Fabrication of Submicrometer InGaAs/AlAs Resonant Tunneling Diode Using a Trilayer Soft Reflow Technique With Excellent Scalability

Abstract

A trilayer soft reflow fabrication method using solvent vapor that resulted in a submicrometer resonant tunneling diode (RTD) is reported in detail. The processing steps are simple, time efficient and are all based on conventional i-line photolithography. The trilayer soft reflow technique is able to shrink the emitter lateral width from 1 down to 0.35 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="TeX">\(\mu \) </tex-math></inline-formula> m (65% reduction) using a solvent at a very low temperature (<50°C). Studies of device’s peak current density ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="TeX">\(J_{P}\) </tex-math></inline-formula> ) suggest that excellent scalability is achieved as the emitter area reduces from <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="TeX">\(\sim 29\) </tex-math></inline-formula> down to <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="TeX">\(\sim 0.5~\mu \) </tex-math></inline-formula> m <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="TeX">\(^{{{2}}}\) </tex-math></inline-formula> with no significant increase in peak voltage ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="TeX">\(V_{P}\) </tex-math></inline-formula> ) due to high series resistance normally associated with submicrometer dimensions. The valley current ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="TeX">\(I_{V}\) </tex-math></inline-formula> ), however, increases due to side-wall damage introduced by the reactive ion etching (RIE) process. As a result, the peak-to-valley-current ratio decreases from 5.0 (6.3) to 3.8 (4.1) in forward (reverse) direction as the emitter area decreases. We therefore successfully demonstrated the fabrication of a submicrometer RTD using a trilayer soft reflow technique that has the benefit of excellent scalability, high throughput, repeatable, and a reliable low-cost process.