Scaling behavior of columnar structure during physical vapor deposition

TL;DR

This study develops a quantitative model for thin film columnar growth during vapor deposition, revealing how chamber pressure influences morphology and providing predictions for future experimental validation.

Contribution

It introduces a Gaussian flux model and Monte Carlo simulations to quantitatively analyze the effects of pressure on columnar structure formation, advancing beyond qualitative models.

Findings

Higher pressure widens deposition angles and increases column diameters.

Column diameter and wavelength follow power-law behavior with pressure.

Exponents saturate around 0.6 at higher pressures.

Abstract

The statistical effects of different conditions in physical vapor deposition, such as sputter deposition, have on thin film morphology has long been the subject of interest. One notable effect is that of column development due to differential chamber pressure in the well-known empirical model called Thornton's Structure Zone Model. The model is qualitative in nature and theoretical understanding with quantitative predictions of the morphology is still lacking due to, in part, the absence of a quantitative description of the incident flux distribution on the growth front. In this work, we propose an incident Gaussian flux model developed from a series of binary hard-sphere collisions and simulate its effects using Monte Carlo methods and a solid-on-solid growth scheme. We also propose an approximate cosine-power distribution for faster Monte Carlo sampling. With this model, it is observed that higher chamber pressures widen the average deposition angle, and similarly increase the growth of column diameters (or lateral correlation length) and the column-to-column separation (film surface wavelength). We treat both the column diameter and the surface wavelength as power laws. It is seen that both the column diameter exponent and the wavelength exponent are very sensitive to changes in pressure for low pressures (0.13 Pa to 0.80 Pa); meanwhile both exponents saturate for higher pressures (0.80 Pa to 6.7 Pa) around a value of 0.6. These predictions will serve as guides to future experiments for quantitative description of film morphology under a wide range of vapor pressure.