One Stop Micro

Imagine a silicon wafer with some features already micromachined on it. You now want to make some vias to provide connectivity from the backside of the wafer. How would you do that? One option would be to laser micromachine these vias, but then you are worried about what kind of damage the laser would create to the structures already on the wafer.

May be you have this impression of a red-hot laser burning through the wafer in one quick second- been watching too many Bond movies lately?

The fact is, the heat affected zone is very small- provided you use the right kind of laser. An ultrafast laser will have the smallest HAZ, followed by the UV and then the IR. A CO2 laser will surely be unacceptable. So what kind of numbers are we talking about? For an ultrafast, the HAZ typically would be sub-micron, for the UV lasers with pulse-widths in the low nanosecond range, the HAZ will be a few microns at the most, and much more for IR lasers.

If the features are 10s of microns away you are safe from a thermal point of view- but not from debris. Debris is going to be scattered aruound much further, and cleaning it completely without damaging the sorrunding structures is going to be very difficult or impossible.

If you ask a service provider if there is going to be heat damage to structures that are 100 micro away from the vias, the answer is going to be a no. But remember, debris and cleaning issues will have to be addressed