Characterization of GaN Device Interconnect Metallization Reliability

Abstract

The gallium nitride (GaN) semiconductor market continues to rapidly expand because GaN device technology offers considerable performance advantages compared to gallium arsenide (GaAs) and silicon (Si) devices. GaN has inherently higher breakdown field strength, charge density, and electron velocity at high voltage. These material properties permit GaN devices to operate at higher bias voltages and higher current densities than GaAs and Si devices. Commercial applications can utilize RF power amplifiers at higher frequencies (> 2 GHz) and higher power (> 400 W) in a single packaged GaN transistor. However, this higher power density operation requires examination of the degradation and reliability of these GaN devices at elevated temperatures. The evaporation deposited gold interconnect metallization of GaN HFET devices was stressed to evaluate its high temperature reliability. Optimized test structures were designed to assess the electromigration wear-out in evaporated deposited Au films encapsulated with SiN passivation. A current density of 1 MA/cm2 with oven stress temperatures in excess of 335 °C was applied to large quantities of Au interconnects. The selected failure criteria of 50% resistance increase yielded Au lifetime distributions that followed typical log-normal electromigration failure statistics. All log-normal sigma values were less than 0.6 which is an indication of a mono-modal failure mechanism. The activation energy value was measured from multiple stress temperatures. Physical characterization of the evaporated Au interconnect structures are discussed along with a comparison to electroplated Au interconnects.