Stability of Sputter Deposited Al-Cu Bilayers on SiO 2 .

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Alloys of copper with small amounts of aluminum have recently been investigated as the interconnect metal directly on SiO 2 or as the low resistivity diffusion barrier/adhesion promoter between copper and SiO 2 . In the present work the electrical stability of the metal-oxide-semiconductor ͑MOS͒ capacitors of such alloys on thermal oxide on p-silicon was investigated. MOS samples preannealed at 250°C and subjected to bias temperature stressing ͑BTS͒ at 200 and 250°C under an electrical field of 1.5 or 2 MV/cm showed stable C-V behavior with no observed shifts along the voltage axis. However, an observed decrease in the C ox by about 4-5% was associated with the higher BTS temperature or the field. Such changes were not observed if the preanneal was performed at 300°C instead of 250°C. Our X-ray photoelectron spectroscopy ͑XPS͒ analyses of the metal/SiO 2 interface suggest that the observed instabilities in samples preannealed at 250°C ͑not observed in those preannealed at 300°C͒ are related to the interface interactions between Al ͑in the alloy͒ and SiO 2 . The higher temperature preanneal or higher BTS conditions led to stabilization of this interface leading to stable MOS behavior as is also supported by the results of the I-V measurements which is also presented and discussed in this work.Copper interconnection schemes, offering lower resistivity and better electromigration resistance, have recently been introduced in high performance devices/circuits. 1 Future continued applications of copper will depend on the availability of very low resistivity adhesion promoter/diffusion barrier ͑APDB͒ needed between copper and the interlayer dielectric ͑ILD͒. 2-4 The presently used APDB material is thick ͑10-20 nm͒ and has very high resistivity ͑у200 ⍀-cm͒ countering the resistivity advantages of using copper. 1 In recent years copper alloyed with Al, B, Mg, Ta, and others has been investigated for application as the interconnect-metal in lieu of the pure copper. 5,6 Of these alloying elements extensive work has been focused on Al or Mg in Cu because of larger thermodynamic affinity of Al and Mg for oxygen ͑see Ref. 1 for discussions͒, thus making them suitable to interact with SiO 2 ͑or ILD͒ and form a bonded interface. Also Al and Mg were found to accumulate on the surface to form a passivating oxide thus preventing corrosion of Cu during heat-treatments or in actual use conditions. Even pure Al ͑in thickness range of 50-100 Å͒ have been shown to act as an effective APDB material between Cu and SiO 2 . 7 It is hypothesized, based on thermodynamic factors and X-ray photoelectron spectroscopy ͑XPS͒ analysis, that Al interacts with SiO 2 leading to the formation of an interfacial Al-Si x -O y layer 8,9 which acts as effective APDB layer as shown by electrical data of the MOS capacitors and Scotch tape peel tests. This paper addresses the relationships between formation conditions and electrical stability of the barrier under test conditions. It is shown that a complete preanneal is necessary for the effectiveness of APDB ...

Section: Resultsmentioning

confidence: 90%

Evolution of the Cu-Al Alloy/SiO[sub 2] Interfaces during Bias Temperature Stressing

Wang¹,

Murarka²,

Yang³

et al. 2001

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“…First, Al does not diffuse into oxide at these test conditions. 13 Second, if gate metal ions are being injected into the insulator, successive shifts of the flatband voltage should occur with time unless a barrier to further drift is formed. Contaminated Al may introduce mobile impurities but this possibility is ruled out because of the stability seen in the same Al on dry oxide compactors.…”

Section: Resultsmentioning

confidence: 99%

Electrical Behavior of Cu Thin Fluorinated PECVD Oxide MIS Capacitors

Mallikarjunan

Murarka

Steinbrüchel

et al. 2000

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This paper reports the results of extensive bias temperature annealing investigations made with metal-insulator semiconductor (MIS) capacitors of copper and fluorinated plasma-enhanced chemical vapor deposition (PECVD) oxide. Reduction of resistancecapacitance delay is necessary to improve interconnect performance. While copper has been accepted as the new interconnect metal, several low dielectric constant materials are being considered as potential replacements for silicon oxide. Fluorinated silicon oxides deposited by the PECVD process have a moderately low dielectric constant (K ϭ 3.0-3.7). The film structure and electrical behavior of fluorinated films was found to depend on the flow rate of the fluorine precursor C 2 F 6 . In several cases, both fluorinated and nonfluorinated oxides exhibit significant leakage currents. The reason for such poor electrical behavior has been related to the presence of pinholelike defects (which were identified by KOH etch testing) in these oxides. The existence of such pinholes is believed to be associated with nucleation and growth processes during the deposition and the thickness of the deposited dielectric (100 nm) used in this investigation.) unless CC License in place (see abstract). ecsdl.org/site/terms_use address. Redistribution subject to ECS terms of use (see 128.255.6.125 Downloaded on 2015-03-15 to IP ) unless CC License in place (see abstract). ecsdl.org/site/terms_use address. Redistribution subject to ECS terms of use (see 128.255.6.125 Downloaded on 2015-03-15 to IP ) unless CC License in place (see abstract). ecsdl.org/site/terms_use address. Redistribution subject to ECS terms of use (see 128.255.6.125 Downloaded on 2015-03-15 to IP

“…1 Previous studies have shown that a thin layer of aluminum suppressed the migration of copper into the oxide. 4 Bilayer ͑of Cu/Al͒, with as low a thickness of aluminum as 5-10 nm, have been shown to act as an effective adhesion promoter/diffusion barrier. 5 It has also been reported that Al atoms, on thermal annealing, diffused outward through the Cu to form a passivation layer on copper surface.…”

mentioning

confidence: 99%

Surface Segregation of Al of the Bilayers of Pure Cu and Cu-Al Alloy Films

Wang¹,

Murarka²,

Bedell

et al. 2001

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The segregation of Al at the surface of pure Cu and Cu-5 atom % Al alloy thin film bilayers was investigated as a function of the Al content, anneal temperature and time, and annealing ambient. Rutherford backscattering spectrometry was used to follow Al movement through the thickness of the film. Al appears to segregate on the surface as an oxide. The amount of Al segregating on the surface of the samples annealed at temperatures р400°C increases to about 14 ϫ 10 15 atoms/cm 2 . At the same time, a small amount of Al is retained in the overlying Cu through which Al is diffusing to the surface. The Al at surface is equivalent to ϳ3 nm Al 2 O 3 . The formation of this oxide was self-limiting at temperatures less than the crystalline transformation temperature of Al 2 O 3 and has structure similar to the surface oxide on pure Al, grown at similar temperatures. At higher temperatures ͑500 and 600°C͒ the oxide apparently crystallizes, allowing migration of Al and O 2 , thus leading to continued growth of the oxide. It is hypothesized that the residual oxygen ͑or other oxidizing species like water͒ reacts with Al arriving on the surface, providing the thermodynamically favored driving force to migrate Al from the alloy film through the overlying pure Cu film to the surface leading to both the homogenization of the Al content in the bilayer and oxide formation on the surface.