L09-CVD_a - Chemical Vapor Deposition Physical Vapor...

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Chemical Vapor Deposition
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Physical Vapor Deposition (PVD) So far we have seen deposition techniques that physically transport material from a condensed phase source to a substrate. The material to be deposited is somehow emitted from the source already in the form that we need for the thin film (ex.: evaporation, sputtering). No chemical reactions are assumed. In fact, they are generally unwanted. If there are chemical reactions (as in reactive sputtering) they are simple reactions with no by-products. The critical parameters are physical (temperature, pressure, voltage applied, etc.)
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Chemical Vapor Deposition (CVD) Deposition can also take place due to a chemical reaction between some reactants on the substrate. In this case reactant gases (precursors) are pumped in to a reaction chamber (reactor). Under the right conditions (T, P), they undergo a reaction at the substrate. One of the products of the reaction gets deposited on the substrate. The by-products are pumped out. The key parameters are chemical (reaction rates, gas transport, diffusion).
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Fundamental CVD Processes 1. Convective and diffusive transport of reactants to the reaction zone 2. Gas phase reactions 3. Transport of reactants to the substrate surface. 4. Chemical and physical adsorption 5. Surface reactions leading to film formation 6. Desorption of volatile by- products 7. Convective and diffusive transport of by-products away from the reaction zone Main Gas Flow Region Gas-phase reactions Transport to Surface Adsorption Surface diffusion Re-adsorption Desorption Nucleation, island and step growth Substrate Film
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Choice of Chemical Reactions The precursors have to be volatile (gaseous).
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L09-CVD_a - Chemical Vapor Deposition Physical Vapor...

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