Surface modification and cleaning enhancement of TaSi(N) films with dilute hydrofluoric acid

Abstract

Amorphous TaSi(N) alloy films are of great interest for application in the fabrication of reticles for next generation lithography and for incorporation into semiconductor devices as barrier layers for Cu processing. The stress characteristics of TaSi(N) films are critical when used as an absorber on x-ray and extreme ultraviolet lithography masks, or as a scatterer for electron projection lithography masks. One little understood, but critical characteristic of these films, is that they undergo a stress change towards a less tensile or more compressive state upon interaction with a buffered oxide etch (BOE). We have investigated the cause of this behavior using synchrotron radiation based high-resolution core level (Ta 4f and Si 2p) photoemission spectroscopy. Our results indicate that, upon interaction with a BOE, the surface oxide undergoes a major reorganization and the Ta gets heavily oxidized, resulting in the formation of Ta2O5. Such a reaction would lead to a buildup of strain in the oxidized region, which we interpret as being the contributing factor for the observed stress changes in the TaSi(N) thin films. Furthermore, annealing the surface results in a significant reduction of the oxide desorbtion temperature from 650 to 450 °C due to the HF interaction. This can be attributed to a change in the bonding configuration by HF, wherein the Si–O bonds are broken and weak Ta–O bonds are formed, causing the loosely bonded oxide to desorb at lower temperatures.