Reduction of Spikes on the Sides of Patterned Thin Films for Magnetic Tunnel Junction Based Molecular Device Fabrication

TL;DR

This paper presents a cost-effective, rapid method to produce spike-free patterned thin films for magnetic tunnel junction devices by optimizing photolithography parameters through systematic experiments.

Contribution

It introduces a novel soaking step in the photolithography process and identifies key parameters affecting photoresist profile quality, enhancing device fabrication.

Findings

Baking temperature is the most influential factor.

Optimal parameters: 4000 rpm, 100°C bake, 60s presoak, 15s UV exposure.

Method reduces spikes, improving device performance.

Abstract

Sputter thin film deposition after photolithography often produces unwanted spikes along the side edges. These spikes are a significant issue for the development of magnetic tunnel junction (MTJ)-based memory and molecular spintronics devices, microelectronics, and micro-electro-mechanical systems because they influence the properties of the other films deposited on the top. Our molecular spintronics devices that utilize MTJ as the testbed are almost short-lived and encountered high background current that masked the effect of molecular transport channels placed along the sides of MTJs. Therefore, tapered thin film edges are critically needed in devices. Here, we report a very cost-efficient and fast way of creating an optimum photoresist profile for the production of spike-free patterned films. This approach is based on performing a soaking in the photoresist developer after baking and before the UV exposure. However, the success of this method depends on multiple factors accounted for during photolithography - photoresist thickness (spin speed), baking temperature, soaking time and exposure time. Our recent experiments systematically studied the effect of these factors by following the L9 experimental scheme of the Taguchi Design of the experiment (TDOE). We discovered that baking temperature was the most influential parameter; presoak time and photoresist thickness were two other influential factors; exposure time was the least effective factor. We also found that 4000 rpm, 100 C soft baking, 60 s soaking, and 15 s UV exposure yielded the best results. Finally, the paper also discusses the interdependence of selected factors, and the impact of the individual levels of each factor. This study is expected to benefit MEMS and micro/nanoelectronics device researchers because it attempts at finding a cheaper and faster alternative to creating an optimum photoresist profile.