While the recent MEMS Executive Congress focused on electro-mechanical applications, occasionally MEMS processing techniques were highlighted for strictly electrical purposes, with no mechanical component.
In one example, ICEMOS talked about their collaboration with MEMS manufacturer Omron for a new way of making superjunction power transistors.
Superjunction transistors overcome the Ron/breakdown tradeoff issue using alternating p and n stripes. In theory, these can be arranged a number of different ways, but, according to ICEMOS, the typical way it’s done now is horizontally, by growing a series of epitaxial layers of opposite doping. This, they say, is an expensive way of doing things.
Instead, they’ve gone vertical. The way they do this is by etching trenches using DRIE in Omron’s fab. They then use a sidewall implant – which is almost vertical, but tilted ever so gently – to dope the sides of these trenches.
Even though this uses a process that, to a standard CMOS fab, would be non-standard, they say it’s still cheaper than the multi-epi way of doing things. They also say that they can make smaller devices this way.
You can find out more about what they do from this PDF presentation…