Protection of MOS capacitors during anodic bonding

Authors: Schjølberg-Henriksen K.¹; Plaza J.A.²; Rafí J.M.²; Esteve J.²; Campabadal F.²; Santander J.²; Jensen G.U.³; Hanneborg A.¹

Source: Journal of Micromechanics and Microengineering, Volume 12, Number 4, 2002 , pp. 361-367(7)

Publisher: IOP Publishing

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Abstract:

We have investigated the electrical damage by anodic bonding on CMOS-quality gate oxide and methods to prevent this damage. n-type and p-type MOS capacitors were characterized by quasi-static and high-frequency CV-curves before and after anodic bonding. Capacitors that were bonded to a Pyrex wafer with 10 m deep cavities enclosing the capacitors exhibited increased leakage current and interface trap density after bonding. Two different methods were successful in protecting the capacitors from such damage. Our first approach was to increase the cavity depth from 10 m to 50 m, thus reducing the electric field across the gate oxide during bonding from approximately 2 × 10⁵ V cm^-1 to 4 × 10⁴ V cm^-1. The second protection method was to coat the inside of a 10 m deep Pyrex glass cavity with aluminium, forming a Faraday cage that removed the electric field across the cavity during anodic bonding. Both methods resulted in capacitors with decreased interface trap density and unchanged leakage current after bonding. No change in effective oxide charge or mobile ion contamination was observed on any of the capacitors in the study.

Language: English

Document Type: Miscellaneous

Affiliations: 1: University of Oslo, PO Box 1048 Blindern, N-0316 Oslo, Norway 2: Centro Nacional de Microelectrónica, Campus UAB, 08193 Cerdanyola, Barcelona, Spain 3: SINTEF Electronics and Cybernetics, PO Box 124 Blindern, N-0314 Oslo, Norway

Publication date: 2002-01-01