Particulate contamination in tungsten low pressure chemical vapor deposition: An experimental study

Particulate contamination is a leading cause for low yields of logic and me mory devices. As circuit feature sizes decrease, submicron particles will h ave a greater effect on the yield. In this article, particulate contaminati on during the fabrication of tungsten multilevel interconnects is investiga ted. Particles can be carried into the chamber with the incoming gas or the y may be generated due to the reactive chemistry present during processing. Tungsten films are deposited using silane (SiH4) reduction of tungsten hex afluoride (WF6). Higher deposition rates can-be obtained by increasing the deposition pressure. However, particle generation has been found to occur a t higher pressures. The particle generation occurs at a SIH4:WF6 inlet mole ratio greater than 1. At high pressures and wafer temperatures (>20 Torr, 425 degrees C), particle deposition is suppressed and the particle exits th e chamber with the exhaust gas. The experimental data show that the particl e generation is not a result of classical homogeneous nucleation or heterog eneous nucleation. The particles are produced from a gas reaction between S i and W containing species. A theory is developed that explains the observe d particle generation, as a function of process pressure, temperature and S iH4:WF6 mole ratios. (C) 1999 American Vacuum Society. [S0734-211X(99)05002 -7].