Effects of deliberate copper contamination from the plating solution on the electrical characteristics of MOSFETs

N-channel and p-channel metal-oxide-semiconductor (MOS) transistors of various (W/L) ratios down to 0.24-μm channel length have been used to investigate the effects of deliberate backside copper (Cu) contamination on the MOS field-effect transistor (MOSFET) electrical parameters. The backside of the wafer was flooded with copper sulphate (CuSO₄) solution and air-dried. High-temperature annealing was carried out to drive Cu into silicon. It was discovered that the backside Cu contamination did not result in any undesirable effects on the MOS device performance. The MOS device parameters such as threshold voltage V_TO, transconductance G_m, drain saturation current I_DSAT, off-current I_off, and junction leakage current for n⁺/p and p+/n diodes displayed no significant degradation, even after 5 h of annealing at 400°C in nitrogen ambient. Secondary ion mass spectroscopy data shows that Cu diffused into silicon only over a short distance, leading to little or no degradation of MOSFETs and junction diodes