Influence of exposure energy and heat treatment conditions on through-glass via metallization of photoetchable glass interposers

Abstract Photoetchable glasses (PEGs) have been widely used in three-dimensional integrated circuits as interposers. However, the high costs associated with laser through-hole technology have limited their utilization in high-frequency circuitry and packaging. Ultraviolet lithography may reduce the cost and improve through-hole properties allowing PEGs to become a preferred practice and lend them to wider usage. Herein, we investigate the viability of PEGs by systematically studying the structural, compositional, and morphological properties of their through-hole composite structures as a function of several key process parameters including exposure energy and annealing conditions. Results indicate that both exposure energy and annealing temperature and duration have compensating effects. Optimized through-glass vias (TGVs) were determined to result from an annealing temperature of 560 °C, an annealing time of 60 min, and an exposure energy of 6 J/cm2. Metallization of through-holes was carried out using magnetron sputtering of an adhesion layer of Ti followed by a Cu layer. The morphology and composition of through-hole metallization, analyzed by electron microscopy and energy dispersive X-ray spectroscopy, revealed surfaces to have sharp, well-defined edges with smooth surfaces. The proposed PEG interposer processing methodologies described here offer renewed optimism for the efficient fabrication of channels and through-vias for microfluidic and integrated circuits and other three-dimensional electronic and hybrid systems.