Scanning force microscopy measurements of latent image topography in chemically amplified resists

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Abstract
Noncontact scanning force microscopy topography measurements of exposed and undeveloped photoresists are reported. A negative chemically amplified photoresist, SAL605, was patterned by electron beam direct writing of 1 μm line linear gratings, and 5 mm pads. A relief image of exposed unbaked resist has been observed of the order of a few Å, and then monitored as a function of time after exposure. This relief image undergoes a topography transformation with postexposure bake (PEB), yielding a ridge located at the exposed–unexposed region interface, extending several nanometers in vertical and about one micrometer laterally. The effect has been investigated as a function of PEB time and exposure dose. Correlations of the observed phenomena with optical film thickness monitoring techniques and previously reported data on the photoresist chemical changes during exposure and PEB are discussed. Two independent mechanisms contributing to the image formation are identified. The data show that the local chemistry of the latent image at the edges of feature is different than in wider features. This has important implications for the application of chemically amplified resists to high-resolution lithography.

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