Automated on-wafer millimeter wave measurements demo – WMS Series Part 2 of 6
0 Comments


The WaferPro Express software sits at the intersection of Keysight instruments and WaferPro over control software; which in turn drives
the wafer program. Using this tool, we can efficiently get automated measurements across a wafer and ready for modeling. Given our WaferPro Express project setup,
Network Analyzer calibration, and probe alignment, we are now ready to see measurements in action. Let’s first do a manual measurement on our MESFET and capacitor structures, and then run a test plan sequence. After a right-click and Run Manual Measurement command, we get to a window that enables basic prober manipulation and initiates the measurement. After hitting the Contact button, the chuck
is raised and the probes make contact. We then click Measure, and wait for a moment as the measurements are performed. Looks like the measurement is done. Let’s see some plots. Here we see DC I-V measurements, S-parameter measurements, and FT. One may similarly make manual measurement of the capacitor structure. After selecting the device, we once again
right-click and select Run Manual Measurement. Using the Move To button, we can have the probe pop over to the right location, and then hit Contact. Once again, we hit Measure and then wait for a little while. Now that the measurement is done, we can look at plots. Each column of plots represents each of the four S-parameters, S11, S22, S21, and S12. Besides running manual measurements on individual devices, we can measure all the devices listed at each of the desired reticles within the
wafer. In other words, we can run our full test plan. As shown here in the wafer map, we have three reticle locations and two devices within each reticle representing six complete measurements. Notice that both WaferPro Express and the Velox Prober Control Software are in sync with each other. We hit the button Start/Resume Test Plan. And since we did not do this already, the
software will ask us to specify a location to store all the data. The default location is a subdirectory under the project called data. That should be fine. We hit Start Measure, specify our measurement temperature, and let the measurement run. The test plan initiates by making contact
to a GaAs MESFET measuring both DC I-V and S-parameters. Then we touch down on the capacitor structure to measure S-parameters. We now visit the first device in the second
reticle in the middle of the waver. Fast-forwarding a little bit, the prober transitions to the last capacitor in the third reticle. Once this is done, it goes back to our original home position with the probes up. We can now review the large volume of data we have generated, even with our small set of measurements. Wherever you see the green Result OK comment, we can double-click that to display a multi-plot of the data. Here we look at some capacitor S-parameter data. And here we look at this particular MESFET’s DC I-V and S-parameter data. In this demo, we just showed that we can measure S-parameters in an automated fashion across the wafer. Pretty cool right? Well, we didn’t show you how we got there, yet. It turns out there are a number of steps to
be able to do this, which we will present in separate videos. First, we need to configure WaferPro Express so that it may drive instruments like the B1500A and the PNA-X. We also need to connect WaferPro Express to the probe station via the Velox software. Next, we need to align the probes to the wafer and generate a wafer map. Once this is done, we may step from reticle-to-reticle with micron level accuracy. We want RF S-parameters on only the device, and not the cabling or probe structures. To move the measurement reference plane to the probe tips, we need to execute an on-wafer calibration. Cascade provides a special structure to do this, and we walk through the procedure. Lastly, we need to specify what we want to measure, which device and which reticle on the wafer, which tests and which bias conditions. This is really where WaferPro Express comes in, enabling efficient definition of measurement routines, wafer automation, and data handling.

Leave a Reply

Your email address will not be published. Required fields are marked *