Recipe design to prevent tungsten (W) coating on wafer backside for those wafers with poly Si on wafer backside

A method of chemical vapor deposition, vapor purging and pressure equalization in a vacuum chamber for depositing a layer of a refractory material on the frontside of a wafer made of semiconductor material without depositing residual refractory materials onto the wafer backside which comprises:

• providing a wafer chucking means in the vacuum chamber, a wafer chucking pressure control means, a source of an inert gas, a source of deposition gases, a source of purge gases, a chamber pressure control means, a pressure equalization means;
• placing the wafer backside on the wafer chucking means;
• maintaining a first chucking pressure by the wafer chucking pressure control means, flowing the inert gas to the backside of the wafer via the wafer chucking means;
• maintaining a first chamber pressure by the chamber pressure control means, the first chamber pressure being higher than the first chucking pressure;
• introducing a source of deposition gases into the chamber for the purpose of depositing a layer of refractory material on the frontside of the wafer;
• after depositing the layer of refractory material, purging the chamber of residual deposition gases by introducing the purge gases into the chamber;
• maintaining a second chamber pressure and a second chucking pressure respectively by the chamber pressure and the chucking pressure control means;
• after purging the chamber of residual gases, equalizing the pressure between the chamber and the wafer backside by engaging the pressure equalization means;
• and
• maintaining a third chamber pressure by the chamber pressure control means.