Adhesion problem between copper and nickel

I'm beginner engineer of microelectronics department of one of the local universities. I have a problem with copper deposition on thin nickel layer. My task is deposit thick (until 50 mcm)copper film on thin layer of nickel.

My substrate: Al2O3 (wafer) - Titan (5 mcm) - Nickel (0,1 mcm).
My copper electrodeposition solution: CuSO4*5H2O - 150 g/L, H2SO4 (1,84) - 100 g/L, current density - from 0,01 A/cm2 to 0,02 A/cm2.

I got some copper films with good properties, but my problem is in full or almost full ABSENCE of adhesion between copper and nickel films. Copper film on nickel doesn't pass the scotch tape method. I can't use activation processes - only defatting.