Highly Reliable Thin Hafnium Oxide Gate Dielectric
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ABSTRACT HfO 2 is the one of the potential high-k dielectrics for replacing Si0 2 as a gate dielectric. HfO 2 is thermodynamically stable when in direct contact with Si and has a reasonable band gap (-5.65eV). In this study, MOS capacitors (Pt/IHfO 2/Si) were fabricated by depositing HfO2 using reactive DC magnetron sputtering in the range of 33-135A followed by Pt deposition. During the HfO2 deposition, 02 flow was modulated to control interface quality and to suppress interfacial layer growing. By optimizing the HfO2 deposition process, equivalent oxide thickness (EOT) can be reduced down to -11.2 A with the leakage current as low as 1X1O2 A/cm2 at +I.OV and negligible frequency dispersion. HfO 2 films also show excellent breakdown characteristics and negligible hysteresis after high temperature annealing. From the high resolution TEM, there is a thin interfacial layer after annealing, suggesting a composite of Si-Hf0 with a dielectric constant of = 2 X K SiO 2. INTRODUCTION The scaling down of gate oxide thickness is necessary for not only high performance of I.C. chips but also for suppressing short channel effects, and improving subthreshold characteristics [1]. However, such aggressive gate oxide scaling brings increased direct tunneling current [2] , which leads to increased standby-power dissipation and degradation of the noise margin of CMOS inverter [3]. Therefore, to overcome these limitations without
sacrificing capacitance, gate dielectric materials having high dielectric constant, low leakage current, good thermal stability, and interface characteristics compatible to Si are needed as alternative gate dielectrics. However, many high-k dielectric materials such as Ta 20 5 , and TiO 2 are thermally unstable when in direct contact with Si [4]. Therefore, additional passivation layers such as Si3N 4 between high-k and Si substrate or N 2 implantation into channel region is needed to prevent interfacial reaction [5,6]. On the other hand, some metal binary oxide such as HfO2 , ZrO 2,Y20 3, and A120 3 have been shown to be thermally and chemically stable with Si. Among them, HfO 2 is the most stable oxide with the highest heat of formation (AHf), reasonable band gap of 5.65eV [7], and a lattice constant of 5.1A indicating a low misfit factor to Si. In spite of very promising properties as a gate dielectric, very little work has been done, especially in the thin region. In this study, the electrical and physical properties of ultra-thin HfO 2 capacitors with EOTs down to 11.2 'Awill be demonstrated. EXPERIMENT Metal Insulator Semiconductor (MIS) capacitors with HfO 2 dielectric were fabricated on p-type silicon wafers. Active regions with 5X10- 5/cm 2 were defined using field oxidation and patterning. Thin HfO 2 was reactive dc sputtered from a Hf target. During Hf sputtering, 02 flow was modulated to control the interface quality and to suppress interfacial layer growth (Fig. 1). 81 Mat. Res. Soc. Symp. Proc. Vol. 592 © 2000 Materials Research Society
During t1 , Ar is the only gas in the chamber. 02 is i
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