Gaseous precursors: directly introduced

Heating method adopted
Induction heating （感应加热）(cold-wall reactor)
Internal resistance heating （内置电阻加热） (cold-wall
2
Principles of Chemical Vapor Deposition
Role of Thermodynamics in CVD Process
Thermodynamics is essential to understand the CVD
process and the underlying science for the key factors

Principles of CVD
mass transportation reaction kinetics nucleation and growth

CVD and modified CVD systems Examples in synthesizing nanostructured materials
on a substrate without incorporation of undesired particles.

Horizontal Mode: the reactor is horizontally placed, and the gas flow is parallel to the surface of the substrate
and concentration;

Through increasing the temperature and total pressure
and decreasing the total flow rate to realize particle growth.
3. 2 Chemical Vapor Condensation (CVC)
CVD for Preparing Nanoparticles

Gas-phase nucleation and controlled growth of the
particles are of prime concern;

The particle size is controlled by the number of nuclei
II.
At higher temperatures: limited by interdiffusion of
gaseous reactants and products through the boundary
layer
III.
At still higher temperatures: homogeneous nucleation resulting in precipitation of solid particles occurring

Mass transport of reactants to the growth surface
through a boundary layer by diffusion;

Chemical reactions on the growth surfac new material into the growth front;

Vertical Mode: the reactor is vertically placed, and the gas flow is vertical to the surface of the substrate
Newly Developed CVD Techniques

Metalorganic CVD (MOCVD): using matalorganic


Key Points Description of CVD Process (2)


The growth rate is determined by the slowest step
Kinetic control of CVD process: occurred when
mass-transfer coefficient is very large compared to
直接沉淀
扩散控制
反应控制
CVD过程中温度对薄膜生长速度的影响
I.
At low temperatures: limited by strongly temperaturedependent rate of heterogeneous nucleation, and by adsorption and kinetic effect
precursor molecules adsorb onto a substrate held at an
elevated temperature. These adsorbed molecules will be either thermally decomposed or reacted with other gases/vapors to form a solid film on the substrate. Such a gas-solid chemical reaction at the surface of a substrate is

Step 1 and Step 3 are dependent, both of them affect the chemical reaction rate and are coupled by the stoichiometry（化学计量）of the reaction Step 2 is exceedingly complex, involving surface and/or gaseous reaction, simultaneous chemical/physical adsorption-desorption, and nucleation process Boundary layer: a space above the substrate resisting diffusion, varying with time, the distance in the horizontal reactor etc.
precursors to reduce the growth temperatures and achieve higher film quality

Plasma-enhanced CVD (PECVD): using plasma as
energetic source

Photo-CVD: using ultraviolet as energetic source
Three major growth modes
层状生长
超晶格 超晶格 层+岛状生长
岛状生长
3 Experimental Approach

How to design a CVD system?
Geometry, Shape, Composition of the substrate
The type of the deposition process used The nature of the deposited materials
the product of the kinetic rate constant and the system pressure

Diffusionally controlled CVD process: occurred when the opposite is true

Temperature effect on growth rate
conditions, a chemical system will rapidly fall to the minimum Gibbs free energy and lead to the formation of solid reaction products.
Three Steps Consisting the CVD Process
Metals, semiconductors and ceramics Amorphous, polycrystalline or single crystalline The properties depending upon the growth conditions
Contents in The Chapter
including vapor transport, reaction kinetics, nucleation and growth of deposited materials. For most of the systems, CVD
requires high temperature and low pressure. Under these

Removal of the gas-phase reaction by-products from the
growth surface.
反应物
气态副产物
边界层
化学反应
衬
底
化学气相沉积过程的扩散模型
（1）反应物运输通过边界层；
（2）表面反应形成固态沉积物；
（3）去除气相反应副产物.
Key Points Description of CVD Process
Economic factors

How to introduce precursors into reactor?
Solid or liquid precursors: using carrier gas passing