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debonded glass wafer that can be cleaned the pivot distance are listed in Table 2.
to remove adhesive residues and recycled The smallest radius is 307mm when the
multiple times, which is common practice lifting is 2mm and the pivot distance is
for glass wafers used in laser debonding 35mm. Figure 9 plots the relationship
processes. between the radius of curvature and
Edge t r i mm i ng and gr i ndi ng the bending stress of glass wafer for
conditions. Before bonding, an edge Table 2: Calculated radius from typical lifting height two thicknesses, 0.5mm and 0.7mm.
trimming process was applied to the Si and pivot distance values. A horizontal, blue line indicates the
wafer using a dicing saw tool (DFD6361) to the edge strength to assess the risk of typical, low-end edge strength value
from Disco (see Figure 5). The purpose glass failure due to bending. The bending of glass wafers made by Corning. The
of edge trimming is to reduce the risk of stress generated on the glass edge can be low-end strength value is much higher
interfacial delamination and edge chipping than the stress generated by the tightest
during the backside thinning process. The curvature 307mm during the debonding
edge trimmed profile is 100µm in width and process (blue arrow marks). Therefore,
50µm in depth. After bonding, a multi-step, the glass wafer can be used in the
backside thinning process was performed debonding process without failure. From
using the Disco grinder (DGP8761). The the low-end strength line and curvature,
first step is to use a coarse wheel grit the allowable bending curvatures are
to remove the bulk of the excess wafer 167mm and 234mm for 0.5mm and
thickness until it reaches 92µm. The second 0.7mm thick glass, respectively.
step is to use the finer wheel grit to grind
the Si thickness from 92µm to 52µm. The Summary
final step is to use the finest grit to precisely For semiconductor wafer thinning,
and slowly polish the Si thickness to the glass is an ideal carrier material because
target thickness of 50µm. of the following: 1) its ability to deliver
Results. The debonding results are Figure 9: Relation between the radius of curvature variable CTE to match the wafer CTE;
summarized in Figure 6. All samples and the bending stress. 2) flexible thickness to minimize shape
were successfully debonded, independent change during thinning and post-
of the adhesive system used, and no estimated from the radius of curvature thinning processing; 3) transparency to
damage was observed on the wafers. with beam bending theory as Eq. 1 below: enable bonding quality control; and 4)
The images in Figure 7 show the intact compatibility with multiple debonding
carrier and device wafers with some technologies. This paper demonstrated
imprints in the remaining adhesive layer successful debonding.
at the initiator position, which is typical
for mechanical debonding. The bulk where t is the wafer thickness, E is Acknowledgements
adhesive is on the glass for material Young’s modulus of the glass wafer, We thank Hsiang-Hung Chang of
A (device release) or on the device for and r is the bending radius during the Industrial Technology Research Institute
material B (carrier release). Adhesive debonding process. (ITRI) in Taiwan for providing Si
residues or imprints of the initiator can The bending radius, r, is obtained from wafer edge trimming and thinning. We
be removed in the subsequent cleaning the lifting height, h, and the distance at also thank MK Cornfield of Corning
step. As mentioned above, the debonded pivot from lifter, l, as shown in Table 2. Incorporated for providing editorial
glass carriers are in excellent condition Eq. 2 is based on the assumption that the support to this article.
with no mechanical f laws. Af ter deformation is simply cylindrical.
removing the adhesive traces on the glass Reference
surface, the carrier can be easily reused 1. J. Zhang, Y. Xiao, A. Teng, I. Dutta,
with no issue. V. Singh, L. Yang, M. Li, “Advanced
Stress calculation. The bending packaging carriers for WLFO
stress on the wafer during the debonding The calculated radius of curvature applications,” Chip Scale Review,
process can be calculated and compared r from the typical lifting height h and pp. 20-26, Jul/Aug, 2019.

Biographies
Julia Brueckner is the Sales & Business Development Manager at Corning Incorporated, Wiesbaden,
Germany. She joined Corning in 2019 to support the Precision Glass Solutions (PGS) business unit and is
responsible for customers in the EMEA region. She received her PhD in Physical Chemistry from Heidelberg U.
Email BrueckneJ@corning.com

Jay Zhang is the Business Development Director at Corning Incorporated in Corning, NY, USA. He joined
Corning in 2000 and is responsible for new business development as well as program management. He obtained
his PhD in Applied Physics from Yale U. and an MBA from Cornell U.

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