Push-Pull Capacitance Probes for Differential Measurement

All right, on our setup here, we’re looking at two probes; a top push-pull probe, and a bottom push-pull probe you see down under here. Then we have a platen. This is an aluminum platen, and that’s a very smooth surface to put silicon wafers on. Here we have a sample of a silicon wafer here so we can slide target material underneath the probes. We’re doing a full differential measurement to measure the thickness.

Our first step is calibrating the two probes that we have, we have push-pull probes top and bottom. We have a piece of silicon wafer that is has been measured and is 105 microns thick. We’re going to slide this in the gap between the two probes, and using this allen wrench to get it centered in there. All right so our test sample is centered now we’re going to come over here…

All right we’ve slid our test sample in and we’re going to show how we calibrate this. We’ve called up under the measurement tab here set up channel one we click on that this is the situation we have here, two push-pull probes, and we’re gonna put our sample thickness in. So this is 105 microns thick. We simply put 105 in there, we click ok, oh sorry calibrate. So we’re now calibrated to that sample 105 microns, so I’m going to click on OK, and we’re all set we’re good to go. We can see up in the window here that our real-time measurement is 105 microns.

So we can remove the calibration sample, next we’re going to measure some of the copper foil samples.

All right we’re measuring the copper foil, we’ve put our first target sheet on the platen here between the two probes, we’re looking at the center of the copper we know it’s 18 microns. Here we’re reading 19 so it’s at 1 micron high, we’re also running the monitor so you can see the thickness change.

I’m going to slide the copper to the 12 o’clock position, up near the top of the sample, see what we can see we’re now reading, 16. I’m gonna go to the nine o’clock position we’re reading 17. Going to the six o’clock position reading 24. I’m going to move over to the three o’clock position and we’re reading 24. We’re going to slide back to the center, and I see we’re crossing some dents, so we’re back to the center again, and we’re seeing 22, actually, and adjusting it slightly, there now we’re back to what I believe is the center. So why are we seeing values that are higher than 18? That’s because of the dents in the copper, causing that and if we slide around we can also see these bumps and changes here.