Time varying segmented pressure control

An apparatus for processing a substrate, comprising

• a processing chamber;
• a substrate support for supporting the substrate within the processing chamber;
• a gas inlet for providing gas into the processing chamber;
• an exhaust pressure system, which exhausts gas around a periphery of the substrate, wherein the periphery around the substrate is divided into at least three parts, wherein the exhaust pressure system controls exhaust pressure to control a velocity of the gas over the substrate, wherein the exhaust pressure system provides an independent exhaust pressure control for each part of the periphery for the at least three parts, wherein the exhaust pressure system comprises:
• a plurality of exhaust ports spaced around the periphery of the substrate;
• a segmented pressure ring formed by at least three segments, wherein the segmented pressure ring is placed adjacent to the plurality of exhaust ports around the periphery of the substrate;
• and
• a drive system, wherein the drive system is able to independently move each segment to allow a segment to be in a closed position while another segment is in an open position;
• and
• an exhaust pressure controller controllably connected to the drive system for azimuthally, cyclically, and sequentially changing the pressure for each part, wherein the exhaust pressure controller comprises non-transient computer readable media, comprising computer readable code for controlling the drive system to cyclically and sequentially move each segment of the at least three segments to provide an azimuthally rotating venting.