The effect of bevel film removal on wafer warpage and film stress

The main objective of this study was to identify if there is any change in wafer warpage after bevel clean process, which might lead to higher film stress at device area in further processes. Correlation between bevel film Etch Rate (ER) and wafer warpage was also investigated. 25 kA thermal oxides (Tox) were etched on back side with various thicknesses remaining to generate a different amount of wafer warpage and thus different film stress on the front side of wafers. It was found that the thinner backside thickness leads to higher warpage with dome shape and film stress on front side. Test results indicate that bevel clean process did not increase the wafer warpage, on the other hand reduced the warpage about 1~4% compared to pre-bevel clean process in case of Tox. 3 kA silicon nitride (SiN) also showed the higher warpage of bowl shape with no films on back side compared to the un-etched one. No significant change in warpage was also observed in SiN. The correlation relationship of bevel ER and wafer warpage was significantly low, which provides a steady ER performance regardless of the warpage of monitor wafers.