Electrical Characteristics of TaO x N y for High-k MOS Gate Dielectric Applications
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Electrical Characteristics of TaOxNy for High-k MOS Gate Dielectric Applications
Kiju Im, Hyungsuk Jung, Sanghun Jeon, Dooyoung Yang* and Hyunsang Hwang Department of Materials Science and Engineering, Kwangju Institute of Science and Technology, #1, Oryong-dong, Puk-gu, Kwangju, 500-712, KOREA *Jusung Engineering, #49, Neungpyeong, Opo, Kwangju-gun, Kyunggi, 464-890, KOREA
ABSTRACT In this paper, we report a process for the preparation of high quality amorphous tantalum oxynitride (TaOxNy) via ammonia annealing of Ta2O5 followed by wet reoxidation for use in gate dielectric applications. Compared with tantalum oxide(Ta2O5), a significant improvement in the dielectric constant was obtained by the ammonia treatment followed by light reoxidation in a wet ambient. We confirmed nitrogen incorporation in the tantalum oxynitride (TaOxNy) by Auger Electron Spectroscopy. By optimizing the nitridation and reoxidation process, we obtained an equivalent oxide thickness of less than 1.6nm and a leakage current of less than 10mA/cm2 at -1.5V. Compared with NH3 nitridation, nitridation of Ta2O5 in ND3 improve charge trapping and charge-to-breakdown characteristics of tantalum oxynitride. INTRODUCTION The scaling of gate dielectric thickness represents the most important issue in the development of the next generation of metal-oxide-semiconductor field effect transistor (MOSFET) devices. Considering the technology roadmap, an equivalent oxide thickness of less than 1.5nm will be necessary to meet the requirements for sub-100nm MOSFET devices [1]. Due to the low dielectric constant and high tunneling leakage current, the scaling of SiO2 to the thickness below 2.5nm is impossible. To satisfy the requirements for sub-100nm MOSFET devices, it will be necessary to develop materials with excellent electrical characteristics, such as a dielectric constant higher than 30, an interface state density of less than 1x1011/cm2-eV, a tunneling current of less than 10mA/cm2 at the operating bias condition and negligible hysterisis. No alternative high dielectric constant materials, which are capable of meeting the above requirements for sub-100nm MOSFET devices have been reported to date. Although Ta2O5 has been investigated in terms of MOS gate dielectric applications, it is difficult to obtain an equivalent oxide thickness of less than 2nm with acceptable leakage current [2,3]. Since an approximately 1nm-thick interfacial SiO2 layer is necessary to minimize interface state density C1.8.1
and the intermixing of silicon and Ta2O5, the dielectric constant of Ta2O5 is not sufficient to obtain an equivalent dielectric thickness of less than 2nm. It is known that nitrogen plasma annealing can significantly reduce leakage current and trap density [4]. In addition, it has been reported that the dielectric constant of Ta2O5, when deposited on a Ru layer was significantly improved by rapid thermal nitridation [5]. In this paper, we wish to report the preparation of a TaOxNy thin film, formed by nitridation followed by wet reoxidation of Ta2O5 for ga
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