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Process Analysis and Simulation

The research activity on analysis, modeling, and simulation addresses both processes and phenomena. Scientific and engineering problems are attacked with aim to illuminate physical mechanisms, reveal critical parameters, and achieve desired system/process behavior.

It focuses on plasma discharges and covers both low (<1-10 Pa) and atmospheric pressure processes. It deals with the bulk phase of the plasma (reactors) as well as the interaction of plasma with surfaces. It handles all spatial scales of the events taking place during plasma processing, from the order of centimeters of a plasma reactor or a plasma jet to the order of micrometers or nanometers on a) a plasma-wetted rough surface or b) a conventional trench in microelectronics. It addresses micro- and nano-electronics, engineering of functional surfaces, as well as alternative applications of plasma in agriculture and biomedicine. 

The aims are the investigation of mechanisms, process design, and the development of shortcut models or numerical methods for the reduction of the computational cost. Our tools are homemade, open source, and commercial code. The computational frameworks are usually hybrid, combining continuum and stochastic approaches. Besides the publications, our effort has yielded to two user-friendly software tools. The first for the study of chemical kinetics in the bulk plasma (www.plasma-r.com) and the second for the study of profile evolution of micro- and nano-trenches or holes during plasma etching (www.phietch.com).

Besides plasma processing, chemical vapor deposition (CVD) has been also studied. The major aim is the investigation of the interaction between the microscale of the features (e.g., trenches) and/or the nanoscale of the deposited films and the macroscale of the CVD reactor. A hybrid multiscale modeling framework has been developed and parallel techniques have been utilized to reduce the computational cost.

Besides fabrication processes, the wetting behavior and water condensation on surfaces has been investigated. In particular, the transition from partially wetted (Cassie-Baxter) state to the fully wetted (Wenzel) state, critical for the robustness of superhydrophobic surfaces, has been studied by calculating the energy barrier between these states. Additionally, the dropwise condensation on surfaces, critical for heat transfer and water harvesting applications, has been investigated through a thermal resistance model.

Infrastructure

The current infrastructure for numerical analysis and simulation is a computer cluster consisting of 11 workstations with a total of 316 cores and 1184 GB of RAM.

Categories of the activityThe activity on process (and phenomena) analysis and simulation can be categorized into 6 areas, namely, A) plasma reactors at low pressure, B) plasma etching of micro- and nanostructures, C) roughening of plasma-wetted surfaces, D) plasma reactors at atmospheric pressure, E) chemical vapor deposition of films in structures and open areas, and F) wetting and condensation on surfaces. The highlights of the research in each area can be found in the following list of key publications.

Simultaneous plasma etching and deposition of etch-inhibitors: The effect of etching selectivity, fraction and sticking probability of etch-inhibitors, and angular distribution of ions on the surface morphology and circularly averaged PSD.

Effect of surface charging on plasma induced surface roughness. Simulation of the rough-profile evolution of polymeric substrates vs. etching time (a) without charging and (b), (c) with charging.

3D modeling of pattern and line edge roughness transfer during plasma etching with an abstractive simple geometric model. The level set method was utilized.

Multiscale simulation of low-pressure plasma etching: Surface morphology vs. etching time, pressure, power, and radial distance on the wafer of a plasma reactor.

Linking the operating parameters of low-pressure plasma reactors with surface roughening by a multiscale modeling framework.

Etching map for SiO2 holes as a function of the fluorine, fluorocarbon, and ion flux on the surface (A: Deposition, B: RIE lag, C: intense RIE lag and etch stop, D: inverse RIE, E: ARIE for AR=3-7, F: ARIE up to AR=7).

Plasma simulation of the deep Silicon etching by the BOSCH process. The level set method was used and treated multiple materials. The effect of flux shadowing and neutral species reemission on the trench depth and sidewall ripples; (a) without and (b) with shadowing and reemission. (c) SEM image of a trench etched with the BOSCH process.

Two mechanisms for the roughness increase during plasma etching of Si. (a) Mechanism with “hard” inhibitors. (b) Mechanism with “soft” inhibitors.

A Monte Carlo modeling framework for the investigation plasma etching with simultaneous deposition of etch-inhibitors.

Simulation of turbulent flow (LES and realizable k-ε models) in atmospheric pressure plasma jets. Flow visualization and mole fractions after the nozzle of the kINPen 09 reactor.

A hybrid framework for the evolution of plasma etched surfaces coupling a Monte Carlo model with the level set method.

A fast novel model for cross-field atmospheric pressure plasma reactors. Comparison with the detailed 2D plasma model and measurements in the COST reference reactor.

Wetting transitions on patterned surfaces. Free energy of the Cassie-Baxter to Wenzel transition on a pillared surface.

Wetting transitions on patterned surfaces. Free energy of the Cassie-Baxter to Wenzel transition on a grooved surface.

Wetting transitions on patterned surfaces with a modified phase-field method. Free energy and energy barriers of the Cassie-Baxter to Wenzel transition.

Multiple scales in a chemical vapor deposition reactor.

Multiscale computational framework for chemical vapor deposition reactors. The effect of microscale substrate features on the macroscale of the reactor.

Multiscale computational framework for chemical vapor deposition reactors. Applications to W and Si deposition in microtrenches.
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