Increased Thermal Stability of Co-silicide Using Co-Ta Alloy Films
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Increased Thermal Stability of Co-silicide Using Co-Ta Alloy Films
Min-Joo Kim1, Hyo-Jick Choi1 and Dae-Hong Ko1 Ja-Hum Ku2, Siyoung Choi2, Kazuyuki Fujihara2 and Ho-Kyu Kang2 and Hoo-Jeung Lee3 1 Department of Ceramic Engineering, Yonsei University 134 Shinchon-Dong, Seodaemoon-ku, Seoul 120-749, South Korea 2 Process Development Team, Semiconductor R&D Division, Samsung Electronics Co., Ltd., Yongin-City, Kyungki-Do, Korea 3 Stanford University, Stanford, California 93405, USA
ABSTRACT
The silicidation reactions and thermal stability of Co silicide formed from Co-Ta/Si systems have been investigated. In case of Co-Ta alloy process, the formation of low resistive CoSi2 phase is delayed to about 660oC, as compared to conventional Co/Si system. Moreover, the presence of Ta in Co-Ta alloy films reduces the silicidation reaction rate, resulting in the strong preferential orientation in CoSi2 films. Upon high temperature post annealing in the furnace, the sheet resistance of Co-silicide formed from Co/Si systems increases significantly, while that of Co-Ta/Si systems maintains low. This is due to the formation of TaSi2 at the grain boundaries and surface of Co-silicide films, which prevents the grain boundary migration thereby slowing the agglomeration. Therefore, from our research, increased thermal stability of Co-silicide films was successfully obtained from Co-Ta alloy process.
INTRODUCTION
Recently, self-aligned silicide (SALICIDE) technology is widely used as demand for high performance device gains. Further, new merged device, such as logic and DRAM, is now in demand. Usually, the employment of the Co-salicide process is limited up to 800oC. If the temperature is above 800 oC, thermal degradation occurs due to the agglomeration of the Cosilicide films. As a result Co silicide and silicon interface morphology becomes rough, which leads to the increase of junction leakage current and sheet resistance. Thermal processes are used to anneal the capacitor dielectric in DRAM devices (800 oC) and to activate impurities in analog devices (950 oC)[1]. Therefore in merged processes, it is necessary to suppress thermal K6.5.1
degradation of the silicide during high temperature processes. Thus, in order to apply Cosilicide to merged DRAM and Logic processes, improvement of thermal stability is required. Recently, the single layer process using Co and Si has been replaced by several processes to be made for the formation of a high yielding and reproducible silicide. In order to improve the films uniformity and thermal stability, several processes such as using Co/Ti bilayer [2-5] or interlayer oxide [6-7] were previously reported. However these processes are complicated and are not suitable for current device structures. In this paper, to improve thermal stability and film uniformity of Co-silicide, we proposed a new Co-salicide process using Co-Ta alloy films.
EXPERIMENT
Two types of substrates, p-type (100) silicon and undoped polysilicon wafers were used in this work. 250nm thick polycrystalline silicon films were
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