Characterization of High-κ Nanolaminates of HfO₂ and Al₂O₃ Used as Gate Dielectrics in pMOSFETs

Abstract

In order to combine the merits of both HfO₂ and Al₂O₃ as high-κ gate dielectrics for CMOS technology, high-κ nanolaminate structures in the form of either Al₂O₃/HfO₂/Al₂O₃ or Al₂O₃/HfAlO_x/Al₂O₃ were implemented in pMOSFETs and electrically and microstructurally charachterized. ALD TiN film was used as the metal gate electrodes for the pMOSFETs. After full transistor-processing including a rapid thermal processing step at 930 °C, the HfO₂ film in the former nanolaminate was found to be crystallized. In contrast, the HfAlO_x layer in the latter nanolaminate remained in the amorphous state. Both types of pMOSFETs exhibited a hysteresis as small as ∼20 mV in C-V characteristics in the bias range of +/− 2 V. They also showed a reduced gate leakage current. The pMOSFET with the Al₂O₃/HfAlO_x/Al₂O₃ nanolaminate was characterized with a subthreshold slope of 77 mV/decade and a channel hole mobility close to the universal hole mobility curve. The pMOSFET with the Al₂O₃/HfO₂/Al₂O₃, however, exhibited a subthreshold slope of 100 mV/decade and a ∼30% lower hole mobility than the universal curve.