Software:Quantemol

Quantemol Ltd is based in University College London initiated by Professor Jonathan Tennyson FRS and Dr. Daniel Brown in 2004. The company initially developed a unique software tool, Quantemol-N, which provides full accessibility to the highly sophisticated UK molecular R-matrix codes, used to model electron polyatomic molecule interactions. Since then Quantemol has widened to further types of simulation, with plasmas and industrial plasma tools, in Quantemol-P and Quantemol-D.

Quantemol-N

The Quantemol-N software system has been developed to simplify use of UK R-matrix codes. It provides an expert interface for non specialists to perform ab initio electron-molecule scattering calculations. Quantemol-N calculates a variety of observables for electron molecule collisions including:

• Elastic cross sections
• Electronic excitation cross sections
• Electron impact dissociation rates
• Resonance parameters
• Radial charge density calculation
• Dissociative electron attachment cross sections
• Ionisation cross sections
• Differential cross sections
• Momentum transfer sections
• Vibration excitation cross sections

Applicable simulations

Quantemol-N is capable of tackling a variety of problems;

• Closed shell molecules
• Open shell molecules, and radicals
• Neutral and positively charged species
• Molecules of up to 17 atoms. (Neopentane has been successfully simulated, with improvements allowing more atoms in the future, and rapid movement towards Biomolecules)

Accuracy

A study on the key benchmark molecule; water, gave results more accurate than obtainable experimentally (Faure et al. 2004).

Experimentally, there are problems measuring large cross sections at low angles; this applies to any molecule with a large dipole moment. Being a simulation, this is not a problem for Quantemol-N.

Relevant Publications

• Quantemol-N: an expert system for performing electron molecule collision calculations using the R-matrix method

Jonathan Tennyson, Daniel B. Brown, James J. Munro, Iryna Rozum, Hemal N. Varambhia and Natalia Vinci

Journal of Physics: Conference Series 86, 012001 (2007)

doi: 1742-6596/86/1/012001

• Calculations of Cross Sections Data for Scattering of Electrons on HBr

Radmilovic-Radjenovic M., Petrovic Z.L.,

Acta Physica Polonica A, 117 (2010),745-747

• Electron-impact rotational excitation of the carbon monosulphide (CS) molecule

Varambhia H. N., Faure A., Graupner K., et al.

Monthly Notices of the Royal Astronomical Society, 403 (2010), 1409-1412

• Cross-sections for the scattering of electrons with BF₃

M. Radmilovic-Radjenovic, H. N. Varambhia, M. Vranic, J. Tennyson, Z. Lj. Petrovic.

Publ. Astron. Obs. Belgrade No. 84 (2008), 57-60

• R-matrix calculations of low-energy electron alkane collisions

Hemal N. Varambhia, James J. Munro and Jonathan Tennyson

International Journal of Mass Spectrometry, 271, 1-7 (2008)

• Electron collision with the HCN and HNC molecules using the R-matrix method

Hemal N. Varambhia and Jonathan Tennyson

Journal of Physics B: Atomic, Molecular and Optical Physics, 40, 1211-1223 (2007)

• Tool opens door to quantum modelling

29 March 2005, by Harry Yeates, Electronics Weekly

• Quantemol-N from plasma etch and lasers to earth's ionosphere

15 March 2005, III-Vs Review

Quantemol-P

The etching of silicon wafers using gaseous plasmas underpins the rapid advance in computer technology that has powered the global economy, and will continue to do so for the foreseeable future. Currently, experimental testing is used to establish the relevant plasma mixes to generate the desired etch. Such testing is an expensive and time-consuming process even for relatively minor improvements in the processes. Simulation allows much of this process can be done outside of the reactor at reduced cost and improved efficiency. Quantemol-P provides users with a means to simulate these processes.

One of the key fundamental processes in etch plasmas is the collision of low-energy electrons with molecules. But for many years the associated molecular data has been missing from the plasma researchers' toolkit. Measurements of these collisions are both expensive and difficult to perform, and their theoretical determination requires the use of sophisticated procedures based on the application of quantum mechanics.

Program use

Quantemol-P assists in the research for new plasma recipes and optimizes given processes by simulating etch machines. The simulation inputs used match those of the plasma processing tools: e.g. power, pressure, gas flow rate, time, volume.

The program couples molecular data and plasma models to provide full information on the various plasma processes. This gives users more insight into the problem than usually obtainable.

A variety of technical plasmas can be simulated; including plasma etch reactors, plug-flow reactors and well-mixed reactors.

The plasma model in Quantemol-P is based on the zero-dimensional global-kinetics simulation code GLOBALKIN developed over a number of years by Kushner and co-workers.

Relevant Publications

• Global plasma simulations using dynamically generated chemical models

James J. Munro and Jonathan Tennyson

Journal of Vacuum Science and Technology A, 26, 865 (2008)

Quantemol-VT

Quantemol-Virtual Tool is an expert software system for the simulation of industrial plasma processing tools. Q-VT builds upon the comprehensively validated Hybrid Plasma Equipment Model (HPEM) codes developed by renowned plasma physicist Professor Mark Kushner for simulating non-equilibrium low pressure (up to 1 Torr) plasma processes. Q-VT includes an intuitive user interface, data visualisation and analysis capabilities, and convenient job/batch management.

Applications include:

• Tool design and development
• Modelling of discharge and wafer level chemistry kinetics
• Model etch/deposition uniformity
• Examine tilting effects (when used with additional feature scale profile model, specifically compatible with Synopsys software)
• Large wafer size simulation (12 inch and more)

What Q-VT can model:

• Plasma tool geometry alterations
• Advanced volume and surface chemistries
• Variation of key plasma state variables with process parameter changes
• Ion flux on wafer level: ion energy/ angular distribution functions, and fluxes of all species along the wafer
• Non-Maxwellian electron dynamics
• Complex electromagnetic plasma interactions (current coils, permanent magnets, multi-frequency power supply, plasma circuit interactions)

Benefits of Q-VT

• Experimentally validated simulation system
• Experimentally validated simulation system focused on modelling plasma tools
• User-friendly tool-like interface
• Sets of validated plasma chemistries and cross-sections are provided with the licence
• Example libraries include numerous chambers
• Easy-to-use drawing tool for chamber design and modification: a tool simulation set-up service can be provided
• Ability to model complex plasma phenomena with additional modules (dust/radiation transport, ion kinetics, external circuits, etc.)
• Multi-run management system for managing large numbers of simulations
• Advanced reactor scale visualisation of scalar and vector plasma properties
• Experimental results importing
• Ability to easily distribute and manage jobs over a cluster

Quantemol-DB

The Quantemol database (QDB) is a database of plasma processes developed by Quantemol Ltd at University College London in 2016. The database contains chemistry data for plasma chemistry modelling with pre-assembled and validated chemistry sets, and is updated by Quantemol and contributing users. A peer-reviewed article detailing the database and service was published in 2017.

One of the most challenging aspects in plasma modelling is insufficient chemistry data. The purpose of QDB is to provide a forum for collaborative effort between academia and industrial research to access, compare and improve the understanding of plasma chemistry sets influencing plasma behaviour.

Approach to validation

The principles established for the validation of chemistry sets are that:

1. There is experimental benchmarking from open sources (where available) and also directly provided by industrial partners (collaborating on the Powerbase project) and database contributors.
2. Calculations are performed for a range of models thereby reflecting the underlying quality of input data (example models used for validation include HPEM, Global_Kin, ChemKin).
3. The models used to produce the data are validated on a case by case basis.
4. Numerical uncertainties are quantified with thresholds set for validation where possible.

This methodology is specifically applied to atomic and molecular calculations using the principles established in the publication "Uncertainty Estimates of Theoretical Atomic and Molecular Data", which was produced for the International Atomic Energy Agency and focused on "data that are most important for high temperature plasma modeling" with the "ultimate goal to develop guidelines for self-validation of computational theory for A+M [Atomic and Molecular] processes".

It is recognised that while the validation of chemistry sets directly may still be uncertain, the validation of data produced by models using this data will often be more easily obtained.

QDB users are invited to validate chemistry sets either directly or by validating the results of models which use these chemistry sets as inputs. Validation of the chemistry sets provided in the database will be based on the foundations of Uncertainty Quantification for calculations of complex systems.

For chemistry simulation, the scaling law based on the parameter study is a common methodology for this validation. For higher dimensional simulation, the behaviour of the species and the surface will be used for comparison.

Referencing is provided for users downloading chemistry sets, to ensure that relevant citations to chemistry set and validating experiments are included and can be used for publications.

Validation of Individual Chemistry Reactions

Rate coefficients of each reaction are included in the validated chemistry set for a similar range of temperature and pressure.

The main validation method for individual reactions is compared with alternative theoretical calculations/estimations and experimental measurements. For unknown reactions different calculation methods are used:

• Quantemol-N (R-matrix method) calculations for electron molecule scattering reactions
• Scaling law, mathematical methods of estimation and expert opinion to estimate necessary data
• Quantum and Transition State Theory for unknown heavy particle reactions

External links

• Quantemol Official Site
• Quantemol-N: an expert system for performing electron molecule collision calculations using the R-matrix method
• Calculations of Cross Sections Data for Scattering of Electrons on HBr
• Electron-impact rotational excitation of the carbon monosulphide (CS) molecule
• Cross-sections for the scattering of electrons with BF₃
• R-matrix calculations of low-energy electron alkane collisions
• Electron collision with the HCN and HNC molecules using the R-matrix method
• Tool opens door to quantum modelling
• Quantemol-N from plasma etch and lasers to earth's ionosphere
• Global plasma simulations using dynamically generated chemical models