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Figure 2: Wafers that have gone through high-precision polishing could achieve a TTV well below 1µm. This example shows a 300mm diameter wafer with thickness
variations on the order of 0.2µm in the 3, 6, 9 and 12 o’clock directions, respectively.
He re, we u se subsc r ipt “s” t o device wafer often has metallization inversely proportional to the square of
designate the material properties of the and dielectric materials in the wafer the carrier wafer thickness.
semiconductor wafer on the carrier: E s makeup. In the case of through-silicon As a result of understanding the
for Young’s modulus, t s for the wafer vias (TSVs), Cu-filled vias may occupy relationships noted above, we now
thickness, υ s for Poisson’s ratio, and α s a significant volume fraction of the offer glass wafers that cover a wide
for the thermal expansion coefficient. entire wafer, making the effective range of CTEs with fine granularity.
F o r t h e c a r r i e r g l a s s , w e u s e CTE higher than that of pure Si. If F i g u r e 3 sho w s a v a i l a b i l i t y
subscript “g” for the same parameters the device wafer is made of a non- between CTE values ranging from
accordingly. L is the size of the carrier. Si material, such as GaAs or sapphire 3-12.5ppm/°C. For products in the
From this simplified relationship, or SiC, the carrier wafer also needs red box, the carrier glass wafers also
one clearly sees that for the bonded to deliver a matching CTE to these deliver a high Young’s modulus and
wafer pair, CTE matching between the materials, respectively. In the same flexibility in wafer thickness. Wafers
semiconductor wafer and the carrier formula, one also realizes two other can be made all the way to 5mm in
is the most direct and impactf ul high-impact parameters: the shape thickness. The light blue diamonds
factor in minimizing distortion. In Si distortion is inversely proportional to indicate products that typically do
wafer thinning applications, a typical the glass’s Young’s modulus; it is also not exceed 1mm in thickness with a
somewhat lower Young’s modulus.
B e c a u s e m e c h a n i c a l p o l i sh i n g
techniques that produce the ultra-low-
TTV characteristics are independent
of the glass’s ther momechanical
properties, all the available glass types
in Figure 3 can be manufactured to
have ultra-low-TTV.
ALoT: Advanced Liftoff
Technologies
ALoT is an acronym for Advanced
Li f t- of f Te ch nolog ie s — a b r o a d
term that describes our portfolio of
temporary bonding technologies. The
original motivation behind developing
A LoT was to suppor t the use of
Corning’s ultrathin Willow glass [2] in
®
making thinner, lighter, more flexible
and durable displays by leveraging
Figure 3: Corning’s carrier wafer offering covers the entire 3-12.6ppm/°C range with fine granularity. Products
in the red box have high Young’s modulus by design as well as thickness flexibility all the way to 5mm. existing display panel infrastructure.
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