Nanoscale Chemically Self-Aligned Thin Films Using Simultaneous Adjacent Deposition and Etching

For electronic circuit fabrication, deposition and etching are commonly performed as individual processes in separate reactor systems. Several vapor/surface exchange and conversion reaction mechanisms are known where material deposition simultaneously liberates another volatile species at the surface deposition site. In contrast, surface reactions that achieve simultaneous delocalized deposition and etching in neighboring regions on a patterned surface are not well known. We have recently discovered that at low temperature (<400°C) using a single set of vapor phase reactants, it is possible to achieve deposition in a desired growth region while simultaneously etching a neighboring region on a patterned film surface. As a primary example, we find that at 220°C, atomic layer deposition (ALD) of tungsten can proceed simultaneously with chemical vapor etching (CVE) of TiO₂. For a range of materials and process conditions, thermodynamic modeling confirms that deposition and etching are both energetically favorable. Akin to high temperature selective epitaxy reactions, the resulting net deposition is inherently self-aligned with the pre-patterned starting surface because the etching reaction locally consumes the deposition reactant, thereby avoiding unwanted nuclei. Using simultaneous deposition and etching, we show area-selective deposition of tungsten on nanopatterned surfaces with 200 nm half-pitch. Thermodynamic modeling and initial experimental results show that the concept extends to a range of other material systems, indicating that simultaneous deposition and etching provides opportunities for low temperature bottom-up self-aligned patterning for electronic and other nanoscale systems.