Ta-Pt Alloys as Gate Materials for Metal-Oxide-Semiconductor Field Effect Transistor Application

Abstract

In this work we explore the thermal stability of sputter-deposited Ta-rich Ta-Pt alloys. The effects of group III and V impurities on their work function are also investigated. The Ta content ranges from 65 to 82 at.%. The main phase is sigma Ta-Pt. The binding energies of core-level electrons of Ta and Pt are changed due to the intermixing of Ta and Pt, which is evidence that the work function of alloys is changed in metallic alloy systems. Binding energies are thermally stable up to 800 degrees C. Moreover, the incorporation of Pt in Ta film induces poor crystallization and a compound phase of Ta-Pt alloys. Transmission electron microscopy analysis confirmed the absence of a clear grain boundary in Ta-Pt alloys. The Ta and Pt depth profile shows uniformity in depth after 800 degrees C annealing for 30 min. The diffusion and distribution of impurities in the alloys were studied by secondary ion mass spectroscopy. Arsenic cannot diffuse in the alloys following annealing at 800 degrees C for 30 s. In contrast, boron can easily diffuse at 800 degrees C. The incorporation of impurities with a dosage of 5 x 10(15) cm(-2) in 60 nm Ta-Pt alloy by implantation did not significantly change the flat-band voltage following annealing at 800 degrees C. (C) 2009 The Japan Society of Applied Physics