Atomic Layer Deposition and Patterning of 15-185 nm Thick Al₂O₃Films with Microplasma Arrays for Low-Temperature Growth and Sub-300 nm Lateral Feature Resolution

Aluminum oxide (Al2O3) films 15-185 nm in thickness have been grown on Si(100) by a modified atomic layer deposition (ALD) process in which the oxygen precursor is dissociated by a 50 × 20 array of microcavity plasmas. The unique characteristics of microplasmas with respect to electron temperature, specific power loading, and operation at elevated pressures enable the efficient dissociation and excitation of strongly bound precursors such as O2. Microplasma arrays are also sufficiently compact so as to be situated in proximity to the substrate, thereby allowing for transient, excited atomic or molecular species to interact with the surface but without the attendant damage to the growing film or substrate inherent with direct plasma ALD systems. Conformal growth of the oxide within tapered Si trenches having depths up to 3.5 μm and widths below 40 nm is realized, and the mean variation in the thickness of 25 nm thick films is ∼0.3 nm over a 50 mm diameter Si wafer. For a substrate temperature (Ts) of 50 °C, the film growth rate remains constant at 2.25 Å/cycle up to ∼700 cycles, and surface analysis confirms the the O:Al stoichiometric ratio to be 1.52 ± 0.10. MOS capacitors fabricated from 30 nm thick Al2O3 films yield capacitance-voltage (C-V) curves at 1 MHz having a hysteresis of 100 mV that falls to <1 mV if the Al2O3 film is postannealed at 400 °C. The measured breakdown electric field strength for 30 nm films is 4.1 MV/cm for Ts = 50 °C (6.1 MV/cm for postannealed films). Patterned, 68 nm thick films with lateral dimensions <2 μm have also been realized by film growth at 50 °C and the subsequent lift-off of a photoresist. By patterning features with e-beam lithography prior to film growth and lift-off, we have fabricated arrays of ∼210 nm diameter Al2O3 discs (and diamonds).