IUVSTA 15th International Vacuum Congress (IVC-15), AVS 48th International Symposium (AVS-48), 11th International Conference on Solid Surfaces (ICSS-11)
    Plasma Science Thursday Sessions
       Session PS-ThP

Paper PS-ThP30
Highly Selective Etching of Al/AlN Structures for Metallization of SAW Devices

Thursday, November 1, 2001, 5:30 pm, Room 134/135

Session: Plasma Etching Poster Session
Presenter: F. Engelmark, Uppsala University, Sweden
Authors: F. Engelmark, Uppsala University, Sweden
I.V. Katardjiev, Uppsala University, Sweden
G.F. Iriarte, Uppsala University, Sweden
Correspondent: Click to Email
Metallization is a critical step in the fabrication of high frequency thin AlN film based SAW devices. Both state-of-the-art lithography as well as high selectivity and anisotropy during etching of Al with respect to AlN are required for low loss and high performance devices. In this work, the etch rates of reactively sputtered AlN, sputtered Al, thermal SiO@sub 2@ and Shipley 1813 photo resist as well as the selectivity between Al/AlN, Al/SiO@sub 2@ and resist/Al have been systematically studied during ICP RIE. Emphasis is focused on obtaining high Al etch rates, while at the same time keeping the etch rate of AlN and that of the resist sufficiently low. High anisotropy is obtained by passivating the sidewalls by the addition of oxygen. The recipe developed is based on a modified Al etch using a mixture of BCl@sub 3@, Cl@sub 2@, O@sub 2@ and Ar. The parameters varied were gas composition, process pressure, substrate bias and ICP power. Generally it is found that the Al etch rate exhibits a maximum with the O@sub 2@ flow, while the AlN etch rate decreases monotonically. Substrate bias is found also to be an important parameter with respect to both etch rates and selectivity. At optimized conditions (500 W ICP power, 35 W chuck power, 50 sccm BCl@sub 3@, 25 sccm Cl@sub 2@, 10 sccm O@sub 2@, 0 sccm Ar, pressure 10 mTorr) the Al etch rate is 1700 nm/min with a selectivity of 58 towards AlN and 10 towards the resist. The same recipe, slightly modified, has also shown similar Al etch rates when etching Al over SiO@sub 2@ with a selectivity of up to 180. High anisotropy of the Al etch rate is observed with increasing O@sub 2@ flow. The former has been determined from cross-sectional SEM observations.