Field effect transistor monitors

Abstract

Method and apparatus for measuring or determining characteristics, such as the actual effective width of a first conductive medium of a given design width produced by an integrated circuit process. The first conductive medium is formed apart from and parallel to a second and similar conductive medium of a given design width on an insulating medium which is disposed on a semiconductor substrate. The substrate has a first conductivity region and first and second parallel strips of a second and opposite conductivity disposed at one surface thereof within the first conductivity region for forming a channel of a given length. The first and second conductive media are arranged orthogonal to the first and second strips. A first voltage is applied between the first conductive medium and the first parallel strip and a second voltage is applied between the second conductive medium and the first parallel strip. Current is measured in the second parallel strip upon application of the first voltage and upon application of the second voltage. The actual or effective widths of the first and second conductive media are then determined by utilizing relationships between the measured currents and known constants, such as the design widths of the conductive media. In one embodiment, the etch bias of the conductive media may be obtained by forming the first and second media with different design widths. In another embodiment, the precision of alignment of an element at one level with an element at another level may be obtained by providing first and second parallel edges of a channel at one level and disposing at another level an edge of each of the first and second conductive media over the channel and parallel to the edges of the channel.