Plasma etch characteristics of nitrogen trifluoride gas mixtures

Semiconductor manufacturing involves a complex series of sequential pattern transfer processes. The design rules needed to successfully manufacture advanced gigabit microdevices must include plasma processes with a high degree of etch anisotropy and high reaction selectivity of over-layered materials. Even with the continued tightening of anisotropy and selectivity requirements, little has been published regarding the interdependence of these important etch characteristics. The main objective of this research was to develop and define the parametric dependencies of silicon to silicon dioxide reaction selectivity and silicon etch anisotropy.; Plasma etching was investigated using NF3 mixtures to generate a low-pressure reactive plasma. Nitrogen trifluoride was mixed with combinations of argon, CF2Cl2 or chlorine. Plasma pressure, power density and chemical composition were varied. Silicon and silicon dioxide reaction rates and silicon to silicon dioxide reaction selectivity were established. The etch anisotropy obtained from a patterning process was also investigated.; For mixtures of NF3 in argon, reaction selectivity was found to be highest under processing conditions that minimize cationic bombardment of the surfaces. Selectivity approaching 90:1 was obtained for a plasma of 25% NF3 in argon at 250 watts power and 800 millitorr. Reaction selectivity was also found to be a function of concentration and pressure. Mixtures of NF3, CF2Cl2 and argon were investigated. In general, silicon to silicon dioxide reaction selectivity was lower for gas mixtures containing CF2Cl2. The highest selectivity of 50:1 was obtained for conditions of low power and high pressure.; Anisotropy trends were established using mixtures of NF3 in argon. Over the range of power and pressure investigated, anisotropic etch profiles in silicon could not be obtained. For mixtures of NF3, CF2Cl2 and argon, the anisotropy improved as the degree of ion bombardment increased. Anisotropic profiles in etched silicon were obtained using 62% CF2Cl2, 25% NF3 in argon at high power and low pressure. The use of a polymer forming chemistry with NF3 provides a method for improving etch anisotropy while keeping the reaction selectivity at levels of approximately 20:1.