A novel technique for studying the growth of electroless copper deposition into high aspect ratio structures is presented. The advantage of this technique is that growth into 100 to 400 mu m long trenches with aspect ratios of 500:1 can be studied without any etching into the substrate. This technique allows us to determine diffusion kinetics, overall growth rates, and to predict step coverage into trenches and vias. The results indicate that electroless copper growth at 40 degrees C into 0.7 mu m tunnels is diffusion controlled with an effective diffusion coefficient in the range of 2.0 to 8.9 x 10(-5) cm(2)/s.