The Characterization of Initial Growth of Polycrystalline Silicon Germanium Films on Zirconium Oxide
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The Characterization of Initial Growth of Polycrystalline Silicon Germanium Films on Zirconium Oxide Dong-Won Kim, Freek Prins, Kil-Soo Ko, C. H. Lee, Dim-Lee Kwong, and Sanjay Banerjee Microelectronics Research Center, The University of Texas at Austin, Austin, TX 78712, U.S.A ABSTRACT In this study, the initial growth characteristics of a SiGe film realized by ultrahigh-vacuum chemical vapor deposition (UHV CVD) using GeH4 and Si2H6 on high-K gate oxide, ZrO2, has been investigated in the temperature range from 475°C to 550°C. The influence of surface reactions on growth characteristics such as the incubation of growth, roughness of the SiGe layer, and the interface reaction of the SiGe film with ZrO2 were studied using atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM). From our analysis we conclude that ZrO2 reacts with Si and forms zirconium silicide in the temperature range between 500°C and 550°C. The surface roughness of amorphous SiGe layers increase from 0.5nm to 1.5nm by increasing Ge content from 0.1 to 0.3. A further increase of surface roughness is observed from less than 1nm to 5nm as SiGe layer transitions from an amorphous to a poly crystalline layer.
INTRODUCTION Polycrystalline silicon-germanium (poly SiGe) has recently been shown to be an alternative to polycrystalline silicon (poly Si) as gate electrodes for advanced submicron complementary metal oxide semiconductor fieled effect transistors (CMOSFETs) [1]. New applications of SiGe include narrow bandgap base regions in bipolar transistor [2]. In large-area electronics such as flat panel displays and thin films transistors (TFTs), the advantages of poly SiGe over poly Si include low process temperature, low activation energy of dopants, and high carrier mobility [15]. However, some phenomena are not clear, such as the reduced boron penetration in oxides during a CMOS process and the effect of the Ge content on the Hall mobility and the resistivity of doped poly-SiGe. Furthermore, the initial stage of the SiGe film formation and nucleation which are known to control the film structure and hence film properties [6] are not clearly understood. Recent efforts on alternate gate dielectrics materials for replacing silicon dioxide on standard CMOS technology have focused on high K gate dielectrics which provide higher dielectric constants, reduced leakage, improved resistance to boron diffusion, and better reliability characteristics [7-10]. However, most high K dielectric materials are not thermally stable in direct contact with silicon [7]. An interface layer between the high K dielectric materials, Si substrate and Si poly gate is necessary to prevent the interface reaction. This additional layer complicates the fabrication processes. Therefore the investigation of alternative gate electrode materials is desirable. In the present study, the initial growth characteristics of a SiGe film realized by ultrahighvacuum chemical vapor deposition (UHV CVD) using GeH4 and disilane on ZrO2 have be
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