The present disclosure relates to a semiconductor processing apparatus having a reaction chamber which can include a baseplate having an opening; a moveable substrate support configured to support a substrate; a movement element configured to move a substrate held on the substrate support towards the opening of the baseplate; a plurality of gas inlets positioned above and configured to direct gas downwardly towards the substrate support; and a sealing element configured to form a seal between the baseplate and the substrate support, the seal positioned at a greater radial distance from a center of the substrate support than an outer edge of the substrate support. In some embodiments, the sealing element can also include a plurality of apertures extend through the sealing element, the apertures configured to provide a flow path between a position below the sealing element to a position above the sealing element.