Measurement of a micro-solderball height using a laser projection method

Abstract

This paper describes the use of a laser projection method for measuring the height of a micro-solderball/bump. In this method, the shadow of a bump on a semiconductor wafer to be investigated is cast onto the wafer surface by a fully collimated laser beam and the corresponding shadow image is recorded by a CCD camera mounted on a long-working distance microscope. Two methods of calculating the height of the solderball from its projected lengths are described. The experimental results obtained from these two methods are compared favourably with that obtained using a commercial optical profiler. © 2004 Elsevier B.V. All rights reserved.