Effects of Chemical-Electrical and Mechanical Parameters on Electrical-induced Chemical Mechanical Polishing of GaN

Overcoming the low fabricating efficiency of traditional chemical mechanical polishing (CMP) for Gallium nitride (GaN) is a challenge owing to its high hardness, high brittleness, and chemical inertness. Here, electrochemical etching is proposed to increase the material removal rate and acquire a high-quality surface on GaN wafers. To reveal the synergistic etching mechanism of oxidizing agent and corrosion inhibitor on the GaN wafers, electrochemical etching experiments were carried out. The optimal etching solution contained 4 wt% H2O2 and 10 mmol/L purified terephthalic acid. Experiments with various polishing parameters were comparatively investigated to verify the auxiliary effect of etching and determine the ideal parameters. Cathodoluminescence spectroscopy shows that the electrochemical etching removes the SSDs completely and the CMP process with befitting parameters does not induce supernumerary SSDs.

Zr-Th-U MINERALS IN HIGH-MG DIORITE OF THE CHELYABINSK MASSIF (SOUTH URALS) – EVIDENCE FOR CRUST–MANTLE INTERACTION

Zr-Th-U minerals, namely baddeleyite, zircon and U-Th-oxide, were found in high-Mg diorite from the Late Devonian – Early Carboniferous synplutonic dyke in granodiorites of the Chelyabinsk massif, South Urals. Micron-sized minerals were investigated by electron microscopy and cathodoluminescence spectroscopy. Their chemical compositions were determined by electron probe microanalysis that was optimized to ensure more precise measurements of the composition of minerals. Baddeleyite grains are found as inclusions in amphibole crystals and reside in intergranular areas. The former retain their composition and show no traces of corrosion or substitution. In the intergranular areas, baddeleyite grains were replaced by polycrystalline zircon due to the reaction with an acid melt, and the U-Th-oxide precipitated inside baddeleyite simultaneously, which suggests the restite origin of baddeleyite. The main features of the baddeleyite composition are extremely high concentrations of ThO2 and UO2 (to 0.03 wt. % and 1.0 wt. %, respectively), which may be due to the metasomatic interaction between the mantle peridotite and the crustal or carbonatite fluid or melt.