Step coverage study of indium-tin-oxide thin films by spray CVD on non-flat substrates at different temperatures
Introduction
Indium-tin-oxide (ITO; tin-doped In2O3) transparent conducting films are widely used for flat panel displays, transparent heaters, and infrared shielding of buildings and automobiles. Commercially produced ITO films are generally deposited by physical vapor deposition (PVD) processes, such as sputtering. Recently, however, ITO films have been successfully deposited by spray chemical vapor deposition (CVD) at a deposition temperature of 350 °C using an ethanol solution of indium (III) chloride and tin (II) chloride [1], [2], [3]. The advantages of this method are that it is simple, inexpensive, and can be done in air. The lowest resistivity of the as-deposited films (1.7 × 10− 4 Ω cm) was compatible to those deposited using a sputtering process [4], [5], [6], [7], [8]. In the previous paper [2], the films were annealed in a reducing atmosphere (N2–0.2%H2; gas flow rate, 300 ml/min) at 600 °C for 120 min. The minimum resistivity (7.7 × 10− 5 Ω cm) was the lowest among the films fabricated by a chemical process.
Deposition on submicron patterned substrates is indispensable for applications involving high density devices with three-dimensional structures. Generally, conformal deposition of patterned substrates is relatively easy with the CVD process, though it is difficult with PVD [9]. Deposition on submicron patterned substrates of metallic films [10], [11], [12], [13], oxide films [14], [15], [16], and ferroelectric films [17] by CVD process has been reported. A previously reported case of deposition of transparent conducting films on patterned substrates was actually aluminum-doped zinc oxide (AZO) film using the sputtering method [18], and this process has not been reported for ITO films. Furthermore, the report of this AZO film did not describe the step coverage and the opening size. In the present study, ITO films were deposited on submicron patterned substrates by spray CVD.
Section snippets
Experimental
Indium (III) chloride, InCl3 3.42H2O (purity, 99.99%) and tin (II) chloride, SnCl2 1.41H2O (purity, 99.9%) were dissolved in ethanol (purity, 99.5%) and stirred for 12 h or more. The concentration of the total metal ions in the solution was fixed at approximately 0.1 mol/l. The solutions were prepared with 7 at.% Sn. The solution was sprayed manually in air with an inexpensive atomizer used for cosmetic purposes. It was already reported that the average size of the drops prepared a similar
Deposition on the non-flat Si substrates at 300–350 °C
The X-ray diffraction spectra of all films corresponded to the peak of In2O3 powders (cubic bixbyite structure [19]). The (400) peak became stronger as the film thickness increased.
Fig. 1 shows cross-sectional FE-SEM images of ITO films with a different number of sprays deposited on non-flat Si substrates with an opening size of 1 μm. The ITO films sprayed 50 times already covered all surface areas including the top surface, side walls, and bottom, as shown in Fig. 1-a. The film thickness
Conclusion
An ethanol solution of indium (III) chloride and tin (II) chloride was sprayed onto non-flat Si substrates heated at 300–350 °C. The ITO films were sprayed onto the non-flat Si substrates with 1-μm openings, providing 93% step coverage. The opening size became smaller and smaller as the number of sprays increased, thus resulting in lower step coverage. Moreover, the ITO films could not be deposited in the grooves when the opening size was less than 0.18 μm. Step coverage can be improved by
Acknowledgments
The authors thank Prof. Y. Shirai of our Institute for the use of X-ray fluorescence analyzer and the Ministry of Education, Culture, Sports, Science and Technology (MEXT) for financial support of “High-Tech Research Center” Project (2005–2009).
References (19)
- et al.
Thin Solid Films
(2002) - et al.
Sol. Energy Mater. Sol. Cells
(2004) - et al.
J. Non-Cryst. Solids
(1997) - et al.
Thin Solid Films
(2003) Mat. Sci. Forum
(2003)- et al.
J. Appl. Phys.
(1992) - et al.
J. Electrochem. Soc.
(1993) - et al.
Appl. Phys. Lett.
(1977) - et al.
J. Appl. Phys.
(1983)
Cited by (24)
Growth of Al:ZnO nano-flowers by pulsed laser ablation deposition
2024, Optics and Laser TechnologyDeposition of high-transmittance ITO thin films on polycarbonate substrates for capacitive-touch applications
2021, VacuumCitation Excerpt :In addition, some of the TCO thin films are widely used as transparent conducting elements for addressing various alphanumeric displays. ITO thin films can be prepared via several methods, such as the sol-gel technique [4,19], pulsed laser deposition (PLD) [2,20], pulsed DC sputtering [10–12], radio frequency (RF) sputtering [12,16,21], RF-superimposed DC magnetron sputtering [22], spray chemical vapor deposition [23], laser sintering [24], and vacuum evaporation [25]. Among these deposition techniques, sputtering is the most widely adopted due to its high deposition rate, good reproducibility, and capability of large-area deposition [10–12,16,21].
High-throughput optimization of near-infrared-transparent Mo-doped In<inf>2</inf>O<inf>3</inf> thin films with high conductivity by combined use of atmospheric-pressure mist chemical-vapor deposition and sputtering
2017, Thin Solid FilmsCitation Excerpt :A typical scanning electron microscope (SEM) image at 30,000 × magnification of the surface of an IMO film is displayed in Fig. 3. Such surface morphology is commonly seen in In2O3-based polycrystalline films deposited by similar techniques, including spray CVD [22,50] and aerosol-assisted CVD [19]. As shown in this figure, the IMO films obtained in this study were composed of crystalline grains with diameters of approximately 100 nm, and they were densely and uniformly packed together.
Slot-die coating of organic thin films for active-matrix organic light-emitting diode displays
2016, Thin Solid FilmsCitation Excerpt :For more systematic analysis, we have also calculated the film conformity, defined as T2/T1 (≤ 1) in Fig. 3. It is well known that vacuum deposition (e.g., physical or chemical vapor deposition) provides thin films with larger thickness on the sidewalls near the top corner of a trench [21]. On the contrary, those films fabricated by solution coating show larger thickness on the sidewalls near the bottom corner of a bank.
SF<inf>6</inf>/Ar plasma textured periodic glass surface morphologies with high transmittance and haze ratio of ITO:Zr films for amorphous silicon thin film solar cells
2015, VacuumCitation Excerpt :The Hall mobility was shown as 27.06 cm2/V·s for the as-deposited ITO:Zr/AZO films, while Hall mobility increased from 15.66 to 27.09 cm2/V·s with the increase of glass etching time from 30 to 75 min. From the sheet resistance and electrical properties of ITO:Zr/AZO films, we can conclude that minor variation in the electrical properties was observed, due to the various step coverages [12,29,30]. Our textured glass ITO:Zr films showed the higher haze ratio, compared to the conventional FTO glass.