The Integration of Plasma Enhanced Atomic Layer Deposition (PEALD) of Tantalum-Based Thin Films for Copper Diffusion Bar
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The Integration of Plasma Enhanced Atomic Layer Deposition (PEALD) of TantalumBased Thin Films for Copper Diffusion Barrier Applications Degang Cheng and Eric T. Eisenbraun School of NanoSciences and NanoEngineering, The University at Albany-SUNY, Albany, New York 12203, U.S.A. ABSTRACT A plasma-enhanced atomic layer deposition (PEALD) process for the growth of tantalumbased compounds is employed in integration studies for advanced copper metallization on a 200mm wafer cluster tool platform. This process employs terbutylimido tris(diethylamido)tantalum (TBTDET) as precursor and hydrogen plasma as the reducing agent at a temperature of 250°C. Auger electron spectrometry, X-ray photoelectron spectrometry, and X-ray diffraction analyses indicate that the deposited films are carbide rich, and possess electrical resistivity as low as 250µΩ-cm, significantly lower than that of tantalum nitride deposited by conventional ALD or CVD using TBTDET and ammonia. PEALD Ta(C)N also possesses a strong resistance to oxidation, and possesses diffusion barrier properties superior to those of thermally grown TaN. INTRODUCTION Continued down-scaling of interconnect dimensions has placed a high priority on the development of robust copper barrier/liner materials and processes [1, 2]. In particular, liners with low electrical resistivity, good thermal stability, effective barrier performance, and which possess resistance to copper dewetting are of interest for such applications [1, 2]. Moreover, the associated processes used to deposit these materials need to be carried out at reduced temperatures to allow integration with thermally fragile polymeric dielectrics, and are required to yield smooth, conformal films in high aspect ratio structures, with monolayer-scale thickness and uniformity control. Chemical vapor deposition (CVD)-based processes such as atomic layer deposition (ALD) are well suited for these applications. Additionally, as TaNx-based liners are the material of choice for current copper barrier applications, there are benefits to extending this material set rather than undertaking a transition to new material systems. Given this, several groups have investigated ALD-grown TaN films for this purpose [3, 4]. These processes, which use ammonia as the reducing/nitriding agent, tend to yield films with relatively high resistivities (i.e. >1000µΩ-cm). Accordingly, several groups have investigated plasma-enhanced ALD (PEALD) as a potential process to deposit these materials with more suitable properties for use in emerging nanoelectronics applications [5, 6]. When PEALD is employed in concert with organotantalum precursors, carbon-doped TaNx films (Ta(C)N) are observed to be deposited [5]. The work discussed herein involves evaluating the integration and barrier properties of PEALD Ta(C)N films deposited in-situ with MOCVD copper layers for advanced copper metallization applications. Potential advantages of PEALD-grown Ta(C)N over thermally grown ALD TaN for copper barrier applications are also discussed. FILM PREPARATION
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