Telling it like it is on the inside of production semiconductors as seen at Chipworks

Wednesday, May 4, 2011

Intel Goes Tri-Gate at 22-nm!

In a pair of press and analyst briefings this morning, Mark Bohr and Steve Smith announced that Intel will indeed be using a 3D transistor structure for their 22-nm product, settling one of the big questions about Intel's process development over the last few years - do they stay planar or not? (And, incidentally, settling a bet between me and Scott Thompson - Scott wins!)

The big debate at IEDM last year about advanced CMOS was whether transistor structures would move to a 3D structure (finFET, tri-gate, whatever label you choose), or use ultra-thin SOI layers to attain fully depleted operation. The debate was not resolved - I was definitely left with the impression that the adherents in both camps held to their opinions, which probably means we will have two process groupings, much as we have with the gate-first/gate-last high-k/metal gate (HKMG) structures.

Intel have come down on the side of tri-gate - apparently the decision was taken in 2008, after their researchers had showed that the gate-last HKMG gate structure would work in 3D, and that the planar version could not give enough of a performance boost. So for the last three years they've been developing the process and getting it manufacturable for the production of the Ivybridge product line later this year.

Intel's Research and Development Sequence to Reach the Tri-Gate 22-nm Node

I may have lost the bet about planar, but my gut feel that their HKMG process could be extended to 22-nm seemed to be right, since Mark confirmed that they are using gate-last (replacement gate) technology, with evolutions of existing NMOS and PMOS strain technology. Immersion lithography and double patterning will be used where necessary, and no extra mask layers are needed so the additional cost is only 2 - 3%. And apparently it's scalable to 14 nm!

The schematic below shows a gate formed on three sides of three fins, to give more drive strength than available from one fin:

Schematic of Tri-Gate Across Three Fins (Source - Intel)

When translated to gate-last HKMG, it looks like this in this Intel image from 2007 (the section is through three gates, with three fins buried under oxide running across the field of view):

Gate-Last HKMG Tri-Gate Transistors (Source - Intel)

And now a new image from today's briefing, showing an array of transistors with six fins in the centre, and some with two fins at the top right and bottom left:

Intel Tri-Gate Transistors (with STI and gate mold oxide removed) (Source - Intel)

Clearly this means a whole new set of design and layout paradigms, and we can see evidence here of double patterning using fin and gate masks, with cut masks to define the individual fins and gates.

During the briefings, Mark also scotched the rumour that appeared a few weeks ago about a hybrid process, where the SRAM is tri-gate and other areas are planar - all of the chip area will be tri-gate. In addition a parallel SoC process is being developed so that the Atom line of products can be extended to 22-nm.

For us commentators, going tri-gate was always a possibility for Intel; they have been publishing papers on the topic for almost ten years, with a flurry of them five years ago - here's an image from a press briefing in 2006:

TEM Image of HKMG Tri-Gate Transistor, Sectioned Through the Fin(Source - Intel)

Their R-D-M (Research-Development-Manufacturing) methodology has been well established for quite a while now, and enabled them to keep to their schedule of a new process generation every two years. Based on comments today, we can expect to see 22-nm production in the second half of this year, and product on the shelves in the New Year.

Then we'll see what it really looks like!