Effect of impurities on the fixed charge of nanoscale HfO2 films grown by atomic layer deposition

Hf O 2 films were grown by atomic layer deposition using two different precursor chemistries—HfCl4 and tetrakis(diethylamido)hafnium (TDEAH) with H2O as the oxidant. Electrical measurements on capacitor structures fabricated using the films showed a 0.4V positive shift in the flatband voltage for the chloride-HfO2 with respect to the amide-derived HfO2, indicating a considerable negative fixed charge in the dielectric. Secondary ion mass spectrometry depth profiles of the gate stack showed that Cl segregated preferentially at the HfO2∕SiO2 interface for chloride-derived HfO2. In situ vacuum anneals of the HfCl4-derived films at 500°C did not affect the profile, indicating that Cl is stably bonded at that interface. A similar analysis of the TDEAH-derived HfO2 showed very low concentrations of C, N, and H impurities. A positive fixed charge of +4.5×1011∕cm2 was extracted for the amide-HfO2 whereas a negative fixed charge of −1.86×1012∕cm2 was estimated for the chloride-HfO2. Thus, Cl incorporation can significantly alter both the magnitude and sign of the fixed charge in the HfO2∕SiO2∕Si gate stacks.