1.  Field of the Invention
The present invention relates to the fabrication of charge coupled imagers, and more particularly to an improved method for etch thinning silicon devices. 
2.  Description of the Prior Art
It has been proposed to make charged coupled imagers (CCI) with the pixel area thinned to nominally 10 microns.  This is done so that photons may enter the device through the rear unencumbered, rather than through the pixel interconnects on the front side.  The processing involves fabricating the CCI in a p-type epi-layer which is on a p.sup.+ substrate (&lt;100&gt;orientation, 10 to 20 mils thick).  After CCI fabrication is completed device thinning is employed.  One thinning technique is to use a buried p.sup.++ layer as a virtual etch stop for KOH, the etchant.  This technique, however, is not yet a practical art.  Another technique uses a 1:3:10 etch (HF:HNO.sub.3 :Acetic), but drips H.sub.2 O.sub.2 into the etchant.  This tends to passivate the silicon and stop the etching too soon.