A study of PECVD silicon oxygen(x) fluorine(y) films as ILD and stability of interaction with metals

Fluorinated silicon oxide ({dollar}rm SiOsb{lcub}x{rcub} Fsb{lcub}y{rcub}{dollar}) films were investigated as an ILD material. The {dollar}rm SiOsb{lcub}x{rcub} Fsb{lcub}y{rcub}{dollar} films were prepared in a PECVD reactor using TEOS, O{dollar}sb2{dollar}, and either {dollar}rm Csb2 Fsb6{dollar} or NF{dollar}sb3{dollar}. Both deposition rate and refractive index decrease with increasing fluorine (F) gas flow rate. The films from NF{dollar}sb3{dollar} have higher deposition rate and refractive index compared to those from {dollar}rm Csb2 Fsb6{dollar}. This is probably related to the fact that a NF{dollar}sb{lcub}rm x{rcub}{dollar} plasma does not etch SiO{dollar}sb2{dollar} while a CF{dollar}sb{lcub}rm x{rcub}{dollar} plasma etches SiO{dollar}sb2{dollar}.; The {dollar}rm SiOsb{lcub}x{rcub} Fsb{lcub}y{rcub}{dollar} films have a lower dielectric constant (k) than undoped SiO{dollar}sb2{dollar}. Based on FTIR and nuclear reaction analysis (NRA) measurements, it is concluded that F concentration or film density alone cannot be responsible for the decrease in k. The reason for the decrease in k is believed to be a change in the {dollar}rm SiOsb{lcub}x{rcub} Fsb{lcub}y{rcub}{dollar} film structure itself with the incorporation of F.; Special attention was paid to the interaction of F in the {dollar}rm SiOsb{lcub}x{rcub} Fsb{lcub}y{rcub}{dollar} with metals. For Al and Cu-1%Al, F diffusion through the metal film was rapid at typical annealing temperature. With Al, the diffused F accumulated on the top surface of the metal film, and no F was present in the bulk of the film. Also, the formation of AlF{dollar}sb3{dollar} was observed at the Al/{dollar}rm SiOsb{lcub}x{rcub} Fsb{lcub}y{rcub}{dollar} interface. With Cu-1%Al, some F was present in the bulk. Cu showed almost no reaction with F.; PECVD SiO{dollar}sb2{dollar} and various barrier layers (Ta, TaN, and TiN) were studied for F diffusion into Al films. F diffused through a PECVD SiO{dollar}sb2{dollar} layer on {dollar}rm SiOsb{lcub}x{rcub} Fsb{lcub}y{rcub}{dollar} and reacted with Al at the surface. Ta produced significant improvement in reducing F diffusion into Al compared to TaN, although a trace of F was still observed in Al. On the other hand, TiN did not show F diffusion through Al, however, TiN itself reacted with F.; The effect of various plasma treatments of the {dollar}rm SiOsb{lcub}x{rcub} Fsb{lcub}y{rcub}{dollar} was investigated. These treatments were designed to deplete the {dollar}rm SiOsb{lcub}x{rcub} Fsb{lcub}y{rcub}{dollar} surface of F and thus passivate it with respect to its interaction with the metal. Most plasma treated samples showed an increase in k, even though they resulted in reduced F diffusion through Al. However, the best plasma treatments with CF{dollar}sb4{dollar}/O{dollar}sb2{dollar} produced a substantial reduction of F diffusion from the {dollar}rm SiOsb{lcub}x{rcub} Fsb{lcub}y{rcub}{dollar} films into Al without increasing the k.