Molecular-beam study of gas-surface chemistry in the ion-assisted etching of silicon with atomic and molecular hydrogen and chlorine

Abstract

Modulated molecular-beam mass spectrometry and quartz crystal microbalance techniques were used to study the etching of Si by the combinations of H/H2, Cl/Cl2, HCl, and Ar+ ion bombardment at room temperature. Without ion bombardment, only H atoms etch Si spontaneously. While the addition of Cl or Cl2 stopped H etching instantaneously, the addition of HCl had no effect. With Ar+ ion bombardment at 2 keV, the addition of HCl to the etching of Si with H, Cl, or Cl2 did not influence the etch rates. No DCl was observed when D atoms and HCl molecules were incident on Si simultaneously. This confirms that HCl does not dissociatively chemisorb on Si instantaneously. During ion-assisted etching, the addition of fluxes of H atoms, Cl atoms or Cl2 molecules increased the Si etch rate significantly. The Si etch rate for Cl atoms and Cl2 molecules was identical within experimental error provided the total chlorine flux was kept constant. The etch products observed were primarily SiClx. The addition of H atoms to the ion-assisted etching of Si with Cl increased the etch rate the same amount as with Cl2 but four times more HCl was formed with Cl atoms. Several hydrogenated chlorosilane peaks were observed with the mass spectrometer and these peaks were larger with Cl2 than with Cl. The addition of either Cl or Cl2 to the H/Ar+/Si system decreased the etch rate. These observations suggest the recombination of H and Cl to form HCl is not rate limiting in these etching processes.