Optical constants and absorption properties of Te and TeO thin films in the 13-14 nm spectral range

Abstract

Undesired mask-induced effects caused by thick absorber layers in EUV photomasks reduce the quality of the projected patterns at the wafer stage in EUV photolithography scanners. New materials with better absorption properties than the state-of-the-art absorbers, TaN and TaBN, are required to mitigate these effects. In this work, we investigated the optical properties (δ and k) of Te and TeO films in the 13-14 nm range, and the absorption properties of these two materials at 13.5 nm. δ and k are obtained through fitting experimental values of reflectivity versus angle of incidence in the EUV range. We follow a methodology which combines different characterization techniques (X-ray reflectivity, EUV reflectivity, and X-ray photoemission spectroscopy) to reduce the number of free parameters in models and hence, increase the reliability of the optical constants obtained. At 13.5 nm, we obtain δ=0.03120, k = 0.07338 for Te, and δ=0.04099, k = 0.06555 for TeO. To experimentally verify the absorption properties of these materials, different thicknesses of Te and TeO films are cast on top of a state-of-the-art mask-quality EUV multilayer with 66.7% reflectivity at 13.5 nm. We found that a reflectivity of ∼0.7% can be attained with either 32.4 nm of Te, or 34.7 nm of TeO, greatly surpassing the absorption properties of TaN and TaBN. The morphology and surface roughness of the Te and TeO films deposited on the multilayer are also investigated.

Determination of optical constants of thin films in the EUV

“…When comparing our data at 91.85 eV to the existing literature of direct measurements of the optical constants [30,31,32,33,34,35,36], we find the differences in values, that are summarized in figure 4 alongside those, calculated from atomic scattering factors [10,37,38]. Of those references, the data of Windt et al on Mo, Pt, Ru, and Ta [30], as well as the data of Rodríguez-de Marcos et al on Te [36], Hosoya et al on Ta [35] were obtained from reflection type measurements and are therefore very comparable to ours with respect to methodology and outcome. An exception is the value of Diel et al on Ni [32], which is far off our value and the one from CXRO [10].…”

“…From atomic scattering factors: black triangles[10], green triangles[37,38], from reflectance measurements: blue rectangles[30]. From various other studies: magenta diamonds, Mo[31], Ni[32], Pt[33], Ru[34], Ta[35], Te[36].…”

Impact of Annealing Temperature on the Morphological, Optical and Photoelectrochemical Properties of Cauliflower-like CdSe0.6Te0.4 Photoelectrodes; Enhanced Solar Cell Performance

“…Figure 1e shows the Te 3d spectral region of the CdSe 0.6 Te 0.4 sample annealed at a temperature of 350 • C. The spectra of the Te 3d show characteristic peaks at binding energies of 573.75 and 584.20 eV, which correspond to the Te 3d 5/2 and Te 3d 3/2 states, respectively (shown in Figure 1e) [4,40,41]. The Te 3d core-level spectra show the two other peaks observed at binding energies of 576.66 and 586.96 eV, which are assigned to Te 3d 5/2 oxide and Te 3d 3/2 oxide, respectively [42]. The XPS survey spectrum of both CdSe 0.6 Te 0.4 samples shows the two other peaks at the binding energies of 284.56 and 531.56 for the C ls and O 1s peaks, respectively.…”

High-precision optical constant characterization of materials in the EUV spectral range: from large research facilities to laboratory-based instruments

“…The incorporation of prior knowledge and further measurements such as transmission electron microscopy (TEM), atomic force microscopy (AFM), X-ray photoelectron spectrometry (XPS) or X-ray reflectometry (XRR) at shorter wavelengths, are crucial in the development of suitable layer models. The reliability of the determined optical constants is enhanced when combining complementary data [13,14]. A refined depth-dependent frequency analysis of XRR measurements as discussed in Saadeh et al 2021 [15] can be helpful to narrow the parameter range of the layer thicknesses and to fix the order of the thin oxidation layers.…”