Activation of Low k Dielectrc Surfaces for ALD Barrier Formation
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0990-B09-02
Activation of Low k Dielectrc Surfaces for ALD Barrier Formation Junjun Liu1, Junjing Bao2, Hualiang Shi2, and Paul S. Ho2 1 Tokyo Electron, Austin, TX, 78741 2 Microelectronics Research Center, The University of Texas at Austin, Austin, TX, 78758 EXTENDED ABSTRACT Atomic layer deposition (ALD) processes of Cu diffusion barriers are known to have shown strong sensitivities to the substrate surface chemistry.[1-3] The initial interfacial chemical reactions control the uniformity and morphology of the barrier and become essential for the formation of good barrier layers with a sharp and strong interface. With in-situ x-ray photoelectron spectroscopy (XPS) monitoring of ALD Ta-based barrier processes, surface silanol, amine and benzene groups have been found to provide reactive sites for the ALD precursors; or in other words, substrate surface terminated with those surface groups is ìactiveî in ALD nucleation. On the other hand, methyl groups which are incorporated in organosilicate (OSG) low k dielectrics for lower dielectric constant and surface hydrophobicity are detrimental to ALD nucleation. [4-6] The slow nucleation issue of ALD processes on pristine OSG low k surfaces is avoided in actual manufacturing because the patterning processes cause surface carbon depletion and result in a polar surface active in ALD nucleation. [7-10] However, due to weak mechanical strength and poor resistance against chemical and plasma damage, porous OSG ultra low k dielectrics are susceptible to deep damage induced during etch/ashing/clean processes, resulting in degraded dielectric and electrical properties and aggravated surface roughness. Much effort is being dedicated to minimizing such damage in the first place. [11-12] As a second choice, surface silylation of damaged ULK dielectrics [13-15] has been explored as a post-patterning remedy intended for dielectric restoration and surface planarization which may become essential for the successful implementation of porous ULK dielectrics. Coming out of these additional process steps with modified surface chemistry, the porous low k dielectric surfaces may require reactivation to ensure a robust ALD barrier process. Two routes of surface activation have been studied. First, beams of reactive submolecular radicals were employed to activate inactive OSG surfaces. Pure radical beams, amine radicals in particular, were found to be effective in the surface activation. Fig.1 presents the growth curves and XPS spectra for ALD tantalum nitride processes on an untreated OSG surface and the low k surface pre-treated with amine radicals. The improvement is attributed to the replacement of surface methyl groups with amine groups. Excluding the energetic ion species, the radical beam pretreatment is expected to provide a low damage surface activation method. The second route is to modify the surface chemistry with molecules of bi-functionality, such as surface silylation. Tri-alkyl-substituted silylation agents were found to be detrimental to the initiation of the subsequent ALD bar
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