Paper TF+SS-WeM3
Amorphous In₂O₃ and Sn-doped In₂O₃ Layers by ALD Prepared using Trimethyl Indium and Ozone

Wednesday, October 21, 2015, 8:40 am, Room 114

Abstract:

Among the transparent conducting oxides (TCOs), Indium oxide (In₂O₃) possesses a wide band gap of 2.9 Ev at room temperature yielding high optical transparency and also exhibits good chemical stability. When doped with tin to form Indium tin oxide ( ITO ), the electrical conductivity increases greatly allowing this material to be used in a wide range of applications including touch screens displays, light-emitting diodes, liquid crystal displays, and sensors. Further amorphous TCOs have several advantages over their crystalline microstructures e.g. lower temperatures deposition which tend to simplify the deposition methods for mainly for plastics for flexible electronics. The lack of grain boundaries in amorphous materials, isotropic nature allows a simpler scheme for uniform etching with lower surface roughness. Unlike crystalline TCOs, the amorphous TCOs electrical and optical are also strongly influenced by the oxygen content of the films. As ALD offers the potential to deposit ITO over large areas at low temperature with high uniformity to address some of these applications, but the viability of this method hinges on developing a robust In₂O₃ ALD process. Trimethyl indium (TMIn) is an attractive economical precursor for In₂O₃ ALD because it offers the advantages of a high vapor pressure and availability in high volume.

In this study we examined the ALD of In₂O₃ using alternating exposures to TMIn and different oxygen sources: O₃ (ozone), O₂, H₂O, and H₂O₂. We first used in situ quartz crystal microbalance (QCM) and mass spectrometry measurements to evaluate the effectiveness of the different oxygen sources and found that only ozone yielded sustained growth. These measurements also provided details about the In₂O₃ growth mechanism and enabled us to verify that both the TMIn and the O₃ surface reactions were self-limiting. Next, we prepared ALD In₂O₃ films on a variety of substrates and characterized them using X-ray diffraction, UV-vis. Spectrometry, spectroscopic ellipsometry, X-ray photoelectron spectroscopy, Hall probe measurements, scanning electron microscopy, and atomic force microscopy. We found that at deposition temperatures of 100-200^oC the amorphous growth per cycle was nearly constant at ~0.4 Å/cycle and the films were dense and pure. At higher growth temperatures the In₂O₃ growth rate increased due to thermal decomposition of the TMIn. We succeeded in doping the amorphous In₂O₃ films with tin by substituting tetrakis-(dimethylamino) tin for the TMIn in a fraction of the growth cycles and observed that the electrical conductivity improved substantially in these films.