Exploitation of semi‐sequential reactive ion etch processes to fabricate in‐plane Si structures

The work reports on the exploitation of semi‐sequential deep reactive ion etching (RIE) processes for realisation of deep vertically etched Si structures on Si substrate applicable in fibre‐optic sensing systems. These processes employ different mixtures of gases including hexaflourosulphide, hydrogen and oxygen in a RIE system with a programmed passivation and etching sub‐cycles. In the so‐called semi‐sequential processes, the intermediate purging steps are eliminated, which results in remaining little trace of reactant gases from the previous sub‐cycle in the RIE machine's chamber, which can participate in the process of current sub‐cycle. For the sake of minimum optical losses, which are accomplished by highly smooth vertical sidewalls, several etching processes were applied. In these processes, by controlling the etching parameters such as the flow of gases, plasma power and timing of each subsequence, the process can be controlled for minimum under‐etch and surface roughness and maximum verticality of sidewalls. However, time and cost considerations should also be noted in the optimum fabrication process.