Y shape gate formation in single layer of ZEP520A using 3D electron beam lithography

• Single layer of ZEP520A are used to fabricate Y shape profile.
• 3D EBL with Monte Carlo simulation are used to achieve desired profile with Beamer software.
• 50 nm Y shape gate have been successfully replicated using this method.
• Advantages of Y shape gate over T shape gate are discussed.

This paper reports our novel work on Y shape gate formation in a single layer of ZEP520A resist by electron beam lithography (EBL) for high electron mobility transistors (HEMTs). Dose modification is first calculated by three dimensional proximity effect correction (3D PEC) with Monte Carlo (MC) simulations and contrast curves. This method enables Y gates with sub-100 nm foot-widths to be fabricated. The Y-shape profile of single layer ZEP520A resist with one step exposure has been systematically assessed and compared with that of the conventional T shape profile. It has been demonstrated that the Y shape profile is as good as the T shape profile. However, Y shape profile in resists for Y-gates exhibits unique advantages over T shape gates. First, the process is simple with one layer resist other than bilayer or tri-layer resist stack; second, the cross-sectional area in the same space zone is bigger than T shape gate, so the device resistance is lower than that one; third, the Y gate has higher mechanical reliability and smaller horizontal space occupancy. The quality of resist profile when using single layer ZEP520A resist will be detailed in this paper.

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