Scanning probe oxidation of SiC, fabrication possibilities and kinetics
considerations
M. Lorenzoni,1 B. Torre1
1
Nanophysics, Istituto Italiano di Tecnologia, via Morego, 30, 16163 Genova, Italy
Supplementary information
Materials and experimental details:
Si side polished n-type 6H-SiC (0001) wafers (res. 0.02 – 0.1 Ω cm) were sonicated for 10 minutes
in acetone, ethanol, DI H2O immediately before processing, this cleaning procedure preserves the
native SiO2 layer or any further oxidation deriving from manufacturers chemipolishing, that
employs alkaline (pH > 10) slurry of colloidal silica . The following exposure of SiC surface to a
solution of aqueous HF (5 wt% for 30 seconds) results in the removal of native oxide and surface
OH-termination (water contact angle ≈ 35°). The resulting surface has a root mean squared
roughness (RRMS) of 0.14 nm (see figure S1).
Figure S1: AFM topography of SiC 6H – 0001 (Si) surface CMP polished; wet etched in HF 5% for 30 seconds. Sample
annealed in vacuum overnight at 400°C; Contact mode topography. RMS of the surface is 0.14 nm. Terraces are about
160 nm wide and the step height is approx. 2 Å (profile box).
Oxidations were performed with an Asylum MFP- 3D with integrated software to control
lithographic parameters (Microangelo), operating in contact mode in air, in a closed cell that allows
the control of ambient relative humidity (RH). The loading force was limited below 10 nN to reduce
contact pressure during oxidation process. It was possible to achieve a writing speed of 10 µm s -1
with optimal results in speed range between 0.2 and 5 µm s -1. The probes employed during the
fabrication tests were SiN Au coated Olympus OMLC – RC 800 (k = 0.042 Nm-1; typical tip radius
≈ 30 nm), the maximum bias applicable is ± 20 V. The same (OMLC – RC 800) probes were
employed during conductive AFM measurements (see figure S2).
Kelvin probe force microscopy measurements have been performed by means of an Asylum MFP
3D in dry nitrogen flux (RH < 4%) at room temperature using Pt coated probes (Olympus OMCLAC240TM, spring constant 2 N/m, resonance frequency 75 kHz). It must be remarked that the
oxide patterns on which KPFM was performed have been generated by parallel continuous lines
displaced 50 nm at a speed of 1 µm s-1 and a constant bias of 15V while, the in work by Chiesa and
Garcia (ref. 26: M. Calleja and R. Garcıa, Applied Physics Letters 76, 3427 (2000)), patterns were
intentionally fabricated by single short pulses (< 10 ms) in order to prove the effect of space charges
in the early stages of oxidation.
Figure S1: Conductive AFM measurements of SiO2 features on Si(100) p type: topography (a) and current at 3V tip
bias (b); SiOxC y features on SiC n type: topography (c) and current at 3V tip bias (d). In both current images the
insulating nature of oxide is confirmed.
Figure S2: Examples of patterns obtained on 6H SiC: (a) AFM topography 3D images of 5 µm wide stripes. (b) AFM
topography 3D images of a hexagonal pattern.