A method and apparatus for retaining a workpiece against a workpiece holder are described. A flexible member can be used to provide a substantially uniform force to securely retain the workpiece, which can allow the workpiece to be consistently positioned in a process module. In one detailed embodiment, a barrier to fluid entry is formed between the workpiece and a ring for retaining the workpiece against a workpiece holder. This provides a reliable seal during fluid processing to prevent fluid from reaching the underside of a workpiece. In various embodiments, the workpiece holder can be used to align a workpiece in a process module or to hold one or more workpieces in a configuration that allows for higher throughput.