End point detection and control of laser induced dry chemical etching

Abstract

An end point detection technique indicates when a pulsed excimer laser, operating on a chromium clad copper substrate in the presence of chlorine gas, has etched through the chromium layer. The excimer laser vaporizes successive layers of the chromium chloride reaction product, which form on the region being etched, until, when all of the chromium has been removed from the region, a copper chloride reaction product layer forms on the region and is vaporized. A dye laser directs a probe beam into a zone spaced above the region being etched and is pulsed about 12 microseconds after each pulse of the excimer laser to allow time for the vaporized reaction products to reach the zone. The probe beam has a first wavelength of 433.3 nm. which induces the vaporized copper chloride in the zone to fluoresce at a second wavelength of 441.2 nm. A narrow band photodetector detects the fluoresced 441.2 nm. wavelength light to indicate that the end point has been reached, and the detection of the end point is used to terminate the pulsing of the excimer laser to end the etching process.