A study on the effectiveness of different cap oxides for preventing fluorine out-diffusion from FSG

In this paper, we investigate the effect of fluorine out-diffusion from fluorinated-silicate-glass (FSG) film stacks. The FSG film stack consists of 2 kÅ cap oxide/6 kÅ FSG/2 kÅ liner oxide. Different cap oxide and liner oxide materials were studied in this work. The samples were annealed at 410°C for several hours to simulate the various backend annealing processes. SIMS was used to measure the F distribution in the FSG film stack. We found that silicon nitride (SiNx) could effectively inhibit F diffusion from the FSG film. But this film stack was not stable under ion beam and electron beam irradiation. Plasma-Enhanced (PE) oxide cap on FSG film could not inhibit F diffusion from the FSG film very well, but it was stable under SIMS ion beam and electron beam irradiation. We also found that silicon rich oxide (SRO) inhibited F out-diffusion, and that the film stack was stable during SIMS analysis. Why does SRO inhibit F out-diffusion? From the SIMS results, we found N in the SRO film. Furthermore, the higher the concentration of N in the SRO film, the less the F diffused out. A series of experiments were carried out to study the effect of introducing nitrogen in both SRO and FSG in preventing F out-diffusion from FSG