Steamer vs. torch in PV manufacturing—a cost of ownership comparison
Steamer vs. torch in PV
manufacturing—a cost of
ownership comparison
Jeff Spiegelman, RASIRC, San Diego, California, USA
Introduction
article looks at the cost advantages of using
This article looks at the cost
Improvements to first generation solar
purified steam instead of torches in photo-
advantages of using purified
cells will require the use of lower cost
voltaic manufacturing processes.
steam instead of torches in
multicrystalline (mc)-silicon, thinner wafers
photovoltaic manufacturing
and additional oxide layers to improve cell
Key oxidation factors affecting
efficiency. Higher efficiency can be achieved
processes.
profit
through the addition of front and rear
Many factors are involved in calculating
oxide passivation layers. Dry oxidation is
the total cost of ownership. These can be
too slow at low temperatures and at high
grouped into two categories: factors related
temperatures prevents the use of lower
Keywords: Purified Steam, Wet
to yield (number of good die) and factors
cost multicrystalline silicon wafers. This is
related to cost (total cost of all die)—see
Thermal Oxidation, Pyrolitic
driving the industry to add a wet oxidation
Chart 1.
Torch
step to grow the passivation layers.
In wet thermal oxidation, steam or
Yield
water vapor is added to accelerate the
Yield is defined as the number of die that
oxidation growth rate. Oxide is the critical
pass final test. The total number of die
material in wet thermal oxidation, so the
per unit time is a function of throughput,
method of generation determines the
which is controlled by the process recipe
yield and throughput, and the ultimate
(growth rate), plus maintenance time
success of the device in the marketplace.
and unscheduled work stoppages. The
Any improvements in the steam generation
throughput calculation should also include
process go straight to the bottom line. This
start up delays with equipment, installation
and permits because these affect the market
window and cannot be recovered.
Total bad die (yield loss) is subtracted from
the total die and is related to problems
with across-wafer uniformity, wafer-to-wafer
uniformity, and run-to-run uniformity,
warpage, particles and overall film quality or
electrical performance.
Cost
Process cost is the sum of materials
consumed during oxidation, consumables
used to process the wafers, maintenance
parts, labor to process and maintain the
tools, and testing associated with the quality
level attained by process control.
Facilities cost include the cost to
prepare the facility to grow oxide, tool cost
and depreciation, installation and piping,
permits, inspections, and insurance that
takes into account safety.
Chart 1. Key oxidation factors affecting profit.
6 – Global Solar Technology – May/June 2009
www.globalsolartechnology.com
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