Technology Development of 3D Silicon Plasma Etching Processes for Novel Devices and Applications

Deep reactive ion etching (DRIE) is a standard technique for silicon micro- and nanofabrication in semiconductor industries. However, this technology is confronted with unprecedented challenges, as the critical dimension of structures is continuously shrinking following Moore’s law, and various stringent technical requirements are becoming usual to enable emerging technologies and devices. Since there is still no other technique that can replace DRIE in a foreseeable future, profound process optimizations become a necessity for robust etching performances, high fabrication accuracies, more versatility and flexibility to enable complex structure manufacturing. As a typical strategy for DRIE, Bosch process has been studied extensively since last century, however, the high sidewall roughness induced by switched etching sequences make the process less favorable for nanoscale engineering.
In this thesis, a modified Bosch process has been proposed, which is termed as DREM (Deposit, Removal, Etch Method) process. Compared with a standard Bosch process, DREM process enables a much higher etching selectivity, more precise control over structure profiles, and less sidewall roughness. Various silicon micro- and nanostructures have been fabricated to demonstrate the capability of DREM process, e.g. silicon microstructure with aspect ratio of 50, nanostructures with aspect ratio of 26 and minimized sidewall roughness, etc. A modified DREM process is also developed for fabricating three dimensional (3D) silicon micro- and nanostructures. Up to 10 layers of suspended structures can be created conveniently by a single etching procedure, with a considerably better profile control compared with previous studies.
The fabricated 3D silicon micro- and nanostructures exhibit intriguing optical and mechanical properties. Two applications have been investigated: firstly, 3D silicon mesh structures are integrated with zinc oxide nanowires, and enhanced performances are observed for photocatalytic reactions and photocurrent generations; secondly, a 3D silicon photonic crystal membrane is fabricated, which possesses a complete photonic band gap, embedded planar cavities are also feasible for applications as organic solvent sensor and optical filters.
The above-mentioned technological developments are enabled by multiple real time monitoring techniques, such as optical emission spectroscopy and optical emission interferometry. Process optimizations have also been performed for electron beam lithography to achieve high resolution sub-10 nm patterns, which are employed for etching processes.