Optical component and clamp used in lithographic apparatus

A method of thermally conditioning an optical element having a curved optical surface used in a lithographic apparatus, the optical element including a set of closed channels, wherein regions at a heat transfer surface of the optical element that are exposed to the set of closed channels are positioned along a curved profile similar to that of the curved optical surface, the method comprising:

• delivering, via a pump, a fluid as a heat transfer medium into the set of closed channels of the optical element;
• receiving, via a temperature sensor, temperature values across the curved optical surface, or receiving, via a model, a heat distribution across the curved optical surface;
• and
• controlling, based on the temperature values or the heat distribution, a property of the fluid to maintain a uniform temperature distribution across the optical element during imaging of a pattern using the lithographic apparatus, wherein the controlling comprises:
• determining a location on the curved optical surface having relatively high temperature values;
• identifying one or more closed channels of the set of closed channels that are nearest to the determined location;
• and
• adjusting the property of the fluid within the one or more closed channels so that temperature at the determined locations is maintained within a desired temperature range.

A non-transitory computer-readable media comprising instructions therein, the instructions, when executed by one or more processors, configured to cause at least:

• delivery, via a pump, of a fluid as a heat transfer medium into a set of closed channels of an optical element having a curved surface;
• receipt, via a temperature sensor, of temperature values across the curved surface, or receipt, via a model, of a heat distribution across the curved surface;
• and
• control, based on the temperature values or the heat distribution, of a property of the fluid to maintain a uniform temperature distribution across the curved surface during imaging using the optical element, wherein the control comprises:
• determination of a location on the curved optical surface having relatively high temperature values;
• identification of one or more closed channels of the set of closed channels that are nearest to the determined location;
• and adjustment of the property of the fluid within the one or more closed channels so that temperature at the determined locations is maintained within a desired temperature range,
• wherein regions at a heat transfer surface of the optical element that are exposed to the set of closed channels are positioned along a curved profile similar to that of the curved surface.

An optical element comprising:

• a first member having a curved optical surface and a heat transfer surface;
• and
• a second member that comprises at least one recess, the at least one recess sealed against the heat transfer surface to form at least one closed channel between the first member and the second member to allow fluid to flow therethrough for thermal conditioning of the curved optical surface,
• wherein one or more regions of the heat transfer surface exposed to the at least one closed channel are positioned along a curved profile similar to that of the curved optical surface, and
• wherein the heat transfer surface includes a first set of recesses, each recess of the first set of recesses having a region located at a substantially constant distance from the curved profile of the curved optical surface.