Transistors Built With ZrO 2 And HfO 2 Deposited From Nitratos
- PDF / 325,738 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 73 Downloads / 167 Views
Transistors Built With ZrO 2 And HfO2 Deposited From Nitratos Stephen A. Campbell1 , Noel Hoilien1 , Tiezhong Ma1 , Fang Chen1 , Ryan Smith2 , And Wayne Gladfelter2 1 Department of Electrical Engineering, 2 Deptartment of Chemistry, University of Minnesota, 1 200 Union Street, 2 207 Pleasant Avenue Minneapolis, MN. 55455 USA Abstract The electrical performance of transistors built using thin films of the column IVB metal oxides ZrO 2 and HfO 2 deposited from their respective anhydrous metal nitrate precursors is presented. In contrast to earlier work on TiO 2 , which is thermodynamically unstable on silicon, ZrO2 and HfO 2 form well-defined oxynitride interfacial layers and have a good interface with silicon with much less fixed charge. The inversion layer mobility for an HfO 2 / SiO x Ny / Si stack is comparable to that of a conventional SiO x Ny /Si interface. Introduction As field effect transistors are scaled deep into the submicron, the equivalent oxide thickness (EOT) of the gate insulators for these devices is shrinking as well. The 2000 National Technology Roadmap for Semiconductors1 suggests that the EOT must decrease from 1.9 to 2.5 nm at the 180 nm node, which is now in production, to 1.2 to 1.5 nm at the 90 nm node which should be in production by 2004, to 0.8 to 1.2 nm at the 60 nm node, scheduled for 2008 production. Further scaling would require devices with EOTs well below 1.0 nm. Brar, et. al. 2 , and Buchanan and Lo3 , have studied the electrical properties of thin layers of SiO 2 and have shown that this leakage increases approximately four orders of magnitude for every nm decrease in thickness. At 1.0 nm direct tunneling produces approximately 100 Amp/cm2 . At some point this leakage current becomes excessive, either due to power dissipation or to reliability. While the exact limit for SiO 2 -based gate dielectrics is application dependent, it is clear that a new gate insulator will be needed if the EOT is ever to be scaled below 1.0 nm, and that this new material must have a permittivity well above that of SiO 2 (i.e. 3.9). In this work we have studied two prototype replacements for SiO 2 . The permittivity of these materials, ZrO 2 and HfO 2 , is generally reported to be between 15 and 25, but they are more stable on silicon than other high permittivity materials such as Ta2 O5 and TiO 2 . Chemical vapor deposition of ZrO 2 and HfO 2 has been demonstrated using a variety of precursors including the halides (e.g. ZrCl4 ), alkoxides (e.g. Zr(OC(CH3 )3 )4 , βdiketonates (Zr(thd)4 , where thd = 2,2,4,4 tetramethylhepta-3,5-dionato), and most recently, the anhydrous metal nitrates4 5 . The latter forms the basis for this work since hafnium nitrate (Hf(NO3 )4 or HN) and zirconium nitrate (Zr(NO3 )4 or ZN) are carbon and hydrogen free precursors. This provides significant advantages over the other sources since the deposition temperatures can be much less than those used for the halides and the lack of carbon in the film obviates the need for post deposition oxygen and/or water vapor anneals, both of
Data Loading...
