The Influence of Substrate Doping on Silicide Formation with Tungsten Deposited From Tungsten Hexafluoride

Abstract

The influence of substrate doping on the WSiz formation is investigated. Ion implantation was used to dope Si wafers with either B, Al, P, As or Sb. Implanted doses were in the range from 1 × 1013 to 5 × 1016at./cm2. Dopant activation was always performed before tungsten deposition in a hot wall LPCVD system. The sillcidation was monitored by means of Rutherford backscattering spectrometry (RBS), and the dopant redistribution was analyzed by secondary ion mass spectroscopy (SIMS). The suicide formation on p-type substrates was retarded at high doping levels, whereas that on the n-type substrates showed a more complex behavior. In the latter cases, the silicidation could be either retarded or unaffected, depending on the dopant concentration. Sb doped wafers exhibited a slightly increased silicidation rate with doping level, while P and As doped wafers showed a peak, reaction rate for intermediate doping levels. SIMS analysis revealed a segregation of B and P into the suicide during formation, while Al, As and Sb were snowplowed and accumulated at the WSi2/Si interface. Binary and ternary compounds of Al, P and As with W and Si were found by X-ray diffraction for the highest doping levels.