AVS 45th International Symposium
    The Science of Micro-Electro-Mechanical Systems Topical Conference Monday Sessions
       Session MM+PS-MoM

Paper MM+PS-MoM10
Test Structure Experiments and Modeling of Very Deep Dry Etching Processes for MEMS Applications

Monday, November 2, 1998, 11:20 am, Room 324/325

Session: MEMS Processing and Deep Si Etch Technology
Presenter: S. Abdollahi-Alibeik, Stanford University
Authors: S. Abdollahi-Alibeik, Stanford University
J.P. McVittie, Stanford University
K.C. Saraswat, Stanford University
Correspondent: Click to Email
One successful approach for getting the desired high (~ 4µmm/min) etch rates for MEMS device fabrication is separating the etch and passivation steps in order to eliminate the interference in chemistry. The focus of this work is on the understanding and modeling of the very deep (>100µmm) trench etch process based on this approach. Experiments were done to investigate different aspects of both deposition and etch phases. C@sub 4@F@sub 8@ gas was used for the deposition phase. The deposited material is a CF@sub x@ polymer. It was observed that the deposition rate is highly dependent on the ion flux and ion energy received by the surface. This can be modeled as an increase in the effective sticking probability of the deposition species. While polymer deposition in an overhang test structure is not that conformal, the rate of passivation does not change when the trenches become very deep. The above model and the fact that the trench sidewalls receive little ion flux can explain this discrepancy. In addition, ion reflection also appears to be important since sidewall deposition shows a dependence on the opposite sidewall. For the etch phase SF@sub 6@ gas was used. Lag experiments show that the transport of the etchant species down the trenches depends on the deposition phase. The lag was higher for a larger ratio of etching to deposition time. The fact that ion bombardment of the CF@sub x@ polymer releases F atoms can be the reason for this change in lag behavior. Incorporation of the model into the SPEEDIE profile simulator will be shown.