MOS structures quality under annealing influence

Abstract

This paper reports the experimental results relative to the characterization of a MOS structure with polysilicon grid, after high temperature annealing under dry oxygen. These results permitted to observe a change of the chemical composition of the layers deposited on SiO 2 , in relation with the oxidation rate growth. One notes in particular, a growth of the peaks intensities associated to Si-O and Si-O-Si bonds, translating an increasing of the oxygen quantity in the polysilicon. One also observes a tendency toward the disappearance of some bonds of Si-H x (x=1, 2, 3) and Si-Si type, to the profit of others as Si-O-Si and Si-O, what explains itself by hydrogen atoms desorption under annealing effect. On the other hand, the electrical results confirm that the concentration of free carriers stretches toward the doping one, for the high levels of doping used here, while the mobility increases with the growth of annealing temperature. Otherwise, the C(V) curves show that the flat band tension V FB undergoes a growth linked to the oxidation temperature increasing, what is justified by the diffusion activation of charges like O 2 - and B - , and their trapping in the oxide. Besides, the interface states density D it that is in the order of 2×10 12 cm -2 eV -1 , characterizes an oxide of medium quality and is reduced of half when the annealing temperature passes the 1000°C.