Contamination, shortages become bigger worries at advanced nodes.
In the grand scheme of the semiconductor supply chain, electronic gases are something most engineers and scientists never think about. Behind the gleaming machinery and brightly labeled tubes, however, these gases allow wafers to be etched, kept at optimum temperatures, and prepared for the application of thin films.
Electronic gases are remarkably well managed in high-volume fabs, which is a good thing. Many are caustic, highly flammable, and often dangerous to human health. The fact that no one can recall any major accidents involving these gases speaks volumes about just how finely tuned these processes have become. But as chips become more complex and difficult to manufacture, gases are being used in greater volumes—and they’re becoming more problematic.
To put this in perspective, market researcher Techcet expects the electronic gases market to grow 6.2% to $3.72 billion. That’s up from $3.5 billion in 2014, which saw a 5.8% increase from the prior year. Specialty gases, meanwhile, are projected to grow 6.5% for a total of $2.4 billion, while bulk gases will grow 5.8% to $1.3 billion
This represents a significant part of the semiconductor supply chain, and its importance is growing on many fronts. Multi-patterning, for example, requires more electronic gases, and shortages that are beginning to pop up in multiple areas could threaten volume production at the most advanced nodes.
“With multi-patterning and lithography, there are more steps, more materials, and there is a non-linear increase in gases,” said Anish Tolia, vice president of global marketing at Linde Electronics. “This means more specialty gases, such as laser gas mixes and etch gases.”
Supplies of some of these gases are limited. Some are naturally occurring. Others are manufactured in limited supplies using very expensive processes.
“There may be only one or two places in the world that produce them,” said Tolia. “Germane gas (GeH^4) is only available in a few places in the world. With helium, the United States controls a good chunk of that. That comes from natural gas, but all natural gas does not contain helium. They process that in Qatar along with natural gas, and in Darwin, Australia and Russia. But it is not a renewable resource, so there is a lot of attention on recyclable systems.”
Germane gas, which is used in thin film deposition, is produced in China and the Ukraine.
Helium is used much more broadly as a coolant in a variety of processes. In 2013, when there was talk of the U.S. government shuttering its National Helium Reserve, and cutting off 35% of the world’s helium supply, it set off a panic that sent helium prices soaring. The Helium Reserve had been created in 1925 to supply helium for airships, and in the 1950s it began use as an industrial coolant, but the facility has been in debt since the 1990s. A bill passed by Congress in 2013 postponed that problem, with the U.S. government continuing to sell off cheap helium and agreeing to auction off the gas over the next decade, but that supply eventually will run out.
Supply is a big issue for other gases, as well. Techcet noted that supply and demand issues will affect nitrogen trifluoride and xenon, both of which are used in wafer etching; tungsten hexafluoride, used for chemical vapor deposition; and neon, which is used in excimer laser gas mixtures as a buffer for Argon and Krypton.
As the demand for these gases increases, though, so does the stress being put on systems that have been in place for decades. Contamination is a growing worry, in part because of stresses on the system and in part because finer geometries require ever-more-accurate mixtures.
“With double and multi-patterning there is a greater need to control every little thing,” said Tolia. “We’ve been getting demand from customers to tighten quality and decrease the variability from lot to lot.”
That requires improvements in gas metrology the same way more advanced metrology is used to measure defects or features on a die.
“Filtering, packaging and moving around all of these gases is a problem,” said Todd Edlund, senior vice president and COO at Entegris. “And you can’t solve contamination by looking at one element.”
The result of contamination can be yield loss or chip defects, and like everything else it’s getting harder to control at advanced nodes. This explains why some of the largest chipmakers have multi-party joint development agreements for materials and components.
“Multi-processing is just one of the key things that is driving this,” said Edlund. “It’s also finFETs and 3D NAND. All of this requires very specialized chemistry, and we’re getting a lot more specifications by customers at advanced nodes. That goes beyond just the chemistry, too. We are putting analytical engineers on the ground to develop processes to provide more specific solutions.”
Behind this shift is a growing difficulty in measuring defects in particles. When something goes wrong in a gas mixture, it’s not as if that registers on some monitor.
“You need to be able to see if it’s fixed or not, and to do that you really have to see it on a wafer, he noted. “It’s getting more and more expensive to deliver that kind of metrology.”