Atomic Layer Deposition and Patterning of 15–185 nm Thick Al₂O₃ Films with Microplasma Arrays for Low-Temperature Growth and Sub-300 nm Lateral Feature Resolution

Abstract

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 (T s) 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 T s = 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).

Ultrasound harmonic generation and atomic layer deposition of multilayer, deep-UV mirrors and filters with microcavity plasma arrays

“…Recently, Kim et al [ 24 ] demonstrated that the introduction of microplasma arrays into atomic layer deposition (ALD) systems reduces the reliance on substrate temperature, thereby allowing dielectric films of high electrical and optical quality to be deposited at temperatures considerably lower than those normally required. Specifically, microplasma arrays provide a compact means for dissociating strongly bound precursors such as O and NO but, of equal importance, also produce radicals and excited species capable of favorably altering the chemistry at the interface between the substrate and growing film so as to permit the substrate temperature to be reduced significantly.…”

“…Experiments conducted at the University of Illinois have deposited both Al O and Ga O films at substrate temperatures of 50 C and room temperature, respectively, by this process known as microplasma-assisted ALD (MALD). Aluminum oxide films 30 nm in thickness, for example, were characterized electrically in metal-oxide/semiconductor capacitors (MOSCAPs) and found to have values of electrical breakdown strength ( ) above 4.1 MV/cm [ 24 ]. Another asset of microplasma arrays for film deposition, growth, and etching is their compact size, which allows for multiple arrays to be situated within the reactor and in proximity to one or more substrates.…”

Commercialization of microcavity plasma devices and arrays: Systems for VUV photolithography and nanopatterning, disinfection of drinking water and air, and biofilm deactivation for medical therapeutics

“…Over the entire 20 cm 2 surface area of a 5 cm diameter Si wafer, the variation (i.e., 1 standard deviation) in the thickness of 25 nm Al 2 O 3 films is 0.3 nm, despite the fact that the cumulative cross‐sectional area of the microcavities in the plasma array is only 2.5 cm 2 . From the viewpoint of electronic devices, perhaps the most important result is that films grown at 50°C and postannealed at 400°C have dielectric breakdown strengths of 6.1 MV/cm, [ 49 ] which lies within a factor of 2 of the highest values in the literature for Al 2 O 3 films grown at much higher temperatures. Because of the low substrate temperatures now accessible with MALD, electronic devices can be fabricated on flexible substrates such as PET.…”