Performing an ultrasound on a wafer to align it

Using very high-frequency sound waves, researchers at ARCNL have found a way to detect nanostructures buried under many layers of opaque material. Their findings may be useful to spot grating lines used for wafer alignment during semiconductor manufacturing. As these indispensable markers get buried deeper and deeper under layers of materials during the manufacturing process, they become harder and harder to spot with the technique that’s normally used: light.

Fortunately, many materials that are opaque to light do pass on sound waves. So similar to performing an ultrasound, the ARCNL researchers sent sound waves into layers of materials you might find on a wafer, stacked on top of a grating. Actually, they shot short laser pulses at it, knowing this would induce high-frequency sound waves in the opaque material. The frequency of the waves is much higher than those used in medical echoes – the higher the frequency, the smaller the features that can be discerned. Obviously, for finding nanostructures, very high-frequency waves are necessary.