Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!wuarchive!texbell!vector!chip
From: chip@vector.Dallas.TX.US (Chip Rosenthal)
Newsgroups: comp.arch
Subject: Re: Claimed bug in 80286
Message-ID: <729@vector.Dallas.TX.US>
Date: 3 Sep 89 05:16:37 GMT
References: <1989Aug13.023601.594@utzoo.uucp> <310@hitech.ht.oz> <21352@cup.portal.com> <1877@brwa.inmos.co.uk> <609@unicads.UUCP> <1989Aug27.192947.888@ziebmef.mef.org>
Reply-To: chip@vector.Dallas.TX.US (Chip Rosenthal)
Organization: Dallas Semiconductor
Lines: 30

mcp@ziebmef.mef.org (Colin Plumb) writes:
>>> The 386 and beyond have both device type and mask stepping numbers
>> Do you mean the x,y of the individual die on the wafer!?!?!?  Yikes!
>
>No, this has nothing to do with stepper motors.

Not only that, but his misconception had nothing to do with stepper motors
either.

Photolithogrophy is often done with a mask which contains the image of
one die or a small number of dice, and this mask is stepped across the
wafer exposing the wafer one part at a time.  In the old days (and sometimes
still today), the mask will contain the image of a layer for the entire
wafer, and hence the wafer is exposed all at once.

One nice thing about step and repeat is you can get much better imaging,
i.e. by using a 10x reticle.  With projection, you generally use 1x.
After all, a 60 inch mask to make a 6" wafer would be a bit *ahem*
unwieldy.  On the other hand, a defect on a step-and-repeat mask is
catastrophic -- one bit of poop and you've blown the entire run.

In the old days, it wasn't always so obvious when a mask had a problem.
The technique was to throw a wafer on the xerox machine and make a
transparency.  You then place every wafer in the batch under the transparency
one at a time, and mark off the locations of good dice.  The locations
left without a mark were probably due to mask defects.

-- 
Chip Rosenthal / chip@vector.Dallas.TX.US / Dallas Semiconductor / 214-450-5337
"I wish you'd put that starvation box down and go to bed" - Albert Collins' Mom