Study On The Antireflective Nano-periodic Structure On Si Surface Via Nanoimprint Lithography

The intrinsic Fresnel reflection of Si surface, which causes more than30%of theincident light to be reflected back from the surface, seriously influences the photoelectricconversion efficiency of Si-based semiconductor photoelectric devices, such as solar cell andinfrared detector. Recently, how to find a simple and efficient method, which is also suitablefor mass production, aiming to suppress the undesired reflectivity and therefore improve theefficiency of the devices has become the research focus.Periodic subwavelength-structured surfaces (SWS) with a period smaller than theincident light wavelength have stable structure and excellent antireflection properties, and itis a sample and effective method to minimize surface reflections. As a candidate for thenext-generation lithography, Nanoimprint Lithography (NIL) is a low-cost, high-resolution,high throughput method, which has advantages in micro-and nanofabrication. In the paper,we study the fabrication of the mold and the antireflective periodic nano-structure on Sisurface using NIL.The mold for NIL was usually fabricated by traditional lithography such as extremeultraviolet (EUV), focused ion beams (FIB) lithography, electron beam (EB) lithography.However, those approaches are always time-consuming and expensive process. Instead ofbeing formed by traditional lithography, the anodic aluminum oxide (AAO), with highlyregular structures and high pore density, is the mold to achieve periodic structures for NIL.We successfully transferred a2D nanoporous array structure to the Si surface via the NILand AAO. The pore diameter and the interpore distance of the Porous Silicon (PS) are wellconsistent with that of AAO template. The interval, the diameter and the height of thehexagonal array structure are350nm to560nm,170nm to480nm and200nm,respectively.The antireflection properties of the SWS are seriously affected by the period, height andsurface morphology of the nanopillars. In order to deeply understand these effects, wesuccessfully transferred three different nano-structured morphologies to the Si surface viathe NIL and ICP, including cut-paraboloid nanopillar structure, ladder-shaped nanopillarstructure and bullet-like nanopillar structure. The reflectivities of these nanopillar arrayed Sisurfaces were tested in the wavelength range of400to2500nm with an incident angle of8° during the measurement. Compared to the unstructured Si, the reflectivity of these structuredSi surfaces has a significant decrease in the test area. The results are confirmed with theeffective medium and rigorous coupled-wave theory.