Dataset for "AlN overgrowth of nano-pillar-patterned sapphire with different offcut angle by metalorganic vapor phase epitaxy"

Data collection method:

Secondary electron images were captured using a Hitachi S-4300 scanning electron microscope (SEM). An accelerating voltage of 5 kV was used to collect the images

Technical details and requirements:

DTL patternings have been performed on 2-inch sapphire wafers. A stack of two layers was spin-coated at 3000 rpm to obtain a ~ 270 nm bottom antireflective coating (BARC) (Wide 30W – Brewer Science) layer thickness, followed by either a layer of high-contrast positive resist (Dow® Ultra-i 123 diluted with Dow® EC11 solvent). A bake at 150°C of the BARC enables a wet-developable process and thus to create an undercut profile. DTL (PhableR 100, Eulitha) was then used to expose the resist with a coherent 375 nm light source with an energy density of 1 mW.cm-2 (Fig. 1a). A 1 μm pitch with 550 nm opening mask was employed which result in a Talbot length of 3.80 μm. A Gaussian velocity integration was applied and 8 Talbot lengths travel distance has been chosen to assure a homogeneous integration on several Talbot motifs. After a certain exposure time (which defines the exposure dose), the sample was baked for 1 min 30 sec at 120°C on a hot plate. The wafer was developed in MF-CD-26 for 180 to 240 sec (depending on the dose employed). The undercut profile created in the BARC after exposure and development was employed as a lift-off layer. 200 nm Ni layers were deposited via e-beam evaporation to produce metal masks in the circular opening at the surface of the wafer. Subsequent lift-off was achieved by soaking the wafer in MF-CD-26 developer. The wafers were cleaned in a 2 min reactive-ion etching (RIE) oxygen plasma to remove any BARC residue. Then, an ICP dry etch system was used to create nano-pillars in sapphire substrates. The experiments were performed with a Cl2/BCl3/Ar chemistry of 5/50/5 sccm, a temperature of 5°C, a pressure of 8 mTorr, 100 W RF power and 600 W ICP source power. Finally, the masks were etched away in aqua-regia solution (HCl:HNO3, 3:1).