In this paper, we proposed a new design of the test mask to measure the amount of the out-of-band (OOB) light from an extreme-ultraviolet (EUV) light source by detuning the period of the multilayer (ML), rather than changing the material of the absorber, to suppress reflection of EUV light. The new OOB test mask also reflects essentially the same OOB light as that of the production mask at each wavelength in the whole OOB spectral range. With the help of the new OOB test mask, the contributions to the background intensity from in-band flare and OOB light can be correctly separated and an accurate optical-proximity-correction (OPC) model can be established.
Resolution (R), line-width roughness (L), and sensitivity (S) are three key indices describing the performance of a resist. When optimizing a resist to compromise the RLS trade-off in extreme-ultraviolet lithography, outgassing of the resist also needs to be considered, because it will cause deposition of cleanable and non-cleanable contaminants on the surface of the projection optics and reduce the throughput of the exposure tool. In this paper, the dependence of outgassing of a resist on its compositions, such as types of photo-acid generator, quencher, and acid liable group as well as their loadings are investigated systematically through a set of specially prepared resist samples. The outgassing of these samples is tested on EUVOM-9000 from Litho Tech Japan. The lithographic performances of these samples are also characterized on the ASML NXE3100. Directions for optimizing resist lithographic performance under the constraint of resist outgassing are proposed.
We investigated the effect of quencher type and loading concentration in OoB-insensitive EUV resists via actual
exposure on the latest EUV scanner and stochastic simulation using Prolith. Model resist samples with two quencher
types, conventional base type and photo-decomposable base type, at variant loading concentrations were prepared and tested. Basic indicators of lithographic performance, such as depth of focus, energy latitude, and line-width roughness were significantly improved by 80 nm, 8.4% and 25%, respectively along with a moderate increase of sensitivity (ca. 5mJ/cm2) under the optimized quencher condition. Meanwhile, we further quantitatively analysis the outgassing-induced contamination growth to realize the quencher distribution engineering effect on outgassing issue in EUV lithography. In addition, stochastic simulation for EUV resist featuring various types of quenchers provides certain correlation with the experimental results.
In this paper, the impact of resist on the lithographic process window is investigated. To estimate the resolution
limit of EUVL due to the limitation from resist performance, a simplified resist model, called diffused aerial image
model (DAIM), is employed. In the DAIM, the resist is characterized by the acid diffusion length, or more generally,
resist blur. Lithographic process windows with resists of various blurs are then calculated for different technology nodes.
It is concluded that the resist blur needs to be smaller than 8 nm to achieve a reasonable window for the technology node
with the minimum pitch of 32 nm. The performance of current resists can barely fulfill this requirement. Investigation of
a more refined resist model is also initiated.
In this paper, definition of line/space patterns at 44-, 32-, and 22-nm pitches using extreme-ultraviolet lithography
(EUVL) is investigated by aerial image simulation. The results indicate that extending EUVL to the 22-nm pitch requires
reducing the mask shadowing effect, which implies reducing the mask absorber thickness as well as maintaining the
6-degree angle of incidence on the mask, if the reduction ratio of the imaging system is to be kept at 4. Reduction of the
mask absorber thickness can be realized by implementing attenuated phase-shifting masks. Otherwise, all critical
patterns must be laid out in single orientation.
A programmed-defect mask consisting of both bump- and pit-type defects on the LTEM mask substrate has been
successfully fabricated. It is seen that pit-type defects are less printable because they are more smoothed out by the
employed MLM deposition process. Specifically, all bump-type defects print even at the smallest height split of 1.7 nm
whereas pit-type defects print only at the largest depth split of 5.7 nm. At this depth, the largest nonprintable 1D and 2D
defect widths are about 23 nm and 64 nm, respectively.