chex42_hw4_s2003

chex42_hw4_s2003 - UNIVERSITY OF CALIFORNIA SANTA BARBARA...

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UNIVERSITY OF CALIFORNIA SANTA BARBARA DEPARTMENT OF CHEMICAL ENGINEERING CHE 142 and ChE 242: Microelectronics Processing Spring 2003 Homework # 4 (Due May 14, 2003) Problem #1 Consider the deposition of material A on a solid surface (substrate) from decomposition of gaseous reactant AB via the overall reaction AB (g) A (s) + B (g) . The reactant, AB, is fed into the reactor diluted in an inert gas. The reactant gas flows over the surface and a stagnant layer with thickness δ forms above the substrate as shown in Figure l. The boundary layer thickness, δ , is inversely proportional to the square root of the gas flow rate Q. In a series of experiments, deposition rate as a function of substrate temperature, T, was determined to vary as shown in Figure 2. There are two different hypotheses for the deposition mechanism. Your objective is to determine which deposition mechanism is consistent with the data in Figure 2. I will lead you to the answer through a series of questions. Both hypotheses agree that the important reactions do not occur until AB enters the stagnant layer, but they differ in where the decomposition occurs. Hypothesis 1 There are no gas phase reactions. AB diffuses through the stagnant film and decomposes on the substrate surface to yield A via the reaction AB s k → A + B. The reaction rate is given by R = k s C AB where k s is the surface reaction rate constant (e.g., in cm/s) and C AB is the AB concentration (e.g., in mole/cm 3 ) immediately above the surface.
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This note was uploaded on 12/29/2011 for the course CHE 142 taught by Professor Ceweb during the Fall '09 term at UCSB.

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chex42_hw4_s2003 - UNIVERSITY OF CALIFORNIA SANTA BARBARA...

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