IC Industry Award Winner Metrology Test Yield Award VueTrack Technology 16
CASCADE MICROTECH’S VueTrack technology is a unique software feature that enables unattended wafer-level testing at multiple temperatures, automatically making probe-to-pad adjustments at every site, adjusting for thermal imbalance. This technology works together with the eVue digital imaging system’s downward-looking camera to accurately position probing needles exactly where you need them on the pad. Idle time is significantly reduced or even eliminated in measurements that are short in duration since the operator no longer needs to manually adjust the probe for every temperature. As a result, test cell efficiency is utilized to its fullest, and the only idle time occurs when waiting for a wafer change. VueTrack technology enables
increased productivity and reduces idle time by revolutionizing the probe-to-pad alignment process. Since repeatable electrical contact is vital for reliable test data, ensuring automatic error correction without operator intervention enables full usage of a wafer prober’s potential. VueTrack’s on-site probe tip and wafer location measurements in combination with a single downward-looking microscope ensure that the best possible alignment is continuously maintained throughout the test plan, eliminating errors. VueTrack adjusts for movement of the probes and the pads in X, Y and Z caused by thermal chuck temperature fluctuation. A maximum of 12 probe tips can be tracked to produce a “best fit” touchdown on the device pads. The accompanying software settings train the system with images of the required probe tips so that it may not be necessary to train every probe tip on your probe card since the “trained” probes refer back to the reference point and are automatically
justified. The number of memorized probe tips can be adjusted to best suit current test needs.
The on-site probe-to-pad alignment technique utilizes a coordinated sequence of small Z movements in the wafer stage and internal fine focus stage of an eVue digital imaging system. By eliminating the need for XY chuck movements and making only very small Z movements of the thermal chuck, alignment errors can be determined and corrected in thermal conditions identical to the electrical test. By keeping the thermal chuck on-site during the probe tip and wafer tracking mode, it does not induce any thermal imbalance to the prober and can reduce or eliminate the need for soak times in most test scenarios. It is even possible to make numerous corrections per site if the electrical test allows for probe separation. This is a powerful advantage of the new on-axis technique, since it can virtually eliminate transition and die soak times for short duration measurements. The new on-site probe-to-pad
correction approach utilized by VueTrack improves every test segment that impacts productivity so that idle time is nearly eliminated. The only idle time remaining is when a test plan is complete and the prober is waiting for a manual wafer change. Transition and die soak times for short test durations can be decreased when the touchdown duration is short. Alignment correction times are likewise improved with an automatic approach. VueTrack makes it possible to track and align the probe to the pad in complex structures, even in the large temperature range needed in today’s statistical tests. Test results are then obtained more quickly and test productivity is optimized.
www.euroasiasemiconductor.com Issue IV 2010
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