Wafer-on-Wafer Stacking by Bumpless Cu–Cu Bonding and Its Electrical Characteristics

Author

Tan, Chuan Seng ; Peng, Lan ; Li, Hong Yu ; Lim, Dau Fatt ; Gao, Shan

Author_Institution

Nanyang Technol. Univ., Singapore, Singapore

Volume

32

Issue

7

fYear

2011

fDate

7/1/2011 12:00:00 AM

Firstpage

943

Lastpage

945

Abstract

Face-to-face stacking of wafer-on-wafer is successfully demonstrated on 200-mm wafers using bumpless Cu-Cu bonding. The Cu bonding structures are fabricated using a damascene metallization process and recessed prior to bonding. The Cu surface topology is optimized and carefully cleaned prior to bonding. Bonded Cu structures are found to provide sufficient mechanical strength to sustain shear force during wafer thinning. Cu-Cu ohmic contact is formed as confirmed from the crossbar Kelvin structure, and its contact resistance is found to be sensitive to the time lapse between cleaning and bonding. The measured contact resistance is attributed to imperfections such as voids and oxide precipitates at the bonding interface.

Keywords

copper; mechanical strength; metallisation; ohmic contacts; three-dimensional integrated circuits; wafer bonding; 3D integrated circuit; Cu; bonding interface; bumpless copper-copper bonding; contact resistance; copper surface topology; copper-copper ohmic contact; crossbar Kelvin structure; damascene metallization process; electrical characteristics; face-to-face stacking; mechanical strength; shear force; wafer thinning; wafer-on-wafer stacking; Bonding; Contact resistance; Copper; Rough surfaces; Stacking; Surface roughness; Surface treatment; 3-D integrated circuits (ICs); Cu–Cu bonding; face-to-face (F2F); wafer-on-wafer (WoW);

fLanguage

English

Journal_Title

Electron Device Letters, IEEE

Publisher

ieee

ISSN

0741-3106

Type

jour

DOI

10.1109/LED.2011.2141110

Filename

5771046