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 SF6 and O2 gas mixture. We found aluminum oxide to be an extremely resistant mask, etched only 0.05 nm/min. The value for the Si to Al2O3 selectivity reached 70 000:1.