Not long ago we covered a set of inspection tools announced by KLA-Tencor. They have recently announced yet another inspection tool, which they call CIRCL. The idea is that it’s actually three or four tools in one, with stations for frontside, backside, and edge inspection as well as one for spot check and review all integrated into one cluster, with loaders for up to three lots at a time.
(And yes, apparently backside matters. Years ago when I worked in the fab, it was particles on the frontside that were a problem. These days, a particle on the back can actually have noticeable effects on the front. That’s just crazy…)
These stations can be run in parallel, either for a single lot, with each wafer making the rounds, or for three lots, with each lot occupying a station.
This setup is intended to identify defects of 5 µm or larger, whether particles or defocus issues or any of a host of problems that may indicate that adjustments are necessary to the equipment before yield drops.
The system includes user-programmable logic that helps minimize inspection: the results of the first inspection will determine which other inspections are needed; the user-programmed logic drives that decision. So if a wafer looks clean to start with, it gets little further attention; if there are problems seen, then the nature of those problems determines where the wafer will spend extra time.
Just to contrast this setup with the ones we discussed before, this is a rougher inspection – meaning it goes more quickly, at 155 wafers per hour, inline. The others are inline as well, but they look for defects on the scale of the design rules – much smaller, so they take longer, and therefore lots are sampled more sparsely than they are for CIRCL inspection.
You can find more information in their release…