A substrate support system comprises a substrate holder having a plurality of passages extending between top and bottom surfaces thereof. The substrate holder supports a peripheral portion of the substrate backside so that a thin gap is formed between the substrate and the substrate holder. A hollow support member provides support to an underside of, and is configured to convey gas upward into one or more of the passages of, the substrate holder. The upwardly conveyed gas flows into the gap between the substrate and the substrate holder. Depending upon the embodiment, the gas then flows either outward and upward around the substrate edge (to inhibit backside deposition of reactant gases above the substrate) or downward through passages of the substrate holder, if any, that do not lead back into the hollow support member (to inhibit autodoping by sweeping out-diffused dopant atoms away from the substrate backside).