Stress in “cathodic” plasma oxides as a function of processing parameters

Abstract

Stress in SiO₂ films grown via a “cathodic” plasma oxidation process has been examined as a function of growth and processing conditions. The total stress for oxides grown at 350° C in either 85% Ar/15%O₂ or 100% O₂ ambients at 700 W, 4 MHz, and a total pressure of 80 mTorr was found to be identical. It was observed that annealing these oxides for 24 hr at 700° C in an ultra-pure oxygen ambient did not have any effect on the electrical properties, but that the stress did increase slightly. Electrical properties were measured on MOS capacitors, specifically focusing on net fixed oxide charge and breakdown strength. In addition, both as-grown and annealed samples were subjected to 8.5 × 10⁶ rad(SiO₂) Al K_α ionizing radiation to simulate exposure to X-ray lithography. Notwithstanding the generation of a large areal density of net coulombic charge in the insulator, the presence of these defects did not cause a measurable change in the interfacial stress level. Surprisingly, it was found that about 16% of the wafers plastically deformed during oxide growth at 350° C and about 35% of the wafers were found to be deformed after annealing of the oxides at 700° C. Dry, thermal oxides grown at 700° C were seen to possess similar electrical properties but exhibited a higher stress than the plasma oxides.