The reliability of ultrasonic bonded Cu to Cu electrode for 3D TSV stacking

Abstract

We investigated the mechanical property of Cu–Cu joints bonded using an ultrasonic bonding and evaluated the reliability of 3D structure stacked by through silicon via (TSV) on glass substrate. TSV was fabricated by using the deep reactive ion etching and then Cu was filled by electroplating in via. TSV carrier and Si chip with grooved electrode were ultrasonic-bonded on the glass substrate with various bonding times. The frequency of vibration in the ultrasonic bonding system was 40 kHz with transverse ultrasonic. The die shear test was conducted in order to investigate the bonding strength of Cu–Cu joints. To evaluate the reliability of ultrasonically bonded Si chip and TSV carrier, the electrical resistance of joints was monitored during the temperature cycling (TC) test. The conditions of TC test were between −40 and 125 °C and cycle time was 30 min. The bonding strength of Cu–Cu joints increased with bonding times up to 1.0 s. However, the result of bonding strength showed that excessive processing time rather decreased the bonding strength and, too much applied pressure or bonding time caused breakage of carriers and chips. Temperature cycling test showed that the electrical resistance increased with increasing cycles.