By Paula Doe, SEMI
As the rate of traditional scaling slows, the chip sector looks increasingly to materials and design to move forward on multiple paths for multiple applications. Figuring out more effective ways to collaborate across silos will be crucial.
- Paradigm shift requires co-optimization
“Scaling has hit a wall, and there is no longer any single path forward,” noted Larry Clevenger, BEOL Architect and Technology Definition, IBM Research, at the SEMI Strategic Materials Conference 2016 (September 20-21). “The materials set we use in the middle and back end of line is running out of steam. We need new materials and design co-optimization.” He noted EUV would much improve the critical tight pitch areas for the memory and BEOL for 7nm-5nm logic. But reducing the parasitics in the metal interconnect in middle of the line and BEOL will also be critical, with good results demonstrated from new materials like Si:P and Ge:Ga meta-stable alloys, cobalt instead of tungsten, self-forming encapsulation of copper by cobalt, and airgaps, all of which would require optimization of an ecosystem of appropriate cleaning, deposition and wet process technologies for integration. Changing the design to route the critical paths directly up to higher wiring levels where the wires are larger would also help reduce resistance.
“It’s a paradigm shift that what was once a process deviation is now an excursion,” said Archita Sengupta, Intel senior technologist, noting the need for new specialized tools to measure, monitor and control the process to detect ever tinier defects sooner. “We need more proactive cooperation across the supply chain for bottom up control of quality from suppliers.”
Showing impressive examples of imaging and computation enabling doctors to reduce errors in breast cancer detection by 85 percent, and even to operate on a beating heart, using Nvidia GPUs and artificial intelligence, Nvidia’s director of Advanced Technology John Hu noted, “We are at a real inflection point for demand for more compute power, and we can’t get there by just process scaling any more. We are going to have to rely on new architectures to rescue us from the increasingly imperfect reality of materials and processes.”
While almost every speaker stressed the increasing need for the different segments of the supply chain from materials to design to work more closely together to move technology forward along many new paths, the materials suppliers in the audience felt that progress could be better to make this happen. Some audience members talked among themselves of now being invited more often into the fabs to discuss material development, but still not being told much detail about the key target parameters. Material suppliers in the audience raised the issues of the time and expense needed to qualify their second sources for raw materials and precursors, to get the needed environmental certifications, and to find access to the expensive exotic multi-technology metrology tools capable of finding contaminates too small to see with conventional methods, before they could even bring in any potential material to be evaluated for use several years in the future.
Although speakers kept referring to the past Golden Age of Moore’s Law of regular two-year dimensional scaling, before the proliferation of alternatives, Tim Hendry, retiring Intel VP, Fab Materials, pointed out that it hadn’t really seemed like a Golden Age at the time. “As I remember, we thought it was pretty hard back then too.”
- Look to self-aligned and selective processes as scaling boosters
As lithography scaling slows down, new approaches will make creative use of deposition and etch to keep improving pattern resolution. “14nm is a real sweet spot technically for lithography that will be with us for a long time,” noted Anton DeVilliers, Tokyo Electron America director of Patterning Technology, suggesting a toolkit of assorted self-alignment and selective deposition and etch processes likely to see increasing use as resolution boosters as an alternative to pushing the lithography, such as collars at key points to protect the pattern, or self aligned patterning by selective etching.
Adding a protective ALD collar holds a key region open during etch to widen the process window and prevent shorts from process variation in tight pattern areas.
ALD snap collar holds the critical part of M1 pattern open to widen window in LELELE process…
So that overlay variation that would typically create a short…
Instead creates the desired pattern. Source: TEL
Using materials with different etch selectivity for different parts of a pattern, such as for alternate lines, enables the creation of a self aligned pattern at higher resolution than the lithography. Different etch selectivity in alternate metal tracks could also reduce the number of exposure passes and improve overlay tolerance. “For 5nm nanowires, we’ll have to use selective ALD and ALE, controlled by self assembling monolayers,” noted DeVilliers. “We’ve done each of these steps on a tool, but now the challenge is to put them all together.”
- Progress on 3D alternatives
“To maintain the pace of progress we’ll have to change everything—we can’t do it with Moore’s Law,” said Bill Bottoms, chairman and CEO, Third Millennium Test Solutions, updating on the international effort to create a Heterogeneous Integration Roadmap. “Future progress will come from bringing active elements closer together through integration at the system level, with interconnect with photonics and plasmonics.” The aim is to map future needs to better enable precompetitive collaboration. The first edition of the roadmap is now slated to come out in March.
CEA-Leti researchers meanwhile are reporting good progress on lowering the temperatures of the various processes needed to build a second chip directly on top of a first, for monolithic 3D CMOS-on-CMOS integration. Performance of the bottom chip degrades if the process temperatures for the top chip are >500°C, mainly because the NiPt silicide deteriorates, but replacing the NiPt with a more stable NiCo and adding an Si cap looks promising to increase stability. The 8nm active active layer for the top device is bonded atop the bottom device at room temperature and annealed 300C. Nanosecond laser thermal annealing and low temperature solid phase epitaxy regrowth help bring down temperatures for dopant activation. Cycles of deposition and etch replace selective epitaxy for the source and drain, while different precursors reduce process temperatures to 500-550C. “Later this year at IEDM we’ll demonstrate top CMOS made at 500°C with these developments,” said Philippe Rodriguez, CEA-Leti research engineer.
- Get used to the slow growth world
The semiconductor industry will see silicon demand (MSI) pick up from this year’s 0.6 percent increase to ~3.8 percent growth in 2017, and ~6.3 percent in 2018, as some uncertainty about interest rates and government policy in major countries resolves, according to the econometric semiconductor forecast from Hilltop Economics and LINX Consulting. “We got comfortable with 3 percent GDP growth in the world that we sell chips into, but since the 2009 recession we are only seeing about 2.4 percent growth,” said Duncan Meldrum, chief economist, Hilltop Economics. He noted that economists keep saying the world will get back to its regular 3 percent growth next quarter or year, but it hasn’t happened, probably because high government debt levels in most major economies tends to reduce growth by about reduces it. Silicon demand grows a little faster than GDP, but its trends generally track that global growth number more than in the past as the electronics industry matures.
- Wafer level fan out will shake up package materials sector
Now that it appears the 40 to 50 percent improvement in performance in the newest Apple A10 processor is largely from its wafer-level fan out packaging from TSMC, demand for the packaging approach is ramping fast. “This is one of the fastest ramps we’ve seem for a package in a long time,” said TechSearch International president Jan Vardaman. “It’s a very disruptive technology that will have a big impact on the industry.” The thinner, lower-cost packaging approach is also showing up in RF and audio codec chips in mobile phones, with ~2 billion units just in Samsung and Apple phones, potentially bringing big changes to the packaging materials market. Laminate substrate suppliers will see demand plunge, copper post suppliers will see little change, and makers of wafer-level dielectrics could potentially see 3X growth in volume. “But don’t think you’ll see that in revenue, since customers will really beat the prices down.”
And in a final note, the gathered materials sector paused in a moment of silence for Dan Rose, who passed away on September 19. Dan was a well-known market researcher and founder of Rose Associates with a focus on materials market data.