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

The electrical properties and the long-term stability of the resistivity ha ve been studied for polysilicon films heavily doped with phosphorus (P) and adjusted by boron (B) compensation. Phosphorus was found to block the acce ss of hydrogen (H) to the dangling bonds. A theoretical model for the drift in resistivity under electrical and thermal stress showed the number of pa rticipating H atoms to be two orders of magnitude smaller than the number o f grain-boundary traps. The activation energy for the n-type film was 0.5 /- 0.1 eV. Whereas the total drift was reduced in the compensated n-type fi lms, 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 t raps followed the U-shaped density of states in their concentration depende nce. 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 trap s had a lower activation energy, 0.3 +/- 0.1 eV, and a higher rate constant for the dissociation of the bonds to H. The f-factor for singly n-type fil ms was found to be 0.52.