Characterization of High-K Nanolaminates of HfO_2 and Al_2O_3 Used as Gate Dielectrics in pMOSFETs

摘要

In order to combine the merits of both HfO_2 and Al_2O_3 as high-K gate dielectrics for CMOS technology, high-K nanolaminate structures in the form of either Al_2O_3/HfO_2/Al_2O_3 or Al_2O_3/HfAlO_x/Al_2O_3 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℃, the HfO_2 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 Al_2O_3/HfAlO_x/Al_2O_3 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 Al_2O_3/HfO_2/Al_2O_3, however, exhibited a subthreshold slope of 100 mV/decade and a ～30% lower hole mobility than the universal curve.