US Patent 7582493 Distinguishing between dopant and line width variation components

A test structure includes first and second pluralities of transistors. The first plurality of transistors includes gate electrodes of a first length. The second plurality of transistors includes gate electrodes of a second length different than the first length. A channel area of the transistors in the first plurality is substantially equal to a channel area of the transistors in the second plurality. A method for using the test structure includes measuring a performance metric of the first and second pluralities of transistors. Variation in the performance metric associated with the first plurality of transistors is compared to variation in the performance metric associated with the second plurality of transistors to identify a random length variation component associated with the first plurality of transistors.