AVS 51st International Symposium
    MEMS and NEMS Tuesday Sessions
       Session MN+MS+PS+TF-TuA

Paper MN+MS+PS+TF-TuA5
Etching of High Aspect Ratio Structures in Si using SF@sub 6@-O@sub 2@-HBr and SF@sub 6@-O@sub 2@-Cl@sub 2@ Plasmas

Tuesday, November 16, 2004, 2:40 pm, Room 213C

Session: Nano/MEMS Manufacturing and Plasmas
Presenter: S. Gomez, University of California, Santa Barbara
Authors: S. Gomez, University of California, Santa Barbara
J. Belen, University of California, Santa Barbara
M. Kiehlbauch, Lam Research Corporation
E.S. Aydil, University of California, Santa Barbara
Correspondent: Click to Email
Plasma etching of high aspect ratio (depth-to-width) structures in Si is a crucial step in manufacturing trench capacitors for memory devices, and integrated components for microelectromechanical systems (MEMS). We have investigated etching of deep (~3-10 µm) and narrow (~0.2-0.5µm) features with high aspect ratios (~10-50) using plasmas maintained in mixtures of SF@sub 6@, O@sub 2@ and HBr gases, and in mixtures of SF@sub 6@, O@sub 2@ and Cl@sub 2@ gases as an alternative to the Bosch process. Experiments were conducted in a low pressure (25 mTorr), high density, inductively coupled plasma etching reactor with a planar coil to maintain the discharge and with radio frequency (rf) biasing of the substrate electrode to achieve independent control of the ion flux and ion energies. Specifically, we have studied HBr and Cl@sub 2@ addition to SF@sub 6@/O@sub 2@ plasmas and O@sub 2@ addition to SF@sub 6@/HBr and to SF@sub 6@/Cl@sub 2@ plasmas. We have analyzed the effect of these additions on the etch rate and feature profile using Si wafers patterned with 0.2 µm diameter holes in a SiO@sub 2@ mask. Visualization of the profiles using SEM is complemented by plasma diagnostics such as optical emission and mass spectroscopies to understand the key factors that control the anisotropy and etch rate. Upon adding HBr to an SF@sub 6@/O@sub 2@ plasma, a silicon oxybromide film forms on the sidewall, reducing undercut and increasing taper. However, subsequent reduction of O@sub 2@ gas increases mask undercut and isotropic etching by reducing sidewall oxidation. On the other hand, adding Cl@sub 2@ to an SF@sub 6@/O@sub 2@ plasma causes a reduction of O density and a weak silicon oxychloride film forms on the sidewall. This chlorinated film is more easily etched by F, therefore increasing mask undercut. Subsequent reduction of O@sub 2@ gas further increases mask undercut and isotropic etching.