Copper diffusion barrier performance of tantalum nitride films deposited by the chemical vapor deposition technique

Increasing demands on computer chip technology require exploration of novel materials, deposition techniques and characterization methods. Currently copper interconnects are being used in the typical back end-of-line (BEOL) integration schemes due to copper's low resistivity (1.7 μΩ-cm) and enhanced resistance to electromigration. Copper interconnects require a barrier layer to prevent diffusion into the dielectric layer. One material being used for the barrier layer is tantalum nitride (TaN_x). Tantalum nitride is expected to perform well as a copper diffusion barrier because of its refractory nature and excellent thermal, chemical, and mechanical properties. In addition, it can be deposited in amorphous form where the diffusion path along grain boundaries is eliminated.; Reported herein are the development and evaluation of a tantalum nitride (TaN_x) thin film deposited by thermal chemical vapor deposition (CVD) for application in giga-scale integration (GSI) BEOL copper metallization protocols. The source chemistries used were tantalum pentafluoride (TaF ₅) and ammonia (NH₃).; The development and optimization of CVD TaN_x employed a two-stage approach with the first stage investigating the reaction kinetics and the second stage using a systematic design of experiment (DOE) approach. The optimization resulted in amorphous Ta₃N₅ films with <0.7at % fluorine contamination, full bulk orthorhombic Ta₃N₅ density (9.851 g/cm3), and a resistivity >10 −5μΩ-cm for 50 nm films.; The copper diffusion barrier properties of the CVD tantalum nitride films were assessed in Cu/TaN_x/Si structures using nitrogen-rich PVD TaN analogs as a baseline. Thermally activated barrier failure was studied as a function of barrier thickness using Rutherford backscattering spectroscopy (RBS) and Secco etch studies to establish baseline metrics for copper diffusion into the barrier and silicon substrate. Additionally, a leading low dielectric constant material was used in a metal-insulator-semiconductor (MIS) structure to evaluate the electrical copper diffusion barrier performance of CVD TaN _x films using the triangular voltage sweep (TVS) method.; Results are also presented from the thermally and electrically promoted copper diffusion through CVD TaN_x films, leading to the identification of the possible failure mechanisms of the barrier material.; 1G. Brauer, J. Weidlein, J. Straehle, Z. Anorg. Allg. Chem. (1966), 348(5–6), 298–308...