Low-k Dielectric Obtained by Noble Gas Implantation in Silicon Oxide
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0914-F03-04
Low-k Dielectric Obtained by Noble Gas Implantation in Silicon Oxide H. Assaf1, E. Ntsoenzok2, M-O. Ruault3, and S. Ashok4 1 CERI, CNRS, 3a, rue de la férollerie, Orleans, 45071, France 2 LESI, University of Orleans, 21 rue de loigny la bataille, Chartres, 28000, France 3 CSNSM, CNRS-IN2P3, Batiment 108-F, Orsay, 91405, France 4 Department of Engineering Science, the Pennsylvania State University, 212 Earth and Engineering Science Building, University Park, Pennsylvania, PA, 16802 Abstract Thermally-grown 220nm-thick silicon oxide layers were implanted at room temperature with 300keV Xe at doses ranging from 0.5 to 5x1016Xe/cm2. As-implanted samples exhibit bubbles in silicon oxide for all doses. Annealing at T≥400°C results in the disappearance of bubbles from SiO2 layer for the dose of 1x1016Xe/cm2. But for the higher doses of 3.5 and 5x1016Xe/cm2, the bubbles are very stable and remain in the sample even after very high thermal annealing. Capacitance measurements show a strong decrease in the dielectric constant k of the implanted SiO2 sample from 4 (reference sample) to 1.5. Introduction Ever since the advent of Si microelectronics, SiO2 the native oxide of Si, has been the material of choice for gate as well as interlevel dielectric. As device scaling continues below 0.25µm, cross-talk effects become more pronounced and capacitive propagation delays in interconnects become exponentially larger, dominating intrinsic device delay1. There is then a need to replace SiO2 (with k~4) by materials with lower permittivity (or dielectric constant, k)2. Basically, in low-k materials, the dielectric constant is reduced through a reduction in electronic polarization3 or through the introduction of porosity4. Many studies5,6 have demonstrated that implantation technique is a promising way to decrease the dielectric constant of SiO2. Fluorine and carbon implantation in silicon oxide results in the replacement of Si-O bonds by less polar Si-F or Si-C. These implantations provide oxides with a k of about 3.4. We previously reported a dielectric constant value less than 1.5 after Xe implantation in SiO27. This low value is attributed to the bubble/cavity formation in silicon oxide. These nanostructures induce porosity in SiO2 and this porosity is thought to be responsible of k reduction. However reduction of polarizability of this material due to the broken Si-O bonds by implantation can also play a role in the decrease of the dielectric constant. Here we report on the formation and thermal growth of bubbles along with the thermal evolution of K in Xe-implanted SiO2. Experimental procedure The samples used in this study were 220nm-thick SiO2 thermally grown on Si substrates. The samples were implanted, at room temperature , with 300keV Xe. Such an energy results in Xe implantation at a depth of 125nm as simulated by SRIM (Stopping and Range of Ions in Matter8). Four doses were used in this study: 0.5, 1, 3.5 and 5x1016Xe/cm2. After implantation, the samples were annealed for 1 hour in a nitrogen ambient at temperatu
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