Size of semiconductor devices in large-scale integration has reached the submicron range where gate oxide films in metal oxide semiconductor (MOS) devices need to be fabricated at a nanometer scale. Atomic layer deposition (ALD) is a technology for depositing dielectric films with monolayer precision by repeating adsorption of a source gas on substrate that is subsequently reactivated for further adsorption [1]. Zirconium oxide (ZrO₂) is believed to be a candidate as the high-k gate oxide material [2]. The growth temperature for the ZrO₂ deposition has been desired to be decreased to near room temperature (RT) because the interfacial layer is formed by the solid phase reaction with heating process [3]. In this work, we developed a RT atomic layer deposition of ZrO₂ with tetrakis (ethylmethylamino) zirconium (TEMAZ) and a remote-plasma excited water vapor.

A p-type Si(100) substrate with a resistivity of 8-12 Ωcm was used as a sample. Prior to the experiment, the sample was cleaned with a buffered HF acid solution and sulfuric acid-hydrogen peroxide mixture. TEMAZ as the zirconium precursor was introduced with a variable leak valve. An induction plasma system generating oxidizing gas was installed to the ALD chamber as shown in Fig.1. The source gas for the oxidizing gas is a mixture of H₂O vapor and Ar gas. The plasma was generated in a glass tube with an induction coil with a frequency of 13.56MHz and a RF power of 30 W. Before the ALD process, the substrate surface was treated with the plasma excited water vapor for 5 min to be terminated with OH groups. For the ZrO₂ deposition, we repeated the cycle of TEMAZ saturation and the oxidizing gas treatment at RT. The TEMAZ exposure was set to 1.12×10^-3 Torr×100 s. The saturation of TEMAZ on the hydroxylated surface has been confirmed by the IR absorption spectroscopy. The plasma excited oxidizing gas was injected for 150 s. The oxidization state of the ZrO₂ film was evaluated by X-ray photoelectron spectroscopy (XPS). The thickness of the grown film was measured by spectroscopic ellipsometry.

Fig.2 shows Zr3d spectra obtained from ZrO₂ on Si grown by the present ALD. According to the increase in the ALD cycles, the Zr3d_5/2 peak at around 181.9 eV evolves. The peak position indicates the full oxidized ZrO₂ growth on Si [4]. Fig.3 shows the ZrO₂ thickness as a function of the ALD cycle. The linear increase of ZrO₂ thickness with the ALD cycle indicates that the ZrO₂ is grown in the ALD mode. The growth rate is estimated to be 0.14 nm/cycle. This value is comparable with those released in the conventional thermal ALD studies [5].

To conclude, we developed the non-heating, RT ALD of ZrO₂ with the plasma enhanced technology. We are now investigating the electrical characteristics of ZrO₂ MOS on Si and Ge, which will be released elsewhere. The RT grown ZrO₂ films might be also applicable for the anticorrosion coatings on plastic material. In the conference, we present not only the details of growth experiment but also discuss the growth kinetics of RT ALD.

Acknowledgement

This work was partly supported by JST-CREST. We would like to express the deepest appreciation to AIR-LIQUIDE for the high quality precursor of TEMAZ.

 

References

[1] S. M. George, Chemical Reviews, 110 (2010) 111.

[2] D. Q. Xiao, G. He, P. Jin, J. Gao, J. W. Zhang, X. F. Chen, C. Y. Zheng, M. Zhang, Z. Q. Sun, Journal of Alloys and Compounds, 649 (2015) 1273.

[3] C. M. Perkins, B. B. Triplett, P. C. Mclntyre, K. C. Saraswat, S. Haukka, and M. Tuominen, Applied Physics Letters, 78 (2001) 2357.

[4] D. Majumdar, D. Chatterjee, Journal of Applied Physics, 70 (1991) 988.

[5] K. Kukli, M. Ritala, and M. Leskelä, Chemical Vapor Deposition, 6 (2000) 297.