TMAH IPA ANISOTROPIC ETCHING CHARACTERISTICS

The main advantages of tetramethyl ammonium hydroxide (TMAH)-based sol utions is their full compatibility with IC technologies. In this work a new etching system of TMAH/IPA (isopropyl alcohol) is suggested. The influence of the addition of IPA to TMAH solutions on their etching c haracteristics is presented. The etch rates of (100) oriented silicon crystal planes decreases linearly with decreasing the IPA concentratio n for all experimental conditions. Etch rates for TMAH/IPA solutions ( 10-45 mum/h) are lower than those for KOH/IPA solutions (30-100 mum/h) but they are still applicable for micromachining purposes. The etch r ates of most commonly used masking layers in IC technologies has been investigated. Low-pressure chemical vapour deposited (LPCVD) Si3N4 and thermally-grown SiO2 have excellent stability in TMAH/IPA solutions. Low-temperature deposited silicon oxide (LTO) etch rates are low enoug h to be used as masking layers in anisotropic etching processes. Quali ty of etched surfaces is mainly dependent on TMAH wt.% concentration. For pure TMAH solutions the observed undercutting ratio (5-7) is much larger than in KOH case. The addition of IPA to TMAH solutions reduce the undercutting by a factor of more than 2 and leads to smoother surf aces of sidewalls etched planes. We have studied briefly the p++ etch- stop characteristics by means of heavily boron-implanted layers. The e tching selectivity with respect to high boron-doped silicon is improve d in TMAH/IPA solutions. Implant doses used in our experiments (2 x 10 (16) ion/cm2) stands the etching during more than 90 min.