Influence of substrate temperatures on the properties of GdF_3 thin films with quarter-wave thickness in the ultraviolet region

Abstract

High-quality coatings of fluoride materials are in extraordinary demand for use in deep ultraviolet (DUV) lithography. Gadolinium fluoride (GdF₃) thin films were prepared by a thermal boat evaporation process at different substrate temperatures. GdF₃ thin film was set at quarter-wave thickness (∼27 nm) with regard to their common use in DUV/vacuum ultraviolet optical stacks; these thin films may significantly differ in nanostructural properties at corresponding depositing temperatures, which would crucially influence the performance of the multilayers. The measurement and analysis of optical, structural, and mechanical properties of GdF₃ thin films have been performed in a comprehensive characterization cycle. It was found that depositing GdF₃ thin films at relative higher temperature would form a rather dense, smooth, homogeneous structure within this film thickness scale.

Optical Characterization of Gadolinium Fluoride Films Using Universal Dispersion Model

“…The symbol D(•) denotes the Dawson function (integral) [37]. Relation (17) includes only the excitation of electrons from occupied localized electron states to unoccupied localized states, but localized states also contribute to the absorption involving delocalized (extended) states, i.e., to the so-called Urbach tail. The Urbach tail can be explained as the transitions of the electrons from the localized valence states to the extended unoccupied conduction states and the transitions from the extended valence states to the localized unoccupied states [38].…”

“…The internal scattering in the film (extinction) increases with the size of the grains and the scattering losses at the interfaces also increase due to the roughness [15,16]. In addition, films with large grains show a porosity that negatively affects the extinction coefficient in the transparent region due to the presence of localized states [17][18][19]. The localized states originate in the surface states of the grains as well as in the adsorbed substances in the pores, which constitute unstable components depending on the environmental conditions.…”

Optical characterization of inhomogeneity of polymer-like thin films arising in the initial phase of plasma-enhanced chemical vapor deposition

“…The foregoing statements are illustrated, for example, in characterizing homogeneous thin films in papers [20] , [21] , [22] , [23] , [24] , [25] and inhomogeneous thin films in papers [26] , [27] , [28] , [29] , [30] , [31] . It should be emphasized that a correct choice of both the structural and dispersion models represents a necessary condition for the successful and correct optical characterization of inhomogeneous thin films.…”

Optical Characterization of Inhomogeneous Thin Films Deposited onto Non-Absorbing Substrates

“…While significant attention has been dedicated to developing suitable methods for the optical characterization of homogeneous thin films, as evidenced by the abundance of publications on the subject represented here by a small selection [1][2][3][4][5][6][7][8][9], much less attention has been paid to the optical characterization of inhomogeneous thin films with refractive index profiles along the axis perpendicular to the film boundaries. Nevertheless, several papers have addressed this issue [10][11][12][13][14][15][16][17][18][19][20][21][22][23][24].…”