Pair of electrodes for DBD plasma process

Abstract

The present invention concerns a device (10) for the surface treatment of a substrate (1) by dielectric barrier discharge that enables the generation of a cold filamentary plasma at atmospheric pressure, comprising a reaction chamber, in which are positioned means for supporting and/or moving the substrate (2) and at least two electrodes (3, 4) arranged in parallel on either side of the means for supporting and/or moving the substrate (2), of which one electrode (3) is intended to be brought to high voltage and a counter-electrode (4) to be earthed. It is characterised in that the counter-electrode (4) has a width (l.sub.ce) and a length (L.sub.ce) that are respectively smaller than the width (l.sub.e) and the length (L.sub.e) of the electrode (3), and in that the counter-electrode (4) is positioned so that it is enclosed in an orthogonal projection (5) of the electrode (3) on a plane containing the counter-electrode (4). The invention also concerns a surface treatment process, in particular for layer deposition, that calls for such a device.

Claims

1. A device for the surface treatment of a substrate by dielectric barrier discharge that enables the generation of a cold filamentary plasma at atmospheric pressure, comprising: a reaction chamber; rollers in the chamber for supporting and/or moving the substrate; and at least two electrodes arranged in parallel on either side of the substrate, of which a first electrode is connected to a high voltage power supply and a second electrode is a counter-electrode that is earthed, wherein the counter-electrode has a width (l.sub.ce) and a length (L.sub.ce) that are respectively smaller than a width (l.sub.e) and a length (L.sub.e) of the first electrode, and in that the counter-electrode is positioned so that it is enclosed in an orthogonal projection of the first electrode on a plane containing the counter-electrode, wherein the device does not include any dielectric barrier and that allows an insulating substrate that itself alone forms the dielectric barrier to pass.

2. The device according to claim 1, wherein the counter-electrode is positioned so that it is enclosed in a centered manner in the orthogonal projection of the first electrode on the plane containing the counter-electrode.

3. The device according to claim 1, wherein the width of the counter-electrode (l.sub.ce) is smaller than that of the first electrode (l.sub.e) by at least 10 mm.

4. The device according to claim 1, wherein the length of the counter-electrode (L.sub.ce) is smaller than that of the first electrode (L.sub.e) by at least 10 mm.

5. The device according to claim 1, wherein a distance between the first electrode and the substrate is greater than 2 mm.

6. A process for the surface treatment of a substrate, which comprises the following: providing a device according to claim 1; feeding or passing a substrate into the reaction chamber; putting into operation a power supply that is stabilised in amplitude and frequency comprising a very high-voltage (VHV) and high-frequency (HF) transformer comprising a secondary circuit, the at least two electrodes being connected to the terminals thereof; generating in the secondary circuit of this transformer a stabilised high-frequency electric voltage of such a value that it causes the generation of a filamentary plasma in the reaction chamber between the at least two electrodes; feeding into the reaction chamber a mixture, the composition of which is such that on contact with the plasma, it breaks down and generates substances able to react with the surface of the substrate; keeping the substrate in the chamber for a sufficient period of time to achieve the desired treatment on at least one of its faces.

7. The process according to claim 6, which is a process for depositing a layer onto a substrate.

8. The process according to claim 7, wherein the mixture fed into the reaction chamber comprises an organic precursor of silicon, and that it generates a layer of SiO.sub.2.

9. A glass sheet coated with a layer of SiO.sub.2 deposited by the process according to claim 8.

10. The device according to claim 3, wherein the width of the counter-electrode (l.sub.ce) is smaller than that of the first electrode (l.sub.e) by at least 20 mm.

11. The device according to claim 4, wherein the length of the counter-electrode (L.sub.ce) is smaller than that of the first electrode (L.sub.e) by at least 20 mm.

12. The device according to claim 5, wherein the distance between the first electrode and the substrate is greater than 3 mm.

13. The process according to claim 8, wherein organic precursor of silicon is HMDSO.

14. A device for the surface treatment of a dielectric substrate by dielectric barrier discharge, comprising: a reaction chamber; a first electrode connected to a power supply; and a counter electrode that is earthed, wherein the first electrode and the counter electrode are parallel to one another and are separated by a space sufficient for passage of the substrate, and wherein the counter-electrode has a width (l.sub.ce) and a length (L.sub.ce) that are respectively smaller than a width (l.sub.e) and a length (L.sub.e) of the first electrode, wherein the device does not include any dielectric barrier other than the substrate, and wherein during operation the device is configured to generate a cold filamentary plasma at atmospheric pressure.

15. The device according to claim 14, wherein the counter-electrode is positioned so that it is enclosed in an orthogonal projection of the first electrode on a plane containing the counter-electrode.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) These aspects as well as other aspects of the invention will be clarified in the detailed description of particular embodiments of the invention with reference to the drawings of the figures, wherein:

(2) FIG. 1 is a schematic front view of an installation for depositing layers on a substrate according to the invention, in which the insulating substrate serves as dielectric barrier;

(3) FIG. 2 is a schematic front view of an installation for depositing layers on a substrate according to the invention, in which the dielectric barrier is adjacent to the counter-electrode;

(4) FIG. 3 is a schematic side view of an installation for depositing layers on a substrate according to example 1 of the invention, in which the insulating substrate serves as dielectric barrier.

(5) The figures are not drawn to scale. In general, similar elements are represented by similar references in the figures.

DESCRIPTION OF EMBODIMENTS

(6) FIGS. 1 to 3 show devices for continuous layer deposition 10 on a glass substrate 1 by dielectric barrier discharge. The glass substrate 1 passes inside a reaction chamber (not shown) in the direction marked by the arrow.

(7) In FIGS. 1 and 3 the substrate 1 is insulating and serves as dielectric barrier between the electrode or electrodes 3, 3a, 3b and the counter-electrode or counter-electrodes 4, 4a, 4b.

(8) In FIG. 2 a plate of insulating material (e.g. made of aluminium) 6 fixed to the counter-electrode 4 serves as dielectric barrier between the electrode 3 and the counter-electrode 4.

(9) The width (l.sub.ce) and the length (L.sub.ce) of the counter-electrodes 4, 4a, 4b are smaller respectively than the width (l.sub.e) and the length (L.sub.e) of the electrodes 3, 3a, 3b and the counter-electrode 4 is enclosed in a centred manner in the orthogonal projection 5 of the electrode 3 on the plane containing the counter-electrode 4.

(10) FIG. 3 shows a layer 7 in the course of being deposited onto the substrate 1 by reaction of a reactive mixture fed in the direction of arrow 8 in contact with the plasma that is also shown schematically.

EXAMPLE 1

(11) In this example the deposition of a layer of SiO.sub.2 onto glass was conducted in dynamic mode (i.e. continuously on the substrate during passage) using an installation as shown in FIG. 3 equipped with two electrode/counter-electrode pairs according to the invention for a treatment area of 240 cm.sup.2, wherein each electrode has a width of 12 cm and a length of 10 cm.

(12) The distance between the glass and the counter-electrodes is fixed at 2 mm and the distance between the glass and the electrodes is fixed at 4 mm. The electrodes extend 20 mm beyond the counter-electrodes over their entire periphery. Before treatment, the glass is at a temperature of 210 C. and has a passage speed of 10 m/min.

(13) The reactive gas mixture is injected between the two high-voltage electrodes from above through an injection slot extending over a length of 10 cm parallel to the length of the electrodes. Two evacuations means for gases that have reacted are placed in front of the first electrode/counter-electrode pair and behind the second electrode/counter-electrode pair. The reactive gas mixture used is composed of oxygen (to eliminate the carbon) and nitrogen (as carrier gas) and HMDSO (Si-based precursor) according to the following flux values: O.sub.2: 10-80 Nl/min; N.sub.2: 200-500 Nl/min; HMDSO: 40-100 g/h. The extraction is fixed at 18 Nm.sup.3/h.

(14) A high-frequency high voltage (128 KHz) is respectively applied between the electrodes 3a, 3b and the counter-electrodes 4a, 4b. The applied voltage is sinusoidal, the counter-electrode is earthed and the high-voltage electrode is alternately negative and positive. The potential difference between the electrodes 3a, 3b and the respective counter-electrodes 4a, 4b causes the generation of a plasma with a discharge power of about 5-20 kW.

(15) This process leads to a high deposition rate: 1500 nm.Math.m/min, i.e. a thickness of SiO.sub.2 of about 150 nm with a passage rate of the substrate of 10 m/min in the following conditions: 300 Nl/min N.sub.2, 40 Nl/min O.sub.2, 60 g/h HMDSO, 15 kW. The thickness of the layer is uniform over its entire surface and the layer is of good quality with little haze (less than 0.6) and a carbon content close to 0.

COMPARATIVE EXAMPLE 1

Not in Accordance with the Invention

(16) In this example the deposition of a layer of SiO.sub.2 onto glass was conducted as in example 1, except that: the length and width of the electrodes and counter-electrodes were respectively identical, i.e. a width of 12 cm and a length of 10 cm, and the distance between the glass and the counter-electrodes was fixed at 0.5 mm and the distance between the glass and the electrodes was fixed at 2 mm.

(17) Both deposition rate of SiO.sub.2 on glass and contamination (soiling) were compared between example 1 and comparative example 1. We have measured that around 40% of the precursor actually reacts for forming either the coating layer on glass or the soiling on the electrode. In comparative example 1, i.e. in a prior art installation, we have measured that around 50% of these 40% which actually react, are deposited as SiO.sub.2 on glass and around 50% as soiling. In example 1, i.e. an example according to the present invention, around 80% of these 40% are deposited as SiO.sub.2 on glass and 20% as soiling. This shows the advantage of the present invention which allows a better deposition rate and a reduction in contamination (contamination may for example lead to coating layer having an increased haze defect).

(18) It will be evident to a person skilled in the art that the present invention is not limited to the examples illustrated and described above.