Chemical Vapor Deposition Quiz

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Questions and Answers

Which of the following is NOT a type of source material used in CVD?

Liquids at room temperature (correct)

Gasses

Volatile liquids

Sublimable solids

High process temperatures are an advantage of CVD.

False

What factor is considered when choosing substrates for CVD?

Adsorption and surface reactions

The preferred reaction temperature in CVD should be lower than the ________ of the substrate.

melting point Signup and view all the answers

What does the variable F represent in the equations provided?

The flow rate Signup and view all the answers

Match the following components with their respective functions:

F1 = Diffusion flux of reactant to the wafer F2 = Flux of reactant consumed by surface reaction hG = Mass transfer coefficient kS = Surface reaction rate Signup and view all the answers

In steady state, F equals F1 and F2.

True Signup and view all the answers

What does the symbol N represent in the equations?

Number of atoms per unit volume in the film Signup and view all the answers

The growth rate of the film is determined using the equation v = F / __________.

N k_S + hG N Signup and view all the answers

Match the following variables with their corresponding meanings:

F = Flow rate N = Number of atoms per unit volume Y = Mole fraction of incorporating species CT = Total concentration of all molecules in gas phase Signup and view all the answers

What is the first step in the CVD process?

Introduce reactive gases to the chamber Signup and view all the answers

CVD processes are generally slower than physical vapor deposition (PVD).

False Signup and view all the answers

Name one advantage of using Chemical Vapor Deposition (CVD).

High growth rates possible. Signup and view all the answers

CVD is also known as __________ when referring to the growth of epitaxial films.

vapor phase epitaxy Signup and view all the answers

Which step is most important for the growth rate in the CVD process?

Surface reactions Signup and view all the answers

Match the following steps of the CVD process with their descriptions:

Transport of reactants to the deposition region = Step 1 Transport of byproducts through boundary layer = Step 6 Gas adsorption by substrate surface = Step 3 Surface reactions = Step 4 Signup and view all the answers

MOCVD is also referred to as OMVPE.

True Signup and view all the answers

What limits the reaction rate during the CVD process?

Gas transport and surface chemical reaction rate. Signup and view all the answers

Study Notes

Chemical Vapor Deposition

CVD is a thin film deposition method where chemical reactions occur on a substrate surface.
The process involves introducing reactive gases into a chamber where the gases are activated by heat or plasma.
Gases adsorb on the substrate surface, reacting to form a film.
Volatile byproducts are transported away from the substrate and exhausted.

CVD Process Steps

Step 1: Transport of reactants to the deposition region.
Step 2: Transport of reactants from the main gas stream through the boundary layer to the wafer surface.
Step 3: Adsorption of reactants on the wafer surface.
Step 4: Surface reactions, including chemical decomposition or reactions, surface migration to attachment sites (kinks and ledges); site incorporation; and emission and redeposition.
Step 5: Desorption of byproducts.
Step 6: Transport of byproducts through the boundary layer.
Step 7: Transport of byproducts away from the deposition region.
Steps 2-5 are crucial for determining the growth rate.
Steps 3-5 are closely related and can be grouped together as "surface reaction" processes.

CVD Advantages and Disadvantages

CVD offers high growth rates and good reproducibility.
It can deposit materials that are difficult to evaporate.
CVD can grow epitaxial films, which are also known as "vapor phase epitaxy (VPE)."
Metal-Organic CVD (MOCVD) is also referred to as Organo-Metallic VPE (OMVPE).
CVD generally produces higher film quality and more conformal step coverage compared to physical vapor deposition.
Disadvantages include high process temperatures, complex processes, toxic and corrosive gases, and potential film impurities (e.g., hydrogen incorporation).

CVD Sources and Substrates

CVD sources can be gases, volatile liquids, sublimable solids, or combinations.
Source materials should be stable at room temperature, sufficiently volatile, have high enough partial pressure for good growth rates, have a reaction temperature below the substrate's melting point, produce the desired element on the substrate with easily removable by-products, and have low toxicity.
Substrates should be chosen considering their adsorption and surface reaction properties.
For example, WF6 deposits on Si but not on SiO2.

Film Growth Rate Derivation

Film growth rate is derived using a model similar to the Deal-Grove model for thermal oxidation.
The growth rate is influenced by the diffusion flux of reactant species and the surface reaction flux.
The growth rate equation is derived by equating the diffusion flux and the surface reaction flux in steady state.
The growth rate equation is dependent on the mass transfer coefficient, surface reaction rate, concentration of reactant in the gas phase, and the mole fraction of the incorporating species.

Factors Affecting Film Growth Rate

The growth rate can be controlled by adjusting the gas transport to and from the surface, the surface chemical reaction rate, the surface temperature, and the partial pressure of the reactant.
When the surface reaction rate is much faster than the diffusion rate, the growth is primarily limited by diffusion.
When the diffusion rate is much faster than the surface reaction rate, the growth is primarily limited by the surface reaction.
When the diffusion and surface reaction rates are comparable then both are important for the film growth.

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Description

Test your understanding of the Chemical Vapor Deposition (CVD) process, a crucial thin film deposition method. This quiz covers key steps involved in the CVD process, including reactant transport, adsorption, and surface reactions. Assess your knowledge and learn more about how films are formed through chemical reactions.