Apparatus and methods for reliable and efficient detection of voltage contrast defects

An inspection system for detecting defects in a plurality of features on a semiconductor device, each of the features being designed to have a particular potential when scanned with an electron beam, the system comprising:

• beam generator for generating an electron beam;
• a detector for detecting electrons;
• and
• a controller arranged to:
• cause the beam generator to scan an electron beam over a first and a second set of feature portions, wherein the first set is designed be substantially identical to the second set of feature portions when there is no defect present;
• generate a first image of the first set of feature portions and a second image of the second set of feature portions from electrons detected by the detector emitted from the scanned feature portions in response to the scanned electron beam;
• subtract the first image from the second image to generate a difference image;
• when the difference image has a significantly sized defect feature that represents a difference between the first set of feature portions and the second set of feature portions and the defect feature has about a same aspect ratio as a one of the scanned feature portions, determine that the defect feature indicates an electrical defect within the scanned features;
• and
• when the difference image has a significantly sized defect feature that represents a difference between the first set of feature portions and the second set of feature portions and the defect feature has a different aspect ratio than a one of the scanned feature portions, determine that the difference feature indicates a physical defect.

A computer program product for detecting defects in a plurality of features on a semiconductor device, each of the features being designed to have a particular potential when scanned with an electron beam, the computer program product comprising:

• at least one computer readable medium;
• computer program instructions stored within the at least one computer readable product configured to cause the inspection system to:
• provide a first and second image of a first and second set of feature portions, respectively, generated as a result of scanning an electron beam over the first and second set of feature portions, wherein the first set of feature portions are designed be substantially identical to the second set of feature portions when there is no defect present;
• subtract the first image from a second image to generate a difference image;
• when the difference image has a significantly sized defect that represents a difference between the first set of feature portions and the second set of feature portions and the defect has about a same aspect ratio as a one of the scanned feature portions, determine that the defect indicates an electrical defect within the scanned features;
• and
• when the difference image has a significantly sized defect that represents a difference between the first set of feature portions and the second set of feature portions and the defect has a different aspect ratio than a one of the scanned feature portions, determine that the defect indicates a physical defect.

A method of inspecting a semiconductor device using a scanning electron microscope, the method comprising:

• providing reference data;
• producing scanned data by performing a voltage contrast inspection on a test structure of the semiconductor device with the scanning electron microscope;
• identifying electrical defects in the test structure by comparing the scanned data with the reference data;
• and
• automatically filtering out physical defects from the electrical defects when comparing the scanned data with the reference data.