Product Code: JLA_5_1_13

Authors:
R. Patel
G. Baisch
IBM Corporation, GTD, Hopewell Junction, New York

Since the early 1980's discovery of the ability of excimer lasers to etch polymers precisely and cleanly with minimal thermal damage, excimer lasers have been used actively in the semiconductor industry for various manufacturing processes. In the present study a process for laser cutting of polymers has been investigated. A laser beam of controlled cross‐sectional shape is imaged onto a polymer surface. The geometry of the cutting path is controlled by precise movement of a sample mounted on a 2‐axis computer controlled work stage. This type of a process is useful for applications such as selective laser cutting or laser marking of polymers. A parametric study of laser cutting of polymers using a 30 watt average power, 308 nm wavelength, XeCl pulsed laser was carried out. The effect of incident laser fluence and laser frequency were studied to determine maximum single pass cutting speed for a given thickness of polymer. Three different types of polymers were studied. Polymer films of different thickness were spin‐coated on a silicon wafer and were cured to their respective full cure temperature. Polymer thicknesses from 7 microns to 38 microns were studied. Incident laser fluence was varied from 200 mj/cm² to 1.0 J/cm². Laser frequency was varied from 1 Hz to 50 Hz. An analytical formula for optimum single pass cutting speed as a function of the etch rate of a polymer, laser frequency, laser beam length in cutting direction, and polymer thickness was developed. Experimental results obtained indicate that cutting speed is directly proportional to the incident laser fluence and laser frequency, and is inversely proportional to polymer thickness. Predictions of optimum cutting speed obtained from the analytical formula for different polymers were in good agreement with the experimentally measured values.