Abstract
In the paper the technological factors influencing test structure gate length were described. The influence of test structure gate placement (Schottky metallization between ohmic contacts, on mesa and on GaN surface) was analyzed and discussed. Moreover, various distances between ohmic contacts paths were tested. Except for experimental investigations, simulations using finite elements method in COMSOL were performed for the same structure. The modelling results revealed crucial impact of a gap beyond the mask on the electric field distribution in photoresist layer. The smallest value of relative error of test finger lengths was observed for finger parts placed between ohmic paths on mesas. It was explained by thicker lift-off double layer between ohmic paths and the smallest Y-gap compared to test fingers placed on mesa and outside of it. Simulation did not bring an explanation of larger values of relative error for smaller distance between ohmic paths.
Highlights
Continuous increase of scale of integration of electronic devices cause that the optical lithography faced its resolution limitation of used wavelength
According to Rayleigh’s equation, enhancement of resolution could be assured by decrease of wavelength or higher numerical aperture of lens systems [1]
The dedicated test structures were made during AlGaN/GaN HEMT (High Electron Mobility Transistor) devices fabrication
Summary
Continuous increase of scale of integration of electronic devices cause that the optical lithography faced its resolution limitation of used wavelength. The dedicated test structures were made during AlGaN/GaN HEMT (High Electron Mobility Transistor) devices fabrication. Each transistor in the module on the wafer consisted of two test structures that differed in designed distance between ohmic contact paths:. Type 1 - designed distance of 3 μm plus designed length of test finger, c 2017 ADVANCES IN ELECTRICAL AND ELECTRONIC ENGINEERING different areas on which the test structures fingers were sample exceeded 90 %. Area B – Schottky metallization on mesa, QualitativVeOaLnUaMlyEs:i1s5o|fNtUhMe BeEleRc:t2ri|c2f0i1e7ld| JdUiNstEribution in the Y-gap, photoresist and LOL (Fig. 2) during exposing was performed based on simulations using finite element. Y3-.gap, rResuelstiungltfsrom non-uniform spin coating of the photoresist due to ohmic contacts presence on the AlGaN/GaN surface - filled with vacuum duriInng tehxepfoisrustres,tep the mean value of fingers lengths in three areas was estimated (Fig. 3).
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