Gold films were deposited on quartz-crystal microbalances by decomposing C7H7F6O2Au (dimethyl gold hexafluoroacetylacetonate) with 2–10-keV Xe+, Kr+, Ar+, Ne+, or He+ ion beams. The number of molecules decomposed per incident ion (i.e., the total decomposition yield) was determined as a function of ion mass and energy. The total decomposition yield increases with increasing ion mass and ion energy, and is approximately proportional to the nuclear stopping power. A binary collision model and a thermal spike model are developed that relate the energy deposited by the ion, at the substrate surface, to the total number of molecules decomposed. Both models predict total decomposition yields that are in reasonable agreement with the experimental measurements; however, the variation of total yield with changes in ion mass and energy are best described by the binary collision model. The success of both models demonstrates that the energy deposited into the substrate surface through the ion-solid interaction is responsible for the decomposition of adsorbed molecules.
A finely focused ion beam is scanned over a surface on which a local gas ambient of dimethyl gold hexafluoro acetylacetonate is created by a directed miniature nozzle. The incident ions induce the selective deposition of gold along the path traced by the beam. The 15-keV Ga+ ion beam current is 100 pA and the beam diameter is 0.5 μm. Gold lines of 0.5 μm width and Gaussian profile are written. The film growth rate corresponds to five atoms deposited per incident ion. The focused ion beam deposited films contained 15% Ga, but less than 5% of other impurities, such as O or C. Deposition was also observed with broad ion beams of 750 eV Ar+ and 50 keV Si+. The resistivity of the films varied from 2×10−5 to 1.3×10−3 Ω cm.
Gold films were deposited on quartz crystal microbalances (QCM) by decomposing C7H7F6O2Au [dimethyl gold hexafluoroacetylacetonate, or DMG(hfac)] with a 5 keV argon ion beam. A model for ion beam induced deposition is presented which relates the net deposition yield to the gas adsorption, the decomposition cross section, and the sputtering yield. The deposition rate was measured in situ as a function of ion current, gas pressure, and substrate temperature using the QCM. The deposition yield (mass deposited per incident ion) increased with increasing gas pressure and decreasing substrate temperature. The QCM was also used to measure the adsorption of DMG(hfac). The results demonstrated that the variation in deposition yield with temperature and pressure was proportional to the number of DMG(hfac) molecules adsorbed per cm2. Based on the observed correlation between deposition yield and adsorption, a decomposition cross section for 5 keV argon ions of 2×10−13 cm2 was estimated.
An experimental system for measuring ion-beam-induced deposition yield is described. Gold films were deposited on quartz-crystal microbalances (QCM) by decomposing dimethyl gold hexafluoroacetylacetonate molecules (C7H7F6O2Au) with a 5-keV argon-ion beam. The QCMs provide an in situ measurement of the deposition rate as a function of ion dose, dose rate, gas pressure, and substrate temperature. The deposition yield, or mass deposited per incident ion, is shown to increase with increasing pressure and decreasing temperature. The yield is independent of the ion dose rate, which implies that the deposition process is not due to macroscopic heating. The deposition yield is shown to depend on the sputter yield of the substrate. The density of the deposited films was determined to be about 10 g/cm3, which is about half the density of bulk gold (19.3 g/cm3). The difference in density is due to carbon contamination in the deposited films.
The influence of diffraction on the shape and size of features printed using x-ray proximity printing is reviewed, and the effect of image blurring on these results is described. Diffraction can alter the shape of a printed feature, and the systematic shape changes observed in resist images can be explained using simple scaling based on Fresnel diffraction. In addition, the linewidth change with exposure dose is independent of feature type and size, and depends only on the square root of the mask to wafer gap. The shape of printed features and the linewidth change with dose can be modified by smearing the aerial image at the wafer plane. This can be achieved by adding beam divergence or by varying the angle of incidence of the x-ray beam onto the mask (wobbling). A technique for incorporating wobble into an exposure system is described, and exposures of contact holes, spaces, lines, and line-space arrays using this technique are presented. For example, 0.35 μm square contact holes normally print diamond shaped at a 40 μm gap. However, the same contact holes are round in resist when 4 mrad of wobble is incorporated into the exposure. The linewidth change for a 10% increase in dose is 24 nm at a 40 μm gap with 5 mrad of wobble. This linewidth change with exposure dose is larger than the 20 nm measured for exposures at a 40 μm gap without wobble. Finally, wobbling during exposure can either increase or decrease the absolute linewidth of a feature in resist at a given exposure dose.
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