Many lithography candidates, such as ArF immersion lithography with double-patterning/double-exposure techniques,
EUV lithography and nano-imprint lithography, show promising capability for 22-nm half-pitch generation lithography.
ArF immersion lithography with double-patterning/double-exposure techniques remains the leading choice as other
techniques still lack the conclusive evidence as the practical solution for actual production. Each of the prospective
lithography techniques at 22-nm half-pitch generation requires masks with improved accuracy and increased complexity.
We have developed a new electron beam mask writer, EBM-8000, as the tool for mask production of 22-nm half-pitch
generation and for mask development of 16nm half-pitch generation, which is necessary for the practical application of
these promising lithography technologies.
The development of EBM-8000 was focused on increasing throughput and improving beam positioning accuracy. Three
new major features of the tool are: new electron gun with higher brightness to achieve current density of 400 A/cm<sup>2</sup>,
high speed DAC amplifier to accurately position the beam with shorter settling time, and additional temperature control
to reduce the beam drift.
The improved image placement accuracy and repeatability, and higher throughput of EBM-8000 have been confirmed
by actual writing tests with our in-house tool.
It depends for the writing time of variable shaped electron-beam (VSB) writing system on the number of writing shots. For shortening of writing time, it is most effective to reduce the number of shots. However, Resolution Enhancement Technologies (RET), such as OPC and PSM, make the VSB shot number increase explosively, in addition to reduction of LSI pattern size, and worsens the writing throughput. This is a serious problem for VSB mask writer, and the improvement of a writing throughput is required. In order to solve this problem, we inquired towards diversifying beam shape only from a rectangle.
First, we investigated about the curtailment effect of the number of shots by trapezoid aperture adoption. Some latest VSB writer has adopted a triangle shaped aperture to compose the slanting figure in the LSI pattern efficiently. We investigated the efficiency of forming the slanting figure with trapezoid or parallelogram apertures compared with initial triangle aperture shot number. As the result of that, shown in Fig.1, we obtained the result that the shots number was reduced into 50% or more compared with initial triangle shots number. And, we examined a possibility of uniting and applying the character projection (CP) technique, which is adopted as EB direct writing (DW), to mask writing. Since pattern size is, for example, 4 times larger in the case of mask writing compared with the case of EBDW, the area that can extract a common CP pattern out from LSI patterns at mask writing is smaller than EBDW. Then, we extracted CP aperture pattern from cell library data for logic LSI. We obtained the result, shown in Fig.2, that the shot number that was used CP aperture was reduced into about 35% compared with initial VSB shots number. However, the arrangement number of aperture has restriction, and if the arrangement number decreases, the curtailment rate of the shots number will fall. These two techniques are fundamentally effective in curtailment of writing shots number. Furthermore, we will discuss with the possibility of applying these techniques to mask writing and with some problems to solve for the application of these techniques.