Deposition and Characteristics of Tantalum Nitride films by Plasma Assisted Atomic Layer Deposition as Cu Diffusion Barr
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DEPOSITION AND CHARACTERISTICS OF TANTALUM NITRIDE FILMS BY PLASMA ASSISTED ATOMIC LAYER DEPOSITION AS CU DIFFUSION BARRIER Kyoung-Il Na1, Se-Jong Park, Woo-Cheol Jeong2, Se-Hoon Kim2, Sung-Eun Boo2, Nam-Jin Bae2, and Jung-Hee Lee The School of Electronic and Electrical Engineering, Kyungpook National University, Daegu 702-701, Korea 1 The School of Sensor Engineering, Kyungpook National University, Daegu 702-701, Korea 2 Comtesc Incorporated, Daegu, Korea ABSTRACT For a diffusion barrier against Cu, tantalum nitride (TaN) films have been successfully deposited by both conventional thermal atomic layer deposition (ALD) and plasma assisted atomic layer deposition (PAALD), using pentakis (ethylmethlyamino) tantalum (PEMAT) and ammonia (NH3) as precursors. The growth rate of PAALD TaN at substrate temperature 250℃ was slightly higher than that of ALD TaN (0.80 Å/cycle for PAALD and 0.75 Å/cycle for ALD). Density of TaN films deposited by PAALD was as high as 11.0 g/cm3, considerably higher compared to the value of 8.3 g/cm3 obtained by ALD. The N : Ta ratio for ALD TaN was 44 : 37 in composition and the film contained approximately 8∼10 atomic % carbon and 11 atomic % oxygen impurities. On the other hand, the ratio for PAALD TaN layers was 47 : 44 and the respective carbon and oxygen contents of TaN layers decreased to 3 atomic % and 4 atomic %. The stability of 10 nm-thick TaN films as a Cu diffusion barrier was tested through thermal annealing for 30 minutes in N2 ambient and characterized by XRD, which proves the PAALD deposited TaN film to maintain better barrier properties against Cu below 800℃. INTRODUCTION Copper (Cu) interconnection is the most promising candidate for next-generation high-speed ultra large integrated circuit (ULSI), because copper exhibits lower resistivity and larger electro/stress migration resistance than conventional Al-based materials [1]. However, it is well known that Cu can diffuse easily into Si and SiO2 to form copper silicide at a temperature as low as 200℃. Moreover, Cu acts as a deep-level contaminant in Si that deteriorates the device performance [2]. Tantalum nitride (TaN) has many good advantages as a diffusion barrier. It shows not only relatively high melting point (2100℃) but also thermo-dynamical stability with respect to Cu. Atomic layer deposition (ALD) processing method is based on self-limiting
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surface reaction occurring between substrate surface and the depositing film, ensuring monolayer thickness control, and therefore enabling the growth of perfectly conformal, continuous, and atomically smooth films [3]. In this work, we investigated two different of TaN layers, which were deposited by conventional thermal ALD and plasma assisted ALD (PAALD), on the thermal stability as diffusion barrier for the structures of Cu
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