通孔尺寸对铜互连应力迁移失效的影响

在200℃温度下进行了700h双层铜互连(M1/M2)的应力迁移加速老化试验, 结合有限元分析和聚焦离子束(focused-ion-beam,简称FIB)技术研究了通孔直径分别为500和350nm的铜互连应力诱生空洞失效现象, 探讨了应力诱生空洞的形成机理, 并分析了通孔尺寸对铜互连应力迁移的影响. 结果表明,M1互连应力和应力梯度在通孔底部边缘处达到极大值. 应力梯度在应力诱生空洞成核过程中起主导作用, 由张应力产生的过剩空位在应力梯度作用下沿Cu M1/SiN界面作扩散运动并在应力梯度极大值处成核生长成空洞. 由于M1互连应力沿横向方向变化较快, 因此应力诱生空洞的横向生长速率较大. 当通孔直径增大时,互连应力和应力梯度值增大, 并导致应力诱生空洞的生长速率上升. 关键词： 铜互连 应力迁移 应力诱生空洞 失效

The effect of via size on the stress migration of Cu interconnects

Accelerated stress-migration testing under 200℃ of Cu (M1/M2) interconnects has been done for 700h. Finite element analysis and focused-ion beam techniques have been used to study the stress-induced voiding in the Cu interconnects with vias of 500 and 350nm in diameter. The voiding mechanism and the effect of via size on the stress migration have been studied. The results show that peak values of stress and stress gradient in M1 lines are reached underneath the edge of vias. The stress gradient shows crucial effect on the voiding process. The vacancies introduced by thermo-mechanical stress diffuse along Cu M1/SiN interfaces under the force of stress gradient and nucleate at the peak values of the stress gradient. The void grows faster along the length direction because the stress in M1 lines changes faster horizontally. The stress and stress gradient increase with increasing via diameter, leading to a faster voiding rate.