HW4 - dopants. Assume the activation energy for diffusion...

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HW 4 (Due 2/11 Mon) 5-13 When a Cu-Zn alloy solidifies, one portion of the structure contains 25 atomic percent zinc and another portion 0.025 mm away contains 20 atomic percent zinc. The lattice parameter for the FCC alloy is about 3.63×10 -8 cm. Determine the concentration gradient in (a)atomic percent Zn per cm; (b)weight percent Zn per cm;and (c)Zn cm cm atoms 3 5-21 Consider a 2-mm-thick silicon (Si) wafer to be doped using antimony (Sb). Assume that the dopant source (gas mixture of antimony chloride and other gases) provides a constant concentration of 10 22 atoms/m 3 . If we need a dopant profile such that the concentration of Sb at a depth of 1 micrometer is 5×10 21 atoms/cm 3 .What will be the time for the diffusion heat treatment ? Assume that the silicon wafer to begin with contains no impurities or
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Unformatted text preview: dopants. Assume the activation energy for diffusion of Sb in silicon is 380 kJ/mole and D for Sb diffusion is 1.310-3 m 2 /s. 5-33 We can successfully perform a carburizing heat treatment at 1200C in 1 h. In an effort to reduce the cost of the brick lining in our furnace, we propose to reduce the carburizing temperature to 950C. What time will be required to give us a similar carburizing treatment ? 5-36 A ceramic part made of MgO is sintered successfully at 1700C in 90 minutes. To minimize thermal stresses during the process, we plan to reduce the temperature to 1500C. Which will limit the rate at which sintering can be done: diffusion of magnesium ions or diffusion of oxygen ions? What time will be required at lower temperature?...
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