Study of implanted dopant distribution in polysilicon - tantalum silicide gate structures.
22 July 1986
The distribution of implanted dopants (As and B) between tantalum silicide and polycrystalline silicon (polySi) in the composite gate structure was studied. This problem is a matter of concern because any decrease in the dopant concentration in polySi results in a shift in the threshold voltage of the MOS transistor. The main tools of our study were Rutherford Backscattering Spectroscopy (RBS) for the determination of As dopant concentration and Secondary Ion Mass Spectroscopy (SIMS) for B dopant concentration. Two implantation schemes were studied: 1. into TaSi(2) and 2. into polySi prior to TaSi(2) deposition. The results indicate that during subsequent heat treatment arsenic tends to stay in polySi while boron readily accumulates in tantalum silicide. From the measured data, the segregation coefficients for As and B in tantalum silicide/polySi system are 1:2 and 10:1, respectively.