Definition of 15 nm half pitch grating structures by electron beam lithography double exposure techniques

• 15 nm half pitch resist structures in 40 nm HSQ resist.
• Using standard processing, without salty development or development at high temperatures.
• Realized using double exposure technique.
• Alignment accuracy between subsequent exposures better than 5 nm.

In this work a novel technique for the definition of 15 nm half pitch line/space grating structures by means of an electron beam double exposure approach using a Vistec EBPG 5200 e-beam tool is presented. The 1:1 line/space ratio grating is defined in two subsequent lithographic process cycles in which two 1:3 line/space grating shifted by twice the line width are exposed. This allows the definition of such dense 15 nm half pitch gratings without the need of using salty development, hence in a CMOS compatible fashion.The main challenge of this approach, the overlay accuracy between the two subsequent exposures, is addressed by a sophisticated strategy regarding the fabrication of the markers used to align both exposures. Using this strategy overlay accuracy better than 5 nm has been achieved for the majority of the fabricated structures.

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