Nanolithography in polymethylmethacrylate: An atomic force microscope study

This work addresses the formation and development of very dense nanolithographic resolution patterns in polymethylmethacrylate (PMMA) of two molecular weights (MWs), 950 and 50 K. The patterns were lithographically defined by a JEOL JBX-5DII e-beam lithography system operated at 50 kV with a Gaussian probe standard deviation of 8-10 nm. The lithographic patterns consisted of pads of widths from 1 to 20 mu m with a 50 nm gap of exposure in the center and single pass line gratings of periods 40, 60, 80, and 100 nm. Atomic force microscope images were acquired. Latent images of the 50 nm gap were observed over a much larger range in dose and pad size, than observed in developed samples. The morphologies of the two unpatterned resists were comparable exhibiting a granular type structure with average particle diameters of 52-53 nm and root mean square surface roughness of 0.2-0.3 nm. In developed patterns, the morphologies and resolution of the two MW resists were very different. The 950 K resist exhibited better resolution and contrast than the 50 K resist. The results are discussed in the context of the exposure and development of macromolecular resists. [S0734-211X(98)14606-1].