Elemental depth profiling in transparent conducting oxide thin film by X-ray reflectivity and grazing incidence X-ray fluorescence combined analysis

H. Rotella (1) , B. Caby (1) , Y. Ménesguen (2) , Y. Mazel (1) , A. Valla (3) , D. Ingerle (4) , B. Detlefs (1) , M.-C. Lépy (2) , A. Novikova (2) , G. Rodriguez (1) , C. Streli (4) , E. Nolot (1)

1 CEA-LETI - Commissariat à l'énergie atomique et aux énergies alternatives - Laboratoire d'Electronique et de Technologie de l'Information
2 LNHB (CEA, LIST) - Laboratoire National Henri Becquerel (CEA, LIST)
3 LITEN - Laboratoire d'Innovation pour les Technologies des Energies Nouvelles et les nanomatériaux
4 Atominstitut

The optical and electrical properties of transparent conducting oxide (TCO) thin films are strongly linked with the structural and chemical properties such as elemental depth profile. In R&D environments, the development of non-destructive characterization techniques to probe the composition over the depth of deposited films is thus necessary. The combination of Grazing-Incidence X-ray Fluorescence (GIXRF) and X-ray reflectometry (XRR) is emerging as a fab-compatible solution for the measurement of thickness, density and elemental profile in complex stacks. Based on the same formalism, both techniques can be implemented on the same experimental setup and the analysis can be combined in a single software in order to refine the sample model. While XRR is sensitive to the electronic density profile, GIXRF is sensitive to the atomic density (i. e. the elemental depth profile). The combination of both techniques allows to get simultaneous information about structural properties (thickness and roughness) as well as the chemical properties. In this study, we performed a XRR-GIXRF combined analysis on indium-free TCO thin films (Ga doped ZnO compound) in order to correlate the optical properties of the films with the elemental distribution of Ga dopant over the thickness. The variation of optical properties due to annealing process were probed by spectroscopic ellipsometry measurements. We studied the evolution of atomic profiles before and after annealing process. We show that the blue shift of the band gap in the optical absorption edge is linked to a homogenization of the atomic profiles of Ga and Zn over the layer after the annealing. This work demonstrates that the combination of the techniques gives insight into the material composition and makes the XRR-GIXRF combined analysis a promising technique for elemental depth profiling.

Mots clés: thin film; Grazing-Incidence X-ray Fluorescence (GIXRF); X-ray reflectometry (XRR); Depth profiling; Transparent conducting oxide; non-destructive characterization; instrumentation; structural properties; chemical properties; optical properties; annealing; spectroscopic ellipsometry; ionizing radiation

Domaines: Micro et nanotechnologies/Microélectronique

H. Rotella, B. Caby, Y. Ménesguen, Y. Mazel, A. Valla, et al.. Elemental depth profiling in transparent conducting oxide thin film by X-ray reflectivity and grazing incidence X-ray fluorescence combined analysis. Spectrochimica Acta Part B: Atomic Spectroscopy, 2017, 135, pp.22-28. ⟨10.1016/j.sab.2017.06.011⟩. ⟨cea-02957331⟩