Towards Quantification of Contaminants in Electrodeposited Cu Films

A Cu electroplating process is typically used in semiconductor industry for the on-chip fabrication of interconnects on non-planar (patterned) wafer surfaces with feature dimensions ranging from the sub-10nm level (advanced Damascene applications) up to the micrometer level (Through Silicon Via technology). The presence of particular additives in the plating bath during the electroplating is a crucial prerequisite for the successful fill of vias and trenches with Cu. The accumulation of contaminants in the resulting Cu film is known to significantly decelerate the post-deposition recrystallization that is mandatory to improve the conductivity of these interconnects. It is therefore vital to develop new analytical techniques allowing a precise (true) quantification of the contamination level in the Cu deposit. Classical Secondary Ion Mass Spectrometry (SIMS) depth profiling approaches only provide semi-quantitative information on the contamination level with a poor depth resolution.

In this contribution we report on a recently developed quantitative depth profiling technique with sub-nanometer depth resolution based on laser ablation ionization mass spectrometry (LIMS). The high vertical depth resolution, a high dynamic range >10⁸ coupled with a high detection sensitivity of ~ 10 ppb allows the identification/quantification of trace amounts of contaminants localized at grain boundaries of the Cu deposit. Results of the LIMS techniques are compared with complementary 3D atom probe tomography experiments.

To demonstrate the capabilities of these analytical techniques we use copper films electrodeposited in the presence of SPS (bis-(sodium-sulfopropyl)-disulfide) and Imep (polymerizates of imidazole and epichlorohydrin) additives as model system. This approach allows the targeted insertion of grain boundaries into the Cu film perpendicular to the growth (depth profiling) direction.