Lithographic apparatus, method for unloading a substrate and method for loading a substrate

Abstract

A method for unloading a substrate from a support table configured to support the substrate, the method including: supplying gas to a gap between a base surface of the support table and the substrate via a plurality of gas flow openings in the support table, wherein during an initial phase of unloading the gas is supplied through at least one gas flow opening in an outer region of the support table and not through any gas flow opening in a central region of the support table radially inward of the outer region, and during a subsequent phase of unloading the gas is supplied through at least one gas flow opening in the outer region and at least one gas flow opening in the central region.

1 . A method for unloading a substrate from a support table configured to support the substrate, the method comprising:
 supplying gas to a gap between a base surface of the support table and the substrate via a plurality of gas flow openings in the support table,   wherein during an initial phase of unloading the gas is supplied through at least one gas flow opening in an outer region of the support table and not through any gas flow opening in a central region of the support table radially inward of the outer region, and   during a subsequent phase of unloading the gas is supplied through at least one gas flow opening in the outer region and at least one gas flow opening in the central region.   
     
     
         2 . The method of  claim 1 , wherein:
 during the initial phase of unloading the gas is supplied through at least one gas flow opening in the outer region and not through any gas flow opening in the central region and any gas flow opening in an intermediate region of the support table radially inward of the outer region and radially outward of the central region,   during an intermediate phase of unloading the gas is supplied through at least one gas flow opening in the outer region and at least one gas flow opening in the intermediate region and not through any gas flow opening in the central region, and   during the subsequent phase of unloading the gas is supplied through at least one gas flow opening in the outer region, at least one gas flow opening in the intermediate region and at least one gas flow opening in the central region.   
     
     
         3 . The method of  claim 2 , wherein:
 during the intermediate phase of unloading gas is supplied through at least one gas flow opening in the intermediate region at a first pressure greater than ambient pressure, following which gas is supplied through at least one gas flow opening in the intermediate region at a second pressure less than the first pressure.   
     
     
         4 . A method for loading a substrate onto a support table configured to support the substrate, the method comprising:
 extracting gas from a gap between a base surface of the support table and the substrate via a plurality of gas flow openings in the support table,   wherein during a first phase of loading the gas is extracted through at least one gas flow opening in a central region of the support table and not through any gas flow opening in an intermediate region of the support table radially outward of the central region and any gas flow opening in an outer region of the support table radially outward of the intermediate region,   during a second phase of loading the gas is extracted through at least one gas flow opening in the central region and at least one gas flow opening in the intermediate region and not through any gas flow opening in the outer region, and   during a third phase of loading the gas is extracted through at least one gas flow opening in the central region, at least one gas flow opening in the intermediate region and at least one gas flow opening in the outer region.   
     
     
         5 . The method of  claim 4 , wherein:
 during the first phase of loading gas at a pressure greater than ambient pressure is supplied through at least one gas flow opening in the intermediate region and/or at least one gas flow opening in the outer region.   
     
     
         6 . The method of  claim 4 , wherein:
 when the substrate is being lowered towards the support table, the gas is extracted through at least one gas flow opening in the central region, at least one gas flow opening in the intermediate region and at least one gas flow opening in the outer region;   when the substrate reaches a predetermined distance above the support table, the gas is not extracted through any gas flow opening in the central region, any gas flow opening in the intermediate region and any gas flow opening in the outer region; and   when the substrate has touched down onto the support table, the first phase of loading, the second phase of loading and the third phase of loading are performed.   
     
     
         7 . The method of  claim 2 , wherein:
 the intermediate region surrounds the central region; or   the intermediate region comprises a plurality of non-overlapping intermediate sub-regions between which a flow of gas is restricted; and/or   the outer region surrounds the intermediate region.   
     
     
         8 . The method of  claim 1 , wherein the outer region comprises a plurality of non-overlapping outer sub-regions between which a flow of gas is restricted. 
     
     
         9 . A method for loading a substrate onto a support table configured to support the substrate, the method comprising:
 lowering the substrate towards the support table;   when the substrate is being lowered towards the support table, controlling an underpressure source to apply an underpressure so as to extract gas from a gap between a base surface of the support table and the substrate via a plurality of gas flow openings in the support table,   when the substrate reaches a predetermined distance above the support table, controlling the underpressure source to stop applying an underpressure in fluid communication with any of the gas flow openings in the support table; and   when the substrate has touched down onto the support table, controlling the underpressure source to restart applying an underpressure so as to extract the gas via the plurality of gas flow openings in the support table.   
     
     
         10 . The method of  claim 9 , wherein when the substrate has touched down onto the support table, the underpressure source is controlled to build up the underpressure gradually in a plurality of phases such that a flow of the gas extracted from the gap via the plurality of gas flow openings gradually increases.