Characterization of Binary and Attenuated Phase Shift Mask Blanks for 32nm Mask Fabrication Thomas Faure 1 , Emily Gallagher 1 , Michael Hibbs 1 , Louis Kindt 1 , Ken Racette 1 , Richard Wistrom 1 Amy Zweber 1 , Alfred Wagner 2 , Yasutaka Kikuchi 3 , Toru Komizo 3 , Satoru Nemoto 3 1 IBM Corporation, 1000 River Street, Essex Junction, VT, 05452 2 IBM Corporation, 1101 Kitchawan Road, Yorktown Heights, NY, 10598 3 Toppan Photomasks Inc., 1000 River Street, Essex Junction, VT, 05452 ABSTRACT During the development of optical lithography extensions for 32nm, both binary and attenuated phase shift Reticle Enhancement Technologies (RETs) were evaluated. The mask blank has a very strong influence on the minimum feature size and critical dimension (CD) performance that can be achieved on the finished reticle and can have a significant impact on the ultimate wafer lithographic performance. Development of a suitable high resolution binary mask making process was particularly challenging. Standard chrome on glass (COG) binary blanks with 70 nm thick chrome films were unable to support the required minimum feature size, linearity, and through pitch requirements. Two alternative mask blank configurations were evaluated for use in building high resolution binary masks: a binary (BIN) mask blank based on the standard attenuated PSM blank and an Opaque MoSi on Glass (OMOG) mask blank consisting of a newly- developed opaque MoSi [1]. Data comparing the total process bias, minimum feature size, CD uniformity, linearity, through pitch, etch loading effects, flatness, film stress, cleaning durability and radiation durability performance of the different binary and attenuated PSM mask blanks are reported. The results show that the new OMOG binary blank offers significant mask performance benefits relative to the other binary and attenuated PSM mask blanks. The new OMOG blank was the opaque mask blank candidate most capable of meeting 32nm binary mask fabrication requirements.. Keywords: OMOG, binary photomask, mask blank, 32 nm masks 1. INTRODUCTION During the early development of optical lithography for the 32 nm node, the IBM Mask House was asked to provide both high resolution attenuated phase shift masks and binary masks. In 2006, there were only two possible binary mask blank options: a 70nm thick chrome on glass (COG) and a binary stack composed of an attenuated phase shift mask blank with the chrome layer left in place (called “BIN” here). More specifically, the BIN mask blank is a 67nm thick MoSi attenuated phase shift layer and a 49nm thick chrome layer. The compelling advantage of the BIN blank relative to the 70nm COG blank was thinner chrome layer and the associated reduction in process bias. The reduced bias improves the minimum mask feature size resolution, a requirement for the 32nm node. A new binary mask option was developed by Toppan and ShinEtsu 1 and became available in early 2007. This option consisted of a 40nm opaque MoSi shading layer, a 20nm MoSi antireflective layer, and an ultrathin 10nm chrome hard mask. The chrome was used only for pattern transfer to the underlying MoSi films. At the end of the mask making process the ultrathin chrome hard mask layer is removed; the final binary mask consists of the patterned opaque MoSi films on top of the quartz substrate. For the purposes of this paper, we will refer to this new binary mask blank as Opaque MoSi on Glass or OMOG. The ultrathin chrome mask OMOG blank offers advantages over the BIN and COG options: the potential to use thinner e-beam resists, achieve lower process bias, and decrease chrome etch loading effect. These changes result in improved resolution, less reliance on density correction software, and overall improved CD uniformity. From the lithographic user perspective, the OMOG blank offers an opportunity to expose a mask without any chrome in the 193nm optical stepper, avoiding the radiation-induced chrome oxide defect growth that can occur with COG and BIN masks. This effect is described by Tchikoulaeva et. al. 2 Based on these potential benefits, the new OMOG binary blank was evaluated for 32nm node high Photomask Technology 2008, edited by Hiroichi Kawahira, Larry S. Zurbrick, Proc. of SPIE Vol. 7122, 712209 · © 2008 SPIE · CCC code: 0277-786X/08/$18 · doi: 10.1117/12.801950 Proc. of SPIE Vol. 7122 712209-1 2008 SPIE Digital Library -- Subscriber Archive Copy