Customized 2D Structures for High Throughput Electromigration Measurements

Abstract

Customized 2D wires are designed for high throughput electromigration testing on model Al and Cu thin films. Two direct writing approaches for defining the 2D wires are compared with photolithography. Electromigration effects on Al and Cu thin films are studied on 2D wires obtained applying both methods. A self‐developed four‐point probe is used to apply current through the test wires while measuring the potential drop along the wires. Photolithography is selected as the main method to outline the wires in order to have reproducible results in a high throughput manner. The errors of electromigration assessment are empirically evaluated by analyzing the data scattering for a large number of measured 2D wires. Inductively coupled plasma optical emission spectrometry (ICP‐OES) is performed on the photoresist removal solution before and after the lift‐off process. No traces of metallic elements are detected in both cases confirming the proposed mechanism.

Gallium-Enhanced Aluminum and Copper Electromigration Performance for Flexible Electronics

“…Here, a rather narrow region on the Cu–Ga library reaches j max values in an excess of 1.6 MA cm –2 , while the value measured on pure Cu test wires remains slightly below 1.2 MA cm –2 . 51 This increase of the ability to withstand electromigration can again be linked to the same 2D transition threshold discussed before for alloys with thickness below 250 nm. Screening the j max mapping resulted in identification of Cu-5 at.…”

“…Droplets of the molten material can be observed around the failure line, most likely as a result of the local temperature increase by the Joule effect. 51 Both anodic (on the left side) and cathodic (on the right side) regions are clearly visible, each having its own damage front more accentuated toward the middle of the test line. The magnified image of the anodic damage front presents a snapshot into dynamics of the grain evolution occurring during the electromigration.…”

“…In order to assess the dynamic behavior of Al, Cu, and their alloys under high electron fluxes, a standardized design of the test wire is needed to be implemented. 51 In this way, statistical measurements and reproducibility tests may be easily performed and a comparison between different alloys ability to withstand electromigration becomes straightforward. Different aspect ratios of test wires were explored, and the most suitable design was selected for this study.…”

“…Developing the resist was done in an AZ 726 MiF bath for 240 s. More details about the wire sizing and design were previously reported. 51 Following this route, more than 300 wires were pre-patterned uniformly distributed on each processed SiO 2 wafer (see Figure S1 ). After thin film deposition, the lift-off procedure was performed using NG101 (MicroChemicals, Germany) etchant/removal solution.…”

“…Additional information can be found elsewhere. 51 After metallization, the lift-off procedure was performed using ethanol.…”