Atomic layer deposition of tantalum nitride for ultrathin liner applications in advanced copper metallization schemes
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A metal–organic thermal atomic layer deposition (ALD) approach was developed for the growth of ultrathin tantalum nitride (TaNx) films by alternate pulses of tert-butylimido trisdiethylamido tantalum (TBTDET) and ammonia (NH3). An optimized ALD process window was established by investigating saturation of film-growth rate versus TBTDET and NH3 exposures, as controlled by the length of reactant pulses and the duration of the inert gas purge cycles separating the reactant pulses. The resulting low-temperature (250 °C) ALD process yielded uniform, continuous, and conformal TaNx films with a Ta:N ratio of 1:1. Carbon and oxygen impurity levels were in the 5–8 at.% range. Associated film conformality in 100-nm trench structures with 11:1 aspect ratio was nearly 100%.
I. INTRODUCTION
It is expected that emerging metallization schemes for intra-chip gigascale integration schemes will continue in the near future to employ copper (Cu) as the interconnect material of choice1 due to its low resistivity and enhanced resistance to electromigration. The use of copper will be coupled to the introduction of successive generations of low dielectric constant () materials with continuously smaller .2 The transition to Cu/low- technology nodes has generated significant material and process challenges in the formation of reliable Cu-based metallization schemes. In particular, a critical need exists for the identification and optimization of conformal, “zerothickness” (thickness below 10 nm), diffusion barrier/ liner materials that prevent the migration and intermixing of Cu with the adjacent dielectric and semiconductor regions of the chip. Physical vapor deposition (PVD) techniques, especially collimated and ionized sputtering, have successfully been used for the deposition of liner materials for Cu-based interconnects. However, as feature sizes are scaled down below 70 nm, PVD-based techniques are projected to face increasing challenges in their ability to provide the film conformality and thickness control required for zero-thickness liners in high aspect ratio via structures and trench structures.3 Chemical vapor deposition (CVD) methods may offer
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Address all correspondence to this author. e-mail: [email protected] J. Mater. Res., Vol. 19, No. 2, Feb 2004
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attractive alternatives, mainly as a result of more conformal film coverage due to their ability to engage actively the substrate surface in the deposition process. Particular interest has recently been generated by atomic layer deposition (ALD), also known as atomic layer CVD, ALCVD, or atomic layer epitaxy. It is a CVD-based deposition method that offers a superior degree of control over film thickness, owing to the self-limiting nature of the surface reactions that occur during ALD. It distinguishes itself from conventional CVD processes through a number of distinctive features that include the alternate rather than concurrent supply of chemical sources and the nonpyrolytic nature of its reactions; name
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