Automatic photomask inspection system and apparatus

In an optical inspection apparatus including carriage means for transporting two like objects along an inspection path, means for illuminating corresponding portions of the objects, and electro-optical means for individually inspecting the illuminated portions, an improved electro-optical means comprising:

• first and second separate optical systems for respectively collecting light from the corresponding portions of the inspected objects, each said separate optical system including
• a movable member,
• an objective lens carried by said movable member for collimating light rays received from one of said objects,
• a variable focal length lens assembly for receiving the collimated light rays and focusing them onto an image plane, and
• light sensitive means for receiving the focused light rays and developing an electrical signal;
• and
• photosensitive detector means responsive to the collected light and operative to generate electrical signals commensurate therewith.

In an optical inspection apparatus including carriage means for transporting two like objects along an inspection path, illuminator means for illuminating corresponding portions of the objects, and electro-optical means for individually inspecting the illuminated portions, an improved illuminator means comprising:

• a single source of illumination;
• and
• first and second separate optical means for communicating light from said source to each of said corresponding portions of the object to be inspected, each of said optical means including,
• an objective lens for collimating light received from said source of illumination,
• a first reflector for redirecting said beam of collimated light along a first line normal to the optical axis of said objective lens,
• a second reflector for again redirecting said beam of collimated light back toward said optical axis and along a second lens parallel to said first line,
• focusing means disposed along said second line for focusing said collimated light onto said corresponding portion of the object to be inspected;
• a first member for carrying said focusing means back and forth along said second line;
• a second member for carrying said second reflector back and forth along said second line;
• and
• means coupling said first and second members together so that movement of said focusing means over a particular distance causes said second reflector to be moved in the same direction and over a distance equal to one-half said particular distance.

Optical inspection apparatus for detecting differences between two like objects, comprising:

• carriage means for supporting the objects to be inspected and for simultaneously moving such objects along an inspection path;
• illuminator means for illuminating corresponding portions of said objects as they are moved along said path;
• electro-optical means for individually inspecting said illuminated portions and for developing first and second electrical signals respectively corresponding thereto;
• means for digitizing said first and second signals;
• means for individually storing the digitized first and second signals in a manner which corresponds to their positional relationship to the scanned objects with the result being that electronic maps of said first and second objects are provided;
• means for correlating the stored map of said first signal relative to said second signal to achieve best fit;
• means for comparing the correlated first and second signals and for defining a particular class of differences therebetween as a defect;
• and
• means for displaying said defects.