Coarse Polishing Research Articles

Sequential multiple-laser-assisted polishing of free-standing CVD diamond substrates

Abstract Diamond, the best thermal conductor known, is the ultimate choice as a substrate material for the fabrication of denser, smaller and faster electronic packages. Consequently, in recent years, worldwide efforts have focused on the design of manufacturing transparent technologies for post-synthesis processing (polishing, planarization, metallization, die attach,, etc.) of diamond substrates In this study, a manufacturing-transparent, cost-effective, non-vacuum, laser-assisted coarse polishing technique for thick free-standing CVD diamond substrates was investigated [2]. The thickness of the substrates varied from 700 to 1000 μm, with the average grain size ranging from 150 to 200 μm. The average surface roughness (Ra) of the substrates, measured using contact surface profilometry, was between 20 and 30 μm. The substrates were initially irradiated with a Nd-YAG laser (λ = 532 nm) for coarse material removal, followed by an ArF excimer laser (λ = 193 nm) for finer surface finishing. Under optimized conditions, the average surface roughness (Rrma) was reduced from 25 to 5 μm with the Nd-YAG laser, and further to less than or equal to 1 μm with the excimer laser. The technique, which is the fastest processing technique known to the authors, is capable of polishing a 1 cm × 1 cm × 0.07 cm substrate in 50 s.

Reduction of ac losses of Nb3Sn by surface treatment

Large reductions in the ac losses of Nb3Sn were obtained by surface treatment of thick layers of Nb3Sn formed by reacting Nb-1% Zr with liquid tin. The surface treatments studied were chemical etching, electropolishing, and mechanical polishing. The significant reduction in the losses is attributed to the removal, by polishing, of a porous outer layer of Nb3Sn which forms at the Nb3Sn–liquid-Sn interface and extends into the material. The porosity of this layer results in low surface and bulk current densities (hence high losses) compared to the material further away from the surface. Low losses (∼1 μW/cm2 at 500 rms A/cm) can be obtained by fine mechanical polishing, electropolishing, or chemical etching of the surface. Mechanical polishing can produce the smoothest surfaces but introduces damage beneath the surface which is detrimental to achieving very low losses. When this damaged layer is either etched away or annealed, however, the losses can be made smaller than 1 μW/cm2 at 500 rms A/cm. The lowest losses were obtained by annealing after rather coarse mechanical polishing. This behavior is attributed to the creation of new pinning centers near the surface after cold working and annealing.