VUV synchrotron radiation processing of thin palladium acetate spin-on films for metallic surface patterning

Thin palladium acetate films have been used for laser deposition (or prenucleation) of palladium lines, which can be used as a catalyst for electroless plating of other metals, notably Cu, to build up thicker conductors. This palladium deposition process was carried out using a CW argon ion laser at 514.5 nm for the first time in 1987 [l] then at 351 nm [2]. This visible-laser-induced deposition of palladium is a photothermal process since the Pd-acetate film precursor has no significant electronic absorption above 350 nm (see spectrum (a) in fig. 3). Powerful visible laser radiation has to be used to heat up the absorbing area of a substrate to initiate a deposition and therefore, this process cannot be carried out on a transparent substrate like quartz. Further, UV extimer laser (ArF at 193 nm, KrF at 248 nm or XeCl at 308 nm) was used for the same processing [3] since the film precursor has strong UV absorption at about 210 nm (see spectrum (a) in fig. 3). Although the processing with the UV excimer laser pulses was carried out on UV transparent substrate like quartz, it was still doubtful whether this process is photolytic or photothermal when the laser fluence threshold for prenucleation had been found for each UV excimer laser wavelength (see Visible Ar+ (514.5 nm) lo5 W cm -z Gross et al. [l] Ar+ (351 nm) 104 w cm-’ Cole et al. [2] XeF (351 nm) > 200 mJ cm -2 Esrom and Wahl [3]