Effect Of C:F Deposition On Etching Of SiCOH Low-k Films In CHF₃ Dual-frequency Capacitively Coupled Plasma

As the device dimension continuous shrinking in ultralarge-scale integrated chips, the resistance-capacitance (RC) delay of interconnects becomes a major problem, which leads to the signal propagation delay,dissipation and cross-link between metal interconnects. In order to address these problems, the traditional SiO₂ insulating layer must be replaced with low dielectric constant (low-k) and ultralow dielectric constant (ultralow-k, k < 2) materials. As the substitution of SiO₂, the porous ultralow dielectric constant materials have received more close attention recently.The etching of porous low-k materials is a key step in the ULSI fabrication. Compared with that of SiO₂, the etching rate of SiCOH films increases with reduced film density due to the existing of pores in the film, resulting in roughness, the formation of micro-trenches, and variations in the etched depth, which make the precise profile control of etched patterns uncontrollable in the etching process. To solve these problems, dual-frequency capacitively coupled fluorocarbon plasma, such as C2F6 and CHF₃ plasma, were used to etch SiCOH low-k films. During etching SiCOH low-k films, however, the C:F films can deposit at the top of SiCOH low-k films. The C:F layer deposited at the low-k films is the main inhibitor for the transport of species and the delivery of activation energy to the etched films, which can make important effect on the etching process.In the thesis, the effect of C:F deposition on SiCOH etching in 60MHz/2MHz CHF₃ dual-frequency capacitively coupled plasma (DF-CCP) was investigated by adjusting low-frequency (LF) power. The bonding configurations, compositions and microstructures of etched films were analyzed by FTIR, XPS and AFM. The relative density of CF2 and F radical in the CHF₃ DF-CCP was also measured by OES. The results shows that during the SiCOH etching, the C:F layer can deposit at the etched SiCOH films. With the LF power increase, the etching process takes a transition from films deposition to films etching. With the process transition, the microstructure of C:F layer changes from the dense coverage layer to the porous C:F layer and to the C:F filling gap. The variation of C:F layer microstructure is related to the energetic ions bombardment and the CF2 concentration in the plasma. At the higher LF power, the high energetic ions and the lower CF2 concentration lead to the suppressing of C:F deposition at the surface of etched films. The weak C:F deposition is of advantage to the F radicals transport and the activation energy delivering to the C:F-SiCOH film interface. Therefore, SiCOH films can be etched at the higher LF power.