Atomic Layer Deposition and Characterization of HfO 2 Films on Noble Metal Film Substrates Kaupo Kukli, a,f,z Titta Aaltonen, a Jaan Aarik, b Jun Lu, c Mikko Ritala, a, * Sandro Ferrari, e Anders Hårsta, d and Markku Leskelä a a Department of Chemistry, University of Helsinki, FIN-00014 Univ. Helsinki, Finland b Institute of Physics, University of Tartu, 51010 Tartu, Estonia c Ångström Microstructure Laboratory, Department of Engineering Sciences, Uppsala University, SE-751 21 Uppsala, Sweden d The Ångström Laboratory, Department of Materials Chemistry, Uppsala University, SE-75121 Uppsala, Sweden e Laboratorio MDM-INFM, 20041 Agrate Brianza (MI), Italy HfO 2 films were grown by atomic layer deposition from HfCl 4 and H 2 O on atomic layer deposited 40-70 nm thick platinum, iridium, and ruthenium films in the temperature range 200-600°C. The phase formed in the 30-50 nm thick HfO 2 films was monoclinic HfO 2 dominating over amorphous material without noticeable contribution from metastable crystallographic polymor- phs. The metal-dielectric-metal capacitor structures formed after evaporating Al gate electrodes demonstrated effective permittivity values in the range 11-16 and breakdown fields reaching 5 MV/cm. Iridium electrode films showed the highest stability in terms of reliability and reproducibility of dielectric characteristics. © 2005 The Electrochemical Society. DOI: 10.1149/1.1922888 All rights reserved. Manuscript submitted November 19, 2004; revised manuscript received January 11, 2005. Available electronically May 24, 2005. Functional metal oxides, such as HfO 2 , are investigated in microelectronics as high-permittivity dielectric layers in metal- oxide-semiconductor devices, 1,2 in metal-insulator-metal MIM capacitors, 3-5 and tunnel junctions. 6 In general, the MIM capacitors have value for several applications, such as radio frequency circuits, variety of configurations in analog integrated circuits, electron emis- sion devices, tunneling transistors, and in dynamic random access memory DRAM cells. 7-10 Various metal oxides may be considered as component insulator layers in MIM devices. 11 Different metals, such as Ir, 12 Ru with RuO 2 , 13 and Pt, 3,14 can be applied as capacitor 3 or gate 3,12,14,15 electrodes for metal oxide dielectric lay- ers. For complementary metal oxide semiconductor CMOS tech- nology applications, noble metals may serve in dual-gate metal ap- proach as high work function 4.9-5.2 eV with Ru, 4.6-5.5 eV for Pt; 5.0-5.7 eV for Ir replacements to polysilicon in low-threshold voltage p-MOS devices. 16-19 HfO 2 films can be deposited for MIM application by a number of methods, such as sputtering, 3 metallorganic chemical vapor deposi- tion MOCVD, 20 pulsed laser deposition, 21 and atomic layer depo- sition ALD. 20,22 In the case of films grown between metal elec- trodes, one of the key issues that has to be considered is the interface stability between the dielectric and the electrodes. 14,23 Studies on ALD of HfO 2 or other metal oxides on metals or conductive nitrides are rather scarce. Frequently studied MIM dielectric materials ob- tained by alternative techniques are Al 2 O 3 24 and Ta 2 O 5 . 25-28 There exists a study on MIM capacitors with ZrO 2 dielectric layers and W bottom electrodes both grown by ALD. 29 HfO 2 has been obtained by ALD from halide precursors and its dielectric behavior was studied between TiN electrodes. 30 Recent works report the ALD of HfO 2 from alkylamide precurors on gold substrates 31 and describe the exploitation of ALD-grown HfO 2 mixed with Al 2 O 3 in MIM struc- tures for integrated circuit IC applications. 32,33 This study describes the growth and properties of HfO 2 films on metal film substrates, while the substrate films were grown by ALD processes studied and established earlier. 34-37 Attention has been paid to the evolution of crystal growth and the dominant phase com- position in the as-deposited films. The behavior of basic dielectric properties, such as permittivity and breakdown voltage, was exam- ined against deposition temperature. Experimental HfO 2 thin films were grown on metal Pt, Ir, Ru films at 300°C in a flow-type ALD reactor, 38 using HfCl 4 and H 2 O as precursors and 2 s precursor pulse and purge times. Prior to HfO 2 deposition, the 60-80 nm thick Ru and Ir, and 20-30 nm thick Pt films were grown in another ALD reactor 39 on RCA-cleaned Si substrates pre- covered with 3-4 nm thick ALD Al 2 O 3 films. The Pt films were grown at 300°C using methylcyclopentadienyltrimethyl platinum,  MeCpPtMe 3 , and oxygen as precursors. 34,35 Ruthenium films were grown at 350°C from biscyclopentadienylruthenium and oxygen. 35,36 Iridium films were grown from tris2,4- pentanedionatoiridium  Ir acac 3  and oxygen at 300°C. 37 In addi- tion, reference Si substrates covered with chemically grown 1.2 -1.8 nm thick SiO 2 layers were used in the experiments simulta- neously with metal film substrates in order to compare the growth rates and structure of the HfO 2 films. The film thickness and structure were evaluated from X-ray re- flection XRR and grazing incidence X-ray diffraction GIXRD patterns measured with a Bruker D8 Advance X-ray diffractometer. The composition profiles were obtained from selected films using time-of-flight secondary ion mass-spectrometer TOF-SIMS ION- TOF IV in negative polarity regime with primary Ga + ion source with 25 keV energy, 1 pA current, and 50  50 m raster. Depth profiling was done by sputtering with Cs + ion source with energy 0.5 keV, 50 nA current, and 200  200 m raster was applied. The base vacuum in the measurement chamber was 5  10 -9 mbar. The samples were introduced in the chamber without any surface pre- cleaning procedure. Transmission electron microscopy TEM was employed for some samples to examine the crystallinity and inter- facial layers between HfO 2 and metal film using a field emission gun TECNAI F30 ST operated at 300 kV. Electron energy loss spec- troscopy EELS was in some cases applied in order to check the composition of the interfacial layer formed between oxide and metal layers. The capacitance-voltage C-V curves were recorded at room temperature on Al/HfO 2 /Pt,Ir,Ru capacitor structures with e-beam evaporated Al dot electrode area 2.04  10 -7 or 5.2  10 -8 m 2 us- ing a HP 4284A precision LCR-meter. The bias voltage step was 0.05 V. The period between voltage steps was 0.5 s. The ac voltage level applied to the capacitor was 0.05 V, while the frequency of the ac signal was varied between 100 kHz and 1 MHz. The current- voltage curves were measured with a Keithley 2400 Source Meter in the stair sweep voltage mode, while the voltage step used was * Electrochemical Society Active Member. f Also at: Institute of Experimental Physics and Technology, University of Tartu, 51010 Tartu, Estonia. z E-mail: kaupo.kukli@ut.ee Journal of The Electrochemical Society, 152 7 F75-F82 2005 0013-4651/2005/1527/F75/8/$7.00 © The Electrochemical Society, Inc. F75 ) unless CC License in place (see abstract). ecsdl.org/site/terms_use address. 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