Pulsewidth Dependence of Laser Scribing of Transparent Conductive Oxides in the Picosecond Regime

Abstract

Continuous improvement and innovation in laser processing methods and laser architectures are needed to further improve device efficiencies and reduce overall device manufacturing costs. In particular, P1 and P3 laser scribes of transparent conductive oxide layers, such as F:SnO2 or Al:ZnO (AZO) employed in thin film solar cell devices conventionally have been processed by Q-switched diode-pumped solid state lasers (DPSS) operating in the nanosecond regime. The principal wavelength employed for F:SnO2 scribing has been in the near infrared at or near 1064 nm while AZO has also been widely scribed at harmonic wavelengths, including in the near ultraviolet at or near 355 nm. Scribes produced with these laser systems often display undesirable sidewall non-uniformities, heat affected zones, film lift off, cracking, and excessive residual debris. Further, Q-switched DPSS laser architectures face scaling challenges as improvements in beam positioning technology demand laser performance at pulse repetition frequencies substantially higher than 200 KHz in order to keep pace with improvements in beam positioning speed and overall system throughput requirements. In addition, the lifetime and reliability of Q-switched ultraviolet DPSS lasers are well-known to be negatively impacted by the high photon energy in comparison to comparable pulse energy infrared laser systems. Recently, substantial work has been performed to investigate the effectiveness of sub-nanonsecond lasers on key laser scribing processes, including P1 molybdenum and P2 and P3 CdTe and a-Si scribes. In this work, we extend these investigations to evaluate the pulsewidth dependence of TCO laser scribe process performance and quality produced by 1064 nm master oscillator fiber power amplifier (MOFPA) laser systems in the picosecond regime.