nickds1

TLV Die record - how is it set?

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On some series of the MSP430, as we all know, there is a chip-series-unique serial number that can made from the lot/wafer ID plus the die X & Y positions - a total of 8 bytes.

 

How are the X & Y positions & lot/wafer ID (and the other die-specific data) changed for each die - the masks can't be changed easily, so I would assume that some sort of fusible link was used that is programmed in after testing and before its sawn into individual die... are they fusible links or some other mechanism? e.g. the DS2401 uses a laser-programmed ROM.... 

 

Thanks

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These are just guesses, I'd have thought the XY position would be OK if there's one mask for the whole wafer (with a repeated and almost identical section for each IC). Maybe there's a second overlaid mask for the wafer ID.

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I agree with Fred, the whole wafer would be 1 mask.

 

The wafer ID might actually be OTP memory segment? That is programmed during die testing. Since a lot of the other TLV segment values differ for each die. Calibration constants etc.

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Normally, wafers like this are stepped as the imagers can't maintain the super-fine focus over the whole wafer (this is certainly the case for fine-resolution chips such as modern CPUs).

 

The wafer is stepped so that each die is imaged in turn - the tables cost an absolute fortune as they have to have phenomenal repeatability and the design of the lens is an enormously specialised art - only a few people in the world do it. 

 

Quoting a friend in another forum (who is a lens designer for these machines):

 

 

 ICs are produced by depositing layers of material onto a silicon substrate, coating it with photo-resist, exposing the resist in a thing like a glorified slide projector, then developing it and etching away the original material (or implanting the whole thing in an ion implanter to dope the exposed area of silicon). Anyone who's had a go at making their own PCBs will understand the principal. It's the detail that's astonishing. First of all, as mentioned above, the smallest feature printed on the silicon can be as little as 40nm across. Lets get that in perspective. A human hair (the universal indicator of smallness in the same way that football pitches and double-decker buses are the universal bigness indicators) is about 80 microns in diameter, so one micron is one 80th of a hair. 40nm is four hundredths of one micron, so about 1/2000th of a hair. Features that small have to be printed with perfect definition across a field up to 30mm square. Since the silicon substrate (or wafer, as they're known) we're talking about is up to 300mm in diameter, a grid of exposures is made, with the wafer being moved on a stage under the lensfrom step to step (hence stepper) until the whole wafer is covered. 

That's the easy bit. 

Chips are made up from up to thirty layers of material, each one with its own pattern, which of course has to be aligned to the one below to an accuracy of about .01 microns. Think about that. The wafer is 12" in diameter, and is sitting on a stage made of quartz about 15mm thick. That in turn sits on piezo feet that keep the image in focus (depth of field is around 1 micron). This whole assembly weighs about thirty kilos, and has to be aligned under the lens, focussed, exposed, then moved to the next image, aligned again to .01 micron, focussed and exposed in a cycle that takes around one second. To achieve this, the stage sits on an air cushion on top of a lump of granite that weighs around half a ton, and is driven in x and y by a couple of hefty great linear motors, position being measured by laser interferometers. This one-second cycle covers a wafer in about thirty five shots, so a wafer goes through in about 45 seconds, hour after hour, day after day. Astonishing.
tripwire likes this

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