Materials and Physical Properties of Novel High-k and Medium-k Gate Dielectrics
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Materials and Physical Properties of Novel High-k and Medium-k Gate Dielectrics Ran Liu, Stefan Zollner, Peter Fejes, Rich Gregory, Shifeng Lu, Kim Reid, David Gilmer, Bich-Yen Nguyen DigitalDNA Laboratories, Motorola, Mesa, AZ 85202, USA Zhiyi Yu, Ravi Droopad, Jay Curless, Alex Demkov, Jeff Finder, Kurt Eisenbeiser Physical Science Research Laboratories, Motorola, Tempe, AZ 85202, USA ABSTRACT Rapid shrinking in device dimensions calls for replacement of SiO2 by new gate insulators in future generations of MOSFETs. Among many desirable properties, potential candidates must have a higher dielectric constant, low leakage current, and thermal stability against reaction or diffusion to ensure sharp interfaces with both the substrate Si and the gate metal (or poly-Si). Extensive characterization of such materials in thin-film form is crucial not only for selection of the alternative gate dielectrics and processes, but also for development of appropriate metrology of the high-k films on Si. This paper will report recent results on structural and compositional properties of thin film SrTiO3 and transition metal oxides (ZrO2 and HfO2). INTRODUCTION The continued shrinking of the CMOS device size for higher speed and lower power consumption drives the conventional SiO2 gate oxide approaching its thickness scaling limit [1]. Severe direct tunneling and reliability problems at extremely small thickness will soon set a barrier for this naturally given material. Alternative dielectric materials with a higher dielectric constant, k, and thus larger physical thickness than SiO2 will be required to reduce the gate leakage as the gate length is scaled below 100 nm. Successful integration of high-k dielectrics into CMOS technology poses enormous challenges. Among many desirable properties, potential candidates must have a higher dielectric constant, low leakage current, and thermal stability against intermixing or diffusion to ensure sharp interfaces with both the substrate Si and the gate metal (or poly-Si). Extensive characterization of such materials in thin-film form is crucial not only for selection of the alternative gate dielectrics and processes, but also for development of appropriate metrology of the high-k films on Si. For insulating materials, there are two major contributions to the static dielectric function
ε 0 = 1 + 4π ( χ electron + χ lattice ) ,
(1)
i.e., the dielectric responses of valence electrons and lattice vibrations. The electronic dielectric constant can be estimated by
χ electron ~
hω P E PG
2
,
(2)
K1.1.1
where ωP is the plasma frequency of the valence electrons and EPG is an “average bandgap” (know as Penn gap). Since the electronic contribution is usually less than 16 and larger for insulators with smaller energy gaps, it is not wise to pursue materials with high electronic dielectric constant as high-k gate dielectrics. Therefore, the high dielectric constant should be generated from the ionic contribution
χ lattice
1 ~ V
∑
(e
* i
)(
⋅ ξ i ei* ⋅ ξ i
ω i2
i
)
+
,
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