Etch characteristics of cooper thin film using continuous-wave and pulse-modulated plasma of CH3COOH/Ar

초록

Copper has low leakage and low power consumption due to its lower resistance and faster signal transmission than aluminum. Copper has a high electron migration resistance and is a stable interconnect material. When copper is used as interconnect, it is prepared by damascene process which includes electroplating and chemical mechanical polishing. Since copper has very low reactivity and copper compounds often have high vapor pressure, it is known to be very hard material to etch using a conventional dry etching. As the critical dimension of the devices is diminished under tens of nanometer, the fatal disadvantages of the damascene process are revealed, which demands the development of novel dry etching technique of copper thin films. In this study, the etch characteristics of copper thin films masked with SiO2 films were examined under CH3COOH/Ar gas using inductively coupled plasma reactive ion etching. The etch rate of copper films and SiO2 hard mask, and the etch selectivity of copper films to SiO2 mask, and the etch profile were investigated as a function of CH3COOH in CH3COOH/Ar gas. Major etch variables including coil rf power, dc-bias voltage to the substrate, and the process pressure were applied to evaluate the etch rate, etch selectivity and etch profile. The evolution of etch profile of copper films in CH3COOH/Ar was observed to understand the etch process. The optical emission spectroscopy of the plasmas produced from various CH3COOH concentration in CH3COOH/Ar was measured to determine the active species in the plasmas. In addition, the energy dispersive X-ray spectroscopy and X-ray photoelectron spectroscopy for the etched copper surfaces were performed to elucidate the etch mechanism by identifying the copper compounds, if any. Besides, pulse-modulated plasma has been applied to etch copper films, which has the variables such as the on-off duty ratio and the frequency of the plasma. The effects of pulsemodulated plasma on the etch characte