Nanostructured surfaces
Formation of submicron relief structures on the surface of sapphire substrates
Kryuchyn A.A., Rubish V.M., Shihovets O.V., Pankratova A.V.
 Institute for Information Recording of the NAS of Ukraine. M. Shpak str 2, Kyiv-03113, Ukraine. E-mail: kryuchyn@gmail.com
      Microrelief structures on the surface of sapphire substrates are widely used in the manufacture of LEDs, diffractive optical elements and long-term storage media. Most epitaxial structures for LEDs are grown on profiled sapphire substrates, which allows to achieve high efficiency in 1.5-2 times of light output from LEDs [1]. Microrelief diffraction optical elements (DOE) are formed on sapphire substrates, designed to operate at high radiation powers and temperatures [2]. Microrelief sapphire substrates are also proposed to be used to create long-term data storage media. The formation of relief on the surface of the sapphire substrate is difficult due to its high chemical resistance. The proposed methods of creating a relief on the surface of the sapphire substrate can be divided into two groups - the formation of microrelief in the material of the substrate and obtaining a microrelief image in the material applied to the surface of the sapphire substrate. To create a microrelief on the surface of sapphire substrates can use the method of nanospheres lithography [3].The main problems in creating a microrelief on the surface of sapphire substrates are the removal of static electric charge in the process of ionic-chemical etching of substrates and obtaining a protective mask with windows of specified sizes, through which etching of sapphire substrate. To create submicron relief structures on the surface of sapphire substrates, we used two-layer masks consisting of chromium and photoresist films. Elements of submicron sizes were formed on the photoresist layer by direct laser writing. The chromium film was chemically etched through windows in the photoresist. Plasma-chemical etching through a two-layer mask produced relief elements on the surface of a sapphire substrate with dimensions (0.3–0.7) µm and depth (0.1–0.2) µm. 
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