Gas supply line arrangements for inhibiting particle contamination in substrate processing

In some examples, a gas supply line arrangement is provided for inhibiting particle contamination in a substrate process chamber. An example gas supply line arrangement comprises a cleaning gas source for a clean cycle of the substrate process chamber, a purge gas source for a purge cycle of the substrate process chamber, and a gas supply line to carry cleaning gas and purge gas towards the substrate process chamber. A three-port valve in the gas supply line arrangement comprises a valve inlet connected to the gas supply line, a first valve outlet in fluid communication with the substrate process chamber, the first valve outlet operable to admit or prevent a passage of cleaning gas to the substrate process chamber, and a second valve outlet connected to a divert line and operable to admit or prevent a passage of particle-containing purge gas to the divert line.