エレクトロマイグレーションの原子集積に伴う局所的高応力場のマイクロ・ナノワイヤ創製への応用

抄録

Electromigration (EM) technique is a growth method of metallic micro/nanowires. In general, EM deteriorates the metallic interconnects in integrated circuits by forming micro/nanoscale structures referred to as voids and hillocks. Voids and hillocks are generated by the depletion and accumulation of atoms, respectively. Recently, the EM technique for fabricating metallic micro/nanowires was reported, and the fabrication of Al microwires was demonstrated. The EM technique can fabricate Al micro/nanowires with high-aspect ratio, higher purity, and single crystal resulting in higher mechanical strength. The passivation constraining the deformation of metallic interconnect due to accumulation of atoms and the artificial hole through which metallic atoms are extruded are key factors. Rigid passivation generates the higher localized stress field in the metallic interconnect with accumulation of atoms. This higher stress field can push atoms out through the hole and the extruded metallic atoms becomes to grow a wire. This work reports the effect of the passivation thickness on fabrication performance. Two samples with different passivation thickness was used. The growth rate was experimentally measured to evaluate the performance. X-ray diffraction system was used to obtain the values of residual stress in passivation, showing that higher absolute value of compressive residual stress resulted in lower growth rate of an Al microwire. As a result, the lower absolute value of compressive residual stress increases the fabrication performance and can decrease the delamination risk of topmost passivation deposited by sputtering. On the other hand, the too thinner passivation resulting in lower absolute value of compressive stress increases the risk of passivation crack due to accumulation of atoms by EM. The optimized thickness of passivation can be determined based on this finding.