Selective Area Deposition for Microelectronics
Introduction – A Novel Process
Work is underway at the LPICM to invent and study techniques to produce Area Selective Deposition (where a film grows on one type of surface but not on another). While this phenomenon is under investigation using Atomic Layer Deposition (ALD) and Chemical Vapor Deposition (CVD), we are investigating the use of Plasma Enhanced Chemical Vapour Deposition (PECVD) to selectively grow silicon thin films.
Experimental Demonstration of ASD by PECVD
The process we have developed and are investigating is the PECVD of silicon from a SiF4/H2/Ar gas mixture, which occurs selectively between SiOxNy and AlOx surfaces. A photo of the result of this process is shown in the figure below. The clear square at the bottom is an area of the substrate covered in AlOx, and no deposition occurs in this area. The rest of the substrate is covered in SiOxNy, and microcrystalline silicon grows normally in these areas.
Understanding the Phenomenon
The boundaries of the process window for this effect have been determined; for example, in-situ ellipsometry studies showed that deposition can be initiated on AlOx surfaces by increasing the temperature of the electrodes or increasing the RF plasma power, leading to a loss of selectivity). However, the physical origin of this phenomenon was not clear. Through a collaboration with the ILV group at UVSQ (Versailles), we have used X ray photoelectron spectroscopy (XPS) along with Scanning Transmission Electron Microscopy (STEM) to confirm that the Al-F bonds that exist in abundance on the AlOx surface block any deposition of silicon on it (under well-defined plasma conditions). This is shown in the figure below, which gives a map of the elements, showing the high concentration of fluorine at the AlOx surface (now known to be Al-F bonds).
Understanding the origin of the phenomenon will allow us to extend this process to other materials and surfaces. Our results have been published in the following journal articles:
- Ghewa Akiki, Daniel Suchet, Dmitri Daineka, Sergej Filonovich, Pavel Bulkin, and Erik V. Johnson, Area Selective Deposition of Silicon by Plasma Enhanced Chemical Vapor Deposition using a Fluorinated Precursor, Applied Surface Science 531 (2020) 147305. DOI: 10.1016/j.apsusc.2020.147305
- Ghewa Akiki, Mathieu Frégnaux, Ileana Florea, Pavel Bulkin, Dmitri Daineka, Sergej Filonovich, Muriel Bouttemy and Erik V. Johnson, Origin of Area Selective Plasma Enhanced Chemical Vapor Deposition of Microcrystalline Silicon, Vac. Sci. Technol. A 39 (2021) 013201, DOI: 10.1116/6.0000653