Identifying and compensating for slip-plane dislocations in photolithographic mask alignment

A method of detecting slip dislocations on a rectangular semiconductor die, comprising:

• providing a silicon wafer with <1-0-0>
• crystal lattice orientation;
• defining on the wafer a rectangular die site, said die site having four sides and four corners defining an enclosed rectangular die area and oriented such that the sides of the die site are substantially aligned with the <1-0-0>
• crystal lattice orientation of the wafer;
• disposing on the wafer a plurality of alignment marks, four of the alignment marks disposed in close proximity to a respective one of the four corners of the die area, said alignment markings defining corners of a four-sided alignment shape;
• measuring the distances between the alignment marks for the die site;
• determining a squareness factor for the die site by computing a difference between measured distances corresponding to diagonals of the four-sided alignment shape;
• and
• performing, if the squareness factor is greater than a pre-defined threshold value or if the measured distances between alignment marks corresponding to sides of the alignment shape differ from expected values therefor by greater than a pre-defined tolerance, the step of indicating one or more slip-plane dislocations as having occurred since disposing the alignment marks.

A method of discriminating between slip dislocation and rotation of a die site, comprising:

• providing a silicon wafer with <1-0-0>
• crystal lattice orientation;
• defining on the wafer a rectangular die site, said die site having four sides and four corners defining an enclosed rectangular die area and oriented such that the sides of the die site are substantially aligned with the <1-0-0>
• crystal lattice orientation of the wafer;
• disposing on the wafer a plurality of alignment marks, four of the alignment marks disposed in close proximity to a respective one of the four corners of the die area, said alignment markings defining corners of a four-sided alignment shape;
• testing for a slip dislocation;
• if a slip dislocation is found, indicating a slip dislocation error;
• if no slip dislocation is found, testing for a rotation of the die site;
• and
• if a rotation error is found, indicating a rotation error.