Parametric Failure Analysis Using Wafer Map Display


Due to inherent variations in the manufacturing process, performance and yield of IC chips are subject to cross wafer distributions. In order to gain an early control of out of range failures and increase the yield, it is very important for a yield engineer to have a way to display distributions of any SPICE model parameter extracted during the E-test. This information is also useful to circuit designers during the design/layout phase to predict where certain early failures may occur in the circuit and do proper redesigns. The wafer map display of parametric failure distributions are the exact features designed for these engineers.


Two or three colors can be used to depict parametric ranges. If only pass or fail parametric range is defined (leaving the other range blank), two colors will be used. If user insists to define pass and fail ranges, then three colors will be used: pass, fail, and others. The third color is very useful to depict the unusual or incomplete specification of the parametric ranges.


A new SetUp button is introduced on the wafer map screen. This button invokes the DISPLAY SETUP screen (Figure 1) used for defining attributes used in relational database search. The range SetUp button (Figure 2) invokes the RANGE SETUP screen where parameters can be selected. For a given parameter MIN and MAX values can be set for both pass and fail regions. A database of parameter values can be either automatically created by UTMOST or converted from a custom database. With selection of parameters complete, and their pass/fail ranges designed, a user can quickly generate a large number of wafer maps of parametric failures by simply selecting a parameter on the wafer map screen (Figure 3).


Figure 1. Display setup screen for Attribute Selection.

Figure 2. Range setup screen for pass/fail range specification.

Figure 3. A typical wafer map display of parametric failure distribution in SPAYN.

New DATA button on the wafer map screen is used to invoke a data summary window in which all displayed data is summarized along with corresponding attributes. The final wafer map can be saved in a postscript file. The file is suffixed by .dsum and stores along with the data corresponding attributes selected.