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Effects of Nanometer-Scale Surface Roughness and Applied Load on the Bond Strength and Contact Resistance of Cu-Cu Bonded 3D ICs

Published online by Cambridge University Press:  01 February 2011

Hoi Liong Leong ,
Chee Lip Gan ,
Carl V. Thompson ,
Kin Leong Pey  and
Hongyu Li
Hoi Liong Leong
Affiliation:
hlleong@tsmc.com, Singapore-MIT Alliance, Advanced Materials for Micro- and Nano-Systems, 4 Engineering Drive 3, Singapore, 117576, Singapore
Chee Lip Gan
Affiliation:
clgan@ntu.edu.sg, Singapore-MIT Alliance, Advanced Materials for Micro- and Nano-Systems, 4 Engineering Drive 3, Singapore, 117576, Singapore
Carl V. Thompson
Affiliation:
cthomp@MIT.EDU, Singapore-MIT Alliance, Advanced Materials for Micro- and Nano-Systems, 4 Engineering Drive 3, Singapore, 117576, Singapore
Kin Leong Pey
Affiliation:
eklpey@ntu.edu.sg, Singapore-MIT Alliance, Advanced Materials for Micro- and Nano-Systems, 4 Engineering Drive 3, Singapore, 117576, Singapore
Hongyu Li
Affiliation:
lihy@ime.a-star.edu.sg, Institute of Microelectronics, 11 Science Park Road, Singapore, 117685, Singapore
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Abstract

The effects of total surface roughness of Cu bond layers and applied load during bonding on the bond strength and the contact resistance of the bonded interface were studied for three-dimensional (3D) devices. The 3D structures were fabricated by thermocompression bonding of two wafers, each fabricated with a Cu damascene process. The average bond strength of the samples was found to increase with increasing load, and with decreasing roughness. On the other hand, the average contact resistance increased as the total surface roughness of the bonded interface increased, as well as when the applied load decreased. The increase in bond strength (and also the dicing yield) is related to a smaller true contact area, which can be estimated using a model based on contact mechanics theory. The theory takes into account the roughness of the bonded surface, the applied load during bonding and the nominal bond area. A contact resistance model can also be used to estimate the contact resistance of bonded interfaces based on their true contact area. However, within each set of measurements, a significant spread about the average value of bond strength and contact resistance was observed, suggesting issues of contact and bonding non-uniformity of the wafers. Nonetheless, the contact resistance values given by the model were in good agreement with the minimum values observed in experiments, which may represent the ideal cases of bonding of rough surfaces. Our results show that the impact of surface roughness and applied load on the contact resistance of Cu-Cu thermocompression bonds can be quantified experimentally, and understood in the context of established theory for contact mechanics.

Keywords

bondingCuelectrical properties
Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 1036: Symposium M – Materials and Hyperintegration Challenges in Next-Generation Interconnect Technology , 2007 , 1036-M02-05
Copyright
Copyright © Materials Research Society 2008

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