Pyrolytic Laser Direct Writing of Nickel Over Polyimides
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PYROLYTIC LASER DIRECT WRITING OF NICKEL OVER POLYIMIDES
S.J. Bezuk, R.J. Baseman*, C. Kryzak, K. Warner, G. Thomes 55121 UNISYS Corp., Semiconductor Operations, St. Paul, MN Abstract Polyimides are of great interest as insulators for microelectronic fabrication due to their low dielectric constant and planarizing properties. However, they are thermally sensitive films. Nonetheless, preliminary results clearly demonstrate that nickel lines readily can be laser-pyrolytically drawn over polyimide films. While elevated laser power will damage underlying polyimide films, microelectronic quality nickel lines can be drawn using nickel carbonyl at relatively low laser intensities over polyimides with little or no change in the electrical characteristics. Polyimide's lower thermal conductivity relative to silicon dioxide facilitates increased nickel deposition rates. Self-limiting effects have been observed during the deposition that can lead to near microelectronically ideal line cross sections. Introduction The use of laser direct writing to deposit or etch metal interconnect introduces many possibilities for improving integrated circuit and circuit package manufacturing. These laser techniques exploit the use of focused laser beams for their highly localized processing capability. In addition, some laser techniques do not require masks for the fabrication of patterns. Thus, laser direct writing can be used to repair defective circuits and photomasks, to manufacture small numbers of circuits economically, and to develop novel, yield improving IC packaging techniques [1,2,3,4,5]. Currently, the dominant trend in microelectronics toward increasing device performance and packaging density has raised strong interest in the study of polyimide materials [6,7]. The advantages of polyimides as interconnect dielectrics include their superior planarization properties, low dielectric constants, and excellent thermal stability relative to other plastics. Therefore, the lower temperature and local metal deposition characteristics of laser direct writing in conjunction with the superior electrical and mechanical properties of polyimides offer strong incentives for investigating the compatibility of the two technologies. We report on the laser CVD of nickel on polyimide and the effects that this deposition has on the electrical and mechanical surface properties of polyimides. Thermally and chemically induced surface degradation was electrically probed by measuring surface leakage current at various substrate temperatures after chemically removing the laser deposited nickel lines. Emphasis was placed on the importance of tailoring the laser processing in order to optimize the electrical performance of the desired metal interconnect. The effects that laser power, gas pressure, and scan rate have on the aspect ratio of deposited metal lines are also discussed and compared with similar depositions on silicon dioxide. *Current Address: IBM, T. J. Watson Research Center, P. 0. Box 218, Yorktown Heights, New York 10598
Mat. Res. Soc. Symp.
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