Investigations of the Ga⁺ focused-ion-beam implantation in resist films for nanometer lithography applications

A focused-ion-beam (FIB) machine is a versatile tool used extensively in the IC industry for conducting failure analysis, prototype fabrication, and device repair. Lithography can also be performed by the FIB technique for direct patterning of photoresists, followed by wet or dry development. We studied how the property of resist regions changes during oxygen dry development in the NERIME (the negative-resist-image-by-dry-etching) process after subjecting to FIB-assisted gallium implantation. The NERIME process is a single-layer scheme, in which DNQ/Novolak-based resists are exposed by gallium ions with FIB, followed by near-ultraviolet flood exposure, silylation, and oxygen dry etching. This process can yield both positive and negative resist images. In addition, the NERIME technique can achieve a nanometer resolution down to 80 nm and a high aspect ratio for the processed patterns. A scanning-transmission-electron-microscope (STEM) analysis of the resist regions FIB-implanted with gallium ions has revealed that there is a ∼15-nm-thick gallium oxide (Ga₂O₃) layer on the surface. The presence of the gallium oxide layer was found to provide an increased resistance against subsequent oxygen dry development. It was concluded that the NERIME process could be used for a specific CMOS processing task, such as high-resolution lithography over resist surfaces with complex topography.