Reliability of Electrodeposited Copper and Ecrcvd Siof Films for Multilevel Metallization
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ABSTRACT The effect of a post plasma treatment on the dielectric properties and reliability of fluorine doped silicon oxide (SiOF) films deposited by electron cyclotron resonance chemical vapor deposition (ECRCVD) was studied. Also, the thermal stability of an electrodeposited Cu / sputtered Ta interconnect system with SiOF intermetal dielectrics was examined by annealing in a vacuum furnace. The stability of the dielectric constant of SiOF films was improved by 0, post plasma treatment. Surface modification by the plasma treatment was effective in prevention of water absorption. The Cu/Ta/SiOF/Si system was thermally stable at least up to 500 C for 3h. For the Cu/Ta/SiOF/Si multilayer structure, the plasma treatment seemed to play a big role in suppressing the interdiffusion between SiOF and metal interconnects. By C-V measurement, the
electrical stability of the Cu/Ta/SiOF/Si multilayer structure was found to be stable up to 5001C for2 h. INTRODUCTION In multilevel interconnections, it has been predicted that RC delay of ULSI circuits will limit operating speed of devices as parasitic resistance and capacitance increase. Propagation delays due to parasitic capacitance from interconnects are one of the main causes for reducing speed performance in advanced ICs as interconnect dimensions are scaled down[l]. Therefore, many semiconductor researchers are preparing to bring in copper and low-k based interconnects to replace the traditional aluminum/SiO 2 systems, which will require radical and fundamental changes in many different technologies. The most recent example of this came with the use of low-k (3.5-3.6) F-doped silicon dioxides, once viewed as a drop-in replacement for Si0 2 [2-6]. Copper/low-k interconnects provides several advantages over the traditional Al/SiO2 approaches, 93 Mat. Res. Soc. Symp. Proc. Vol. 565 ©1999 Materials Research Society
including the ability to significantly reduce the number of levels of metal required, which also increasing chip speed, minimizing power dissipation and reducing manufacturing costs. Copper also offers improved reliability in that its resistance to electromigration is much better than aluminum's[3]. In this work, in order to improve the stability of the SiOF film, oxygen plasma treatment was applied to as-deposited SiOF films. Furthermore, the reliability of electrodeposited Cu and low-k SiOF films was investigated using a thermal annealing treatment in a vacuum furnace. EXPERIMENT The SiOF films were deposited using an electron cyclotron resonance chemical vapor deposition (ECRCVD) system (AsTeX Model AX4505). The SiOF films were deposited as a function of SiF4/O2 gas flow ratio. The gas flow ratio was varied from 0.2 to 1.0. The microwave power and substrate temperature during deposition were fixed at 700 W and 300"C, respectively. The deposition time was adjusted to deposit films of appropriate thickness for analytical measurements. The substrates employed in this study were B-doped p-type Si (100) wafers. The post plasma treatment of the SiOF films was carried
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