Optimization study of VLSI interconnect parameters

In this paper, we present the results of optimizing interconnect parameters to satisfy chip-level targets in future device generations. The optimization approach used is based on existing system-level models and can optimize the number of wire levels, speed, chip size, and power in sequence, with the optimization variables being all interconnect parameters such as pitches, thicknesses, etc. We also study the trade-offs resulting from various interconnect process limitations and choices. The findings of this study, in brief, are: 1) while the thickness of the interlayer dielectric (ILD) can be scaled without adverse effects on speed so that the hole aspect ratio is held constant at about 3.0 across generations, it is important to provide extremely thick ILD films in excess of 4 pm in the upper wire levels, 2) while the maximum wire thickness can be safely held to about 2 μm in the upper wire levels, extremely thin wires of less than 0.1 pm thickness will soon be needed in the lower wire levels to reduce capacitance, 3) while wire resistivity reduction is desirable it is much more important to reduce the ILD dielectric constant aggressively, and 4) chip size constraints can impact the speed extremely and need to considered carefully. These results can be used to construct an optimal interconnect technology roadmap and can be an invaluable aid in guiding interconnect process development