The present invention pertains to an apparatus and method useful in semiconductor processing. The apparatus and method can be used to provide a seal which enables a first portion of a semiconductor processing chamber to be operated at a first pressure while a second portion of the semiconductor processing chamber is operated at a second, different pressure. The sealing apparatus and method enable processing of a semiconductor substrate under a partial vacuum which renders conductive/convective heat transfer impractical, while at least a portion of the substrate support platform is under a pressure adequate to permit heat transfer using a conductive/convective heat transfer means. The sealing apparatus comprises a thin, metal-comprising layer, typically in the form of a strip or band, brazed to at least two different surfaces within said processing chamber, whereby the first and second portions of the semiconductor processing chamber are pressure isolated from each other. Preferably, the metal-comprising layer exhibits a cross-sectional thickness of less than about 0.039 in. (1 mm). The invention is particularly useful when there is a differential in linear expansion coefficient of at least 3.times.10.sup.-3 in./in./.degree.C., measured at 600.degree. C., between the surfaces to be bridged by the thin, metal-comprising layer.