Test structures for seed layer optimisation of electroplated ferromagnetic films

Application of a Test Structure for Minimising Seed Layer Thickness of Electroplated Ferromagnetic Films

“…Figure 3 shows results from [1] of the measured radial thickness of the Ni electroplated electrodes on three different thicknesses of Al/Ni seed layers with a total plating current of 0.65 mA (Note: a single power supply was used, with the wafer and thief currents [3] being individually recorded). Figure 4 shows this setup.…”

“…These results indicated that it is feasible to electroplate on patterned moulds using very thin seed layers. However, it should be noted that the thickness (conductivity) of the seed layers significantly affects the plating rates and radial uniformity, especially for the 5/5 nm (Al/Ni) seed layer combination [1].…”

“…Cu and NiFe. This paper uses a previously reported test structure [1] to quantify the IR drop across a wafer when electroplating on seed layers with a thickness of a few nanometres. More importantly, it demonstrates how IR drops resulting from thin seed layers can be significantly reduced by using dummy structures as current shunts on the mask layout.…”

“…In many cases the seed and electroplated film are the same metal and care is needed with dimensional control. Clearly a more ideal situation is to use a seed layer with a good etch selectivity with respect to the electroplated film [1] to minimise any undercut and preserve the dimensions of the electroplated film. At the same time, for structures with dimensions approaching the seed thickness any undercut can result in the structure being released.…”

“…It is also designed so that the resistance between any two adjacent electrodes will be the same for uniformly deposited films. The semi-automated design software is detailed in reference [1].…”