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John Peck, David Thompson, and Cynthia Hoover Praxair Inc., Tonawanda, New York 14151 (Received 20 February 2004; accepted 10 June 2004)

A low-temperature (320–480 °C) metal-organic chemical vapor deposition (MOCVD) process was developed for the growth of ruthenium and ruthenium oxide thin films. The process used bis(ethylcyclopentadienyl)ruthenium [Ru(C5H4C2H5)2] and oxygen as, respectively, the ruthenium and oxygen sources. Systematic investigations of film formation mechanisms and associated rate limiting factors that control the nucleation and growth of the Ru and RuO2 phases led to the demonstration that the MOCVD process can be smoothly and reversibly modified to form either Ru or RuO2 through simple and straightforward modifications to the processing conditions–primarily oxygen flow and substrate temperature. In particular, films grown at low oxygen flows (50 sccm) exhibited a metallic Ru phase at processing temperatures below 480 °C. In contrast, films grown at high oxygen flow (300 sccm) were metallic Ru below 400 °C. Above 400 °C, a phase transition was observed from Ru to RuOx (0 < x < 2.0) to RuO2 as the processing temperature was gradually increased to 480 °C.

I. INTRODUCTION

Ruthenium (Ru) and ruthenium oxide (RuO2) are attractive materials for complementary metal-oxide semiconductor (CMOS) gate electrode applications due to their desirable physical, electrical, and chemical properties. In particular, these materials are known to be highly refractory and to exhibit robust diffusion barrier properties and low resistivity values of 7 and 46 ␮⍀ cm for the metallic and oxide phases, respectively.1–4 In particular, ruthenium-based electrode materials have demonstrated excellent thermal stability not only on silicon dioxide (SiO2) but also on other high-dielectric constant (k) materials, such as zirconium oxide (ZrO2), Zr-silicates and yttrium-silicates.5–7 In terms of processing techniques, physical vapor deposition (PVD) approaches, such as sputtering, have been extensively explored for the growth of Ru and RuO2 for incorporation in gate electrode applications.5–7 However, such processes display undesirable features that include possible structural, morphological (surface roughening), or electrical damage to the underlying ultrathin a)

Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2004.0372 J. Mater. Res., Vol. 19, No. 10, Oct 2004

gate dielectric layers due to ion-enhanced sputtering effects.8 These undesirable features also include the observation that sputtered Ru-based films typically possess high levels of compressive stress, potentially leading to reliability concerns.9 Furthermore, film profiles in PVD processes are typical of line-of-sight deposition techniques, a characteristic that severely restricts their application in ultra-high-aspect ratio topographies of emerging device generations, where conformal step coverage is a critical requirement. Such devices include, for example, non-standard double gate metal-oxide-semiconductor field-effec