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Formation of indium-tin oxide (ITO) films by the dynamic mixing method
264
Formation of indium-tin mixing method
Nuclear Instruments
and Methods in Physics Research B59/60
(1991) 264-267 North-Holland
oxide (ITO) films by the dynamic
Y. Nakane a, H. Masuta b, Y. Honda b, F. Fujimoto b, T. Miyazaki ’ and S. Yano ’ aDepartment of General Education, Hokkaido Polytechnic College, Otaru, Hokkaido 047-02, Japan b Institute of Scientific and Industrial Research, Osaka University, Ibaraki, ’ Nitto Denko Corporation, Ibaraki, Osaka 567, Japan
Osaka 567, Japan
Indium-tin oxide (ITO) films are prepared on silica glass substrates by the dynamic mixing method, that is, indium and tin are simultaneously evaporated on the substrates and the oxygen ions with energies of 10, 2 and 0.6 keV are also simultaneously bombarded normal to the substrate surface. The film thickness is about 500 A and the substrate temperature is lower than 50 o C. Films formed with 10 keV ions have a preferred orientation of the [ill] axes of InrO, crystals which are normal to the film surface and the film with the deposition rates O/In = 3.2, and Sri/In = 0.19 has a transmittance of 96% and an electric resistivity of 7 X 10m3 52 cm. Films prepared with 0.6 keV ions and O/In = 2.1, Sri/In = 0.2 have a transmittance of 92% and a resistivity of 2.5 X 10m4 G cm. The film has a preferred orientation of the [llO] axes which are normal to the film surface. Films produced with 2 keV have no definite preferred orientation and have worse quality than those prepared with 10 and 0.6 keV.
1. Introduction Indium-tin oxide (ITO) films are well known for their low electric resist&y and high light transmittance and are frequently utilized as electrodes of liquid crystal, solar cells and in the field of optoelectronics [l-3]. The films are usually produced by the sputtering method; especially the magnetron sputtering method is powerful for rapid formation of films [4-61. However, it is difficult to produce high quality films on a substrate at low temperatures by these methods and to control the composition of films. Sometimes the films have to be annealed at high temperatures after the deposition. If the substrate is a polymer or semiconductor, preparation at low temperatures is necessary. One of the present authors (F.F.) and his collaborators have developed a method to prepare the coating film, the so-called dynamic mixing (or IVD) method, and formed various kinds of nitride films [7,8]. In this method, one element is evaporated on the substrate and the other (nitrogen in the nitride case) is simultaneously bombarded as ions. The energy of ions is 0.2-40 keV which is much lower than in the case of ion implantation. The dynamic mixing method has various advantages compared with other methods; (1) the adhesion between the film and the substrate is strong, (2) thick coating films can be produced, (3) the films can be prepared at low temperatures and (4) most of the films are crystallized and the crystal orientation varies with the preparation condition and the ion beam direction. Utilizing
Elsevier Science Publishers B.V. (North-Holland)
these advantages of the dynamic mixing method, the IT0 films are produced. In the present article, we will report the preparation conditions, the properties and the crystallization of the films.
2. Experiment A standard apparatus employing the dynamic mixing method was reported in a previous paper [9]. We modified the distance of electrodes in a rectangular bucket-type multi-aperture ion source with tungsten filaments, in order to change the working range of the ion energy from 2-40 to 0.6-M keV. The numerical ratio of atomic and molecular ions was considered to be about unity also in the case of nitrogen. The basic pressure of the preparation chamber was of the order of lo-’ Torr and the pressure during the operation was about 5 X lo-’ Tot-r. The ion beam current was changed from 50 to 100 PA/cm’, so that the temperature of the substrate made of silica glass was always kept below 50 o C. Indium and tin were simultaneously evaporated onto the substrate from individual evaporators and the oxygen ion beam also bombarded the substrate normal to its surface with energies (E,) of 10, 2 and 0.6 keV. The deposition rates of metals were measured by the corresponding thickness monitors. The deposition rate of oxygen was estimated by the current of the ion source, which might be overestimated because of the strong divergence of the ion beam. The film thickness was about 500 A.
265
Y. Nakane ef al. / Formation of IT0 fibs The structure of the films was studied by the B - 28 X-ray diffraction of Cu-Ka X-rays. The bonding states of indium, tin and oxygen were investigated by the X-ray photoelectron spectroscopy (XPS) of Mg-Ka X-rays. The composition of the films was calculated from the height ratio of each peak in the Auger electron spectra (AES) considering the atomic sensitive factor. The transmittance of light of wavelength 6000 A was measured by a spectrophotometer and the electric resistivity was obtained by the Van der Pauw method.
3. Results and discussions The relation between the deposition rate (O/In)dep the composition ratio from the Auger electron is shown in fig. 1. The amount spectra (AW, (O/In),,,, of oxygen was measured only by the signal from the oxygen peaks in the bound state and that of indium was decided by the total intensity of the peak, because the signals from indium metal and those bound with oxygen atoms could not be separated. The open and closed circles represent the values observed from the samples prepared with 10 and 0.6 keV ions, respectively. In the region (O/In),, < 2, the values of (O/In), increase linearly. This means that all oxygen atoms make bonding with the metal atoms and the excess metal atoms are included as metallic atoms. In the > 2, all indium atoms make In,O, and region (O/In),,, the extra oxygen atoms are included in the films in a free state. Figs. 2a-2c show the X-ray diffraction patterns of the films prepared under the following conditions: the energy of oxygen ions was 10 keV, the deposition rate and
l
1OkeV
0 6OOeV In
w2 ,4 c z
-______D#
0
1
___*-,-
03_-.--
.
.
0
0
I
1
I
,
1
2
3
4
( Olh)DEP Fig. 1. Relation between the deposition rate (O/In),, and the composition ratio obtained from the AES (O/In),. The amount of oxygen was measured only from the signal of the oxygen peaks at the bound state.
30
&I
50
Fig. 2. X-ray diffraction patterns of IT0 films: oxygen ion energy is 10 keV, Sri/In = 0.19 and O/In = 4.5 (a), 2.7 (b) and 1.5 (c).
Sri/In = 0.19 and the deposition rate O/In = 4.5, 2.7 and 1.5, respectively. The variations of the electric resistivities and the transmittances of light with the values of O/In are given in fig. 3. The X-ray diffraction patterns of figs. 2a and 2b show that the films consist of the In,O, crystallites only. The amorphous part comes from the silica glass substrates. The [ill] axes of In,O, crystals are preferentially oriented normal to the film surface, and especially the crystals in the films prepared with O/In = 4.5 are almost completely oriented. In films prepared under the condition of oxygen deficit, the diffraction peaks due to the metallic indium are dominantly observed as seen in fig. 2c. The result agrees with that of fig. 1. The transmittance of the films formed with O/In > 2.5 reaches up to 96% and then rapidly decreases with the decrease of the O/In value as seen in fig. 3. The resistivity has a peak with a maximum value of 3 x 10e2 a cm at O/In = 2.5. This peak was frequently observed not only in the present case but also in the films prepared by other methods and is considered to arise from the situation that the vacancies of the oxygen sites act as scatterers for carriers with the increase of vacancies, though the vacancies are the origin of carriers 151. III. ION-ENHANCED
DEPOSITION
Y. Nakane et al. / Formation of IT0 films
266 E.=lOkeV %/In: 0.19
loo
A
80
n f-’
10-3’
i
I
I
I
1
2
3
DEPOSITION
O/ln=Z.l
(4
A
I
4 RATE
( O/In
5
I
)
Fig. 3. Variations of the transmittance of light (6000 A) and the resistivity vs O/In for 500 A thick films: oxygen ion energy is 10 keV and Sri/In = 0.19.
Accordingly, the resistivity increases in the region of lower oxygen density than that of minimum resistivity. When the deposition rate increases, the resistivity decreases up to 7 x 10e3 D cm at O/In = 3.2 and then it increases. This increase arises from the excess oxygen atoms. The decreases of the transmittance and the resistivity in the region O/In < 2.5 are caused by the metallic indium in the films, as indicated by the X-ray diffraction analysis mentioned earlier. The same measurements as those shown in fig. 3 on the transmittance and resistivity were carried out on films prepared with Sri/In = 0.26. They show similar results, that is, the transmittance and resistivity in the region O/In < 2.5 rapidly decrease, the resistivity has a peak at O/In = 2.5, the minimum value of the resistivity in the region O/In > 2.5 is 9 X 10K3 Q cm and the transmittance in O/In > 2.5 is about 96%. Figs. 4a and 4b show the X-ray diffraction patterns of the films prepared with an ion energy E, of 0.6 keV, with O/In = 2.1 and 3.4, respectively, and Sri/In = 0.2 was fixed. In the case of O/In = 2.1, the preferred orientation of the films was almost completely along the [llO] axes normal to the substrate surface. With increasing O/In, the (400) and (222) reflection peaks appeared in the diffraction patterns and the preferred orientation of the films prepared with O/In = 3.4 was nearly along the [ill] axes normal to the substrate surface. Fig. 5 shows the corresponding electric resistivity and transmittance of light as a function of O/In. The resistivity of the films is lower than those with E,, = 10 and 2 keV. In particular the resistivity and the transmittance of the
I
I
30
40
I
f
50 29 (deg.)
Fig. 4. X-ray diffraction patterns from IT0 films: oxygen ion energy is 0.6 keV, %/In = 0.2 and O/In = 2.1 (a) and 3.4 (b).
film prepared with O/In = 2.1 were 2.5 X 10e4 CI cm and 92%, respectively. The diffraction patterns from IT0 films produced by 2 keV oxygen ions with O/In = 3.4 and Sri/In = 0.28 were also measured. In these patterns, the broad (440)
I
I L= 600eV Sn/In=O.Z
s -
100 ;
Y 2 - 80
6 Z z
-
60
LO
- 20
lb46 0
0
1 2 DEPOSITION
RATE
3 (01 In )
4
Fig. 5. Variations of the transmittance of light (6000 A) and the resistivity vs O/In for 500 A thick films: oxygen ion energy is 0.6 keV and Sri/In = 0.2.
261
Y. Nakane et al. / Formation of IT0 films
DEPOSITION
RATE
(Srdln
)
Fig. 6. Variations of the transmittance of light (6000 A) and the resistivity vs Sri/In for 500 A thick films: oxygen ion energy is 10 keV and O/In = 2.7.
reflection from In,O, could be observed but the intensity was low. Moreover the broad and small peaks of the (222) and (400) reflections could be seen. This means that the films consist of small polycrystallites oriented almost randomly. The transmittances and the minimum resistivities of films in this case were 85-90% and 1.5 X lo-’ D cm respectively, in the region O/In > 3.4. Both values are worse than those in the case of films manufactured with 10 and 0.6 keV ion beam. The reason is that the films consist of small crystallites and the crystal growth is not good. Fig. 6 shows the results of the transmittance and resistivity of films produced with a fixed deposition rate O/In of 2.7 and for various values of Sri/In. The best condition can be obtained at Sri/In = 0.3 and the values of the transmittance and resistivity are 95% and 5 X 1O-3 Q cm, respectively.
4. Conclusion IT0 films were prepared on silica glass substrates by means of the dynamic mixing method. In films prepared with the deposition rate O/In > 2.0, indium and tin make bonding with oxygen and iridium atoms to form
InzO, crystallites. The excess oxygen atoms existed in a free state in the films. In films formed with O/In < 2.0, excess indium atoms existed in the metallic state. Films formed with 10 keV ions had a preferred orientation of the [ill] axes of In,O, crystals which were normal to the film surface, and especially those with excess oxygen consisted of almost completely oriented In,O, crystallites. In the region O/In > 2.5 and Sri/In = 0.19, the transmittance was 96% and the minimum value of the resistivity was 7 x 10T3 Q cm for O/In = 3.2. In the region O/In c 2.5, the transmittance and resistivity rapidly decreased because of the existence of metallic indium and tin in the films. The resistivity has a peak at O/In = 2.5. This peak often appears regardless of the ion energy. The film prepared with 0.6 keV oxygen ions and O/In = 2.1 and Sri/In = 0.2 had a minimum resistivity of 2.5 X 10T4 0 cm and a transmittance of 92%. In this film the diffraction pattern measured by the B - 28 method showed the (440) reflection peak. This result represents that the quality of the IT0 films oriented with the [llO] axes parallel to the surface normal is better than those with the [ill] axes. At 2 keV, the films were not well oriented. The quality was worse than those formed at 10 and 0.6 keV. The production of the IT0 films with 2 keV was in the transient situation from the [llO] axial orientation to the [ill] one. Therefore the crystal growth and the quality were not good.
References [l] A.L. Dawar and J.C. Joshi, J. Mater. Sci. 19 (1984) 1. [2] K.L. Chopra, S. Major and D.K. Panda, Thin Solid Films 102 (1983) 1. [3] C.M. Lampert, Solar Energy Mater. 6 (1981) 1. [4] K. Itoyama, Jpn. J. Appl. Phys. 17 (1978) 1191. [5] M. Buchanan, J.B. Webb and D.F. Williams, Appl. Phys. Lett. 37 (1980) 213. [6] S. Ray, R. Banerjee, N. Basu, A.K. Batabyal and A.K. Barua, J. Appl. Phys. 54 (1983) 3497. [7] M. Satou, F. Fukui and F. Fujimoto, Proc. Int. Workshop by Professional Groups on Ion-based Techniques for Film Formation (Ionies Corp., Ltd., Tokyo, 1981) p. 349. [8] F. Fujimoto, Vacuum 39 (1989) 361. [9] Y. Andoh, Y. Suzuki, K. Matsuda, M. Satou and F. Fujimoto, Nucl. Instr. and Meth. B6 (1985) 111.
III. ION-ENHANCED
DEPOSITION
Formation of indium-tin mixing method
Nuclear Instruments
and Methods in Physics Research B59/60
(1991) 264-267 North-Holland
oxide (ITO) films by the dynamic
Y. Nakane a, H. Masuta b, Y. Honda b, F. Fujimoto b, T. Miyazaki ’ and S. Yano ’ aDepartment of General Education, Hokkaido Polytechnic College, Otaru, Hokkaido 047-02, Japan b Institute of Scientific and Industrial Research, Osaka University, Ibaraki, ’ Nitto Denko Corporation, Ibaraki, Osaka 567, Japan
Osaka 567, Japan
Indium-tin oxide (ITO) films are prepared on silica glass substrates by the dynamic mixing method, that is, indium and tin are simultaneously evaporated on the substrates and the oxygen ions with energies of 10, 2 and 0.6 keV are also simultaneously bombarded normal to the substrate surface. The film thickness is about 500 A and the substrate temperature is lower than 50 o C. Films formed with 10 keV ions have a preferred orientation of the [ill] axes of InrO, crystals which are normal to the film surface and the film with the deposition rates O/In = 3.2, and Sri/In = 0.19 has a transmittance of 96% and an electric resistivity of 7 X 10m3 52 cm. Films prepared with 0.6 keV ions and O/In = 2.1, Sri/In = 0.2 have a transmittance of 92% and a resistivity of 2.5 X 10m4 G cm. The film has a preferred orientation of the [llO] axes which are normal to the film surface. Films produced with 2 keV have no definite preferred orientation and have worse quality than those prepared with 10 and 0.6 keV.
1. Introduction Indium-tin oxide (ITO) films are well known for their low electric resist&y and high light transmittance and are frequently utilized as electrodes of liquid crystal, solar cells and in the field of optoelectronics [l-3]. The films are usually produced by the sputtering method; especially the magnetron sputtering method is powerful for rapid formation of films [4-61. However, it is difficult to produce high quality films on a substrate at low temperatures by these methods and to control the composition of films. Sometimes the films have to be annealed at high temperatures after the deposition. If the substrate is a polymer or semiconductor, preparation at low temperatures is necessary. One of the present authors (F.F.) and his collaborators have developed a method to prepare the coating film, the so-called dynamic mixing (or IVD) method, and formed various kinds of nitride films [7,8]. In this method, one element is evaporated on the substrate and the other (nitrogen in the nitride case) is simultaneously bombarded as ions. The energy of ions is 0.2-40 keV which is much lower than in the case of ion implantation. The dynamic mixing method has various advantages compared with other methods; (1) the adhesion between the film and the substrate is strong, (2) thick coating films can be produced, (3) the films can be prepared at low temperatures and (4) most of the films are crystallized and the crystal orientation varies with the preparation condition and the ion beam direction. Utilizing
Elsevier Science Publishers B.V. (North-Holland)
these advantages of the dynamic mixing method, the IT0 films are produced. In the present article, we will report the preparation conditions, the properties and the crystallization of the films.
2. Experiment A standard apparatus employing the dynamic mixing method was reported in a previous paper [9]. We modified the distance of electrodes in a rectangular bucket-type multi-aperture ion source with tungsten filaments, in order to change the working range of the ion energy from 2-40 to 0.6-M keV. The numerical ratio of atomic and molecular ions was considered to be about unity also in the case of nitrogen. The basic pressure of the preparation chamber was of the order of lo-’ Torr and the pressure during the operation was about 5 X lo-’ Tot-r. The ion beam current was changed from 50 to 100 PA/cm’, so that the temperature of the substrate made of silica glass was always kept below 50 o C. Indium and tin were simultaneously evaporated onto the substrate from individual evaporators and the oxygen ion beam also bombarded the substrate normal to its surface with energies (E,) of 10, 2 and 0.6 keV. The deposition rates of metals were measured by the corresponding thickness monitors. The deposition rate of oxygen was estimated by the current of the ion source, which might be overestimated because of the strong divergence of the ion beam. The film thickness was about 500 A.
265
Y. Nakane ef al. / Formation of IT0 fibs The structure of the films was studied by the B - 28 X-ray diffraction of Cu-Ka X-rays. The bonding states of indium, tin and oxygen were investigated by the X-ray photoelectron spectroscopy (XPS) of Mg-Ka X-rays. The composition of the films was calculated from the height ratio of each peak in the Auger electron spectra (AES) considering the atomic sensitive factor. The transmittance of light of wavelength 6000 A was measured by a spectrophotometer and the electric resistivity was obtained by the Van der Pauw method.
3. Results and discussions The relation between the deposition rate (O/In)dep the composition ratio from the Auger electron is shown in fig. 1. The amount spectra (AW, (O/In),,,, of oxygen was measured only by the signal from the oxygen peaks in the bound state and that of indium was decided by the total intensity of the peak, because the signals from indium metal and those bound with oxygen atoms could not be separated. The open and closed circles represent the values observed from the samples prepared with 10 and 0.6 keV ions, respectively. In the region (O/In),, < 2, the values of (O/In), increase linearly. This means that all oxygen atoms make bonding with the metal atoms and the excess metal atoms are included as metallic atoms. In the > 2, all indium atoms make In,O, and region (O/In),,, the extra oxygen atoms are included in the films in a free state. Figs. 2a-2c show the X-ray diffraction patterns of the films prepared under the following conditions: the energy of oxygen ions was 10 keV, the deposition rate and
l
1OkeV
0 6OOeV In
w2 ,4 c z
-______D#
0
1
___*-,-
03_-.--
.
.
0
0
I
1
I
,
1
2
3
4
( Olh)DEP Fig. 1. Relation between the deposition rate (O/In),, and the composition ratio obtained from the AES (O/In),. The amount of oxygen was measured only from the signal of the oxygen peaks at the bound state.
30
&I
50
Fig. 2. X-ray diffraction patterns of IT0 films: oxygen ion energy is 10 keV, Sri/In = 0.19 and O/In = 4.5 (a), 2.7 (b) and 1.5 (c).
Sri/In = 0.19 and the deposition rate O/In = 4.5, 2.7 and 1.5, respectively. The variations of the electric resistivities and the transmittances of light with the values of O/In are given in fig. 3. The X-ray diffraction patterns of figs. 2a and 2b show that the films consist of the In,O, crystallites only. The amorphous part comes from the silica glass substrates. The [ill] axes of In,O, crystals are preferentially oriented normal to the film surface, and especially the crystals in the films prepared with O/In = 4.5 are almost completely oriented. In films prepared under the condition of oxygen deficit, the diffraction peaks due to the metallic indium are dominantly observed as seen in fig. 2c. The result agrees with that of fig. 1. The transmittance of the films formed with O/In > 2.5 reaches up to 96% and then rapidly decreases with the decrease of the O/In value as seen in fig. 3. The resistivity has a peak with a maximum value of 3 x 10e2 a cm at O/In = 2.5. This peak was frequently observed not only in the present case but also in the films prepared by other methods and is considered to arise from the situation that the vacancies of the oxygen sites act as scatterers for carriers with the increase of vacancies, though the vacancies are the origin of carriers 151. III. ION-ENHANCED
DEPOSITION
Y. Nakane et al. / Formation of IT0 films
266 E.=lOkeV %/In: 0.19
loo
A
80
n f-’
10-3’
i
I
I
I
1
2
3
DEPOSITION
O/ln=Z.l
(4
A
I
4 RATE
( O/In
5
I
)
Fig. 3. Variations of the transmittance of light (6000 A) and the resistivity vs O/In for 500 A thick films: oxygen ion energy is 10 keV and Sri/In = 0.19.
Accordingly, the resistivity increases in the region of lower oxygen density than that of minimum resistivity. When the deposition rate increases, the resistivity decreases up to 7 x 10e3 D cm at O/In = 3.2 and then it increases. This increase arises from the excess oxygen atoms. The decreases of the transmittance and the resistivity in the region O/In < 2.5 are caused by the metallic indium in the films, as indicated by the X-ray diffraction analysis mentioned earlier. The same measurements as those shown in fig. 3 on the transmittance and resistivity were carried out on films prepared with Sri/In = 0.26. They show similar results, that is, the transmittance and resistivity in the region O/In < 2.5 rapidly decrease, the resistivity has a peak at O/In = 2.5, the minimum value of the resistivity in the region O/In > 2.5 is 9 X 10K3 Q cm and the transmittance in O/In > 2.5 is about 96%. Figs. 4a and 4b show the X-ray diffraction patterns of the films prepared with an ion energy E, of 0.6 keV, with O/In = 2.1 and 3.4, respectively, and Sri/In = 0.2 was fixed. In the case of O/In = 2.1, the preferred orientation of the films was almost completely along the [llO] axes normal to the substrate surface. With increasing O/In, the (400) and (222) reflection peaks appeared in the diffraction patterns and the preferred orientation of the films prepared with O/In = 3.4 was nearly along the [ill] axes normal to the substrate surface. Fig. 5 shows the corresponding electric resistivity and transmittance of light as a function of O/In. The resistivity of the films is lower than those with E,, = 10 and 2 keV. In particular the resistivity and the transmittance of the
I
I
30
40
I
f
50 29 (deg.)
Fig. 4. X-ray diffraction patterns from IT0 films: oxygen ion energy is 0.6 keV, %/In = 0.2 and O/In = 2.1 (a) and 3.4 (b).
film prepared with O/In = 2.1 were 2.5 X 10e4 CI cm and 92%, respectively. The diffraction patterns from IT0 films produced by 2 keV oxygen ions with O/In = 3.4 and Sri/In = 0.28 were also measured. In these patterns, the broad (440)
I
I L= 600eV Sn/In=O.Z
s -
100 ;
Y 2 - 80
6 Z z
-
60
LO
- 20
lb46 0
0
1 2 DEPOSITION
RATE
3 (01 In )
4
Fig. 5. Variations of the transmittance of light (6000 A) and the resistivity vs O/In for 500 A thick films: oxygen ion energy is 0.6 keV and Sri/In = 0.2.
261
Y. Nakane et al. / Formation of IT0 films
DEPOSITION
RATE
(Srdln
)
Fig. 6. Variations of the transmittance of light (6000 A) and the resistivity vs Sri/In for 500 A thick films: oxygen ion energy is 10 keV and O/In = 2.7.
reflection from In,O, could be observed but the intensity was low. Moreover the broad and small peaks of the (222) and (400) reflections could be seen. This means that the films consist of small polycrystallites oriented almost randomly. The transmittances and the minimum resistivities of films in this case were 85-90% and 1.5 X lo-’ D cm respectively, in the region O/In > 3.4. Both values are worse than those in the case of films manufactured with 10 and 0.6 keV ion beam. The reason is that the films consist of small crystallites and the crystal growth is not good. Fig. 6 shows the results of the transmittance and resistivity of films produced with a fixed deposition rate O/In of 2.7 and for various values of Sri/In. The best condition can be obtained at Sri/In = 0.3 and the values of the transmittance and resistivity are 95% and 5 X 1O-3 Q cm, respectively.
4. Conclusion IT0 films were prepared on silica glass substrates by means of the dynamic mixing method. In films prepared with the deposition rate O/In > 2.0, indium and tin make bonding with oxygen and iridium atoms to form
InzO, crystallites. The excess oxygen atoms existed in a free state in the films. In films formed with O/In < 2.0, excess indium atoms existed in the metallic state. Films formed with 10 keV ions had a preferred orientation of the [ill] axes of In,O, crystals which were normal to the film surface, and especially those with excess oxygen consisted of almost completely oriented In,O, crystallites. In the region O/In > 2.5 and Sri/In = 0.19, the transmittance was 96% and the minimum value of the resistivity was 7 x 10T3 Q cm for O/In = 3.2. In the region O/In c 2.5, the transmittance and resistivity rapidly decreased because of the existence of metallic indium and tin in the films. The resistivity has a peak at O/In = 2.5. This peak often appears regardless of the ion energy. The film prepared with 0.6 keV oxygen ions and O/In = 2.1 and Sri/In = 0.2 had a minimum resistivity of 2.5 X 10T4 0 cm and a transmittance of 92%. In this film the diffraction pattern measured by the B - 28 method showed the (440) reflection peak. This result represents that the quality of the IT0 films oriented with the [llO] axes parallel to the surface normal is better than those with the [ill] axes. At 2 keV, the films were not well oriented. The quality was worse than those formed at 10 and 0.6 keV. The production of the IT0 films with 2 keV was in the transient situation from the [llO] axial orientation to the [ill] one. Therefore the crystal growth and the quality were not good.
References [l] A.L. Dawar and J.C. Joshi, J. Mater. Sci. 19 (1984) 1. [2] K.L. Chopra, S. Major and D.K. Panda, Thin Solid Films 102 (1983) 1. [3] C.M. Lampert, Solar Energy Mater. 6 (1981) 1. [4] K. Itoyama, Jpn. J. Appl. Phys. 17 (1978) 1191. [5] M. Buchanan, J.B. Webb and D.F. Williams, Appl. Phys. Lett. 37 (1980) 213. [6] S. Ray, R. Banerjee, N. Basu, A.K. Batabyal and A.K. Barua, J. Appl. Phys. 54 (1983) 3497. [7] M. Satou, F. Fukui and F. Fujimoto, Proc. Int. Workshop by Professional Groups on Ion-based Techniques for Film Formation (Ionies Corp., Ltd., Tokyo, 1981) p. 349. [8] F. Fujimoto, Vacuum 39 (1989) 361. [9] Y. Andoh, Y. Suzuki, K. Matsuda, M. Satou and F. Fujimoto, Nucl. Instr. and Meth. B6 (1985) 111.
III. ION-ENHANCED
DEPOSITION