By David Lammers

Ever since Intel uncloaked its tri-gate transistor a year ago, technology watchers have had to make do with the few images Intel released at that time.

Now, the long-awaited Chipworks images are on-line, following the company’s initial teardown report (Intel’s 22nm tri-gate transistors exposed) posted Monday (April 23). One initial surprise was the shape of the Intel fin, rounded on top and tapered or sloped on the sides.

Dick James

Chipworks senior technology analyst (and chief  blogger) Dick James said the 22nm teardown process got started when he saw a review of an Intel 22nm server chip on the Anandtech site, which included a helpful link to a site in Hong Kong which had the server processors for sale, even though the server MPUs are not officially on sale until June.

Chipworks (Ottawa) ordered half a dozen of the Intel Xeon E3-1230V2 Server CPUs, at $300 per processor, and they arrived on April 1. Though Chipworks has been burned before with counterfeit die inside packages with new markings, the 22nm chips from Tao Bao in Hong Kong turned out to be genuine, and Chipworks went back and bought more.

Fortunately, Chipworks had upgraded its transmission electron microscope (TEM) in January, replacing an out-of-date model with an FEI Osiris TEM, a much more automated system. The new TEM  pumps down to a vacuum state more quickly, and alignment checking also is automated.

The Osiris TEM can do 400,000-times magnification. However, the microscope requires a sample thickness of about 80nm, which means that the images of the Intel transistors show more than is sometimes optimum: with a fin shown next to a gate, for example. “While the fin may be only 5-15nm wide, the sample has to be 80nm thick to get it in to the TEM. That increases the difficult of imaging. You are always seeing a gate and the fin, for example,” James said.

Looking at finFETs takes some getting used to, compared with planar transistors. “You definitely have got to be able to think in 3D. With a regular transistor I can explain how it works with one cross section. With finFETs, I need one image to show the shape of the fin, and another to show the shape of the gate, in right angles to each other. It is a bit more complicated from that point of view,” said James, who has worked for 17 years at Chipworks after earlier employment at semiconductor fabs in his native England.

Another complication is that the one-to-one ratio between structures and transistors doesn’t apply. One transistor can have multiple fins — six or more — while one fin can have multiple transistors.

Since each fin is a defined height and width, designers use quantized fins to create a wider PMOS, for example. “It is a whole different ballgame. These are quantized transistors, so the designers have to think in multiples of a single unit,” James said.

Designers must learn to use quantized gates with finFETs. The SRAM shown here has s a 6-transistor SRAM cell; the transistors marked T2 and T5 use two fins, while the others have one fin. T2 and T5 have gates twice as wide as T1, T3, T4, and T6. (Source: Chipworks)

The Virtues of a Tapered Fin

The Chipworks images show an Intel transistor with a rounded top and tapered, sloping sides. James said that was an interesting and surprising early observation, because many of the photos of finFETs shown in recent years at IEDM and other conferences — by Sematech, Imec, TSMC, and others — all have shown a vertical fin. Intel’s own schematic diagrams show an idealized structure with straight sides.

A lattice image of the NMOS fin structure shows a rounded fin with tapered sides. (Source: Chipworks)

James speculated that Intel’s tapered fin is easier to manufacture, and the rounded top evens out the electric field at the top of the fin. “Any pointed surface has a higher electric field than a flat surface, so the rounded structure may even out the electric field between the fin and the gate. Our speculation about why it is rounded relates to the fact that if the transistor had square corners on the fin, it would crank up the electric field and make the device less reliable.”

Also, etching straight walls is difficult, making it likely that the etching steps are probably easier with a tapered fin. James said flash memories also often have rounded corners in order to avoid damaging the gate dielectric on the memory cell.

The gate oxide and metal gate are much the same as Intel’s earlier planar transistor, and the PMOS stressing mechanisms also are similar. Intel appears to have changed the metal fill at the center of the gate, using tungsten instead of aluminum and titanium aluminum. James said they feel fairly confident of that conclusion because the “very dark” area appears to be the same color as the W contacts.

On the other hand, Chipworks at this point has “no idea what the stress mechanisms for NMOS are.” Intel is no longer using the nitride stressors it employed at the 90nm and 65nm nodes, because there is not enough room around the gate. At 45nm, Intel used a mixture of metals on the gate to put tensile stress on the channel. “That may be possible (with tri-gate), but it doesn’t show. If there is stress in the NMOS, it is different from the 32nm approach,” he said.

TEM image shows the transition between PMOS and NMOS gates. The mottled TiN layer is in the PMOS, but not the NMOS. Some epitaxial SiGe can be seen on the source/drain of the PMOS fin. (Source: Chipworks)

I asked James if Intel’s technologists cooperate with Chipworks as it struggles to figure out what the images show. He said he posts the blogs first, and hopes for some reaction steering him in the right direction later, if the initial conclusions are faulty.

“Sometimes one or another person from Intel will get back to me, and say, ‘I can’t tell you where you were wrong, but this is not quite right. And they are fairly cordial when I meet them at IEDM. When I am chatting with them, they might say ‘You are pretty well right 90 percent of the time,’ which I take as a compliment since we are groping in the dark on something like this.”

By David Lammers

The quality of life has improved at the GlobalFoundries Fab 8 here in upstate New York. Sure, people here are breathing easier now that yields are up at the company’s fab in Dresden, Germany, and winter has turned to a luscious spring here at Malta, located north of Albany.

The gut-level joy comes because the fab’s new cafeteria opened on Monday, April 16. I arrived the next day to do some interviews about how the fab is staffing up, getting ready for volume production later this year.

When time came for lunch, we made our way down to the spanking-new cafeteria. I saw a sign for sushi, and went over there, thinking there might be some plastic packages of pre-made sushi, the kind you can pick up at the grocery store when you are in a hurry.

Instead, there was a real Japanese sushi chef at work, knife in hand, who began making the two rolls I ordered. Two other customers soon arrived, as I heard a Japanese man and woman behind me speaking in anticipation about the various kinds of sushi available. They were in the fab to install equipment, and had discovered a little island of gastronomic home.

The GlobalFoundries fab, like most semiconductor operations, is an international place, with people from 30 countries among the 1,300 (and growing) employees. Judging by the visitor’s log in the lobby, there is a steady stream of visiting contractors who hail from abroad. Half of the GlobalFoundries employees come from outside the area.

These workers from abroad have raised the standards for the Fab 8 cafeteria, said Angelo Mazzone, the CEO of a company which runs five cafeterias and six restaurants in the area. “We have a lot of people here from Singapore and Dresden, and these people from overseas know so much about food,” Mazzone said.

Each food station has a bona fide chef, and there is a full-time coffee barista who offers drinks made from beans sourced from around the world. “The people from Dresden like real strong coffee,” Mazzone noted.

Angelo Mazzone (left) with good customer Travis Bullard at the GlobalFoundries Fab 8 cafeteria.

One of his challenges was to develop a base of suppliers able to supply the variety of foods offered at the cafeteria. One objective is to offer a complete meal for $6, but most people spend between $7 and $10 on lunch.

Travis Bullard, who handles corporate public relations at the Malta site, said GlobalFoundries is part of a bigger trend among high-tech companies offering good food to their workers. Before coming to Malta, Bullard worked in Austin at the new Longhorn campus of AMD, and he said his former employer also has a deluxe cafeteria. Google and Apple apparently are at the forefront of a trend to offer healthy food, either for free or for very low prices.

At Malta, the goal is for the cafeteria to pay for itself, Mazzone said. Right now, the cafeteria is open from 5:30 a.m. to 7 p.m. “It may be open 24/7 at some point, but that comes at a big cost,” he noted. The fab is in the midst of a beautiful forest, well away from any restaurants. A round-the-clock food supply will be a necessity once volume production begins later this year.

GlobalFoundries is ahead of schedule on its hiring plans, Bullard said, and expects to have 1,600 working at the fab in a few months, up from 1,300 now. Before the cafeteria opened, there were more than a thousand construction workers who were fed well from a big tent at the construction site. Mazzone converted a shipping container, the kind which moves cargo on ships, into an outdoor kitchen to supply the fab builders with cooked food. That worked well, but food brought in can’t compete with a real kitchen.

Bullard said the cafeteria is a place where the workers can come together and talk. “People bump into each other in the cafeteria and start talking about things they are working on. We never had that before this place opened. It’s an intangible benefit.”

An army marches on its stomach, and foundries are no different. Packing a lunch day after day can be a drag, and so it is no wonder that the GlobalFoundries workers were smiling broadly last week. The sushi is excellent.