Patent ID: 7961296

Claim:
A lithographic apparatus comprising: an illumination system configured to condition a radiation beam with an illumination mode including an off-axis radiation beam emerging from an illumination pole and inclined at an angle with respect to an optical axis; a support constructed to support a patterning device, the patterning device being capable of imparting the radiation beam with a pattern in its cross-section to form a patterned radiation beam and further being capable of diffracting the off-axis radiation beam into a zeroth-order diffracted beam and a first-order diffracted beam oppositely and asymmetrically inclined with respect to the optical axis; a projection system having a pupil plane and configured to project the patterned radiation beam onto a target portion of the substrate; a phase adjuster constructed and arranged to adjust a phase of an electric field of a radiation beam traversing an optical element of the phase adjuster disposed in the pupil plane; and a controller constructed and arranged to retrieve data representative of the pattern and of the illumination mode, to identify an area where the first-order diffracted beam traverses the pupil plane, to optimize an image characteristic of an image of the pattern by calculating a desired optical phase of the first-order diffracted beam in relation to the optical phase of the zeroth-order diffracted beam, to map the area on a portion of the optical element, and to apply heat to or extract heat from, the portion to change an index of refraction of the portion of the optical element in accordance with the desired optical phase.