Plasma processes as advanced methods for cavity cleaning

of 80 /80
Plasma processes as advanced methods for cavity cleaning N. Patron , R. Baracco, L. Phillips, M. Rea, C. Roncolato, D. Tonini and V. Palmieri … pushing the limits of RFS Legnaro 2006

Embed Size (px)

description

Plasma processes as advanced methods for cavity cleaning. N. Patron , R. Baracco, L. Phillips, M. Rea, C. Roncolato, D. Tonini and V. Palmieri. … pushing the limits of RFS Legnaro 2006. ETCHING a main process. CLEANING a post processs. Hydrocarbons. Removal of ~ 100 μm. Water. - PowerPoint PPT Presentation

Transcript of Plasma processes as advanced methods for cavity cleaning

  • Plasma processes as advanced methods for cavity cleaningN. Patron, R. Baracco, L. Phillips, M. Rea, C. Roncolato, D. Tonini

    and V. Palmieri pushing the limits of RFSLegnaro 2006

  • CLEANINGa post processs Hydrocarbons Water Oxygen, Nitrogen and other adsorbed gases ETCHINGa main process Removal of ~ 100 mReduce surface roughness Reduce surface contamination Remove damaged layers

  • WET ETCHING Chemical etching Electropolishing Electromachining DRY ETCHING PLASMA ION GUN Sputtering Reactive ion etching Ion beam cleaning Reactive ion beam etching

  • Lets analyze one by one the different DRY ETCHING techniques

  • Reactive ion etching DRY ETCHING PLASMA ION GUN Sputtering Ion beam cleaning Reactive ion beam etchingOne example from our experience:

  • Cu frame used in CUORE experiment for the detencion of a dobble decadiment We have been given the task to find a way to eliminate ppb contamination of 232 Th from the Cu surfaceCUORE Cryogenic Underground Observatory for Rare Events

  • Dry etching methods are very clean

  • Smooth surfaceBut Physical Methods treatment can become an enemy..Thin grain boundaries

  • Coarsening of grain boudariesRough surface

    A deeper etchingCleaner surface, but higher demagnetization factor

  • Sputtering Plasma Etching For cleaning it might good It isnt a fast routine method Whenever applying dry etching a fundamental comprehension of the role of Grain boundaries and grain Demagnetization factor is necessary.(vacuum systems, flanges to be mounted)

  • Reactive ion etching DRY ETCHING PLASMA ION GUN Sputtering Ion beam cleaning Reactive ion beam etching

  • Mostly developed for Nb-based Josephson junctions switching devices.Gas mixture more frequently used are: CF4/O2(a,b), CCl3F(c), SF6/O2(d); I2, XeF2(e).a) M. Chen and R. H. Wang, J.Vac.Sci. Technol. A, Vol. 1, No. 2, Apr/June 1983b) J. N. Sasserath and John Vivalda, J.Vac.Sci. Technol. A, Vol. 8, No. 6, Nov/Dec 1990c) J. W. No, Nucl. Inst. and Meth. 212 (1083) 73d) B. J. Curtis and H. Mantle, J.Vac.Sci. Technol. A, Vol. 11, No. 5, Sep/Oct 1993e) X. L. Fu, P. G. Li, A. Z. Jin, H. Y. Zhang, H. F. Yang, W. H. Tang, J.Vac.Sci. Technol. B, Vol. 23, No. 2, Mar/Apr 2005

    Reactive gasses are injected in the plasma

  • RF reactive ion etching deviceParallel plate RF powered etcher operating at 13.56 MHzUsing CF4 and O2 as the reactive gas mixtureM. Chen and R. H. Wang, J.Vac.Sci. Technol. A, Vol. 1, No. 2, Apr/June 1983From Literature

  • Etching rates are functions of O2 percentageM. Chen and R. H. Wang, J.Vac.Sci. Technol. A, Vol. 1, No. 2, Apr/June 1983J. N. Sasserath, J. Vivalda, J.Vac.Sci. Technol. A, Vol. 8, No. 6, Nov/Dec 1990From Literature

  • Niobium etching rate = 30 m/h

    Jay N. Sasserath and John Vivalda, J.Vac.Sci. Technol. A, Vol. 8, No. 6, Nov/Dec 1990Niobium etching rate = 2,4 m/h

    M. Chen and R. H. Wang, J.Vac.Sci. Technol. A, Vol. 1, No. 2, Apr/June 1983From Literature

  • CCl3F-vapour rf discharge processingJ. W. No, Nucl. Inst. and Meth. 212 (1083) 73Eliminate secondary electron emission problems of multipactoring from lead-plated copper quarter-wave resonators.Flurine ions and radicals are very agressive, No suggests that CF4 should work too.

  • LNL ACTUAL RESULTSEtching rate: 12,7 m/h Niobium DC diode sputtering with CF4 Pressure of 410-2 mbar Sample voltage: - 1250 V

  • Reactive ion etching DRY ETCHING PLASMA ION GUN Sputtering Ion beam cleaning Reactive ion beam etching

  • Two main type of sources

  • Kaufman sourcesBroad-beam source with an extracting grid in wich a cathodic filament sustains a magnetical confined plasma

  • Best confinament condition for
  • Gridless source

  • We used a gridless sourceIt is more simple and its easier to be modified if eventually we want to reduce its dimension to use it inside of a cavity

    It needs only one power supply

  • Source IG1: parametersThe cathode is grounded

    The anode is at +2kV

    Gas process is Argon

  • LNL ACTUAL RESULTSION BEAM ETCHING Energy: 2 KeV Pressure of 410-2 mbar Substrate to source:170 mmAr2,3 m/hCF412,7 m/hREACTIVE ION ETCHING Diode sputterind with CF4 Pressure of 410-2 mbar

  • Gas fluxPlasma regionRotational extracting gridA possible cavity application

  • Reactive ion etching DRY ETCHING PLASMA ION GUN Sputtering Ion beam cleaning Reactive ion beam etching

  • Atmospheric-pressurePlasma

  • AP plasma RF RF resonance AP Plasma Jet DC CORONA MICROWAVE MW plasma torch

  • Why could ATM plasma be useful? To clean surfaces from carbon contamination or adsorbed gases. To etch surfaces using plasma activated chemicals, without any need of a vacuum system. To add an efficient cleaning step to the cavities surface treatments To substitute some dungerous steps of Nb cavity chemistry

  • An example of a surface treatment

  • AP plasma RF RF resonance AP Plasma Jet DC CORONA MICROWAVE MW plasma torch

  • DC corona plasma Corona discharges accur only if the electric field is sharply NONUNIFORM, typically where the size r of one electrode is much lower than the distance. It may be seen as luminous glow around the more curved electrode. The electric fields minimun value for the ignition is around 30 kV/cm. ElectrodesHigh field gradientLow field gradientDischargeCorona

  • DC Corona dischargeA non-self-sustaining current of 10-14 A can be detected.

    It is due to ions produced by cosmic rays.The corona is ignited.A luminous layer around the electrode where the E field is the highest can be seen.A self sustaining discharge makes the current jump to ~10-6 A.Massive production of O3Vapplied VcoronaCoronas are operated at currents/voltages below the onset of arcing

  • The Corona Mechanism The extablisment of a corona begins with an external ionization event generating a primary electron and it is followed by an electron avalanche. The second avalanches are due to energetic photons :NEGATIVE CORONAPOSITIVE CORONA

  • Positive Corona It appears more uniform than the corresponding negative corona thanks to the homogeneous source of secondary avalanche electrons (photoionization). The electrons are concentrated close to the surface of the curved conductor, in a region of high-potential gradient and therefore the electrons have a higher energy than in negative corona. Produce O3

  • Negative Corona It appears a little larger as electrons are allowed to drift out of the ionizing region, and so the plasma continues some distance beyond it. The electron density is much greater than in the corresponding positive corona but they are of a predominantly lower energy, being in a region of lower potential-gradien. The lower energy of the electrons will mean that eventual reactions which require a higher electron energy may take place at a lower rate. Produce a larger amount of O3

  • Why could corona plasma be useful? UV/O3 treatments has been proved to be capable of producing clean surfaces in less than 1 minute(f). Ozone production could be easily used to clean the cavities surfaces from carbon contaminants.

    f) J. R. Vig, J.Vac.Sci. Technol. A, Vol. 3, No. 3, May/Jun 1985

  • The early stage of our studiesNegative Corona inside a 1,5 GHz cavityDischarge voltage 30kVStrong production of O31,5 GHz seamless Cu Cavity

  • Positive Corona inside a 1,5 GHz cavityDischarge voltage 25kVProduction of O31,5 GHz seamless Cu Cavity

  • To have a more uniform corona plasma it is necessary to have the same electrode distance along all the lenght of the cavity.

    It is important to verify if the 2-6 eV electron and ion energy could be used for surface chemical etching or cleaning using reactive gases.

  • Attempts for understanding and studies

  • Cathode cavity shapedNegative corona inside the cavity

  • AP plasma RF RF resonance AP Plasma Jet DC CORONA MICROWAVE MW plasma torch

  • RF Resonance plasmaOur purpose was to ignite an atmosferic resonance plasma inside a cavity. Relate the mode exctitation to the shape of the plasma inside the cavity in order to control and eventually direct the plasma more or less close to the internal surface of the cavity.Study the surface modification due to the plasma physical or chemical action.

  • Excitation mode TM010Electric fieldModule of Magnetic fieldModule of Electric fieldMagnetic fieldLateral viewBase view

  • 6 GHz cavityCavityTM010 plasma at a power of 50 W

  • 1,5 GHz cavity

  • Pill-box cavity for the excitation mode TE111RF power supply frequency range

  • Excitation mode TE111Module of Electric fieldMagnetic fieldModule of Magnetic fieldElectric fieldBase ViewLateral View

  • What do we expectA plasma ball in the center of the cavity when we excite the TM010 mode, as we have seen in the 6 GHz cavity.A rod of plasma along a diameter at the center of the cavity pointing to the surface, when we excite the TE111.

  • view portLoop antennaAl Pill-Box

  • We found the resonance frequencies of the modes TM010 and TE111.Using a loop antenna we tried to ignite the plasma by exciting at the TE111 modes resonance frequency.We found out by observing that the plasma shape wasnt changing while moving away from the resonance frequency that we werent observing a plasma due to a resonance mode excitation.

  • AP plasma RF RF resonance AP Plasma Jet DC CORONA MICROWAVE MW plasma torch

  • Atmospheric Pressure Plasma Jetg) V. J. Tu, J. Y. Jeong, A. Schutze, S. E. Babayan, G. Ding, G. S. Selwyn, R. F. Hicks, J.Vac.Sci. Technol. A, Vol. 18, No. 6, Nov/Dec 2000h) J. Y. Jeong, S. E. Babayan, V. J. Tu, J. Park, I. Henins, R. F. Hicks, G. S. Selwyn, Plasma Sources Sci. Technol. 7 (1998) 282-285

    Gas mixtureO2+He2O2+He2 +CF4O2+He2+CF4O2+He2+CF4O2+He2+CF4MaterialKaptonSiO2TaWTaEtching Rate8 m/min(g)1,5 m/min(g)2 m/min (g) 1 m/min (g) 6 m/min (h)

  • 13,56 MHz / 2,45 GHz APPJ Device Water outWater inGas inRF connectionInner electrodeIonization spaceOuter electrode

  • 13,56 MHz

  • Future APPJ source developementPlasma and chemicals exit radially from the nozzle

  • AP plasma RF RF resonance A P P J DC CORONA MICROWAVE MW plasma torch

  • MW Atmospheric Plasma TorchGas InletMW 2,45 GHz waveguideQuarz tube placed at l / 4MW 2,45 GHz Plasma ignited inside a quartz tube at 500W

  • SODifferent etching methodes and devices has been explored.

    There are some ideas of exploring the use of reactive gases like CF4 or NF3 in both the vacuum and plasma processes.

    Still a lot of studies needs to be done

  • Advice and suggestionsTHANK YOU

  • The End? or the beginning

  • Paschen curve

  • Factors/ Systems ApjetDiffuse Dielectric BarrierCoronaMicrowaveMethodHelium Process Gas with added reactive gasDielectric Cover on Electrode with He process gasSharply Pointed Electrode at HVWave Guides Resonant Cavity. ComplexFrequency2-60 MHz RF1-100 KHz ACDC/Pulsed Pwr2.45 GHzPlasma Density Electrons/cm3 (volume average)1011-10121091081011Reactive Species: O/cm3101610131013? (Limited due to ozone generation)Undesirable byproducts: Ozone/cm3101610181013HighTemperatureLowLowHigh at edgeRF Substrate HeatingUniform GlowYesYes?NoPoint SourceProcess MethodsDownstream or In-situIn-situIn-situDownstreamFlexible ShapesYesYesNoNoHazardsLowHigh Ozone Substrate Damage High VoltageHigh OzoneSignficant Health & Safety (microwave) + High OzoneScalable to large area?YesYesNoNo

  • If the applied voltage V is less than the ignition voltage for a Corona discherge Vc than a non-self-sustaining current of 10-14 A can be detected. It is due to ions produced by cosmic rays. If the applied voltage V is less than the ignition voltage for a Corona discherge Vc than a non-self-sustaining current of 10-14 A can be detected. It is due to ions produced by cosmic rays.

  • Vapplied VcoronaThe corona is ignited, a luminous layer around the electrode where the E field is the highest can be seen. The discherge current jump to 10-6 A. It is a self sustaining discharge.

  • The Corona Mechanism The extablisment of a corona begins with an external ionization event generating a primary electron and followed by an electron avalanche.The second avalanches process is due to :NEGATIVE CORONAPOSITIVE CORONA-Electron emission from the cathode-Photoionization-Photoionization

  • Future developements and studiesCavityCatodeCatodes edges facing the cavity where the corona will be ignited

  • Future developements and studiesCatodeCatodes edges facing the cavity where the corona will be ignitedCavity

  • Whats next on LNL superconductivity group?

  • Focused Ion BeamNiobium etching rate using I3 = 72 m3/min

    Niobium etching rate using XeF2 = 60 m3/min

  • Which source to be used?

  • Gridless source IG1: technical designCoilCooled anodeInlet gasIonization areaMagnetic extractorTeflon chamber

  • 6 GHz cavityCavityTM010 plasma at a power of 50 W

  • Excitation mode TM010Electric fieldModule of Magnetic field

    Cleaning methods are efficient to remove recantamination from.Etching methods are ment to removeWe tried to analize how efficient are the etching techniques mentioned here by reading the litterature, and from our experimental experience.Dry etching form a group of methods used to attach a solid surfface with a gas or a vapour. The etching process can be physical if for example its carried on by ionic bombardament, or can be chemical an hence carried on by a chemical reaction at the surface. Dry etching methods can be devided into 2 separate groups depending on the experimental setup in wich they are operating.1)We can have PLASMA ething techniques when the plasma is generated in the same chambers where theres the sample to etch. 2)We can have ION GUN techniques when the plasma is generated in a separate chamber from where ions are extracted and accelerated towards the substrate.In sputtering and in ion beam cleaning the etching is due to energy transfer from Ar+ ions forming the plasma to the surface of the substrates.In reactive ion etching and reactive ion beam etching there are chemical species which diffuse through the plasma, reach the substrate and react with its surface. Here the only role played by the plasma is to produce reactive gasseous species.We tried to analize how efficient are the etching techniques mentioned here by reading the litterature, and from our experimental experience.Dry etching form a group of methods used to attach a solid surfface with a gas or a vapour. The etching process can be physical if for example its carried on by ionic bombardament, or can be chemical an hence carried on by a chemical reaction at the surface. Dry etching methods can be devided into 2 separate groups depending on the experimental setup in wich they are operating.1)We can have PLASMA ething techniques when the plasma is generated in the same chambers where theres the sample to etch. 2)We can have ION GUN techniques when the plasma is generated in a separate chamber from where ions are extracted and accelerated towards the substrate.In sputtering and in ion beam cleaning the etching is due to energy transfer from Ar+ ions forming the plasma to the surface of the substrates.In reactive ion etching and reactive ion beam etching there are chemical species which diffuse through the plasma, reach the substrate and react with its surface. Here the only role played by the plasma is to produce reactive gasseous species.If we consider one of the most common plasma etching techniquewe had the problem to remove U and th contaminations of ppbIn facts observing this target used for magnetron sputtering we can see a smooth surface and a GB of about 10mm radiusIf we want to a carry on a deeper etching for obtain a higher degree of purity of the film, we may go towards problemsIf we use the target for longer time, so with a longer etching time we can obtain bigger Grains but rougher surface, this might leed to rising in the dmagnetization factor.So we may say thatWe tried to analize how efficient are the etching techniques mentioned here by reading the litterature, and from our experimental experience.Dry etching form a group of methods used to attach a solid surfface with a gas or a vapour. The etching process can be physical if for example its carried on by ionic bombardament, or can be chemical an hence carried on by a chemical reaction at the surface. Dry etching methods can be devided into 2 separate groups depending on the experimental setup in wich they are operating.1)We can have PLASMA ething techniques when the plasma is generated in the same chambers where theres the sample to etch. 2)We can have ION GUN techniques when the plasma is generated in a separate chamber from where ions are extracted and accelerated towards the substrate.In sputtering and in ion beam cleaning the etching is due to energy transfer from Ar+ ions forming the plasma to the surface of the substrates.In reactive ion etching and reactive ion beam etching there are chemical species which diffuse through the plasma, reach the substrate and react with its surface. Here the only role played by the plasma is to produce reactive gasseous species.A directed chemical etching process in which chemically active ions are accelerated along electric field lines to meet a substrate perpendicular to its surface

    This is an example of Nb RF reactive etching, it is shown the dependence of the etching rate with the oxygen percentage in the plasmaUsing a similar device others have reached etching rates ofWe tried to analize how efficient are the etching techniques mentioned here by reading the litterature, and from our experimental experience.Dry etching form a group of methods used to attach a solid surfface with a gas or a vapour. The etching process can be physical if for example its carried on by ionic bombardament, or can be chemical an hence carried on by a chemical reaction at the surface. Dry etching methods can be devided into 2 separate groups depending on the experimental setup in wich they are operating.1)We can have PLASMA ething techniques when the plasma is generated in the same chambers where theres the sample to etch. 2)We can have ION GUN techniques when the plasma is generated in a separate chamber from where ions are extracted and accelerated towards the substrate.In sputtering and in ion beam cleaning the etching is due to energy transfer from Ar+ ions forming the plasma to the surface of the substrates.In reactive ion etching and reactive ion beam etching there are chemical species which diffuse through the plasma, reach the substrate and react with its surface. Here the only role played by the plasma is to produce reactive gasseous species.We tried to analize how efficient are the etching techniques mentioned here by reading the litterature, and from our experimental experience.Dry etching form a group of methods used to attach a solid surfface with a gas or a vapour. The etching process can be physical if for example its carried on by ionic bombardament, or can be chemical an hence carried on by a chemical reaction at the surface. Dry etching methods can be devided into 2 separate groups depending on the experimental setup in wich they are operating.1)We can have PLASMA ething techniques when the plasma is generated in the same chambers where theres the sample to etch. 2)We can have ION GUN techniques when the plasma is generated in a separate chamber from where ions are extracted and accelerated towards the substrate.In sputtering and in ion beam cleaning the etching is due to energy transfer from Ar+ ions forming the plasma to the surface of the substrates.In reactive ion etching and reactive ion beam etching there are chemical species which diffuse through the plasma, reach the substrate and react with its surface. Here the only role played by the plasma is to produce reactive gasseous species.Distinzione vari tipi di scariche con le freccie tipi dry and wet etchingDistinzione vari tipi di scariche con le freccie tipi dry and wet etchingNEGATIVE It appears a little larger than the corresponding positive corona, as electrons are allowed to drift out of the ionising region, and so the plasma continues some distance beyond it The total number of electrons, and electron density is much greater than in the corresponding positive corona the lower energy of the electrons will mean that reactions which require a higher electron energy may take place at a lower rate

    Coronas are efficient producers of ozone in air. A positive corona generates much less ozone than the corresponding negative corona, as the reactions which produce ozone are relatively low-energy. Therefore, the greater number of electrons of a negative corona leads to an increased production.We ignite a corona plasma using a 60 kV voltage power supplyDistinzione vari tipi di scariche con le freccie tipi dry and wet etchingWe managed to ignite the plasma inside a 6 GhZ cavityWe found out by observing that the plasma shape wasnt changing while moving out from the resonance frequency that we werent observing a plasma du eto a resonance mode excitation.

    Distinzione vari tipi di scariche con le freccie tipi dry and wet etchingHere we can see a schematic of the atmospheric plasma jet device. This source consists of two concentric electrodes through which a gas can flow. By applying 13.56 MHz or 2.45 GHz power to the inner electrode the gas discharge is ignited. 5/3 mm500-685 WDistinzione vari tipi di scariche con le freccie tipi dry and wet etching