Improvement of the resolution and accuracy of chemical-amplification positive resist for 0.13-μm reticle fabrication

Abstract

ABSTRACTWe have developed a novolak-based chemical-amplification resist for 0. 13-rim or later reticle fabrication. Forthe 0. 13.jim or later design-rule reticle-fabrication with OPC patterns, the resist resolution is required under 0.2-.tm on the mask substrate. To improve the chemical-amplification resist resolution, it is necessary to control theacid-diffusion in the resist film. We have developed the technique of the acid-diffusion control with neutral-saltadditives. By use of the resist with this technique, we could fabricate 0. 14-jim I/s patterns on a CrOx substrate ata dose of 9.3-iC/cm2 (50kV). The resist has a good margin of doses.Keywords: novolak-based chemical-amplification resist, resist resolution, acid-diffusion control, neutral-saltadditives 1. INTRODUCTION A novolak resin-based chemical amplification (CA) positive resist has been developed for 0. 13-j.tm design-rule reticle-fabrication using 50-kY e-beam reticle writer HL-800M. Novolak-resin-based resists have good process stability such asPost-Exposure Delay (PED) and Post-Coated Delay (PCD) and a good dry and wet etching durability. To achieve the next-generation reticle fabrication with OPC patterns, better critical-dimension (CD) control and cross-sectional pattern controlare necessary.It is well-known problems that CA positive resists form and/or T-top profiles due to the loss of photo-generated acidmolecules at the resistisubstrate interface and/or resists surface [1,2]. In a previous paper [1], we reported that the CA resistshows footing —round corners at the bottom of the profile — in the cross-sectional resist profiles on a mask (a chromium-oxide (CrOx) substrate). In addition, acid-diffusion in CA resists during post exposure baking (PEB) is the critical issue. Toperform next-generation reticle fabrication, these problems must be suppressed.To improve the resist profiles, substrate treatments [3,4] or the addition of bases to the resist solution [5-7] have beeninvestigated. On the other hand, there have been many studies on acid-diffusion suppression methods using basic orphotodecomposable basic additives [6,7]. However, substrate treatment may increase the number of defects and the processsteps in the photomask fabrication. The addition of bases, on the other hand, may lower resist sensitivity.To reduce the and/or T-top profiles, therefore, we investigated a new resist composition. The use of a matrix resinwhose molecular-weight distribution (MWD) can be controlled - for example, a tandem-type resin - is an effective methodto improve the performance of a conventional novolak resin-based positive photoresist [8]. In a previous paper [9], wereported a performance of the CA resist with the MWD-controfled (MWDC) matrix resin. The MWDC was very effectiveto enhance the resist resolution. For 0. 13-mm or later reticle fabrication, however, the resist performance is still moreimproved. Therefore, the acid-diffusion control is applied to the MWDC novolak based resist. We have been also proposed*