Poly-Si Unetch Failure Due to Etching Rate Dependence of Si Orientation

The origin of poly-Si unetch failure in FinField-effect transistor (FinFET) was defined as an etch rate dependence of a specific Si grain in Si poly crystalline. We analyzed a failure in a FinFET based static random access memory (SRAM). Abnormal point in a passive voltage contrast result was measured by nano-probing and fast Vth shift was detected at a pull down node in SRAM. Transmission electron microscopy (TEM) was applied to find out the cause of the failure, finding that poly-Si in dummy gate was not successfully etched. High-resolution TEM and fast Fourier transformation analysis showed that there was a (111) Si grain. The etch rate of (111) Si is 1–2% of (110) Si, which leads poly-Si unetch failure in gate in a FinFET structure.