Highly anisotropic reactive ion etching of Bi0.4Sb1.6Te3 thermoelectric films via optimized CH4/H2/Ar plasma chemistry

Etching serves as a core process in the patterning of micro- and nano-devices, directly influencing the precision and performance of miniaturised components. Particularly for Bi 2 Te 3 -based thermoelectric films, these exhibit broad application prospects in flexible electronics, infrared sensing, and on-chip thermal management. However, challenges such as lateral undercutting, deviations in stoichiometric ratios due to elemental selectivity, and residual surface polymers during etching severely constrain the performance of such devices. Here, the reactive ion etching (RIE) process of p-type Bi 0.4 Sb 1.6 Te 3 films in CH 4 /H 2 /Ar plasma is comprehensively investigated, revealing the synergistic regulation mechanism of gas chemistry, physical bombardment, and ion energy on etching behaviour. Results indicate that the CH 4 /H 2 ratio governs the etching pathway: low CH 4 /high H 2 conditions enable highly anisotropic etching but predispose to selective Te etching; increasing CH 4 improves uniformity, yet excessive levels induce carbonaceous deposits. Furthermore, the Ar flow rate effectively modulates surface morphology through physical bombardment, while radiofrequency (RF) power requires balancing etch rate enhancement with surface integrity preservation. Subsequently, optimised process parameters were established at CH 4 (2 sccm)/H 2 (20 sccm)/Ar(15 sccm) with RF power set at 200 W, achieving high anisotropy (nearly vertical sidewalls), a clean surface, and favourable thermoelectric performance. This research provides crucial guidance for the precision patterning of Bi 2 Te 3 -based micro-thermoelectric devices.