Hillock Formation of SnO 2 Thin Films Prepared by Metal-Organic Chemical Vapor Deposition Kyung-Hee PARK, Hyun-Wook RYU, Yong-Jin SEO 1 , Woo-Sun LEE 2 , Kwang-Jun HONG 2 , Dong-Charn SHIN 2 , Sheikh A. AKBAR 3 and Jin-Seong PARK 2 Research Institute of Energy Resources Technology, Chosun University, 375 Seosuk-dong, Gwangju 501-759, Korea 1 Daebul University, 72 Samho-myeon, Yeongam-gun 526-702, Korea 2 Chosun University, 375 Seosuk-dong, Gwangju 501-759, Korea 3 CISM, 291 Watts, 2041 College Rd, Columbus, OH 43210, USA (Received May 28, 2003; revised June 19, 2003; accepted June 28, 2003; published November 10, 2003) SnO 2 thin films were deposited at 375  C on an alumina substrate by metal-organic chemical vapor deposition (MOCVD). The number of hillocks on the thin-film surface increased with air annealing. The oxygen content and binding energy during air annealing at 500  C came close to those of stoichiometric SnO 2 . The cauliflower-like hillocks observed seem to be the result of the continuous migration of tiny grains to release the stress of an expanded grain. [DOI: 10.1143/JJAP.42.7071] KEYWORDS: thin films, MOCVD, tin dioxide, hillock formation, annealing treatment There has been increasing interest in metal oxides because of their interesting properties with doping and application of advanced technologies. Of these oxides, a SnO 2 is of interest as an oxidation catalyst, a gas sensor material, a thin-film microbattery, and a transparent conductor. SnO 2 films have been fabricated by a number of techniques, including spray pyrolysis, sputtering, chemical vapor deposition (CVD), and evaporation. Although there have been many reports on the formation or smoothing of hillocks of thin films, these reports lack consistency. 1–3) Hillocks on thin-film surfaces deteriorate light reflection, ultra large scale integration (ULSI) pattern resolution, and device performance because they are dependent on surface morphology or roughness. A chemical mechanical process is a useful method for removing submicroscale hillocks. 4) An understanding and control of microstructure and surface morphology are required for the advanced application of tin oxide films. In this paper, we report the effect of the variation of morphology with annealing for tin oxide films deposited by the CVD technique on and explain hillock formation. A SnO 2 thin film by MOCVD was grown on an Al 2 O 3 substrate. Ultrapure Ar gas was introduced into a bubbler to carry di-n-butyltin(IV) diacetate (DBDTA: [(CH 3 CO 2 ) 2 - Sn((CH 2 ) 3 CH 3 ) 2 ]) vapor. Gaseous DBDTA reacted with O 2 on an Al 2 O 3 substrate to form a SnO 2 film inside a quartz cylinder tube. The process temperature was 375  C and the bubbler temperature was maintained at 120  C. A mass flow controller (MFC) controlled the flow rate of Ar and O 2 . The thickness of the SnO 2 films and annealing conditions were taken as control parameters. The film thickness and morphology were measured by field-emission scanning electron spectroscopy (FE-SEM; Hitachi S-4700) and spectroscopy ellipsometry (J.A. Wool- lam Co. M-2000V). X-ray photoelectron spectrometry (XPS; ESCALAB-250) was used to determine Sn–O binding energy and Sn/O ratio. In XPS, monochromatized Al K was used as the X-ray source with a photon energy of 1486 eV. To compare the XPS spectra of thin-film SnO 2 and standard SnO 2 , commercial high-purity SnO 2 powder was used as a raw material for the standard bulk specimen with a diameter of 12 mm and a thickness of 2 mm, and the process followed a typical ceramic process that involves sintering at 700  C for 2 h in an air atmosphere. The dependence of surface morphology on annealing temperature is shown in Fig. 1. Figure 1(a) shows an FE- SEM image of the as-deposited film at 375  C for 2 min. The film with a thickness of approximately 15 nm shows a uniform textured surface having tightly packed crystallites connected to each other by common boundaries with small cracks or grooves between the grains. Figures 1(b) and 1(c) show the surface images of the films deposited at 375  C for 2 min and heat-treated at 300  C and 500  C, respectively. A few cauliflower-like hillocks are observed in Fig. 1(b) and many large hillocks are observed in Fig. 1(c). The FE-SEM images of the surface and cross section of the SnO 2 film deposited at 375  C for 16min are shown in Fig. 2 after annealing at 500  C for 30min in air and N 2 atmospheres. We can observe few hillocks in the case of N 2 annealing but many hillocks in air annealing. The hillocks are cauliflower- shaped and made up of agglomerated tiny grains. (a) 200nm (c) (b) Fig. 1. SEM images of SnO 2 thin films deposited at 375  C for 2min before (a) and after annealing for 30 min at (b) 300  C and (c) 500  C. 200 nm (a) (b) Fig. 2. Top surface and cross-sectional images of SnO 2 thin films deposited at 375  C for 16 min. Films annealed at 500  C for 30min in (a) air and (b) N 2 gas. Jpn. J. Appl. Phys. Vol. 42 (2003) pp. 7071–7072 Part 1, No. 11, November 2003 #2003 The Japan Society of Applied Physics 7071 Short Note