Hello
I'm designing a three zone oxidation- / diffusion furnace for my own,
small semiconductor laboratory. The furnace itself is more or less
finished, but the diffusion tube has still to be choosen / bought. A
perfect material for the tube would be fused quartz (like HSQ300/400
from Heraeus or 214 LD / LDH from GE). But once the tube has been run
in, the temperature mustn't go below about 300 °C, otherwise the tube
will crack as an effect of devitrification.
Now I have the following problem: As I use this furnace only a few
times a month, it's
a) too expensive for me, to keep the furnace always running at about
300-400°C standby, as a lot of current and nitrogen is used.
b) a potential fire hazard if something should happen (although there
are overtemperature sensors) while I'm not in the lab for a longer
time.
c) too expensive to buy and install a new quartz diffusion tube for
every run of the furnace.
So I looked for alternative materials. Finally I found two interesting
materials:
-Alsint 99.7% (recrystallized Al2O3 min. 99.7%, non****ous)
-Halsic-I (SiSiC, reaction bonded, silicon infiltrated silicon
carbide,
non****ous)
Now my questions are:
-Do these materials withstand repeated ramping up from room
temperature to the max. process temperature of 1300 °C and after
processing back to room temperature again without any cracking?
-Are these materials usable as a process tube in a
diffusion-/oxidation furnace for semiconductor processing? Or is there
too much outgassing of alkali- and other ions which will contaminate
the silicon wafers?
-Do you know of even better diffusion tube materials and where I can
get them (manufacturer / distributor)?
My process / furnace parameters are:
Outer atmosphere: air at atmospheric pressure
Inner atmosphere(s): nitrogen, argon, oxygen, oxygen with H20 va****,
all at atmospheric pressure with a slow laminar flow along the process
tube.
Temperature: max. 1300 °C, usually 1000 - 1100 °C
Tube outer diameter: 70 mm or 150 mm (has still to be determined)
Zones: 3
Power: max. 7,5 kW
I hope someone can help me along with this problem, as it's really
difficult to get informations about the suitability of these materials
for semiconductor processing.
Many thanks in advance and kind regards,
Alex
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