Sputtered W–N diffusion barriers

Abstract

The thermal stability of reactively sputtered tungsten–nitrogen alloy thin films is investigated for the application as diffusion barriers in silicon contact metallizations. The composition of W–N barriers is varied over a wide range including pure W. Aluminum, gold, and silver are used as low resistivity overlayers. Metallurgical interactions at temperatures ranging from 500 to 900 °C are studied. Incorporating nitrogen into tungsten advantageously stabilizes all three systems. The overall failure takes place rapidly above critical temperatures that depend on both the metal overlayer and the microstructure of the barrier. In some cases, W–N alloys can effectively prevent interdiffusion at temperatures as high as 800 °C for 30 min.

Thermal stability and nitrogen redistribution in the 〈Si〉/Ti/W–N/Al metallization scheme

“…4 This shows that the W 70 N 30 layer effectively inhibits interdiffusion between AI and Si at 550 ·c. On the contrary, significant interdiffusion is observed in the (Si)l1500 A Til940 A W 70 N 30 12400 A AI sample after the same heat treatment (Fig.…”

“…Details of the W-N alloy depositions can be found in Ref. 4 Another set of samples with titanium silicide contact layers in lieu of Ti were also prepared. The titanium silicide films were sputter deposited from a composite TiSi 2 target at a rate of -400 A/min.…”

“…In a recent work, it was demonstrated that interdiffusion between AI and Si can be suppressed by an interposed layer of W-N alloy film up to temperatures as high as 600 °C. 4 However, in a realistic contact structure, it is always desirable to include an additional conducting film between the barrier layer and the Si substrate to provide good ohmic contact at the metal-semiconductor interface, particularly when the contact resistivities of the barrier on Si are unacceptably high. 5 In the present work, we investigate the thermal stability of the ( Si) /Ti/W-N/ AI structure.…”

Amorphous (Mo, Ta, or W)–Si–N diffusion barriers for Al metallizations

“…Four different substrates were used for our experiments: unpatterned ͑100͒ silicon and oxidized silicon for 4 He backscattering, x-ray, scanning electron microscopy ͑SEM͒, and secondary-ion-mass spectrometry ͑SIMS͒ analyses; graphite for compositional determination by backscattering, photoresist-patterned silicon containing vertical n ϩ p shallow-junction diodes; and single-crystal NaCl substrates for transmission electron microscopy. The lateral contact area and junction depth of the diodes are 250ϫ250 m 2 and 280 nm, respectively.…”

“…Methods of analysis include electrical tests of shallow-junction diodes, 4 He ϩϩ backscattering spectrometry, x-ray diffraction, transmission electron microscopy, scanning electron microscopy, and secondary-ion-mass spectrometry. At the proper compositions, the M-Si-N films prevent Al overlayers from electrically degrading shallow-junction diodes after 10 min anneals above the melting point of aluminum.…”