Gas-based backside protection during substrate processing

A method of protecting the backside of a substrate disposed in a process chamber during processing, comprising the steps of:

• applying a vacuum to a backside region of the substrate through a platen to restrain the wafer on the platen;
• introducing a process gas comprising a mixture of a first reactant gas and a carrier gas into the process chamber;
• introducing a backside gas comprising a mixture of a second reactant gas and an inert gas to a periphery of the substrate backside;
• and
• maintaining a positive pressure differential between backside gas pressure at the periphery of the substrate backside and process gas pressure in the process chamber.

A method of protecting the backside of a substrate disposed in a process chamber during processing, the substrate having a frontside to be processed and a backside, comprising the steps of:

• applying a vacuum to a region of the substrate backside through a platen to restrain the wafer on the platen,
• introducing a process gas into the process chamber to establish a process gas pressure therein;
• and
• introducing a backside gas into a peripheral space defined by a surface of the platen and the periphery of the substrate backside, the backside gas being a different gas than the process gas and being introduced at a pressure in excess of the process gas pressure so that the backside gas vents from the peripheral region into the process chamber to exclude the process gas from contact with the backside periphery of the substrate.