<title>New Portable Conformable Mask Method For Excimer Laser Lithography</title>

Abstract

New PCM (Portable Conformable Mask) method for excimer laser lithography has been developed. It consists of RD2000N (Hitachi Chemical Co., Ltd) as the top imaging layer, and PMGI (Poly-dimethyl glutarimide, Shipley Co., Ltd) as the bottom planarizing layer. In order to evaluate several kinds of deep UV resists and to search for a suitable resist process, we constructed an excimer laser exposure system, which is composed of a KrF excimer laser emitting at 248 nm with a bandwidth of 0.005 nm, and all quartz projection optics with a numerical aperture of 0.30, and a reduction ratio of 1/5. The excimer laser can produce about 100 mJ per pulse in the narrow bandwidth region. Spectral narrowing was accomplished by inserting etalons within the laser optical cavity. The reticle pattern was transferred to the wafer through the reduction lens. The energy density was about 15 mJ/cm2 at the wafer. From the evaluations of resist materials using the exposure system, it has been shown that RD2000N has high sensitivity and high resolution capability at the wavelength of KrF excimer laser. In the experiments of the PCM method, 0.5 μm thick RD2000N top layer was exposed and developed with an aqueous developer. RD2000N has very strong absorption in deep UV region, so can function as an adequate contact mask for the PCM method. After the top layer was delineated, that pattern was transferred to 1.0 μm thick PMGI as the bottom layer with deep UV flood exposure and subsequent developing of PMGI. With the PCM method, we have achieved 0.5 μm line and space resist patterns with aspect ratio of 3. The method is free from RIE treatment and thought to be more practical than a typical tri-layer resist which needs oxygen RIE for the bottom layer patterning.