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backgrinding (BG), chemical vapor
deposition (CVD), or other chemical
processes. By hardening the adhesive
layer before loading into several
p r o c e s s e s , t he d eg r a d a t io n a nd
softening of the adhesive layer during
these processes can be prevented.
To distinguish this UV irradiation at
405nm for polymerization of the resin
before chemical or thermal processing
from the use of UV irradiation at
254n m for N 2 gas generation, we
refer to the 405 nm-wavelength UV
irradiation as “pre-UV.” By using pre-
UV irradiation, the adhesive got rigid
and the adhesion strength gets lower.
This crosslinking of the adhesive resin
Figure 4: Wafer thickness variation in an 8-inch wafer and edge appearance after backgrinding supported also improves chemical and thermal
with a glass carrier and SELFA. resistances because the resin is stiffly
bonded and it prevents components
by radical polymerization and the ca n be a ch ieve d w it hout N 2 ga s in the adhesive from dissolving or
adhesion layer becomes rigid. The generation occurring if high-energy decomposing in chemical or thermal
tensile modulus of elasticity of the UV radiation were used. Figure 3 processes, respectively.
adhesion layer increases from about shows some suggested applications, For t he s e c ond a p p r o a ch – t o
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1~10 x 10 Pa before UV irradiation, such as laminating the self-releasing decrease affinity to the adherend – the
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to 1~10 x 10 Pa after UV irradiation. a d h e sive t a p e t o t h e wa fe r a n d surface polarity of the adhesive resin
By using low-energy UV irradiation, irradiating using 405nm UV light is controlled by adding low polarity
polymerization in the adhesive layer before loading into processes like components into the adhesive layers.
By adding low polarity components
to the adhesive layers, the surface
polarity is lowered and the rise in
the adhesion strength because of
heat becomes moderated, as shown
in Figure 3. This means the tape can
be removed easily after the thermal
processes. Combi ni ng these t wo
methodologies—pre-UV and adding a
low polarity component—enables easy
removal of SELFA from the wafer
after processing.
Process applicability
To deter mine the applicabilit y
of SELFA as a temporary bonding
material, the following points were
evaluated: 1) total thickness variation
(TTV) after BG; 2) chemical resistance;
3) thermal resistance; 4) gas debonding;
and 5) residue after tape removal. The
evaluation followed the process flow
shown in Figure 3.
Figure 4 shows the wafer thickness
variation after BG supported by a glass
carrier with SELFA. The wafer was
ground down smoothly from 750µm
to 50µm without wafer cracking and
the TTV of the thin wafer was less
than 3µm. It means that smooth BG
can be realized by having the hard
carrier supported with SELFA without
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46 Chip Scale Review January • February • 2021 [ChipScaleReview.com]
