CCD-world: RG problem

[Iyer, Venkat]

The following was posted to CCD-world:

Dear Rogers ?? (I forgot who inititated it)

Regards the RG threshold voltage shift problem:

A shift as large as you are observing probably occurs from plasma
charging. One of the dry plasma etch processes may be the culprit for
this.  Possibly one of the latter steps like the via etch.

Try and check the following:

1. Ask the foundry if they have seen problems with plasma charging. 
Sometimes there are machine related endemics.

2. Find out what dry etch processes are being used, power and gas ratios
etc.

3. See if there is a distribution across the wafer. Very important !!

4. It is typically a good idea to add ESD protection to the RG pad.  Do
you have this ?  If you do then the above 3 can be ignored.

5. Also check to see if there is an antenna affect that exacerbates the
problem during dry etching.

6. Finally you can use a CHARM wafer, which is basically a bunch of
EEPROMS used to measure Vt shift. A bit costly but maybe well worth it. 
Like MypixelJim pointed out you may have one of your own EPROMs with
oxide/nitride interface charging up.  A classic MNOS stack.  

Actually once upon a time I thought it would be cool to backside charge
a thinned CCD with this stack.  I tried but it didnt work.  Funny how
mother nature works, it usually puts charges where you dont want them.

Cheers and good luck,

Venkat Iyer 

Sensor Design Group 
PerkinElmer Optoelectronics 
345 Potrero Ave 
Sunnyvale, CA-94086 
(408)RETICON ext.263      fax:(408)738-3832 
http://www.perkinelmer.com/reticon 

 



 

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