Design and method of fabricating phase-shift masks for extreme-ultraviolet lithography by partial etching into the EUV multilayer mirror

Abstract

Phase Shift Masks (PSMs) for Extreme Ultraviolet Lithography (EUVL) have the potential for extending the lithographic capability of EUVL to at least the 22-nm node. Typical PSM structures, such as for attenuated PSMs (Att-PSMs), are similar to those of binary masks in the sense that patterned structures of one or more layers of phase shifter are deposited on the EUV multilayer mirror to provide the correct amount of attenuation and phase shift. However, another type of PSM implemented by etching into the Mo/Si multilayer, rather than by adding lithographic structures on top of the Mo/Si multilayer (additive approach), can also provide the required phase shift for both attenuated and hard PSMs. One of anticipated technical challenges, i.e. terminating etching at a specific depth with good surface uniformity can be solved by employing an etch stop layer (ESL) embedded at a target depth inside the multilayer. In designing PSMs using this subtractive fabrication technique, the position and thickness of the ESL should be optimized, so that optical function of the multilayer substrate with embedded ESL should be same or close to when it does not have any embedded layer. According to simulation, the print bias for PSMs by etching into the multilayer stack to create the phase shift is smallest and near ideal compared to other types of PSMs or binary masks fabricated by conventional methods. The increase of depth of focus by 25-75% for contacts using an attenuated PSM and by 50-100% for lines using an ideal hard PSM is another lithographic advantage as well. The design and method of fabricating PSMs by etching into the multilayers is described, which include the optimization of the thickness and depth of the embedded layer. Experimental results of the multilayer etch process demonstrate initial feasibility of the subtractive approach to fabricating EUV PSMs.Keywords: Extreme ultraviolet lithography, masks, phase shift masks, attenuated phase shift masks, hard phase shift masks 1. Downloaded From: http://proceedings.spiedigitallibrary.org/ on 06/20/2016 Terms of Use: http://spiedigitallibrary.org/ss/TermsOfUse.aspx Proc. of SPIE Vol. 5037 323 Downloaded From: http://proceedings.spiedigitallibrary.org/ on 06/20/2016 Terms of Use: http://spiedigitallibrary.org/ss/TermsOfUse.aspx Proc. of SPIE Vol. 5037 327 Downloaded From: http://proceedings.spiedigitallibrary.org/ on 06/20/2016 Terms of Use: http://spiedigitallibrary.org/ss/TermsOfUse.aspx

Ultrahigh efficiency EUV contact-hole printing with chromeless phase shift mask

“…To test the real world performance of the checkerboard phase mask we used the etched multilayer phase shift mask method [8]. Figure 7 shows the fabrication process flow we followed.…”

Evaluation of the critical dimension control requirements in the ITRS using statistical simulation and error budgets

“…All other aberration terms were assumed to be zero. For EUV, the aberration values described by Han et al 12 were used instead. To model aberration variation over the exposure field, ∆Z i ranged from -Z i to +Z i .…”

Stochastic resist patterning simulation using attenuated PSM for EUV lithography

“…A simple thickness reduction, however, can lead to the deterioration of the imaging properties [8]. Therefore, the phase shift concept has been suggested as a potential method of extending the resolution limit, but it has fabrication issues that must be addressed before it can be applied in manufacturing [9][10][11].…”