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Laser‐assisted bonding (LAB) is an advanced technology in which a homogenized laser beam is selectively applied to a chip. Previous researches have demonstrated the feasibility of using a single‐tier LAB process for 3D through‐silicon via (TSV) integration with nonconductive paste (NCP), where each TSV die is bonded one at a time. A collective LAB process, where several TSV dies can be stacked simultaneously, is developed to improve the productivity while maintaining the reliability of the solder joints. A single‐tier LAB process for 3D TSV integration with NCP is introduced for two different values of laser power, namely 100 W and 150 W. For the 100 W case, a maximum of three dies can be collectively stacked, whereas for the 150 W case, a total of six tiers can be simultaneously bonded. For the 100 W case, the intermetallic compound microstructure is a typical Cu‐Sn phase system, whereas for the 150 W case, it is asymmetrical owing to a thermogradient across the solder joint. The collective LAB process can be realized through proper design of the bonding parameters such as laser power, time, and number of stacked dies.

Sequential cyclic etching of copper thin films was performed using HBr/Ar gas and Ar plasma. The first step involved the formation of CuBrx layers by exposing copper thin films to HBr/Ar gas, and the second step involved the removal of the CuBrx layers by Ar ion sputtering. HBr/Ar gas was used to form the CuBrx layers, and the growth of CuBrx layers could be saturated under certain conditions. Ar ion sputtering was optimized under the condition that led to the removal of the CuBrx layer and prevented the copper sputtering. The formation and removal of the CuBrx layers were confirmed by x-ray photoelectron spectroscopy analysis. The etch depth per cycle was estimated to be approximately 1.2 nm. The 120-cycle etching of copper films patterned with an SiO2 hard mask exhibited good etch profiles without any redepositions or etch residues. The cyclic etching of copper thin films using HBr/Ar gas was proposed as a promising etching technique.

Pulse-modulated plasma etching of copper masked using SIO2 films was conducted via a CH3COOH/Ar. The etch characteristics were examined under pulse-modulated plasma. As the duty ratio of pulse decreased and the frequency of pulse increased, the etch selectivity and etch profile were improved. X-ray photoelectron spectroscopy and indicated that more copper oxides (Cu2O and CuO) and Cu(CH3COO)2 were formed using pulse-modulated plasma than those formed using continuous-wave (CW) plasma. As the concentration of CH3COOH gas in pulse-modulated plasma increased, the formation of these copper compounds increased, which improved the etch profiles. Optical emission spectroscopy confirmed that the active ingredients of the plasma increased with decreasing pulse duty ratio and increasing frequency. Therefore, the optimized pulsed plasma etching of copper via a CH3COOH/Ar gas provides better etch profile than that by CW plasma etching.

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