|M.Sc Student||Joseph Shay|
|Subject||TiSiN Films Produced by CVD as Diffusion Barriers for Cu|
|Department||Department of Materials Science and Engineering||Supervisor||Professor Emeritus Moshe Eizenberg|
The decrease in microelectronic device dimensions and the continuos effort to increase the speed and performance of devices have led to the need to replace the current metallization of Al(Cu) with Cu. This metal must be isolated from the neighboring dielectrics by a thin diffusion barrier layer. The need for conformality and for the use of extremely thin layers serves as a driving force to look for chemical vapor deposition as the future deposition method.
TiSiN films produced by using a cyclic process of thermal decomposition of tetrakis-dimethylamino-titatnium followed by H2/N2 plasma and a flash of SiH4 are attractive candidates as diffusion barriers for Cu metallization in future devices. In this research we have studied the microstructure, chemical composition and bonding of the film and its interface with Cu metallization and a low dielectric constant material called Black Diamond. The microstructure of the film as determined by high resolution transmission electron microscopy was found to consist of nanoscale TiN grains embedded in an amorphous matrix of Ti-Si-N. X-ray photoelectron spectroscopy results indicate that most of the silicon atoms are bonded to nitrogen in the form of Si3N4. The film composition was measured using Auger electron spectroscopy. It was found that the plasma treatment reduces the level of carbon in the film and enhances its crystallinity. This causes a dramatic reduction of the resistivity. The plasma treated film shows no oxygen uptake, and the resistivity remains constant upon long term air exposure. X-ray reflectivity measurements show an increase in the films density and a reduction of its thickness as a result of the plasma treatment. The barrier integrity was evaluated using secondary ion mass spectrometry (SIMS) and SECCO etch pitting test. In the plasma treated samples, Cu diffusion was detected by SIMS after annealing at 500ºC. Etch pits were first observed after annealing at 600ºC. It was found that the plasma treatment improves the barriers ability to prevent copper diffusion to the substrate due to the higher density of the treated film, while SiH4 only slightly improves the barrier integrity due to the formation of Si3N4, which is known as one of the best diffusion barriers for copper.