May 28, 2014

KLA-Tencor’s New Reticle Inspector

posted by Bryon Moyer

Seems like no aspect of IC design and production escapes the need for All Things to Get Harder and Harder, requiring ever-better solutions. Today we look at reticle inspection, and, in particular, at KLA-Tencor efforts to adapt their Teron system, originally intended for mask shop use, to the needs of production fabs. The idea is that, when new reticles come into the fab, they need to be inspected as a basic QC step. And, after 300-600 or so uses, they need to be re-qualified to make sure that acquired defects aren’t reducing die yield.

One practical consideration is floorspace. The volume of reticles is increasing due, for example, to multiple patterning, which multiplies the number of reticles for some layers. 14-nm flows literally double the number of reticles as compared to 20 nm. No one wants to add more machines to handle the extra load; fab managers would rather increase the processing capabilities of the “space” currently allocated to inspection, placing an extra burden on the equipment.

So what kinds of defects are the inspection systems looking for? There are several, but haze seems to be a big one. Haze represents the slow deposition of chemicals – presumably from various other processing steps – onto the reticle. Obviously the best solution is to eliminate the sources of the haze, and progress has been made on that, but some remains – and, of course, it’s now harder to detect.

For one thing, it used to predominate in open spaces, where it’s easier to pick out. Now it tends to collect along the sides of features, making it harder to see. Also, because there’s less haze, you’re looking for smaller, more isolated defects than before, when a cloud-like collection would be more evident. The presence of optical proximity correction (OPC) features makes this harder, since they can be hard to distinguish from defects.

Other things to look for include evidence of the chrome, which makes up the actual pattern, “migrating” – narrowing or flattening after cleaning, as well as simple “fall-on” defects that won’t fall off.

So how do you go about finding these things? There are a number of techniques, some of which work and some of which no longer do. In the end, a combination works best.

  • Simple optical inspection can be used, but it has to be “actinic” – that is, use the same wavelength of light that will be used during wafer patterning: 193 nm.
  • For repeating patterns, it used to be helpful to compare neighboring versions of the same feature. But that is less useful today because, even though the original layout of each cell may be the same, the OPC features may be different, so the cells are no longer identical on the reticle.
  • Production reticles often have more than one die instance, so it can be useful to compare neighboring dice on the reticle. But for leading-edge processes, single-die reticles are more common – as are shuttle wafer reticles, which have multiple dissimilar dice that can’t be compared. So this technique isn’t so useful anymore.
  • Modeling can help. KLA-Tencor generates models offline and uses them in real time to compare to what’s actually being seen.
  • KLA-Tencor also uses a technique that they consider to be one of their differentiating strengths: a “difference image.” They capture images of how light is transmitted and reflected through the reticle. From each of those, they calculate what the other ought to look like. So, for instance, from the reflected image, they calculate what the transmitted image would be in the absence of any defects. And vice versa. They can then subtract the calculated versions from the observed versions – calculated transmitted vs. observed transmitted, and likewise for reflected – and use the differences to pinpoint defects. This is a compute-intensive operation that places a heavy load on the inspection equipment.

The processing power they’ve built into their just-announced Teron SL650 is intended to handle the inspection complexity with a high signal-to-noise ratio while still accommodating the increased number of reticles it needs to handle.

Figure_cr-red.jpg

(Image courtesy KLA-Tencor)

You can find more on the new system in their announcement.

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May 22, 2014

Wireless Power and Heating

posted by Bryon Moyer

We covered wireless power before, and one of the points of differentiation was that of inadvertent heating of nearby items. With systems using the lower 200-kHz frequency range, nearby largish metal items like coins and keys can heat up. The systems themselves are designed to detect this and shut the charger down, which addresses the safety issue. It’s just a bother if you think your phone is being charged when in fact it isn’t due to something else around there.

But then it was pointed out that heating can theoretically be an issue for any frequency; it’s just a matter of the thickness of the material and the frequency used. Higher frequencies would create heating in thinner objects; lower frequencies would heat thicker objects. Which means that the 6.78-MHz range of charging can also cause heating for some thinner range of metallic items.

So in the MHz range, keys and coins are fine; is there anything else that might accidentally come in range? Turns out there is one thing: CDs, which have a very thin foil in them (standard kitchen-grade aluminum foil is too thick). And, confirming with WiTricity, yes, they can actually heat up. (And system designers can detect the issue and shut down, just as the lower-frequency systems do. Which means the phone-didn’t-charge bother could happen there too). It could probably be argued that it’s less likely for a CD to be in the way (and, one might ask, who still uses CDs, anyway?) But, they were eager to point out, in cases where there was heating, they had never seen an instance of a CD actually losing any data.

That’s all well and good, at least until I started extrapolating the Cota technology (which we covered today), which uses RF at 2.4 GHz. If the MHz range affects CDs, it’s pretty much impossible to imagine something so thin that the GHz system would affect it. Just following that line of thought, I then realized that integrated circuits have extremely thin films of metals in them. Could this be a problem?

I asked this of Ossia, and they reminded me that the signal power being delivered to charge a phone is no higher than what the phone itself transmits. So if the phone isn’t heating its own metal, then the charging shouldn’t either.

Bear in mind that neither of us did the calculation to see if those IC thin films fall into a range that would even theoretically be affected; the power argument makes it an academic calculation. It also occurs to me on further hindsight that this isn’t resonant charging; it is, as PowerByProxi pointed out, more like harvesting RF for energy. So that might change the entire scenario.

So, in summary:

  • 200-kHZ resonant systems can heat objects like keys and coins; systems can detect and shut down for safety
  • 6.78-MHz resonant systems can heat CDs; systems can detect and shut down for safety
  • 2.4 GHz RF systems should have no heating issues.
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May 20, 2014

Who Uses Power-Over-Ethernet?

posted by Bryon Moyer

Maxim recently released a reference board (called Pasadena) that implements power-over-Ethernet (PoE). As we were discussing it, I inquired about who is really using PoE. I mean, I’m familiar with it, and yet I hardly ever hear anything about it actually being used.

Figure.jpg

(Image courtesy Maxim)

They pointed out three specific target markets:

  • Wireless routers
  • Cameras
  • Point-of-sale (PoS… no, not that PoS) terminals. Cash registers, for most of us.

The top two share characteristics in that they’re likely to be positioned in some inconvenient place. PoS terminals… not so much. But they all a) need power and b) send data. So why not do both on the same wire?

This makes perfect sense, by definition, for a wireless access point. That device has no choice but to have a wired connection into the network. That’s what it does – aggregate wireless onto a wire. So might as well bring power in as well on that same wire if it can handle the load.

For the other two, the calculus depends on whether communication is wireless or not. Cameras have a lot of data to send, so a wire might make sense. But if it’s wireless, then it will still need a wire for power unless it can harvest (or take advantage of distance wireless power, which we’ll talk about soon… not clear it can provide enough power for this though). So, assuming PoE can provide the power, you can either use wired-communication-and-power or wired power/wireless communication. It’s a single wire either way.

Portable PoS terminals are typically wireless, but they don’t count because they’re also battery-powered; they get zero wires. So for fixed PoS terminals, you’ll always need at least one wire. If you’re using wired Ethernet, then you’ll need that – might as well bring power along for the ride (again, if there’s enough juice).

Part of this is simply the logic that one wire is easier than two. While true, that understates the issue, because the two wires are not the same. Stringing Ethernet comes with far fewer code requirements than stringing 120 (or 240) V. One you can literally do yourself; the other requires an electrician. (Seriously, I know you’re a smart guy… hire an electrician anyway.)

All of this said, I certainly don’t have visibility into a lot of PoE actually being deployed. Feel free to comment below either if you or someone you know is deploying it or if there’s some other barrier that’s getting in the way.

There’s more info on the Pasadena board here.

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