Thin film deposition with time varying temperature

TL;DR

This paper investigates how time-varying substrate temperatures influence the surface roughness and morphology during thin film deposition, using a statistical model validated by computer simulations.

Contribution

It extends dynamic scaling theory to account for temperature changes during deposition, revealing their significant impact on surface roughness evolution.

Findings

Temperature decrease can cause rapid roughness growth with exponents > 1/2.

Local roughness exhibits anomalous scaling depending on temperature decrease.

Increasing temperature leads to non-monotonic roughness evolution due to competing effects.

Abstract

We study the effects of time-dependent substrate/film temperature in the deposition of a mesoscopically thick film using a statistical model that accounts for diffusion of adatoms without lateral neighbors whose coefficients depend on an activation energy and temperature. Dynamic scaling with fixed temperature is extended to predict conditions in which the temperature variation significantly affects surface roughness scaling. It agrees with computer simulation results for deposition of up to ${10}^4$ atomic layers and maximal temperature changes of $30 K$, near or below the room temperature. If the temperature decreases during the growth, the global roughness may have a rapid growth, with effective exponents larger than 1/2 due to the time-decreasing adatom mobility. The local roughness in small box size shows typical evidence of anomalous scaling, with anomaly exponents depending on the particular form of temperature decrease. If the temperature increases during the growth, a non-monotonic evolution of the global roughness may be observed, which is explained by the competition of kinetic roughening and the smoothing effect of increasing diffusion lengths. The extension of the theoretical approach to film deposition with other activation energy barriers shows that similar conditions on temperature variation may lead to the same morphological features. Equivalent results may also be observed by controlling the deposition flux.