Acoustic Microscopy: Recent Applications in Semiconducting Devices

In recent works we have demonstrated that the acoustic microscope using focussed lenses was able to image through or inside opaque materials. Metallic liquids such as mercury are necessary to insure the transit of acoustic energy towards the object with minimum losses. The operating frequency can be easily raised up to 2 gigahertz with a conventionna] 0.2 millimeter diameter lens , corresponding to a resolution in the range 0.3 to 1 pm and a penetration up to 20 wm. Typical applications are reported such as annealing polycristalline silicon on monocristalline silicon by means of a beam laser scan. On the other hand, we present the low frequency microscope operating in the range 50 to 200 MHz with a lens diameter around 5 millimeters which allows a penetration of about 0.5 millimeter in silicon with a lateral resolution of the order of 10 microns. Applications in non destructive evaluation of bonding contacts of integrated circuits are shown.