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 vari ous (W/L) ratios down to 0.24-mum channel length have been used to investig ate the effects of deliberate backside copper (Cu) contamination on the MOS field-effect transistor (MOSFET) electrical parameters. The backside of th e wafer was flooded with copper sulphate (CuSO4) solution and air-dried. Hi gh-temperature annealing was carried out to drive Cu into silicon. It was d iscovered that the backside Cu contamination did not result in any undesira ble effects on the MOS device performance. The MOS device parameters such a s threshold voltage V-T0, 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 degreesC 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.