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Reactive deposition of In2O3 films on nucleated-crystallite substrates
Thin Solid Films, 221 (1992) 1-4
1
Letter
Reactive deposition of In203 films on nucleated-crystallite substrates S. Muranaka Department of Chemistry, College of Liberal Arts and Science, Kyoto University, Kyoto (Japan) (Received June 9, 1992; accepted July 13, 1992)
oscillator and the substrates were maintained at room temperature and about 100 °C respectively. The structure of the films was examined using transmission electron microscopy and electron diffraction and the electrical resistivity of the films was measured using a four-point probe method. Light transmission measurements were made using a double-beam spectrophotometer. The resistivity and light transmission were also measured for films deposited on quartz glasses for comparison.
1. Introduction Numerous studies have been carried out over many years to prepare indium oxide films for the application of their transparent-conductive nature. Several workers have reported the preparation of films using reactive deposition [1-6]. This technique features simple deposition apparatus and procedures as compared with techniques using ionized particles. However, high quality films are formed only on substrates heated above 150 °C, and below this temperature opaque films are deposited which have low conductivity because of their disordered structure [1-4]. Recently, coatings of In203 films on heat-sensitive materials such as polymerized films have been requested for use as transparent electrodes or antistatic coatings. For this purpose, attempts have been made to deposit films at lower substrate temperatures using crystallite-nucleated substrates. This paper describes the effect of Au-, Ag- or In-nucleated substrates on the structure of the films together with some physical properties.
2. Experimental procedures Films were deposited in a conventional high-vacuum chamber which was evacuated using an oil-diffusion pump. The substrates were about 20 cm from an evaporation source. After the vacuum chamber was evacuated to less than 6.7 x 10 -4 Pa, Au and Ag of purity 99.99% and In of purity 99.999% was coated on both SiO films and quartz glasses, and then, without breaking the vacuum of the chamber, indium oxide films were deposited on the substrates which had fresh sublayers. These sublayers were about 10 or 30 A, thick. The oxygen pressure during film deposition was about 0.27 Pa, and the deposition rate about 1 A. s- t. The film thickness was in the range 550-3000 A. The deposition rate and the film thickness were monitored using a quartz crystal
3. Results and discussion Figure 1 shows transmission electron micrographs and electron diffraction patterns for Au films and for In203 films of thickness 550 ,l, deposited on the Au films at 100 °C. The indium oxide films deposited on the Au films of I0 A. were mainly crystalline In203 with a trace of the amorphous form (Fig. l(c)), while those deposited on the Au films of 30 A were completely crystalline (Fig. l(d)). A trace of the amorphous phase was identifiable from faint diffuse lines in the diffraction patterns (Fig. l(c)). The films contained many crystallites which grew on Au particles. The number density of crystallites was greater in the films deposited on the thicker Au films. As seen in Figs. l(a) and l(b), the Au particles were much larger for the thicker sublayer, while coalescence reduced the number density. Thus, larger Au particles act more effectively as nucleation centers for the growth of crystallites, resulting in the crystallized films on the thicker Au sublayers. Figure 2 shows transmission electron micrographs and electron diffraction patterns for indium oxide films deposited at I00 °C on In or Ag films. The microstructres of the In and Ag sublayers were quite similar to those of the Au sublayers of the corresponding thicknesses, although the size of the particles and their number density were slightly dependent on the types of metal deposits. The results obtained for the indium oxide films deposited on the In films were very similar to those for the films deposited on the Au films (Figs. 2(a) and 2(b)). The films also grew in the crystallized form on the thicker In films with the aid of larger In particles. However, the films deposited on the Ag films were quasi-amorphous, regardless of the thickness of Ag deposits (Fig. 2(c)). The microstructure of the films, consisting of a major amorphous part and a small number of crystallites, was almost the same as that of
Elsevier Sequoia
2
Letter
(a)
(b)
(c)
(d)
~
' It m
Fig. 1. Electron micrographs and electron diffraction patterns of Au films and InzO 3 films: (a) 10 ]~ Au films, (b) 30 ~ Au films, (c) In203 films deposited on 10 ,~ Au films and (d) InzO 3 films deposited on 30 ,~ Au films.
the film deposited on SiO substrates [5]. Thus, Ag particles have little influence on the growth of films. Table 1 shows the values of the electrical resistivity of indium oxide films deposited at 100 °C. The films deposited on the Au or In films exhibited resistivities lower than those deposited on glass substrates (about 4.5 × 10 -3 f~cm) and on the Ag films. With the ira-
T A B L E 1. Electrical resistivity of I n , O 3 films deposited on Au, In and Ag sublayers of thickness 10 A or 30/~ Thickness of sublayer (,~,)
10 30
Resistivity ( ~ cm) Au sublayer
In sublayer
Ag sublayer
2.2 x 10 ~ 1.5 x 10 3
2.5 x 10 .3 2.0 x 10 3
4.2 x 10 ~ 4 . 0 x 10 3
provement in the crystallinity, the conductivity of the films was slightly increased. Figure 3 shows the optical transmission curves for the indium oxide films deposited at 100 °C. The transmission curve for the films deposited on the glass substrates is also included for comparison. The crystalline films deposited on both In films with 10/~ and 30 ,~ thickness exhibited a high transmittance of about 85%. Owing to light absorption by Au particles [7], the transmittance was slightly reduced for the films deposited on the 10,~ Au films and much reduced for those deposited on the Au films with thickness of 30 ,~. For the In sublayers, light absorption by the In particles gradually increased with decreasing wavelength below 450 nm. The films deposited on the Ag films showed lower transmittance because of the quasi-amorphous structure in addition to the effects of light absorption by Ag particles [7],
Letter
(a)
3
<
(b)
(c) Fig. 2. Electron micrographs and electron diffraction patterns of In203 films deposited on In and Ag films of different thicknesses: (a) In films with 10 ~ thickness, (b) In films with 30 ,~ thickness and (c) Ag films with 30 ,~ thickness. An arrow indicates a diffraction line from the Ag lattice.
1(30
i
[
I
I
0
8~ 0
,.- ............... / " "
....................
~40
.........................ebc
"
I
20 I
500
600
Wave[ength (nm) Fig. 3. Transmission spectra of 3000/k ln203 films deposited on various kinds of sublayers: curve a, 10 A In films; curve b, 30 A In films; curve c, 10 A Au films; curve d, 30 A Au films; curve e, 10/k Ag films; curve f, 30/k Ag films; curve g, glass substrates.
4
All the films deposited at room temperature were amorphous, regardless of the type of sublayer. The films displayed a high electrical resisivity (10 - 2 10-192 cm) and a low light transmittance (below 50%) because of their disordered structure. The conclusion is that films grow in a crystalline form on Au- and In-nucleated substrates at 100 °C, and in a quasi-amorphous form on Ag-nucleated substrates. With the improvement of the crystallinity of films, electrical resistivity decreases slightly and light transmittance increases substantially.
Acknowledgment The authors would like to thank Dr. Y. Oka for valuable discussions.
Letter
References I s. Noguchi and H. Sakata, J. Phys. D, 13 (1980) 1129. 2 Z. Ovandyahu, B. Ovryn and H. W. Kraner, J. Electroehem. Soc., 130 (1983) 917. 3 Z. Ovandyahu, J. Phys. C, 19 (1986) 5187. 4 I. Hamberg and C. G. Granqvist, J. Appl. Phys., 60 (1986) R213. 5 S. Muranaka, Y. Bando and T. Takada, Thin Solid Films, 151 (1987) 355. 6 T. Nagatomo, Y. M'urata and O. Omato, Thin Solid Fihns, 192 (1990) 17. 7 P. Rouard and G. Rasigni, Optica Acta. 14 (1967) 27.
1
Letter
Reactive deposition of In203 films on nucleated-crystallite substrates S. Muranaka Department of Chemistry, College of Liberal Arts and Science, Kyoto University, Kyoto (Japan) (Received June 9, 1992; accepted July 13, 1992)
oscillator and the substrates were maintained at room temperature and about 100 °C respectively. The structure of the films was examined using transmission electron microscopy and electron diffraction and the electrical resistivity of the films was measured using a four-point probe method. Light transmission measurements were made using a double-beam spectrophotometer. The resistivity and light transmission were also measured for films deposited on quartz glasses for comparison.
1. Introduction Numerous studies have been carried out over many years to prepare indium oxide films for the application of their transparent-conductive nature. Several workers have reported the preparation of films using reactive deposition [1-6]. This technique features simple deposition apparatus and procedures as compared with techniques using ionized particles. However, high quality films are formed only on substrates heated above 150 °C, and below this temperature opaque films are deposited which have low conductivity because of their disordered structure [1-4]. Recently, coatings of In203 films on heat-sensitive materials such as polymerized films have been requested for use as transparent electrodes or antistatic coatings. For this purpose, attempts have been made to deposit films at lower substrate temperatures using crystallite-nucleated substrates. This paper describes the effect of Au-, Ag- or In-nucleated substrates on the structure of the films together with some physical properties.
2. Experimental procedures Films were deposited in a conventional high-vacuum chamber which was evacuated using an oil-diffusion pump. The substrates were about 20 cm from an evaporation source. After the vacuum chamber was evacuated to less than 6.7 x 10 -4 Pa, Au and Ag of purity 99.99% and In of purity 99.999% was coated on both SiO films and quartz glasses, and then, without breaking the vacuum of the chamber, indium oxide films were deposited on the substrates which had fresh sublayers. These sublayers were about 10 or 30 A, thick. The oxygen pressure during film deposition was about 0.27 Pa, and the deposition rate about 1 A. s- t. The film thickness was in the range 550-3000 A. The deposition rate and the film thickness were monitored using a quartz crystal
3. Results and discussion Figure 1 shows transmission electron micrographs and electron diffraction patterns for Au films and for In203 films of thickness 550 ,l, deposited on the Au films at 100 °C. The indium oxide films deposited on the Au films of I0 A. were mainly crystalline In203 with a trace of the amorphous form (Fig. l(c)), while those deposited on the Au films of 30 A were completely crystalline (Fig. l(d)). A trace of the amorphous phase was identifiable from faint diffuse lines in the diffraction patterns (Fig. l(c)). The films contained many crystallites which grew on Au particles. The number density of crystallites was greater in the films deposited on the thicker Au films. As seen in Figs. l(a) and l(b), the Au particles were much larger for the thicker sublayer, while coalescence reduced the number density. Thus, larger Au particles act more effectively as nucleation centers for the growth of crystallites, resulting in the crystallized films on the thicker Au sublayers. Figure 2 shows transmission electron micrographs and electron diffraction patterns for indium oxide films deposited at I00 °C on In or Ag films. The microstructres of the In and Ag sublayers were quite similar to those of the Au sublayers of the corresponding thicknesses, although the size of the particles and their number density were slightly dependent on the types of metal deposits. The results obtained for the indium oxide films deposited on the In films were very similar to those for the films deposited on the Au films (Figs. 2(a) and 2(b)). The films also grew in the crystallized form on the thicker In films with the aid of larger In particles. However, the films deposited on the Ag films were quasi-amorphous, regardless of the thickness of Ag deposits (Fig. 2(c)). The microstructure of the films, consisting of a major amorphous part and a small number of crystallites, was almost the same as that of
Elsevier Sequoia
2
Letter
(a)
(b)
(c)
(d)
~
' It m
Fig. 1. Electron micrographs and electron diffraction patterns of Au films and InzO 3 films: (a) 10 ]~ Au films, (b) 30 ~ Au films, (c) In203 films deposited on 10 ,~ Au films and (d) InzO 3 films deposited on 30 ,~ Au films.
the film deposited on SiO substrates [5]. Thus, Ag particles have little influence on the growth of films. Table 1 shows the values of the electrical resistivity of indium oxide films deposited at 100 °C. The films deposited on the Au or In films exhibited resistivities lower than those deposited on glass substrates (about 4.5 × 10 -3 f~cm) and on the Ag films. With the ira-
T A B L E 1. Electrical resistivity of I n , O 3 films deposited on Au, In and Ag sublayers of thickness 10 A or 30/~ Thickness of sublayer (,~,)
10 30
Resistivity ( ~ cm) Au sublayer
In sublayer
Ag sublayer
2.2 x 10 ~ 1.5 x 10 3
2.5 x 10 .3 2.0 x 10 3
4.2 x 10 ~ 4 . 0 x 10 3
provement in the crystallinity, the conductivity of the films was slightly increased. Figure 3 shows the optical transmission curves for the indium oxide films deposited at 100 °C. The transmission curve for the films deposited on the glass substrates is also included for comparison. The crystalline films deposited on both In films with 10/~ and 30 ,~ thickness exhibited a high transmittance of about 85%. Owing to light absorption by Au particles [7], the transmittance was slightly reduced for the films deposited on the 10,~ Au films and much reduced for those deposited on the Au films with thickness of 30 ,~. For the In sublayers, light absorption by the In particles gradually increased with decreasing wavelength below 450 nm. The films deposited on the Ag films showed lower transmittance because of the quasi-amorphous structure in addition to the effects of light absorption by Ag particles [7],
Letter
(a)
3
<
(b)
(c) Fig. 2. Electron micrographs and electron diffraction patterns of In203 films deposited on In and Ag films of different thicknesses: (a) In films with 10 ~ thickness, (b) In films with 30 ,~ thickness and (c) Ag films with 30 ,~ thickness. An arrow indicates a diffraction line from the Ag lattice.
1(30
i
[
I
I
0
8~ 0
,.- ............... / " "
....................
~40
.........................ebc
"
I
20 I
500
600
Wave[ength (nm) Fig. 3. Transmission spectra of 3000/k ln203 films deposited on various kinds of sublayers: curve a, 10 A In films; curve b, 30 A In films; curve c, 10 A Au films; curve d, 30 A Au films; curve e, 10/k Ag films; curve f, 30/k Ag films; curve g, glass substrates.
4
All the films deposited at room temperature were amorphous, regardless of the type of sublayer. The films displayed a high electrical resisivity (10 - 2 10-192 cm) and a low light transmittance (below 50%) because of their disordered structure. The conclusion is that films grow in a crystalline form on Au- and In-nucleated substrates at 100 °C, and in a quasi-amorphous form on Ag-nucleated substrates. With the improvement of the crystallinity of films, electrical resistivity decreases slightly and light transmittance increases substantially.
Acknowledgment The authors would like to thank Dr. Y. Oka for valuable discussions.
Letter
References I s. Noguchi and H. Sakata, J. Phys. D, 13 (1980) 1129. 2 Z. Ovandyahu, B. Ovryn and H. W. Kraner, J. Electroehem. Soc., 130 (1983) 917. 3 Z. Ovandyahu, J. Phys. C, 19 (1986) 5187. 4 I. Hamberg and C. G. Granqvist, J. Appl. Phys., 60 (1986) R213. 5 S. Muranaka, Y. Bando and T. Takada, Thin Solid Films, 151 (1987) 355. 6 T. Nagatomo, Y. M'urata and O. Omato, Thin Solid Fihns, 192 (1990) 17. 7 P. Rouard and G. Rasigni, Optica Acta. 14 (1967) 27.