Method and system for thermally conditioning an optical element

A lithographic projection method, comprising

• transferring a pattern from a patterning structure onto a substrate, utilizing an optical element supported by a support;
• and
• thermally conditioning the optical element, the conditioning comprising
• irradiating the optical element with radiation;
• not-irradiating the optical element with the radiation;
• allowing heat flow between the optical element and a conditioning fluid that is held in a conditioning fluid reservoir in the support;
• and
• providing a fluid flow of the conditioning fluid, to supply thermally conditioned fluid to the reservoir,
• wherein a flow rate of the fluid during the irradiating of the optical element is lower than a flow rate of the fluid when the optical element is not-irradiated, and
• wherein pressure variations of the conditioning fluid are counteracted in order to keep a fluid pressure of the conditioning fluid in the reservoir at or near a predetermined fluid pressure range.

A lithographic apparatus, configured to transfer a pattern from a patterning structure onto a substrate, the apparatus comprising:

• a projection system configured to project a pattern imparted to a radiation beam onto a target portion of a substrate, the projection system comprising a plurality of optical elements;
• and
• a thermal conditioning system configured to thermally condition at least one of the optical elements of the projection system, the thermal conditioning system comprising
• a heat exchanger configured to allow heat exchange between a conditioning fluid and the optical element,
• a flow controller configured to control the flow rate of the conditioning fluid to a support that supports the optical element, and to provide a first flow rate during an idle mode of the optical element, and to provide a second flow rate during a radiation projection mode of the optical element, wherein the second flow rate is lower than the first flow rate,
• wherein the second flow rate is zero, and
• wherein pressure variations of the conditioning fluid are counteracted in order to keep a fluid pressure of the conditioning fluid in the reservoir at or near a predetermined fluid pressure range.

A method for thermally conditioning an optical element supported by a support, the method comprising:

• irradiating the optical element with radiation;
• flowing heat between the optical element and a conditioning fluid that is held in a conditioning fluid reservoir in the support;
• and
• supplying thermally conditioned fluid to the reservoir at a flow rate,
• wherein the flow rate of the fluid during the irradiating is lower than the flow rate of the fluid when the optical element is not being irradiated with radiation,
• wherein the fluid flow rate is substantially zero during the irradiating, and
• wherein pressure variations of the conditioning fluid are counteracted in order to keep a fluid pressure of the conditioning fluid in the reservoir at or near a predetermined fluid pressure range.