Samsung gave the first detailed look at its long-awaited 7nm process at the VLSI Symposia in Honolulu last month at a press conference. The talk was especially newsworthy because Samsung is likely to be the first to introduce a new form of lithography, known as EUV because it uses extreme ultra-violet light, that has been in development for some 30 years. Chipmakers currently rely on lithography tools from ASML or Nikon with an argon fluoride (ArF) excimer laser that produces deep ultra-violet light with a wavelength of 193nm. These scanners also use a technique called immersion lithography to enhance the resolution, but they still can’t pattern critical features at the most advanced nodes without complex and costly multi-patterning steps. The introduction of ASML’s EUV lithography, which uses a completely different laser-produced plasma to generate 13.5nm light, provides several potential advantages.
First, it enables accurate patterning of much smaller features to extend scaling. Samsung’s 7nm process has a 27nm fin pitch and a 54nm gate pitch, which results in the smallest FinFET transistors reported to date. It also has the smallest high-density SRAM cell size at 0.0262 square microns. The overall result is a 40 percent shrink in comparison with its current 10nm process used to manufacture Qualcomm’s Snapdragon 845 and Samsung’s own Exynos 9810.
Second, the use of EUV results in better pattern fidelity and less variability at these dimensions. in other words, what you print, is what you get. Samsung emphasized that the 70 percent better pattern fidelity versus current 193nm ArF immersion scanner with multi-patterning provides a big advantage when ramping advanced logic to manufacturable yields.
Samsung produced 256Mb high-density SRAM test chips using the 7nm platform and achieved yields of more than 50% with good operation. The company also produced a 7nm application processor with a quad-core CPU, six-core GPU and SRAM caches that was fully operational. The 7nm EUV technolgy will deliver 20-30 percent higher transistor performance and use 30-50% lower power–an improvement over the early 7nm EUV test results that Samsung presented at last year’s conference in Kyoto.
At its annual Foundry Forum last month, Samsung said it was on track to start risk production of 7nm later this year. Competitors such as Intel are still wrestling with yields for their 10nm technology and now expects to start production of mainstream processors sometime in 2019. The node names are misleading and Intel’s 10nm process, which uses ArF immersion with self-aligned quadruple patterning, is similar to the foundries’ 7nm nodes. The 10nm process has a fin pitch of 34nm and gate pitch of 54nm, and a SRAM cell size of 0.0312 square microns. Intel is also working on EUV but has not said when it will introduce it in volume manufacturing.