| 摘要 |
An apparatus and method for precisely detecting very small distances between a measurement probe (128) and a surface, and more particularly to a proximity sensor using a constant liquid flow and sensing a liquid mass flow rate within a bridge to detect very small distances. Within the apparatus the use of a flow restrictor (120,122) and/or snubber (110) made of porous material and/or a liquid mass flow rate controller (106) reduces turbulence and hydraulic noise and thus enables detection of very small distances in the nanometer to sub-nanometer range. An application in immersion lithography is thus foreseen. A further embodiment wherein a measurement channel of a proximity sensor is connected to multiple measurement branches, thereby providing multiplexing of probes, used e.g. for topography mapping. <IMAGE>
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