Selective-Area Laser-Assisted Processing for Microelectronic Multi-Chip Interconnect Applications

ABSTRACTLaser direct-write processes are attractive complements to traditional methods of fabricating microelectronic circuitry. This paper is a summary of our work in applying such processes to high-density inter-chip interconnection modules, such as those using copper conductors on polyimide dielectric layers. We begin by discussing the requirements which laser processes must satisfy in order to be useful in this application. An analytical model of laser heating is then described, which aids in understanding the thermal problem of absorption of visible-wavelength laser light by polyimide. Calculations using this model are consistent with experimental observations. Finally, we focus on one laser processing technique: laser chemical vapor deposition. We describe a new process for laser chemical vapor deposition of tungsten on polyimide, which enables the formation of low resistance contacts (≈ 0.1 Ω) between the deposited tungsten films and pre-patterned nickel-coated copper conductors. Lines approximately 30 /m wide and 34 µm thick were deposited at a scan rate of 93 µm/s. From four-point resistance measurements of different lengths of deposited films, the tungsten film resistivity is estimated to be two to three times the bulk value.