DE102011005834A1 - Monitoring plasma or flame at atmospheric pressure, comprises measuring optical emission of plasma or flame by spectrometer and determining based on characteristics of plasma or flame, and using intensity-calibrated spectrometer - Google Patents

Abstract

Monitoring a plasma or a flame at atmospheric pressure, comprises measuring optical emission of the plasma or flame by means of a spectrometer (3) and determining based on the characteristics of the plasma or flame, where an intensity-calibrated spectrometer is used.

Description

The invention relates to a method for monitoring a plasma or a flame.

The treatment and refinement of material surfaces plays an important role in the improvement of material properties, the optimization of manufacturing processes and the economical use of raw materials. In recent years, surface functionalizations have become firmly established through the use of plasma or flame treatment methods. In particular, the plasma processes are characterized by comparatively high energy and raw material efficiency and environmental compatibility.

To ensure product quality in the manufacturing process, process monitoring and quality controls are indispensable. These processes are controlled via the control or optimization of process parameters such as plasma power, contact time, variation of the process gas composition or addition of precursor substances for a layer deposition. A success of the respective production step is checked retrospectively on the produced intermediate or end product. By trial and error, the most suitable set of process parameters for the desired treatment result can be determined.

Out [ E. Schmachtenberg, A. Hegenbart, "Monitoring Plasma Processes by OES", Vacuum in Research and Practice 17 (2005), No. 6, 318-323 .] is known to monitor plasma processes, for example, for the treatment of plastic components for the purpose of process logging and quality assurance online by means of optical emission spectroscopy. The plasma treatment is carried out at low pressure in a process chamber. Optical emission spectroscopy measures emissions of the plasma jet, which are used to determine the characteristics of the plasma jet.

From the US 2005/0068519 A1 For example, a method and system for monitoring the status of a system component in a process chamber is known. The system component is exposed to light from a light source. The interaction of the light with the system component is monitored to determine the status of the system component. To monitor a coating process in a vacuum or non-vacuum environment, such as by plasma, for example, an infrared spectrometer is used, which provides information about a gas composition.

The invention is based on the object to provide an improved method for monitoring a plasma or a flame.

The object is achieved by a method having the features of claim 1.

Advantageous embodiments of the invention are the subject of the dependent claims.

In a method according to the invention for monitoring a plasma or a flame at atmospheric pressure, optical emissions of the plasma or the flame are measured without contact by means of a spectrometer. The emissions are used to determine the characteristics of the plasma or the flame. According to the invention, an intensity-calibrated spectrometer is used, that is to say the radiation of different lines in different spectral ranges can be absolutely compared with one another. In this way an absolute statement about parameters of the plasma or the flame at atmospheric pressure is possible.

The optical emission spectroscopy offers the possibility of in-situ measurement in the process without its influence, since the measurement is non-contact.

Through the analysis for the respective process of suitable spectral lines and spectral bands and the direct evaluation of the progressions of the spectral lines and spectral bands, a quality assurance can be achieved in the ongoing process. By means of the spectral plasma analysis and corresponding monitoring for the stability control of the processes, a process control for process assurance and quality guarantee can be realized.

• – Verlauf mindestens eines Spektralbands,
• – Vorkommen bestimmter Partikel,
• – Partikeldichte,
• – zeitliche Variation der Partikeldichte
• – Struktur einer Molekülstrahlung, insbesondere Molekülemission, Molekülbanden.

In the measured optical emissions at least one of the following characteristics can be determined:

• - course of at least one spectral band,
• - occurrence of certain particles,
• - particle density,
• - temporal variation of the particle density
• Structure of molecular radiation, in particular molecular emission, molecular bands.

In one embodiment of the invention, a vibration temperature of a molecule is determined from a ratio of vibrational bands of a molecule transition, wherein a rotational temperature of a molecule is determined from a ratio of rotational lines. A total radiation of the molecule is determined from the vibration temperature and from the rotation temperature, wherein a number of the molecules is determined from the total radiation. The determination of the total radiation of a molecule is only possible with an intensity-calibrated spectrometer. The determined total radiation can then be used, for example, for the actinometry of molecular particle densities.

In the measured optical emissions, a self-absorption of radiation lines is preferably determined and taken into account in the determination of the characteristics. The line self-absorption hardly plays a role due to the low particle density in vacuum processes. However, it is advantageous to consider them at the much larger particle density at atmospheric pressure.

By means of actinometry, a particle density ratio of the different species can be determined via an intensity ratio of spectral lines and / or molecular bands of different species. The actinometry provides quantitatively meaningful results only with an intensity-calibrated spectrometer.

The characteristics are preferably determined by means of a plasma model. As atmospheric pressure plasma models, the following well-known models are mentioned here: "Local Thermal Balance (LTE)", "Partial Local Thermal Balance (PLTE)" and "Collisional Radiative Model (CRM)". Depending on the pressure range and the temperature of the atmospheric plasma, the valid model is used.

On the basis of the specific characteristics, at least one of the parameters plasma power, burner power, contact time, composition of fuel gas or working gas, throughput of fuel gas or working gas, throughput of a precursor can be controlled and / or regulated via a control loop, preferably by means of a P, PI, PD - or PID control.

Preferably, the optical emissions are measured and analyzed in real time, so that a control of the process parameters can be done in real time.

The plasma or flame can be used in a process for treating a surface in which a plasma jet is generated either from a working gas or a flame jet from a fuel gas. The surface is coated with the plasma jet or the flame jet. The treatment of the surface is carried out at atmospheric pressure. By varying process parameters, investigating dependencies of the spectral results on the varied parameters and adapting the results to different atmospheric pressure plasma processes, an in-situ analysis of the plasma process is achieved. The process of surface treatment is not affected by the non-contact measurement of optical emissions.

An essential advantage of atmospheric pressure processes, in particular atmospheric pressure plasma processes, is the ease of integration into production processes by the elimination of vacuum reaction spaces and the low investment costs compared to low-pressure plants. The size of the workpieces whose surfaces are to be treated is no longer limited by the dimensions of a vacuum chamber. Atmospheric pressure techniques can be used to treat a variety of materials. Thus, for example, outgassing materials can be treated, the treatment at low pressure is not possible. In particular, atmospheric pressure plasma processes are also suitable for temperature-sensitive materials due to the low heat input.

Preferably, based on the determined spectral characteristics of the atmospheric pressure processes, parameters of the surface treatment are controlled and / or regulated. In this way, the success of the treatment process during the treatment of the surface can be monitored and modified according to the desired result, so that a subsequent verification can be omitted. Thus, process stability and product quality can be increased. Accordingly, the industrial applicability of the surface treatment improves and there is less waste. Less waste will result in higher levels of customer satisfaction and a lower level of complaints as well as savings in natural resources and improved environmental sustainability.

The treatment of the surface may consist in an activation or in a coating of the surface by means of the plasma jet or flame jet.

In a coating, a so-called CVD method (chemical vapor deposition), at least one precursor material is supplied to the working gas and / or the plasma jet or the fuel gas and / or the flame jet and reacted in the plasma jet or flame jet. Subsequently, at least one reaction product of at least one of the precursors is deposited on the surface and / or on at least one layer arranged on the surface.

Likewise, initially only one activation and subsequently a coating or also an activation following on a coating can be provided.

The throughputs of working gas and precursor can be controlled independently of each other. In addition to the distance of the plasma source to the coating surface is thus another means for influencing the layer properties, such as the layer thickness or the refractive index available. Likewise, gradient layers can be realized in this way. By suitable choice of these process parameters and the precursors used, for example, the following properties of the surface of the substrate are selectively changeable: scratch resistance, self-healing ability, barrier behavior, reflection behavior, transmission behavior, refractive index, transparency, light scattering, electrical conductivity, antibacterial behavior, friction, adhesion, hydrophilicity, hydrophobicity, Oleophobicity, surface tension, surface energy, anti-corrosive effect, dirt-repellent effect, self-cleaning ability, photocatalytic behavior, anti-stress behavior, wear behavior, chemical resistance, biocidal behavior, biocompatible behavior, electrostatic behavior, electrochromic activity, photochromic activity, gasochromic activity.

The measurement of the optical emissions may be at a single location or at at least two different locations of the plasma jet or flame jet or the surface. According to this number, the spectrometer has a number of channels through which the optical emissions are supplied to it.

This can be done, for example, according to the number of channels via a respective optical waveguide. Preferably, each of the optical waveguides for coupling the optical emissions on a collimator optics. A collimator serves to parallelize incident rays of the plasma jet or flame jet to be examined, so that it acts like a virtually infinitely distant radiation source.

The generation of the plasma can be done in a free-jet plasma source. In this method, a high-frequency discharge between two concentric electrodes is ignited, which is led out by a gas stream, the forming hollow cathode plasma as Plasmajet from the electrode assembly usually several centimeters into the free space and the surface to be coated. The precursor can be introduced both before the excitation in the working gas (direct plasma processing) and then in the already formed plasma or in the vicinity (remote plasma processing). Another possibility of plasma generation is the exploitation of a dielectrically impeded discharge. In this case, serving as a dielectric working gas, in particular air, passed between two electrodes. The plasma discharge takes place between the electrodes, which are supplied with high-frequency high voltage. Likewise, a glass substrate itself can be used as a dielectric by passing the gas flow between a metallic surface electrode and the flat glass substrate.

The precursor is preferably introduced in the gaseous state or as an aerosol into the working gas or the plasma stream. Liquid or solid, in particular pulverulent precursors can also be used, but are preferably converted into the gaseous state before introduction, for example by evaporation. Likewise, the precursor can first be introduced into a carrier gas, entrained therefrom, and introduced together with it into the working gas or the plasma stream.

The deposited layer preferably comprises at least one of silicon, silver, gold, copper, iron, nickel, cobalt, selenium, tin, aluminum, titanium, zinc, zirconium, tantalum, chromium, manganese, molybdenum, tungsten, bismuth, germanium, niobium , Vanadium, gallium, indium, magnesium, calcium, strontium, barium, lithium, lanthanides, carbon, oxygen, nitrogen, sulfur, boron, phosphorus, fluorine, halogens and hydrogen. In particular, the layers contain oxidic or / and nitridic compounds of silicon, titanium, tin, aluminum, zinc, tungsten and zirconium.

The precursor used is preferably an organosilicon and / or an organo-titanium compound, for example hexamethyldisiloxane, tetramethylsilane, tetramethoxysilane, tetraethoxysilane, titanium tetraisopropylate or titanium tetraisobutylate.

In this way, for example, barrier layers can be realized, which reduce the permeability to gases and water.

In a preferred embodiment, a first layer having a barrier effect and then at least one further layer as a functional layer, preferably having at least one of the abovementioned properties, are deposited on a lime-sodium-silicate glass (standard float glass). The barrier layer, on the one hand, reduces the passage of water, carbon dioxide and other substances from the atmosphere to the surface of the glass substrate. On the other hand, migration of sodium in particular from the glass into the functional layer is reduced so that its activity is retained. The functional layer can be applied to the still hot or already cooled glass by the same method or by another coating method.

As the working gas, air, steam or other gas can be used, for example, oxygen, nitrogen, noble gases, hydrogen, carbon dioxide, gaseous hydrocarbons or a mixture thereof.

For example, propane can be used as the fuel gas for the flame treatment, air or oxygen being supplied for combustion. The fuel gas can be premixed with air or oxygen. The mixing ratio between fuel gas and oxygen or air can also be controlled and / or regulated as parameters on the basis of the determined characteristics.

For example, surfaces made of a plastic, glass, metal, ceramic, glass ceramic, wood or textile can be coated or activated.

Embodiments of the invention will be explained in more detail below with reference to a drawing.

It shows:

1 a schematic view of an arrangement for process control in atmospheric pressure plasma processes for the treatment of a surface with a treatment device, a spectrometer and a control.

1 shows a schematic view of an arrangement 1 for process control in atmospheric pressure plasma processes for the treatment of a surface with a treatment device 2 , an intensity-calibrated spectrometer 3 and a regulation 4 , preferably a P, PI, PD or PID control.

The treatment facility 2 can be designed as a Beflammungsanlage, for example, a flame treatment system of the company SURA Instruments GmbH consisting of a gas supply, burner and a Precursordosierungs unit. In the gas supply unit, a fuel gas, for example propane (C ₃ H ₈ ), premixed with air in a certain ratio, passed into the burner, ignited there and burned. Subsequently, under atmospheric pressure conditions, a surface of a substrate is coated. Such Beflammungsanlagen can be used for example for the activation of plastics, since they are relatively simple and inexpensive and are characterized by low operating costs. Flaming processes have also been established in the deposition of thin films. In this case, a layer-forming compound (precursor) is added as a gas or aerosol in the fuel gas. This makes it possible to evenly coat large surfaces of substrates with relatively little expenditure of time. The previously existing problem that only thermally strong materials such. As glass, could be coated, has been minimized by the development of special burner geometries.

The treatment facility 2 can also be designed as a plasma system, for example, a plasma blaster system from Tigres. Gerstenberg GmbH. This plasma system provides a potential-free, open plasma with only moderate heat load for the surface to be treated. In a nozzle, a high-frequency plasma is generated, which is guided by means of compressed air onto the substrate surface. With this plasma system uncomplicated pressure or adhesive pretreatment without the use of chemicals is possible. The operating costs are low, since the plasma system with high efficiency has unusually long service life and consumes only little compressed air. By adding a layer-forming substance (precursor), thin layers can be deposited at atmospheric pressure and without severe thermal stress on the substrate. Thus, this method is very well suited for integration into manufacturing processes.

By means of the spectrometer 3 For example, optical emissions of the plasma jet or flame jet or surface during the treatment are measured. On the basis of the measured optical emissions, characteristics of the plasma jet or flame jet are determined.

In the example shown, three collimator optics are used to record the optical emissions 5.1 . 5.2 . 5.3 which are directed to different locations of the flame, the plasma or the surface and optical data in respective optical fibers 6.1 . 6.2 . 6.3 inject. The spectrometer 3 has a corresponding number of channels. There may be a different number of channels fiber optic cables 6.1 to 6.n and collimator optics 5.1 to 5.n be provided.

• – Lage und zeitlicher Verlauf mindestens einer Spektrallinie und/oder eines Spektralbands,
• – Vorkommen bestimmter Partikel des Brennergases oder Arbeitsgases,
• – Vorkommen bestimmter Partikel, die sich aus dem Precursor bilden,
• – Partikeldichte,
• – zeitliche Variation der Partikeldichte,
• – Struktur einer Molekülstrahlung, insbesondere Molekülemission, Molekülbanden.

The characteristics determined from the optical emissions can be:

• Position and time course of at least one spectral line and / or spectral band,
• - occurrence of certain particles of the burner gas or working gas,
• - occurrence of certain particles which form from the precursor,
• - particle density,
• Temporal variation of the particle density,
• Structure of molecular radiation, in particular molecular emission, molecular bands.

From a ratio of vibrational bands of a molecular transition, a vibration temperature of a molecule is determined, wherein a rotational temperature of a molecule is determined from a ratio of rotational lines. A total radiation of the molecule is determined from the vibration temperature and from the rotation temperature, wherein a number of the molecules is determined from the total radiation.

In the measured optical emissions, a self-absorption of radiation lines is preferably determined and taken into account in the determination of the characteristics.

By means of actinometry, a particle density ratio of the different species can be determined via an intensity ratio of spectral lines of different species.

The characteristics are preferably determined by means of a plasma model.

The presence of certain particles can occur from so-called peaks occurring in the spectrum, ie. H. local maxima are determined with steep slopes. The particle density can be derived from an intensity value of the respective peak. The temporal variation of the particle density can be determined by analyzing the changes in the intensity values of the peaks in time-sequential spectra.

The determined characteristics become the regulation 4 supplied, for example via analog / digital outputs.

• – Plasmaleistung,
• – Brennerleistung,
• – Kontaktzeit des Plasmastrahls oder Flammstrahls mit der Oberfläche,
• – Zusammensetzung von Brenngas oder Arbeitsgas,
• – Durchsatz von Brenngas oder Arbeitsgas,
• – Durchsatz des Precursors
• – Verhältnis der Durchsätze
• – Mischungsverhältnis des Brenngases mit Luft oder Sauerstoff

The control controls and / or regulates parameters of the surface treatment on the basis of the determined characteristics. These parameters can be, for example:

• - plasma power,
• - Burner power,
• Contact time of the plasma jet or flame jet with the surface,
• - composition of fuel gas or working gas,
• Throughput of fuel gas or working gas,
• - Throughput of the precursor
• - Ratio of throughputs
• - Mixing ratio of the fuel gas with air or oxygen

Preferably, the optical emissions are measured and analyzed in real time, so that the regulation of the process parameters can be done in real time.

Furthermore, a computer system is used for process monitoring and process control 7 with the spectrometer 3 connected, for example via a USB interface or an IEEE 1394 interface (Firewire).

The treatment of the surface may consist in an activation or in a coating of the surface by means of the plasma jet or flame jet.

In a coating, a so-called CVD method (chemical vapor deposition), at least one precursor material is supplied to the working gas and / or the plasma jet or the fuel gas and / or the flame jet and reacted in the plasma jet or flame jet. Subsequently, at least one reaction product of at least one of the precursors is deposited on the surface and / or on at least one layer arranged on the surface.

Likewise, initially only one activation and then a coating or an activation following a coating can be provided.

By suitable choice of the process parameters and the precursors used, for example, the following properties of the surface of the substrate are selectively changeable: scratch resistance, self-healing ability, barrier behavior, reflection behavior, transmission behavior, refractive index, transparency, light scattering, electrical conductivity, antibacterial behavior, friction, adhesion, hydrophilicity, hydrophobicity, Oleophobicity, surface tension, surface energy, anti-corrosive effect, dirt-repellent effect, self-cleaning ability, photocatalytic behavior, anti-stress behavior, wear behavior, chemical resistance, biocidal behavior, biocompatible behavior, electrostatic behavior, electrochromic activity, photochromic activity, gasochromic activity.

The generation of the plasma can take place in a free-jet plasma source or by means of dielectrically impeded discharge.

The precursor is preferably introduced in the gaseous state or as an aerosol into the working gas or the plasma stream. Liquid or solid, in particular pulverulent precursors can also be used, but are preferably converted into the gaseous state before introduction, for example by evaporation. Likewise, the precursor can first be introduced into a carrier gas, entrained therefrom, and introduced together with it into the working gas or the plasma stream.

The deposited layer preferably comprises at least one of silicon, silver, gold, copper, iron, nickel, cobalt, selenium, tin, aluminum, titanium, zinc, zirconium, tantalum, chromium, manganese, molybdenum, tungsten, bismuth, germanium, niobium , Vanadium, gallium, indium, magnesium, calcium, strontium, barium, lithium, lanthanides, carbon, oxygen, nitrogen, sulfur, boron, phosphorus, fluorine, halogens and hydrogen. In particular, the layers contain oxidic or / and nitridic Compounds of silicon, titanium, tin, aluminum, zinc, tungsten and zirconium.

The precursor used is preferably an organosilicon and / or an organo-titanium compound, for example hexamethyldisiloxane, tetramethylsilane, tetramethoxysilane, tetraethoxysilane, titanium tetraisopropylate or titanium tetraisobutylate.

In a preferred embodiment, a first layer having a barrier effect and then at least one further layer as a functional layer, preferably having at least one of the abovementioned properties, are deposited on a lime-sodium-silicate glass (standard float glass). The barrier layer, on the one hand, reduces the passage of water, carbon dioxide and other substances from the atmosphere to the surface of the glass substrate. On the other hand, migration of sodium in particular from the glass into the functional layer is reduced so that its activity is retained. The functional layer can be applied to the still hot or already cooled glass by the same method or by another coating method.

As the working gas, air, steam or other gas can be used, for example, oxygen, nitrogen, noble gases, hydrogen, carbon dioxide, gaseous hydrocarbons or a mixture thereof.

For example, surfaces of a plastic, glass, metal, ceramic, glass ceramic, wood, paper or textile can be coated or activated.

LIST OF REFERENCE NUMBERS

1

Arrangement for the treatment of a surface

2

treatment facility

3

spectrometer

4

regulation

5.1 to 5.n

collimator optics

6.1 to 6.n

optical fiber

7

computer system

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• US 2005/0068519 A1 [0005]

Cited non-patent literature

• E. Schmachtenberg, A. Hegenbart, "Monitoring Plasma Processes by OES", Vacuum in Research and Practice 17 (2005), No. 6, 318-323 [0004]

Claims (11)

Method for monitoring a plasma or a flame at atmospheric pressure, using a spectrometer ( 3 ) optical emissions of the plasma or the flame are determined on the basis of which the characteristics of the plasma or the flame are determined, characterized in that an intensity-calibrated spectrometer is used. A method according to claim 1, characterized in that in the measured optical emissions of at least one of the following characteristics is determined: - course of at least one spectral band, - occurrence of certain particles, - particle density, - temporal variation of the particle density - Structure of molecular radiation. A method according to claim 2, characterized in that a vibration temperature of a molecule is determined from a ratio of vibrational bands of a molecular transition, wherein a rotational temperature of a molecule is determined from a ratio of rotational lines, wherein a total radiation of the molecule from the vibration temperature and from the rotational temperature is determined in which a number of the molecules are determined from the total radiation. Method according to one of the preceding claims, characterized in that a self-absorption of radiation lines is determined in the measured optical emissions and taken into account in the determination of the characteristics. Method according to one of the preceding claims, characterized in that a particle density ratio of the different species is determined by means of actinometry via an intensity ratio of spectral lines and / or molecular bands of different species. Method according to one of the preceding claims, characterized in that the characteristics are determined by means of a plasma model. Method according to one of the preceding claims, characterized in that based on the characteristics of a control loop at least one of the parameters plasma power, burner power, contact time, composition of fuel gas or working gas, flow rate of fuel gas or working gas, flow rate of a precursor is controlled and / or regulated. A method according to claim 7, characterized in that a P, PI, PD or PID control is used. Method according to one of the preceding claims, characterized in that the optical emissions measured at at least two different locations of the plasma jet or flame jet and the spectrometer ( 3 ) are supplied in at least two channels. Method according to one of the preceding claims, characterized in that the optical emissions of the spectrometer ( 3 ) via at least one optical waveguide ( 6.1 to 6.n ). Method according to Claim 9, characterized in that the optical waveguide ( 6.1 to 6.n ) for coupling the optical emissions with a collimator optics ( 5.1 to 5.n ).

Images