Gas Gauge, Lithographic Apparatus and Device Manufacturing Method

摘要

A gas gauge has a gas delivery tube arranged to determine a distance to an object. The gas delivery tube includes a gas conduit through which a suitable measurement gas is supplied. The measurement gas leaves the gas delivery tube under pressure via an outlet and impinges on the object in an interaction area, wherein a pressure of a recoiled gas is measured by a pressure detector. A gas having a low atomic number may be used. The pressure sensor may include a membrane positioned in the gas delivery tube at least partially enveloping the gas conduit at or near the gas outlet. The pressure sensor may include a membrane disk arranged about the gas conduit. The pressure sensor may include a suitable plurality of pressure elements arranged in a substantially common plane and which may be spaced apart yet enveloping the gas conduit.