Method and system for optimizing illumination in an optical photolithography projection imaging system

A method of forming an image of a reticle object in a radiation-sensitive medium using an imaging system having a depth of focus, an entrance pupil, an imaging plane located within the depth of focus, and a source of illumination, the method comprising the steps of:

• (a) generating and storing a target object image corresponding to the reticle object;
• (b) generating and storing an actual aerial image of the reticle object;
• (c) comparing the actual aerial image to the target object image including providing and storing comparison data;
• (d) optimizing the illumination provided by the source of illumination in response to the comparison data for imaging the reticle object through the entrance pupil and onto the imaging plane;
• and
• (e) exposing the reticle to said optimized illumination to form an aerial image and to transfer said aerial image into the radiation-sensitive medium placed at said imaging plane.

Apparatus for providing optimal illumination in an imaging system, comprising:

• (a) a source of illumination;
• (b) an imaging lens having an entrance pupil and depth of focus;
• (c) a reticle having one or more features to be imaged;
• (d) a target aerial image comprising one or more target features corresponding to said one or more features to be imaged;
• (e) an imaging plane;
• (f) determination means for determining aerial images at said imaging plane of one or more of said reticle features;
• (g) image analyzing means, coupled to said determination means, for comparing said aerial images of said one or more of said reticle features determined by said determination means to corresponding ones of the target features to define an illumination that minimizes a difference between said one or more of said reticle features and said corresponding ones of the target features, and for generating a first output signal representing said illumination;
• and
• (h) illumination control means, coupled to said image analyzing means and said source of illumination, for controlling said source of illumination based on said first output signal so that said source of illumination provides said illumination that minimizes the difference between said one or more of said reticle features and said corresponding ones of the target features.

An illumination optimization system for use with an imaging apparatus including a source of illumination, an imaging lens having an entrance pupil and depth of focus, a reticle having one or more features to be imaged, and an imaging plane, the optimization system comprising:

• (a) determination means for determining aerial images at the imaging plane of one or more of the reticle features;
• (b) image analyzing means coupled to said determination means, for comparing said aerial images of said reticle features determined by said determination means to a target aerial imaged for generating illumination data defining an illumination that minimizes the difference between said reticle feature aerial image and said target aerial image, and for outputting said illumination data;
• and
• (c) illumination control means, coupled to the source of illumination and said image analyzing means, for controlling said source of illumination based on said illumination data such that said source of illumination provides said illumination that minimizes the difference between said reticle feature aerial image and said target aerial image.

A method of operating an imaging system comprising the steps of:

• a) illuminating an object to be imaged with an adjustable illumination source such that the object projects an actual aerial image through an entrance pupil onto an image plane;
• b) generating data representing the actual aerial image;
• c) retrieving from a database target data that defines an ideal aerial image;
• d) comparing the data representing the actual aerial image with the target data and generating optimization data in response to the comparing;
• and
• e) adjusting the controllable illumination source in response to the optimization data such that differences between the target image and the actual aerial image are decreased.