AVS 47th International Symposium
    MEMS Wednesday Sessions
       Session MM-WeA

Paper MM-WeA1
Surface Micromachining - Process Modeling

Wednesday, October 4, 2000, 2:00 pm, Room 309

Session: MEMS Processing
Presenter: C.C. Wong, Sandia National Laboratories
Authors: C.C. Wong, Sandia National Laboratories
P. Ho, Sandia National Laboratories
R.W. Walker, Los Alamos National Laboratory
R.P. Pawlowski, Sandia National Laboratories
Correspondent: Click to Email
Advances in microsystem technology are allowing increasingly complex micro-structures to be built. The ability to visualize structures during the design phase is becoming correspondingly more important. Surface micromachining involves multiple deposition (CVD) and etching (plasma or wet) steps, and each step can introduce non-idealities to the geometry of the structure. Virtual prototyping can speed the design process and reduce the time lost when flaws are discovered during fabrication. Predicting the true dimensions of the final product requires that the effects of the manufacturing processes be modeled accurately. At Sandia, we are developing detailed "physics-based" models to generate the correct shape of micro-features. A modular approach examines the various processes used in device fabrication, and separates the disparate length scales in the fabrication processes. The initial studies investigate the low pressure CVD of polysilicon from silane, which deposits the structural Si material. First, models of the process reactor, MPSalsa (3D) and OvenD (two coupled 1D models), analyze the reacting flows in the multi-wafer furnace. Using a published silane mechanism, the predicted deposition rates for the standard conditions agree with experiment (within 15%). Results from the reactor-scale models are then used as boundary conditions for feature-scale models of the time-dependent evolution of the polysilicon. Simulations using TopoSim3D reproduce the observed conformal deposition. Wet-etch processes to remove sacrificial oxide layers are also being studied. Preliminary analyses using the 3-D GOMA code give reasonable agreement between experiment and the predicted position of the advancing etch front.