How it Works: Atomic Layer Deposition Valves
The atomic layer deposition (ALD) process deposits thin films of precursor materials onto substrates one atomic layer at a time to impart such properties as conductivity, chemical resistance, and strength. Research and development operations utilize ALD systems to investigate new applications for producing advanced technologies such as semiconductor wafers, nanoelectronics, and optics.
Problem: The atomic layer deposition (ALD) process deposits thin films of precursor materials onto substrates one atomic layer at a time to impart such properties as conductivity, chemical resistance, and strength. Research and development operations utilize ALD systems to investigate new applications for producing advanced technologies such as semiconductor wafers, nanoelectronics, and optics. Labs also use ALD to experiment on novelty applications including coatings for drill bits, dental implants, food packaging, and even butterfly wings.
Due to the high operating costs associated with ALD, R&D operations require dependable systems that offer long service lives and allow for the efficient use of expensive precursor gas. So, when Cambridge NanoTech first started manufacturing ALD systems in 2003 and experienced frustrating clogs in the systems’ valves, company founder Dr. Jill Becker needed a solution that would minimize downtime.
“The first valves we were using needed to be replaced once a month,” Becker says. “That meant operators had to cool the system down, go in there with wrenches, take everything apart, and replace the valves with ones that were sure to cause downtime again in the future.”
|Cambridge NanoTech’s gas delivery assemblies for atomic layer deposition systems feature Swagelok® ALD valves connected to a carrier/purge gas source and stainless steel cylinders filled with precursors.|
Solution: To extend the life of Cambridge NanoTech’s gas delivery assemblies, Becker needed a valve that provided a highly improved cycle life, better temperature compatibility, and low maintenance. These capabilities could dramatically reduce the overall cost of ownership for ALD processing. She found the solution in Swagelok® ALD valves, which enable Cambridge NanoTech to produce dependable gas delivery assemblies that achieve precise, controlled delivery of precursor gas.
One reason for the precise gas delivery timing is the ability of one ALD valve to perform two functions—precursor delivery and purging. The alternative would be a subassembly of several valves, which can introduce timing variability. Inconsistent delivery times result in an increase in the quantity of precursors consumed, which leads to higher cost of ownership.
In its most basic form, the ALD valve design consists of three ports. Carrier gas enters through one port and exits through another. Precursor gas enters through a third port, which is a small, precise orifice that delivers minimum chemical volume. This three-port configuration delivers a steady flow of carrier gas into the ALD chamber. At precisely timed intervals the carrier gas flow is interrupted by a brief pulse (<15 milliseconds) of precursor gas. The carrier gas moves the precursor into the deposition chamber where precursor atoms attach to the substrate being coated.
“Through precise delivery, nearly all of the precursor gas is used in the deposition process,” Becker says. “The delivery is so precise that a system running at full capacity 24/7 may take three months or longer to use a 25-cc cylinder of precursor.”
In Cambridge NanoTech’s ALD tool, the ALD valves are part of a subassembly that also employs Swagelok VCR® end connection fittings, valves, and tubing links. This subassembly is dependable and low maintenance, and, if necessary, easily serviceable.
“It’s very important for us to make tools that are easy to service,” Becker says. “We want people to recognize parts and be able to adjust or replace components easily. For example, the cylinders that hold precursor gas take less than two minutes to exchange.”
The ALD valves contribute to the low maintenance design. They offer a very high cycle life of up to 100 million cycles, minimizing valve changes. High-purity grade PFA seats, non-hemispherical shaped diaphragms, high temperature tolerances, and consistent flow rates enable extended life, high performance, and dependability in ALD applications.
“With Swagelok’s ALD valves, we are getting millions of cycles without any problems. In fact, we have yet to break one,” Becker says.
For more information visit: www.swagelok.com.