A study of low temperature crystallization of amorphous thin film indium-tin-oxide

Deposition of tin-doped-indium-oxide (ITO) on unheated substrates via low e nergy processes such as electron-beam deposition can result in the formatio n of amorphous films. The amorphous-to-crystalline transformation was studi ed in this system using in situ resistivity, time resolved reflectivity, gl ancing incidence angle x-ray diffraction, and transmission electron microsc opy. The resistivity of 180 nm thick In2O3 (9.9 wt. %SnO2) was monitored du ring isothermal anneals at 125, 135, 145, and 165 degrees C. The dependence of the resistance on the volume fraction of crystalline phase was establis hed using glancing incidence angle x-ray diffraction and a general two phas e resistivity model for this system was developed. These studies show that, upon annealing, as-deposited amorphous ITO undergoes both a structural rel axation and crystallization. Structural relaxation of the amorphous materia l includes local ordering that increases the ionized vacancy concentration which, in turn, increases the carrier density in the material. Kinetic grow th parameters were extracted from the data, which reveal that the relaxatio n of the amorphous structure occurs via a process that obeys a first order reaction rate law, while crystallization occurs via classical nucleation an d growth with a growth mode parameter that is consistent with two- to three -dimensional transformation geometry. Both the relaxation and crystallizati on processes have an activation energy of approximately 1.3+/-0.2 eV. Time resolved reflectivity analysis of the electron beam deposited ITO reveals t hat there is a sharp and monotonic decrease in reflectivity during the anne al of the sample which is associated with the amorphous relaxation process. (C) 1999 American Institute of Physics. [S0021-8979(99)06912-1].