A Technique for Contactless Copper Electrodeposition for 3D Packaging Applications

Contactless bottom-up electrodeposition of nickel for 3D integrated circuits

“…Since, the process is carried out under acidic conditions (pH $ 2), the possibility of a competing hydrogen evolution reaction (HER) also arises. 8 A similar passivation effect has been observed by Knotter 20 in his publication on the etching mechanism of silicon dioxide, however this was with n-type doped silicon. Reproducibility of nickel deposition results has been reported to be the best in the pH range of 3.3 to 4.5, because at further lower pH, signicant current is used up in HER, which lowers the current efficiency.…”

“…With hydrouoric acid as the silicon dioxide etching agent in their contactless bottom-up electrodeposition process for copper, Patterson et al described an increasing resistance with time in the system eventually leading to total passivation at the voltage limit of their potentiostat. 8 A similar passivation effect has been observed by Knotter 20 in his publication on the etching mechanism of silicon dioxide, however this was with n-type doped silicon. Since the silicon samples used in experiments by Patterson et al were p-type (100) doped it was concluded that porous silicon formation, like that seen by Uhlir 21 in germanium and silicon electrochemical etching, was a more likely culprit for passivation.…”

“…Previously, 8,23 the effect of different solution parameters like temperature, copper sulfate concentration and sulfuric acid concentration on the deposition of copper were investigated. Previously, 8,23 the effect of different solution parameters like temperature, copper sulfate concentration and sulfuric acid concentration on the deposition of copper were investigated.…”

Investigations of solution variables in a contactless copper electrodeposition process for 3D packaging applications

“…The technique presented in this manuscript was shown viable for copper deposition on blanket wafers in an earlier publication by Patterson et al [9] but had deposition rate limitations. The developments discussed in this research work eliminate the current density limitations and improve copper deposition uniformity by adjusting deposition solution characteristics.…”

“…1, in which the front side (Ti/Ni) of the sample is exposed to a solution of copper sulfate and sulfuric acid with a sacrificial copper anode immersed in it. The contact on the back side of the wafer was made using a solution as described in the previous work by Patterson et al [9]. The electrons generated by electrochemical oxidation of silicon on the back side of the wafer are transported to the front side where cupric ions from the solution accept them and deposit on to the surface.…”