Silica, SiO2, is formed on silicon as an electrically insulating layer for micro

Question

Silica, SiO2, is formed on silicon as an electrically insulating layer for microelectronic devices. Silica is formed when silicon is exposed to O2 gas at an elevated temperature. At 900C, it takes 90 minutes for the oxygen to diffuse from the surface to form a 0.06 micron (0.06 x 10-6 m) thick layer of SiO2 on a very thick silicon plate. At this same temperature, how long (total time, in minutes) would it take for oxygen to diffuse to form a 0.13 micron thick layer of SiO2? Assume that the silicon can be treated as a semi-infinite solid with a constant concentration of oxygen at the surface. (Hint: What is true of the oxygen concentration at the Si/SiO2 interface?)

Explanation / Answer

x=sqrt(4Dt)

0.17=sqrt (4*36e-4t)

0.17^2/4*36e-4=t=5.8e-2 s

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