I have my doubts that changing to copper will reduce your spike... because it's the inductance that makes the spike, not the resistance.
Here's a diagram from another topic, just for reference as a half-bridge diagram with the parasitic inductors; the top FET (M2) is being used as a diode but it's functionally the same as it being independently driven. Motor phase is L1. When the top FET is ON, current goes through the parasitic inductors L5 and L7. When you turn it OFF in order to turn ON the bottom FET (M1), these inductors will create the voltage spikes as they are being starved of current. And similarly for the bottom FET, but with parasitic L4 and L6+L9.