Silicon dry etching using fluorine-based gas for nanoscale cone and grating structure fabrication

Abstract

Dry etching technique is widely used in creating high aspect ratio nanostructures currently. This pattern transfer process has better performance in the profile controlling compared with wet etching technique. For the plasma etching, fluorine-based plasmas are mainly used for rapid isotropic silicon etching process. To achieve an anisotropic profile, SF6/C4F8 and SF6/O2 are generally used in the etching process. These anisotropic profiles, such as cones and pillars, are widely used in photovoltaic and optoelectronic devices. However, current research related to cone structure fabrication are a more random process. The size of the profile cannot be precisely controlled. Although there are some recipes can result in a taper profile, but large amount of C4F8 gas also inhibits further etching. In addition, the etching process with the mixture of C4F8 and SF6 gases always raises the concern about chamber contamination issues. In this thesis, some solutions are proposed to solve such problems. The traditional pseudo-Bosch process has been optimized by introducing a periodical oxygen clean step to remove the fluorocarbon polymer deposition during process. The cone array of a controllable size is fabricated by combining with optimized pseudo-Bosch process and maskelss etching. Another two ways of fabricating cone array are also introduced which are shrinking SiO2 mask and photoresist mask. Unlike SiO2 masks that spontaneously form a tapered structure when they are almost consumed, photoresist masks can be manually applied oxygen plasma to shrink periodically for a controllable cone array fabrication. In addition, the detailed investigation of near room temperature SF6/O2 etching is presented to prove it is possible to be an alternative way of pseudo-Bosch process in cone or grating structure fabrication.