CVD System: A Quick Overview of Chemical Vapor Deposition and its Application

 chemical vapor deposition system

Chemical vapor deposition is a practical method to synthesize well-controlled dimensions and structures with high purity. Whether one needs to develop a single layer, multiple-layer, composite, or finally functional coatings, chemical vapor deposition system is the go-to solution these days.

What does the process of chemical vapor deposition involve?

In CVD system, a single precursor gas flows into a chamber that contains the substrate to be coated. The vapor of reactive compound (an easily volatilized liquid or solid in some cases) is sublimed and then directed to the reaction zone via carrier gas. A thin film is deposited on the substrate surface with the help of a chemical reaction or decomposition of gas mixture or in the vicinity at a fixed temperature. 

The precursors used in the CVD process can be single source or dual source in origin. While single-source precursors are generally used for successive thin film production, dual source precursors involve the interaction between different precursors for synthesis of thin film. 

In both cases, it is vital to transport the gas phase precursors with a carrier gas for the synthesis of thin films.

Most commonly used carrier gases are N₂, He and Ar, especially when highly reactive or pyrophoric compounds are involved in the CVD process. In some cases, reactions involve an energy input from the carrier gas such as H₂ or O₂ enrichment. 

A chemical vapor deposition system must:

• Ensure the controlled transport of the reactant and diluent gases to the reaction zone
• Maintain a defined substrate temperature 
• Safely remove the gaseous by-products

To form thin layers with chemical vapor deposition at atmospheric pressure (APCVD), there are four basic types based on gas flow and operation principles:

• Horizontal tube displacement flow type
• Rotary vertical batch type
• Continuous-deposition type using premixed gas flow
• Continuous-deposition type employing separate gas streams

Any CVD Process, including APCVD, involves the following operations. 

First, the reacting gas is transported to the reactor. Thermal equilibrium temperature is achieved for the gas and then, composition through gas-phase collisions and reactions takes place. Lastly, near-equilibrium species are directed to the reactant surface and surface chemical reactions start to occur to create a thin film.

Here is the summary of the chemical vapor deposition process:

• Active gaseous reactants are created.
• The precursor is transported to the CVD system reactor.
• Gas phase precursor is decomposed to remove gaseous by-products and develop reactive intermediates.
• Gaseous reactants are then directed onto the substrate area.
• Surface diffusion takes place for nucleation and thin-film growth
• Desorption of by-products and mass transport away from the active reactive zone. 

Application of Chemical Vapor Deposition System

CVD systems are used for the synthesis of a variety of thin-film coatings, such as:

• Nanodiamond coatings
• CVD diamond coatings
• Micro-crystalline CVD diamond coatings
• Graphene
• Carbon Nanotubes (CNT) 

Chemical vapor deposition systems are widely used in universities and research laboratories for deposition of high-quality thin films.