A chuck method of and apparatus (50, 150, 300) for supporting a substrate (W) during processing of the substrate, where the substrate has a lower surface (WL). The apparatus facilitates heat transfer away from the substrate during processing of the substrate. The apparatus comprises a chuck body (60) having an outer edge (70) and a rough upper surface (64U). The substrate is arranged adjacent the rough surface such that the substrate lower surface and the roughened upper surface form a gap (100) therebetween. The apparatus further includes a central gas conduit (80) passing through the chuck body. The central conduit has a second end (82b) open to the roughened upper surface and a first end opposite the second end connected to a gas source (86). The conduit is arranged such that a gas can flow through the conduit into the gap and toward the chuck body outer edge. The gas used has an atomic or molecular weight that is greater than that of helium. The surface roughness, the substrate lower surface and the flow of the heavier gas in the gap contribute to defining an accommodation coefficient α and a mean free path λ such that the ratio α/λ is higher than that of prior art apparatus.