Thermally reflowed ZEP 520A for gate length reduction and profile rounding in T-gate fabrication

Abstract

Articles you may be interested inImproved etch resistance of ZEP 520A in reactive ion etching through heat and ultraviolet light treatment Low temperature ZEP-520A development process for enhanced critical dimension realization in reactive ion etch etched polysilicon Novel electron beam lithography technique for submicron T-gate fabricationThe characteristics of thermally reflowed ZEP 520A-7 (ZEP), a resist commonly used in electron beam lithography, are presented for use as a gate stem resist layer in T-gate process development. As-developed ZEP lines possess a resist sidewall profile that displays varying amounts of undercut, which are determined by the conditions used to expose the line. The authors find that after thermal reflow, the top of the ZEP profile becomes substantially rounded in shape, mitigating "metal cathedraling" problems, a yield-affecting issue that becomes more pronounced as the gate length is reduced. In addition to profile rounding, a linewidth reduction of over 100 nm is observed, and this process has been used to produce gate lengths in the 30-40 nm range. The changes in feature size and the final profile shape depend on the as-developed sidewall angle. Additionally, the ZEP reflow process saturates after a certain amount of time, so reproducibility is not hindered by a lack of precise control in timing. As larger lines can be used to produce smaller features via reflow, the potential for faster throughput exists due to the use of a higher beam current, which would normally limit the attainable minimum feature size. [http://dx.

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“…A standard Cl 2 /BCl 3 -based dry etch was then used to achieve mesa isolation. Next, Pt/Au (20/400 nm) T-gates were fabricated by electron-beam lithography using a photoresist reflow process [13], with L G of 80 nm, a gate head length of 450 nm, a gate stem height of 280 nm, and a total gate width W G of either 2 × 75 μm or 2 × 25 μm. The source-drain spacing L S D was 3.1 μm and the gate-drain spacing L G D was 1.6 μm.…”