NiW 合金电镀填充 TSV

After Damascus revolution, the metal copper as  conductive material and CMP (chemical mechanical  process) technique replacing an old process in the industry,  have led to an industrial transformation. To meet the  requirement of state-of-the-art electronic products, more  and more different materials and devices must be stacked  together to reduce the volume of IC chips and signal  transmission delay. Electrodeposition plays an important  role in metallization development, especially copper  electrodeposition, which is a critical technology and  generally used in 3D (Three-Dimensional) chip packaging.

For the future technological trends of the 3D  packaging, TSH (Through Silicon Hole) and TSV (Through  Silicon via) connection play a key role in the manufacturing  process, where copper process dominates the final reliability.  However, the packaging materials with different CTEs (Cu:  17.5 ppm; Si: 2.5 ppm) will induce large stresses at the  interfaces, resulting in cracks and extrusion defects between  dielectric layer and silicon substrate.

To reduce the thermo-mechanical stress and effectively  enhance durability of silicon wafer we use tungsten as a  filling material, which has similar physical characteristic  (W CTE: 4.5ppm) to silicon to enhance the durability of  the silicon wafer.  

Fig1

Figure 1. Thermal reliability test of Cu-TSV and Ni/W-TSV.  A lot of small voids and creak were observed in the  Cu-TSV after the thermal annealing treatment at 500℃ for  4 hr. The issue did not occur in the case of Ni/W-TSV. The  structure of the Ni/W-TSV was still intact after the thermal  annealing at 500℃ for 4 hr.

The traditional process for making TSV is a dry  process. It includes many steps, from the via formation to  the copper eletrodeposition of copper in via. We replace the  copper by Ni-W alloys and reduce the TSV process without  Cu seed layer deposition. The process promotion can reduce  the cost and solve the issue of CTE mismatch.

According to an empirical equation[3] of Ni-W  CTEaverage, we can predict the CTE value by calculating  tungsten content in the alloy. Figure 1 shows the results of  thermal reliability test. A lot of small voids and creak were  observed in the Cu-TSV after a thermal annealing treatment  at 500℃ for 4 hr. In addition, copper protrusion on the TSV was also obvious after the thermal annealing. However,  these issues did not occur in the case of Cu-free TSV  (Ni/W-TSV). The structure of the Ni/W-TSV was still intact  after the thermal annealing at 500℃ for 4 hr, indicating  that Ni-W alloy is very stable because of its low CTE.