Low-dielectric-constant nonporous fluorocarbon films for interlayer dielectric

Low-dielectric-constant (k < 2.0) nonporous fluorocarbon films are formed using a new microwave-excited low electron temperature and high-density plasma system with a dual-shower-plate structure. In the new system, the material gas (C₅F₈) is supplied by a lower shower plate inserted in the diffusion plasma region of very low electron temperature (around 1-2 eV). An upper shower plate is used for supplying the plasma excitation gas in a uniform downflow in the chamber. Since such a gas flow pattern can prevent the penetration of the material gas into the plasma excitation region, the overdecomposition of the material gas can be markedly suppressed as compared with that in the case of using conventional plasma systems such as an electron cyclotron resonance (ECR) plasma source. As a result, fluorocarbon films can be formed by maximizing the original characteristics of material gases. The fluorocarbon films formed using the new system have not only low k but also low leakage current density, sufficient mechanical strength, strong adhesion, high heat resistance and good surface smoothness. Therefore, such films can be used in interlayer dielectrics in ultralarge-scale integration (ULSI) devices.