Explosion At Mitsubishi Materials

Analysis: What happened and why it matters to the semiconductor industry.


A big explosion at a semiconductor plant shocked the electronics community last month. This article discusses what happened and the fallout on the semiconductor industry.

The explosion occurred at the Mitsubishi Materials Yokkaichi plant in Yokkaichi, Mie Prefecture, at about 2 p.m. on Jan. 9. Five people were killed and 12 others were injured, some seriously.

Mitsubishi Materials issued press releases (reference 1 and reference 2) in the days following the explosion. The company blamed the explosion on the removal of the heat exchanger for the hydrogen purification equipment following a routine cleaning process. The explosion occurred when the lid of the equipment was opened after the completion of the pre-wash. The company noted there was no additional damage to the surrounding machines, which led it to conclude that the heat exchanger itself was the cause of the explosion, although the exact cause is still under investigation.

The heat exchanger, which was covered with trichlorosilane (HCi3Si) for maintenance and inspection work, was cleaned with water just before the incident happened. The explosion was so powerful that it blew the lid — 1 meter in diameter and weighing 440 pounds — 10 meters.

Mitsubishi Materials President Yao Hiroshi, during his New Year’s speech (reference 3) on Jan. 6—three days before the explosion—identified “CSR, health and safety” as one of the four major challenges for the company. “The safety of employees should be addressed at high priority. We will continue to increase the awareness on safety to ensure compliance with the basic rules towards realizing the aim to achieve ‘zero accidents’ in the plant.”

Mitsubishi shut down the plant following the accident. No date has been given for its planned reopening.

More damage
So what is the impact of this explosion to the semiconductor industry? Mitsubishi Materials produces polycrystalline silicon, which is the raw material of semiconductor silicon wafers. It supplies polycrystalline silicon to single crystal silicon ingot manufacturers such as Nissin Chemical Industry and SUMCO. SUMCO is a joint silicon wafer venture between Sumitomo Metal Industries and Mitsubishi Materials Silicon.

Nissin Chemical is part of the Shin-Etsu Chemical group. Japan’s Shin-Etsu and SUMCO reportedly own half of the world’s silicon wafer market in terms of share. In fact, it was this global leadership position that first attracted Mitsubishi Materials to become the supplier for SUMCO.

According to Nikkei Sangyo Shimbun, the production capacity of polycrystalline silicon at the Yokkaichi plant is approximately 2,800 tons per year, of which 70% of the capacity produced is supplied to SUMCO. The newspaper reported that supplies had fallen to about 70%.

In the polycrystalline silicon market Germany’s Wacker and the United States’ Hemlock account for majority of the world’s supply, followed by Japan’s Tokuyama, which has about 20% market share. The production capacity of Tokuyama is 9,200 tons per year. However, it was reduced to about 6,200 tons after Tokuyama started a new solar cell plant in Malaysia last year (reference 4). Although the specific percentage of polycrystalline silicon production by Tokuyama for semiconductors is unknown, 2,800 tons of Mitsubishi Materials seems to appear like a small figure. Based on this figure alone, assuming a fast recovery on the production capacity of Mitsubishi Materials, the impact on the semiconductor industry would not be so severe.

The stock market tells a different story. Mitsubishi Materials was 376 yen per share on Jan. 9. It dropped to 370 yen the next day, and dropped another 3.7% to 362 yen on Jan. 14. The share price SUMCO was 916 yen on the Jan. 9, dropping to 894 yen on Jan. 10 and to 864 yen on Jan. 14.

The shortage of polycrystalline silicon was suddenly big news. Some observers have noted that silicon is the second most abundant element on the planet after the oxygen. In descending order of abundance, it’s O, Si, Al, Fe, Ca, Na, K, and Mg.

But it’s not just the abundance of silicon that matters. The original element material of crystal silicon is silicon oxide (SiO2). SiO2 is reduced by hydrogen to produce the low-purity metal silicon. Then, it is converted to trichlorosilane using a distillation process to increase the purity. The polycrystalline silicon is finally produced by further reduction by hydrogen. So it is not just the shortage of polycrystalline silicon that matters—it is the capability to mass-produce polycrystalline silicon. This problem should be watched carefully.

1. Mitsubishi Materials press release(2014/01/09)
2. Mitsubishi Materials press release(2014/01/10)
3. Mitsubishi Materials press release(2014/01/06)
4. Homepage of Tokuyama

The Japanese version of this article is located here.


DrDoug says:

After the massive price run up of poly-Si in late 2008 (US$450/kg) oodles of poly manufacturers charged into the business. This drove the price down to something close to US$16/kg in recent months. There is plenty of poly-Si capacity in the world. Plants have shutdown everywhere due to the extroadinarily low price and can be brought online as needed. The bigger issue is the exhaust products from TCS and DCS (SiHCl3 and SiH2Cl2). The polysiloxanes formed in the exhaust from these precursors are highly flammable and explosive. They only require some mechanical energy to light them off. Everybody who knows about Si epitaxy or bulk poly-Si growth is well acquainted with the hazards of the exhaust system. Only the public is in the dark. Note that the description by Mitsubishi does not clearly identify the metasatable polysiloxanes in the exahust as the cause, nor does it even mention them. TCS itself is flammable. But the partially oxidized polysiloxanes are “da bomb”.

JoeJoe says:

Trichlorosilane (HCl3Si) is highly water reactive. Generates hydrogen- flammable gas and hydrogen chloride- corrosive gas. In a fire, may also generate phosgene- toxic gas. Will also react violently with alcohols, strong acids or bases, oxidizers and amines. Every Trichlorosilane MSDS has these warnings. Spark when lifting lid? Possibly from the lifting device used (440 pound lid)?

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