Extracted from the paper presented at the poster session by M. ABOURIDA^a, H. GUILLON^b, C. JIMENEZ^b, J. M. DECAMS^b, O. VALET^a, P. DOPPELT^a, F. WEISS^c.

We have investigated the silver metallization by MOCVD using a mesitylene solution of a carboxylate silver complex as precursor. Silver films were grown on different substrates such as SiO₂/Si, MgO, and glass, by using a Qualiflow Inject liquid delivery and vaporization system.
Overall, a comprehensive study of the dependence of Ag film thickness, microstructure and crystallographic orientation on the main process parameters such as deposition temperature, deposition time and the substrate type was elucidated.

PURPOSE

Silver is the most conductive of all the metals and for this reason is potentially useful for high-speed microelectronics applications. Also, silver films were used as barrier to limit diffusion of high-temperature superconducting ceramics. Thus, silver is a reasonable alternative to more commonly used contact materials, such as copper and aluminium.
Owing to their good volatility, fluorinated compounds have been up to now the most commonly used MOCVD silver precursors. The presence of fluorine atoms, in these molecules, lead to liquid compounds and facilitated their evaporation in bubbling systems, but the drawback is that deposited films are often contaminated by fluorine impurities.

However, less volatile non-fluorinated silver compounds can be of good value when they are properly evaporated. Thus, silver carboxylates Ag(O₂CR), R = alkyl, constitute an alternative class of precursors for Ag CVD which, until very recently, appear to have been rarely used because of their poor volatility. To overcome the problem of poor volatility of this class of compound, an optimized liquid supplying and vaporization methodology has been developed and tested.
In this study, we report the successful use of 2,2-dimethylpropionate silver(I) (silver pivalate) previously reported as precursor for Ag metallization. Indeed, using the Qualiflow Inject liquid delivery and evaporation system we have been able to properly evaporate and deposit the previous silver precursor on different substrates such as SiO₂/Si, MgO, and glass.

RESULTS - Thickness and conductivity

According to the scanning electron microscope (SEM), the silver film thicknesses were in the range 250-800nm. Silver films grown at 275°C and above were all conducting and for almost all samples, the conductivity was closely related to the thickness. The SEM image of a cross section of the Ag/Si film grown at 280°C is shown in figure below. The film is dense, and of a high uniform thickness. The average film thickness was about 300 nm.

Silver films with continuous structures were found to be good conductors when they were carbon-free. Thus, at room temperature the electrical resistivity measurements was in the range 2-4 µOhm.cm, which is only slightly higher than the known value for bulk silver (1.587 µOhm.cm at 20°C).