Reactive ion etching of a 20 nanometers tungsten gate using a SF6∕N2 chemistry and hydrogen silsesquioxane hard mask resist

Abstract

This article reports on a direct method for patterning a tungsten gate in the decananometric range using high-resolution electron-beam lithography and reactive ion etching (RIE). Electron-beam lithography is based on the use of hydrogen silsesquioxane for its remarkable properties as a negative-tone resist, for its high resistance to dry etching and its capability to deliver extremely straight sidewalls. The transfer of the resist pattern into the tungsten gate stack is ensured by RIE based on a chemistry using sulfur hexafluoride and nitrogen. An optimization of the tungsten etching step is performed by investigating the impact of the RIE power, gas flows, and pressure on both the anisotropy and selectivity with respect to silicon dioxide. Finally, the integration of a p-type metal-oxide-semiconductor field effect transistor with a tungsten gate and platinum silicide Schottky source∕drain was demonstrated and characterized to show that current-voltage characteristics do not exhibit symptoms of plasma-induced damage.