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Research Papers

Theoretical Analysis and Experimental Quantification of the Gas Leakage Due to Electrical Feedthroughs in Anodic Bonding

[+] Author and Article Information
Qimin Liu

State Key Laboratory of Transducer Technology,
Institute of Electronics,
Chinese Academy of Sciences,
University of Chinese Academy of Sciences,
No.19 Beisihuan West Road,
Haidian District, Beijing 100190, China
e-mail: liuqimin1228@163.com

Lidong Du

State Key Laboratory of Transducer Technology,
Institute of Electronics,
Chinese Academy of Sciences,
No.19 Beisihuan West Road,
Haidian District, Beijing 100190, China
e-mail: lddu@mail.ie.ac.cn

Zhan Zhao

State Key Laboratory of Transducer Technology,
Institute of Electronics,
Chinese Academy of Sciences,
No.19 Beisihuan West Road,
Haidian District, Beijing 100190, China
e-mail: zhaozhan@mail.ie.ac.cn

Cheng Liu

State Key Laboratory of Transducer Technology,
Institute of Electronics,
Chinese Academy of Sciences,
University of Chinese Academy of Sciences,
No.19 Beisihuan West Road,
Haidian District, Beijing 100190, China
e-mail: liuchengvbl@sina.com

Zhen Fang

State Key Laboratory of Transducer Technology,
Institute of Electronics,
Chinese Academy of Sciences,
No.19 Beisihuan West Road,
Haidian District, Beijing 100190, China
e-mail: zfang@mail.ie.ac.cn

1Corresponding author.

Contributed by the Electronic and Photonic Packaging Division of ASME for publication in the JOURNAL OF ELECTRONIC PACKAGING. Manuscript received June 17, 2013; final manuscript received April 19, 2014; published online July 24, 2014. Assoc. Editor: Mark D. Poliks.

J. Electron. Packag 136(3), 031015 (Jul 24, 2014) (6 pages) Paper No: EP-13-1050; doi: 10.1115/1.4028013 History: Received June 17, 2013; Revised April 19, 2014

In this paper, theoretical analysis and experimental quantification of the gas leakage issue due to feedthroughs in anodic bonding are presented. The theoretical analysis was conducted to quantitatively analyze the influence of metal feedthroughs in anodic bonding on the package quality based on the plate elastic deformation theory and the theory of gas flow in capillaries. To validate the analysis, absolute capacitive pressure sensors were fabricated with gold feedthroughs in the silicon–glass bonding interface. The dimensions of the leakage microchannels due to feedthroughs were quantified experimentally and the leakage rate following the anodic bonding was measured using a helium leak detector. The deviations from calculated values were less than 30% in different channel dimensions and 38.3% in leakage rates between theoretical analysis and experimental studies. To address this issue, a new structure was designed, fabricated and characterized where localized Si–Au eutectic bonding was used to improve the package quality. By fine tuning two key parameters of bonding temperature and feedthrough step height, the new design was demonstrated to improve the hermetic levels by at least two orders of magnitude compared to the conventional design without eutectic bonding.

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Figures

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Fig. 1

(a) 2D and (b) 3D schematics of the silicon to glass anodic bonding with feedthroughs in the bonding interface

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Fig. 2

Equivalent model of a vacuum cavity with connections to the outside world through feedthrough-induced microchannels

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Fig. 3

(a) Structure of the capacitive pressure sensor, (b) top view, and (c) cross-sectional view of the leaky microchannel due to metal feedthroughs

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Fig. 4

Comparisons between experimental results and theoretical predictions on dimensions of microchannels due to electrical feedthroughs

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Fig. 5

(a) The schematic view of the new capacitive pressure sensor and (b) backside view through the glass with h2 < h1

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Fig. 6

Fabricated sensors with feedthrough height of 500 Å in the new design: (a) wafer level view (see through the glass) and (b) single chip view

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