Ion-assisted etching of W film by an Ar⁺ beam in XeF₂ with the addition of H₂, N₂, or O₂

W etching is carried out by an Ar⁺ beam in XeF₂ with the addition of H₂, N₂ or O₂. The energy of the beam is 400 eV and the current is 0.2 μA. The spontaneous etching rate in XeF₂ with the addition of N₂ or O₂ decreases by about 0.6 times compared with that in XeF₂ (2×10^-6 Torr), for which the total pressure of the mixed gas is 2×10^-5 Torr. The nitrogen or oxygen atoms attached on the W surface disturb the attachment between W and fluoride atoms. The ion-assisted etching rate increases by about 1.5 times in XeF₂ by adding N₂ or O₂ compared with that in XeF₂ (2×10^-6 Torr), for which the total pressure of the mixed gas is 2×10^-5 Torr. It is speculated that the addition of N₂ or O₂ gas to fluorinated gas acts upon the surface reaction to suppress the sidewall etching rate when the mask patterned W gate line is plasma etched by the same kind of gas - - mixture. The mixing layer is thought to be formed by W and nitrogen or by an oxygen atom by ion-assisted etching. The W–W bond in the mixing layer is thought to be weaker than that in W film both physically and chemically, which makes the etching increase. The thickness of the mixing layer is estimated to be about 10 Å. But the spontaneous ion-assisted etching rate did not change in the case of H₂ addition. © 2001 American Vacuum Society.