Submicron Patterns on Sapphire Substrate Produced by Dual Layer Photoresist Complimentary Lithography

Abstract

In this study, the combined technologies of dual-layer photoresist complimentary lithography (DPCL), inductively coupled plasma-reactive ion etching (ICP-RIE) and laser direct-write lithography (LDL) are applied to produce the submicron patterns on sapphire substrates. The inorganic photoresist has almost no resistance for chlorine containing plasma and aqueous acid etching solution. However, the organic photoresist has high resistance for chlorine containing plasma and aqueous acid etching solution. Moreover, the inorganic photoresist is less etched by oxygen plasma etching process. The organic and inorganic photoresists deposit sequentially into a composite photoresist on a substrate. The DPCL takes advantages of the complementary chemical properties of organic and inorganic photoresists. We fabricated two structures with platform and non-platform structure. The non-platform structure featured structural openings, the top and bottom diameters and the depth are approximately 780 nm, 500 nm and 233 nm, respectively. The platform structure featured structural openings, the top and bottom diameters and the depth are approximately 487 nm, 288 nm and 203 nm, respectively. The precision submicron or nanoscale patterns of large etched area and patterns with high aspect ratio can be quickly produced by this technique. This technology features a low cost but high yield production technology. It has the potential applications in fabrication of micro-/nanostructures and devices for the optoelectronic industry, semiconductor industry and energy industry.

Formation of submicron relief structures on the surface of sapphire substrates

“…Highfrequency ion-chemical etching of sapphire (fhf = 13.56 MHz) was also reported in CF4 medium (Tetrafluoromethane) [4]. The high chemical resistance of sapphire makes it necessary to apply the dry etching of multilayer masks [9]. One of the layers of the mask is often a layer of metallic chromium, which is necessary to reduce the electrification of the processed sapphire substrate (the specific electrical resistance of sapphire is 10 19 Ohm cm) [10]., A compensation of the charge on the surface in contact with the plasma is necessary during plasma etching of the sapphire substrates.…”

“…The rate of chemical etching of sapphire is 1 μm/min. [9]. The method of nanosphere lithography can be used to create a microrelief on the surface of sapphire substrates [6].…”

“…The height of relief elements and their density on the surface can vary significantly depending on the process parameters [1,2]. Although this method is effective, it is potentially dangerous for the health of operators [9]. To obtain relief structures in the material of sapphire substrates, dry etching in inductively coupled plasma through a mask formed by photolithography is also used [2].…”