimate the molecular beam and to expose the reactant molecules to the substrate only. The pulse duration at the position of the sample can, in principle, be varied from 1 ms up to continuous operation. For the experiments described below a constant pulse duration of about 100 ms was used. The repetition rate of the pulsed valve can be up to 100 Hz. The experiments were carried out at 0.1 Hz the 10 s interlude allows the reactant gas to be pumped completely. 

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