Mechanical integrity of polysilicon films exposed to hydrofluoric acid solutions

The results from a comparative study of Young´s modulus, residual stress, and membrane burst pressure of undoped LPCVD polysilicon films exposed to various concentrations of hydrofluoric acid (HF) are presented. A reversal from compressive to tensile stress through a high-temperature anneal for large-grain polysilicon is an important (although ancillary) result of this study. As HF concentration is increased, residual stress decreases, while Young´s modulus increases. Membrane burst pressure and estimated fracture strain show a significant decrease with increasing HF concentration. A significant result is that the change in the mechanical properties studied from exposure to pure HF or 1:1 DI:HF is identical. Furthermore, in relation to exposure to 10:1 DI:HF solutions, this change is small. However, with the addition of a buffering agent in a 10:1 buffered oxide etchant solution, the changes in the mechanical properties, particularly the films fracture strain, are reduced appreciably