Patent ID: 6950183

Claim:
A method for inspecting masks used to project patterns in photolithographic imaging comprising: providing a photolithographic mask having a pattern field thereon, where in normal production use the pattern is transferred by a reduction projector as a demagnified pattern on a production substrate; providing a movable field-defining aperture adjacent the mask, the aperture having a field area less than, and capable of defining a pattern subfield comprising only a portion of, the entire photolithographic mask pattern field; providing an energy source and a test substrate sensitive to energy from the source; aligning the field-defining aperture with a pattern subfield comprising only a portion of the entire photolithographic mask pattern field; using the energy source, projecting the pattern subfield onto the test substrate and exposing onto the test substrate the pattern subfield at a size between that normally exposed on a production substrate and the actual size of the pattern subfield on the photolithographic mask; and inspecting the exposed pattern subfield on the test substrate for defects in the photolithographic mask.