Fabrication of atomic-level step-terrace structure of sapphire using atmospheric pressure plasma

Abstract

Sapphire with atomic-level step-terrace structure is a high-quality epitaxial growth substrate. However, the traditional manufacturing methods combining chemical mechanical polishing (CMP) and high-temperature annealing (HTA) are limited by processing efficiency and the size of the annealing furnace chamber. This study proposes a novel process for fabrication of atomic-level step-terrace structure of sapphire using atmospheric pressure plasma. Firstly, microwave plasma-assisted polishing (MW-PAP) is used to rapidly reduce the roughness of the lapped surface, and then subsurface damage is repaired and the step-terrace structure is formed by plasma-enabled atomic-scale reconstruction (PEAR). Surface composition and morphology analyses have shown that based on the mechanism of hydroxyl dehydration condensation, MW-PAP can reduce the Sa roughness from 146 nm to 4.6 nm within 30 min. Subsurface characterizations indicate that during the MW-PAP process, the surface damage layer is converted into an amorphous phase and rapidly removed. The amorphous layer and sub-surface damage are repaired in the subsequent PEAR process, leading to an improvement in sapphire crystallinity. Additionally, in situ scratching experiments indicate that during the PEAR process, scratches can be healed under the influence of atomic migration due to plasma irradiation. Simultaneously, driven by the minimization of surface energy, surface atoms are induced to migrate and the step-terrace structure is formed. The plasma-based hybrid processing is conducted in an atmospheric environment, enabling the formation of step-terrace structure from lapped sapphire in approximately one hour, which is expected to enrich the manufacturing theory of high-quality substrates.