Fabrication Of Submicron Hemt Mushroom Gate Structure Using Electron Beam Lithography And Its Characterization

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Date
2008-12
Authors
Yusof, Ashaari
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Abstract
In this research study, 200 run gatelength HEMT gate structures with mushroom-shaped profile have been designed, fabricated and characterized. This allows HEMT to operate in frequencies suitable for microwave and millimeter-wave telecom applications. Gate design consisting of a lOx 10 array of 10 individual gate strips was used as basis for patterning. Throughout the fabrication step, standard semiconductor processes such as electron beam lithography, wet etching, metal deposition and lift-off process were used. Electron beam dose optimization method was employed, in which variable dose values were expesed on PMMA tri-Iayer resist system based on the gate design. Subsequently, the HEMT gate structures were characterized using SEM, AFM and FIB. It was found that at central beam dose of 192 IlC/cm2 , gate lengths of 200 run have been achieved. The mushroom effect has been successfully constructed based on the cross-sectional analysis. Additionally, Schottky contact between gate metal and HEMT epi-Iayers has been obtained. The HEMT n+ GaAs Cap layer was recessed for 40 run and TilPti Au gate metal stack was deposited to create the Schottky contact. The calculated Schottky contact barrier height, th, between the gate metal stack and AIGaAs Supply layer, was found to be 0.65 eV.
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Keywords
Mushroom Gate Structure , Using Electron Beam Lithography
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