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ALD of Copper and Copper Oxide Thin Films for Applications in Metallization Systems of ULSI Devices

: Waechtler, T.; Oswald, S.; Roth, N.; Lang, H.; Schulz, S.E.; Gessner, T.

presentation (PDF; )

AVS, the Science and Technology Society:
ALD 2008. DVD : June 29 - July 2, 2008, Bruges, Belgium
17 Folien
International Conference on Atomic Layer Deposition (ALD) <8, 2008, Bruges>
Conference Paper, Electronic Publication
Fraunhofer ENAS ()

As a possible alternative for growing seed layers required for electrochemical Cu deposition of metallization systems in ULSI circuits, the atomic layer deposition (ALD) of Cu is under consideration. To avoid drawbacks related to plasma-enhanced ALD (PEALD), thermal growth of Cu has been proposed by two-step processes forming copper oxide films by ALD which are subsequently reduced.

This talk, given at the 8th International Conference on Atomic Layer Deposition (ALD 2008), held in Bruges, Belgium from 29 June to 2 July 2008, summarizes the results of thermal ALD experiments from [(nBu3P)2Cu(acac)] precursor and wet O2. The precursor is of particular interest as it is a liquid at room temperature and thus easier to handle than frequently utilized solids such as Cu(acac)2, Cu(hfac)2 or Cu(thd)2. Furthermore the substance is non-fluorinated, which helps avoiding a major source of adhesion issues repeatedly observed in Cu CVD.

As result of the ALD experiments, we obtained composites of metallic and oxidized Cu on Ta and TaN, which was determined by angle-resolved XPS analyses. While smooth, adherent films were grown on TaN in an ALD window up to about 130°C, cluster-formation due to self-decomposition of the precursor was observed on Ta. We also recognized a considerable dependency of the growth on the degree of nitridation of the TaN. In contrast, smooth films could be grown up to 130°C on SiO2 and Ru, although in the latter case the ALD window only extends to about 120°C. To apply the ALD films as seed layers in subsequent electroplating processes, several reduction processes are under investigation. Thermal and plasma-assisted hydrogen treatments are studied, as well as thermal treatments in vapors of isopropanol, formic acid, and aldehydes. So far these attempts were most promising using formic acid at temperatures between 100 and 120°C, also offering the benefit of avoiding agglomeration of the very thin ALD films on Ta and TaN. In this respect, the process sequence shows potential for depositing ultra-thin, smooth Cu films at temperatures below 150°C.