03_Growth=) - Bulk Crystal Growth Si crystal structure and...

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(Gan 2010/11) Bulk Crystal Growth Si crystal structure and defects Si refining (revision) Bulk crystal growth Czochralski Float Zone Solute redistribution Normal freezing Rapid freezing Wafer preparation (revision) Gettering Readings: Plummer sections 3.1, 3.2, 3.3, 3.5.2, 3.5.3
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(Gan 2010/11) Si Crystal Structure Diamond lattice Face Centered Cubic (FCC) Two merged FCC cell, offset by a/4 in all 3 directions 4 atoms in second FCC cell lie within the first FCC cell
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(Gan 2010/11) Defects in Crystals 1. Point defects Vacancy Interstitial atom or interstitialcy Substitutional atom (dopant/impurity) 2. Line defects Dislocation (edge/screw) 3. Area defects Stacking fault Twinning (grain boundary) 4. Volume defects Void Precipitate I V Dislocation Stacking Fault Precipitate
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(Gan 2010/11) Production of Si Wafers Raw materials (quartzite, carbon) Metallurgical grade silicon (MGS) Electronic grade silicon (EGS) Si ingots Arc furnace Decomposition chamber or fluidized bed Czochralski technique Si wafers Shaping operations
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(Gan 2010/11) Production of Metallurgical Grade Silicon (MGS) Equipment: Submerged-electrode arc furnace Raw Materials: Sources of silicon are found in quartzite (SiO 2 ), which is in quartz rock, sands, crystals Silicon dioxide is reduced by carbon found in coal, coke and wood chips to Si (Lee)
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(Gan 2010/11) Production of MGS Reactants are converted to silicon carbide by the reaction SiO 2 + 3C SiC + 2CO (g) SiC and SiO 2 descend to hottest part of reactor, zone III, where Si is formed by the following reactions: SiO 2 + 2SiC 3Si + 2CO (g) 2SiO 2 + SiC 3SiO (g) + CO (g) SiO gas is cooled by rising through the descending charge of reactants, and is retained by the reaction: SiO (g) + CO (g) SiO 2 + C MGS is approximately 98% pure (Lee)
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(Gan 2010/11) Production of Electronic Grade Silicon (EGS) Step 1 Objective: To produce chlorosilanes, SiCl 4 , SiHCl 3 from MGS Equipment: Fluidized-bed reactor Process: Grind MGS into fine powder Powder reacts with anhydrous HCl in fluidized bed to form chlorosilanes and chlorides of impurities (e.g. AlCl 3 , BCl 3 , PCl 3 ) Principle reaction to produce SiHCl 3 : Si (MGS) + 3HCl SiHCl 3 + H 2 Purification of SiHCl 3 is done by fractional distillation Schematic of fluidized-bed reactor for production of chlorosilanes (Crossman and Baker, 1977). (Lee)
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(Gan 2010/11) Production of EGS Step 2 Objective: To produce rods of ‘pure’ Si Equipment: Siemens reactor Process: Hydrogen reduction of purified SiHCl 3 at 1000°C, similar to chemical vapour deposition, SiHCl 3 (g) + H 2 (g) 2Si (s) + 6HCl (g) Another method to produce Si is by pyrolysis of silane at 600°C, SiH 4 (g) Si (s) + 2H 2 (g) Fluidized bed is replacing Siemens-type reactors due to it slower power consumption and continuous operation (Lee)
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(Gan 2010/11) Production of EGS Byproducts of decomposition process are purified to be either reused or sold Polysilicon rods of EGS, with diameter up to 0.2m and several metres in length are produced (Lee)
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03_Growth=) - Bulk Crystal Growth Si crystal structure and...

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