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sheet properties. If we assume the post-
thinning wafer layer is significantly thinner
than the carrier, the warp expression is:

Table 1: CTE values of commonly used wafer types.
Here we use subscript s to designate the the wafer to be thinned, its Young’s Packaging Carriers (APC) product was
material properties of the semiconductor modulus engineered to be relatively engineered to have a relatively high
wafer to be thinned: E s for Young’s high, and its thickness to be optimized Young’s modulus and a wafer thickness of
modulus, t s for the wafer thickness, υ s within the constraints of the application. up to 2mm.
for Poisson’s ratio, and α s for the thermal The transparent nature of glass makes
expansion coefficient. For the carrier glass, laser debonding possible, and the same Mechanical debonding of a glass
we use subscript g for the same parameters transparency also makes bonding quality
accordingly. L is the size of the carrier. control simple and straightforward. Other carrier
From the simplified formula shown glass benefits include: the ability to reach a Because of their excellent transparency,
above, we can see the trends clearly. The very low total thickness variation (TTV), glass carrier wafers are often associated
warp is linearly proportional to CTE its reusability, etc. Figure 2 compares with laser debonding. This does not have
mismatch, as well as the temperature glass to Si and the backgrinding tape to be the case. Glass carriers provide
differential between bonding and (BGT) used for wafer thinning. benefits for the mechanical debonding
operation; it is inversely proportional to the Figure 3 shows the availability of glass process as listed below.
carrier’s Young’s modulus; and the warp wafers that cover the range of 3-13ppm°C Enabling visual inspection. Glass
is also inversely proportional to the square from Corning. Corning’s Advanced carriers add value to the mechanical
of the carrier thickness. When we use the debonding by enabling visual inspection
typical conditions encountered in wafer
thinning and post-thinning processing, we
see these trends in Figure 1.

Benefits of glass as a carrier
The discussions above focused on three
levers for a carrier to help manage warp.
We discuss specific requirements and
constraints for each of the three below.
CTE is the most important attribute.
Table 1 shows the CTE of the most
commonly used wafer types. These include
Si on the low-CTE end, all the way to
LiTaO 3 on the high-CTE end. Glass can
cover the entire CTE range, and if the
market warrants the investment, a glass
company can design and make glass with
very fine granularity, down to ~0.2ppm/°C.
Young’s modulus. Young’s modulus
is an effective lever to control warp when
a perfect CTE match is not possible.
While popular glass compositions Figure 2: Comparison of substrates used for wafer thinning and their bonding properties.
typically show Young’s modulus in the
65-75GPa range, a highly technical glass
can exhibit Young’s modulus as high as
140GPa. In the real world, compromises
must be made between performance
and manufacturability, which translates
into cost.
Carrier thickness. Carrier thickness
is another lever available to the user. The
thickness-squared relationship makes
it highly effective in controlling warp,
especially in the 0.5-1.0mm range.
Glass is an ideal carrier wafer material
because it can offer a CTE that matches
Figure 3: CTE and Young’s modulus of APC wafer products from Corning Incorporated.

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