In a method of forming a layer, a substrate is loaded into a chamber and placed at a home position that is a first relative angular position. A process cycle is performed a number of times while the substrate is at the home position. The cycle includes directing source gas onto the substrate at a first location adjacent the periphery of the substrate, purging the chamber, directing reaction gas onto the substrate from the first location, and purging the chamber. The cycle is performed another number of times while the substrate is at another relative angular position, i.e., at a position rotated about its general center relative from the home position.