## 2 Experimental  
### Hardware  
Before describing the PECVD systems used to realize this work, we would like to first give some clarifications about the safety needed for using an F\({}_{2}\)-gas mixture with the existing hardware. The delivery lines of an F\({}_{2}\)-gas mixture (F\({}_{2}\)/Ar/N\({}_{2}\)) from the gas cylinder to the CVD chambers were modified; however, most parts of the already existing single-wall stainless steel lines could be reused. A dry N\({}_{2}\) gas flow insured the line purge for an easy change of the F\({}_{2}\) cylinder. In some papers [7], it is relevant to use double-wall stainless tubes for flowing pure F\({}_{2}\) gas, or a gas mixture containing more than 40% of F\({}_{2}\). For our study, as the F\({}_{2}\)-gas mixture has lower F\({}_{2}\) content, it was possible to flow it using the existing hardware facilities. Based on the long-term experiences of the Solvay Fluor GmbH in the field of F\({}_{2}\) and F\({}_{2}\)-gas mixtures, a passivation of the newly installed gas facilitation was performed [8]. It was important to slowly flow the F\({}_{2}\)-gas mixture in the gas delivery system. The formation of metal fluorides inside the stainless steel surface of the gas line (Fe, Cr, Ni) due to reactions of the stainless steel elements with fluorine atoms permits achieving a durable passivation. Thus, the gas lines are protected from any corrosion. Further safety precautions were taken into account by placing the gas cabinet, the gas delivery system, and the F\({}_{2}\) cylinder inside a closed cabinet with a safety exhaust. F\({}_{2}\) sensors installed in the safety exhaust of the gas cabinets near the system were connected to the safety valve at the F\({}_{2}\)-gas cylinder and automatized to cut off gas flow in case of F\({}_{2}\) detection. In this study, the test runs were realized in two different PECVD systems that were located in the clean room of the Fraunhofer EMFT. 200-mm Si substrates were used. Both PECVD chambers were evacuated down to approximately 40 mTorr using a dry pumping system. One of the PECVD systems was a lamp-heated parallel-plate PECVD reactor from Applied Materials. TEOS (Tetraethyl orthosilicate)-based SiO\({}_{2}\) films were deposited by applying 13.56 MHz RF power (radio frequency). The standard cleaning chemistry was C\({}_{2}\)F\({}_{6}\)/O\({}_{2}\) with a small amount of NF\({}_{3}\) addition in the second cleaning step. An additional F\({}_{2}\)/Ar/N\({}_{2}\) gas line was installed, connecting a new gas cabinet located outside the cleanroom with the PECVD reactor. The other PECVD chamber was made by the company Kobus, which is situated in France. The Aluminium Nitride (AlN) susceptor, which is a chuck for silicon wafers, has a resistive heating element filament to heat it to a desired chuck temperature. The standard cleaning process uses a mixture of C\({}_{2}\)F\({}_{6}\) and O\({}_{2}\) for chamber cleaning after oxide deposition. After polysilicon deposition, a NF\({}_{3}\) gas using a remote plasma source (RPS) unit was used as the chamber clean. The RPS running at 400 kHz (MKS; \"Paragon\", 6 kW RF power) was mounted on the top of the Alta-CVD reactor by Fraunhofer EMFT to allow chamber cleaning using the F\({}_{2}\)-gas mixture as well as the widely used NF\({}_{3}\) process. Therefore, the original gas mixing block was modified. The RPS sits directly above the top gas inlet of the chamber lid, whose hardware was adapted to shorten the distance between the RPS outlet and the chamber inlet in order to reduce the path of the generated F-radicals by some cm to reach the CVD chamber. It is worth mentioning that the same type of the gas mass flow controller (MFC) was used in both chambers for direct comparison and control of the total amount of F\({}_{2}\)-gas mixture flow. The gas mixture used for the RPS cleaning technique was 30% F\({}_{2}\)/Ar/N\({}_{2}\).