Copper contamination effect on the reliability of devices in the BiCMOS technology

Abstract

Copper (Cu) will be used to replace aluminum in the next generation metallization due to its low resistivity and high electromigration resistance. However, copper is a fast diffuser in silicon and silicon dioxide, and it is detrimental to the devices if it gets into the active region. We have investigated several approaches to contaminating with Cu the back surface of a fully processed BiCMOS wafer in order to study its effect on devices. In order to estimate the amount of Cu driven to the active region, a simulated drive-in diffusion experiment is used. Vapor Phase Decomposition--Atomic Absorption Spectrometry is used to measure Cu on the front surface of the wafer after annealing. In a fully processed BiCMOS wafer, the internal gettering: oxygen precipitation occurs at the initial high temperature process steps. This oxygen precipitation acts as trapping centers and an intrinsic barrier that prevents impurities that may be driven from the back surface of the wafer. The effectiveness of the internal gettering of a simulated BiCMOS processed wafer is measured in comparison to a monitor wafer which has no internal gettering. Electrical measurement shows an increase in the base current in a Gummel Plot measurement of the Bipolar device after Cu contamination. This effect is most visible for a wafer that has been annealed at 550 degree(s)C for 30 minutes.