ELSEVIER IqIICRO~-~ Microelectronic Engineering 46 (1999) 383-387 DUV resists in negative tone high resolution electron beam lithography Falco C.M.J.M. van Delft and Frans G. Holthuysen Philips Research Laboratories, Prof. Holstlaan 4, 5656 AA Eindhoven, The Netherlands Phone: +31 40 27 43124, Fax: +31 40 27 42346, e-mail: (internet) vandelf@natlab, research.philips.com Shipley's chemically amplified DUV resists UVN-2 (negative tone) and UV-5 (positive tone) have been studied for their high resolution capabilities in electron beam lithography. UV-5 is also capable of negative tone behaviour in case of e-beam overexposure. This effect is shown to be due to direct electron beam cross linking su- perimposed on the normal catalytically induced positive tone behaviour. The ultimate resolution for 100 nm thick UVN-2 is below 50 nm for single lines, when using the shortest possible developing time in order to prevent swelling. The best obtained positive tone resolution of UV-5 is 50 nm for single trenches and 120 nm for 1:1 lines and spaces. The best obtained negative tone resolution of overexposed UV-5 is below 90 nm. This negative tone behaviour is accompanied by a 60% swelling of a 100 nm thick layer, which swelling is most probably related to the relatively long developing time. This swelling is not observed for a 485 nm thick UV-5 layer. 1 INTRODUCTION 2 EXPERIMENTAL Reliable commercially available electron beam resists are hard to get. As an alternative, chem- ically amplified DUV resists can be used [1]. Nega- tive tone resists are commercially not important in DUV lithography, because mask tone reversal and the projection illumination allow a coverage inde- pendent throughput for any desired pattern. In elec- tron beam lithography, however, the sequential writing requires negative tone resists for high resolu- tion single lines in order to maintain a reasonable throughput. In this work, Shipley's negative tone chemically amplified DUV resist UVN-2 has been studied for its high resolution capabilities. This resist is the successor of UVN, which allowed 140 nm lines and spaces and 70 nm single lines to be made [1]. Another way for obtaining negative tone behaviour in e-beam writing is the overexposure of positive tone resists. Although this results in poor resolution for most (novolac) systems, in a few cases resolutions below 100 nm have been reported [2]. In this work, also Shipley's positive tone chemically amplified DUV resist UV-5 has been studied for its (positive and) negative tone high resolution capabilities. Silicon wafers (4 inch) were coated with TriChloroPhenylSilane primer and baked for 120 s at 200 °C on a hotplate. UVN-2 and UV-5 resists solu- tions were, if necessary, diluted with ethyllactate in order to obtain the desired layer thickness by means of spin coating on a CONVAC spinner (during 45 s at 5000 rpm) [1]. UV-5 layers were soft baked for 60 s at 130 °C, exposed in an Electron Beam Pattern Gen- erator (EBPG Philips-Leica 4V-HR) at 50 kV, direct- ly followed by a Post Exposure Bake (PEB) for 60 s at 135 °C (unless otherwise stated), directly devel- oped by hand in 0.26N PD523 at 20 °C during 60 s, rinsed in demineralized water and blown dry in N 2 . UVN-2 layers were softbaked for 60 s at 110 °C, ex- posed in the same EBPG at 50 kV, directly followed by a PEB for 60 s at 95 °C (unless otherwise stated), directly developed by hand at 20 °C in 0.26N PD523 during 5 s or in 0.17N 2:1 PD523:H20 during 15 s, rinsed in 1:9 PD523:H20 during 5 s, rinsed in dem- ineralized water and blown dry. Test structures of crossing lines and spaces were written at various ex- posure doses. Scanning Electron Micrographs were made using a Philips XI.A0 FEG SEM. 0167-9317/99/$ - see front matter © 1999 Elsevier Science B.V. All rights reserved. PII: S0167-9317(99)0011 2-4