Negative resist image by dry etching: a novel surface imaging resist scheme

Top surface imaging (TSI) is an established technique that can be used to improve resolution in optical, ultraviolet and electron-beam lithography into the nanometer region. This paper describes a novel top surface imaging process, which incorporates ion-beam exposure, silylation and dry development, and can support nanometer resolution. The negative resist image by dry etching (NERIME) process is a TS1 scheme for DNQ/novolak based resists and can result in either negative or positive resist image depending on the processing conditions. Results show that focused Ga+ ion-beam exposure with a dose in the range of 1-50 muC cm(-2) at 30 keV can successfully prevent silylation of the resist, thus resulting in the formation of positive image after the dry etching. A negative image can be formed by using a second ion-beam exposure with a dose higher than 900 muC cm(-2) at 30 keV to pattern lines into the original exposed resist area. The NERIME processed patterns down to 0.1 mum have been formed in Shipley SPR505A resist, and exhibit highly vertical sidewalls due to the ion-beam exposure and oxygen dry development. Results show that this novel TSI scheme could be successfully applied for fabrication of critical CMOS process steps, such as deep isolation trench formation and lithography over substantial topography. (C) 2003 Elsevier Science B.V. All rights reserved.