An apparatus and method for processing a microelectronic substrate comprises a main chamber and a movable boundary. The main chamber comprises a main chamber wall enclosing a main chamber interior. The movable boundary is disposed within the main chamber interior, and is movable between a first position and a second position. At the first position, the movable boundary at least partially defines a sub-chamber in which a substrate can be processed. The sub-chamber is fluidly isolated from the main chamber interior, and provides an environment suitable for a high-pressure processing of the substrate such as cleaning or surface preparation. The sub-chamber can be maintained at a high pressure while the main chamber is maintained at either a low pressure, an atmospheric pressure, or at a vacuum. The apparatus can be directly coupled to an external substrate handling and/or fabrication module, such that the main chamber interior provides a buffer between the sub-chamber and the external module. At the second position of the movable boundary, the substrate can be loaded into or removed from the apparatus, such as by transfer to or from any external module provided.