Dosage micro uniformity measurement in ion implantation

Abstract

A design of a test chip for determining the dopant uniformity of an ion implantation within a area of the order of several tens of microns is disclosed and a method for it's measurement provided. The object of the test chip is particularly adapted to sense dopant concentration variations caused by the variation of density in the spot of the ion implantation beam and can be used to determine optimal overlap of adjacent beam scans. The test chips use arrays of MOSFETs arranged in a pattern with channel lengths parallel to the path of the ion implantation beam and provide a contiguous set of incremental concentration measurements across the paths of the ion implantation beam scans. The gate threshold voltages are measured and related to the active dopant impurity concentration in the channel area. The width of the concentration increment is therefore equal to the channel length. The magnitude and the long range uniformity of active dopant impurity can be determined over a large portion of the wafer or, with a high resolution, over a relatively small area with magnitude of device dimensions.