Siemens process

Siduron [1982-49-6] Siegemte Siemens-Martin process Siemens process... 

The purification method that has become a near-standard is the Siemens process, where hydrogen reduces SiCl or SiHCl on the surface of a resistance-heated (to about 1150°C) high purity siUcon rod. The rod is usually U-shaped to reduce the height of the furnace. The result is a siUcon ingot several cm in diameter and >2 m long. It is tempting to write the siUcon tetrachloride—hydrogen reaction as... 

The thermal decomposition of silanes in the presence of hydrogen into siUcon for production of ultrapure, semiconductor-grade siUcon has become an important art, known as the Siemens process (13). A variety of process parameters, which usually include the introduction of hydrogen, have been studied. Silane can be used to deposit siUcon at temperatures below 1000°C (14). Dichlorosilane deposits siUcon at 1000—1150°C (15,16). Ttichlorosilane has been reported as a source for siUcon deposition at >1150° C (17). Tribromosilane is ordinarily a source for siUcon deposition at 600—800°C (18). Thin-film deposition of siUcon metal from silane and disilane takes place at temperatures as low as 640°C, but results in amorphous hydrogenated siUcon (19). 

R. E. Siemens, Process for Recorey of Nickelfrom Domestic Eaterites presented at the 1976 Mining Convention, U.S. Bureau of Mines, 1976. 

Siemens process - [SILICONCOMPOUNDS - SILANES] (Vol 22) -for pure silicon [SILICON AND SILICON ALLOYS - PURE SILICON] (Vol 21)... 

Trichlorosilane (TCS) is the basic material for the production of hyperpure silicon for the semiconductor industry according to the Siemens process. It is produced by hydrochlorination of technical-grade silicon Si + 3HC1 SiHCls + H2 [1 - 5]. The process aims at maximizing the selectivity toward the main product TCS and at minimizing the by-products like silicon tetrachloride (STC), dichlorosilane (DCS) and the so-called high boilers. Despite decades of industrial practice, the hydrochlorination of silicon is poorly understood. 

The historical development of European ozonators and ozone production are reviewed. The OttO/ van der Made, and Siemens processes for generating ozone are described. Recent improvements and Innovations are indicated. Two distinct operations are considered conditioning of the air to be submitted to the electric discharge, and contact between the ozone and the water. 

In Europe from 1907 to 1930, three ozone generating processes were successfully submitted to the test of industrial applications the Otto, the Van der Made, and Siemens processes. Since 1930, there has been a tendency toward improving the production equipment of these processes with a view to reducing its size and eliminating certain production drawbacks, such as the too frequent breakage of dielectrics. 

Scrap, a rejected and nonprime material from the semiconductor was the main supply route in the early days of PV. Due to the fast growth of the market, scrap is not sufficient and the main source today is nonprime polysilicon, deliberately produced by operating the conventional Siemens process with more economical parameters (e.g., faster production rates, lower energy... 

Therefore, the vertical crucible-free floating zone (FZ) technique was developed soon [1] to grow very pure silicon single crystals without any contact of the molten zone with foreign materials. If already very pure silicon is used as starting material, the purification effect of the FZ technique is less important than the exclusion of newly introduced impurities. The state-of-the-art Siemens process provides polycrystalline feed rods of highest purity, hence, additional FZ purification runs are dispensable and, above all, would be too costly. 

In principle, the diameter of a silicon rod produced after the Siemens process (see part I) is limited. The endothermic deposition from SiHCl3 takes place at a temperature of the rod surface of >1,100°C and is established by an axial electric current. As the hottest region, the core region of the rod has the highest conductivity, which causes self-bunching of the heating current. If the rod diameter exceeds 160-180 mm, the silicon melting temperature can be reached in the core. When silicon melts, the electric conductivity jumps by a factor of about 30. Therefore, most of the current will be concentrated in the molten core. If that melt solidifies, the rod will brake by the specific volume expansion of ca. 8%. 

Another attempt to make feed rods for FZ crystal growth from cheap starting material is to melt solar (or lower) grade raw silicon in a quartz crucible and pull a rod of the desired diameter after the CZ method, not necessarily a single crystal. A lot of impurities can be removed by segregation and in the subsequent FZ step, almost all oxygen and most of the other impurities can be removed, too. However, the actual costs of such an approach must be carefully considered, but it is still an option to overcome the diameter limitations of the Siemens process. 

Silicon can also be deposited at the surface of hot silicon particles hovering in a fluid bed by pyrolytic decomposition of SiH4 or SiHClo. The result is granular silicon with a purity grade between very good solar and medium semiconductor quality. Compared with the Siemens process, the deposition... 

In the energy intensive Siemens process (Fig. 2), MG silicon and hydrochloric acid are combined in a... 

One company is modifying the final polysilicon deposition step in the Siemens process. The new method uses a graphite pipe heated to 1500°C, beyond... 

The Union Carbide process for trichlorosilane production is an alternative. Tetrachlorosilane is hydrogenated through a bed of granular MG silicon, using one of the reactions commonly used for the recycling of the byproduct SiCU in the Siemens process ... 

For industrial use, silicon can be classified into three categories according to their purity metallurgical grade silicon (MG-Si, 2N), solar grade silicon (SOG-Si, 6N-7N), and semiconductor grade silicon (SEG-Si, 11N-12N). Currently MG-Si is produced by carbothermic reduction of sihca. The world production of MG-Si, excluding ferrosihcon, was ca. 1.5 million metric ton in 2011 [1]. S(Xj-Si is mainly produced from MG-Si by Siemens process which involves the... 

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