Effect of impurities on the fixed charge of nanoscale HfO 2 films grown by atomic layer deposition

Abstract

HfO 2 films were grown by atomic layer deposition using two different precursor chemistries - HfCl 4 and tetrakis(diethylamido) hafnium (TDEAH) with H 2O as the oxidant. Electrical measurements on capacitor structures fabricated using the films showed a 0.4 V positive shift in the flatband voltage for the chloride-HfO 2 with respect to the amide-derived HfO 2, 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 HfO 2/SiO 2 interface for chloride-derived HfO 2. In situ vacuum anneals of the HfCl 4-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 HfO 2 showed very low concentrations of C, N, and H impurities. A positive fixed charge of +4.5 × 10 11/cm 2 was extracted for the amide-HfO 2 whereas a negative fixed charge of -1.86×10 12/cm 2 was estimated for the chloride-HfO 2. Thus, Cl incorporation can significantly alter both the magnitude and sign of the fixed charge in the HfO 2/SiO 2/Si gate stacks. © 2006 American Institute of Physics.