Application of laser-cleaning technique for efficient removal of via-etch-induced polymers

Abstract

A relatively new approach in removing the sidewall and bottom polymers resulting from reactive ion etching of via holes using a noncontact, dry laser-cleaning technique has been investigated. Pulsed excimer laser irradiation at 248 nm has been found capable of removing tbe via-etched-induced polymers at fluences limited by the damage threshold of the underlying Al-Cu metal film with TiN antireflective coating Experimental results have shown that the Al-Cu metal film with TiN coating has a damage threshold of about 250-280 mJ cm-2. This is confirmed by simulations of the laser interaction with the via structure. A fluence window of 150-200 mJ cm-2 for efficient laser cleaning is also determined from the ablation rate data using tbe relation in the limit of Beer's law absorption. Results have also shown that the ablation rate when irradiating at an angle is not only comparable to that at vertical incidence but even registers higher values for most of the ablation rate data obtained. An optimum incident angle for laser cleaning of 45° can be determined from the results.