China’s Demand for Nitrogen Trifluoride Sees Double-digit Growth

By Luo Yamin, China National Chemical Information Center

As an excellent plasma etching gas and reaction chamber cleaning agent in the electronics industry, nitrogen trifluoride (NF3) has been used extensively in the manufacture of semiconductor chips, flat panel displays, solar cells, optical fibers and other areas, taking advantage of its fast reaction speed and high efficiency. Compared with carbon tetrafluoride or the mixture of carbon tetrafluoride and oxygen, NF3 has a higher etching rate and better selectivity without contaminating the surface during the etching of silicon and silicon nitride. Especially in the etching of integrated circuit (IC) materials with thickness under 1.5 μm, NF3 can easily fulfill the requirements of the process since it has advantages both in etching rate and selectivity. NF3 can also be used alone or in combination with other gases as the etching gas in the plasma etching process. As a cleaning gas, NF3 performs better than those widely consumed cleaning gases such as carbon tetrafluoride, perfluoroethane and perfluoropropane. The better effectiveness of NF3 can make up for its higher price. On the one hand, the utilization rate of NF3 in the remote plasma cleaning process of a CVD reaction chamber can be as high as 95% - 99%. On the other hand, in order to reduce the effects of exhaust to the atmosphere, semiconductor companies are usually required to convert residual fluorinated gases in exhaust into harmless inorganic compounds. Unlike perfluorocarbons which only decompose completely above 1 200℃, NF3 can decompose at 700 – 800℃. Thus it can save energy and reduce costs. In recent years, all new CVD facilities developed by wafer equipment companies have switched to using NF3 as the main cleaning gas.
   In 2008, the UN’s Framework Convention on Climate Change (UNFCCC) listed NF3 as one of the greenhouse gases. The atmospheric lifetime of NF3 is 740 years and its global-warming potential value is 17 200. In the past thirty years, the concentration of NF3 in the atmosphere has increased 20 times, i.e. increased 11% annually. Most of the NF3 emission occurs in the Northern Hemisphere. In 2006, the amount of NF3 detected in the atmosphere was less than 1 200 tons (now some actually believe it was 4 500 tons), while the figure increased to 5 400 tons in 2008 and 8 000 tons in 2010. Currently, the contribution of NF3 to the greenhouse effect is 0.04% of the contribution of carbon dioxide. Although the UNFCCC added NF3 into the list of gases that need to be regulated, there is no corresponding restriction on the emission of NF3 in the Kyoto Protocol.

I. China’s NF3 industry
is just beginning.

The research of NF3 in China started in the 1980s, mainly in the 718th Research Institute of China Shipbuilding Industry Corporation. Early products were mainly used in military fields because NF3 can serve as rocket propellant. The development of the NF3 industry in China can be largely divided into three stages: first, the production scale was relatively small and the products were mainly for in-house use; second, the industrialization of NF3 in the late 1990s was accelerated by the development of the electronics industry; now, production lines of NF3 in China have been put into operation one after another since 2001, and the technical level is not far behind that in developed countries. However, in comparison to the scale and the growth rate of the global NF3 industry, the development of the domestic NF3 industry is relatively slow.
   China’s NF3 production capacity was 800 t/a in 2011. The total output of three major producers, 718th Research Institute of China Shipbuilding Industry Corporation, China Nuclear Honghua Specialty Gases Co., Ltd (stopped production in 2012) and Liming Research Institute of Chemical Industry, was about 640 tons in 2011. The newly built 900 t/a production unit of the 718th Research Institute of China Shipbuilding Industry Corporation will reach its design capacity in 2012; Jiangsu OCI New Materials Co., Ltd, invested by OCIM Inc of South Korea, will also be put into operation in 2012. Therefore, the total capacity of NF3 in China will reach 2 700 t/a at the end of 2012.
China is a net importer of NF3. In 2011, the import volume was about 700 tons, and the export to import ratio was about 1:22.
   In 2011, the domestic consumption of NF3 was more than 1 300 tons. The consumption in the manufacturing of semiconductor chips, flat panel displays and solar cells accounted for approximately 60%, 30%, and 10% of the total consumption, respectively.

II. Domestic consumption of NF3 is expected to increase greatly.

China has become the world's largest IC market and an important driving force in the growth of the global IC market. In 2010, the sales revenue of China's IC industry was RMB144 billion, accounting for only 8.6% of the world total; the self-sufficiency rate was less than 20%. By 2015, China's IC industry is expected to double its scale and the sales revenue will reach RMB330 billion. This means the annual growth will be about 17%. As of the end of 2010, there were 61 wafer production lines in China, including 41 small and medium size (150, 125 and 100 mm) ones and 20 large (300 and 200mm) ones. The number of wafer production lines is expected to reach 80 to 90 by 2015. That way, the demand for NF3 in the chip manufacturing industry may increase 15% to 17% each year from 2012 to 2015.
   Currently, the two major cleaning gases used in the manufacturing of flat panel displays are NF3 and sulfur hexafluoride, and sulfur hexafluoride has the lower cost of the two. From 2006 to 2010, production lines of LCD panels with a total investment of over RMB100 billion had been put into operation in cities like Kunshan, Chengdu, Shenzhen, Beijing and Wuhan. The total capacity of TFT LCD panels in mainland China will surpass Japan and rank third in the world by 2014. As for solar cells, China’s output in 2011 was 11GW, up 37% year-on-year, accounting for about 48% of the world total. From 2012 to 2014, the growth of the flat panel display industry and the solar cell industry is expected to slow down; still, demand for NF3 in these two industries is expected to increase 12% to 14% each year.
   Seeing the demand from three industries, i.e. semiconductor chips, flat panel displays and solar cells, the consumption of NF3 in China is expected to exceed 2400 t/a by 2015. From the point of view of domestic capacity, products in China can basically meet the demand by then, and only some high-purity products will need to be imported.

III. NF3 is still irreplaceable.

NF3 is the substitute for carbon tetrafluoride and sulfur hexafluoride. However, the latter two still occupy a certain market share due to their lower costs. Some companies use sulfur hexafluoride as a cleaning gas instead of NF3 only because it is much cheaper than NF3, not due to performance considerations. Real substitutes for NF3 are fluorine gas and carbonyl fluoride.
   To completely replace NF3 with fluorine gas on a global scale is difficult because to transport fluorine gas using cylinders is unsafe, and on-site supply of fluorine gas requires a relatively large investment in facilities. Considering that the global demand for NF3 increases 15% each year, it is estimated that carbonyl fluoride may not be able to fully replace NF3 even after 10 years due to the limit of the capacity (the expected capacity of carbonyl fluoride in 2015 is less than 4 000 t/a). Although these products will compete with each other in the future, NF3 will still dominate the market in a certain period of time.
   The global supply of NF3 will remain relatively tight in the next few years. To accelerate the replacement of NF3 with fluorine gas or carbonyl fluoride, some hope that NF3 will be included in the list of gases with restricted emission in the Kyoto Protocol in the future. Carbonyl fluoride is undoubtedly a promising product and worthy of research and development.