Optical auto focusing system and method for electron beam inspection tool

A system for inspecting a specimen, the system comprising:

• an illumination system including an illumination source for providing an illumination flux;
• a light pattern plate associated with a pattern;
• an optical system for guiding the illumination flux and projecting the pattern onto a surface of a specimen;
• a detection system for detecting the illumination flux reflected from the surface of the specimen;
• a stage system for receiving a first control signal and in response to at least the first control signal moving the specimen in one or more of a first dimension, a second dimension, and a third dimension, the first dimension and the second dimension forming a plane, the third dimension being perpendicular to the plane;
• an image processing system for generating one or more images based on at least information associated with the detected illumination flux, each of the one or more images including a first image part for the pattern and a second image part for the specimen;
• and
• a focus processing system for receiving information associated with the one or more images from the image processing system, sending at least the first control signal to the stage system, and generating at least a second control signal;
• an electron-beam inspection system for receiving at least the second control signal and in response to at least the second control signal performing one or more inspections for the specimen at one or more locations.

A system for inspecting a specimen, the system comprising:

• one or more components configured to:
• provide an illumination flux through a pattern plate and a lens to a surface of a specimen to project a pattern onto the surface of the specimen, the pattern being associated with the pattern plate;
• detect the illumination flux reflected from the surface of the specimen with a detector;
• process information associated with the detected illumination flux;
• generate a first image based on at least information associated with the detected illumination flux, the first image including a first image part for the pattern and a second image part for the specimen;
• adjust the lens to a state in order to achieve a first predetermined quality for the first image part;
• move the specimen to a first position in order to achieve a second predetermined quality for the second image part, the first image with the lens at the state and the specimen at the first position being a reference image;
• move the specimen in one or more of a first dimension and a second dimension to a second position, the first dimension and the second dimension forming a plane;
• generate a second image based on at least information associated with the detected illumination flux, the second image including a third image part for the pattern and a fourth image part for the specimen;
• process information associated with the first image part of the reference image and the third image part of the second image;
• generate a signal based on at least information associated with the third image part of the second image and the first image part of the reference image;
• adjust the specimen in a third dimension to a third position in response to the signal, the third dimension being perpendicular to the plane;
• perform a first inspection for the specimen at the third location.