Diffusion and oxidation of plasma-enhanced chemical-vapor-deposition silicon nitride and underlying metals

Abstract

Plasma-enhanced chemical-vapor deposition (PECVD) was employed to grow silicon nitride at various temperatures to find its application in magnetic random access memory. Diffusion and oxidation of PECVD nitride (SiNx:H) and underlying metals (Ta and Cu) have been studied through Auger electron spectroscopy measurements. Oxygen content on the SiNx:H surface and characteristic sputtering time (t0), after which the oxygen signal falls below the measuring errors of the system, were used to characterize the oxidation of SiNx:H films. It is found that both oxygen content and t0 increase significantly for decreasing deposition temperature. The oxygen content is larger for SiNx:H films with lower Si/N ratios. Cu oxidation was investigated through changing sample loading methods. Strong oxidation was observed for samples loaded at higher temperatures, while almost no oxidation was detected for samples loaded at room temperature and heated to the deposition temperature after pumping the chamber to high vacuum. Strong diffusion of Si into Cu film was detected for high-temperature-deposited layers. Independent of loading methods, the Si concentration in Cu increases dramatically as the deposition temperature increases after exceeding 150 °C, whereas there is nearly no observable Si signal in Ta for the whole deposition temperature range. The Cu signal was also detected in nitride films deposited at 200 °C, while Cu cracks were observed when the deposition temperature was larger than or equal to 250 °C.