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acoustic microscopy (CSAM). The standard mitigation method is to
introduce edge trimming around the entire wafer before bonding.
Post-grinding thickness measurement in two perpendicular
directions, shown in Figure 10, indicated total thickness variation
from wafer center to wafer edge. Discounting the wafer edges, TTV
seems to be around 0.4µm. We believe stack TTV (~0.2µm), debris
shedding from edge delamination, equipment vibration during
grinding and the measurement technique itself all contributed to
this result.
Work is continuing to further optimize ALoT bonding quality and
bonding strength. Grinding conditions such as down pressure, wheel
RPM, and feed speed/direction are also under study.

Summary
Precision wafer thinning supported by a carrier wafer can take
advantage of two enabling capabilities reported in this work: ultra-
low-TTV glass carrier, and near-zero-TTV temporary bonding.
The resulting stack TTV can be as low as 0.2µm for wafer size
<200mm; for a 300mm wafer, stack TTV can be as low as 0.4µm.
While ultra-low-TTV glass carrier wafers are now commercially
available, the ALoT bonding method as well as the thinning
Figure 9: After grinding LT to a thickness of 5µm, the LT wafer shows more processes are still under further development.
Future work includes optimizing the ALoT bonding strength and
severe chipping all around the wafer.
quality to reach even thinner target thicknesses, as well as applying
CMP to the ground surface before attempting to bond the thin LT
to a permanent substrate such as Si.
Acknowledgments
The following Corning employees made significant contributions
to the reported work: Erica Chang, Chris Kuo, Andy Kuo, Julie
Tseng, Gwako Liang, Robert Manley, Han-hee Jo, Prantik
Mazumder, Julia Brueckner and Kuniaki Yamazaki. The author also
wishes to acknowledge DISCO Corporation in Japan for performing
LT wafer thinning down to a thickness of 5µm, and Dr. Frank Wei
of DISCO Hi-Tec America for insightful technical discussions. This
paper was originally presented at the 25th Electronics Packaging
Technology Conference (EPTC 2023) and was edited for publication
in Chip Scale Review.

References
1. J. Zhang, et al., “Advanced packaging carriers for WLFO
Figure 10: Thickness measurement in the X and Y directions indicate total TTV
~0.4µm. Because the stack TTV is ~0.2µm, other factors such as debris shedding, applications,” Chip Scale Review Jul/Aug 2019, pp. 20-26.
and equipment vibration during grinding and measurement may have contributed 2. S. Garner, et al., “Flexible glass and its application for
to the LT TTV. electronic devices,” 24th International Workshop on Active-
Matrix Flat Panel Displays and Devices: TFT Technologies
Figure 8 shows the wafer after grinding LT to a thickness of and FPD Materials, Proc., pp. 28-33, Aug. 8, 2017.
15µm. Only minor chipping is evident at the 9:30 position. Figure 3. P. Mazumder, et al., “Temporary bonding technologies for
9 shows the same wafer when fine grinding further thinned the LT thin wafer handling,” 2018 Meet. Abstr. MA2018-02, p. 950.
layer to a thickness of 5µm. Much more chipping can be seen all 4. T. Takai, et al., “Incredible high-performance SAW
around the wafer. This indicates the ALoT bonding strength may resonator on novel multi-layered substrate,” 2016 IEEE
be insufficient. It is well known in the semiconductor industry that Inter. Ultrasonics Symp. (IUS), Tours, France, 2016, pp. 1-4.
bonding is usually weaker around the wafer edge even if voids and 5. http://www.nanoindustry.su/files/article pdf/4/article
other defectivities are not observed visually or by confocal scanning 4630_330.pdf

Biography
Dr. Jay Zhang is Business Development Director with Corning’s Advanced Optics division, Corning, NY.
He has been with Corning over 20 years in various business development and program management roles.
His recent focus is leading innovation efforts at creating differentiated glass wafer products and solutions
that meet challenging applications requirements. He is also active in collaborating with ecosystem partners
to demonstrate new product value propositions. He obtained his PhD in Applied Physics from Yale U. and his
MBA from Cornell U. Email zhangjj@corning.com

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