atomic, molecular and optical data requirements for plasma processing 20 th escampig, novi sad, july...

Atomic, Molecular and Optical Data requirements for plasma processing

20th ESCAMPIG, Novi Sad,

July 13 – 17, 2010

Nigel MasonThe Open University

Workshop on data needs for plasma physics

• Session to discuss fundamental processes and applications in plasma processing

• This talk will review our knowledge of the fundamental processes

• Discuss what we know and what we don’t know. • and comment on the critical need for

DATA BASES

ESCAMPIG 2010

• At this meeting a wide range of plasmas will be discussed.

Technological plasmas in semiconductor industry, CVD, magetrons and pollution abatement

Related to Nanotechnology

Biophysics and medical applications

Plasmas cover a wide range

• Divide into three categories;

• Low pressure • Atmospheric

plasma• Fusion plasma

However, in order to understand all of these, we require knowledge of the fundamental processes – physical and chemical !

So how do we collect such data ?

Look at the plasma !

Optical spectroscopy

(and IR and UV !)

Optical Spectroscopy Identify chemical species;May gain knowledge ofGas Temperature;Electron Temperature E fields (U Czarnetski and S Hamaguchi CARS

for atmospheric pressure plasmas)

Optical Spectroscopy What data do we need ?

Absorption spectra

Emission spectra

Einstein coefficients

but also …

OpticalSpectroscopy What data do we need ?

• Branching ratios (cascade)

• Stark & Doppler broadening

• Temperature dependence

• Quenching rates

Optical Spectroscopy What data do we need ?

• And what we cant measure

(easily)

• Dark states (forbidden transitions)

• Short lived radicals

• Dust

• Anions

Charged species

• Electrons

• Ions

Electrons

Measure electron flux and temperature

• Langmuir probe

• Thompson Scattering

• Some problems in reactive/corrosive gases

• And limited temporal resolution

Measure ion flux and composition

• Measure ion mobility – not distinct

• Mass spectrometry – hard to do in situ. fragmentation patterns, kinetic energy effects (radicals ?)

Dynamics and Chemistry

• Need to build models/simulations to test observations

Dynamics and Chemistry

• Need to build models/simulations to test observations

• Only as good as data you put into them

(even if you know the physical parameters)

Ideal is to have the ‘Virtual factory’

Plasma modelling and database assessment

• What data is needed ?

Electron impact processes• Energy resolved cross sections• Average temperature dependent rate coeffs• Dissociation/ionisation processes (including DEA, DR)

• Collisions with fragments (eg CF3 and CF2 )

• Emission cross sections for diagnostics• SURFACE REACTIONS

• So how good is the data base ?

So where are we now in electron studies ?

• Electron – atom scattering

• Really quite good now at least for light atoms

• Elastic, excitation (including resonances)

• Ionisation

Elastic Scattering - rare gases

0 30 60 90 120 150 180

Present DataMimnagh et al.McEachran & Stauffer

2 sr-1

Scattering Angle (degrees)

Kr10 eV

0 30 60 90 120 150 180

Present

Srivastava et al.

McEachran & Stauffer WoA

McEachran & Stauffer WA

6 cm2 sr

Kr20 eV

0 30 60 90 120 150 180

Present

Srivastava et al.

McEachran & Stauffer WoA

McEachran & Stauffer WA

6 cm2 sr

Kr30 eV

Cho, McEachran, Tanaka, BuckmanJPB 37 4639 (2004)

• Electron –molecule interactions

• Very poor c.f. atoms

• Difficulty is complexity of target

• New processes – dissociation – drives chemistry

Electron –molecule interactions

Total cross sections;

Accurate to some 5%

(allow for forward scattering)

Lowest energies few meV !

Total cross sections for electron scattering

1 10 1000

CH3I 1.62 D CH3Br 1.81 D CH3Cl 1.87 D CH3F 1.85 D

0 m2 )

Electron energy (eV)Szmytkowski and collaboratorsSzmytkowski and collaborators

)exp(0 nlII

Elastic cross sections;

Accurate to some 10% - good standardsAngular range – can now measure 0 to 180

So momentum transfer cross section data are improving

Elastic scattering - H2O

0 30 60 90 120 150 180

Present

Rescigno & Lengsfield (1992)

Okamoto et al (1993)

Gianturco et al (1998)

Varella et al (1999)

2 sr-1

10 eVElastic

0 30 60 90 120 150 180

Present (CNU)Johnstone & NewellRescigno & LengsfieldOkamoto et alGianturco et alVarella et al

2 sr-1

6 eVElastic

0 30 60 90 120 150 180

Present

Shyn & Cho

Varella et al.

4 eVElastic

Cho, Park, Tanaka, BuckmanJPB 37 625 (2004)

Inelastic cross sections;

Vibrational (but resolution and deconvolution)

Excitation – very poor despite importance

Transmission effects

Rotational excitation…

Vibrational excitationEnergy loss spectra

-0,2 0,0 0,2 0,4 0,60

2stretch

CH2 bend

CH2 twist + wag

CH2 rock

C-C stretch

10eV, 110o

x50x15

Energy loss (eV)

Vibrational excitation - HCOOH

0.5 1 1.5 2 2.5 3 3.5

C - O Stretch

Incident energy (eV)

0.5 1 1.5 2 2.5 3 3.5

C = O Stretch

1 1.5 2 2.5 3 3.5 4

C - H Stretch

0.5 1 1.5 2 2.5 3 3.5

O - H Stretch

Ionisation;

Better data sets

(cf Theory – Kim (BE) and Deutsch Maerk )

But Kinetic effects in products

Dissociative Electron Attachment (DEA)

Production of Negative Ions in Plasmas

e-ABC # -

A(*) - + BC

A (*) - + B + C

Resonance ~ 10 -14 s

Negative ions in plasmas

•Many commercial plasma/etchant gases are electronegative

•E.g. The fluorocarbons, chlorine and oxygen (H2 in fusion plasmas)

• Negative ions may be major negative charge carrier (> ‘free‘ electron flux) e.g. in CF4 and oxygen plasmas 10x electron

Dissociative Electron Attachment –

Question as to how establish cross section

Few/no standards

Kinetic effects in products

Zero energy peaks !

Dissociation to neutrals particularly radicals

Ground state products – in its infancy

Still testing methodologies

No standard

Kinetic effects in products

Dissociation to excited states

Fluorescence– lots of data but

Detector calibrations

Role of cascade

Kinetic energy – Doppler broadening

Summary electron molecule database

• Lots of data • But few complete and self consistent datasets

(N2 best --- Loureiro)• Need to bring database together and cross

reference. • Combine expt with theory on-line calcns

(Quantemol J Tennyson)• Emol database under development

What about other processes ?

• Ion molecule and

• Neutral reactive chemistry

• Similar problems

• Reported rate coefficients may differ by orders of magnitude, depends on temperature, pressure (three body effects)

What about clusters ?

• Important in atmospheric pressure plasmas

• Particularly the role of water/humidity !

• Indeed key role in atmospheric discharges

• (Kushner Bubbles and biological systems)

21.04.23

Mass analysis of ions in atmospheric plasma (Hiden)

Mass analysis of ions in atmospheric plasma --- coronal discharge in air All are clusters no monomers

So cluster chemistry dominates !And key role of water !!!

Anions made by dissociative electron attachment to molecular oxygen

O- in region near wire (glow region)and O2

- in drift region

So cluster chemistry dominates !And key role of water !!!

Clusters formed

Anions cluster to water molecules easily

What about surfaces ?

• Introduce role of heterogeneous chemistry

Characterisation of surface processing

Effects of Plasma Processing Parameters on the Surface

Reactivity of OH(X2Π) in Tetraethoxysilane/O2 Plasmas

during Deposition of SiO2

K. H. A. Bogart, J. P. Cushing and R. Fisher

Surface Processes • Surfaces exposed to plasmas experience bombardment by energetic ions,electrons, neutrals, and photons.

• The detail in which we understand the effects of such bombardment varies widely depending on the particular process.

• The goal of fundamental surface studies, both theoretical and experimental, should be to provide insight and data for process simulation and/or reactor design.

• Examples of the data needed are cross sections and rate constants for energytransfer, reaction, emission, surface diffusion, implantation, reflection,disordering, and recombination. All these processes affect material properties, andall are affected by exposure to the non equilibrium, low-energy plasma.

• http://www.nap.edu/openbook.php?record_id=1875&page=R11

Open Questions

Surface studies

• How to define a cross section on a surface

• Role of molecular orientation

• Role of morphology

• Shift in energy levels and electronic states !

Water ice Note : Blue shift in the solid phase

0.0E+00

2.0E-18

4.0E-18

6.0E-18

8.0E-18

1.0E-17

1.2E-17

1.4E-17

1.6E-17

1.8E-17

2.0E-17

6.0 6.5 7.0 7.5 8.0 8.5 9.0 9.5 10.0 10.5

Photon Energy / eV

Comparison of gas and solid phase Methylamine

Note absence of low lying bands in solid phase

Energy (eV)

5 6 7 8 9 10 11

Gas PhaseSolid Phase

Sputtering

• For physical sputtering and energy transfer, the most important properties of the projectile and target are their masses and their interaction potentials.

• This relative simplicity combined with a wealth of experimental data on sputtering has facilitated the development of sophisticated theories and simulation tools.

Etching feature characterisation

• An understanding of the transfer of energy between surface and ion and the modification of the sidewall surface is needed to model the feature profile and to predict the dependence of etch and deposition rates on microstructure.

• Little is known about the surface chemistry and physics at atmospheric pressure and high temperature (greater than 800°C), which are typical conditions for rapid deposition of diamond and superconducting films.

Beam Surface Experiments • Much of our fundamental

understanding of surface processes occurring during etching and deposition comes from well-controlled plasma simulation experiments in which beams of ions, electrons, neutrals, and photons are directed either at well- characterized surfaces.

• The beams are typically analyzed using mass spectrometry. The surface chemistry is usually diagnosed using XPS, AES etc

Synergy of ion and neutral chemistry

• Experiments have clearly demonstrated synergy between ion bombardment and neutral chemistry in plasma etching

• The etching rate with combination of ion and reactive neutrals exceeds the sum of the individual etch rates for ion sputtering and neutral reaction.

Extending surface studies

• Beam-surface studies have been focused largely on etching reactions,

• But there is perhaps an even greater need for experimental simulation of plasma deposition processes.

• E.g. diamond and diamond-like film deposition from methane and other hydrocarbon plasmas. With appropriate free radical and ion beams, sticking probabilities are key data

What about sticking coefficients ?

Method to Determine the Sticking Coefficient of O2 of Deposited AlDuring Reactive Magnetron Sputtering, Using Mass SpectrometryW P. Leroy, S Mahieu, R Persoons, D Depla (2009)Plasma Processes and Polymers 0.1002/ppap.200932401

Coefficient of 0.107 ± 0.032 for O2 on depositedaluminium during reactive magnetron sputtering.

Mass spectrometry used to measure local, effective O2 partial pressure during sputtering, combined with electron probe microanalysis of theoxygen content in deposited layers, we calculate the sticking coefficient.

• Chemical surface transformations using electron induced reactions/

• DEA produces products that subsequently react on the surface

• E.g. Irradiate film of NF3 and CH3Cl

• Form CH3F

Electron Induced surface chemistry

CH3Cl CH3F

Basice--moleculeinteractions

Resonances

E0 dependence

Control via e--induced chemistry developing electron lithography

e--induced chemistry

Cross sections

Typical reactions and products

Reaction sequences

Surface functionalization

Reactionsat the interface

of materials

Modification of materials properties

- structural- electrical- permeability- optical

Anions and dust/aerosol formation ? • Anions are known to be precursors

of dust formation in plasmas (eg fluorocarbon plasmas etching Silicon wafers) or in silane plasmas

• but we know little on heterogeneous chemistry on dust

• Key to Titan aerosol chemistry ?

So how to assemble necessary databases ?

• Vital but

• How is it assembled and updated ?

• How is data selected ?

• Who pays ?

• One data base or several ?

Any database must fulfill several basic pre-requisites.

• It should be comprehensive with a full listing of experimental and, where applicable, theoretical results.

• Often it is assumed that the most recent results are the most accurate – this is often not the case since often both experimentalists and theoreticians publish ‘calibration data’ when designing new apparatus/codes.

• This data is used to illustrate the general operational performance of their system prior to conducting research on new systems. Such ‘calibration data’ is seldom of the same rigorous quality as the original data against which it is compared Replacing such ‘calibration data’ in a data base for older data is therefore often a mistake and is not the intention of the authors.

Any database must fulfill several basic pre-requisites.

• Any database that aims to be adopted by an applied community should include a list of recommended values.

• These may be subject to compilers’ bias (often the choice of which data set to adopt is a question of ‘gut feeling’ based on the experience and personal knowledge of the authors providing the data).

• Therefore it is necessary to have some method by which databases may be compared with one another.

Summary of database needs

• Develop database that community has ownership of

• Access is easy for posting data

• Discussion is easy !

• Provides up to date summary of data and recommendations

VAMDC is funded under the “Combination of Collaborative

Projects and Coordination and Support Actions” Funding

Scheme of The Seventh Framework Program.

Call topic: INFRA-2008-1.2.2 Scientific Data Infrastructure.

Grant Agreement number: 239108.

• VAMDC will provide a scientific data

e-infrastructure enabling easy access to A+M resources

• Http://www.vamdc.org/

Virtual Atomic and Molecular Data Centre (VAMDC) aims to build a secure, documented, flexible and interoperable e-science environment-based interface to the existing AM data.

The VAMDC will be built upon the expertise of existing AM databases, data producers and service providers with the specific aim of creating an infrastructure that is easily tuned to the requirements of a wide variety of users

The project will cover the building of the core consortium, the development and deployment of the infrastructure and the development of interfaces to the existing AM databases as well as providing a forum for training potential users

VAMDC does not collect or commission data but…

Will be a ‘one stop shop’ access to databases (currently some 17 are planned)

Wants to know what data is needed and the format it is most usefully presented in ; hence supports these meetings and discussions

WHAT DO YOU NEED ? Survey will follow this meeting !

Brussels -Negociation - S1 - 23/01/2009VAMDC - Brussels - Nov 08

Brussels -Negociation - S1 - 23/01/2009

Main Objectives• Atomic & Molecular data underpins a wide range of

basic and applied research and industrial development• VAMDC will provide the extensible scientific data

infrastructure enabling cost effective, European wide access to the increasingly large, distributed and complex A+M resources

• VAMDC will provide flexible interfaces to A+M resources supporting improved producer/consumer linkages

• Existing European wide grid (EGEE), network (GEANT) and application (Euro-VO) infrastructures form the effective baseline platform to create the VAMDC infrastructure

• VAMDC will extend these infrastructures to support common access to A+M data thus placing this primary data at the heart of the scientific progress

Brussels -Negociation - S1 - 23/01/2009

Main Objectives of the Proposal

We will deliver an electronic infrastructure which is general, flexible and useful for collecting and accessing A&M data. In order to demonstrate those properties we will:

• implement VAMDC interface for accessing major existing databases containing heterogeneous data and aimed at different users

• demonstrate data queries across multiple DBs that are focussed on specific research topic(s)

• demonstrate data publishing/quality control process for major A&M data producers

• involve wide user and producer communities in those test applications of VAMDC

Funding

3 million Euros for 42 months from July 1st 2009 to develop this data base

Meetings with major user communities will be held (including the plasma community)

Operational and sustainable by end of project

atomic, molecular and optical data requirements for plasma processing 20 th escampig, novi sad, july...

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