Mechanical Enhancement Of Nanoporous Low-K Films As Interlayer Dielectrics By Ion Implantation
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MECHANICAL ENHANCEMENT OF NANOPOROUS LOW-K FILMS AS INTERLAYER DIELECTRICS BY ION IMPLANTATION Alok Nandini U.Roy, Zubin P. Patel, A.Mallikarjunan1, H.Bakhru and T. -M.Lu1 Department of Physics, University at Albany-SUNY, NY 12222, U.S.A 1 Center for Integrated Electronics, Rensselaer Polytechnic Institute, Troy, New York 12180
ABSTRACT Thin films of Ultra-Low K materials such as Xerogel (K=1.76) and MSQ (K=2.2) 15 were implanted with argon, neon, nitrogen, carbon and helium with 2 x 10 cm-2 and 1 x 16 10 cm-2 dose at energies varying from 20 to 50 keV at room temperature. In this work we showed that the surface hardness of the porous films is improved five times as compared to the as-deposited porous films sacrificing the dielectric constant up to 15% after implantation (e.g., from 1.76 to 2.0). The hardness persists after 450 0 C annealing. It is also shown that implantation can prevent the penetration of chemical gases such as CVD precursors in the Ultra-Low K dielectrics during a CVD process. INTRODUCTION Low dielectric materials are being introduced into current interconnect technologies to meet RC delay goals and minimize cross-talk [1]. These films generally have dielectric constants less than 3 (vs. 4 for silicon dioxide) and very poor mechanical strength [3]. The elastic modulus (E) of the low κ film is typically less than 10Gpa, compared with 70Gpa for SiO2. The poor mechanical strength of the low κ dielectric films increases the risk of thermo-mechanical failures within the Cu/low κ interconnect structure; e.g. thin film delamination and cracking [2]. Maintaining the mechanical integrity of the low κ films with the stresses of fab processing, packaging and reliability testing has proven challenging. Therefore, surface hardening is necessary to withstand processing (e.g. CMP). This paper will address the methods to enhance the mechanical strength of low dielectric films. Results of two classes of material (i.e. Xerogel (porous) and MSQ (organic)) are discussed. EXPERIMENTAL DETAILS Xerogel and Porous MSQ were obtained from SEMATECH in the form of 0.5µm to1 µm thick film was implanted with 20 keV to 50 keV Ar+, Ne+, N+, C+, and He+ to a dose of 2x1015 ions/cm2 and 1x1016 ions/cm2 have yielded significant improvements in hardness of Xerogel and Porous MSQ. The implantation was performed using Low energy Ion Implanter (extrion) facility in the Ion beam Laboratory, University at AlbanySUNY.
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Ion Lattice
Electrons Atoms
hardening of surface ions
Nuclear Collisions
Ion
Fig 1: (a) Physical Process for Ion Implantation (b) Schematic diagram showing surface hardening of porous materials by ion implantation Figure 1(a) and (b) explains the physical interaction between ions and solid (thin film). An ion incident on a lattice is deflected in nuclear collisions with the lattice atoms and also loses energy in collisions with electrons. Measurements of elastic modulus and hardness were performed using a Nano IndenterR II and MTS patented Continuous Stiffness Measurements (CSM) technique [5]. With t
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