Methods and circuits for mask-alignment detection

An integrated circuit comprising:

• a. a first conductive layer extending in a plane defined by perpendicular X and Y dimensions, wherein the first conductive layer is divided into a first plurality of circuit features;
• b. a second conductive layer extending in the plane, wherein the second conductive layer is divided into a second plurality of circuit features;
• c. a contact layer disposed between the first and second conductive layers;
• d. a plurality of alignment detection structures adapted to indicate an extent of misalignment of the first conductive layer and the contact layer in the X dimension, each detection structure including:
• i. a first conductive element selected from among the first plurality of circuit features;
• ii. a second conductive element selected from among the second plurality of circuit features;
• and
• iii. an electrical contact extending through the contact layer between the first and second conductive layers and defining a contact area, the contact area having a contact width in the Y dimension and a contact length in the X dimension;
• iv. wherein the contact length in the X dimension is unique among the plurality of alignment detection structures;
• e. wherein the first conductive layer is aligned with the contact layer in the X dimension to within a first maximum alignment tolerance and in the Y dimension to a second maximum alignment tolerance;
• f. wherein the contact area is proportional to a first extent to which the first conductive layer is aligned with the contact layer in the X dimension;
• and
• g. wherein the contact area is independent of a second extent to which the first conductive layer is aligned with the contact layer in the Y dimension.

A mask-alignment detection structure adapted to indicate an extent of misalignment between a conductive layer extending in a plane defined by perpendicular X and Y dimensions and a contact layer extending in the plane, wherein the conductive layer includes a plurality of circuit features aligned with the contact layer in the X dimension to within a first maximum alignment tolerance and in the Y dimension to a second maximum alignment tolerance, the mask-alignment detection structure comprising:

• a. first and second conductive elements selected from among the plurality of circuit features;
• and
• b. a first electrical contact extending through the contact layer and in contact with the first conductive element, the first electrical contact defining a first contact area having a first contact width in the Y dimension and a first contact length in the X dimension;
• and
• c. a second electrical contact extending through the contact layer and in contact with the second conductive element, the second electrical contact defining a second contact area having a second contact width in the Y dimension and a second contact length in the X dimension;
• d. wherein the first contact area is proportional to a first extent to which the conductive layer is aligned with the contact layer in the X dimension and the second contact area is inversely proportional to the first extent;
• and
• e. wherein the first and second contact areas are independent of a second extent to which the first conductive layer is aligned with the contact layer in the Y dimension.