SI23626A - Method for dynamically controlling the density neutral atoms with an active element in a plasma vacuum chamber and a device for treatment of solid materials by using the present method - Google Patents

Abstract

The subject invention is a method for dynamically controlling the density neutral atoms with an active element in a plasma vacuum chamber (4) and a device for treatment of solid materials by using the present method. Control system through measurement and record ingdensity of neutral atoms of oxygen, nitrogen or hydrogen admission input data (17 and 18), under which generates control signals for adjusting and controlling the position of the active element (20), with a high coefficient of a heterogeneous surface recombination of oxygen atoms, nitrogen or hydrogen, with the corresponding engine (21). The system includes the density of neutral oxygen atoms,nitrogen or hydrogen through various methods such as catalytic probe (22), optical emission spectroscopy (23 and 24), optical absorption spectroscopy and titration. This kind of control enables dynamic control of the density of neutral atoms in around the treated sample, which is independent of the workpiece other discharge parameters, and are actively changing the density neutral atoms in the presence or absence of a workpiece independently of the other discharge parameters.

Description

METHOD FOR DYNAMIC DENSITY CONTROL OF NEUTRAL ATOMS IN THE Plasma Vacuum Chamber and Device for the Treatment of Solid Materials by this Method

The subject of the invention are methods for dynamically controlling the density of neutral atoms with an active element in a plasma vacuum chamber and a device for treating solid materials using the method described. The control system, through the measurements and recording of the density of neutral oxygen, nitrogen or hydrogen atoms, receives the input data on the basis of which it generates control signals for adjusting or controlling the position of the active element, with a large coefficient for heterogeneous surface recombination of oxygen, nitrogen or hydrogen atoms, with a suitable engine. The system captures the density of neutral oxygen, nitrogen or hydrogen atoms by various methods such as catalytic probe, optical emission spectroscopy, optical absorption spectroscopy and titration. This control enables the dynamic control of the density of neutral atoms in the vicinity of the treated sample (hereinafter: the workpiece) independently of the discharge parameters, and the active change of the density of the neutral atoms in the presence or absence of the workpiece independently of the discharge parameters.

View the problem

Today, weakly ionized, highly dissociated gas plasma is increasingly used to treat a wide variety of materials. Plasma treatment of materials is characterized by exceptional quality, stability and ecological integrity. Very often oxygen, nitrogen or hydrogen plasma is used in various technologies, especially as an alternative to environmentally unfriendly wet chemical processes. It is used primarily for plasma purification, activation of organic materials, selective etching of polymer composites, cold ashing of biological samples, and in medical applications for the sterilization of sensitive materials and for the synthesis of nano materials.

Plasma is a partially ionized gas. The basic parameters of the plasma are: electron temperature or energy distribution function of electrons, density of neutral atoms, density of neutral molecules in excited states, with emphasis on metastable states, and density of charged heavy particles or ions or positively and negatively charged molecules and atoms.

Thermal equilibrium plasmas are known where a sufficient level of ionization is obtained by heating the gas. In such plasmas, the concentrations of electrons, ions, neutral atoms and molecules and the kinetic energy of the thermal motion of the particles are uniquely temperature dependent. The problem is the required temperature, because the gas needs to be heated above 10 ⁴ K. Therefore, we use laboratory-generated thermally nonequilibrium plasmas, where the ionization of atoms or molecules is achieved, among other things, by gas discharge. There are various types of discharges such as hot cathode direct current, high frequency radio frequency or RF and microwave or MV and combined. In the case of a charge with a strong external electric field in the gas, the free electrons, which are in each case present in the gas at low densities, are accelerated to an energy suitable for ionization of atoms or molecules. The external electric field may be DC or AC. It only matters that the electrons are accelerated to a sufficiently high energy that allows ionization. The transmission of energy by a high-frequency electric field is much more efficient for light electrons than heavy ions, so in plasma generated by high-frequency discharge, the electron temperature or thermal energy of the electrons is much higher than the ionic energy.

When processing materials, it is very important to know the density of plasma particles in the workpiece environment, since the method and intensity of the treatment depend strongly on the particle flux density on the workpiece surface. In addition, concentration gradients of different plasma particles may exist in the treatment chamber, so it does not matter where our workpiece is located. It is also often the case that the workpiece represents a strong sink of plasma particles, so that the particle flux density to the surface also depends on the size and material characteristics of the workpiece.

Of all the particles in the weakly ionized plasma, precisely neutral atoms have the most important influence on the physical and chemical reactions on the surface of the material being treated. Ions have higher potential energy than neutral atoms and are therefore more chemically active. If you wanted a substantial

-3 fraction of ionized atoms, a thermal equilibrium or hot plasma would be required for the ionization to reach a sufficient level. On the other hand, in cold or thermally nonequilibrium plasmas, there is a significantly higher proportion of neutral atoms, which are usually more stable than ions. Neutral atoms are recombined upon contact with a wall with a probability determined by the coefficient for heterogeneous surface recombination of atoms - which may be very low - while the ions on the wall are definitely recombined with a probability close to 1.

Thus, the density of oxygen atoms in the plasma system with the workpiece depends precisely on the properties of the sample being treated and on the discharge parameters. These parameters are power, frequency and phase of the generator, vacuum level, gas inlet pressure, reactor chamber design, etc.

The major problem is the precise knowledge and conservation of the density of neutral atoms in the workpiece environment independently of the discharge parameters, since this often represents a changing particle sink, and the active change of the density of neutral atoms in the presence or absence of the workpiece independently of the discharge parameters.

The state of the art

Thermal disequilibrium plasma is utilized in many ways, for both academic and industrial purposes. A device for generating plasma with a density of neutral atoms is described in patent SI21903A. Laboratory plasma reactors are used in the selective plasma etching of polymer composite materials, especially semiconductor devices, for the CVD (Chemical Vapor Deposition) method, for surface cleaning, and in medical applications, the use of plasma is important in the sterilization of sensitive materials. Plasma is also present in the latest technologies, such as. synthesis of nanomaterials.

Some of the above methods use neutral atoms to process, so knowing and actively controlling the density of neutral atoms is of the utmost importance, as it improves the efficiency and quality of the machining processes themselves.

There are numerous methods for controlling the density of ions, electrons, and atoms, most of all providing uniform plasma density in the area of the sample being processed. Very common

-4 is the use of two or three electrode systems, where at least one electrode is used for DC bias on the workpiece and the rest for plasma excitation. Each of the electrodes is connected to its source via a matching member and through a feedback loop connected to a control system that controls either the input power or voltage at the electrodes or the frequency of the RF power source via the control signals. Such methods are mainly used to control electron temperature, ion density, or uniform plasma density. The latter are achieved by varying the discharge parameters of the plasma system, as described in US6174450B1, US2004060660A1 and US2009126634A1. However, the problem of active control of neutral atoms remains independent of the discharge parameters.

Also, the methods described in US5266364A, US6383554B1, US2003141821A1, US2003155079A1 and US2010224321A1 adjust or maintain the density of atoms, electrons and ions, and in some cases the density of plasma, by varying the discharge parameters. The aforementioned patents differ from one another in the way they capture plasma parameters and how the local particle distributions are controlled. Individual methods perform regulation based on capturing magnetic flux measurements inside the plasma US5266364A, detecting plasma density using a US6383554B1 heterodyne millimeter wave interferometer, relative to the measurement of current between two electrodes in plasma US2003141821A1, quantitative and spatial control of the gas flow into the plasma US795 RF1315A5 Phase differences between the plasma excitation radio frequency source and the radio frequency source that allows bias on the substrate US2010224321A1. In the described procedures, the main disadvantage again is the control of the particle density in the plasma system by varying the discharge parameters.

Some methods are a little more abstract, such as control of particles in the plasma system by injecting neutral or plasma sound waves, as described in US5350454A. The method allows, through the densities and dilutions of neutral or plasma sound waves, to control the displacement of larger plasma particles, but does not allow the exact density of neutral atoms to be changed.

-5Description of the invention and embodiment

The invention comprises a method for dynamically controlling the density of neutral atoms in a plasma vacuum chamber and a device for treating solid materials using this method. Atoms are monitored with a special active element. The method is based on a feedback control system for motorized position control of the active element, with a large coefficient for heterogeneous surface recombination of oxygen, nitrogen or hydrogen atoms in the main plasma tube. The control of this active element allows dynamic control of the density of neutral atoms in the workpiece environment independently of the discharge parameters, and the change of the density of the neutral atoms in the presence or absence of the workpiece independently of the discharge parameters.

The method for controlling the density of neutral atoms and the device for the treatment of solid materials are described in more detail by means of the figures illustrating FIG. 1 is a schematic view of the vacuum portion of the plasma system; 2 is a schematic view of the electrical or excitatory part of the plasma system, FIG. 3 is a schematic view of the feedback control system of FIG. 4 is a schematic view of an embodiment in a weakly ionized oxygen plasma with an active element with a high coefficient for the heterogeneous surface recombination of oxygen, nitrogen or hydrogen atoms, FIG. 5 is a measurement of the density of neutral oxygen atoms at a pressure of 90 Pa, different excitation powers, and different positions of the active element with a large coefficient for heterogeneous surface recombination of oxygen, nitrogen or hydrogen atoms, FIG. 6 measurements of oxygen plasma dissociation at 90 Pa pressure, different excitation powers and different positions of the active element with a large coefficient for heterogeneous surface recombination of oxygen, nitrogen or hydrogen atoms.

The schematic diagram of the vacuum part of the plasma system is shown in Figure 1. It consists of a precision gas inlet metering valve 2 from cylinder 1, a discharge tube 4, a pressure gauge 3, an air intake valve 7, and a vacuum pump 6 and associated valve

5.

Figure 2 shows the electrical or excitation part of the device, which consists of a high-frequency radio frequency power generator 8, which is connected via a coaxial cable 9 to the harmonizing member 10. The harmonizing member is via two guiding members 11 and 12, which measure the input power into the discharge tube 4 and reflected or reflected power from the antenna coupled to a radio frequency coil for excitation of plasma 13. Plasma excited by the transmission of electromagnetic waves through a radio frequency coil is called inductively coupled plasma. The tuning link consists of two high-voltage, high-frequency, variable capacitors that serve to adjust the impedance of the antenna-plasma system to the impedance of the remaining 50 Ω circuit.

Figure 3 shows a schematic of a plasma system with an added control system. The whole system consists of the main discharge tube 4 and one or two side pipes 14 and 15. The electrical part is a radio-frequency coil 13, which is excited by a high-frequency RF power generator 8. The latter is connected to the harmonizing article 10 via a coaxial cable 9. it captures data at the inputs and dynamically adjusts the output control signal 19 through the feedback signals 17 and 18 through which, through the motorized interface 21, it controls the active element 20 with a large coefficient for heterogeneous surface recombination of oxygen, nitrogen or hydrogen atoms. The data is captured either with a catalytic probe 22 or with an optical fiber 23 connected to the spectrometer 24. Any combination of these data acquisition methods is also possible.

The control method described here directly controls the density of neutral atoms in the presence or absence of a workpiece that represents a particle sink, independent of the discharge parameters.

In the embodiment of Figure 4, an active element 20 with a large coefficient for heterogeneous surface recombination of oxygen, nitrogen or hydrogen atoms was used, and its position was

- We changed manually. The active element can be any product with a high coefficient for the heterogeneous surface recombination of oxygen, nitrogen or hydrogen atoms, and primarily a bundle consisting of a series of ordered wires with a nanostructured surface. The wires are typically arranged longitudinally according to the orientation of the active element. The nanostructured surface typically consists of nanowires oriented perpendicularly to the geometric surface of the wires. Such a configuration provides a high likelihood of heterogeneous surface recombination of oxygen, nitrogen or hydrogen atoms, while minimizing the resistance to gas flow in their surroundings. The length of the active element with a large coefficient for heterogeneous surface recombination of oxygen, nitrogen or hydrogen atoms was 40 cm, of which a maximum of 13 cm was exposed to plasma. Oxygen plasma was used, and the plasma reactor had a main discharge tube 4 with a length of 80 cm and a diameter of 4 cm and a side tube 14 with a length of 10 cm and a diameter of 1.5 cm. Plasma was created with a radio frequency coil 13, with six sheaths wrapped around the main tube, 5.5 cm in length. The radio frequency coil was connected to a high-frequency RF power generator 8 via co-ordination article 10 via coaxial cable 9. Data on the density of neutral atoms were captured with a nickel optical catalytic probe 22 and an optical fiber 23 coupled to an Avantes 3648 24 spectrometer for optical emission analysis of plasma spectroscopy. The density of individual plasma particles was monitored and recorded via computer 25. With this embodiment, we demonstrated and demonstrated the ability to control the density of neutral atoms independently of discharge parameters by varying the position of the active element by a large coefficient for heterogeneous surface recombination of oxygen, nitrogen or hydrogen atoms.

Density measurements of neutral atoms and dissociation measurements performed using the described embodiment in oxygen plasma are shown in Figure 5 and Figure 6. Measurements were made at a pressure of 90 Pa, with six different powers between 0 and 600 W. The position of the active element, with a large coefficient for heterogeneous surface recombination of oxygen, nitrogen or hydrogen atoms, we varied according to the position of the nickel optical catalytic probe and ranged between 4 cm to the right of the tip of the probe and 7.5 cm to the left of the tip of the probe.

The method for dynamically controlling the density of neutral oxygen, nitrogen or hydrogen atoms in a plasma vacuum chamber according to the invention is therefore characterized in that in the vacuum chamber the density of the atoms is controlled by the position of a moving active element with a large

-8coefficient for heterogeneous surface recombination of oxygen, nitrogen or hydrogen atoms. The moving element is connected to a control unit that controls the position of the moving active element via a density meter of oxygen, nitrogen or hydrogen atoms. The moving element can be motorized. The coefficient for heterogeneous surface recombination of the active element is greater than 0.001. An atomic density meter is a catalytic probe or optical spectrometer. A device for treating solid materials with neutral oxygen, nitrogen or hydrogen atoms according to the invention, characterized in that it contains a vacuum vessel, a source of oxygen, nitrogen or hydrogen atoms, a meter for the density of oxygen, nitrogen or hydrogen atoms and a moving active element with a high coefficient for heterogeneous surface recombination of oxygen, nitrogen or hydrogen atoms. An active element with a high recombination coefficient for heterogeneous surface recombination of oxygen, nitrogen or hydrogen atoms, permitting a varying flux density of oxygen, nitrogen or hydrogen atoms between lxl0 ¹⁸ and lxl0 ²⁵ m ' ² s' ¹ , preferably between lxl0 ¹⁹ and 5xl0 ²³ m ' ² s' ¹ .

Claims (6)

PATENT APPLICATIONS A method for dynamically controlling the density of neutral oxygen, nitrogen or hydrogen atoms in a plasma vacuum chamber, characterized in that the density of the atoms in the vacuum chamber is controlled by the position of a moving active element with a large coefficient for heterogeneous surface recombination of oxygen, nitrogen or hydrogen atoms. Method according to claim 1, characterized in that the moving element is connected to a control unit which controls the position of the moving active element via a meter of oxygen, nitrogen or hydrogen atoms. Method according to claim 2, characterized in that the moving active element is motorized. Method according to claim 1, characterized in that the coefficient for heterogeneous surface recombination of the active element is greater than 0.001. 5. The method of claim 2, wherein the atomic density meter is a catalytic probe or optical spectrometer. 6. A device for treating solid materials with neutral oxygen, nitrogen or hydrogen atoms, characterized in that it contains a vacuum vessel, a source of oxygen, nitrogen or hydrogen atoms, a meter for the density of oxygen, nitrogen or hydrogen atoms and a moving active element with a high coefficient for heterogeneous surface recombination of oxygen, nitrogen or hydrogen atoms. -107. A device for the treatment of solid materials with neutral oxygen, nitrogen or hydrogen atoms according to claim 6, characterized in that the active element, with a large recombination coefficient for heterogeneous surface recombination of oxygen, nitrogen or hydrogen atoms, allows a variable current density of oxygen, nitrogen or nitrogen atoms. hydrogen between lxlO ¹⁸ and lxl0 ²⁵ m ' ² s' ¹ , preferably between 1 χ 10 ¹⁹ and 5 χ 10 ²³ m * ² s' *.