Oxygen Defect Stability in Amorphous, C-Axis Aligned, and Spinel IGZO

Abstract

Good control of the doping concentration and profile in the active layer of a transistor is paramount to achieve optimal device reliability and electrical performance. For non-conventional semiconductors such as InGaZnO4 (IGZO), the doping mechanisms and the factors impacting them need to be rediscovered to achieve this control. In IGZO, an important doping mechanism is the formation of oxygen defects. In this work, we map the stability of oxygen defects in IGZO as a function of the defect concentration for three different phases: amorphous, C-axis aligned, and spinel IGZO. By means of a detailed analysis of the evolution of the metal coordination in the three phases, we rationalize the observed similarities and differences. This insight enables us to estimate the doping concentration caused by oxygen scavenging by different contact metals, liner materials, and hydrogen sources introduced during the integration of the material in a transistor flow. From a study of the contact resistance in the Ohmic, high carrier density contact regime, we obtain a lower bound to the contact resistance. We learn that the different carrier concentrations, caused by the variations in oxygen scavenging between contact metals, have a larger impact than the direct difference in contact resistance caused by the intrinsic electronic properties of metals.