PEALD of a Ruthenium Adhesion Layer for Copper Interconnects

Abstract

Ruthenium thin films were produced by plasma-enhanced atomic layer deposition ͑PEALD͒ using an alternating supply of bis͑ethylcyclopentadienyl͒ruthenium ͓Ru͑EtCp) 2 ] and NH 3 plasma at a deposition temperature of 270°C. The film thickness per cycle was self-limited at 0.038 nm/cycle, which was thinner than the thickness obtained from the conventional ALD using oxygen instead of NH 3 plasma. The ruthenium thin film prepared with PEALD had a preferential orientation toward ͑002͒, and it was progressively promoted with NH 3 plasma power. The PEALD of ruthenium shows a merit in controlling ultrathin film thickness with less than 2 nm more precisely and more easily than the conventional ALD, due to the reduced transient period at the initial film growth stage. Also, ruthenium thin film improved the interfacial adhesion of metallorganic chemical vapor deposited copper to diffusion barrier metals by forming Cu-Ru chemical bonds at the interface without degrading the film resistivity of copper.With the increasing performance and packing density required in microelectronic devices, copper has been used as an interconnection metal to enhance operating speed and reliability. 1 Electrochemical plating ͑ECP͒ has now become a routine process for forming copper damascene interconnects, due to its super-filling ability, i.e., it fills trenches and via holes in a bottom-up fashion without any seams or voids. 2 To realize the bottom-up filling processes, a thin and conformal copper seed-layer is required. Currently, physical vapor deposition ͑PVD͒ technique is used to deposit the seed layer. However, one challenge is to find a way to deposit a uniform seed-layer in high aspect ratio via holes and trenches of damascene structures as the feature size decreases. To overcome this technological barrier, studies have examined seedless copper damascene filling with ECP or metallorganic chemical vapor deposition ͑MOCVD͒, in which copper is deposited directly on copper diffusion barrier metals, and copper seed-layer formation using MOCVD or atomic layer deposition ͑ALD͒ have been studied. 3-5 However, the copper films fabricated using ECP, MOCVD, and ALD techniques have poor interfacial adhesion to common copper diffusion barrier metals, such as TiN, TaN, and WN, which causes failure of the copper interconnect system. 6,7 Therefore, an adequate adhesion layer for reliable adhesion is required in utilizing the seedless copper bottom-up filling techniques or preparing the copper seed-layers with MOCVD or ALD.A ruthenium thin film prepared by ALD using bis͑ethylcyclopen-tadienyl͒ruthenium ͓Ru͑EtCp) 2 ] and oxygen gas was reported to have excellent performance as an adhesion layer to improve the interfacial adhesion of MOCVD copper to TiN. 8 However, the oxygen gas used as a reactant can form an interfacial metal oxide film with under-layered diffusion barrier metals, such as Ta and TaN. 9-11 This causes interconnection failure or increases via-hole contact resistance. To address this issue, we have been investigating a plasmaenhanced atomic ...

Plasma-Assisted Atomic Layer Deposition: Basics, Opportunities, and Challenges

“…It has been reported that, for some materials and applications, plasma-assisted ALD affords better material properties than thermal ALD in terms of, for example, film density, 166,167,187,207,214,227,228 impurity content, 120,162,229,241,245,271,290,294 and electronic properties. 30,31,50,68,134,135,154,207,208,211,228,229,242,272,290,294,319 In most cases, these improved material properties are a result of the high reactivity provided by the plasma, which will be addressed in more detail below.…”

“…The high plasma reactivity is also beneficial in particular cases where the nucleation delay is shorter for plasma-assisted ALD than for the equivalent thermal ALD process. 31,164,166,168,169,173,179,183 This aspect also contributes to an increased throughput of ALD reactors.…”

“…Results obtained using Ru(Cp Et ) 2 as a precursor and a NH 3 plasma as the reactant, for example, are reported in the literature quite extensively. [165][166][167][168][169][170][171][172][173][174][175][176] Pure and smooth films with a low resistivity were deposited with substrate-dependent growth rates and nucleation delays ($20 cycles for TiN and almost none for SiO 2 ). NH 3 gas is not reactive with the precursor and the thermal ALD process does not result in film growth.…”

“…However, O 2 gas can be used for thermal ALD of Ru and results in growth rates that are up to 4 times higher compared to the plasma-assisted ALD process with NH 3 plasma as the reactant. 166,173 Ru films were also deposited by employing O 2 gas and an O 2 plasma as the reactant in deposition processes using RuCp(CO) 2 Et.…”

Self-forming Al oxide barrier for nanoscale Cu interconnects created by hybrid atomic layer deposition of Cu–Al alloy

“…Cu thin films fabricated using ALD techniques have poor interfacial adhesion to oxide dielectrics, such as SiO 2 , causing failure of the copper interconnect system. [26][27][28] To evaluate the interfacial adhesion of Cu-Al (4.6 at. %) alloy films and reference Cu-Mn (4.7 at.…”