<title>Fast in situ processing for multichip high density interconnects</title>

Abstract

Three different approaches to fast in situ processing of metal contacts are studied. The goal is to make high density interconnects with width, thickness and pitch respectively of the order of 10, 5 and 25 microns. The direct writing speed should be equal to or faster than 1 cm per second, while maintaining good electrical conductivity and surface adhesion of the metal stripes. The first approach is the classical laser chemical vapor deposition of copper from its bishexafluoroacetylacetonate (Cubishfa) precursor, which is pushed towards the practical limits of maximum writing speed. Seeding of the transparent glass-like substrates with layers of different metals and oxides which are extremely thin helps to increase the writing speed of this process significantly without substantially influencing the substrate's electrical properties. Writing speeds close to 1 cm l are attained. The second approach is to deposit metal from surface layers of metalorganic (MO) cluster compounds like Au55(P03)12Cl6 which have advantageous thermochemistry for the decomposition as well as a high metal content in the MO precursor. Such compounds can be decomposed with a laser to yield quite pure gold lines at speeds up to 10 cm s1. Such layers are also irradiated with ion and electron beams in an effort to try to make submicron metal contacts. The third approach consists of a fast in situ step in which the surface is locally prenucleated by decomposing an ultrathin MO layer with a photon or particle beam. In a second slow parallel processing step, a large number of prenucleated substrates are then developed. The latter implies the selective metal deposition exclusively on top of the prenucleated stripes to create several micron thick metallic electrical contacts. We report on the selective metal deposition on ultrathin Pt prenucleation layers by electroless deposition from a copper sulfate bath, by decomposition from a copper formate solid surface layer, and by low pressure chemical vapor deposition from gaseous Cubishfa. Prenucleation was also tested with other metals.