Solar Cell Fundamentals Lab – Lecture 5A – PECVD SiO2 revised 9

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Be careful what you wish for
SiO2 backside protection
A coating of SiO2 is deposited on
the backside of the wafer to
insolate it from the doping process
PECVD
•
•
•
•
•
Plasma
Enhanced
Chemical
Vapor
Deposition
PECVD is used extensively in the
manufacture of microelectronic devices
because it allows for lower temperature
processes
Just like in sputtering, a
plasma is formed in an electric
field
The plasma allows for the
deposition or growth of films at
lower temperature than would
normally be required in just a CVD
process
Trion ORION III PECVD tool
The plasma can be
viewed through a
viewport on the side
Typical PECVD Process
• The wafer is loaded in into the vacuum
chamber
• The chamber is pumped to vacuum
conditions
• The wafer is heated to deposition
temperatures (300oC typical)
• Gas are introduced that will acts as
precursors to the film growth
Typical PECVD Process
(continued)
• Chamber pressure is regulated to
provide an equilibrium pressure ( gas in,
pumping out)
• RF power is applied to the chamber
creating a plasma
• A film is grown based on the gases
introduced
For our solar cell
• We will be using SiO2 as the
protective layer
Trion ORION III PECVD
Chamber lid open
Heated substrate stage
Can accommodate up to 8”
wafers
Trion ORION III water chiller and dry (no oil)
chemical vacuum pump
Trion ORION III process gas cabinet
TEOS (tetraethylorthosilicon) SiO2 precursor
The backside of the solar cell will
have a color tint. The color will
relate to the SiO2 thickness
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