OPTICAL MEASUREMENT OF STRESS IN THIN MEMBRANES

摘要

Ion Projection Lithography being one of the New Generation Lithography (NGL) techniques, uses Silicon stencil masks. A typical 150 mm stencil mask consists of a thin membrane of 126 mm diameter containing the openings for lithography and a stiff outer ring of bulk wafer material. The thickness of the membrane is in the order of several microns. The membrane has intrinsic stress to keep it flat. To determine the stress of the mask membrane the well known bulging method is used. In the developed equipment an electrostatic force between the membrane and a second electrode replaces the conventionally used gas pressure. The change of curvature of the membrane due to pressure load is determined optically by measuring the change of focal length of an optical system where the membrane serves as a mirror.