Effect Of O₂ Flow Rate And Low-frequency Power On Etching Characteristics Of SiCOH Low-k Films

The rapid development of microelectronic devices has led to the continuous improvement of device performance and the increase of device integrated on a chip. Due to the increase of device density, however, the signal propagation delay, power consumption and cross-link between metal interconnects also increase. In order to reduce the RC sign delay, dissipation and cross-link between metal interconnects, the porous low dielectric constant (low-k) and ultra-low dielectric constant (ultralow-k, k < 2) material recently received more close attention.As a promising candidate for low-k materials in microelectronics, SiCOH low-k films are increasingly paid attention. The etching of porous SiCOH low-k films is one of the most important issues. Usually, the fluorocarbon plasma is used to etch SiCOH low-k films. However, during etching SiCOH low-k films, the C:F films can deposit at the top of SiCOH low-k films, which can make important effect on the etching process and the material performance.In order to reduce the C:F film deposition on the top of SiCOH low-k film, the O₂ addition in fluorocarbon plasma is needed. Therefore, in this thesis, the effect of O₂ flow rate and low frequency on etching characteristics of SiCOH low-k films in the O₂/C₄F₈/Ar,O₂/C₂F₆/Ar 60MHz/2MHz dual-frequency capacitively couple plasma (CCP) was investigated.The results show that during etching SiCOH low-k film using O₂/C₄F₈/Ar dual-frequency plasma, the increase of O₂ flow rate can increase the etching rate of SiCOH films, reduce the surface roughness and eliminate the C:F deposition on the SiCOH films. When etching SiCOH low-k film using O₂/C₂F₆/Ar plasma, the increase of O₂ flow rate can also increase the etching rate of SiCOH films and eliminate the C:F deposition on the SiCOH films, but increase the surface roughness. By optical emission spectroscopy measurement on discharge plasma and the etching rate analysis, it is found that the role of O₂ addition in increasing etching rate is different for O₂/C₄F₈/Ar plasma and O₂/C₂F₆/Ar plasma. In the in O₂/C₂F₆/Ar plasma plasmas, due to the higher F density, the effect of O₂ addition on etching rate increasing is small. While in O₂/C₄F₈/Ar plasmas, due to the lower F density, the effect of O₂ addition on etching rate increasing is enhanced. As for low-frequency power, it is found that during etching SiCOH low-k film using O₂/C₄F₈/Ar plasma, the increase of low-frequency power can increase the etching rate of SiCOH films and reduce the surface roughness. It is due to the increase of F and CF concentration.