Physical-Chemical Evolution upon Thermal Treatments of Al 2 O 3 , HfO 2 and Al/Hf Composite Materials Deposited by ALCVD
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Physical-Chemical Evolution upon Thermal Treatments of Al2O3, HfO2 and Al/Hf Composite Materials Deposited by ALCVDTM B. Crivelli, M. Alessandri, S. Alberici, F. Cazzaniga, D. Dekadjevi1, J. W. Maes2, G. Ottaviani3, G. Pavia, G. Queirolo, S. Santucci4, F. Zanderigo STMicroelectronics, Via C.Olivetti 2, 20041 Agrate Brianza (MI), Italy 1 Laboratorio MDM-INFM, Via C.Olivetti 2, 20041 Agrate Brianza (MI), Italy 2 ASM International, B-3001 Leuven, Belgium 3 Department of Physic and Unita’ INFM – University of Modena, 41100 Modena, Italy 4 Department of Physic and Unita’ INFM – University of L’Aquila, 67010 Coppito (AQ), Italy ABSTRACT This paper presents a systematic investigation of thermal stability of high-k materials deposited on RCA cleaned wafers by ALCVDTM in an ASM PulsarTM 2000 reactor. Physical-chemical evolution of Al2O3, HfO2 and Al/Hf composite materials (nanolaminate and aluminates) was studied considering two types of thermal treatments: quenched vacuum anneals from 300°C to 900°C and furnace atmospheric processes in N2 or O2 at 850°C and 900°C. Material crystallization and changes in film structure were studied by means of TEM, XRD, XRR, XRF, RBS and TOF-SIMS. Non-contact electrical measurements were used to detect modification in EOT and fixed charge. Al2O3 was found still amorphous at 900°C. Not so for HfO2 that crystallized in monoclinic phase at a temperature between 300-400°C. Crystallization temperature and possible phase separation of Al/Hf composite materials were found to be a function of Al2O3 content and film type. In most of these samples, however, a chemical evolution was detected in addition to the above reported crystallization phenomena. All the achieved results demonstrate that depending on thermal treatment conditions, ALCVDTM high-k stability does not only concern phase transition effects but also a transformation of the "SiO2/high-k" system into "doped-SiO2/silicate" stack. INTRODUCTION High-k materials are considered feasible candidates for several applications in 100 nm CMOS generation and beyond. Actually, attention is mainly given to Al2O3, zirconium and hafnium based films due to interesting k value, thermodynamic stability and proper band offset with respect to silicon. One of the major critical requirement for possible high-k integration in transistor and memory devices is however the capability to withstand thermal budget of a complete process flow. In particular, steps as dopant activation, device sealing and sidewall formation have to be sustained. Two different targets for resistance to thermal processing can then be taken into account: rapid thermal treatments up to 1000-1100°C and prolonged processes in 500-900°C temperature range. Effects of rapid post deposition annealings on Al2O3, ZrO2 and Zr pseudo-binary alloys were previously studied. Zirconium oxide was found to be already crystalline as deposited or to crystallize at quite low temperature, while alumina remained amorphous up to 1000°C. Increase in film thermal stability was detected for Zr silicates and a
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