# Dishing Control and Surface Properties Improvement of Nano Twinned Copper/Polyimide (Nt-Cu/PI) Patterned Wafer by Electro- Kinetic Force Assisted Chemical Mechanical Planarization (EKF-CMP)

Cheng Jhong, Yueh-Hsun Tsai, Li-Shin Lu, Chih Chen, Le Nam Quoc Huy, Chao-Chang A.Chen

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Cheng Jhong, Yueh-Hsun Tsai, Li-Shin Lu, Chih Chen, Le Nam Quoc Huy, et al.. Dishing Control and Surface Properties Improvement of Nano Twinned Copper/Polyimide (Nt-Cu/PI) Patterned Wafer by Electro- Kinetic Force Assisted Chemical Mechanical Planarization (EKF-CMP). International Conference on Planarization/CMP Technology, Oct 2023, Kanazawa, Japan. hal-04270314

HAL Id: hal-04270314

https://hal.science/hal-04270314v1

Submitted on 4 Nov 2023

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# Dishing Control and Surface Properties Improvement of Nano Twinned Copper/Polyimide (Nt-Cu/PI) Patterned Wafer by Electro-Kinetic Force Assisted Chemical Mechanical Planarization (EKF-CMP)

Cheng Jhong<fnref n="1" />, Yueh-Hsun Tsai<fnref n="1" />, Li-Shin Lu<fnref n="2" />, Chih Chen<fnref n="3" />, Le Nam Quoc Huy<fnref n="1" />, and Chao-Chang A. Chen<fnref n="1" />,<fnref n="4" />*

## ABSTRACT

Nano-twinned copper (Nt-Cu) is a promising material for the copper-to-copper direct bonding in 3D IC fabrication due to its superior strength and thermal stability. This study focuses on improving the ultimate surface roughness and dishing of Nt-Cu bumps in Nt-Cu/polyimide (PI) patterned coupon wafers through the electro-kinetic force assisted chemical mechanical planarization (EKF-CMP) process. COMSOL Multiphysics simulations reveal an increasing particle concentration near the wafer-slurry interface. The electroosmotic flow (EOF) enhances the effective abrasion rate of abrasive particles above the pad asperities, while the external mechanical abrasion in EKF-CMP results in higher material removal rate (MRR), lower surface roughness (Ra), and lower non-uniformity (NU) compared to conventional CMP. Experimental results demonstrate that the EKF-CMP reduces the processing time by approximately 20% and diminishes the dishing of Nt-Cu and PI by 16.35% and 3.31%, respectively. The surface roughness (Ra) of the bumps after EKF-CMP is reduced to 0.25 nm, which is 24% lower than the conventional CMP value. Additionally, by monitoring the coefficient of friction (CoF) during the EKF-CMP process, endpoint detection of the exposed Nt-Cu surface has been achieved, enabling precise control of the exposed height of Nt-Cu bumps and potentially increasing the yielding rate in advanced 3D-IC chips. Feasibility of the developed EKF-CMP of Nt-Cu patterned bump has been demonstrated and further applications for heterogeneous integration of 3D ICs are expected.

<footnote n="1">¹Dept. of Mechanical Engineering, National Taiwan University of Science and Technology, Taiwan</footnote>

<footnote n="2">²Dept. of Industrial Engineering and Management, National Quemoy University, Taiwan</footnote>

<footnote n="3">³Dept. of Materials Science and Engineering, National Yang Ming Chiao Tung University, Taiwan</footnote>

<footnote n="4">⁴CMP Innovation Center (Taiwan R.O.C.)</footnote>

<footnote>*Corresponding author: artchen@mail.ntust.edu.tw</footnote>