Investigation on the variation of the step-terrace structure on the surface of polished GaN wafer

- An atomic step-terrace structure was achieved on GaN surface after CMP.
- Double step-terrace structure (a-a or a-b type) on GaN surface was confirmed, and the two types can be controlled by adjusting the abrasive concentration.
- The material removal mechanism of GaN according to the variation of atomic step-terrace morphology was presented.

An atomic step-terrace topography could be achieved on the surface of gallium nitride (GaN) wafer when it was polished by our colloidal silica (SiO2) based slurry. The corresponding roughness was as low as 0.07 nm (scan area 1 × 1 µm2). The atomic step-terrace topography was proved to be determined by the crystal structure of GaN. Due to the variation of atomic step-terrace topography, the effects of chemical components and mechanical factors on the material removal mechanism were investigated. The results showed that the topography would not be destroyed when adopting slurry with reagent only, and the chemical components could only act on the reactant of GaN. However, in case of SiO2 abrasives were added into the slurry, the step edge on the GaN surface would be disrupted after polishing. Moreover, the step-terrace structure could be changed by adjusting the abrasive concentration in the slurry. A double step-terrace structure with two types (a-a or a-b type) was observed, and the total widths of both the two type double step-terrace structure were the same.