Electroless nickel underlayer deposited between copper filler and silicon substrate: effect of bath pH

ABSTRACT

This research proposed intermediate materials between Cu filler and Si wafer to reduce the coefficient of thermal expansion (CTE) mismatch in the through silicon via (TSV) structure. The proposed material is Ni underlayer because it has CTE value between Cu and SiO₂ which is 13 ppm/°C (Cu = 17 ppm/°C, SiO2 = 0.6 ppm/°C). The deposition process of nickel underlayer was conducted using electroless deposition process at various pH value (4.5, 5.5 and 6.5) of plating bath and deposition time (20, 40 and 60 minutes). The deposition behaviour was studied through surface and cross-sectional analysis under scanning electron microscopy (SEM). The Ni thickness was measured using cross-sectional analysis under SEM. The chemical composition of Ni deposits was measured using energy dispersive spectroscopy equipped on SEM. The performance test analysis was conducted using Standard ASTM D3359 (Cross Hatch Tape-Test) for coating adhesion test and 4-Point Probe Test for resistivity measurement. It was found that the optimum pH of the Ni bath is 6.5 due to high stability of plating bath to form uniform Ni deposited on silicon wafer. These optimum coating parameters showed homogeneous and uniform distribution of Nickel deposited on the surface of silicon with excellent adhesion properties for all pH value.

KEYWORDS:

• Through silicon via (TSV)
• electroless nickel
• electroless copper
• silicon wafer

Acknowledgments

The authors would like to express their gratitude to the Ministry of Higher Education, Malaysia under through the Fundamental Research Grants Scheme (FRGS/1/2018/STG07/UTM/02/2) and the team from Electronic Thin Film Laboratory and Materials Science Laboratory, School of Mechanical Engineering, Universiti Teknologi Malaysia (UTM). This research also was financially supported by the UTM Research University Grant (GUP-Tier 1: Q.J130000.2524.19H02 and TDR; Q.J130000.3551.06G33).

Disclosure statement

No potential conflict of interest was reported by the authors.

Correction Statement

This article has been republished with minor changes. These changes do not impact the academic content of the article.

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Funding

This work was supported by the Ministry of Higher Education, Malaysia (FRGS/1/2018/STG07/UTM/02/2); Universiti Teknologi Malaysia [Q.J130000.2524.19H02]; Universiti Teknologi Malaysia [Q.J130000.3551.06G33].