EUV Resist Materials Design for 15 nm Half Pitch and Below

Abstract

Chemically amplified resist materials with a different sensitivity were prepared to investigate impact of sensitivity on resolution at 15 nm half-pitch (hp) using a EUV microfield exposure tool (MET) at SEMATECH Berkeley. Sensitivity at least slower than 30 mJ/cm 2 was required to resolve 15 nm hp patterns using current EUV resists. It is noteworthy that resolution of 15 nm hp was limited by not only pattern collapse but also pinching of patterns. The same tendency is observed in E-beam patterning at 20 nm hp. A strong relationship between pinching and sensitivity in E-beam exposure indicates contribution of photon-shot noise on the pinching. Clear correlation between diffusion length and pinching using the E-beam exposure indicates that acid diffusion is another contributor on the pinching. Bound PAG into polymer and molecular PAG with a big anchor group showed almost same character on pinching. Key conclusion here is even in a molecular PAG, we can control acid diffusion to achieve 15 nm hp resolution capability. Strategy to improve sensitivity is to utilize resist with high deprotection efficiency. Polymer with a low thermal activation energy on deprotection (low Ea polymer) was demonstrated as a key technology to achieve 15 nm hp resolution with a faster sensitivity below 26 mJ/cm 2. Special rinse material was effective for reducing LWR by ~ 20%. Sensitivity dependency of outgassing have been systematically discussed at first. A good linear correlation between a cleanable outgassing amount and exposure energy strongly indicates tradeoff relationship between outgassing and sensitivity. Applying a new EUV topcoat to resist demonstrated reduction of outgassing from 7.39 nm to below 0.1 nm with maintaining resolution.

Negative-tone Imaging with EUV Exposure toward 13 nm hp

“…We have previously reported that combination of a high Tg and low Ea polymer with a large acid provides an apparently better L/S resolution with maintaining sensitivity [10,24]. In this study, we explored the same idea to determine how acid diffusion length contributes to block mask and isolated dot resolution.…”

“…Our previous study revealed that sensitivity more than 30 mJ/cm 2 is necessary to obtain realistic pattern quality on 15 nm hp and below if we utilize conventional CAR resist and process [10]. Recently Kocsis et al, reported that some metal containing resists can print 9.5 nm L/S using EUV interference lithography tool, but this resist also needs ~50 mJ/cm 2 sensitivity [11].…”

“…Key approach to improve this tradeoff relationship is increasing photo-activated materials during exposure to mitigate stochastic effects by PSN, hence many researchers have investigated metal containing resist to increase EUV absorption coefficient [12][13][14][15]. Although another method to overcome PSN is applying smoothing process [10], this approach is typically not acceptable with respect to resolution.…”

“…The main challenges for EUV resist is to simultaneously satisfy resolution, line-width roughness (LWR), and sensitivity requirements according to ITRS roadmap [1][2][3][4]. While resolution of 13 nm linespace (L/S) pattern has been recently demonstrated using a chemically amplified resist (CAR) with an aqueous 2.38% TMAH developer, major limitation still exists on sensitivity [5][6][7]. Current sensitivity achievement reported so far is 37 mJ/cm 2 which is still higher than industry requirement of 20 mJ/cm 2 [8,9].…”

Polarization-selective polymerization in a photo-crosslinking monomer film

“…Almost exclusively, isotropic photoresists 1,[5][6][7] are employed and an enormous range of structures, components and devices is produced.…”