Highly efficient finishing of large-sized single crystal diamond substrates by combining nanosecond pulsed laser trimming and plasma-assisted polishing

Diamond is an ideal material for fabricating functional components applied in power devices, heat spreaders, and surface acoustic wave. However, diamond's extreme hardness and brittleness nature makes it difficult to grind and polish to meet the roughness requirement for such applications. In this study, a novel hybrid process combining nanosecond pulsed laser trimming comprising a series of selective laser plane ablation (LPA) and plasma-assisted polishing (PAP) was proposed to flatten and smooth large-sized single-crystal diamond (SCD) substrate. When LPA was performed on an uncoated SCD substrate, deep explosion caverns and cracks were generated. Meanwhile, the material was uniformly removed by a few microns when an Au-coated SCD substrate was processed by LPA with the same conditions, in which a self-maintaining graphite layer on SCD surface was generated, and material was removed as a graphite "piston" penetrated into SCD substrate. In the validation of the proposed hybrid process, 10 and 20-mm square Au-coated SCD substrates were flattened by laser trimming for 79 and 538 s, reducing the p–v value of the entire SCD surface by ∼70 and ∼150 μm, respectively. Subsequently, the laser-trimming-processed SCD substrates were smoothed by PAP for 6.5 and 34 h, obtaining flatness of 0.2 and 1 μm or less, and surface roughness of 0.51 and 0.53 nm for SCD substrates of 10 and 20-mm square sizes, respectively. Proven by spectrophotometer and Raman results, no non-diamond phase was generated in the bulk of SCD during laser trimming and diamond surface was detected after hybrid process.