CCD Question

[MYPIXEL at aol.com]

In a message dated 97-11-04 18:15:35 EST, ninkov at cis.rit.edu writes:

<< 

 As I understand it when CCDs are thinned for backside illumination
 purposes the wafers are initially lapped to some intermediate thickness

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Yes, sometimes mechanically and sometimes chemically
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 and then etched to the final desired thickness, which depends on the
 wavelength of operation. 

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Ideally very near the frontside depletion edge but no more than a couple
microns from it.
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 Normally the etch stops (or at least slows
 down significantly) at the interface between the epitaxial and substrate
 silicon. 

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By about a factor of 100 
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 After this etching is concluded (and before backside damage
 control is done) 


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you mean accumulation  (i.e., surface passivation) right?
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what is the rms surface roughness of the back surface?

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This is sometimes called the orange peel (surface under micro-scope looks
like an orange skin). Less than a micron. . .
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 Is that figure larger if you stop at the epi-bulk boundary or if you
 continue even thinner into the epi ?

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good question . . you can't go much beyond the auto substrate doping region
(which is several microns thick typcially) or the global flatness degrades
which is a bigger concern (regions will thin faster than others because of
eddies). 

As far as the orange peel variance I would think it would be the same.
However, this question should be directed to Pauline at SITe who has about 15
years thinning CCDs. Pauline. . .  what do you think?

Jim Janesick


PS. why do you ask this question ..  . are you thinning CCDs?

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 Thanks ...
 
 Zoran >>