Atomically Controlled Impurity Doping in Si-Based CVD Epitaxial Growth
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ATOMICALLY CONTROLLED IMPURITY DOPING IN SI-BASED CVD EPITAXIAL GROWTH JUNICHI MUROTA1, MASAO SAKURABA1 and BERND TILLACK2 1 Laboratory for Nanoelectronics and Spintronics, Research Institute of Electrical Communication, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai 980-8577, Japan. 2 IHP, Im Technologiepark 25, 15236 Frankfurt (Oder), Germany ABSTRACT Atomic-order surface reaction processes on the group IV semiconductor surface are formulated based on the Langmuir-type surface adsorption and reaction scheme. In in-situ doped Si1-xGex epitaxial growth on the (100) surface in a SiH4-GeH4-dopant (PH3, or B2H6 or SiH3CH3)-H2 gas mixture, the deposition rate, the Ge fraction and the dopant concentration are explained quantitatively assuming that the reactant gas adsorption/reaction depends on the surface site materials and that the dopant incorporation in the grown film is determined by Henry's law. Self-limiting formation of 1-3 monolayers of group IV or related atoms in the thermal adsorption and reaction of hydride gases (SiH4, GeH4, NH3, PH3, CH4 and SiH3CH3) on Si(100) and Ge(100) are generalized based on the Langmuir-type model. Epitaxial Si or SiGe grown on N, P or B layers already-formed on Si(100) or SiGe(100) surface is achieved. It is found that higher level of electrical active P atoms exist in such film, compared with doping under thermal equilibrium conditions. Furthermore, the capability of atomically controlled processing for doping of advanced devices with critical requirements for dopant dose and location control is demonstrated for the base doping of SiGe:C heterojunction bipolar transistors (HBTs). These results open the way to atomically controlled technology for ultra-large-scale integrations. INTRODUCTION Atomically controlled processing has become indispensable for the fabrication of ultrasmall MOS devices and Si-based heterodevices, because high performance devices require atomic order abrupt heterointerfaces and doping profiles. The fabrication of high performance Si-based devices for ultra-large-scale integration require atomic level control of process technology. Especially for processing involving surface reaction processes like chemical vapor deposition (CVD), the advancement of the process technology requires atomic-order surface reaction control. Because atomic level flatness of surfaces and interfaces needs to be maintained, low-temperature processing is indispensable in order to suppress thermal degradation such as unexpected reaction and impurity diffusion. Moreover, impurity gas molecules are adsorbed more easily at lower temperatures. An ultraclean environment is a critical requirement. Improvements in the quality of gases and equipment have enabled ultraclean low-temperature processing for atomic-order control [1-3]. Our concept of atomic-level processing is based on atomic-order surface reaction control. The main idea of the atomic layer approach is the separation of the surface adsorption of reactant gases from the reaction process. Atomic-level control has been real
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