近年來，採用高介電材料取代傳統的二氧化矽做為動態記憶體中電容的介電材料似乎有增加的趨勢。二氧化鈦與鈦酸鋇由於具有高介電常數, 故適合應用在動態記憶體中電容的介電材料。我們採用水平、低壓、冷壁式之有機金屬化學氣相沈積法來成長二氧化鈦與鈦酸鋇薄膜，採用的原料為Ba(DPM)2(tetraene)2，Ti(i-OC3H7)4與N2O。其成長速率受到Ti流量、成長溫度與壓力所影響。X光繞射證實二氧化鈦與鈦酸鋇薄膜為多晶結構。由電容-電壓曲線可以得知二氧化鈦與鈦酸鋇的介電常數分別為85與300。而經由熱退火處理在不同溫度及時間的氮氣及氧氣環境下對於結構及電性的影響也被討論。
從掃瞄式電子顯微鏡觀察到二氧化鈦與鈦酸鋇薄膜都具有柱狀結構，並且有晶粒的存在，晶粒邊界會造成漏電流的路徑。我們用熱退火可以稍微降低漏電流的問題。未來期望能將朝向增加介電常數及降低漏電流的目標前進。

Recently, there has been increasing demands for high dielectric materials to replace SiO2 for high-density dynamic random access memories with ultralarge scale integration. TiO2 and BaTiO3 are very promising insulators for applications to DRAMs, as they exhibit higher dielectric constant.The growths of TiO2 and BaTiO3 thin films on (100) silicon are studied by MOCVD using Ti(i-OC3H7)4, Ba(DPM)2(tetraene)2 and N2O as precursors. The growth was performed in a cold wall horizontal system in the temperature range of 350~700℃. The growth rates of TiO2 and BaTiO3 films are affected by the Ti flow rate, growth temperature and reactor pressure. The structures of TiO2 and BaTiO3 films are polycrystalline by X-ray diffraction examinations. The dielectric constant of as-grown TiO2 can reach 85 and BaTiO3 can reach 300 derived by C-V curves with the contact area 3.14×10-4 cm2. In addition, the influences of postannealing treatment under an O2 and N2 ambient with different annealing temperature and time on the structural and electrical properties of as-grown TiO2 films will be also studied.
However, TiO2 and BaTiO3 films have columnar structures acted the paths of leakage current. We use thermal annealing to reduce the leakage current. In the future, to enhance the dielectric constant and reduce the leakage current of the films is the goal in our study.

CONTENTS

Acknowledgment................................i
List of figures...............................vii
List of tables................................x
Abstract......................................xi

1.Introduction...................................1
1-1 Developments in DRAM.........................1
1-2 Promising candidates of high dielectric
constant materials for high-density DRAM.....2
1-3 Comparison of deposition methods of BaTiO3...4
1-4 Advantages of MOCVD..........................5

2.Experiments....................................7
2-1 Growth system of MOCVD.......................7
2-2 Properties of metalorganic precursors........8
2-2-1 Ti metalorganic precursor..................8
2-2-2 Ba metalorganic precursor..................8
2-3 Difficulties of setting up the system........9
2-4 Growth procedures...........................10
2-4-1 Si wafer cleaning procedures..............10
2-4-2 Metal wafer cleaning processes............11
2-4-3 Preparations of TiO2 and BaTiO3 thin
films.....................................11
2-5 Characterizations...........................12
2-5-1 Physical properties.......................12
2-5-2 Chemical properties.......................12
2-5-3 Electrical properties.....................13

3.Results and Discussion........................15
3-1 Dependence of structural and electrical
properties on Ti flow rate..................15
3-1-1 Thickness and growth rate as a function of
Ti flow rate..............................15
3-1-2 Dielectric constant and leakage current
density as a function of Ti flow rate.....16
3-2 Thickness as a function of growth time......17
3-3 Dependence of structural and electrical
properties on thickness.....................17
3-1 Ratio of Ti to O as a function of thickness.17
3-3-2 Grain size as a function of thickness.....18
3-3-3 Dielectric constant and leakage current
density as a function of thickness........18
3-4 Dependence of structural and electrical
properties on growth temperature............19
3-4-1Thickness and growth rate as a function of
growth temperature.........................20
3-4-2 XRD patterns as a function of growth
temperature...............................20
3-4-3 Dielectric constant as a function of growth
temperature...............................21
3-4-4 Leakage current density as a function of
growth temperature.......................22
3-4-5 SEM morphologies as a function of growth
temperature...............................23
3-5 Chemical properties of as-grown TiO2 films on
Si..........................................24
3-5-1 SIMS depth profile of as-grown TiO2 film on
Si........................................24
3-5-2 AES depth profile of as-grown TiO2 film on
Si........................................25
3-5-3 ESCA-XPS compositions analyses of
as-grown TiO2 film on Si..................25
3-6 As-grown TiO2 films on Pt/Ti/SiO2/Si........26
3-7 Improvement of electrical properties by
thermal annealing...........................27
3-7-1 Investigation of structural and electrical
properties by thermal annealing in N2 and
O2 ambient................................27
3-7-2 Investigation of electrical properties by
thermal annealing in O2 ambient with
different temperature.....................31
3-7-3 Investigation of electrical properties by
thermal annealing in O2 ambient with
different time............................32
3-7-4 Investigation of electrical properties by
two-step thermal annealing in N2 and O2
ambient with different temperature........33
3-8 Growth mechanism of BTO on Si...............35
3-8-1 Thickness and growth rate as a function of
reactor pressure..........................35
3-8-2 Grain size and dielectric constant as a
function of reactor pressure..............36
3-8-3 Grain size and leakage current density as a
function of reactor pressure..............37
3-8-4 Thickness and growth rate as a function of
Ti flow rate .............................37
3-8-5 Dielectric constant and leakage current
density as a function of Ti flow rate.....38
3-8-6 X-ray diffraction pattern of BTO on Si....38

4.Conclusions...................................41

References......................................84

References

[1] K. Kim, C. G. Hwang and J. G. Lee, “DRAM Technology Perspective for Gigabit Era,” IEEE Trans. Electron Devices, vol. 45, pp. 598-608, 1998.
[2] S. M. SZE, “Four decades of developments in microelectronics: achievements and challenges’’, 1999.
[3] Q. X. Jia, L. H. Chang and W. A. Anderson, “Low leakage current BaTiO3 thin film capacitors using a multilayer construction,” Thin Solid Films, vol. 259, pp. 264-269, 1995.
[4] S. Yamamichi, A. Yamamichi, D. park, T. J. King and C. Hu, “Impact of time dependent dielectric breakdown and stress-induced leakage current on the reliability of high dielectric constant (Ba, Sr)TiO3 thin-film capacitors for Gbit-scale DRAM’s,” IEEE Transactions on Electron Devices, vol. 46, no. 2, pp. 342-347, 1999.
[5] S. Kamiyama, P. Y. Lesaicherre, H. Suzuki, A. Sakai, I. Nishiyama and A. Ishitani, “Ultrathin tantalum oxide capacitor dielectric layers fabricated using rapid thermal nitridation prior to low-pressure chemical-vapor-deposition”, J. Electrochem. Soc., vol 140, Iss. 6, pp. 1617-1625, 1993.
[6] Y. H. Lee, K. K. Chan and M. J. Brady, “Plasma enhanced chemical vapor deposition of TiO2 in microwave-radio frequency hybrid plasma reactor,” J. Vac. Sci. & Technol., vol. 13, Iss 3, pp. 596-601, 1995.
[7] Y. Abe and T. Fukuda, “TiO2 thin films formed by electron cyclotron resonance plasma oxidation at high temperature and their application to capacitor dielectrics,” Jpn. J. Appl. Phys. Part 2-Letts, vol. 33, Iss 9A, pp. L1248-L1250, 1994.
[8] T. W. Kim, Y. S. Toon, S. S. Yom, and C. O. Kim, “Ferroelectric BaTiO3 films with a high magnitude dielectric constant grown on p-Si by low-pressure metalorganic chemical vapor deposition,” Appl. Surface. Science., vol.90, Iss. 1, pp. 75-80, 1995.
[9] K. Koyama, T. Sakuma, S. Yamamichi, Watanabe and H. Aoki, “A stacked capacitor with (BaxSr1-x)TiO3 for 256M DRAM,” in IEDM Tech. Dig., pp. 823-826, 1991,
[10] E. Tokumitsu, Ryo-ichi Nakamura and H. Ishiwara, “Nonvolatile memory operations of metal-ferroelectric-insulator-semiconductor (MFIS) FET’s using PLZT/STO/Si(100) structures,” IEEE Electron Device Lett., vol. 18, no. 4, pp. 160-162, 1997.
[11] H. J. Frenck, W. Kulisch, M. Kuhr and R. Kassing, “Deposition of TiO2 thin films by plasma enhanced decomposition of tetraisopropyltitanate”, Thin Solid Films, vol. 201, pp. 327-332, 1991.
[12] D. H. Lee, Y. S. Cho, W. I. Yi, T. S. Kim, J. K. Lee and H. J. Jung, “Metalorganic chemical-vapor-deposition of TiO2-N anatase thin-film on Si substrate”, Appl. Phys. Lett. , vol.66 , pp. 815-821, 1995.
[13] M. B. Lee, M. Kawasaki, M. Yoshimoto, B. K. Moon, H. Ishiwara and H. Koinuma, “Formation and characterization of epitaxial TiO2 and BaTiO3/TiO2 films on Si substrate”, Jpn. J. Appl. Phys., vol.34, pp. 808-815, 1995.
[14] The Oxide Handbook, ed. G. V. Samsonov ( IFI/Plenum, New York, pp 316, 1973.
[15] J. Yan, D. C. Gilmer, S. A. Campbell. W. L. Gladfelter and R. G. Schmid, “Structural and electrical characterization of TiO2 grown from titanium tetrakis-isopropoxide (ttip) and ttip/H2O ambients”, J. Vac. Sci. & Technol., vol. B14, pp. 1706-1711,1996.
[16 ] K. A. Vorotilov, E. V. Orlova and V. I. Petrovsky, “Sol-gel TiO2 films on silicon substrates”, Thin solid films , vol 207, Iss 1-2, pp. 180-184 , 1992.
[17] P. Lobl, M. Huppertz and D. Mergel, “Nucleation and growth in TiO2 films prepared by sputtering and evaporation”, Thin solid films, vol 251, Iss 1, pp. 72-79,1994.
[18] D. Guerin and S. I. Shah, “Reactive sputtering of titanium-oxide thin films”, J. Vac. Sci. Technol. A, vol 15, Iss 3, pp. 712-715, 1997.
[19] H. K. Ha, M. Yoshimoto, H. Koinuma, B. K. Moon and H. Ishiwara, “Open air plasma chemical vapor deposition of highly dielectric amorphous TiO2 films”, Appl. Phys. Lett. , vol 68, Iss 21, pp. 2965-2967,1996.
[20] N. Rausch and E. P. Burte, “Thin TiO2 films prepared by low-pressure chemical vapor-deposition”, J. Ectrochem. Soc. , Vol 140, Iss 1, pp 145-149,1993.
[21] A. Turkovic, M. Ivanda, A. Drasner, V. Vranesa and M. Persin, “Raman-spectroscopy of thermally annealed TiO2 thin films”, Thin solid films, vol 198, Iss 1-2, pp. 199-205, 1991.
[22] H. S. Kim, D. C. Gilmer, S. A. Campbell and D. L. Polla, “Leakage current and electrical breakdown in metal-organic chemical-vapor-deposited TiO2 dielectrics on silicon substrates”, Appl. Phys. Lett. , vol 69, Iss 25, pp 3860-3862, 1996.
[23] S. A. Campbell, D. C. Gilmer, X. C. Wang, M. T. Hsieh, H. S. Kim, W. L. Gladfelter and J. H. Yan, “MOSFET transistors fabricated with high permitivity TiO2 dielectrics”, IEEE Tran. Electron Devices, vol 44, Iss 1, pp. 104-109, 1997.
[24] T. Sumi, Y. Judai, K. Hirano, T. Ito, T. Mikawa, M. Takeo, M. Azuma, S. Hayashi, Y. Uemoto, K. Arita, T. Nasu, Y. Nagano, A. Inoue, A. Matsuda, E. Fuji, Y. Shimada, T. Otsuki, “ Ferroelectric nonvolatile memory technology and its applications,” Jpn. J. Appl. Phys., vol 35, Iss 2B, pp 1516-1520, 1996.
[25] A. M. Glass, “ Optical-materials”, Science, vol 235, Iss 4792, pp 1003-1009, 1987.
[26] L. M. Sheppard, “Advances in Processing of Ferroelectric thin films”, Ceram. Bull., vol 71, Iss 1, pp 85-95, 1992.
[27] H. B. Sharma and H. N. K. Sarma, “Electrical properties of sol-gel processed barium titanate films,” Thin Solid Films, vol. 330, Iss. 2, pp. 178-182, 1998.
[28] T. Yoko, K. Kamiya, and K. Tanaka, “Preparation of multiple oxide BaTiO3 fibers by sol-gel Method,” J. Materials. Soc., vol. 25, Iss. 9, pp. 3922-3929, 1990.
[29] H. Shimooka and S. Kohiki, “Thermal behavior of sol-gel derived barium titanate gels,” J. Ceramic. Soc. Jpn, vol. 106, Iss. 7, pp. 703-708, 1998.
[30] K. Iijima, T. Terashima, K. Yamamoto, K. Hirata and Y. Bando, “Preparation of ferroelectric BaTiO3 thin films by activated reactive evaporation”,Appl. Phys. Lett. Vol. 56, No. 6, pp.527-529, 1990.
[31] Y. Yoneda, H. Kasatani,H. Terauchi,Y. Yoshihiko,T. Terashima,Y. Bando, “Ferroelectric phase transition in BaTiO3 films,” J. Crystal Growth, vol. 150, pp. 1090-1096, 1995.
[32] Q. X. Jia, Z. Q. Shi, and W. A. Anderson, “BaTiO3 thin film capacitors deposited by R.F. magnetron sputtering,” Thin. Solid Films., vol. 209, pp. 230-239, 1992.
[33] S. Kim, S. Hishita, Y. M. Kang, and S. Baik, “Structural characterization of epitaxial BaTiO3 thin films grown by sputter deposition on MgO (100),” J. Appl. Phys., vol. 78, Iss. 9, pp. 5604-5608, 1995.
[34] Q. X. Jia, J. L. Smith, L. H. Chang, and W. A. Anderson, “Characteristics of BaTiO3 thin film on Si deposited by RF magnetron sputtering,” Philosophical. Magazine B., vol. 77, Iss. 1, pp. 163-175, 1998.
[35] K. Nashimoto, D. K. Fork and T. H. Geballe, “Epitaxial growth of MgO on GaAs(001) for growing epitaxial BaTiO3 thin films by pulsed Laser deposition, ” Appl. Phys. Lett., vol. 60, No.10, pp.1199-1201,1995.
[36] B. D. Qu, M. Evstigneev, D. J. Johnson, and R. H. Prince, “Dielectric properties of BaTiO3/SrTiO3 multilayered thin films prepared by pulsed Laser deposition, ” Appl. Phys. Lett., vol. 72, No. 11, pp. 1394-1396,1998.
[37] S. Tsunekawa, J. Ichikawa, Y. Yoneda, and T. Ozaki, “AFM observation of 180 degrees domains in BaTiO3 crystals grown by MBE,” J. Korean. Phys. Soc., vol. 32, Iss. S, pp. 777-779, 1998.
[38] R. A. Mckee, F. J. Walker, J. R. Conner, E. D. Specht, and D. E. Zelmon, “Molecular beam epitaxy growth of epitaxial barium silicide, barium oxide, barium titanate on silicon,” Appl. Phys. Letts., vol. 59, Iss. 7, pp. 782-784, 1991.
[39] L. A. Wills, B. W. Wessels, D. S. Richeson, and T. J. Marks, “Epitaxial growth of BaTiO3 thin films by organometallic chemical vapor deposition,” Appl. Phys. Letts., vol 60, Iss. 1, pp.41-43, 1992.
[40] T. W. Kim, Y. S. Toon, S. S. Yom, and C. O. Kim, “Ferroelectric BaTiO3 films with a high-magnitude dielectric constant grown on p-Si by low-pressure metalorganic chemical-vapor-deposition,” Appl. Surface. Science., vol.90, Iss. 1, pp. 75-80, 1995.
[41] J. Zhao, V. Fuflyigin, F. V. Wang, P. E. Norris, L. Bouthilette, and C. Woods, “Epitaxial electrooptical BaTiO3 films by single-source metal-organic chemical vapor deposition,” J. Materials. Chemistry., vol. 7, Iss. 6, pp. 933-936, 1997.
[42] D. Nagano, H. Funakubo, K. Shinozaki and N. Mizutani, “Electrical properties of semiconductive Nb-doped BaTiO3 thin films prepared by metal-organic chemical-vapor deposition,” Appl. Phys. Lett., vol. 72, no. 16, pp. 2017-2019, 1998.
[43] J. Zeng, H. Wang, M. Wang, S. Shang, Z. Wang and C. Lin, “Preparation and ferroelectric properties of BaTiO3 thin films by atmospheric-pressure metalorganic chemical vapor deposition,” Thin Solid Films, 322, pp. 104-107, 1998.
[44] G. Stringfellow, “Organometallic vapor phase epitaxy: Theory and Practice, Academic Press, Boston, 1989.
[45] Y. S. Yoon, W. N. Kang, H. S. Shin, S. S. Yom, T. W. Kim, J. Y. Lee, D.J. Choi and S-S. Baek, “Structural properties of BaTiO3 thin films on Si grown by metalorganic chemical vapor deposition,” in J. Appl. Phys., vol. 73, no. 3, pp. 1547-1549, 1993.
[46] D. Nagano, H. Funakubo, K. Shinozaki and N. Mizutani, “Electrical properties of semiconductive Nb-doped BaTiO3 thin films prepared by metal-organic chemical-vapor deposition,” Appl. Phys. Lett., vol. 72, no. 16, pp. 2017-2019, 1998.
[47] H. J. Cho and H. J. Kim, “Improvement of dielectric properties of (Ba, Sr)TiO3 thin films deposited by pulse injection chemical vapor deposition,” Appl. phys. Letts., vol. 72, no. 7, pp. 786-788, 1998.
[48] H. Zama and T. Morishita, “Metalorganic chemical vapor deposition of YBa2Cu3Ox thin films using Bis-Dipivaloylmethanato-Barium Bis-Tetraethylenepentamine adducts as a novel Barium souce,” Jpn. J. Appl. Phys. vol. 35, part 2, no. 6B, pp. 770-773, 1996.
[49] N. Mizutani, D. Nagano, H. Funakubo, N. Wakiya and K. Shinozaki, “MOCVD preparation and properties of BaTiO3-SrTiO3 solid solution thin film”, J. Korean. Phys. Soc., vol.32, pp.1336-1339, 1998.
[50] F. A. Grant, Rev. Mod. Phys. vol.31, pp.646, 1959.
[51] “Powder Diffraction File,” Joint committee on powder diffraction standards.
[52] L. M. Williams and D. W. Hess, “Structural properties of titanium dioxide films deposited in an rf glow discharge”, J. Vac. Sci. Technol.,vol.1, pp.1810-1819,1983.
[53] P. Babelon, A. S. Dequiedt, H. Mostefa-Sba, S. Nourgeois, P. Sibillot and M. Sacilotti, “SEM and XPS studies of titanium dioxide thin films grown by MOCVD”, Thin Solid Films, vol. 322, pp.63-67, 1998.
[54] S. Kimura, K. Mukai, Y. Nishioka and A. Shintani, “Leakage-current increase in amorphous Ta2O5 films due to pinhole growth during annealing below 600℃”, J. Electrochem. Soc., vol. 130, Iss 12, pp. 2414-2418, 1983
[55] H. Shin, M.r. Deguire and A. H. Heuer, “Electrical properties of TiO2 thin films formed on self-assembled organic monolayers on silicon”, Jpn. J. Appl. Phys., vol 83, Iss 6, pp. 3311-3317,1998.
[56] H. Fukuda, S. Namioka, M. Miura, Y. Ishikawa, M. Yoshino and S. Nomura, “Structural and electrical properties of crystalline TiO2 thin films formed by metalorganic decomposition”, Jpn. J. Appl. Phys. vol 38, Iss 10, pp. 6034-6038, 1999.
[57] C. K. Yang, T. F. Lei and C. L. Lee, “The combined effects of low-pressure NH3-annealing and H2 plasma hydrogenation on polysilicon thin-film transistors”, IEEE Electron Device Lett., vol 15, Iss 10, pp. 389-390 , 1994,
[58] P. Bhattacharya, K. H. Park and Y. Nishioka, “Control of grain-structure of laser-deposited (Ba, Sr)TiO3 films to reduce leakage current”, Jpn. J. Appl. Phys. vol.33, Iss 9B, pp. 5231-5234,1994.
[59] C. Byun, Y. Kim, W. J. Lee and B. W. Lee, “Effect of a TiO2 buffer layer on the C-V properties of Pt/PbTiO3/ TiO2/Si structure”, Jpn. J. Appl. Phys. vol 36, no. 9A, pp. 5588-5589, 1997.
[60] T. Kimura, H. Yamauchi, H. Machida, H. Kokubun and M.Yamada, “Synthesis of novel Sr sources for metalorganic chemical vapor deposition of SrTiO3”, Jpn. J. Appl. Phys, vol 33, Iss 9B, pp. 5119-5124 , 1994.