Happy New Year!!

Congrats!

But isn't this a fairly routine thing for you? How often are revisions necessary after prototyping? Does the layout often need revising when the circuit is okay?

Well done Jim.

Out of curiosity, how does an IC designer fault-find when an IC doesn't work? I guess you can't stick your scope probes in different parts of the circuit to see what's happening like you can with a PCB.

Tim

Usually. But I've had a recent spate of two-turners (*). I thought I was losing my touch.

(*) Mostly due to customers not really specifying what they wanted... but *I* should have more firmly enforced specification reviews. I've now made that a company policy with specifications more thoroughly spelled out and rigorous sign-off procedures, with penalties for specification changes after first silicon.

...Jim Thompson

Tim,

IC's are scoped out much like PCB's. One method is with a microprober. There the die is placed on a 3D micro-positioning stage under an optical microscope and oscilloscope probes as tiny wires are touched to the traces. This method losses steam with about a 1 micron feature size. The next method is to use a scanning electron microscope to image the die and then capture the voltage waveforms with a phenomenon called voltage contrasting and boxcar integration. This works well for repetitive waveforms and has the advantage that it doesn't load the circuit like a mechanical probe capacitance, so rise times of

Actually you can (sometimes, if you provide test pads that are on the top metal layer). They're called pico-probes. Also I tend to make up a test metal pattern that allows checking cells out individually for complex chips.

...Jim Thompson

I spent much of December probing a 0.18u 4-level-metal GHz-frequency chip. It wasn't as painful as I thought it might be: probe points were added using FIB (focused ion beam), and picoprobes can handle GHz signals with no problem these days. FIB is great, but requires ~0.5u clearance around the point on a wire where you want to make contact.

-- Mike --

Mike,

Yes! I'm familiar with the techniques, I've been involved in design both e-beam probes and FIB machines. For the original poster, putting test points on IC's either as part of initial design for testability or forensically by FIB is analogous to putting test points on PCB's. Like I said, you need something of the order of 1um to mechanically probe. Also, e-beam probing not only has response way over 10GHz, it does it with essentially no loading of the circuit. Capacitive loading is *so* low, you have some capability to probe traces buried under Si02 passivation or even a Nitride cap by measuring the voltage fluctuations capacitively coupled to the top surface of passivation. The probe capacitive loading of an e-beam robe is even a tiny fraction of that capacitance.

--Mike

I worked on a couple of E-beam testers at Cambridge Instruments from 1982 to

We never got the stroboscopic pulse width below 500psec, and even getting there was sort of interesting - the electrons are only travel at about 10% of the speed of light in the sort of low voltage column you use for voltage contrast, so the beam-blanking electrodes have to be shorter than 15mm (or some kind of travelling wave structure) which can be tricky. I got one of my (two) patents out of that.

With that sort of narrow pulse, you are often only letting through one electron per pulse or less (not even one electron on some pulses), which makes it rather slow to get a decent image/waveform - a high-brightness source would have helped. We used lanthenum boride sources - a hot field emission source would have been brighter, and probably sufficiently stable for the job, but Cambridge Instruments didn't have access to a suitable source at the time.

Fun stuff.

----- Bill Sloman, Nijmegen

Bill,

My own association was with the Fairchild e-beam group has had been purchased by Schlumberger. I wrote the charged-particle optic simulator, designed some of the microscope objective/spectrometers and designed some beam deflection electronics.

Yes., a LAB6 source isn't bright enough for this. We used a TEM in the released product.

--Mike

Thanks for the info all. Most interesting.

Tim

Then we probably have a common acquaintance in Neil Richardson.

Graham Plows' firm Lintech sold the first commercial electron beam tester as an add-on unit, back around 1982, and my first job at Cambridge Instrunments was getting it working on a couple of Cambridge Instruments electron microscopes - not any easy task, because Graham Plows had a salesman's approach to development, which was to maximise the number of features on his system, rather than spending more time on a smaller number of features that would work reliably.

Neil Richardson was his in-house electronic engineer at the time, and I had some contact with him before he took one of the early units off to Fairchild in California, to get it working and train the people who were going to use it. Effectively, he never came back, and Graham had to hire himself another electronic engineer.

With Graham's example in front of him, Neil did a much better job on the Fairchild-Schlumberger system, and once their unit was on the market, Graham never sold another machine, and ended up closing down Lintech in 1988, and coming to work at Cambridge Instruments as Technical Director (and my boss), where we built a rather better machine than Schlumberger's, which got canned after we'd got it to the stage of a fully working prototype, in part because Graham had resigned.

Interesting story, containing many libellous details only availalbe by e-mail.

We were looking at a hot field emission source, and second column for ion-milling and tungsten deposition, when the EBT2000 project got canned.

The EBT2000 had a digital data acquisition system which allowd us to sample stroboscopicly at close to 12MHz (it should have been 25MHz) independent of the repetition rate of the waveform we were looking at

- which gave the LaB6 source a rather higher effective brightness than it had in the then competing machines.

------ Bill Sloman, Nijmegen

Bill,

Yep. Neil's vision of an e-beam probe did extremely well. As I recall, it had 98% percent market share. Our group was featured on the front cover the Schlumberger annual report one year. I always had a very high regard for him. He moved on from the e-beam group to go to New York to a position something like Grand Chief Technical Executive Adviser or some other wizard-type title of Schlumberger. Then he left that to head up a critical dimension group at KLA, or something else even more executive. There was legal action to prevent him from hiring too many people away from Schlumberger. Myself, as the person who wrote the simulator and did the later optic design Schlumberger make a stink. In the end, I left to write bigger and better simulators and never looked back.

--Mike