Jae-Won Kim

The effect of plasma pre-cleaning on the Cu-Cu direct bonding for 3D chip stacking.

The effect of bonding temperature and plasma treatment on the interfacial adhesion energy of the Cu-Cu direct bonding layers was investigated under 4-point bending test method. Interfacial adhesion energies with increasing bonding temperature, Good-quality Cu to Cu bonding is achieved at the low bonding temperature of 250°C with surface treatment.

Sub-micron aligned Cu-Cu direct bonding for TSV stacking

Cu-Cu direct bonding facilitates fine-pitch interconnection with low electrical resistivity and high electromigration (EM) resistance. However, reliable Cu-Cu bonds result only from high temperature, high pressure and long process time mainly because of its tendency to generate a native oxide that negatively impacts device reliability. Presently, high process temperature is one of the major bottlenecks of Cu-Cu thermo-compression bonding. We developed the optically-aligned, low-temperature Cu-Cu thermo-compression bonding process with sub-micron alignment accuracy. The quantitative analyses of the interfacial adhesion energies and seam voids of Cu-Cu bonds, performed with varying process parameters, showed that bonding temperature and post-bond annealing have the most significant influence on bond properties. By optimizing experimental parameters, we could achieve, even with a short bonding time, the sufficient interfacial adhesion energy (≥ 5 J/m2 for subsequent processes) with no interfacial seam voids. Postbond annealing performed at ≥ 250 ºC drastically improves the interfacial adhesion energy. SmartView™ alignment, enabling the face-to-face Cu-Cu bonding of non-IR transparent wafers, allows less than 0.2 µm (3σ) and 1.0 µm (3σ) of the pre-bond and post-bond alignment accuracies, respectively.

Current stressing effects on the reliability of Cu pillar bump with shallow solder

The intermetallic compound (IMC) growths of Cu pillar bump with shallow solder (thin Sn thickness) were investigated during annealing or current stressing condition. After reflow, only Cu6Sn5 was observed, but Cu3Sn formed and grew at Cu pillar/Cu6Sn5 interface with increasing annealing and current stressing time. The kinetics of IMC growth changed when all Sn in Cu pillar bump was exhausted. The complete consumption time of Sn phase in electromigration condition was faster than that in annealing condition. Under current stressing condition, intermetallic compound growth was significantly enhanced mainly due to the joule heating effects. Kirkendall void was observed at the interface of Cu pillar/Cu3Sn and it affected the mechanical reliability of Cu pillar bumps, which was estimated by die shear test.

Effect of Bonding Process Conditions on the Interfacial Adhesion Energy of Al-Al Direct Bonds

【3-D IC integration enables the smallest form factor and highest performance due to the shortest and most plentiful interconnects between chips. Direct metal bonding has several advantages over the solder-based bonding, including lower electrical resistivity, better electromigration resistance and more reduced interconnect RC delay, while high process temperature is one of the major bottlenecks of metal direct bonding because it can negatively influence device reliability and manufacturing yield. We performed quantitative analyses of the interfacial properties of Al-Al bonds with varying process parameters, bonding temperature, bonding time, and bonding environment. A 4-point bending method was used to measure the interfacial adhesion energy. The quantitative interfacial adhesion energy measured by a 4-point bending test shows 1.33, 2.25, and

Effects of annealing and current stressing on the intermetallic compounds growth kinetics of Cu/thin Sn/Cu bump

6.44\;J/m^2

Annealing temperature effect on the Cu-Cu bonding energy for 3D-IC integration

for 400, 450, and

Correlations between interfacial reactions and bonding strengths of Cu/Sn/Cu pillar bump

500^{\circ}C

Effect of HF & H2SO4 pretreatment on interfacial adhesion energy of Cu-Cu direct bonds

, respectively, in a

Improvement of wafer-level Cu-to-Cu bonding quality using wet chemical pretreatment.

N_2

Wet Etching Characteristics of Cu Surface for Cu-Cu Pattern Direct Bonds

atmosphere. Increasing the bonding time from 1 to 4 hrs enhanced the interfacial fracture toughness while the effects of forming gas were negligible, which were correlated to the bonding interface analysis results. XPS depth analysis results on the delaminated interfaces showed that the relative area fraction of aluminum oxide to the pure aluminum phase near the bonding surfaces match well the variations of interfacial adhesion energies with bonding process conditions.】