Abstract
ABSTRACT A design of experiment for high throughputs GaAs via etch by reactive ion etch is reported herein. GaAs backside via process for connecting of the front side circuits to the backside ground plane will reduce the ground inductance and thus will improve the RF performance of fabricated circuits. A Design of Experiment (DOE) is conducted for GaAs via etch to obtain a high etch rate and smooth via profile with a non-reentrant slope simultaneously on a four mils thick GaAs substrate. Considering the RIE (reactive ion etch) batch system used herein and the characteristics of the GaAs etching mechanism, the Taigui L9 method is selected. The L9 method comprised four parameters, each with three layers, and it can cut the number of experiment runs from sixty-four to nine. Hence, the L9 method designed herein included four major varying parameters, namely pressure, RF power, Cl2 /BCl3 ratio, and Ar flow rate. The three RF power setting are 125W, 150W and 175W, while the three pressure levels are 15mTorr, 25mTorr and 175mTorr.Meanwhile, the three levels of Cl2 to BCl3 ratio are 0.5, 1 and 1.5,and the levels of Ar flow rate are 0,6 and 18sccm. Dependence of output results such as GaAs etch rate, photoresist etch rate, etch selectivity between GaAs and photoresist, and cross-section view of the via hole on the four major parameters are also discussed. A smooth via profile with non-reentrant slope was achieved for a GaAs backside process with a combination of multiple etches including three stages; breakthrough, main etch and overetch.