|
|
MOSIS Technical Notes
Removing Passivation
Removal of passivation from a chip is a very difficult process. If you
have not made mask provision for opening holes to your pads then there
is no possible way to open holes to the pads afterward. The only other
option is to remove passivation from the entire chip. Unfortunately
passivation removal is not very simple because the passivation is
composed of two components that are chemically very different.
The top layer of the passivation is usually silicon nitride. Below the
silicon nitride there is usually either a combination of silicon
dioxide and silicon oxinitride or just silicon dioxide. Both sets of
materials have very different etch chemistry. To make matters more
difficult, it is very difficult to prevent the silicon dioxide etch
chemistry from removing interlevel dielectrics between metal layers
below the pad level.
When a normal pad opening mask feature is used, the problem with
stopping the etch at the pad is taken care of by the metal
itself. This etch-stop feature of the metal prevents removal of
interlevel dielectrics. Without some fairly sophisticated etch
facilities, the chances of removal of passivation without destroying
the chip is very remote.
If you have access to a commercial integrated circuit failure analysis
service in your area, then you could have them remove passivaion from
the chip without great risk to the underlying circuitry. Even with
such facilities, the risk of damage is not zero.
|
Related Links
Fabrication Schedule
Customer Support
MOSIS Products
|
|
|
