Characterization of titanium nitride etch rate and selectivity to silicon dioxide in a Cl-2 helicon-wave plasma

The effects of Cl-2 and N-2 flow rate, substrate bias power, and reaction p ressure on both the titanium nitride and SiO2 etch rate plus the etch selec tivity of TiN/SiO2 in a high-density helicon-wave plasma were studied. It w as found that the bias power has the greatest effect on etch rate and selec tivity, followed by the reaction pressure. As the bias power increased, bot h the TiN and SiO2 etch rate increased significantly. This result is consis tent with the fact that the dominant etch mechanism for both SiO2 and TiN i s an ion-assisted energy driven etch mechanism rather than pure chemical et ching. As the SiO2 etch rate is drastically reduced from 403 Angstrom /min to near zero when the bias power is decreased from 70 to 20 W, the etch sel ectivity 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 mTo rr, the TiN etching rate rose to a maximum at 4 mTorr and then monotonicall y decreased up to a pressure of 10 mTorr. This result is similar to aluminu m etching in a Cl-2/BCl3 helicon-wave plasma. In contrast to the TiN etch b ehavior, the etch rate of SiO2 increased monotonically over the full pressu re range investigated. In addition to the effect on etch rate, the etch sel ectivity of TiN to SiO2 noticeably increased with increasing pressure. Opti cal-emission spectroscopy was used to investigate the cause. It was determi ned that the effect of pressure on etch rate and selectivity could be expla ined by the change of atomic Cl radical density, ion Aux, and ion energy. I t was also observed that both the etch rate of TiN and SiO2 slightly increa sed as Cl-2 flow rate increased from 10 to 90 seem, reaching a maximum at a bout 70 seem. The selectivity of TiN to SiO2 remained around 8-11 in this C l-2 flow rate range. The addition of N-2 seems to have only a small effect on etch rate. (C) 2001 American Vacuum Society.