Properties and thermal stability of chemically vapor deposited W-rich WSix thin films

Abstract

The tungsten-rich (Si/W atomic ratio less than 2.0) chemical vapor deposition (CVD)-WSix layer was found to be an efficient diffusion barrier against Cu diffusion. In this study, the properties and thermal stability of the W-rich WSix films chemically vapor deposited at various deposition temperatures, pressures, and SiH4/WF6 reactant gas flow ratios were investigated. With SiH4/WF6 flow rates of 6/2 seem and a total gas pressure of 12 mTorr, the activation energy of the CVD process was determined to be 3.0 kcal/mole, and the film deposited at 250 degrees C has a Si/W atomic ratio of unity. The WSix, films have a low residual stress, low electrical resistivity, and excellent step coverage. For the WSix layers deposited on Si substrates, the residual stress varies from 7 to 9 X 10(8) dynes/cm(2) depending on the deposition temperature. The resistivity of the WSI, films varies from 200 to 340 mu Omega cm; higher deposition temperatures and SiH4/WF6 flow ratios resulted in higher film resistivities. The as-deposited amorphous WSix layer is thermally stable up to 600 degrees C; however, crystallization of the deposited film takes place at 650 degrees C and WSix was transformed into WSi2 phase when the WSix/Si structure was thermally annealed at temperatures above 650 degrees C. (C) 1999 American Vacuum Society. [S0734-211X(99)03602-1].