Observation of boron acceptor neutralization in silicon produced by CF4 reactive ion etching or Ar ion beam etching

Abstract

It is demonstrated, using two very different techniques (viz., CF₄ reactive ion etching and Ar ion beam etching), that dry etching exposure causes extensive boron acceptor neutralization in silicon. This boron neutralization is observed to occur as far as microns below the etched surface with etching exposures of only ≂1 min. Neutralization occurs if the temperature does not exceed about 180 °C during etching; it may be annealed out by subsequent exposure to such temperatures. Adsorbed water vapor or, alternatively, hydrogen inherent in the silicon is proposed to provide hydrogen‐related species which cause this neutralization. Protons created in the plasma from these sources, or hydrogen‐related species directly liberated from their sources on or in the solid, may be injected into the silicon during the energetic ion impact constantly present in dry etching. This observation of boron neutralization deep below the etched surface demonstrates that dry etching exposure causes extensive permeation of foreign species into the etched material.