Characterization of PECVD Wn x for Copper Barrier Application
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ABSTRACT We evaluated PECVD WNx as a potential copper barrier. Ultrathin (100 A) PECVD WNx films were deposited utilizing WF6/N 2/H2 chemistry. Films with N/W stoichiometries ranging from 0.1 to 1.0 and resistivities between 200 - 1000 gtQ-cm were deposited by varying pressure, deposition temperature, N 2 flow, and H 2 flow. The thermal stability of the films was evaluated by annealing Si/WN, /Cu stacks for 1 hour at temperatures up to 700'C. Barrier failure was detected by sheet resistance change and surface SIMS. The thermal stability was correlated with N/W ratio and free fluorine content as determined by temperature programmed desorption mass spectroscopy. The tests showed that films with N/W ratios between 0.3 and 0.4 had optimal barrier properties, while fluorine was seen to have a detrimental effect on barrier stability. Moreover, tests showed that the substrate affects fluorine concentration as WNx deposited on silicon dioxide has a higher interfacial fluorine content than WNx on silicon. Thus, fluorine contamination at the WNx /Si0 2 interface led to poor electrical reliability as measured by leakage current vs. time on MOS capacitors. INTRODUCTION The semiconductor industry is moving toward copper interconnects to produce faster and less expensive integrated circuits. However, the technical challenges of manufacturing fully integrated copper devices are formidable. One of the critical aspects is the choice of barrier material because copper diffuses into interlayer dielectrics readily, which may result in line-toline leakage and device damage. Physical vapor deposited (PVD) Ta and TaN liners have been experimented with as copper barriers for 0.25 gim and 0.18 g.tm device generations [1-2]. These materials have a nearly amorphous texture that impedes copper diffusion. However, the drawback of the PVD techniques, including ionized PVD, is poor sidewall coverage in high aspect ratio, dual damascene features. Development of conformal, highly reliable copper barriers will be critical for next generation devices. Plasma enhanced chemical vapor deposited (PECVD) WN× has been suggested as a potential copper barrier due to its amorphous nature and relatively low resistivity [3-5]. In the present study we have explored copper barrier properties of ultrathin (100 A) PECVD WN, films deposited from WF6/N 2/H2 precursor chemistry [3]. Applying conventional metallurgical stability tests, we have probed the relationship between barrier performance and film purity and stoichiometry. EXPERIMENTAL The WNx films were deposited in a single wafer, parallel plate reactor. The process window that we studied is shown below:
327 Mat. Res. Soc. Symp. Proc. Vol. 564 01999 Materials Research Society
Temperature Pressure RF Power N 2/WF 6 H2
275 -400 TC 0.45 - 2.5 Torr 30 - 200 W 1 - 12 100 - 600 sccm
PVD Cu films were deposited on the WNx after vacuum break in a conventional PVD chamber. The thickness of the WN, films was measured by spectroscopic ellipsometry and verified on multiple samples by SEM. The film stoichiometry was d
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