Metrology development for extreme ultraviolet lithography: Flare and out-of-band qualification

Abstract

Articles you may be interested inCharacterization of out-of-band radiation and plasma parameters in laser-produced Sn plasmas for extreme ultraviolet lithography light sources Extreme ultraviolet lithography (EUVL) is the leading candidate for lithography beyond the 22 nm half-pitch device manufacturing node. These geometries impose tighter requirements for standard critical dimension metrology and call for new strategies able to quantify and monitor extreme ultraviolet (EUV) specific parameters. In this paper, the approaches to measure two key EUV imaging parameters, namely flare and out-of-band (OoB) radiation, are discussed. EUV sources are known to emit a broad spectrum of wavelengths ranging from EUV to deep ultraviolet (DUV) and beyond. As the DUV can contribute to the photoresist exposure and degrade imaging performance, it is critical to accurately determine the amount of DUV OoB in EUVL exposure tools at the wafer level. In this paper, a methodology using an aluminum-coated reticle to measure the DUV=EUV ratio in resist is discussed. Such a mask is able to provide quantitative in situ information on the scanner DUV content thanks to its ability to transmit DUV and absorb EUV. The experimental OoB results for two EUVL tools are reported and compared with modeling predictions. Flare in EUVL is caused by light scattered by the surface roughness of the optical elements and has a larger impact as compared to optical lithography. As a consequence, a precise and accurate flare metrology is essential to guarantee a proper qualification of the effect, as well as to implement an effective compensation strategy. However, the flare level estimate has been historically based on operator and tool-dependent procedures that are unable to meet the requirements for accuracy and precision dictated by EUVL. A robust in-line approach to flare metrology is developed and qualified. As in the case of OoB, experimental flare results for two EUVL tools are reported. The experimental data are compared to full-chip simulations using the point spread function of the tool's optical system.

Review of resist-based flare measurement methods for extreme ultraviolet lithography

“…The OoB is usually measured with metal blades 26 or with a metal-coated mask. 27 From Table 1 in Ref. 27, 96% of the OoB is reflected from aluminum while almost no EUV light is reflected.…”

“…27 From Table 1 in Ref. 27, 96% of the OoB is reflected from aluminum while almost no EUV light is reflected. At the same time, 60% and 39% of OoB can be reflected from the ML and the absorber, respectively.…”

“…At the same time, 60% and 39% of OoB can be reflected from the ML and the absorber, respectively. Although an aluminum-coated mask is a good option to measure OoB, a normal EUV mask with a large absorber area can also be used to estimate OoB taking into account the ratio result from Lorusso et al 27 The OoB measured from aluminum indicates the total OoB in the EUVL system, while the OoB reflected from absorber and ML are closer to the real case, since the EUV mask absorption of OoB is included. The OoB from the absorber and the ML provides the lower and upper limits in cases where bright and dark fields are co-located on the mask.…”

Effects of out-of-band radiation on EUV resist performance

“…In general, OOB wavelength is reported to be around 150-400 nm and DUV/EUV intensity ratios range from 1% to up to 30% [12][13][14][15] . The issue is that EUV resists are sensitive to both EUV and OOB radiation because a fair amount of EUV photoresists are based on materials designed for 193 nm and 248 nm.…”

Effect of radiation on the defectivity and stability of Ru-capped MoSi multilayer blanks

“…The wavelength of the radiation ranges from λ= 13.5 nm up to λ= 600 nm. During EUV exposure, the mask is exposed to λ= 13.5 nm by in-band and λ= 140 nm to λ= 600 nm by out-of-band radiation [1]. During cleaning, the mask can be exposed to λ= 172 nm up to λ= 1049 nm.…”