A novel fabrication method of needle array combined X-ray gray mask with LIGA process

Abstract

ABSTRACT We have succeeded in fabricating a needle array of polycarbonate by using a three-dimensional LIGA process. The diameter of the bottom of the needle was about 50 P m, and the height was 135 P m. Although a usual LIGA process has been employed to form structure only with vertical sidewalls, it has now become possible to fabricate needle shape structure by employing a technology that combines X-ray gr ay mask with the LIGA proce ss. The X-ray gray mask was composed of Si X-ray absorbers and a SU-8 membrane. The sidewall of the X-ray absorber was diagonally processed by Si tapered-trench-etching technology where the transmission intensity of X-rays could be varied locally. An X-ray lithography experiment was executed by using the X-ray gray mask on a beamline BL-4 in TERAS synchrotron radiation facility at AIST. Using this technology a PMMA resist mast er with three-dimensional structures was made. A Pt layer was sputter deposited as a seed layer on the PMMA resist master, and a Ni mold was fabr icated by an electroforming technology. In addition, needle arrays of polycarbonate (PC) and of polymethyl methacrylate (PMMA) were produced by hot embossing technology. Thus, we succeeded in extending the LIGA process to a three-dimensional process capability by employing X-ray gray mask. Keywords: X-ray lithography, gray mask, Ni electroforming, hot em bossing, LIGA process, needle array, polycarbonate, polymethyl methacrylate