Exploration 1C:
How is Chemistry used
to build ICs?: Making a Capacitor
This animation illustrates
the processes involved in building a capacitor on top of
a doped silicon wafer. The movie is designed
for easy click through of the frames individually.
Process Steps for a Discrete Capacitor
Clicking on the text
links will take you to the Glossary for more information about
the term.
- Begin with Doped
Silicon Substrate
- Grow Oxide
Layer
- Apply Photoresist
Polymer
- Place Mask
over Chip
- Expose Areas to be
Removed to Light
- Remove Mask
- Wash Away Exposed
Photoresist
- Etch Oxide
- Deposit Conductors
- Remove Remaining
Photoresist
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Glossary
- Doped Silicon Substrate
-
- Silicon's conductivity
for the capacitor substrate is enhanced by "doping"
or inserting other atoms into the crystal matrix. In p-doped
silicon, atoms such as boron with 3 valence electrons are inserted
into the crystal. The "p" designation comes from the
holes (or missing electrons) resulting from having atoms present
with 3 valence electrons instead of silicon's four valence electrons.
In n-doped silicon, atoms with five valence electrons,
such as phosphorus, are added resulting in extra electrons present
relative to when all the atoms were silicon. Back
- Oxide Layer
-
- The most common insulator
used in microelectronics is silicon dioxide glass. Silicon dioxide
is a very poor conductor and can be grown on the wafer simply
by heating it in oxygen. Back
- Photoresist Polymer
-
- The photoresist polymer
is a very thin coating of polymer (similar to nail polish) applied
to the wafer surface which will react with light to create areas
which are soluble in different solvents. By removing selected
areas of the photoresist, those areas of the wafer are available
for reactions and modifications while the rest of the wafer is
protected. Back
- Mask
-
- The mask is a very
elaborate template which shields the areas of the photoresist
that are needed for protection and allows light to penetrate
to the photoresist to be removed. Back
- Light
-
- The light used to
initiate transformations in the photoresist polymer is usually
ultraviolet light. For the type of photoresist polymer illustrated
here, the light initiates bond-breaking so that the exposed areas
can be easily washed away. Back
- Conductors
-
- The conductors in
microelectronics are generally formed from deposited conducting
metal such as aluminum. Back
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