What's inside Applied Materials' flowable CVD tool?
Chip density is a growing problem. Packing, and electrically isolating, 400M transistors on an area the size of a pinhead will eventually require stacking them vertically—e.g., DRAM memory 4F2 buried wordline, NAND flash "skyscrapers," and logic FinFETs. For device architectures, that means taller and narrower structures, different types of surfaces and materials that need to be filled under and around (conventional CVD from the bottom/sides tends to pinch at the top), and within a required thermal budget and at a reasonable complexity and cost.
Applied Materials' answer: a liquid flowable CVD, dubbed Eterna FCVD, that "fills anything" with up to 30:1 aspect ratios. It can fill (full and partial) 5nm geometries with "very little overburden," and also around and underneath things like 10nm overhangs, they claim.
The other benefit of the new technology is elimination of carbon, which hampers transistor isolation and causes voltage shifts and leakage. Current spin-on dielectric (SOD) technology requires multiple removal steps to address this, and at anneal temperatures that become problematic when dealing with complex device structures. (Ed Korczynski, former SST senior technical editor and current blogosphere denizen at Betasights.net, says AMAT execs confirm the FCVD precursor is carbon-free from the start, and "never sees the plasma.") FCVD, they claim, translates into a 50% lower integrated cost vs. SOD, and up to a day shorter cycle time, though that will vary by integration scheme and by fab/customer.
Other details about the tool, gleaned from AMAT's presentation and Q&A:
• The technology relies on a "unique" chamber design that allows the precursor to be introduced and deposited in a certain way (and is exclusive to AMAT). Little was revealed about the actual inner workings of the tool, except that much of the benefit is in the hardware. They acknowledged that the precursor does in fact enter the chamber as a liquid, broken up in the top part of the chamber.
|Flowable CVD technology fills any structure, including high aspect ratio and reentrant features, with high-purity oxide. The true bottom-up deposition mechanism allows controllable film thickness, allowing both very thin layers and partial fill. (Source: Applied Materials)|
• There is no separate licensing fee for the precursor (>30 precursors were screened to get the final one), which can be obtained separately, mostly sourced from one supplier. Bill McClintock, VP/GM of the company's dielectric systems and CMP unit, added that the precursor costs "more than 3× less" than what is used with SOD—reminding that cost should include not only how much chemical is used in multiple-step SOD, but also what is not used (e.g. lost off the wafer edges and wasted).
• Chipmakers probably need a couple of these new tools per layer—a minimum of two layers at 2Xnm node, and as many as eight or more in forthcoming vertical structures, according to McClintock. Throughput is "moderate," comparable to the company's HARP tools. However, both he and Randhir Thakur, EVP/GM of AMAT's silicon systems group, emphasized that throughput is the flip side of the coin from cost, pointing to SOD's extra post-treatment steps.
• Filling gaps with a flowable liquid precursor which reacts during deposition to form the film isn't necessarily a new concept. Trikon, for example, "did this a few years back with TEOS and hydrogen peroxide," Gartner's Dean Freeman reminded SST. Thakur noted earlier efforts ran into problems with hardware (how to bring the precursor into the system) and precursor quality (e.g. carbon-free). And removing the carbon ends up improving electrical performance and yields. Thakur indicated isolation and defects that show up in second-order yield problems in chips, "some of those electrical issues are not there" with this flowable CVD approach.
• Applied claims to have "every major memory customer" (it counts five) and one logic firm using the tool, with another logic customer awaiting shipment in 4Q and a third currently in demos. The company projects a $400M market, but is banking that customers will find applications for this FCVD technology beyond 3D structures in new areas: e.g., surface defect masking (where SOD films would be far too thick), planarizing with capping films (for small openings at the top of devices), possibly for some areas that require an ALD-like film (though probably not ALD itself, where films are too thin for this type of tool), or even gapfill for aluminum interconnects. And AMAT expects that the technology will find traction at trailing nodes as well—e.g. qualified at 28nm but then later put into 4Xnm manufacturing, where it could also simplify gapfilling and could save several dollars per wafer. — J.M.