Study of Porous Silica Based Films as Low-k Dielectric Material and their Interface with Copper Metallization
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Study of Porous Silica Based Films as Low-k Dielectric Material and their Interface with Copper Metallization Ilanit Fisher1, Wayne D. Kaplan1, Moshe Eizenberg1, Michael Nault2, and Timothy Weidman2 1 Dept. of Materials Engineering, Technion – Israel Institute of Technology, Haifa 32000, Israel 2 Applied Materials Inc., Santa Clara, CA 95054, U.S.A. ABSTRACT The success of future gigascale integrated circuits (IC) chip technology depends critically upon the reduction of the interconnects RC delay time. This calls for the development of new low dielectric constant (low-k) insulators, and for work on their integration with lower resistivity copper metallization. A porous silica based film prepared by surfactant templated self-assembly spin-on deposition (SOD) is an attractive candidate as a low-k material. In this research we have studied the structure, chemical composition and bonding of the film and its interface with copper metallization. The decomposition and vaporization of the surfactant in the last step of film deposition resulted in a film with an amorphous structure, as determined by XRD and TEM analysis. Its high porosity (35-58%) was confirmed by XRR and RBS measurements. XPS analysis of the Si2p transition indicated three types of bonding: Si-O, O-Si-C and Si-C. The bonding characteristics were also investigated by FTIR analysis. The effect of a hydrogen plasma post-treatment process on the film topography and bonding was determined by AFM and XPS, respectively. It was found that direct H2 plasma exposure significantly affected the surface roughness of the film and type of chemical bonding. The structure and properties of various PECVD deposited capping layers were also studied, as was the interface between the porous dielectric and Ta, TaxN and Cu (PVD deposited films) after annealing at 200-700°C in vacuum environment for 30 min. At temperatures up to 500°C, no significant diffusion of Cu or Ta into the porous film was detected, as determined by RBS. No copper penetration was detected up to 700°C, according to AES and SIMS analysis. However, at 700°C copper dewetting occurred when it was deposited directly on the porous silica based film. INTRODUCTION As feature sizes in ICs approach 0.18 µm and below, the interconnect RC delay time, power consumption and crosstalk noise become very critical problems. Switching to Cu as a replacement for Al(Cu) interconnect metal yields lower electrical resistivity and higher resistance to electromigration. In addition, a new generation of low-k materials (k
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