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Magic Mailing List |
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From: Jeff Sondeen (sondeen AT ISI DOT EDU) Date: Fri Sep 05 2003 - 14:30:09 EDT
Philippe Pouliquen writes: > Tim, > > > I suggest that you write CIF or GDS, then read it back in, and confirm > > that the auto-generated wells comply with the DRC rules (they should). > > I don't think that the auto-generated wells are guaranteed to pass DRC. > Maybe Jeff Sondeen can confirm this, but I think that when you have two N > wells that are near one-another but not fully aligned, so that the overlap > is less than the minimum well width, the bloat-shrink operation that is > supposed to fill in the gap actually creates a narrow bridge. yeah this is especially true for 'cater-corner' cases. historically it has been ignored, and your chip probably isn't at too much risk in the case of selects (which also have the problem), but i think it's safest to always draw both wells (since capactitance extraction (ie. shielding) only works right if both wells are drawn anyway). the .cifcheck techfiles use the (very slow) cif checking rules to check for this, but the solution to any problems it shows is to draw the wells. so just draw them! i think the original question also wondered about the risk that layout conforming to old rules would have if fabbed nowadays after rules have changed. the answer to that is, it depends, but it's quite possible that results will be fatal (0 yield) with no recourse (since rules were violated). it's even possible that the current techfiles (getting dated now) aren't up-to-date... i hope to check them soon. /jeff > > I don't know of any solution to this problem, because widening the bridge > can cause a DRV to neighboring N diffusion. The design rules would need > to be modified to preclude the N diffusion from being too close to the > non-existent N well bridge, and then the CIF rules would need to be > modified to create a wide-enough bridge. > > Here is an example magic file using the SCMOS design rules (the layout if > for Magic 6) which exemplifies the problem: > > magic > tech scmos > timestamp 1062782013 > << ndiffusion >> > rect 11 19 15 23 > rect 19 2 23 6 > << pdiffusion >> > rect 25 16 29 20 > rect 5 5 9 9 > << end >> > > Just write CIF and read it back in. > > Philippe >
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