Application of ultra-thin aluminum oxide etch mask made by atomic layer deposition technique

Abstract

Ultra-thin layers of aluminum oxide (less than 1 nm) were grown by atomic layer deposition (ALD) technique on hydrogen-terminated silicon substrates. A new technique, called "plasma defect etching", was proposed for the continuity evaluation of such a layer. The layer was examined by using it as a mask in silicon etching at cryogenic temperatures in a DRIE reactor. The etch profile was characterized by scanning electron microscopy (SEM) and atomic force microscopy (AFM) techniques. Island formation during initial cycles was confirmed. Thicker aluminum oxide layers (1-5 nm thick) were patterned by wet or dry (plasma) etching and used as a mask for deep silicon etching at cryogenic temperatures in a DRIE reactor, using SF 6 and O 2 gas mixture. We found aluminum oxide to be an extremely resistant mask, etched only 0.05 nm/min. The value for the Si to Al 2 O 3 selectivity reached 70 000:1.

Investigating the Trimethylaluminium/Water ALD Process on Mesoporous Silica by In Situ Gravimetric Monitoring

“…In general, this question is not easy to answer, due to the unknown structure and dimension of such a monolayer [29,30]. The very first layer of a new material on a well-defined crystal structure e.g., SiO 2 crystal or Si wafer, most probably follows the already given crystallinity of the support material (epitaxy).…”

Silicon Porosification: State of the Art

“…This material has extreme selectivity (66 000:1), a fully conformal deposition profile, a deposition temperature of 85 • C, and it does not inflict micromasking. 300,341,342 The pattern transfer to the Al 2 O 3 layer can be done accurately, even when isotropic wet etchants such as phosphoric acid or hydrofluoric acid are used, because an alumina layer that is just a few nanometers thick is enough for through-wafer etching. Silicon nitride is an excellent masking material in KOH etching, but it is consumed quite rapidly during DRIE of silicon.…”

Luminescent Properties of Porous Silicon

“…Amorphous alumina (Al 2 O 3 ) combines the good properties of aluminum and silicon dioxide. This material has extreme selectivity (66,000:1), a fully conformal deposition profile, a deposition temperature of 85°C, and it does not inflict micromasking (Dekker et al 2006;Chekurov et al 2007;Grigoras et al 2007;Sainiemi 2009). The pattern transfer to the Al 2 O 3 layer can be done accurately, even when isotropic wet etchants such as phosphoric acid or hydrofluoric acid are used, because an alumina layer that is just a few nanometers thick is enough for through-wafer etching.…”