Optimizing the processing of sapphire with ultrashort laser pulses

Abstract

The ability to rapidly and precisely generate high-quality features with small dimensions in sapphire is paramount for broadening its appeal and expanding its utilization for consumer electronics applications. Intrinsic properties of sapphire, including high scratch resistance, make it an attractive option for these purposes, but the ability to machine fine features in sapphire substrates with common mechanical and laser-based methods has proved elusive to this point. In this study, we present results from a series of systematic trials to determine the optimum laser processing parameters for drilling 400 μm diameter holes with no cracks or chips and <5° taper in 430 μm thick sapphire wafers with a 0.8 ps 1030 nm source. Holes are drilled at repetition rates from 21 to 1042 kHz, overlaps from 70% to 98%, and translation of the beam waist through the sample at rates from 10 to 200 μm/s. We present qualitative and quantitative results generated from laser scanning microscopy demonstrating that holes with <5° taper and no cracks or chips can be drilled at repetition rates of 260 kHz with 90% and 95% overlap and 521 kHz with 95% overlap. We find that the optimum processing parameters for drilling holes with <5° taper correlates well with the conditions necessary for avoiding chipping, cracking, and back-side damage rings. Holes with <5° taper can be drilled in as short as 4–6 s per holes, and holes with <2° taper can be drilled in 10–12 s per hole.