Ruthenium has been considered as a barrier liner film for copper in advanced back-end-of-the-line (BEOL) metallization schemes in particular for the 10 nm and beyond technology nodes [1]. Ru shows a lower resistivity than traditionally used barrier films such as Ta or TaN [2] as well as negligible solubility with Cu [3] and Ru films can be deposited with a variety of techniques like CVD or PVD [4], which makes it an attractive candidate. However, new advanced BEOL barrier CMP slurries will have to be developed for this application and Ru is considered a very hard material and chemically inert. Hence it is a big challenge to develop advanced node Ru CMP slurries.

Since Ru films can be deposited with various deposition techniques and onto different substrates the removal rate response of these different films to a given slurry can also be dramatically different. For example we found that the removal with a standard Cu-barrier slurry without any additional additives on Ru film type A was only 20 Å/min whereas it was 200 Å/min on the type B film even though both films had been deposited by PVD. Further investigation of the two films showed that the morphology and in particular the grain size was quite different as shown in the SEM images below.

Interestingly, these two images correlate very well with images in [5] of two films which have been deposited at different plasma pressures and the difference in removal rate can be explained by different residual stresses in the two films as a result of the different plasma pressures.

In this paper we will present the characterization of several different Ru films by XRF (film density), XRD (crystal structure), SEM (grain size and structure), AFM (surface roughness), XPS (atomic composition), contact angle (surface energy) and film hardness by micro/nano indentation. The analytical results will be correlated to CMP polishing performance and in particular on how the different films respond to rate boosting additives in the slurry. The goal is to be formulate a customized slurry by understanding the properties of individual Ru films.

References:

1) C.-C. Yang, S. Cohen, T. Shaw, P.-C. Wang, T. Nogami, and D. Edelstein, IEEE Electron Device Lett., 31, 722 (2010).

2) G.K. Schweitzer, L.L. Pesterfield, The Aqueous Chemistry of the Elements, Oxford, 2010.

3) O. Chyan, T.N. Arunagiri, T. Ponnuswamy, J. Electrochem. Soc., 150 C347 (2003).

4) H. Li, D.B. Farmer, R.G. Gordon, Y. Lin, J. Vlassak, J. Electrochem. Soc. 154 D642 (2007).

5) A. S. Alagoz, J.-D. Kamminga, S. Y. Grachev, T.-M. Lu, T. Karabacak, MRS Proceedings 2009