Study of Diffusion Barrier Performance in MOCVD TiN by Transmission Electron Microscopy
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Abstract The diffusion barrier performances of MOCVD TiN films with different thicknesses and various contact layers are compared by both ex situ and in situ TEM experiments. MOCVD TiN films grown at 4250 C and 10 torr without a titanium underlayer show a semi-columnar structure while films grown with a titanium layer are columnar. It is found that the former has better diffusion barrier performance for Al metallization in Si contact holes. In addition, it is found the MOCVD TiN films combined with a TiSi2 contact layer are stable up to 600'C.
I. Introduction Titanium nitride(TiN) has been widely used as a diffusion barrier for integrated circuits(IC) to prevent Si and Al interdiffusion. Currently, sputtering is the most common technique used for deposition of TiN films. However, as the size of IC devices shrinks, the sputtering technique is thought not to be good enough for covering small features owing to poor step-coverage. On the other hand, the chemical vapour deposition(CVD) technique has been able to obtain excellent coverage on small geometries [1]. As a result, CVD TiN has been investigated as a potential candidate for diffusion barriers. Unfortunately, growing TiN films using TiC14 and NH3 by CVD introduces several problems, among which is the incorporation of Cl in the film [1]. Recent studies have shown the use of MOCVD TiN solves many problems associated with CVD TiN while still maintaining good step-coverage [2, 3]. It is also found that the electrical resistivity can be reduced down to 500 ýtQ.cm [4], and that the resistivity is strongly dependent on the types of precursors, the processing conditions and the microstructure [3, 4]. A complete study of the diffusion barrier performance has not been carried out, however, a principle reason being that the diffusion barrier fails by forming local features such as spikes which are difficult to detect by conventional techniques such as sheet resistance measurement or scanning electron microscopy(SEM). In this paper, the diffusion barrier performance of MOCVD TiN in contact holes with various thicknesses will be explored using cross-section TEM in situ and ex situ experiments. Conventional processing uses Ti and TiSi2 films for contact layers and TiN for diffusion barriers, between Si and Al. Consequently, we have performed our test of the diffusion barrier performance using similar configurations.
II. Experimental Procedure All the TiN films were deposited in a loadlocked single-wafer type MOCVD reactor using tetrakis(diethylamino)-titanium, TDEAT, (>99.999% for nonvolatiles) and ammonia, NH3, 205
Mat. Res. Soc. Symp. Proc. Vol. 391 0 1995 Materials Research Society
(99.9995%) as reactant. The precursor, TDEAT, is introduced into a concentric injector/evaporator assembly by a liquid flow controller and then carried into the reactor by N2(99.9999%) [4, 5]. Table I shows the conditions under which the TiN films were deposited in the present study. Most films were grown at 425°C and 10torr. For sample 1, the 100,-Ti layer was sputter deposited on contact
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