Low temperature Topographically Selective Deposition by Plasma Enhanced Atomic Layer Deposition with ion bombardment assistance

Abstract

Area selective deposition via atomic layer deposition (ALD) has proven its utility in elementary nanopatterning processes. In the case of complex 3D patterned substrates, selective deposition processes lead to vertical sidewall coverage only, or top and bottom horizontal surface coverage only, to enable advanced nanopatterning and further miniaturization of microelectronic devices. While many fabrication strategies for vertical only Topographically Selective Deposition (TSD) have already been developed, the horizontal TSD case needs further attention. In this work, we propose a versatile route for the TSD on 3D top and bottom horizontal surfaces along with a proof-of-concept for such selective Ta2O5 thin film deposition. The strategy at stake relies on a plasma enhanced atomic layer deposition process assisted by energetic ion bombardment during the plasma step and followed by a postgrowth wet etching step. The effectiveness of this strategy is based on a careful adjustment of processing temperatures purposely set at low temperature, most probably below the ALD temperature window. Anisotropic ion bombardment via substrate biasing during the plasma step provides an extra amount of thermal energy only to exposed horizontal surfaces, which in turn enables a selective densification of the thin film under growth. The difference in thin film density on horizontal and vertical surfaces enables the property-selective etching of vertical surfaces, generating horizontal TSD. A proof-of-concept for such low temperature TSD is shown in the case of 3D trenched substrates with an aspect ratio of 14.