James N. O'Brien

Picosecond laser micromachining of advanced semiconductor logic devices

Advanced semiconductor logic devices are increasingly complex, typically composed of multiple layers of dielectric, metal, and semiconductor materials. Laser micromachining is employed on these devices to form cut-outs, microvias, and perform partial material removal, including scribing and dicing operations. The recent development of high average power (> 10 W), < 20 ps, 1064 nm diode-pumped mode-locked solid state lasers, operating at pulse repetition frequencies > 100 KHz, enables an attractive short pulsewidth laser process alternative to existing nanosecond process technologies, particularly for laser micromachining of complex alloy structures. Emerging 45 and 65 nm node logic devices may contain greater than eight metal layers, typically aluminum and copper. They may also contain advanced low K layers which have proven difficult to process using conventional mechanical techniques, such as dicing saws. Efficient operation at 355 nm was readily achieved using extracavity conversion by employing non-critically phasematched LBO for SHG and critically phase-matched LBO for THG. Over 3 W at 355 nm at 100 KHz was achieved with an input of 8.5 W at 1064 nm. Preliminary micromachining results on advanced logic devices containing multiple low k and Cu layers at harmonic wavelengths (532 nm and 355 nm) yielded micromachining rates of > 300 mm/s with good workpiece quality.