APPLICATION OF LASER-CLEANING TECHNIQUE FOR EFFICIENT REMOVAL OF VIA-ETCH-INDUCED POLYMERS

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 las er irradiation at 248 nm has been found capable of removing the via-et ched-induced polymers at fluences limited by the damage threshold of t he underlying Al-Cu metal film with TiN antireflective coating. Experi mental results have shown that the Al-Cu metal film with TiN coating h as a damage threshold of about 250-280 mJ cm(-2). This is confirmed by simulations of the laser interaction with the via structure. A fluenc e window of 150-200 mJ cm(-2) for efficient laser cleaning is also det ermined from the ablation rate data using the 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 vertic al incidence but even registers higher values for most of the ablation rate data obtained. An optimum incident angle for laser cleaning of 4 5 degrees can be determined from the results.