Modeling and Optimization of the Step Coverage of Tungsten LPCVD in Trenches and Contact Holes

Abstract

A model is presented to calculate the step coverage of blanket tungsten low pressure chemical vapor deposition (W-LPCVD) from tungsten hexafluoride (WF6). The model can calculate tungsten growth in trenches and circular contact holes, in the case of the WF6 reduction by H2, Sill4, or both. The step coverage model predictions have been verified experimentally by scanning electron microscopy (SEM). We found that the predictions of the step coverage model for the Ha reduction of WF 8 are very accurate, if the partial pressures of the reactants at the inlet of the trench or contact hole are known. To get these reactant inlet partial pressures, we used a reactor model which calculates the surface partial pressures of all the reactants. These calculated surface partial pressures are used as input for our step coverage model. In this study we showed that thermodiffusion plays a very important role in the actual surface partial pressure. In the case where Sill4 was present in the gas mixture trends are predicted very well but the absolute values predicted by the step coverage model are too high. The partial pressure of HF, which is a by-product of the Ha reduction reaction, may be very high inside trenches or contact holes, especially just before closing of the trench or contact hole. We found no influence of the calculated HF partial pressure on the step coverage. Differences between step coverage in trenches and contact holes, as predicted by the step coverage model, were found to agree with the experiments. It is shown that the combination of the step coverage and reactor model is very useful in the optimization towards high step coverage, high throughput, and low WF6 flow. We found a perfect step coverage (no void formation) in a 2 ~m wide and 10 i~m deep (2 x 10 i~m) trench using an average WF6 flow of only 35 sccm, at a growth rate of 150 nm/min. In general, it is shown that the reduction ofWF 6 by SiH~ offers no advantages over the reduction by H2 as far as step coverage is concerned.

Thin Polymer Films with High Step Coverage in Microtrenches by Initiated CVD

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Monte Carlo simulations of atomic layer deposition on 3D large surface area structures: Required precursor exposure for pillar- versus hole-type structures

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Multi-scale modeling of chemical vapor deposition processes for thin film technology

“…A first approach has been to model CVD in small cylindrical holes as a Knudsen-diffusion-and-heterogeneous-reaction process [51,52] based on a one-dimensional pseudo-continuum mass balance equation for the species concentration along the depth of a pore, using a Knudsen diffusion coefficient which is proportional to the pore diameter. This approach has been applied in two-dimensional models as well [53].…”