CHARACTERIZATION OF ENCROACHMENT OF SELECTIVE CHEMICAL VAPOR-DEPOSITION OF TUNGSTEN AT THE EDGE OF CONTACTS

The encroachment of selective chemical vapor deposition of tungsten at the edge of contacts has been examined with RBS, SEM, stylus height measurements, and TEM. Encroachment is minimized by using SiH4 reduction instead of H-2 reduction, a deposition temperature of 340-degrees-C or less, an in situ plasma clean, and a SiH4/WF6 flow ratio greater-than-or-equal-to 0.1. Use of a plasma clean can reduce the W grain size by a factor of four and reduce nonuniform consumption of the polysilicon. The improvements using a plasma clean are associated with an increase in the density of chemical vapor deposition of tungsten nucleation sites.