On 2010-09-03 18:44, Sandy Harris wrote:
On Sat, Sep 4, 2010 at 6:17 AM, John Sessoms<[email protected]> wrote:
Cool. Wonder how much for a 202mm x 254mm?
They are using 12 inch wafers, so 8" by 8" with diagonal at 8*root2 which
is about 8*1.4 = 11'2" is about as big as will fit. 8" by 10" gives 100 + 64
for squares, root 164 for the diagonal, too big for wafer.
And, since wafers are circular, you probably won't see a size like 8" x
10" ... it's close enough to the far reaches of yield on an 8" or so
diameter wafer slice that they're not going to waste the extra space.
They'll make square sensors instead. Now, you might eventually see a
10" x 10", though, if wafer production changes to larger diameter
slices. But vapor depositing 25% more diameter is going to take a /lot/
of additional silicon atoms and time "in the tank".
I'm not sure it's still true, but the actual silicon wafers used to be
produced by using vapor deposition along a wire to create a "circular"
solid (a cylinder), then slicing that cylinder to produce the wafer
"blanks". That means that you hang a wire in an appropriate vessel and
fill the vessel with a gas mixture heavy in silicon. This grows
('deposits') a "crystal" atom by atom, on the wire, then out from it
(I'm taking some liberties here to keep things simple, for the pedants
out there). Increasing the deposition depth from 8" to 10" means a
large amount of extra silicon (maybe as much as twice the silicon, I
haven't done the math), and a concomitant increase in the occurrence of
flaws that make the wafer unusable.
--
Thanks,
DougF (KG4LMZ)
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