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Microelectromechanical Devices > Deposition > Flashcards

Deposition Flashcards

1
Q

lower cleaner room class

A

better conditions

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2
Q

Epitaxy

A

The growth of a single crystal material on top of an already existing substrate.
- you need to perform epitaxy on a single crystal substrate

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3
Q

What are the two types of vapor phase epitaxy?

A
  • Chemical vapor deposition
  • Physical vapor deposition
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4
Q

Chemical vapor deposition is done by

A
  • semiconductor and dopants are grown on the surface of the substrate using reactive gasses
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5
Q

physical vapor deposition is done by

A

semiconductor and dopants are grown on the surface of the substrate by transferring material from pure solid sources

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6
Q

How is CVD implemented?

A

gases in a reactor to initiate gaseous chemical reactions that leave solid by-products condense on the wafer and gas byproducts are pumped away

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7
Q

CVD is good for

A

good thin film step coverage

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8
Q

Low pressure CVD

A

Uses thermal energy to drive reactions depositing them films on the substrate

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9
Q

Plasma enhanced CVD

A

Uses RF energy to give greater control over stresses and film properties

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10
Q

LPCVD

A

Low pressure chemical vapor deposition
- deposits on both sides of the wafer
- Pyrolysis at 500-1000C
- dopants: PH3, B2H6 etc

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11
Q

LPCVD steps

A

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

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12
Q

LPCVD steps

A

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

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13
Q

SI02 growth

A

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)

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14
Q

SI02 growth

A

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)

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15
Q

What limits SIO2 growth?

A

The process is diffusion limited
- growing an oxide layer rapidly slows the diffusion of oxygen to the interface where the reaction takes place

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16
Q

SIO2 wet growth vs dry growth

A

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)

17
Q

Plasma enhanced CVD

A

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.

18
Q

Plasma enhanced CVD

A

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.

19
Q

What is atomic layer deposition (ALD)?

A

Single atomic layers deposited using adsorbed monolayers with specific chemistry

20
Q

what are the advantages of ALD?

A
  • Very good control over layer thickness
  • good uniformity
  • conformal coating
  • extremely thin dielectrics
21
Q

what are the disadvantages of ALD?

A
  • slow
  • cannot be patterned using lift off
22
Q

What is electrodeposition (electroplating)?

A

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

23
Q

What is electrodeposition useful for?

A

When metallic films are desired with thicknesses in the range of 1-100um

24
Q

Disadvantages of electrodeposition?

A

plated metals often exhibit rougher surface than evaporated or sputtered films

25
Q

What is physical vapor deposition and what are the two main methods?

A
  • line of sight ejection of material towards the substrate, that sticks and forms a film
  • sputtering and evaporation are the two main methods
26
Q

What is sputtering?

A

Sputtering uses ions to bombard a target to physically eject material with a sandblasting effect

27
Q

advantages of sputtering

A
  • wide variety of materials, including alloys
  • highly controllable deposition rate
  • better step coverage
  • better film adhesion
  • better film property control
28
Q

disadvantages of sputtering

A
  • ion damage
  • substrate heating
29
Q

How does PVD evaporation work?

A

Heating a material in a vacuum to lower its vapor point so that it evaporates from the crucible.

30
Q

Advantages of PVD evaporation

A

Lower capital cost
- highly directional (good for lift off)
low substrate heating
- high deposition rates

31
Q

Disadvantages of PVD evaporation

A
  • few materials can be used
  • limited controls are available
32
Q

What is molecular beam epitaxy (MBE)?

A

Materials are evaporated at very low pressure to create vapor beams that strike the substrate and deposit materials for epitaxy

33
Q

Advantages of MBE?

A
  • shutters allow for abrupt changes in material composition and doping
34
Q

Disadvantages of MBE?

A

Slow growth rates, 1um per hour
- can deposit controllably just a few atomic layers

35
Q

What does step coverage for highly directional deposition depend on?

A

Geometry and angular application

36
Q

What can step coverage be used for?

A

lift off and shadow masking

37
Q

What can cause issues for step coverage

A
  • mean free path and high surface migration
  • long mean free path and low surface migration
  • short mean free path and low surface migration
38
Q

What is the GLAD (glancing angle deposition method)?

A

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

39
Q

What can residual stress do to materials?

A

Cause layers to be in tension / compression which bends, arcs or curls material after reaching temperature equilibrium

Microelectromechanical Devices (12 decks)

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