Long-term stability and electrical properties of compensation doped poly-Si IC-resistors

The electrical properties and the long-term stability of the resistivity have been studied for polysilicon films heavily doped with phosphorus (P) and adjusted by boron (B) compensation. Phosphorus was found to block the access of hydrogen (H) to the dangling bonds. A theoretical model for the drift in resistivity under electrical and thermal stress showed the number of participating H atoms to be two orders of magnitude smaller than the number of grain-boundary traps. The activation energy for the n-type film was 0.5/spl plusmn/0.1 eV. Whereas the total drift was reduced in the compensated n-type films, the presence of B-P complexes acting as hole traps caused the drift to increase in the p-type films. Hall measurements confirmed the presence of these complexes and showed them to consist of pairs of B and P atoms. The traps followed the U-shaped density of states in their concentration dependence. The trap density was higher in the p-type than in the n-type films due to the B-P hole traps. Compared to the Si dangling bond traps, these traps had a lower activation energy, 0.3/spl plusmn/0.1 eV, and a higher rate constant for the dissociation of the bonds to H. The f-factor for singly n-type films was found to be 0.52.