STUDIES ON STRUCTURAL, ELECTRICAL, COMPOSITIONAL, AND MECHANICAL-PROPERTIES OF WSIX THIN-FILMS PRODUCED BY LOW-PRESSURE CHEMICAL-VAPOR-DEPOSITION

Tungsten silicide (WSix) thin films have been deposited by low-pressur e chemical vapor deposition using silane (SiH4) and tungsten hexafluor ide (WF6) at different fluxes ratio ranging from 44 to 745 onto planar Si(100) wafers covered by 130 Angstrom of SiO2 and 2000 Angstrom of p hosphorus-doped polysilicon layers to reproduce the control gate struc ture of a FLASH-EEPROM. The deposited films have been annealed in oxyg en ambient at 900 degrees C. The composition of as deposited films as well as annealed films has been studied by x-ray photoelectron spectro scopy, Rutherford backscattering spectroscopy, and secondary ion mass spectroscopy. Cross section scanning electron microscopy and atomic fo rce microscopy have been employed to study the thickness and the surfa ce morphology of the deposited layers. The resistivity and the mechani cal properties of the films have been also investigated. The as-deposi ted films have shown, growing the SiH4/WF6 ratio, an increase of the S i/W stoichiometric ratio (until 3), a decrease of the film thickness a nd stress while there is an increase of the sheet resistance. In the c ase of annealed films, which pass from amorphous state to crystalline structure, as detected by x-ray diffraction, there is a strong decreas e of the sheet resistance values as well as of the silicide him thickn ess depending on the SiH4/WF6 ratio, while the presence of a silicon o xide layer with different thickness has been also detected on top of t he silicide layer. (C) 1998 American Vacuum Society. [S0734-2101(98)08 403-6].