Implementation of tungsten metallization in multilevel interconnection technologies

The techniques of experimental design and response-surface methodology have been used to produce empirical models of the deposition and etchback of tungsten in commercially available reactors for a tungsten plug technology. Deposition was carried out in a Genus 8402 LPCVD (low-pressure chemical vapor deposition) batch reactor by the H ₂ reduction of WF₆. Response-surfaces for deposition rate, sheet resistance uniformity, resistivity, and film stress were developed as a function of reactor pressure, reactor temperature, and flow rate of WF₆ at a fixed H₂ flow rate using linear-interactive models. A thin layer of TiN was used to ensure adhesion of tungsten to SiO₂. Etchback of the composite layer of W/TiN to form via plugs was performed in a Tegal 804 single-wafer system with a two-step process using mixtures of SF₆ with C₂F₆ and He with Cl₂ in step 1 and step 2, respectively. Process parameters for both steps were obtained from quadratic models of etch rate and etch uniformity