Paper EM-TuM3
Selectivity Characterization and Enhancement of Metal-Organic Chemical Vapor Deposited (MOCVD) Selective Cobalt Cap for Advanced Back End of Line

Tuesday, November 11, 2014, 8:40 am, Room 314

The continuous shrink of Cu interconnect feature size leads to higher current densities, which lower electromigration lifetimes. The interface between post chemical mechanical polishing (CMP) Cu and dielectric cap has been identified as a key diffusion path for copper atoms, and the adhesion of the interface is critical to electromigration performance [1]. Alternate metallization schemes for copper interconnect using selective CVD Co capping are considered for 22nm technology and below from integration point of view, metal-organic deposition selectivity is the key for leakage and reliability. During the selective CVD Co deposition, both Cu and porous ultra low k dielectric surface are exposed to the metal-organic precursor, insufficient selectivity will increase metal line to line leakage, degrade metal shorts and time-dependent dielectric breakdown (TDDB) performance. In this paper, we focus on selectivity characterization and enhancement of MOCVD selective Co cap process. Selectivity of different precursors are thoroughly evaluated and compared. Lower reaction rate of the carbon based organic group of the Co precursor and the reducing agent was demonstrated to benefit selectivity. Different ultra low k films with various porosity also play a big role in selectivity. Key tuning knobs for the process window have been defined as process pressure and temperature. The quantity of final Co deposition on porous ultra low k surface has been measured by both X-ray fluorescence (XRF) and Total Reflection X-ray Fluorescence (TXRF), which will subsequently be applied to the definition of selectivity, with comparison to the amount on polished Cu surface. XRF measurement shows some disadvantage due to weak signal to noise ratio while TXRF measurement results are more reliable. X-ray photoelectron spectroscopy (XPS) is used to profile the oxygen penetration into pristine film and the self-limited cobalt oxide thickness has been measured at 15A to 25A, which can be modulated by vacuum break between Co cap and dielectric cap, and by surface pre-clean process before dielectric cap deposition.

[1] J. R. Lloyd , M.W. Lane, E. G. Liniger, “Relationship between interfacial adhesion and electromigration in Cu metallization” 2002 IEEE International Integrated ReliabilityWorkshop Final Report, p.32 - 35 (2002)