A support such as a clamp (310) is configured to releasably hold a patterning device such as a reticle (300) to secure it and prevent heat-induced deformation of it. For example, an electrostatic clamp includes a first substrate (312) having opposing first (313) and second (315) surfaces, a plurality of burls (316) located on the first surface and configured to contact the reticle, a second substrate (314) having opposing first (317) and second (319) surfaces. The first surface of the second substrate is coupled to the second surface of the first substrate. A plurality of cooling elements (318) are located between the first surface of the second substrate and the second surface of the first substrate. The cooling elements are configured to cause electrons to travel from the second surface of the first substrate to the first surface of the second substrate. Each cooling element is substantially aligned with a respective burl.