Physical and electrical properties of ZrO2 and YSZ high-k gate dielectric thin films grown by RF magnetron sputtering
Introduction
Recently, as metal oxide semiconductor field effect transistor (MOSFET) devices are scaled down to <100 nm, problems of conventional silicon oxide (SiO2) appeared. SiO2 layer suffered from basic problem of high tunneling leakage current and reduced drive current due to low dielectric constant (k=3.9) with thickness decreased (<2 nm) [1], [2]. Hence, high-k gate dielectrics such as Ta2O5, TiO2, HfO2, ZrO2, CeO2, Y2O3 stabilized ZrO2 (YSZ) [2], [3], [4], [5], [6] were studied to replace SiO2. Most of these materials, however, were not thermally stable directly on Si, due to the formation of metal silicides in the course of fabrication.
ZrO2 and YSZ are one of the most attractive andidates due to its high-k values (∼25 and ∼27, respectively), wide band gap (approximately 5.1–7.8 eV) [7], [8], and good thermal stability in contact with Si [9]. Due to their excellent properties, ZrO2 and YSZ films have been extensively studied as gate dielectric [10]. Wang et al. [11] studied the 6-nm-thick epitaxial crystalline YSZ films with electrical equivalent oxide thickness (EOT) of 1.46 nm and found that the leakage current was about 1.1×10−3 A/cm2 at 1 V. In addition, Zhu and Liu [6] also studied the 6-nm-thick amorphous YSZ films with EOT=1.46 nm and obtained a leakage current to be about 7.58×10−5 A/cm2 at 1 V. Moreover, amorphous films exhibited isotropic electrical properties and can easily be deposited.
In this work, the influence of the sputtering parameter such as, O2-flux, annealing temperature, RF power and target-to-substrate distance (Dts) on physical and electrical properties of amorphous ZrO2 and YSZ films that were prepared at low temperature by RF magnetron sputtering method have been studied.
Section snippets
Experimental
Both ZrO2 and YSZ films were prepared by the RF magnetron sputtering method. The purity of the ZrO2 target was above 99.99% with a diameter of 1 in. The YSZ target were prepared with 8 wt.% Y2O3-stabilized ZrO2. The sputtering gas (Ar) with a purity of 99.99% were introduced to the chamber and controlled by the standard mass-flow controllers. The sputtering pressure was 32 mTorr and p type Si(100) wafer were used as substrates without heating. The substrate–target distance was changed from 30
Results and discussion
Fig. 1(a) shows X-ray diffraction patterns of ZrO2 thin films grown at room temperature without O2-flux. The RF power was 150 W and the annealing temperature varied from 600 to 1200 °C. Below 600 °C, there were no typical diffraction peaks, indicating an amorphous structure. Between 800 and 1000 °C, the films were mainly grown in the [111] orientation, while the crystal growth direction was changed to be [012], at an annealing temperature in the range of 1000–1200 °C. The polycrystal film could
Conclusions
We have deposited ZrO2 thin films on p-Si(100) substrate by RF magnetron sputtering in order to study an influence of deposition parameters (such as annealing temperature, reactive gas, RF power, and Y2O3 dopant) on the physical and electrical properties of the as-grown films. XRD showed that a highly oriented cubic ZrO2 thin film in the [111] direction was obtained after annealing at 800 °C. On the other hand, tetragonal ZrO2 thin film was also grown on Si (100) substrate and the main film
Acknowledgements
This work was supported by the BK21 project of the Ministry of Education Korea, by the CAPST (Center for Advanced Plasma Surface Technology) and by the Korea Science and Engineering Foundation (project No. R01-2003-000-10019-0) at the Sungkyunkwan University.
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