SCANNING FORCE MICROSCOPY MEASUREMENTS OF LATENT IMAGE TOPOGRAPHY IN CHEMICALLY AMPLIFIED RESISTS

Noncontact scanning force microscopy topography measurements of expose d and undeveloped photoresists are reported. A negative chemically amp lified photoresist, SAL605, was patterned by electron beam direct writ ing of 1 mu m line linear gratings, and 5 mm pads. A relief image of e xposed unbaked resist has been observed of the order of a few Angstrom , and then monitored as a function of time after exposure. This relief image undergoes a topography transformation with postexposure bake (F EB), yielding a ridge located at the exposed-unexposed region interfac e, extending several nanometers in vertical and about one micrometer l aterally. The effect has been investigated as a function of FEB time a nd exposure dose. Correlations of the observed phenomena with optical film thickness monitoring techniques and previously reported data on t he photoresist chemical changes during exposure and FEB are discussed. Two independent mechanisms contributing to the image formation are id entified. The data show that the local chemistry of the latent image a t the edges of feature is different than in wider features. This has i mportant implications for the application of chemically amplified resi sts to high-resolution lithography. (C) 1996 American Institute of Phy sics.