Electron spin resonance spectroscopy investigation of ion beam sputtered HfO 2 and SiO 2 thin films B. Langdon, D. Patel, E. Krous, P. Langston, C.S. Menoni Department of Electrical and Computer Engineering Colorado State University, Michelle Shinn FEL Div., Jefferson Lab, Newport News, VA 23606 ABSTRACT In this work we use electron spin resonance (ESR) spectroscopy to investigate defects in dual ion beam sputtered HfO 2 and SiO 2 films. “As-grown” SiO 2 films exhibit an ESR feature consistent with an E’ center associated with an oxygen vacancy previously reported. A similar feature with axial symmetry is seen in HfO 2 films. The defect giving rise to the HfO 2 ESR feature is distributed throughout the film. In addition, post process annealing of HfO 2 and SiO 2 films greatly reduces these defects. Keywords: dielectric thin films, defect characterization, electron spin resonance, hafnium oxide, hafnia, dual ion beam deposition 1. INTRODUCTION The combination of high (HfO 2 ) and low (SiO 2 ) index materials respectively forms the basis of high performance HfO 2 /SiO 2 interference coatings. There is significant interest from a materials stand point to characterize shallow and deep defects in ion beam sputtered HfO 2 and SiO 2 films, and investigate their role in affecting the optical behavior of the coatings under high irradiance. Regardless of the deposition method, HfO 2 used in optical coatings is amorphous because it is deposited at temperatures ranging from ∼ 20 -100 °C. Inherent to the growth process, a gamut of defects can be found in these films. Oxygen vacancies, interstitial ions and substitution impurities are among the most common. Model calculations of monoclinic HfO 2 predict these defects to have binding energies ranging from 2.76 to 5.06 eV, i.e reflecting both deep and shallow character.[1] There is discrepancy, however, in the electronic structure calculations as to whether some of the defects lie closer to the conduction band or to the valence band. An established spectroscopic method that has been used for identification of point defects in bulk materials and amorphous films is electron spin resonance spectroscopy (ESR). The type of defects that have ESR signatures are those that contain unpaired electrons that give rise to paramagnetic signals. Wright, Feeney and Barklie have identified a ESR defect in ultra-pure powdered HfO 2 with g-factors of g || =1.940 and g ⊥ = 1.970 which they identified as an oxygen vacancy in a Hf +3 ion.[2, 3] In thin amorphous HfO 2 films instead the ESR spectra shows different signatures. For example, Kang et al identified from ESR spectra of atomic layer chemical vapor deposited HfO 2 films on Silicon, two type of defects − 2 O and 3 + Hf associated with the interface.[4, 5] Kozlowski et al. used ESR in an attempt to identify changes in the charge state of HfO 2 /SiO 2 stacks upon laser conditioning.[6] These results show how the deposition method, interface characteristics and post-processing protocols impact defect formation in HfO 2 . In this work we use electron spin resonance spectroscopy (ESR) to identify point defects in dual ion beam sputter (DIBS) deposited HfO 2 and SiO 2 thin films. “As grown” SiO 2 films exhibit an ESR feature consistent with an E’ center associated with dangling bonds previously reported.[7] We observe a similar spectral feature in HfO 2 thin films. Post process annealing of the HfO 2 films reduces the ESR peak height feature by approximately 63%. Laser-Induced Damage in Optical Materials: 2008, edited by Gregory J. Exarhos, Detlev Ristau, M. J. Soileau, Christopher J. Stolz, Proc. of SPIE Vol. 7132, 71320M · © 2008 SPIE · CCC code: 0277-786X/08/$18 · doi: 10.1117/12.804459 Proc. of SPIE Vol. 7132 71320M-1 2008 SPIE Digital Library -- Subscriber Archive Copy