Advanced semiconductor metrology using picosecond laser ultrasonics

Picosecond laser ultrasonics, or picosecond ultrasonics, is a technique for studying materials using high frequency acoustic pulses generated and detected by ultrashort optical pulses typically <1ps in duration. The technique can be used to characterise materials with nanometre spatial resolution making it a ‘go to’ technique for accurately measuring the thickness of semiconductor thin films.

Using this technique – semiconductor device developers can determine the quality of the bonding between a film and a substrate, which gives information about a device’s mechanical properties. This information is critical as the overlay and alignment of a lithographically defined pattern on top of an underlying layer is fundamental to device performance. The picosecond ultrasonic technique is particularly valuable to semiconductor device production flows where there may be an opaque layer that interferes with the measurement. In such cases, conventional methods of alignment using light fail.

The Chromacity 520 is a robust and reliable 520nm femtosecond laser system that can be used as a fixed wavelength source to deliver ultrashort pulses with high average powers in the green spectral region. This compact, high-performance laser does not require water cooling and comes with a simple user interface, making it one of the easiest and affordable laser sources to operate. The compact housing of the Chromacity 520 enables simple system integration.