Area-Selective Atomic Layer Deposition of Al2O3 on GaN Using Microcontact-Printed Octadecylphosphonic Acid Layers

Abstract

Area-selective atomic layer deposition (AS-ALD) offers a promising bottom-up route for local dielectric patterning. On GaN, conventional subtractive patterning can introduce plasma-etch-induced damage that degrades interface quality and device performance. To address this issue, we developed a GaN-specific additive patterning route based on microcontact-printed octadecylphosphonic acid (ODPA) inhibitor patterns and thermal Al2O3 ALD at 200 °C, thereby avoiding conventional subtractive plasma etching of the dielectric. Combined density functional theory and experimental analyses of the printed ODPA layers on GaN show that increasing temperature depletes loosely bound physisorbed ODPA species and promotes condensation between ODPA molecules as well as between ODPA and the substrate. This leads to a more condensed and strongly anchored ODPA layer, delaying the initial nucleation of Al2O3 in the nongrowth region. As a result, Al2O3 deposition remains strongly suppressed in the nongrowth region for up to 120 ALD cycles, corresponding to an AES-derived apparent selectivity of 0.966. To improve compatibility with subsequent GaN processing, parasitic Al2O3 and residual ODPA species in the nongrowth region are removed by sequential acetic acid cleaning and O2 plasma treatment. AFM shows no obvious additional surface roughening after treatment, whereas XPS reveals limited oxidation of the exposed GaN surface. After 160 ALD cycles and post-treatment, a clear step height of ∼8.5 nm is obtained. This strategy provides a low-damage route to local Al2O3 dielectric patterning on GaN and may be used for local gate dielectric formation and spatially selective surface passivation.