Influence of interlayer trapping and detrapping mechanisms on the electrical characterization of hafnium oxide/silicon nitride stacks on silicon

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American Institute of Physics
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Al/HfO(2)/SiN(x):H/n-Si metal-insulator-semiconductor capacitors have been studied by electrical characterization. Films of silicon nitride were directly grown on n-type silicon substrates by electron cyclotron resonance assisted chemical vapor deposition. Silicon nitride thickness was varied from 3 to 6.6 nm. Afterwards, 12 nm thick hafnium oxide films were deposited by the high-pressure sputtering approach. Interface quality was determined by using current-voltage, capacitance-voltage, deep-level transient spectroscopy (DLTS), conductance transients, and flatband voltage transient techniques. Leakage currents followed the Poole-Frenkel emission model in all cases. According to the simultaneous measurement of the high and low frequency capacitance voltage curves, the interface trap density obtained for all the samples is in the 10(11) cm(-2) eV(-1) range. However, a significant increase in this density of about two orders of magnitude was obtained by DLTS for the thinnest silicon nitride interfacial layers. In this work we probe that this increase is an artifact that must be attributed to traps existing at the HfO(2)/SiN(x) : H intralayer interface. These traps are more easily charged or discharged as this interface comes near to the substrate, that is, as thinner the SiN(x) : H interface layer is. The trapping/detrapping mechanism increases the capacitance transient and, in consequence, the DLTS measurements have contributions not only from the insulator/substrate interface but also from the HfO(2)/SiN(x) : H intralayer interface.
© 2008 American Institute of Physics. The study was partially supported by the local government (Junta de Castilla y León) under Grant No. VA018A06, and by the Spanish TEC2008 under Grant No. 06698-C02-02 and TEC2007 under Grant No. 63318. The authors acknowledge C. A. I. de Técnicas Físicas, C. A. I. de Espectroscopía y Espectrometría, and C. A. I. de Microscopía y Citometría of the Universidad Complutense de Madrid for technical support.
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