Chemical effect of dry and wet cleaning of the Ru protective layer of the extreme ultraviolet lithography reflector

Abstract

We report the chemical influence of cleaning of the Ru capping layer on the extreme ultraviolet (EUV) reflector surface. The cleaning of EUV reflector to remove the contamination particles has two requirements; to prevent corrosion and etching of the reflector surface and to maintain the reflectivity functionality of the reflector after the corrosive cleaning processes. Two main approaches for EUV reflector cleaning: wet chemical treatments (sulfuric acid and hydrogen peroxide mixture (SPM), ozonated water, and ozonated hydrogen peroxide) and dry cleaning (oxygen plasma and UV/ozone treatment) were tested. The change of surface morphology and roughness were characterized using scanning electron microscopy (SEM) and atomic force microscopy (AFM), while the surface etching and change of oxidation states were probed with X-ray photoelectron spectroscopy (XPS). Significant surface oxidation of the Ru capping layer was observed after oxygen plasma and UV/ozone treatment, while the oxidation is unnoticeable after SPM treatment. Based on these surface studies, we found that SPM treatment exhibits the minimal corrosive interactions with Ru capping layer. We address 2 the molecular mechanism of corrosive gas and liquid-phase chemical interaction with the surface of Ru capping layer on the EUV reflector.* Corresponding author, e-mail address: somorjai@berkeley.edu Material names: Ruthenium, Ruthenium oxide, sulfuric acid, hydrogen peroxide, and ozonated water 3

Structure and morphology of Ru films grown by atomic layer deposition from 1-ethyl-1’-methyl-ruthenocene

“…Characteristic Ru peaks for 3d 3/2 and 3d 5/2 locate at 284 and 280 eV. These peak positions are in agreement with those earlier observed in different studies on Ru films [18,19,25,44,45]. The profiles of the Ru peaks indicate that the influence of the residual carbon is weak, i.e.…”

Impact of surface chemistry

“…New 18-nm manufacturing processes are expected to arrive in 2018. These processes include the following: the growth and deposition of sub-10-nm thin films of low-k insulating materials (for example, SiOC) and high-k gate dielectric materials (for example, SiO x N y ); the conformal etching of deposited thin films with high aspect ratios; high-spatial-resolution patterning with new lithography techniques; the doping of the sub-10-nm silicon channels; and the deposition of new wiring materials with low resistance and high reliability (for example, Cu) (8,(44)(45)(46). The development of these new manufacturing processes leads to a broad range of surface and interface chemistry issues.…”

Improved oxidation resistance of Ru/Si capping layer for extreme ultraviolet lithography reflector

“…The peak at the lower binding energy ͑ϳ529.5 eV͒ is associated with oxygen atoms from RuO 2 and the peak at the higher binding energy ͑531.4ϳ 531.7 eV͒ corresponds to weakly bound oxygen atoms associated with chemisorbed and dissolved ͑subsurface͒ oxygen in the Ru lattice, on the surface, or oxygen from an OH group. 5,19,25 In the case of the spectrum in Fig. 1͑c͒, the peak at 531.7 eV is shifting the entire spectrum to a higher binding energy, as it is dominating the spectrum in the Ru/Si capping layer.…”

“…[7][8][9][10][11][12] Current processes for cleaning EUV lithography reflectors involve many corrosive and oxidizing environments, including acids, bases, UV/ozone, and plasma. 5,6,[13][14][15][16][17][18] However, cleaning processes that involve corrosive chemicals cause surface oxidation of the Ru capping layers, 19 resulting in surface corrosion and deterioration of the EUV reflector. Therefore, it is necessary to develop new types of capping layers that exhibit higher chemical and oxidation resistance.…”