The development of silicon compatible processes for HEMT realisation

Cao, Menglin (2015) The development of silicon compatible processes for HEMT realisation. PhD thesis, University of Glasgow.

Abstract

Compound semiconductor (III-V) devices are crucially important in a range of RF/microwave applications. High Electron Mobility Transistors (HEMTs), as the best low noise high frequency compound semiconductor devices, have been utilised in various applications at microwave and mm-wave frequencies such as communications, imaging, sensing and power. However, silicon based manufacturing will always be the heart of the semiconductor industry. III-V devices are conventionally fabricated using gold-based metallisation and lift off processes, which are incompatible with silicon manufacturing processes based on blanket metal or dielectric deposition and subtractive patterning by dry etching techniques. Therefore, the challenge is to develop silicon compatible processes for the realisation of compound semiconductor devices, whilst not compromising the device performance.
In this work, silicon compatible processes for HEMT realisation have been developed, including the demonstration of a copper-based T-gate with the normalised DC resistance of 42 Ω/mm, and the presentation of a gate-first process flow which can incorporate the copper-based T-gate. The copper electroplating process for fabricating T-gate head with the maximum width of 2.5 µm, low damage inductively coupled plasma molybdenum etching process for realising T-gate foot with the minimum footprint of 30 nm, and the full gate-first process flow with non-annealed ohmic contact are described in detail. In addition, this thesis also describes the fabrication and characterisation of a 60 nm footprint gold-based T-gate HEMT realised by conventional III-V processes, yielding a cutoff frequency fT of 183GHz and maximum oscillation frequency fmax of 156GHz. In the comparison between these two types of HEMT, it is anticipated that a HEMT with the copper-based T-gate would not only have a larger maximum frequency of oscillation fmax, but also an easier incorporation into a silicon based manufacturing fab in terms of process technologies, than a HEMT with the gold-based T-gate.

• Item Type: Thesis (PhD)
• Qualification Level: Doctoral
• Keywords: HEMT Silicon compatible processes
• Subjects: T Technology > T Technology (General); T Technology > TK Electrical engineering. Electronics Nuclear engineering
• Colleges/Schools: College of Science and Engineering > School of Engineering
• Supervisor's Name: Thayne, Professor Iain
• Date of Award: 2015
• Depositing User: Menglin Cao
• Unique ID: glathesis:2015-6803
• Copyright: Copyright of this thesis is held by the author.
• Date Deposited: 28 Oct 2015 16:49
• Last Modified: 03 Nov 2015 10:11
• URI: https://theses.gla.ac.uk/id/eprint/6803