Viscous flow of thermal SiO2

Wafer curvature measurements from 25 to 1075 °C are used to demonstrate viscous flow of thermally grown SiO2 at temperatures as low as 960 °C. Both O2- and steam-grown oxides are examined and found to have viscosities similar to synthetic fused silica. It is recommended that high-temperature Si device processing involving SiO2 be held to below 960 or even 925 °C, after oxide growth to avoid viscous flow and the accompanying structural damage in the oxide. This recommendation holds particularly for device technologies where resistance to ionizing radiation is important. The measurements also demonstrate that gross structural damage resides in the Si beneath steam-grown oxide.