Method for determining the damage potential of the different types of wafer defects

Abstract

A method is presented for devising a model to determine the damage potential of wafer defects. The model takes into account both the defects' type and size. Wafer defects are the most major cause of depressed yields in semiconductor manufacturing. The wafers are first scanned to detect and identify the defects. There are several available tools that can detect and/or categorize the defects by type and size. A model is then formed to predict the probability (single probability) that a single defect on a die will not cause it to be nonfunctional. This model must depend on the size of the defect and an additional undetermined parameter which is specific to the type of the defect. Assuming that the effect of different defects is independent, the probability that a die will be functional when having multiple defects is then simply given by the product of all the single probabilities. At the end of the manufacturing process, the wafers can be electrically tested to determine whether the die are functional or not. An error function can then be formed by adding together the square of: for functional die, one minus the predicted probability; for nonfunctional die, the predicted probability minus zero. A good model should predict close to one for functional die and close to zero for nonfunctional die. By numerically minimizing this error function, the undetermined parameters can be computed. These parameters can then be used to predict the damage potential of defects for future wafers.