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HL: Fachverband Halbleiterphysik

HL 44: Nitrides: Preparation and characterization II

HL 44.10: Vortrag

Donnerstag, 21. März 2024, 16:30–16:45, EW 015

Influence of Surface and Subsurface Damage on GaN Wafer Processing and Laser Facet Fabrication — •Saad Makhladi, Matthias Friedler, Johannes Enslin, Carsten Netzel, Ji-Hye Kang, Erik Freier, and Sven Einfeldt — Ferdinand-Braun-Institut (FBH), Gustav-Kirchhoff-Straße 4, 12489 Berlin, Germany

Backside wafer thinning is an inherent part of the process chain to fabricate diode laser chips, enabling precise wafer cleavage with a high structural quality of the laser facets. However, in the case of gallium nitride (GaN) wafers, their brittleness poses challenges for process control, limiting the process yield. To optimize the backend processing of GaN ridge waveguide laser chips, GaN laser wafers underwent backside thinning employing two different technologies, namely lapping and grinding. The laser chips from these wafers were compared. The investigation included a detailed evaluation of backside surface morphology, wafer edge conditions, and subsurface damage (SSD), with respect to crystallinity, stress and wafer bow. As a result of this study, the probability of unintentional breakage of the wafers during processing has been reduced by a factor of two. The bow radius of thinned chips increases from 0.35 m to 0.65 m, and the depth of the SSD is reduced from 2.1 m to 0.8 m by employing Grinding instead of lapping. Certain wafer backside features were found to lead to cracks, which have the potential to propagate during cleavage to enhance terrace formation. i.e., to reduce the facet quality. Further investigations involve subsequent polishing of the GaN wafer backside and studying its impact on the facet formation of GaN Lasers.

Keywords: Processing; Surface; Bow; Facets; Lasers