Investigation of Deep Dry Etching of 4H SIC Material for MEMS Applications Using DOE Modelling

In this paper the reactive ion etching (RIE) of 4H silicon carbide (SiC) with an SF
₆
/O
₂
/He gas mixture is investigated in an inductively coupled plasma etcher (ICP). Objective is the analysis of the manufacturing process of a SiC diaphragm for a bulk micromechanical pressure sensor, by etching a cavity into silicon carbide wafer. In addition, the selectivity of etching masks made from Nickel and Copper against SiC are examined. By means of Design of Experiments (DOE) in the software JMP, a test series with 29 recipes is set up. The process is varied over the parameters chamber pressure, source power, platen power, SF
₆
flow rate, O
₂
flow rate, clamp cooling and mask material. To evaluate the etched samples quantitatively, cross sections of 29 specimens are made. The results are used to create a mathematically model for the prediction of etching rate, profile angle and occurring micro masking. The model is evaluated by etching samples. Etching a cavity with an opening width of 800 μm to a depth of 300 μm with a maximum etching rate of 4 μm/min, vertical profile walls and a smooth and even etched base is demonstrated. The selectivity of the modelled process is 115 compared to Cu, the observed selectivity of Cu is higher compared to Ni.