Laser release process to obtain freestanding multilayer metal-polyimide circuits

Abstract

Some applications in microelectronics call for freestanding polyimide films with fine metallic wiring patterns that are thinner than commercially available copper-clad polyimide sheets, which are typically greater than 25 μm in thickness. This work describes a laserassisted technique to fabricate freestanding multilayer thin-film wiring with polyimide dielectric insulating layers that are less than 10 μm thick. A release layer consisting of a thin polymeric film is first deposited on an optically transparent carrier and the multilayer thin-film structure is then fabricated on this substrate, with the polymeric release layer sandwiched between the transparent carrier and the multilayer structure. Excimer laser light passes through the transparent carrier and ablates the polymeric layer at the transparent carrier/polymer interface, resulting in separation of the sacrificial carrier from the multilayer structure. The optimal release process is carried out using a 308-nm XeCl excimer laser operating at a fluence of about 100 mJ/cm2.