Tailored Deposition by LPCVD of Non-stoichiometric Si Oxides and their Application in the Formation of Si Nanocrystals E
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0989-A23-01
Tailored Deposition by LPCVD of Non-stoichiometric Si Oxides and their Application in the Formation of Si Nanocrystals Embedded in SiO2 by Thermal Annealing Bruno Morana1, Juan Carlos G. de Sande2, AndrÈs RodrÌguez1, Jes˙s Sangrador1, Tom·s RodrÌguez1, Manuel Avella3, ¡ngel Carmelo Prieto3, and Juan JimÈnez3 1 TecnologÌa ElectrÛnica, Universidad PolitÈcnica de Madrid, E.T.S.I.T., Madrid, 28040, Spain 2 I. Circuitos y Sistemas, Universidad PolitÈcnica de Madrid, E.U.I.T.T., Madrid, 28031, Spain 3 FÌsica de la Materia Condensada, Univ. de Valladolid, E.T.S.I.I., Madrid, 47011, Spain
ABSTRACT Silicon oxide films with excess of Si were deposited by Low Pressure Chemical Vapor Deposition. The growth rate of the films and the excess of silicon in them have been modeled using a Face-centered Central Composite Design experiment. Samples annealed at 1100 ∫C show luminescence (665 nm) at 80 K and at room temperature associated to Si nanocrystals. INTRODUCTION Si nanocrystals embedded in SiO2 have been used in non-volatile memories and optoelectronic devices compatible with the CMOS technology. A simple method to fabricate this kind of structures consists of the precipitation by thermal annealing of the excess of Si incorporated in non-stoichiometric silicon oxide films, which may be obtained using different techniques [1, 2]. In this work, the non-stoichiometric oxide layers have been deposited using a commercial Low Pressure Chemical Vapor Deposition (LPCVD) reactor. To find the experimental conditions that allow us to achieve a sufficiently slow growth rate to be able to control the thickness of the films and to incorporate the desired amount of Si in excess, the system has been characterized using a Face-centered Central Composite Design (FCCD) experiment [3]. The as-deposited samples were characterized by FTIR spectroscopy and spectroscopic ellipsometry to determine their composition, thickness and refraction index. The deposition process was characterized by the growth rate and the excess of Si incorporated in the films. The effect of the post-growth annealing process to form Si nanocrystals has been studied using Raman spectroscopy and Cathodoluminescence spectroscopy. EXPERIMENT Samples preparation The deposition was carried out on Si wafers using a LPCVD deposition system with Si2H6 and O2 as precursor gases and N2 as carrier gas. The process parameters were selected based on our previous results on the deposition of stoichiometric oxides [4]. The pressure was varied between 185 and 300 mTorr and the temperature between 250 and 450 ∫C. The Si2H6 / O2
gas flow ratio was varied between 2 and 5 to ensure that the gas is rich enough in the precursor of Si. The total flow was 102 sccm, being 90 sccm the flow of N2 in all the experiments and 12 sccm the total flow of the reactant species, which was kept constant. The deposition time was two hours except in some samples in which it was three hours. The volume fraction occupied by the excess (E) of Si incorporated into the deposited layers and the growth rate
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