Characterization of titanium nitride etch rate and selectivity to silicon dioxide in a Cl2 helicon-wave plasma

The effects of Cl2 and N2 flow rate, substrate bias power, and reaction pressure on both the titanium nitride and SiO2 etch rate plus the etch selectivity of TiN/SiO2 in a high-density helicon-wave plasma were studied. It was found that the bias power has the greatest effect on etch rate and selectivity, followed by the reaction pressure. As the bias power increased, both the TiN and SiO2 etch rate increased significantly. This result is consistent with the fact that the dominant etch mechanism for both SiO2 and TiN is an ion-assisted energy driven etch mechanism rather than pure chemical etching. As the SiO2 etch rate is drastically reduced from 403 Å/min to near zero when the bias power is decreased from 70 to 20 W, the etch selectivity of TiN to SiO2 significantly rises from 55 to over 500. The effect of pressure was found to be more complex, having a different effect on the etch rate of TiN versus SiO2. By increasing the pressure from 2.5 to 4 mTorr, the TiN etching rate rose to a maximum at 4 mTorr and then monotonically decreased up to a pressure of 10 mTorr. This result is similar to aluminum etching in a Cl2/BCl3 helicon-wave plasma. In contrast to the TiN etch behavior, the etch rate of SiO2 increased monotonically over the full pressure range investigated. In addition to the effect on etch rate, the etch selectivity of TiN to SiO2 noticeably increased with increasing pressure. Optical-emission spectroscopy was used to investigate the cause. It was determined that the effect of pressure on etch rate and selectivity could be explained by the change of atomic Cl radical density, ion flux, and ion energy. It was also observed that both the etch rate of TiN and SiO2 slightly increased as Cl2 flow rate increased from 10 to 90 sccm, reaching a maximum at about 70 sccm. The selectivity of TiN to SiO2 remained around 8–11 in this Cl2 flow rate range. The addition of N2 seems to have only a small effect on etch rate.