Solar Grade-Silicon, Ingot, Wafer Technology and ... - Displaybank

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Solar Grade-Silicon, Ingot, Wafer Technology and Market Trend (2008~2012) 1.3. Poly-silicon Process The solar grade-silicon and its wafer manufacturing technology can be summarized like the figure below. The process starts with metallurgical silicon, MG-Si, which has about 99% purity and undergoes gasification and purification processes to obtain silane gas. The silane gas is extracted at high temperature to obtain solar grade-silicon, SoG-Si. The solar grade-silicon manufacturing process includes Siemens, FBR, and VLD methods. Details of these methods will be discussed in the following chapter. Figure 1.3.1. Silicon Solar Cell Manufacturing Process SAMPLE The silicon obtained from the above process is categorized into chip (chunk), granular, and powder (dust-like) shapes upon the manufacturing method. The silicon is melt again to produce ingot. Czochralski, CZ, method is used to manufacture monocrystalline ingot and heating furnace is used to manufacture multicrystalline ingot blocks. The monocrystalline ingot has limited diameter since it grow crystal vertically and needs to cut edges to produce rectangular wafers that its final wafer size is smaller than the one of multicrystalline ingot method. Currently, the maximum size of the monocrystalline silicon wafer is 156 x 156mm. The solar grade-silicon must satisfy physical property requirements like the following. First requirement is the size of poly-silicon. The size is an extremely All Contents of this report remain the property of Displaybank Jan’09
Solar Grade-Silicon, Ingot, Wafer Technology and Market Trend (2008~2012) important factor in determining silicon’s quality and unit cost. The poly-silicon is categorized into powder (dust-like) type which is smaller than several tens of um, granular type with several mm, and chunk (chip) type which is greater than several cm. For instance, the dust-like type manufactured by so-called free space method has the most effect on manufacturing cost cut among chemical methods using gas reactions. On the other hand, it has a shortcoming that it is difficult to regulate processes while melting silicon to grow crystals, which is a subsequent process, due to large specific surface areas and low density. Hence, the granular or chunk types appear proper considering subsequent processes. The granular type poly-silicon has a high filling density of crucible during crystal growth and enables continuous processes through fixed supply, but it also has large specific surface areas that it is difficult to handle since it is easily contaminated by external environments. The poly-silicon manufactured by Siemens method is mostly chunk type. This type is easy to handle in process, but has a low crucible filling density. The most important physical property of the poly-silicon is purity. The concentration of impurities within the poly-silicon has the biggest effect on the efficiency of solar cells and is the most critical variation in determining SAMPLE manufacturing costs. Impurities included within the silicon interior are generally divided into metal impurities and non-metal impurities. Major metal impurities include Fe, Al, Ti, Ca, Na, Zn, and Cu. Their inclusions may vary upon the initial silica materials and metallurgical silicon manufacturing processes. The poly-silicon must only include less than 1ppba metal impurities like the figure below in order to be used in solar cells. The second method creates trichlorosilane through metallurgical silicon and hydrogenation processes. All Contents of this report remain the property of Displaybank Jan’09
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Solar Grade-Silicon, Ingot, Wafer Technology and ... - Displaybank

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