Deposition Flashcards
lower cleaner room class
better conditions
Epitaxy
The growth of a single crystal material on top of an already existing substrate.
- you need to perform epitaxy on a single crystal substrate
What are the two types of vapor phase epitaxy?
- Chemical vapor deposition
- Physical vapor deposition
Chemical vapor deposition is done by
- semiconductor and dopants are grown on the surface of the substrate using reactive gasses
physical vapor deposition is done by
semiconductor and dopants are grown on the surface of the substrate by transferring material from pure solid sources
How is CVD implemented?
gases in a reactor to initiate gaseous chemical reactions that leave solid by-products condense on the wafer and gas byproducts are pumped away
CVD is good for
good thin film step coverage
Low pressure CVD
Uses thermal energy to drive reactions depositing them films on the substrate
Plasma enhanced CVD
Uses RF energy to give greater control over stresses and film properties
LPCVD
Low pressure chemical vapor deposition
- deposits on both sides of the wafer
- Pyrolysis at 500-1000C
- dopants: PH3, B2H6 etc
LPCVD steps
1) gas phase reactants transported to substrate
2) adsorption of film precursor
3) surface diffusion
4) redesoroption of film precursor
5) nucleation and island growth
desorption of volatile surface reaction products
LPCVD steps
1) gas phase reactants transported to substrate
2) adsorption of film precursor
3) surface diffusion
4) redesoroption of film precursor
5) nucleation and island growth
desorption of volatile surface reaction products
SI02 growth
is done in a tube furnace. It is a consumptive process that reduces the substrate thickness (because 46% of the Sio2 goes into the Si, reducing overall thickness)
SI02 growth
is done in a tube furnace. It is a consumptive process that reduces the substrate thickness (because 46% of the Sio2 goes into the Si, reducing overall thickness)
What limits SIO2 growth?
The process is diffusion limited
- growing an oxide layer rapidly slows the diffusion of oxygen to the interface where the reaction takes place
SIO2 wet growth vs dry growth
Wet growth:
- less dense
- faster
- uses water and carrier gas n2
Dry growth
- produces a denser oxide
slower growing
- uses high temp and carrier gas (n2)
Plasma enhanced CVD
Overcomes the need for high temp and slow process rates by using RF energy in the system
= Allows for low temp deposition and therefore less expensive substrates such as Al.
Plasma enhanced CVD
Overcomes the need for high temp and slow process rates by using RF energy in the system
= Allows for low temp deposition and therefore less expensive substrates such as Al.
What is atomic layer deposition (ALD)?
Single atomic layers deposited using adsorbed monolayers with specific chemistry
what are the advantages of ALD?
- Very good control over layer thickness
- good uniformity
- conformal coating
- extremely thin dielectrics
what are the disadvantages of ALD?
- slow
- cannot be patterned using lift off
What is electrodeposition (electroplating)?
An electrochemical process that metal ions in solution are deposited
- voltage is applied to a substrate in an electrolytic solution
- Usually involves control with an applied electric current
What is electrodeposition useful for?
When metallic films are desired with thicknesses in the range of 1-100um
Disadvantages of electrodeposition?
plated metals often exhibit rougher surface than evaporated or sputtered films
What is physical vapor deposition and what are the two main methods?
- line of sight ejection of material towards the substrate, that sticks and forms a film
- sputtering and evaporation are the two main methods
What is sputtering?
Sputtering uses ions to bombard a target to physically eject material with a sandblasting effect
advantages of sputtering
- wide variety of materials, including alloys
- highly controllable deposition rate
- better step coverage
- better film adhesion
- better film property control
disadvantages of sputtering
- ion damage
- substrate heating
How does PVD evaporation work?
Heating a material in a vacuum to lower its vapor point so that it evaporates from the crucible.
Advantages of PVD evaporation
Lower capital cost
- highly directional (good for lift off)
low substrate heating
- high deposition rates
Disadvantages of PVD evaporation
- few materials can be used
- limited controls are available
What is molecular beam epitaxy (MBE)?
Materials are evaporated at very low pressure to create vapor beams that strike the substrate and deposit materials for epitaxy
Advantages of MBE?
- shutters allow for abrupt changes in material composition and doping
Disadvantages of MBE?
Slow growth rates, 1um per hour
- can deposit controllably just a few atomic layers
What does step coverage for highly directional deposition depend on?
Geometry and angular application
What can step coverage be used for?
lift off and shadow masking
What can cause issues for step coverage
- mean free path and high surface migration
- long mean free path and low surface migration
- short mean free path and low surface migration
What is the GLAD (glancing angle deposition method)?
Mean free path and low surface migration can be taken advantage of by creating nanostructures.
- a cooled substrate decreases surface migration
- rotating the substrate during deposition can create 3D shapes like corkscrew
What can residual stress do to materials?
Cause layers to be in tension / compression which bends, arcs or curls material after reaching temperature equilibrium
