Degradation of thin tungsten filaments at high temperature in HWCVD

• A model for the electrical resistance of a tungsten filament during aging is presented.
• Catalytic activity of the filament drops when W5Si3 precipitation takes place at its surface.
• The catalytic stability of the filament does not depend on its radius in most practical situations.

The degradation of the filaments is usually studied by checking the silicidation or carbonization status of the refractory metal used as catalysts, and their effects on the structural stability of the filaments. In this paper, it will be shown that the catalytic stability of a filament heated at high temperature is much shorter than its structural lifetime. The electrical resistance of a thin tungsten filament and the deposition rate of the deposited thin film have been monitored during the filament aging. It has been found that the deposition rate drops drastically once the quantity of dissolved silicon in the tungsten reaches the solubility limit and the silicides start precipitating. This manuscript concludes that the catalytic stability is only guaranteed for a short time and that for sufficiently thick filaments it does not depend on the filament radius.