ELSEVIER Microelectronic Engineering 35 (1997) 313 -316 MICROELECTRONIC ENGINEERING Development of a 100 nm gate power HEMT using four-layer resist and flexible e-beam exposure strategies P~M. Frijlink |, A. Collet 1, J. Bellaiche 1 and M. Iost 1, M.J. Verheijen 2, H.R.J.R van Helleputte 2, W.G.J. Moors 2 and EC.M.J.M. van Delft 2 l philips Microwave Limeil, LEP , 22 Avenue Descartes, B.P. 15, 94453 Limeil-Brevannes Cedex, France 2philips Research Laboratories, Prof. Holstlaan 4 (WAG-04), 5656 AA Eindhoven , The Netherlands Abstract A 100 nm gate length power HEMT has been fabricated, which can be applied in power amplifiers throughout the millimeter-wave spectrum, as well as in very low noise amplifiers. This process permits amplification up to the W-band. The transistors are made using a double recess and an optimized epitaxial structure in order to maximize the breakdown voltage (Vbdg > 10 V). Excellent uniformity is assured using a dry etch gate recess. In order to reduce the resistance of the gate, a "mushroom" (T-gate) structure is needed for the 100 nm gate, which is made by lift-off using a four-layer PMMA (with MAA) resist and e-beam exposures. By using our Beamwriter User Modifiable Programming Shell (BUMPS) for the EBPG (Philips-Leica 4V-HR), existing layouts can easily be adapted for simultaneous variation (on one wafer) of T-gate central exposure dose, side exposure dose, side exposure width and central-to-side-exposure distance. Combination of the experimental results with exposure and development computer simulations, resulted in an optimized exposure strategy. 1 INTRODUCTION 2 BUMPS E-beam lithography is generally considered to be primarily a research tool. Although the resolution obtainable is much better than with optical produc- tion tools today, the throughput of this sequential writing technique is much too low. Therefore, the production application of e-beam writing is nowa- days mostly restricted to mask making (for the opti- cal production tools) and small scale specialties. In this paper a fabrication process is shown for a 100 nm gate length power HEMT (High Elec- tron Mobility Transistor), which can be applied in power amplifiers throughout the millimeter-wave spectrum, as well as in very low noise amplifiers. In this process, e-beam lithography plays a crucial role; the gates are e-beam written in a four layer PMMA (with MAA copolymer) resist, in such a way, that after metal deposition and lift-off a "mushroom"- shaped gate (T-gate) is obtained, with a 100 nm wide foot, and yet, a big "hat" in order to reduce the resis- tance of the gate. Before metal deposition and lift off, the gate opening is used for a double (asymmetric) recess, with recess extension towards the drain, in order to maximize the breakdown voltage. 0167-9317(97)/$17.00 © 1997 Elsevier Science B.V All rights reserved. PII: S0167-9317(96)00140-2 By using our Beamwriter User Modifiable Programming Shell (BUMPS) for the Electron Beam Pattern Generator (EBPG, Philips-Leica 4V-HR), ex- isting layouts can easily be adapted for simultaneous variation (on one wafer) of T-gate central exposure dose, side exposure dose, side exposure width and central-to-side-exposure distance. BUMPS was writ- ten in order to obtain more flexibility in operating the EBPG. Especially in process optimization for direct write jobs with a complex wafer layout, a high de- gree of flexibility is required. During optimization of the present PMMA (MAA) exposure, at a certain stage, a layout was needed with 90 different pattern/ dose-variation files. Using the standard command list for the EBPG 4-series, it is cumbersome to define a complex layout for an exposure job containing dose variations, complex placements, dropouts, etc.. Fig- ure 1 shows an example of a complex 3 inch wafer exposure layout for exposing the PHEMT structures. The layoutfile consists of (at least) 4 sections. In the symbol section, symbols and variables are defined, a.o. marker type and marker search parameters.