Micromanipulator vision for wafer probing

An overview is presented of a micromanipulator vision system for use in automating various functions during the testing of a wafer for semiconductor parameters and inspection of VLSI circuits. It is assumed that the wafer under test is not necessarily in its proper orientation. It is required that certain probes be lowered automatically onto certain pads to inject test vectors and to read the results for analysis. A methodology was developed for determining the position (especially the vertical distance from the target) of the tip of a probe, so that it can be guided accurately to its target pad. Standard image processing steps used for efficient feature extraction and registration of the target integrated circuit are outlined, and a method of obtaining the vertical distance of the tip of a probe from its target pad is presented. Two different criteria through which it can be established whether a probe is in contact with its target are given. The algorithm developed was tested for touch using different types of tips such as tungsten and tungsten carbide, and with NMOS and CMOS processes. Clean and accurate representations of the probes were extracted from integrated images in all the tests, and in all cases, touch was achieved without the surface being scratched