Theoretical calculation of the acoustic force on a patterned silicon waferduring megasonic cleaning

We have calculated, theoretically, the acoustic pressure field around a lin ear pattern on a silicon wafer immersed in water subjected to a megasonic b eam. The method of calculation is based on a Green's function formalism. Th e acoustic force applied on the pattern by the pressure field is determined as a function of frequency and the angle the incident megasonic beam makes with the wafer surface. The calculation is applied to two types of feature s that may be encountered in megasonic cleaning of integrated circuits prio r to packaging, namely a micron-size silicon ridge and a metal wire (tens t o hundreds of microns in diameter) bonded on a silicon substrate. The calcu lated acoustic shear stress is found to be orders of magnitude smaller than the shear strength of the features. (C) 2000 American Institute of Physics . [S0021-8979(00)03017-6].