Optimization of 1-µm gate length InGaAs-InAlAs pHEMT

Abstract

Purpose

The purpose of this study is to demonstrate a pseudomorphic High Electron Mobility Transistor (pHEMT) cutoff frequency (f_T) and maximum oscillation frequency (fmax) are determined by the role of its gate length (Lg). Theoretically, to obtain an Lg of 1 µm, the gate’s resist opening must be 1 µm wide. However, after the coat-expose-develop (C-E-D) process, the Lg became 13% larger after metal evaporation. This enlargement is due to both resist thickness and its profile.

Design/methodology/approach

This research aims to optimize the 1-µm Lg InGaAs-InAlAs pHEMT C-E-D process, where the diluted AZ®nLOF™ 2070 resist with AZ® EBR solvent technique has been used to solve the Lg enlargement problem. The dilution theoretically allows the changing of a resist thickness to different film thickness using the same coating parameters. Here, for getting a new resist, which is simply called AZ 0.5 µm, the experiment’s important parameters such as the coater’s spin speed of 3,000 rpm and soft bake at 110°C for 5 min are executed.

Findings

The newly mixed AZ 0.5 µm resist has presented a high resolution and undercut profile rather than standard AZ 1 µm resist. Hence, the Lg metallization after using AZ 0.5 µm optimized process showed better results than AZ 1 µm which used the standard process.

Originality/value

The outcome of the optimization has reached that it is possible to get a nearly sub-µm range gate’s opening using a diluted resist, and at the same time retaining a high resolution and undercut profile.

Citation

Islam, N., Yusof, N.S., Packeer Mohamed, M.F., M., S., Akbar Jalaludin Khan, M.F., Ghazali, N.A. and Hairi, M.H. (2023), "Optimization of 1-µm gate length InGaAs-InAlAs pHEMT", Microelectronics International, Vol. 40 No. 1, pp. 63-67. https://doi.org/10.1108/MI-03-2022-0044