Appl. Phys. A54, 538-542 (1992) Applied Solids PhysicsA "" Surfaces © Springer-Verlag 1992 Interdiffusion at Sb/Ge Interfaces Induced in Thin Multilayer Films by Nanosecond Laser Irradiation R. Serna 1, C.N. Afonso l, F. Catalina l, N. Teixeira 2, M.F. da Silva 2, and J.C. Soares 3 1 Instituto de Optica, CSIC, Serrano 121, E-28006 Madrid, Spain 2 Dept. Fisica, ICEN, LNETI, EN 10, P-2685 Sacavem, Portugal 3 Centro de Fisica Nuclear, Univ. Lisboa, P-1699 Lisboa, Portugal Received 11 July 1991/Accepted21 February 1992 Abstract. Thin films consisting of 3 or 4 Sb and Ge alternating layers are irradiated with single nanosecond laser pulses (12ns, 193nm). Real time reflectivity (RTR) measurements are performed during irradiation, and Rutherford backscattering spectrometry (RBS) is used to obtain the concen- tration depth profiles before and after irradiation. Interdiffusion of the elements takes place at the layer interfaces within the liquid phase. The reflectivity transients allow to determine the laser energy thresholds both to induce and to saturate the process being both thresholds dependent on the multi- layer configuration. It is found that the energy threshold to initiate the process is lower when Sb is at the surface while the saturation is reached at lower energy densities in those configurations with thinner layers. PACS: 68.22, 78.47, 78.70 The use of pulsed laser or e-beam processing to induce mix- ing of multilayer thin films has been a very active field of research during the last decade [1-7]. Much work has been devoted to the study of metal/semiconductor systems due to their interest in microelectronics applications [4-6]. Laser irradiation is a suitable means to induce melting of near sur- face materials and therefore diffusion of the elements occurs at high rates within the liquid state. The process is followed by a rapid quenching that can lead to the formation of unique alloys. Real time optical measurements during irradiation have been widely applied to characterize melting-solidification processes in semiconductors [8-10], and its application to the study of diffusion processes is promising. In a previous work [ 11] the microstructures formed upon laser induced liq- uid phase diffusion in Sb/Ge bilayer films have been studied. It was shown that real time reflectivity (RTR) is a suitable tool to determine the duration of the process. Now it will be shown that the analysis of the evolution of the reflectivity can be correlated to the compositional modifications which are taking place in the sample and therefore to the diffusion kinetics itself. The aim of this work is to study interdiffusion processes induced by laser irradiation in Sb/Ge multilayer structures in order to produce homogeneous mixed films. Thin films consisting of 3 or 4 alternate layers of Ge and Sb are irradi- ated with nanosecond single pulses from an excimer laser to induce melting, diffusion and rapid solidification. The evo- lution of the reflectivity during irradiation is recorded in real time, and the degree of mixing is evaluated through the compositional depth profiles obtained from RBS measure- ments. It is found that the duration of the process and the reflectivity changes measured provide unique information to characterize the mixing evolution as a function of the laser energy density. The role of the as grown layer configura- tion is analyzed as well. The presence of Sb at the surface layer leads to lower energy thresholds to initiate the process, and saturation is reached for the film configurations which involve thinner layers. The large diffusion lengths achieved together with the short duration of the process are consistent with diffusion within the liquid phase. 1 Experimental Method The films were grown by alternate sputtering of Sb and Ge in a multitarget dc magnetron system on glass substrates held at room temperature. The base pressure was 2 x 10 -6 Tort and the argon operating pressure was 4.0 x 10-3 Tort. The grown films have a total thickness of about 60 nm and the as deposited Ge layers are amorphous, while the Sb layers are polycrystalline [11, 12]. Three different film configurations have been studied. Two of them consist of three alternate layers of the same thickness (20 nm) being the surface layer either Sb or Ge, in order to modify the coupling of the laser energy. They will be referred hereafter as Sb/Ge/Sb