VERFAHREN ZUM AUFFINDEN EINES BEVORZUGTEN PUNKTES FÜR EINEN LASERSTRAHL IN EINEM LASERSTRAHLINTERFEROMETER UND LASERINTERFEROMETERAPPARAT

摘要

The disclosure relates to a method for endpoint detection in a semiconductor wafer etching ysstem characterised in the steps of: 1) scanning a semiconductor wafer (10) with a narrowly focussed laser beam (24); 2) analyzing a reflected portion of the beam to determine a preferred parking spot (P) on a preferred flat area (#8) of the wafer; 3) parking the beams at the preferred spot; and 4) analyzing the reflected portion of the beam to determine when the preferred flat area has been etched through. The beam spot (18) of the laser beam (24) is amller than the width of the preferred flat area to eliminate noise generated at the transition boundaries of the flat area. Preferably, the wafer is scanned several times along the same beam path to permit the comparison of several scans to determine the preferred parking spot. The apparatus includes a beam forming assembled (62, 64, 66); a scanning assembly which causes the laser beam to scan across the wafer; a detection assembly (76) responsive to a portiom of the laser beam which is reflected off the wafer; and a controller (78) which operates the laser and the scanning assembly and which is responsive to an output of the detection assembly. When output of the detection assembly indicates a cessation of the characteristic etching curve, the controller develops an endpoint detection signal which can automatically shut down the etching system.