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1 Jurnal f the Krean Ceramic Sciety Vl. 48, N. 4, pp. 316~322, DOI: /KCERS The Effect f Vacuum Annealing f Tin Oxide Thin Films Obtained by RF Sputtering Sun-Phil Kim, Yungrae Kim*, Sung-Dng Kim, and Sarah Eunkyung Kim**, Schl f Mechanical Design and Autmatin Engineering, Seul Natinal University f Science and Technlgy, Seul , Krea *Micrsystem Packaging Center, Seul Technpark, Seul , Krea **Graduate Schl f NID Fusin Technlgy, Seul Natinal University f Science and Technlgy, Seul , Krea (Received June 1, 2011; Resived June 17, 2011; Accepted June 20, 2011) RF Sputtering w y œ z ½ vá½ *Á½ Á½ **, w» w» yœw * lj qj MSP» l ** w» w NID w» w ( ; ; ) ABSTRACT Tin xide thin films were depsited by rf reactive sputtering and annealed at 400 C fr 1 h in vacuum. T minimize the influence such as reductin, xidatin, and dping n tin xide thin films during annealing, a vacuum ambient annealing was adpted. The structural, ptical, and electrical prperties f tin xide thin films were characterized by X-ray diffractin, atmic frce micrscpe, UV-Vis spectrmeter, and Hall effect measurements. After vacuum annealing, the grain size f all thin films was slightly increased and the rughness (R a ) was imprved, hwever irregular and calesced shapes were bserved frm the mst f the films. These irregular and calesced crystal shapes and the pssible eliminatin f intrinsic defects might have caused a decrease in bth carrier cncentratin and mbility, which degrades electrical cnductivity. Key wrds: Thin films, Annealing, Cnductivity, Tin cmpunds 1. y (tin xide) y ƒ Ÿ n wš» p š n ƒÿ š. y SnO ƒ xk. yw wš 3.6 ev ˆ ƒ š, nx p š v n, k, transparent heating element ƒ w ƒ y w š. px 1-4) p š SnO yw (metastable)w k 2.7~3.4 ev ˆ ƒ š, TFT(thin film transistr) n š. 5) y, yw,» p w j» w z œ š Crrespnding authr : Sarah Eunkyung Kim eunkyung@seultech.ac.kr Tel : Fax : ,»,, œ ƒ š. p 400 C» z y w š j»ƒ f, e (carrier cncentratin) (mbility)ƒ» n ƒ w ƒ š. 6,7) 400 C š» ww x,» w š j»ƒ f, e ƒ» ƒ j. wr 8,9) 500 C š w š, y ü (phase transfrmatin) x ùkû š. 10,11)», SnO y SnO x š, yƒ j. ƒ y (undped ) rf reactive sputtering w, y y yw œ k z œ ww. œ ƒ y e, Ÿw» p y š w. 316

2 2. x x x z (design f experiment) Taguchi w ww, 16 r. r 2cm 2cm j» brsilicate glass»q w Sn target (99.99%) Ar, O 2 ƒ yww rf reactive sputtering w š, Table 1 x z w ƒ r œ. œ 0.40 Pa(3 mtrr)~1.33 Pa(10 mtrr),»q (25 C)~300 C, š v q 100 W~500 W y g. š 10 sccm/60 sccm š w x ww. w r w ü p t mw w. 12) Ì 2000 Å, (depsitin rate) œ ~0.3 Å/sec ~9.2 Å/sec. 16 r as-dep k, Ÿw,» ww, 400 C, Trr œ 1 w. w X-ray Diffractmeter, (ATX-G, Rigaku) w ƒ (grain) j» d w š, t k AFM(Dimensin 3100, Veec) 1µm 1µm r ew w. Ÿw w UV- Vis spectrmeter(lambda 35, PerkinElmer) w n d w.» d Hall effect measurement(hms-3000, Ecpia) w», e, š d w. Table 1. Depsitin Cnditin f Tin Oxide Thin Films Sample # Temp ( C) Pressure (Pa) Pwer (W) 1 RT 0.40 (3mtrr) RT 0.67 (5mtrr) RT 0.93 (7mtrr) RT 1.33 (10mtrr) (3mtrr) (5mtrr) (7mtrr) (10mtrr) (3mtrr) (5mtrr) (7mtrr) (10mtrr) (3mtrr) (5mtrr) (7mtrr) (10mtrr) 100 Fixed Gas Flw : O 2 = 10 sccm/ar = 60 sccm RF Sputtering w y œ z š y», Ÿw w œ y w x z Taguchi w w ww. œ, v q ƒ û, š» w n ƒ p y w. w š 12) œ, SnO. x z w as-dep r œ w ƒ r p y w š, sputtering œ w r p w t. r 12) as-dep k, Rmarchite-SnO, š Cassiterite- ƒ š. r ùkû, r, ƒ 100 C 8 r wš, SnO. r œ 400 C w š, Fig. 1, SnO, 3ƒ r w p w XRD d ùkü. Fig. 1 Table 2 y w, z r k w. XRD mw y w j» 100 C w r ƒw š 200~300 C w r s ƒ y w w ùkü. j» XRD l (101) w w w peak w ùkü, w peak s(fwhm, Full Width at Half Maximum) w Scherrer w w. 13) k r (grain grwth) w z Fig. 1(a) w. SnO (T m ) ƒƒ 1080 C 1630 C š w, k» r (T dep )ƒ 0.2T m û k x w w w q. ù 14) 400 C mw r w š q. ù w, 400 C œ w» û. w r SnOù x w r z j yƒ ù kù., Fig. 1 (b) (c), z j y, 48«4y(2011)

3 318 ½ vá½ Á½ Á½ Fig. 1. X-ray diffractin patterns f tin xide thin films: (a) Amrphus, (b) SnO, and (c). w wz

4 RF Sputtering w y œ z 319 Table 2. Structure and Grain Size f Tin Oxide Thin Films Structure SnO Amrphus Sample N. Grain Size (Å) As-dep Annealed N/A j»ƒ f y w. wr z peak psitin r, shiftƒ š, r x ü (internal stress) w y. 15) Table 3. Structure and Rughness f Tin Oxide Thin Films Structure SnO Amrphus Sample N. Rughness, R a (Å) As-dep Annealed y r z AFM e t e»(rughness, R a ), SnO, š w Fig. 2 Table 3 ùkü. r t e» û w ƒ š ù, 5 r t e»ƒ ù. Fig. 2. AFM images f tin xide thin films (1 µm µm scan): (a) Amrphus, (b) SnO, and (c). 48«4y(2011)

5 320 ½ vá½ Á½ Á½ ù t e»ƒ z ù Fig. 2 ùkù t ³e w xk š š, p p w (calesce) xk ùkü», r ü t û ƒ ¼. ³ewš xk w AFM j» w, w y w s³ XRD w. Ÿw p w 200~900 nm q n d wš, Ÿw ˆ Tauc gap mw w, 18) Fig. 3 ùkü. z r ˆ edgeƒ sharpw w, w ƒ Ÿ n ƒ w ùküš., ˆ edge yƒ ƒ w n w x w Fig. 3. Transmittance f tin xide thin films: (a) Amrphus, (b) SnO, and (c). w wz

6 RF Sputtering w y œ z 321 ƒw. SnO ˆ edge sharpness n ƒ z w ù w ˆ edge sharpness n ƒ û. w ü w w ƒ ˆ ü x w (defect level)ƒ n ƒ w. y n w x r, y 80% n. 6,8-10) e ƒƒ n w w ƒ š. w w œ 16) Table 3 e ƒ w, w n w. z ƒ SnO ˆ ƒƒ 2.27~2.55 ev 3.19~3.60 ev w 0.1~1.57 ev ƒw, ƒ r z ˆ Fig. 3 ùkü. 500 nm Ì Sn w» p r. d q w ùkù, w Sn r hmic wš» p q j w e. Hall d mw ƒ r» p d w, Table 4 ùkü. z e ƒ w, ƒ r». p 6 r, e cm cm 3 š, w Vs/cm Vs/cm 2 w. ƒ r xk (cnductin type) z ë, e j yƒ ùkû. XRD w, x œ j»ƒ ƒw y. ù z AFM r ³ew ùküš, w e. w m w y ü y y w w, y» w ƒ»» (mechanism) e x (tin interstitial) (xygen vacancy) ƒ x w e w w e. 17) Table 4 z r» w w Hall d e d w w r, d w w r» w ùküš. 4. RF reactive sputtering w y w š, XRD, AFM, UV-Vis spectrmeter Hall Table 4. Electrical Cnductivity f As-depsited and Annealed Tin Oxide Films Structure SnO Amrphus Cncentratin (10 18 cm 3 ) Sample N. Mbility (Vs/cm 2 ) Cnductivity (Ω cm) 1 As-dep Annealed As-dep Annealed As-Dep Annealed # #7 nt measurable nt measurable nt measurable nt measurable # nt measurable 0.12 nt measurable # nt measurable 0.97 nt measurable #13 nt measurable nt measurable nt measurable nt measurable # # # nt measurable nt measurable # # nt measurable 1.62 nt measurable # # nt measurable 2.71 nt measurable 1.46 nt measurable #2 nt measurable nt measurable nt measurable nt measurable nt measurable nt measurable #3 nt measurable nt measurable nt measurable nt measurable nt measurable nt measurable #4 nt measurable nt measurable nt measurable nt measurable nt measurable nt measurable # nt measurable nt measurable «4y(2011)

7 322 ½ vá½ Á½ Á½ measurement mw p w. 400 C œ mw y, Ÿw» p y š w. x as-dep k r w š j»ƒ ƒw y w. š t e» û w ù t ù xk ùkþ. y f g r» ƒ x û. Ÿw p, SnO, š p, n ƒ w y w. w y z œ œ n w j z ù,» f» w w. Acknwledgment 2010 ( w» ) w w» (N ). REFERENCES 1. M. Batzill and U. Diebld, The Surface and Materials Science f Tin Oxide, Prg. Surf. Sci., (2005). 2. B. G. Lewis and D.C. Paine, Applicatins and Prcessing f Transparent Cnducting Oxides, MRS Bulletin, 25 [8] (2000). 3. J. Kim, B. Kim, S. Chi, J. Park, and J. Park, Semicnducting Nanwires Netwrk and Its NO 2 Gas Sensr Applicatin (in Krean), Kr. J. Mater. Res., 20 [4] (2010). 4. S. E. Kim and M. Oliver, Structural, Electrical, and Optical Prperties f Reactively Sputtered, Thin Films, Met. Mater. Int., 16 [3] (2010). 5. W. Gu, L. Fu,Y. Zhang, K. Zhang, L. Y. Liang, Z. M. Liu, and H. T. Ca, Micrstructure, Optical, and Electrical Prperties f p-type SnO Thin Films, Appl. Phys. Lett., (2010). 6. J. L. Huang, Y. Pan, J. Y. Chang, and B. S. Yau, Annealing Effects n Prperties f Antimny Tin Oxide Thin Films Depsited by RF Reactive Magnetrn, Surf. Cat. Tech., (2004). 7. V. V. Kissine, S. A. Vrshilv, and V. V. Sysev, Oxygen Flw Effect n Gas Sensitivity Prperties f Tin Oxide Film Prepared by R.F. Sputtering, Sens. Actuat. B, (1999). 8. I. H. Kim, J. H. K, D. Kim, K. S. Lee, T. S. Lee, J. Jeng, B. Cheng, Y. J. Baik, and W. M. Kim, Scattering Mechanism f Transparent Cnducting Tin Oxide Films Prepared by Magnetrn Sputtering, Thin Slid Films, (2006). 9. E. Cetinrgua, S. Gldsmith, Y. Rsenberg, and R. L. Bxman, Influence f Annealing n the Physical Prperties f Filtered Vacuum Arc Depsited Tin Oxide Thin Films, J. Nn-Crystalline Slids, (2007). 10. Z. R. Dai, Z. W. Pan, and Z. L. Wang, Grwth and Structure Evlutin f Nvel Tin Oxide Diskettes, J. Am. Chem. Sc., (2002) 11. C. Y. K, K. J. Kim, K. H. Kim, and H. Y. Lee, Rm Temperature Depsitin and Heat Treatment Behavir f ATO Thin Films by In Beam Sputtering (in Krean), J. Kr. Ceram. Sc., 37 [11] (2000). 12. Y. Kim, S. P. Kim, S. D. Kim, and S. E. Kim, Characterizatin and Fabricatin f Tin Oxide Thin Film by RF Reactive Sputtering (in Krean), Kr. J. Mater. Res., 20 [9] (2010). 13. C. Suryanaraynara and M. G. Nrtn, X-ray diffractin - A Practical Apprach, p.212, Plenum Press, New Yrk, C. V. Thmpsn, Grain Grwth in Plycrystalline Thin Films f Semicnductrs, Inter. Sci., (1998). 15. T. Ungar, Micrstructural Parameters frm X-ray Diffractin Peak Bradening, Scripta Materialia, 51 [8] (2004). 16. E. Burstein, Anmalus Optical Absrptin Limit in InSb, Phys. Rev., 93 [3] (1954). 17. C. Kilic and A. Zunger, Origins f Cexistence f Cnductivity and Transparency in, Phys. Rev. Lett., 88 [9] (2002). 18. O. Stenzel, The Physics f Thin Film Optical Spectra: An Intrductin, 1 st ed., p.214, Springer, w wz