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Preparation of MgO films on GaAs by metalorganic chemical vapor deposition
__ _l!!!iB
s
ELSEVIER
March 1996
Materials Letters 26 (1996) 233-236
Preparation of MgO films on GaAs by metalorganic chemical vapor deposition J.-H. Boo *, K.-S. Yu, W. Koh, Y. Kim Thin Film Materials Laboratory. Korea Research Institute of Chemical Technology, Yusong. P.O. Box 107. Taejon 305-600, South Korea
Received 5 September 1995; accepted 10 September 1995
Abstract MgO films have been prepared on GaAs(100) substrates by low-pressure metalorganicchemical vapor deposition using Mg(tmhd), as a precursor and oxygen as a carrier gas, where tmhd is 2,2,6,6-tetramethyl-3,5_heptanedionate. Polycrystalline MgO films oriented mainly in the [ 1001 direction were obtained at the substrate temperature of 300°C. However, [l lo]
oriented growth began to appear as the deposition temperature was increased. Deposition at 500°C was found to induce breaking of the GaAs surfaces. Keywords:
MgO films; CVD, Metalorganic; GaAs substrates
1. Introduction
Magnesium oxide is thermodynamically very stable, has low dielectric constant and low refractive index, and has been widely used as substrate for superconducting, ferroelectric, and other oxide films. For practical applications, superconducting or ferroelectric oxide films need to be synthesized on largearea semiconductor substrates. Thus, forming MgO thin films as a buffelr layer on substrates such as GaAs receives an increasing interest in order to grow such oxide films on GaAs [I - 101. Superconducting YBa,Cu,O,_, films were deposited epitaxially on MgO/GaAs(lOO) where MgO thin films were prepared by laser deposition or electron beam evaporation [3,5,6]. Ferroelectric BaTiO, [2], PbTiO, [4], and LiNbO, [9] films were also grown on
* Corresponclmg author.
MgO/GaAs where MgO films were deposited using rf sputter deposition or pulsed laser beam ablation. Films of nonlinear optical materials such as LiNbO, deposited on MgO/GaAs may be used for monolithic electro-optic or frequency doubling applications in conjunction with semiconductor laser diodes. Chemical vapor deposition (CVD) of MgO films has received less attention while physical vapor deposition methods were successfully employed as mentioned above. There have been several reports on CVD of MgO on various substrates since the appearance of the first raport over a decade ago [ 1 l- 181. To our knowledge, however, CVD of MgO films on GaAs was never reported before.
2. Experimental
In this study, a magnesium /3-diketonate complex, Mg(tmhd),, was used as a precursor with oxygen as
00167-577X/96/$12.00 0 1996 Elsexier Science B.V. All rights reserved SSDI 00167-577X(95)00227-8
234
J.-H. Boo et d/Materials
a carrier gas (with a flow rate in the range lo-50 seem) where tmhd is 2,2,6,6-tetramethyl-3,5heptanedionate. Mg(tmhd), was prepared by the reaction of Mg powders (Kant0 Chemical Co., Inc.) with 2,2,6,6-tetramethyl-3,5-heptanedione &rem Chemicals Inc.) in refluxing methanol or tetrahydrofuran (THF). The product was purified by either recrystallization in THF or sublimation under reduced pressure. It was identified by NMR, FT-IR, and mass spectrometry. The melting point of the vacuum-dried product was 133°C. MgO films were prepared using a low-pressure CVD apparatus made of stainless steel. A GaAs(lOO) substrate was cleaned, prior to deposition, with trichloroethylene and rinsed with acetone, methanol, and deionized water. It was then treated with a 36% HCl solution, rinsed with deionized water, and immediately introduced into the CVD chamber. Substrate temperature was monitored by a chromelalumel thermocouple placed on top of the substrate. The composition of the MgO films was determined by X-ray photoelectron spectroscopy (XI’S). The crystallinity of the films was analyzed by X-ray diffractometry (XRD) and scanning electron microscopy @EM). The thicknesses of selected MgO films were measured from their SEM cross sections.
3. Results and discussion The MgO films were grown on GaAs(100) substrates at temperatures between 300 and 500°C. The XRD pattern and SEM image of the MgO film grown at 300°C and annealed at 430°C are shown in Fig. 1. The XRD pattern shows a strong MgO(200) peak and a much smaller MgO(400) peak other than the substrate peaks indicating that the MgO film is strongly [ 1001oriented. Half-micron sized grains with good crystallinity are observed in the SEM image of the same film. The square faces of cubic crystallites are clearly visible, although they are not well aligned, in the SEM image and consistent with strongly [lOO] oriented film growth. X-ray photoelectron survey spectrum of the film is shown in Fig. 2. The oxygen to magnesium ratio of the film calculated from the areas under the Mg 1s and 0 1s peaks is comparable to that of an MgO single crystal. Similar stoichiometry was obtained for the films prepared at other
Letters 26 (1996) 233-236
2
5 4
c
x .%
s
E
20
40
60
80
1 I
Fig. 1. X-ray diffration pattern (a) and SEM image (b) of the MgO film deposited on GaAs(100) at 300°C and annealed at 430°C.
temperatures. The small peaks of Ga 2p and As 2p are thought to be from the outer area of the substrate where MgO deposition did not occur. The XRD pattern of the MgO film on GaAs(100) grown at 310°C and annealed at 450°C also showed a strong (200) peak, but with a weak (220) peak indicating predominantly [lOO] oriented film growth with codeposition of the [llO] oriented crystallites. The SEM image of the same film also showed well-shaped cubic MgO crystallites although the di-
c 1200
800 Binding Energy
400
(eV)
Fig. 2. X-ray photoelectron survey spectrum of the MgO film deposited on GaAs(100) at 300°C and annealed at 430°C.
J.-H. Boo et al./ Materials Leners 26 (1996) 233-236
I@)
235
time. Combination of low-pressure CVD and the use of the single molecular precursor, Mg@nhd),, allowed deposition of MgO on GaAs at temperatures as low as 300°C. In order to avoid disruption of the GaAs surfaces, it was necessary to keep the substrate temperature below 400°C for the CVD process. Subsequent annealing above this temperature did not seem to induce severe structural change of the interface between the film and the GaAs substrate.
Acknowledgements
Fig. 3. X-ray diffration pattern (a) and SEM image (b) of the MgO film deposited on GaAs(lOO) at 500°C without annealing.
rection of the crystallites was not as well aligned as that of the film grown at 300°C and annealed at 430°C. Poorly aligned crystallites are consistent with the broadening of the X-ray diffraction peaks. Finally, an MgO film was prepared on GaAs(lOO) at 500°C. The (200) and (220) peaks in the XRD pattern (Fig. 3a) are lbroader than those of the films described above and the surface of the resulting film is quite rough (Fig. 31)) showing formation of irregular structures consisting of minute crystallites. The intensity of the GaAs(400) peak increased sharply. This is attributed to roughening of the GaAs surface due to the loss of As from the surface which occurs above 400°C [19]. Its X-ray photoelectron spectrum showed much increased peaks of Ga 2p and As 2p indicating that disruption of the GaAs surface has occurred at this deposition temperature. Therefore the resulting surface is thought to be a mixture of GaAs and MgO.
4. Conclusions MgO films were prepared on GaAs(lOO) substrates by chemical vapor deposition for the first
The authors would like to thank the Ministry of Science and Technology of Korea for the financial support. They are also grateful to Dr. K.-Y. Kang and Dr. B. Lee at Korea Electronics and Telecommunications Research Institute for the supply and preparation of the GaAs substrates.
References [l] L.S. Hung, L.R. Zheng and T.N. Blanton, Appl. Phys. Lett. 60 (1992) 3129. [2] K. Nashimoto, D.K. Fork and T.H. Geballe, Appl. Phys. Lett. 60(1992) 1199. [3] D.K. Fork, K. Nashimoto and T.H. Geballe, Appt. Phys. Lett. 60 (1992) 1621. [4] W.-Y. Hsu and R. Raj, Appl. Phys. Len. 60 (1992) 3105. 151 L.D. Chang, M.Z. Tseng, E.L. Hu and D.K. Fork, Appl. Phys. Lett. 60 (1992) 1753. [6] W. Prusseit, S. Corsepius, F. Baudenbacher, K. Hirata, P. Berberich and H. Kinder, Appl. Phys. Lett. 61 (1992) 1841. [7] E.J. Taraa, M. De Graef, D.R. Clarke, A.C. Gossard and J.S. Speck, J. Appl. Phys. 73 (1993) 3276. [S] M. De Graef and D.R. Clarke, Appl. Phys. Lett. 63 (1993) 1044. [9] D.K. Fork and G.B. Anderson, Appl. Phys. Len. 63 (1993) 1029. [lo] M.Z. Tseng, S.Y. Hu, Y.L. Chang, W.N. Jiang and E.L. Hu, Appl. Phys. Lett. 63 (1993) 987. [l I] K. Kamata, Y. Shibata and Y. Kishi, J. Mater. Sci. Lett. 3 (1984) 423. [12] B.S. Kwak, E.P. Boyd, K. Zhang, A. Erbil and B. Wilkins, Appl. Phys. Len. 54 (1989) 2542. 1131T. Maruyama and J. Shionoya, Japan. J. Appl. Phys. 29 (1990) L810. 1141 M. Vallet-Regi, M. Labeau, E. Garcia, M.V. Cabanas, J.M. Gonzalez-Calbet and G. Delabouglise, Physica C 180 (1991) 57.
236
J.-H. Boo er al./ Materials Letters 26 (1996) 233-236
[15] Y.-W. Zhao and H. Suhr, Appl. Phys. A 54 (1992) 451. [16] Z. Lu, R.S. Feigelson, R.K. Route, S.A. DiCarolis, R. Hiskers and R.D. Jacowitz, J. Cryst. Growth 128 (1993) 788. [17] R. Hiskes, S.A. DiCarolis, R.D. Jacowitz, Z. Lu, R.S. Feigelson, R.K. Route and J.L. Young, J. Cryst Growth 128 (1993) 781.
[18] E. Fujii, A. Tomozawa, S. Fujii, H. Torii, M. Hattori and R. Takayama, Japan. J. Appl. Phys. 32 (1993) Ll448. [19] J.Y. Tsao, T.M. Brennan, J.F. Klemt and B.E. Hammons, J. Vacuum Sci. Tcchnol. A 7 (1989) 2138.
s
ELSEVIER
March 1996
Materials Letters 26 (1996) 233-236
Preparation of MgO films on GaAs by metalorganic chemical vapor deposition J.-H. Boo *, K.-S. Yu, W. Koh, Y. Kim Thin Film Materials Laboratory. Korea Research Institute of Chemical Technology, Yusong. P.O. Box 107. Taejon 305-600, South Korea
Received 5 September 1995; accepted 10 September 1995
Abstract MgO films have been prepared on GaAs(100) substrates by low-pressure metalorganicchemical vapor deposition using Mg(tmhd), as a precursor and oxygen as a carrier gas, where tmhd is 2,2,6,6-tetramethyl-3,5_heptanedionate. Polycrystalline MgO films oriented mainly in the [ 1001 direction were obtained at the substrate temperature of 300°C. However, [l lo]
oriented growth began to appear as the deposition temperature was increased. Deposition at 500°C was found to induce breaking of the GaAs surfaces. Keywords:
MgO films; CVD, Metalorganic; GaAs substrates
1. Introduction
Magnesium oxide is thermodynamically very stable, has low dielectric constant and low refractive index, and has been widely used as substrate for superconducting, ferroelectric, and other oxide films. For practical applications, superconducting or ferroelectric oxide films need to be synthesized on largearea semiconductor substrates. Thus, forming MgO thin films as a buffelr layer on substrates such as GaAs receives an increasing interest in order to grow such oxide films on GaAs [I - 101. Superconducting YBa,Cu,O,_, films were deposited epitaxially on MgO/GaAs(lOO) where MgO thin films were prepared by laser deposition or electron beam evaporation [3,5,6]. Ferroelectric BaTiO, [2], PbTiO, [4], and LiNbO, [9] films were also grown on
* Corresponclmg author.
MgO/GaAs where MgO films were deposited using rf sputter deposition or pulsed laser beam ablation. Films of nonlinear optical materials such as LiNbO, deposited on MgO/GaAs may be used for monolithic electro-optic or frequency doubling applications in conjunction with semiconductor laser diodes. Chemical vapor deposition (CVD) of MgO films has received less attention while physical vapor deposition methods were successfully employed as mentioned above. There have been several reports on CVD of MgO on various substrates since the appearance of the first raport over a decade ago [ 1 l- 181. To our knowledge, however, CVD of MgO films on GaAs was never reported before.
2. Experimental
In this study, a magnesium /3-diketonate complex, Mg(tmhd),, was used as a precursor with oxygen as
00167-577X/96/$12.00 0 1996 Elsexier Science B.V. All rights reserved SSDI 00167-577X(95)00227-8
234
J.-H. Boo et d/Materials
a carrier gas (with a flow rate in the range lo-50 seem) where tmhd is 2,2,6,6-tetramethyl-3,5heptanedionate. Mg(tmhd), was prepared by the reaction of Mg powders (Kant0 Chemical Co., Inc.) with 2,2,6,6-tetramethyl-3,5-heptanedione &rem Chemicals Inc.) in refluxing methanol or tetrahydrofuran (THF). The product was purified by either recrystallization in THF or sublimation under reduced pressure. It was identified by NMR, FT-IR, and mass spectrometry. The melting point of the vacuum-dried product was 133°C. MgO films were prepared using a low-pressure CVD apparatus made of stainless steel. A GaAs(lOO) substrate was cleaned, prior to deposition, with trichloroethylene and rinsed with acetone, methanol, and deionized water. It was then treated with a 36% HCl solution, rinsed with deionized water, and immediately introduced into the CVD chamber. Substrate temperature was monitored by a chromelalumel thermocouple placed on top of the substrate. The composition of the MgO films was determined by X-ray photoelectron spectroscopy (XI’S). The crystallinity of the films was analyzed by X-ray diffractometry (XRD) and scanning electron microscopy @EM). The thicknesses of selected MgO films were measured from their SEM cross sections.
3. Results and discussion The MgO films were grown on GaAs(100) substrates at temperatures between 300 and 500°C. The XRD pattern and SEM image of the MgO film grown at 300°C and annealed at 430°C are shown in Fig. 1. The XRD pattern shows a strong MgO(200) peak and a much smaller MgO(400) peak other than the substrate peaks indicating that the MgO film is strongly [ 1001oriented. Half-micron sized grains with good crystallinity are observed in the SEM image of the same film. The square faces of cubic crystallites are clearly visible, although they are not well aligned, in the SEM image and consistent with strongly [lOO] oriented film growth. X-ray photoelectron survey spectrum of the film is shown in Fig. 2. The oxygen to magnesium ratio of the film calculated from the areas under the Mg 1s and 0 1s peaks is comparable to that of an MgO single crystal. Similar stoichiometry was obtained for the films prepared at other
Letters 26 (1996) 233-236
2
5 4
c
x .%
s
E
20
40
60
80
1 I
Fig. 1. X-ray diffration pattern (a) and SEM image (b) of the MgO film deposited on GaAs(100) at 300°C and annealed at 430°C.
temperatures. The small peaks of Ga 2p and As 2p are thought to be from the outer area of the substrate where MgO deposition did not occur. The XRD pattern of the MgO film on GaAs(100) grown at 310°C and annealed at 450°C also showed a strong (200) peak, but with a weak (220) peak indicating predominantly [lOO] oriented film growth with codeposition of the [llO] oriented crystallites. The SEM image of the same film also showed well-shaped cubic MgO crystallites although the di-
c 1200
800 Binding Energy
400
(eV)
Fig. 2. X-ray photoelectron survey spectrum of the MgO film deposited on GaAs(100) at 300°C and annealed at 430°C.
J.-H. Boo et al./ Materials Leners 26 (1996) 233-236
I@)
235
time. Combination of low-pressure CVD and the use of the single molecular precursor, Mg@nhd),, allowed deposition of MgO on GaAs at temperatures as low as 300°C. In order to avoid disruption of the GaAs surfaces, it was necessary to keep the substrate temperature below 400°C for the CVD process. Subsequent annealing above this temperature did not seem to induce severe structural change of the interface between the film and the GaAs substrate.
Acknowledgements
Fig. 3. X-ray diffration pattern (a) and SEM image (b) of the MgO film deposited on GaAs(lOO) at 500°C without annealing.
rection of the crystallites was not as well aligned as that of the film grown at 300°C and annealed at 430°C. Poorly aligned crystallites are consistent with the broadening of the X-ray diffraction peaks. Finally, an MgO film was prepared on GaAs(lOO) at 500°C. The (200) and (220) peaks in the XRD pattern (Fig. 3a) are lbroader than those of the films described above and the surface of the resulting film is quite rough (Fig. 31)) showing formation of irregular structures consisting of minute crystallites. The intensity of the GaAs(400) peak increased sharply. This is attributed to roughening of the GaAs surface due to the loss of As from the surface which occurs above 400°C [19]. Its X-ray photoelectron spectrum showed much increased peaks of Ga 2p and As 2p indicating that disruption of the GaAs surface has occurred at this deposition temperature. Therefore the resulting surface is thought to be a mixture of GaAs and MgO.
4. Conclusions MgO films were prepared on GaAs(lOO) substrates by chemical vapor deposition for the first
The authors would like to thank the Ministry of Science and Technology of Korea for the financial support. They are also grateful to Dr. K.-Y. Kang and Dr. B. Lee at Korea Electronics and Telecommunications Research Institute for the supply and preparation of the GaAs substrates.
References [l] L.S. Hung, L.R. Zheng and T.N. Blanton, Appl. Phys. Lett. 60 (1992) 3129. [2] K. Nashimoto, D.K. Fork and T.H. Geballe, Appl. Phys. Lett. 60(1992) 1199. [3] D.K. Fork, K. Nashimoto and T.H. Geballe, Appt. Phys. Lett. 60 (1992) 1621. [4] W.-Y. Hsu and R. Raj, Appl. Phys. Len. 60 (1992) 3105. 151 L.D. Chang, M.Z. Tseng, E.L. Hu and D.K. Fork, Appl. Phys. Lett. 60 (1992) 1753. [6] W. Prusseit, S. Corsepius, F. Baudenbacher, K. Hirata, P. Berberich and H. Kinder, Appl. Phys. Lett. 61 (1992) 1841. [7] E.J. Taraa, M. De Graef, D.R. Clarke, A.C. Gossard and J.S. Speck, J. Appl. Phys. 73 (1993) 3276. [S] M. De Graef and D.R. Clarke, Appl. Phys. Lett. 63 (1993) 1044. [9] D.K. Fork and G.B. Anderson, Appl. Phys. Len. 63 (1993) 1029. [lo] M.Z. Tseng, S.Y. Hu, Y.L. Chang, W.N. Jiang and E.L. Hu, Appl. Phys. Lett. 63 (1993) 987. [l I] K. Kamata, Y. Shibata and Y. Kishi, J. Mater. Sci. Lett. 3 (1984) 423. [12] B.S. Kwak, E.P. Boyd, K. Zhang, A. Erbil and B. Wilkins, Appl. Phys. Len. 54 (1989) 2542. 1131T. Maruyama and J. Shionoya, Japan. J. Appl. Phys. 29 (1990) L810. 1141 M. Vallet-Regi, M. Labeau, E. Garcia, M.V. Cabanas, J.M. Gonzalez-Calbet and G. Delabouglise, Physica C 180 (1991) 57.
236
J.-H. Boo er al./ Materials Letters 26 (1996) 233-236
[15] Y.-W. Zhao and H. Suhr, Appl. Phys. A 54 (1992) 451. [16] Z. Lu, R.S. Feigelson, R.K. Route, S.A. DiCarolis, R. Hiskers and R.D. Jacowitz, J. Cryst. Growth 128 (1993) 788. [17] R. Hiskes, S.A. DiCarolis, R.D. Jacowitz, Z. Lu, R.S. Feigelson, R.K. Route and J.L. Young, J. Cryst Growth 128 (1993) 781.
[18] E. Fujii, A. Tomozawa, S. Fujii, H. Torii, M. Hattori and R. Takayama, Japan. J. Appl. Phys. 32 (1993) Ll448. [19] J.Y. Tsao, T.M. Brennan, J.F. Klemt and B.E. Hammons, J. Vacuum Sci. Tcchnol. A 7 (1989) 2138.