Name two chemicals used as dopants for PMOS and NMOS, and what are they known as?
- PMOS: Boron (B) & Gallium (Ga), acceptors
2. NMOS: Arsenic (As) and Phosphorous (P), donors
What are two other names for Mask?
Reticle or Working Plate
What’s the difference between positive and negative photoresist?
Positive photoresist: developer will dissolve areas exposed to light, harden other areas
Negative photoresist: developer will harden areas exposed to light, and dissolve other areas.
What’s the technical term for the hardening of photoresist?
polymerize
What’s the “reverse field technique”?
Using negative photoresist
What’s oxidation?
Silicon combines with oxygen or steam at high temperature to form a layer of silicon dioxide (SiO2)
What’s chemical vapor deposition?
A silicon compound such as silane reacts with oxygen to produce silicon dioxide on the wafer surface. (For instance between M1 and M2)
What’s CVD stand for?
Chemical Vapor Deposition
What’s plasma deposition?
Atomic particles in the form of either vapors or ionic gases deposit on the wafer surface.
What’s another name for plasma deposition?
Sputtering
What’s doping?
A specific chemical is driven into the silicon with high energy and speed, usually at an elevated temperature.
What are two other names of doping?
- Ion-implantation
2. Diffusion
What’s annealing?
After doping, the wafer is reheated to about 600 degrees C, which repairs crystal structure damage and improves conductivity.
What extra effect does annealing cause?
The out-diffusion effect, or lateral diffusion effect.
What’s photolithography?
The step in which layer patterns are transferred from masks to the wafer surface by casting an image on the photoresist.
What’s “step and repeat”?
Photolithography creates multiple images at various locations over the entire wafer surface.
What’s plasma etching?
Portions of oxide or other layers, such as poly, are selectively removed (etched) by either chemicals (etchants) or by high-energy electron beams.
What’s CMP stand for?
Chemical Mechanical Polishing
What’s chemical mechanical polishing?
A step which planarizes (smooths) the wafer surface. Done before lithography to provide a flat surface. Can also replace etching in certain situations, such as etching tungsten plugs (contact and via holes) or copper wiring.
What’s the process sequence step #1?
Silicon wafer lightly doped with boron at the time of silicon ingot growth.
What’s the process sequence step #2?
nwell creation:
- Add photoresist
- shine UV
- Add developer solution to remove some PR
- nwell formation through ion-implantation
- chemically remove remaining photoresist
- annealing
What’s the process sequence step #3?
Field oxide creation:
- Add layer of nitride
- Add photoresist
- Shine UV
- Add developer solution
- Plasma etch the exposed nitride
- chemically remove remaining photoresist
- Form field oxide through “wet oxidation technique”. Classic “bird’s beak” shape. (nitride keeps oxide from forming in some places)
- Remove remaining nitride.
What’s the process sequence step #4?
poly creation:
- gate (thin) oxide formation through (dry?) oxidation with carefully controlled oxide thickness (less than 100 angstroms) Doesn’t form on FOX
- poly formation through plasma deposition
- photoresist / UV / developer
- plasma etch poly and gate oxide
- remove remaining photoresist
What’s the process sequence step #5?
P+ and N+ diffusion creation:
- photoresist / UV / developer
- P+ through ion-implantation
- remove remaining photoresist.
- photoresist / UV / developer (possibly same mask with inverse resist type)
- N+ through ion-implantation
- remove remaining photoresist.
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