Structural transformation of acrylic resin upon controlled electron-beam exposure yields positive and negative resists

Zwitter polymers are defined as polymers that undergo transformation from a linear to a crosslinked structure under electron-beam irradiation. A resist polymer may be either linear or crosslinked, depending on electron-beam dosage. The structural transformation of acrylic resin make it suitable for applications in positive and negative resists in the semiconductor field. The contrast ratio and threshold dose both increase with increasing resist thickness for both the positive and negative resists, while the positive resist exhibits better contrast than the negative. The intensity of the characteristic Fourier-transform infrared absorption band at 161.2 cm(-1) (vinyl group) is used to explain the phenomena behind these resist transformations. We evaluate the effects of two important processing conditions: the soft baking and post-exposure baking temperatures. Pattern resolution decreases upon increasing the baking temperature, except for soft baking of the negative resist. The effect of electron dose on the pattern resolution is also discussed in detail for both resists. High electron-beam exposure does not improve the etching resistance of the resist because of the porous nature of the resist that develops after high-dosage irradiation.