In situ studies of diffusion and crystal growth in plasma deposited thin ITO films

Tin-doped indium oxide (ITO) films were deposited on Si(100) substrates without external heating by means of DC-planar magnetron sputtering. A metallic In/Sn (90/10) target and an argon/oxygen gas mixture were used. The flow of the reactive gas oxygen was varied between 0 and 2 seem. DC bias voltages between 0 and - 100 V were used. With increasing oxygen flow, the film structure and composition changed from crystalline metallic In/Sn to amorphous ITO. The diffusion of oxygen into metallic In/Sn films and the amorphous-to-crystalline transformation of ITO were studied using in situ grazing incidence X-ray diffractometry (GIXRD), grazing incidence reflectometry (GIXR), and AFM. In situ measurements of GIXRD were made during annealing in vacuum (10(-6) mbar) at temperatures between 100 and 300 degreesC. Two processes determine the ITO crystal growth: the diffusion of oxygen into the metallic film, and a fast crystallization of amorphous ITO. From the X-ray integral intensities the following kinetic parameters were extracted: diffusion constant, activation energy of the diffusion, reaction order and activation energy of the crystal growth process. The diffusion constants depend on the bias voltage in following manner: D(0 V) < D(-100 V) <D(-50 V). The oxygen flow during deposition does not influence the diffusion constant. The activation energy of the diffusion was determined in films deposited without oxygen flow. Two activation energies were found: E-A = 25 kJ/mol for processes below 150 degreesC and E-A=12.4 kJ/mol for diffusion higher than 150 degreesC. The bias voltage does not influence the activation energy. Crystallization of amorphous ITO occurs via classical nucleation and growth mode parameters, as described by the Johnson-Mehl-Avrami equation. Reaction orders between 2.4 and 3.0 were estimated. This is consistent with a two-dimensional transformation geometry. The activation energy is E-A= 74 kJ/mol for films deposited without bias voltage. (C) 2000 Elsevier Science B.V. All rights reserved.