Evaluation of an advanced chemically amplified resist for next generation lithography mask fabrication

Interest in chemically amplified (CA) resist systems has been increasing for advanced mask fabrication due to their superior e-beam sensitivity, contrast and resolution compared to traditional non-CA e-beam resists on high kV (50-100kV) exposure systems. However, most CA resists available are sensitive to temperature variations during the post apply and/or post exposure (PAB/PEB) process steps. This temperature sensitivity can result in poor CD uniformity across the mask. An advanced positive tone CA resist developed at IBM, KRS-XE, has been investigated for use in the fabrication of NGL masks (the continuous membrane and stencil versions of electron projection lithography as well as proximity x-ray masks). KRS-XE is an improved ketal resist system that is robust towards airborne contaminants, is compatible with 0.263N TMAH aqueous developer and has a wide PAB/PEB process latitude. This CA resist has been found to be insensitive with respect to dose and CD over a PAB temperature range of 105 degreesC to 120 degreesC and a FEB temperature range from room temperature to 110 degreesC. Line/space features down to 75nm have been demonstrated in this resist on the IBM EL4+ 75kV vector scan e-beam system. This paper discusses the performance of KRS-XE with respect to CD uniformity on NGL membrane masks and compares the experimentally obtained results fr-om both KRS-XE and a FEB sensitive CA resist (Shipley UVIII (TM)) against the FEB temperature variations predicted from a finite difference model for each mask format.