1300°C 1100°C 900°C 800°C 700°C 600° C 0.5 0.2 SIHA GROWTH RATE (um/MIN) 0.1 0.05 SICIA 0.02 SIH2Cl2 SIHCI 0.01 0.7 0.8

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1300 C 1100 C 900 C 800 C 700 C 600 C 0 5 0 2 Siha Growth Rate Um Min 0 1 0 05 Sicia 0 02 Sih2cl2 Sihci 0 01 0 7 0 8 1 (378.41 KiB) Viewed 47 times

1300°C 1100°C 900°C 800°C 700°C 600° C 0.5 0.2 SIHA GROWTH RATE (um/MIN) 0.1 0.05 SICIA 0.02 SIH2Cl2 SIHCI 0.01 0.7 0.8 0.9 1.0 1.1 103 (T/ⓇK) Fig. 3.2 Chemical vapour deposition of silicon from various precur- sor gases. The deposition rate depends on the substrate temperature, the gas supply, and the activation energy. In this exercise we address the activation energy that must be provided by heating the substrate during deposition from a gas like CH4, SiH4, etc. Relevant bond enthalpies for this exercise: H-H: 435 kJ/mol, Si-H: 318 kJ/mol, Si-Si: 221 kJ/mol. a. Take the curve for the deposition of silicon from SiH4 of figure 3.2 and compute the activation energy from the part where de 1/T dependence is valid. Hint: The activation energy comes from the exponential behaviour, exp(B/(RT)). R is the universal gas constant (8.314472 J/K/mol). Note that the absolute temperature must be used, so forget about the scale on top. b. Calculate the enthalpy change when going from SiH4 in the gas phase to a situation where the Si atoms are incorporated in a layer (4 neighbours) and the hydrogen is released as H2 molecules. (You will find that this change is much less than the activation energy, showing that there is indeed a barrier to overcome before the reaction takes place)