Abstract
Because the trenches or vias of IC interconnect are very tiny and have large aspect ratio, how to deposit copper without void formation is very important. Development of numerical method from FDM、FEM to BEM or even Free-Element Method enable us to get approximate solution of governing equations, although an analytical solution is impossible to obtained. In this research, the fundamental electrochemical theories are coupled with suitable assumptions to simulate the dynamic deposition profile in electrodeposition of IC copper interconnect. Boundary element method coupled with moving boundary algorithm is used to solve the governing equations. Furthermore, we also formulated a hydrostatic equation to estimate the extent of electrolyte penetrating into sub-micron via. A dimensionless number K is introduced as a wetting indicator. It is predicted that without additives, a seam-type void can be formed. It also shows that lower applied current density, lower aspect ratio trench or higher cupric ion concentration favors void size reduction. Furthermore, shape of the trench is also influential. W1/W2 (ratio of width at trench's opening to that at its bottom) should be smaller than unity for better current distribution. As for wetting, increasing dimensionless number K is beneficial to electrolyte's wettability. Adding surfactant or reducing the pressure can all increase K, so reducing the pressure can be viewed as a "physical" wetting agent. Further wetting-time calculation shows that the electrolyte would penetrate into trench so fast that time required for complete wetting is negligible.