Copper–titanium thin film interaction

Abstract

Interaction between 5 μm thick copper and 50 nm thin titanium films was investigated as a function of annealing temperature and time using MeV 4He+ Rutherford backscattering, X-ray diffraction and dynamic Secondary Ion Mass Spectrometry. Samples were made by depositing 10 nm of titanium on a PECVD silicon oxynitride, followed by 50 nm of titanium nitride and 50 nm of titanium in the said order. In the same system 100 nm of copper were subsequently sputtered; finally 5 μm of copper were grown by electroplating. This complex structure was chosen in order to investigate the possibility of using copper interconnects also in power devices. To investigate the composition and growth of Ti–Cu compound on the buried interface, it was necessary to develop a special procedure. The results of the investigation show the formation of a laterally non-uniform layer of TiCu4, which is presumably preceded by the formation of CuTi. The growth of the compound is kinetically controlled by means of a diffusion coefficient having 1.7 eV activation energy and a 5×10−2 cm2/s pre-exponential factor. The formation of a titanium–copper compound ensures a reliable and low resistance electrical contact especially at the vias. The Ti/TiN/Ti acts efficiently as a sacrificial and inert diffusion barrier. No copper was detected on the silicon oxynitride surface even after a 20-min 500 °C heat treatment.