Evaluation of EUV resist performance below 20nm CD using helium ion lithography

Abstract

For the introduction of EUV lithography, development of high performance EUV resists is of key importance. This development involves studies into resist sensitivity, resolving power and pattern uniformity. We have used a subnanometer-sized 30 keV helium ion beam to expose chemically amplified (CAR) EUV resists. There are similarities in the response of resists to He + ions and EUV photons: both excite Secondary Electrons with similar energy distributions. The weak backscattering of the He + ions results in ultra-low proximity effects. This fact enables the exposure of dense and detailed patterns by focused He + ion beams without the need for proximity correction. This paper presents contact holes and lines at 40-nm pitch in an EUV CAR resist. We have used resist sensitivity, contrast, resolution (CD) and pattern fidelity (LCDU, LWR and dose-to-print) as metrics for a comparison of SHIBL with EUVL. We show that Scanning Helium Ion Beam Lithography (SHIBL) can be a useful and economically attractive technology to (pre-)screen novel EUV resists prior to their final performance evaluation in an EUV scanner.

Impact of pixel-dose optimization on pattern fidelity for helium ion beam lithography on EUV resist

“…Our simulation results are in good agreement with experiments reported by Maas et al. 6 Furthermore, we investigate the advantages of optimizedpixel-dose SHIBL to improve LCDU, LWR, exposure latitude (EL) and throughput. Finally, we compare preliminary modeling results for single-pixel and optimized-pixel-dose SHIBL for a 50-nm-full-pitch LS pattern.…”

“…high contrast) 10 due to high sensitivity of CAR to He-ions and spatial resolution. 6 Furthermore, it is worth mentioning that it has been reported that optical critical dimension (OCD) scatterometry provides a more accurate measure of CD, for a valid number of similar features, than CD-SEM metrology. 11-13 Therefore, we translated our CD-SEM metrology data for LS and CH patterns to YieldStar metrology (ASML OCD scatterometrybased metrology) data using first order fit equations provided by ASML (Veldhoven).…”

“…6 Initially, the line-spread function (LSF) F(y), where y is the trench half-width, was obtained from the 50 nm-fullpitch LS pattern (Figure 1(a)). The LSF exhibits a knee at a trench half-width of 11.6 nm with an asymptotic power-law drop-off of 1/ y 4.5 .…”

“…6 Based on this, Maas et al demonstrated experimentally that SHIBL is indeed a promising and a cost-effective method for pre-screening chemically amplified resists (CARs), and so determining the Z-factor, 7 prior to their final performance evaluation in an EUV scanner. 6 However, in that work, singlepixel SHIBL in CAR resulted in poorer local critical dimension uniformity (LCDU) and slightly lower line-width roughness (LWR) to that of obtained with EUVL. This was partly attributed to the high SE yield in SHIBL which makes He-ions 150 times more effective than EUV photons in patterning a similar CAR.…”

“…This was partly attributed to the high SE yield in SHIBL which makes He-ions 150 times more effective than EUV photons in patterning a similar CAR. 6 Therefore, ion shot noise may be a limiting factor in SHIBL for patterning sensitive CARs, thus hindering pattern fidelity.…”