(Invited) Adsorbate and Impurity Effects during Co Deposition and Planarization for MOL Contact and Beol Metallization
Authors: Kelly James , Kamineni Vimal , Lin Xuan , Liang Yong , Amanapu Hari , Peethala Brown , Raymond Mark , Haran Bala 
Published: February 2020

Cobalt (Co) has attracted interest as a new material for middle of the line (MOL) as well as back end of the line (BEOL) metallization.1-3 For MOL contacts, extension of current tungsten (W)-based metallization approaches to smaller feature sizes is limited by the need for relatively thick barrier and W-nucleation layers. In the case of BEOL metallization, a similar requirement of a relatively thick Cu diffusion barrier (needed to maintain good yield and reliability) along with additional “size-effect” electron scattering result in increased Cu interconnect resistance at narrow feature widths.4 Co metallization offers the possibility of feature fill with relatively thinner barrier layers with no high-resistance nucleation layers and grain growth to lower resistivity with improved seamless fill under reasonable FEOL device compatible thermal budgets. These characteristics, along with good electromigration resistance,5 make Co an interesting future metallization alternative for both MOL and BEOL.
One way to achieve Co fill is by chemical vapor deposition (CVD) followed by an anneal to reflow the material into the cavity and heal any metal seams present. This approach has the advantage of containing the barrier, Co fill and overburden steps within a single platform. The Co deposition and reflow process can have a strong influence on the film purity and feature-scale metal distribution. In Figure 1, the film resistivity is shown for various Co deposition and anneal processes, reflecting the corresponding changes in the resulting film morphology and purity. Figure 2 shows the influence of the anneal ambient on the extent of Co reflow within contact via structures. The movement of the Co is apparently very dependent on the anneal ambient, suggesting a significant influence of adsorbates from the ambient. The behavior of adsorbates during Co reflow, as well as the subsequent Co chemical mechanical planarization process, will be discussed.

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This work was performed by the Research Alliance Teams at various IBM Research and Development facilities.

Figure 1