Kathirgamasundaram Sooriakumar

Investigation of in situ trench etching process and Bosch process for fabricating high-aspect-ratio beams for microelectromechanical systems

The etching processes and mechanisms for sidewall formation were investigated for the in situ trench etching and releasing process, using a magnetically enhanced reactive ion etcher (MERIE), and for the Bosch process, using an inductively coupled plasma (ICP) etcher. For the Bosch process, almost vertical sidewall profiles were obtained up to etching depth of ∼100 μm. The average height of the scallops on the sidewall was ∼70 nm and the average erosion underneath the mask was ∼0.4 μm, when trenches 50 μm deep were formed. This limited the fabrication capability of small feature sized microelectromechanical system structures of less than ∼1 μm. For the in situ processes using MERIE, the reactive ion etching (RIE) lag was significant when the etching depth reached ∼50 μm. The RIE lag was significantly reduced when the ICP was used at pressure below 50 mTorr. Scallops and undercuts were not observed when the in situ process was used. Anger electron spectroscopy and x-ray photoelectron spectroscopy analysis r...

In situ trench etching and releasing technique of high aspect ratio beams using magnetically enhanced reactive ion etching

This article describes an in situ trench etching and releasing technique to fabricate high aspect-ratio beams for high performance microelectromechanical systems (MEMS) accelerometers using magnetically enhanced reactive ion etching (MERIE) technique. In the conventional process, lateral encroachment due to the release etching is severe underneath the SiO2 etching mask. In this process, the sidewall of the beams was passivated by inhibiting layers formed during the HBr/SiF4/O2 trench etching, and the beams were not attacked by the subsequent SF6 release etching. Auger electron spectroscopy showed the etch inhibiting layer to consist mostly of Si and O. This was also confirmed by x-ray photoelectron spectroscopy as SiOx (1<x<2) was detected as a predominant species. The in situ process eliminated (1) sidewall deposition step and (2) floor etching step of the conventional process. In addition, the dependency of MERIE etching rates on open ratio and pattern size was studied for high aspect-ratio MEMS structu...