Contribution of EUV resist components to the non-cleanable contaminations

Abstract

The suppression of outgassing from extreme ultraviolet (EUV) resist needs to be addressed for realizing EUV lithography (EUVL) because outgassing is likely the main contributor to the contamination of mirror optics in EUV scanners, which results in reflectivity loss. Resist outgassing causes two types of contamination: cleanable contamination, involving hydrocarbon contaminants, and noncleanable contamination, involving noncarbon components. The relation of cleanable contamination between EUV-and electron beam (EB)-based evaluations is linear. However, the relation of noncleanable contamination is not clear. In this study, we investigated the contribution of EUV resist components to noncleanable contamination using different photoacid generator components. The cleanability of noncleanable elements (sulfur, iodine, chlorine, and bromine) in contamination films was measured and compared for the EUV-and EB-based outgas testers. The result suggested that the chlorine and bromine contaminants were completely removed after cleaning. On the other hand, sulfur and iodine remained even after cleaning. This suggested that the careful use of iodine in resist materials is necessary due to its high photoabsorption and low cleanability. In addition, the cleaning rate and noncleanability of contaminants in the EUV-based test were larger than in the EB-based test. This suggests that the contamination film in the EUV-based test is more porous than that in the EB-based test.

Acid generation efficiency: EUV photons versus photoelectrons

“…Based on the AHC results presented in this section, it is possible to speculate with the formation of organic volatile species containing iodine (C x H y I) during treatment with hydrogen radicals, such as iodomethane an iodobenzene among other possibilities. It is noted that a similar experiment was conducted in the past [38], however the amount of PAG contained in the resist film was significantly larger (30%wt with respect to polymer solids) and a different iodine-containing material was used . In that case, the iodine surface concentration was reduced during hydrogen cleaning but it was not possible to completely eliminate the iodine signal as measured with XPS, indicating that other factors such as the positioning of the witness sample with respect to the source of hydrogen radicals (hot tungsten filament) or the iodine-to-carbon ratio in the carbonaceous layer could modulate the ability to effectively remove the iodine content from EUV optics surfaces.…”

“…The EUV sensitivity for iodine (dR/R per at%) is considered sufficiently high that only minute iodine quantities are allowed on EUV optics surfaces in order to maintain the reflectivity loss within specifications. Historically, iodine has been considered an element that cannot be readily reacted with hydrogen radicals on EUV optics surfaces as regularly done inside the EUV scanner, and has therefore been considered a non-cleanable element by the resist outgassing community [38]. In principle, the EUV reflectivity loss limit imposed by iodine should preclude the use of iodine-containing species in EUV resist formulations.…”

Relationship between Defects and Stochastic Effect in Chemically Amplified Resists Used for Extreme Ultraviolet Lithography

“…In our experiment, the line-and-space patterns of the EIDEC standard resist 27) were fabricated using the SFET 28,29) for EUV lithography. The numerical aperture of the SFET is 0.3.…”

“…Using the modified method, the dependences of line width and LER on the nominal line width (half-pitch) and exposure dose were analyzed. The exposure experiments of the EIDEC standard resist 27) were carried out using a small-field exposure tool (SFET) 28,29) of EIDEC. The nominal line width was changed from 21 to 60 nm.…”

Acid Diffusion Length in Line-and-Space Resist Patterns Fabricated by Extreme Ultraviolet Lithography

“…Using the modified method, the dependences of line width and LER on nominal line width (half-pitch) and exposure dose were analyzed. Exposure experiments on the EIDEC standard resist 22) were carried out using a small field exposure tool (SFET) 23,24) of EIDEC. The nominal line width was varied from 21 to 60 nm.…”