WCM   Wafer Charging Monitors, Inc.

Frequently Asked Questions
(Advanced FAQ's)

Wafer Charging in Plasma Etching and Ashing

1.Q. Can I run CHARM®-2 wafers through a plasma etcher without seriously damaging them?
A. Yes, if you keep the etching cycle short. CHARM®-2 sensors respond very rapidly, so you do not need to expose CHARM®-2 wafers to the complete etching cycle in order to test the etching process for wafer charging problems. Since only a very short exposure to the live plasma is needed, there will be at most only very minor wear to the wafer. The wafer will still yield valid wafer-charging test results and can be reused a number of times. For more information, please contact WCM.

2.Q. Which plasma etching processes tend to cause wafer charging problems?
A. Poly, metal, and oxide etching can all cause charging problems.

3.Q. Does increasing RF power in plasma etching make the charging problem worse?
A. It can, but experimental evidence supports the theory that plasma nonuniformity, not RF power, is the main factor causing wafer charging in plasma etch processes.

4.Q. Does high DC bias in plasma etching cause wafer charging problems?
A. Not necessarily. Wafer charging depends on the electrical potential developed between the wafer surface and the substrate -- whereas, in plasma etching, most of the so-called "DC bias" is dropped across the plasma sheath (not the wafer).

5.Q. Are downstream strippers less prone to cause wafer charging than conventional dry resist strippers?
A. We can not generalize. In our experience, downstream strippers seem to produce very little wafer charging -- however, with the right process conditions, conventional strippers can also be operated with safe levels of wafer charging.

6.Q. Does via etching cause much wafer charging?
A. In some cases, yes. For more information, see the following references:
7.Q. Does metal etching cause much wafer charging?
A. In some cases, yes. For more information, see the following reference:

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