Effect of underlayer dummy fills on on-chip transmission line

This paper discusses the effect of CMP dummy fill on on-chip transmission-lines. In recent fabrication processes that use Cu wire, CMP dummy fill is inserted to suppress the variation of the metal thickness. In high frequency above 10 GHz, the eddy current in the dummy fills affects the characteristics of on-chip transmission-line. However it is not clear that which dummy fill has the strong impact. This paper evaluates the relationship between the effect and the location of dummy fills by a 3D field-solver. The experimental results show that there is a region where the dummy fills have strong impact on the loss characteristics. The effect of the dummy fills in the region is nearly two times larger than that in the other region.