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We present a new resist and exposure strategy applicable to the fabrication of sub-micron gate-length heterostructure field-effect transistors (HFET) with T-shaped (mushroom) gate contacts. Using selected polymethylmethacrylate (PMMA) resists as well as copolymers (polymethylmethacrylate/methacrylic acid: PMMA/MAA) and by optimization of the layer thicknesses we have established an electron-beam lithography process for fabrication of 0.1 micrometer mushroom-gates. Main advantages of this new concept are the necessity of low accelerating voltages of only less than or equal to 10 kV as well as an adapted thickness of the resist stack which, furthermore, guarantees a large cross-sectional area and hence, low contact resistance. Additionally, an excellent lift-off behavior is obtained. Due to the low accelerating voltage any standard scanning electron microscope can be applied for sub-micron mushroom-gate lithography which drops costs drastically. The complete fabrication process including gate-recess etching shows an excellent reproducibility which guarantees good process control and high yield. The achieved results are comparable with well established T-gate process, thus this new concept should be directly applicable in standard process lines. It should be pointed out that all exposure parameters become almost independent of the substrate property, because the dissipation volume is completely located within the resist layer stack. Thus, the contribution of backscattered electrons to the total dose is negligible.© (1997) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only. |
