AVS 65th International Symposium & Exhibition
    Thin Films Division Thursday Sessions
       Session TF+AS+EL+EM+NS+PS+SS-ThA

Paper TF+AS+EL+EM+NS+PS+SS-ThA4
Investigation of Low Temperature ALD-deposited SnO2 Films Stability in a Microfabrication Environment

Thursday, October 25, 2018, 3:20 pm, Room 104B

Session: IoT Session: Thin Films for Flexible Electronics and IoT
Presenter: Tony Maindron, CEA/LETI-University Grenoble Alpes, France
Authors: T. Maindron, CEA/LETI-University Grenoble Alpes, France
S.M. Sandrez, CEA/LETI-University Grenoble Alpes, France
N.V. Vaxelaire, CEA/LETI-University Grenoble Alpes, France
Correspondent: Click to Email
For applications such as displays (LCD, OLED) or solar cells, it is mandatory to use Transparent Conductive Oxides (TCOs) so as to allow light to extract out of the circuit or for light harvesting, respectively. In display technology, TCOs are also studied so as to replace the silicon technology developed to make the semiconducting channel in thin-film transistors. The mainstream TCO today is indium tin oxide (ITO), (90% indium oxide and 10% tin oxide). It has the advantage of having a high conductivity and a low surface resistivity, of the order of 10 ohm/square, while having a transmittance greater than 85% over the entire visible spectrum. However, it has several drawbacks, including the scarcity of indium and the high cost associated to its extraction process, which has prompted the scientific community to look for alternative TCOs. Among all TCOs, ZnO has been widely studied as a low cost single-metal oxide alternative material to ITO, as well as its multi-metal oxide derivatives using a dedicated metal dopant to control its electrical conductivity, as for instance with Al (ZnO:Al or AZO). One issue however with ZnO films lays in their relative chemical stability to water. It has been shown that films of ZnO or AZO change their physical properties when exposed to moisture: electrical conductivity decreases, roughness can increase, and optical characteristics are modified. By extension, when ZnO-based TCOs have to be finely patterned by photolithography, their high sensitivity to water-based solutions can be a severe issue. In our laboratory, we have noticed that ZnO and AZO films made by ALD at 150 °C typically are not stable in a microfabrication process: a large decrease (~ 20 %) of AZO thickness after the development step of photoresists used to pattern the TCO film has been noticed. One way to stabilize ZnO-based compounds is to anneal the films at high temperatures. However for some dedicated applications that use fragile substrates (plastic films for flexible organic electronics for instance), such post annealing processes at high temperature (typ. > 150 °C) cannot be applied. An alternative is to explore alternative materials to AZO: we found out that SnO2 ALD (150 °C) shows very promising features regarding the stability under a microfabrication environment, while having good electrical and optical characteristics.