| INTERDISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY |
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Detection and formation mechanism of micro-defects in ultrafine pitch Cu–Cu direct bonding |
| Zi-Yu Liu(刘子玉)1, Jian Cai(蔡坚)1,2, Qian Wang(王谦)1, Yu Chen(陈瑜)1 |
1. Institute of Microelectronics, Tsinghua University, Beijing 100084, China;
2. Tsinghua National Laboratory for Information Science and Technology, Beijing 100084, China |
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Abstract In this paper, Cu-Cu interconnects with ultrafine pad pitches of 6 μ m, 8 μ m, and 15 μ m are implemented on the 12 inch wafers by a direct bonding process. Defects are not found by traditional non-destructive (NDT) c-mode scanning acoustic microscopy (c-SAM). However, cross sectional observation of bonding interfaces reveals that micro-defects such as micro seams are located at SiO2 bonding interfaces. In order to examine the micro-defects in the ultra-fine pitch direct bonding process by the NDT technology, a novel “defect-enlarged approach” is proposed. The bonded dies are first annealed in an N2 oven at 300 ℃ for a few hours and then cooled quickly in air. The c-SAM scanning images show large defects at the place where nothing can be detected by c-SAM before this treatment. Cross sectional observation of the bonding interfaces indicates that these defects consist of large size micro seams at the SiO2 bonding interface, especially near Cu pads with an ultrafine pitch of 6 μ m. However, these large defects disappear after several hours at room temperature, observed by c-SAM. It is inferred that the disappearance of these defects inspected by the “defect-enlarged approach” results from the combination of intrinsic micro seams and “weak” bonds in the silicon oxide layer. Then the underlying physical mechanism of these micro-defects is proposed, which is influenced by Cu pad surface topology and bonding models.
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Received: 07 May 2015
Revised: 29 July 2015
Accepted manuscript online:
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PACS:
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81.70.-q
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(Methods of materials testing and analysis)
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43.58.Ls
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(Acoustical lenses and microscopes)
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73.20.Hb
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(Impurity and defect levels; energy states of adsorbed species)
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| Fund: Project supported by the National Natural Science Foundation of China (Grant No. 61274111) and the National Basic Research Program of China (Grant No. 2015CB057205). |
Corresponding Authors:
Jian Cai
E-mail: jamescai@tsinghua.edu.cn
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Cite this article:
Zi-Yu Liu(刘子玉), Jian Cai(蔡坚), Qian Wang(王谦), Yu Chen(陈瑜) Detection and formation mechanism of micro-defects in ultrafine pitch Cu–Cu direct bonding 2016 Chin. Phys. B 25 018103
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