Development of multiple pass exposure in electron beam direct write lithography for sub-32nm nodes

Abstract

ABSTRACT Electron beam direct write lithography is used in the ASIC manufacturing industry to sustain optical lithography for prototyping applications, low volume production and for the development of the next technological nodes. However the standard proximity effects corrections based on dose modulation are not sufficient to provide the patterning accuracy required for the sub-32nm nodes. New methods are needed to push the resolution capabilities of electron beam lithography. In a previous paper, a new writing strategy based on multiple pass exposure has been introduced. It consists in adding small electron Resolution Improvement Features (eRIF) atop the nominal features. Thanks to this new method, critical lines have been patterned with enlarged energy latitude. In this paper, multiple pass exposure is applied to the sub-32nm nodes. The influence of the design of the eRIF is analysed in detail. The best conditions in terms of dose, size and placement of the eRIF are used to establish a methodology to optimize this new strategy. Using multiple pass exposure, the energy latitude was increased up to about 20% which is three times the energy latitude of the standard exposure. Then the impact of multiple pass exposure on the writing time of the elect ron beam tool is studied. It appears that a compromise has to be found between the writing time and the improvement of the energy latitude. Finally it is shown that the resolution capabilities of the electron beam li thography can be increased using the multiple pass exposure strategy. Keywords: electron beam lithography, process improvement, resolution, EBPC, energy latitude