We present a fabrication process allowing the realization of high-Q and small-diameter micropillar cavities. The fabrication involves molecular beam epitaxy, electron-beam lithography, and reactive ion etching (RIE). The introduction of O-2 to the SiCl4 RIE plasma and the dynamic adjustment of its flow rate enable the control of the etched profile throughout the process, through the deposition of silicon oxide on the vertical etched surfaces. The resulting cavities have very smooth, straight, and vertical sidewalls and remain optically and mechanically stable for long periods of time. The optical modes sustained by these cavities exhibit record quality factors in excess of 1200 for pillar diameters close to 400 nm, which underscores the quality of our process. (c) 2005 American Vacuum Society.