In Situ Study of Barrier Layers Using Spectroscopic Ellipsometry and Mass Spectroscopy of Recoiled Ions
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ABSTRACT An in situ study of barrier layers using spectroscopic ellipsometry (SE) and Time-of-Flight (ToF) mass spectroscopy of recoiled ions (MSRI) is presented. First the formation of copper silicides has been observed by real-time SE and in situ MSRI in annealed Cu/Si samples. Second TaSiN films as barrier layers for copper interconnects were investigated. Failure of the TaSiN layers in Cu/TaSiN/Si samples was detected by real-time SE during annealing and confirmed by in situ MSRI. The effect of nitrogen concentration on TaSiN film performance as a barrier was also examined. The stability of both TiN and TaSiN films as barriers for electrodes for dynamic random access memory (DRAM) devices has been studied. It is shown that a combination of in situ SE and MSRI can be used to monitor the evolution of barrier layers and detect the failure of barriers in real-time. INTRODUCTION Continuous scaling down of feature size and the demand for optimized performance of modem devices has resulted in the introduction of a variety of new materials into the device structure. Both the diversity of materials involved and the proximity of multilayer device structures increase the possibility of interactions including diffusion and chemical reactions between film layers. Proper barrier layers help to prevent or reduce these unwanted interactions [1]. For copper interconnects, barrier layers are necessary to prevent copper diffusion into the silicon substrate [2]. In the case of high dielectric constant materials such as (Ba,Sr)TiO 3 for applications in storage capacitor for dynamic random access memory (DRAM), a barrier layer is needed to prevent oxygen diffusion, as well as to avoid reaction between the electrode and silicon vias or plugs [3] during high temperature annealing processes. The thermal stability and barrier performance of these layers emerge as important scientific and technological issues and have therefore been the subject of extensive studies. However, most of studies have been carried out using ex situ and destructive techniques [4-6] such as Rutherford backscattering spectroscopy (RBS), cross-section transmission electron microscopy (XTEM), Auger electron spectroscopy (AES) depth profiles and electrical measurements. The primary objective of this study is to demonstrate an in situ methodology to monitor the evolution of barriers under real processing conditions, and therefore provide real-time information about the performance of barriers in device structures and to have the ability to detect barrier failures in real-time. EXPERIMENT The TaSiN barrier was deposited onto HF dipped p-type Si substrates using reactive ion beam sputtering with a nitrogen background pressure of lxl0-4 Torr. A 4" in diameter TaSi 2 target was used for sputtering with an Ar/0 2 gas mixture flowing through sputtering gun to control the nitrogen concentration in the deposited film. For copper interconnects samples, 135 Mat. Res. Soc. Symp. Proc. Vol. 619 © 2000 Materials Research Society
100nm thick Cu was deposited in Ar on top of 20nm
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