PHOTORESIST ETCHING IN A HOLLOW-CATHODE REACTOR

The submicron photoresist patterning capabilities of hollow cathode and asymmetric diode ("reactive ion etch") reactors are compared here. Confined hollow cathodes etch more than 15 times faster than a diode at a given target voltage, at pressures of 2 Pa and below. Etch directionality has been studied using measurements of undercut in deep submicron patterns. Low-pressure hollow cathode etch anisotropy is similar to that obtained in a diode reactor, at all target voltages. At high target voltages both reactor designs result in less than a few percent of total undercut and sidewall bowing using 0.7-mu-m period, 3-mu-m-thick structures. This level of bowing is often seen in submicron etched apertures; we show how such bowing is affected by mask sidewall slope, and by the aspect ratio of etched structures. We review theories of sidewall bowing, concluding that electrostatic deflection and ion reflection from mask edges cause most of the sidewall bowing under our low-pressure conditions.