Thermodynamic Stability of High-K Dielectric Metal Oxides ZrO 2 and HfO 2 in Contact with Si and SiO2
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Thermodynamic Stability of High-K Dielectric Metal Oxides ZrO2 and HfO2 in Contact with Si and SiO2 Maciej Gutowskia,b, John E. Jaffea a Pacific Northwest National Laboratory Environmental Molecular Sciences Laboratory Theory, Modeling & Simulations Richland, WA 99352, USA b Department of Chemistry, University of Gdańsk 80-952 Gdańsk, Poland Chun-Li Liu, Matt Stoker Advanced Process Development and External Research Laboratory, Motorola, Mesa, AZ 85202, USA Rama I. Hegde, Raghaw S. Rai, and Philip J. Tobin Advanced Process Development and External Research Laboratory, Motorola, Austin, TX 78721, USA ABSTRACT We present experimental results regarding the thermodynamic stability of the high-k dielectrics ZrO2 and HfO2 in contact with Si and SiO2. The HfO2/Si interface is found to be stable with respect to formation of silicides whereas the ZrO2/Si interface is not. The metal oxide/SiO2 interface is marginally unstable with respect to formation of silicates. Cross-sectional transmission electron micrographs expose formation of nodules, identified as silicides, across the polysilicon/ZrO2/Si interfaces but not for the interfaces with HfO2. For both ZrO2 and HfO2, the X-ray photoemission spectra illustrate formation of silicate-like compounds in the MO2/SiO2 interface.
INTRODUCTION The microelectronics industry depends on continual miniaturization of all components, especially metal-oxide-silicon field-effect transistors. However, the industry is approaching the useful limits of SiO2 gate dielectrics, due to the simultaneous need for B3.2.1
sufficient resistance (proportional to gate thickness) and capacitance (inversely proportional to thickness). Alternate gate dielectrics with a dielectric constant K higher than that of SiO2 are needed since then a thicker gate can be used.1,2,3 In addition to a high K, a large band gap, and low density of electrically active defects, an alternate material needs to be thermodynamically stable in contact with silicon to withstand the 900-1000 °C dopant drive-in anneal.2,3 It is known that the chemistries of hafnium and zirconium are more nearly identical than for any other two congeneric elements.4 Thus, both ZrO2 and HfO2, with K greater than 20,5 have emerged as potential replacements for SiO2 (K = 3.9). However, the interface quality of these systems was identified as a critical issue. Here we provide experimental arguments that the ZrO2/Si interface is unstable with respect to the formation of silicides but the HfO2/Si interface is stable. In addition, both metal oxides are unstable when interfaced with SiO2 as they spontaneously form silicates.
EXPERIMENTAL RESULTS A conventional CMOS process technology was used for fabricating polySi/ZrO2 (or HfO2) gate stack MOSFETs on bulk Si. The integration follows a standard process flow until the gate dielectric deposition. The ZrO2 (HfO2) was deposited at 550 °C and annealed at 800 °C. The silicon gate was deposited by rapid thermal chemical vapor deposition (RTCVD) at 590 °C using SiH4.6 Following a gate deposition, the MO2 films were
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