Impact of Etch Processes on the Chemistry and Surface States of the Topological Insulator Bi 2 Se 3 .

The unique properties of topological insulators such as Bi ₂ Se ₃ are intriguing for their potential implementation in novel device architectures for low power and defect-tolerant logic and memory devices. Recent improvements in the synthesis of Bi ₂ Se ₃ have positioned researchers to fabricate new devices to probe the limits of these materials. The fabrication of such devices, of course, requires etching of the topological insulator, in addition to other materials including gate oxides and contacts which may impact the topologically protected surface states. In this paper, we study the impact of He ⁺ sputtering and inductively coupled plasma Cl ₂ and SF ₆ reactive etch chemistries on the physical, chemical, and electronic properties of Bi ₂ Se ₃ . Chemical analysis by X-ray photoelectron spectroscopy tracks changes in the surface chemistry and Fermi level, showing preferential removal of Se that results in vacancy-induced n-type doping. Chlorine-based chemistry successfully etches Bi ₂ Se ₃ but with residual Se-Se bonding and interstitial Cl species remaining after the etch. The Se vacancies and residuals can be removed with postetch anneals in a Se environment, repairing Bi ₂ Se ₃ nearly to the as-grown condition. Critically, in each of these cases, angle-resolved photoemission spectroscopy (ARPES) reveals that the topologically protected surface states remain even after inducing significant surface disorder and chemical changes, demonstrating that topological insulators are quite promising for defect-tolerant electronics. Changes to the ARPES intensity and momentum broadening of the surface states are discussed. Fluorine-based etching aggressively reacts with the film resulting in a relatively thick insulating film of thermodynamically favored BiF ₃ on the surface, prohibiting the use of SF ₆ -based etching in Bi ₂ Se ₃ processing.