Kathleen,

One description is at:
http://www.stsystems.com/pages/process_content.asp?
parentID=1017&contID=1020&menuID=37&subID=54&subsub=YES&menuTitle=Techno
logies&mainMenuTitle=Products%20~%20Applications&parentTitle=Advanced%
20Silicon%20Etching%20(ASE)&contTitle=How%20it%20works

Basically, you alternate brief, shallow etch steps (perhaps 0.5
microns) with passivation steps. The passivation step (C4F8 plasma)
conformally coats everything with an etch resistant polymer. The etch
step (SF6+O2) uses rf on the wafer platen so it is quite vertically
active. The passivation on the floor of the previously etched area
gets removed rapidly and thus the floor of the etched area keeps
etching while the walls are protected. By balancing the amount of
passivation, the duration of the etch, the gas flows and power
levels, the sidewall angle can be precisely 'tuned' to be very
vertical. In an SEM image you can see the slight scalloping of each
etch cycle.

  --Jim
On Jun 27, 2007, at 7:42 PM, Holmes, Kathleen wrote:

> I'm a newbie in the mems business. Would someone please explain the
> Bosch process, or direct me to some literature? Thanks
>
> Regards,
> Kathleen Holmes