Slide 1

Report
Development of Integral Heater for In-Situ Heat Treatment of Silicon Wafers During
Sputter Deposition of Aluminum and Silicon for Solar Cell Fabrication
Kris Durgin
USM TMC-2004
Electrical Engineering Dept.
Temperature profiling of my design characterizing the operating
parameters and heater capability. Two methods were utilized and
compared to minimize error from thermal conduction of thermo-couple
(TC) wire and/or convection from residual gas flow. The left photo has
the TC bonded to wafer surface enclosed by a Pyrex Petri dish.
Measurements in the right photo are taken within a pocket sandwiched
between two silicon wafers. The unit is capable of operating up to 580˚C
in inert gas, low pressure condition for post deposition heat treatment.
Molybdenum (MO) is a refractory metal can withstand operating
conditions > 2000˚C, has a high watt density and is easily machined.
Retention of our 0.0035” foil retaining the stock was accomplished using
adhesive onto a flat laminate base. A semi-circular pattern creates
controlled heated area and enables the correct resistance to be
obtained. The lower right photo reveals the heated area suitable for our
circular wafers.
Machining of glass filled ceramic performed on a
CNC milling. The coolant, (water), is
dispensed from a self devised closed loop
system. By following manufacturer’s
recommended head speed and feed rates with
carbide tooling we achieved professional results.
Design and Fabrication of a High Temperature (600C) Heater for
Use in Heat Treatment of 4-inch Silicon Wafers During and After
Sputter Deposition of Aluminum and Silicon Films for Solar Cell
Fabrication. Arching of plasma at 120VRMS dictated custom design
of a low voltage heater operating at voltages no more than 40VRMS.
Current design employs 24VRMS vaiable power supply.
Below are photos of the actual Aluminum sputtering process. We
employ a DC biased magnetron head designed to capture electrons
and elevate energy state amplify ionization of Argon atoms evident by
the circular pattern in the left photo. The visible plasma glow is an
artifact of photon emission of electrons decaying back to their ground
state and from EM waves emitted by ionized Argon atoms in the 700
to 800 nanometer spectrum shown in the lower right chart.
Under the direction of Dr. M. G. Guvench, various testing schemes are possible in USM’s
Electrical Engineering Micro-Fabrication lab. Four point resistance probing and automated
photovoltaic diode I/V characterization are just two of the many tests at our disposal to
assess deposition of Aluminum onto silicon wafers. It is our intent that future development
of Micro Electro-Mechnical Structures, (MEMS) at USM, may use the very practices
established for sputtering of Aluminum.

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