Simulation of the effect of thin film microstructure on current and temperature distributions in very large scale integrated metallization structures

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Abstract
A two‐dimensional finite element program is used to solve current and temperature distributions in inhomogeneous aluminum and tungstenmetal lines deposited over very large scale integrated topography. Microstructure depictions of both aluminum and tungsten lines are obtained using the process simulator simbad. Density information is then used to calculate conductivity profiles as input to the current and temperature solver simcat. Experimental results are used to calculate and correct for the cooling in the third dimension of the simulation and results are presented regarding the effect of substrate and passivation thickness on line heating. Two examples of the effect of topography and microstructure on the flow of current and heating within metal lines are presented. Aluminum and tungsten lines are deposited over a series of trenches of varying sidewall angle, and the line temperature and maximum current stress are plotted as a function of this angle. The lower density of the tungsten deposited on the sidewalls of the trench is determined to have a significant effect on the operating temperature of the metal line. As a second example the current distribution is compared between two aluminum lines deposited at different substrate temperatures over a 1 μm trench with vertical sides.

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