Krypton and Xenon in Semiconductors
Krypton and xenon are produced from the air. Krypton is naturally present in the air at a concentration of 1 ppm and xenon is present at a concentration of 87 ppb. Both are collected as secondary products of cryogenic air separation at air separation units (ASUs). ASUs separate the components of air based on their boiling points using cryogenic distillation. This is the common method of production for oxygen, nitrogen, argon, as well as rare gases neon, krypton, and xenon. There are many ASUs around the globe. The ability to produce krypton and xenon is not inherently part of the process as it requires additional equipment beyond that required to collect oxygen or nitrogen. The krypton and xenon price when an ASU is planned and built determines if the capability to collect these gases is added.
Worldwide, about 100 ASUs collect krypton and xenon. Larger ASUs are most suitable for the collection because the capital cost per liter of production of krypton and xenon is lower at larger plants. They are normally produced at ASUs producing at least 2000 tons per day of oxygen.
During the separation of the air components, the krypton and xenon are initially concentrated together in the oxygen stream. With similar properties and greater abundance in the atmosphere, krypton is normally collected along with the xenon at a ratio near 10:1 krypton to xenon. About 1.2 kg (200L) of xenon and 7 kg (2000L) of krypton can be produced for each 1000 tons of oxygen produced. As a result, an ASU with oxygen capacity of 2000 tons per day can collect ~900 kg of xenon and ~2500kg per year.
The xenon/krypton mix that is collected at an ASU is typically further purified and separated using another cryogenic column at another location. Because of the high value-to-transportation cost of the krypton and xenon and the high transportation-to-value cost of the oxygen, the ASUs are often built near the oxygen consumers and the krypton and xenon get shipped long distances. These large ASUs typically supply oxygen via pipeline to steel mills or petrochemical facilities.
Like most commodity products, the price for krypton products and xenon depends on the interplay of supply and demand. At any given time, the amount of xenon available is a result of the installed capacity and its operating rate. This operating rate is driven by the oxygen requirements of steel mills and other facilities supplied by the ASUs.
Krypton and xenon demand results from their use in several applications. Krypton is used for production of light bulbs, window insulation, spacecraft propulsion, sputter deposition and in semiconductor manufacturing (etching, annealing, lithography). Xenon is used in the production of light bulbs, specialty detectors, in dark matter research, as an anesthesia, spacecraft propulsion and in semiconductor manufacturing. Krypton and xenon are used in conjunction with halocarbon etchants such as C4F6 and CH2F2 for deep trench etch commonly used for 3D NAND SSD devices. Traditional xenon and krypton applications that continue today are ion implant and transition metal sputtering methods.
Geopolitical events can affect the krypton and xenon supply and demand. In the past few years, some krypton products and xenon production decreased due to covid shutdowns. Recently, supply chains were interrupted, reducing availability due to the conflict in Ukraine.
With all interconnected factors, the price and availability of krypton and xenon for semiconductor manufacturing can depend on window insulation in Wisconsin, steel manufacturing in Shanghai, and satellites launched into orbit.