Wafers are used as carriers for fabrication during the production of integrated circuits (IC). After semiconductor fabrication processes, a plurality of dies is formed on a wafer. These dies are later separated through a die cutting or singulation process in which typically a mechanical or laser saw is used to cut through the wafer between individual chips or dies. To facilitate the die cutting process, relatively narrow sacrificial scribe lines are provided on the wafer along which the cuts are made to separate the dies. A scribe line area comprises the areas of wafer that are not utilized or occupied by the dies. After fabrication, the integrated circuit devices (or IC dies) are typically tested at the wafer level before singulation.
To facilitate wafer level testing before the die cutting process, conductive paths of multi-layer interconnect structures formed within the dies are typically terminated in conductive bond or test pads disposed at the wafer, which may be called the “Process Control Monitor” (PCM) test pads. The PCM test pads allow various electrical tests to be performed to monitor the complex semiconductor fabrication process and check the reliability of the dies before singulation. A plurality of test pads is typically distributed throughout the surface of the wafer in the scribe line areas. Some test pads may be placed on the chip area of a die as well.
With the ever increasing degree of integration, more functions are integrated into a die fabricated with multiple layers, more test pads may be needed for overall process monitor, which results in more area for test pads in the scribe line area and therefore less area for chip die in the wafer. Methods for reducing the testing pads needed are of interest for reducing the test pad area so that more wafer area can be used for dies.
Corresponding numerals and symbols in the different figures generally refer to corresponding parts unless otherwise indicated. The figures are drawn to clearly illustrate the relevant aspects of the various embodiments and are not necessarily drawn to scale.