Effect of Plasma Pre-Treatment on Dewetting Properties of CVD Cu on CVDW 2 N Barrier Layer
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Effect of Plasma Pre-Treatment on Dewetting Properties of CVD Cu on CVD W2N Barrier Layer Degang Cheng, Guillermo Nuesca, and Eric Eisenbraun School of NanoSciences and NanoEngineering, The University at Albany-SUNY Albany, NY12203, U.S.A. ABSTRACT The effect of different plasma pre-treatments of chemical vapor deposited (CVD) tungsten nitride (W2N) surfaces on the dewetting behavior of subsequently grown CVD Cu films was investigated by annealing the resulting film stacks in high purity argon. It was found that a hydrogen plasma pre-treatment significantly improved the resistance to Cu dewetting from the W2N surfaces while ammonia and nitrogen plasma pretreatment slightly accelerated the dewetting process. The proposed mechanisms and ramifications of these findings were discussed. INTRODUCTION Dual damascene processing has been recognized as a key technology to enable copper-based metallization. In order to effectively process such structures, it is essential to develop robust, conformal barrier layer and copper deposition processes which can coat and fill aggressive trenches and via structures. In this respect, as ultra-large-scale integrated circuit devices are continuously evolve towards feature size below 100 nm, chemical vapor deposition (CVD)-based processes, including atomic layer deposition (ALD) become necessary for both diffusion barrier and copper seed layer depositions owing to the capability of such processes to provide the necessary conformality in leading edge nanoelectronics. There has been significant interest in tungsten nitride (W2N) for copper barrier applications because of its excellent thermal, chemical, and mechanical properties [1-6]. In particular, one potential advantage of using W2N as Cu diffusion barrier is that it can be deposited in amorphous form, which is understood to improve barrier properties due to the lack of grain boundaries as fast diffusion paths [1]. Among the processes used to deposit W2N films, both thermal and plasmaassisted inorganic CVD using WF6 have been widely reported [2, 3]. Such thermal CVD processes have relied primarily on the reaction of tungsten hexafluoride (WF6) and ammonia (NH3). This process results in significant particle generation, in addition to the typical issues pertaining to the use of fluorinated tungsten chemistry such as transport and handling of highly reactive fluorinated WF6 and possible incorporation of fluorine in the resulting films [4]. Metalorganic CVD of W2N has also been attempted with complex single W-N sources, such as bis(tertbutylimido)bis(terbtylamido)tungsten [5]. These processes typically require deposition temperatures higher than 450°C, thus making them impractical for integration with candidate low-k dielectric materials, and often lead to the incorporation of carbon and other light element contaminants in the resulting films [5]. To address these challenges, our research group has reported a MOCVD process using tungsten hexacarbonyl, W(CO)6 and NH3 as reactants [6]. Amorphous W2N films have been prepared at temperat
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