Analysis of the improvement of Al–Ta 2 O 5 /SiO 2 –Si structures reliability by Si substrate plasma nitridation in N 2 O N. Novkovski ⁎ Institute of Physics, Faculty of Natural Sciences and Mathematics, Gazibaba b.b., P.O. Box 162, 1000 Skopje, Macedonia abstract article info Article history: Received 4 March 2008 Received in revised form 18 November 2008 Accepted 29 January 2009 Available online 5 February 2009 PACS: 73.40.Qv 73.50.-h 73.61.-r 77.22.Jp Keywords: Tantalum oxide Dielectric properties Nitridation Interfaces Metal-oxide semiconductor structure(MOS) Reliability properties of 30-nm thick insulating films grown by thermal oxydation of Ta deposited on plasma nitrided Si for times varying from 5 to 15 s were studied for the case of constant current stresses. Stress-induced leakage currents of thus obtained Ta 2 O 5 /SiO x N y stacked layers with the stress were monitored by the evolution of the parameters extracted with the use of our recently developed comprehensive model for leakage currents. It is concluded that the nitridation of the substrate prior to the Ta 2 O 5 formation, simultaneously with the increase of the dielectric constant of the stack and the decrease of the leakage currents in fresh samples, improves the reliability properties against constant current stress. The increased charges to breakdown and the decreased trapping in the insulating film were explained by the improved resistance of the interface with substrate to the stress due to the incorporation of a small amount of nitrogen atoms. Since the N atoms are much stronger bonded to the Si substrate, the nitrided interface becomes more resistant to the stress. The optimum observed for nitridation times of about 10 s was explained by the strengthening of the interface with N-atoms without excessive growth of the SiO x N y –Si interfacial layer and without excessive lowering of its injection barriers. © 2009 Elsevier B.V. All rights reserved. 1. Introduction High permittivity (high-k) dielectric materials are nowadays extensively studied as a replacement of the silicon dioxide in various microelectronic applications [1–3]. Specifically, tantalum pentoxide was found to be exceptionally convenient for the use as a dielectric in dynamic random access memories (DRAM) [4]. Effects of various technological processes aimed at further improvement of its dielectric and reliability properties are studied [5–6] for the applications in nanoscale DRAMs [7]. Between them the nitridation of tantalum pentoxide layers attracts particular interest [8]. Reliability properties of such dielectrics are studied by various stress tests [9]. Due to the thermodynamical instability of the Ta 2 O 5 /Si interface, an unavoidable interfacial layer formation occurs. Therefore, thus obtained dielectric has to be studied as a non-uniform or a stacked layer. In numerous important cases, the insulating film can be considered to be composed of two homogeneous parts: a Ta 2 O 5 and an SiO 2 -like interfacial layer. Previously we have developed and used a model for description of the electrical properties of metal-Ta 2 O 5 /SiO 2 –Si structures [10,11]. The above model was applied to the analysis of the stress-induced leakage currents in these structures [12], as well as to the combined conduction and charge analysis [13]. This model is based on the method used much earlier by Frohman–Bentchkowsky and Lenzlinger for describing leakage currents in metal–nitride–oxide–silicon structures [14]. Chanelliere et al. applied a similar method to study various types of Ta 2 O 5 /SiO 2 and Ta 2 O 5 / Si 3 N 4 stacked strucuttres on Si, but only in the case of positive gate polarity, where electrons are injected from the substrate [15]. As we found in [10], in the case of negative gate, an injection of holes from the substrate occurs, since there are almost no free carriers in Ta 2 O 5 layer to be injected into the SiO 2 interfacial layer. In the case of SiO 2 interfacial layers, values of band offsets for electrons and holes obtained by our model precisely agree with the best known literature data from independent experiments, while for films grown on nitrided substrates they provide good agreement with the known SiO x N y bandgaps. It is known that the nitridation of the substrate in N 2 O or NH 3 improves the dielectric and leakage properties of the films [16]. Our study on the electrical and dielectric properties of rf-sputtered Ta 2 O 5 films on rapid thermally nitrided substrates in N 2 O or NH 3 showed that the improvement is due to the increased permittivity of the interfacial layer with nitrogen incorporation, without substantial decrease of the injection barrier heights [17]. Substrate nitridation in soft plasma before Ta 2 O 5 growth substantially improves the dielectric and electrical properties of the insulating film [18]. Thin Solid Films 517 (2009) 4394–4401 ⁎ Tel.: +389 2 3249 857; fax: +389 2 3228 141. E-mail address: nenad@iunona.pmf.ukim.edu.mk. 0040-6090/$ – see front matter © 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.tsf.2009.01.141 Contents lists available at ScienceDirect Thin Solid Films journal homepage: www.elsevier.com/locate/tsf