New strategies for conformal, superconformal, and ultrasmooth films by low temperature chemical vapor deposition

In the following review, the authors describe how the kinetics of film growth can be controlled in innovative ways to achieve the deposition of conformal, superconformal, area-selective, and ultrasmooth films by low-temperature CVD. Illustrative experimental data and kinetic models are given for the growth of a variety of materials, including transition metals, metal oxides, and metal diborides. Key results are as follows: (i) For precursors that exhibit site blocking on the growth surface, CVD can afford a high degree of conformal coverage on very high aspect ratio features. (ii) The problem of conformal coverage has been solved analytically and presented as a conformal zone diagram. (iii) "Nonconformal" precursor molecules can be made to afford highly conformal films by adding a suitable neutral molecule to enhance surface site blocking. (iv) An inhibitor that adsorbs strongly to the growth material, but not to the substrate surface, can be used to moderate the size distribution of nuclei such that the film is ultrasmooth at coalescence. (v) An inhibitor that binds preferentially to hydroxyl sites on an oxide surface can be used to completely suppress film nucleation and afford area-selective growth. (vi) Superconformal growth, which affords a V-shaped coating and complete fill of a deep trench, can be achieved using one of three approaches, depending on the precursor chemistry. (vii) The science and technology of CVD can further be expanded by the chemical design of new precursors that have a favorable combination of high partial pressure, suitable reactivity at low substrate temperature, and ligand groups that desorb cleanly.