Conference

ALD/ALE 2024

CalendarDate & Time
  • August 4th-7th, 2024
LocationLocation
  • Helsinki, Finland

Schrödinger is excited to be participating in the ALD/ALE 2024 conference taking place on August 4th – 7th in Helsinki, Finland. Join us for a presentation by Simon Elliott, Director at Schrödinger, titled “Microkinetic modelling to reveal how the atomic-scale mechanism of deposition or etch plays out at feature and reactor scale.”

Speaker:
Simon Elliott, Director, Schrödinger

Date/Time:
Tuesday, August 6 | 4:45PM

Abstract:
Microkinetic modelling is a technique for determining the turnover of a gas-surface process by solving the coupled kinetic rate equations of its constituent elementary reaction steps [1]. It is widely used in the field of heterogeneous catalysis. Here we present a microkinetic model of the atomic layer deposition (ALD) of alumina from trimethylaluminium (TMA) and water and discuss its utility in investigating growth at macroscopic length and time scales.
We first outline the computational scheme, where elementary steps and their activation energies have been computed with density functional theory (DFT), averaging across a wide variety of geometries. We emphasize the importance of converting the DFT energies to free energies at the temperatures and pressures of interest. The resulting microkinetic model for alumina-on-alumina growth yields measurable quantities (relative growth per cycle and sticking coefficients) as a function of temperature and pressure, which are validated against experiment. For instance, the values of sticking coefficient from the model, s0(TMA)=7×10-3 and s0(H2O)= 3×10-4 at 1 Torr and 300°C, compare well with experiment [2]. Sticking coefficients are crucial inputs for computational fluid dynamics simulations at feature-scale and reactor-scale.
We then show results for how microkinetic modelling can be used in specific scenarios. By adding appropriate elementary steps, the model can reveal the contribution from continuous CVD-style growth under given conditions, or under what conditions ALD can be flipped over into ALE. Alternatively, activation energies can be modified to account for the different chemistry that may exist during nucleation on a substrate, without explicitly modelling any one substrate at the atomic scale. This can be used to test which chemistries are effective in tuning area-selectivity of a process towards various substrates. Finally, we show how a microkinetic model can be used to study the variation of sticking coefficient with pressure and thus account for penetration depth and conformality within high aspect ratio features.
These examples illustrate how existing mechanistic data from atomic-scale DFT can be leveraged in computationally-inexpensive higher-scale models to allow ‘what-if’ experiments to be carried out that link directly to measurements.