STEP COVERAGE PREDICTIONS USING COMBINED REACTOR SCALE AND FEATURE SCALE MODELS FOR BLANKET TUNGSTEN LPCVD

Abstract

A reactor scale model (RSM) for a stagnation point, single wafer reactor for blanket tungsten LPCVD is used to calculate concentrations at the wafer surface. These concentrations and the wafer temperature, which is assumed to be measurable, are needed to determine the local tungsten deposition rate on the wafer and local film conformality (step coverage) in features on patterned wafers. Two feature scale models (FSMs) are used to determine step coverages in infinite trenches which have rectangular initial cross sections and an aspect ratio of five, as a function of reactor operating conditions; 1. a continuum-like diffusion-reaction model (DRM) for simultaneous Knudsen diffusion and heterogeneous surface reactions, and 2. a flux based model which includes ballistic transport of molecules and heterogeneous surface reactions (BTRM).|The RSM establishes “boundary conditions” for the feature scale models, by providing the flux of each species to the local wafer surface. Step coverages predicted using the FSMs with the reactant partial pressures at the wafer surface can be significantly lower than those predicted using reactant partial pressures at the reactor inlet, due to depletion of reactants. The flux based BTRM predicts higher step coverages than the DRM for the same wafer surface conditions.