DEVICE FOR IMPLANTING IONS INTO THE SURFACE OF AN OBJECT TO BE TREATED

Description

Technical field of the invention

[0001] The present invention relates to an installation for implementing an ion implantation process in the surface of an object to be treated, particularly, but not exclusively, an object made of synthetic sapphire, using an ion beam. This installation aims to increase the number of ions that can be implanted in the surface of the object to be treated and the depth to which these ions can penetrate the object. The process can be applied equally well to a solid object or to a powdered object composed of metallic or ceramic particles. Technological background of the invention

[0002] Ion implantation processes involve bombarding the surface of the object to be treated, for example, with a source of single- or multi-charged ions of the electron cyclotron resonance type. Such a setup is also known by its English name, Electron Cyclotron Resonance, or ECR.

[0003] An electron cyclotron resonance (ECR) ion source uses the cyclotron resonance of electrons to create a plasma. Microwaves are injected into a volume of low-pressure gas to be ionized, at a frequency corresponding to the electron cyclotron resonance defined by a magnetic field applied to a region within the gas volume. The microwaves heat the free electrons present in the gas. These free electrons, under the influence of thermal agitation, collide with atoms or molecules, causing their ionization. The ions produced depend on the type of gas used. This gas can be pure or a compound. It can also be a vapor obtained from a solid or liquid material.The ECR ion source is capable of producing either simply charged ions, i.e. ions whose degree of ionization is equal to 1, or multicharged ions, i.e. ions whose degree of ionization is greater than 1.

[0004] As an example, a multicharged ion source of the electron cyclotron resonance (ECR) type is illustrated on the figure 1 attached to this patent application. Very schematically, a multicharged ion source ECR, designated as a whole by the general numerical reference 1, comprises an injection stage 2 into which a volume 4 of gas to be ionized and a microwave 6 are introduced, a magnetic confinement stage 8 in which a plasma 10 is created, and an extraction stage 12 which allows the ions from the plasma 10 to be extracted and accelerated by means of an anode 14a and a cathode 14b between which a high voltage is applied.

[0005] The appearance of the ion beam 16 produced at the output of the ECR ion source 1 is illustrated in the figure 2 attached to this patent application.

[0006] One of the problems encountered with the ion implantation process briefly described above is that as ions penetrate the surface of the object being treated, they create an electrostatic potential barrier that tends to slow down subsequent ions, thus limiting the penetration depth of these ions beneath the surface of the object. Indeed, the more ions are implanted on the surface of the object, the stronger the electrostatic field they create, and the more the surface of the object tends to repel the ions arriving from the ECR ion source, which poses homogeneity problems in the ion implantation process.If the object being treated is electrically conductive, this problem is less pronounced because at least some of the free or weakly bound electrons in the material from which the object is made can recombine with the implanted ions. However, if the object is made of a non-conductive material, the recombination phenomenon between electrons and mono- or multi-charged ions does not occur, and ensuring a homogeneous distribution of ions across the surface of the object is practically impossible.

[0007] Documents JPH01 119668 A and US 2017 / 0207063 A1 rely on the appearance, in the surface of the object to be treated, of an electric current induced by the ultraviolet radiation by means of which this surface is illuminated, to evacuate the excess charges that have accumulated in the object to be treated.

[0008] Document WO2016 / 06779 also describes a method for ion implantation and ion-implanted glass substrates.

[0009] US2007 / 187615 describes a charge control system comprising a tray whose surface is configured to receive a wafer, and a charge monitor arranged relative to the tray so that an ion beam simultaneously strikes a portion of the charge monitor and a portion of the wafer.

[0010] US5522935 describes a device for plasma-assisted chemical vapor deposition for the fabrication of a semiconductor device.

[0011] The document JP07014761 describes a device capable of neutralizing charged bodies such as treated substrates for semiconductor devices. Summary of the invention

[0012] The present invention aims to solve the problems mentioned above and others by providing an installation for implementing a process of implanting ions on the surface of an object to be treated, in particular ensuring a homogeneous distribution of these ions on the surface of the object.

[0013] For this purpose, the present invention relates to an installation for implementing a process of ion implantation on a surface of an object to be treated according to claim 1 annexed to this patent application.

[0014] Thanks to these features, the present invention provides an installation for implementing a surface treatment process for an object in which the object to be treated, placed in a vacuum chamber, is illuminated by means of an ultraviolet light source while simultaneously being bombarded by an ion beam. This installation thus ensures a more homogeneous distribution of ions on the surface of the object being treated, as well as allowing these ions to penetrate deeper beneath the surface of the object.It is understood that, despite the relatively high vacuum within the vacuum chamber, atoms and molecules remain in the chamber's atmosphere. Photons from ultraviolet radiation will strip electrons from these atoms and molecules, which will be attracted by the positive potential of the object's surface and will recombine with ions present on the object's surface, thus neutralizing the electrostatic charges. As a result of this recombination between free electrons in the vacuum chamber and ions implanted on the object's surface, the electrostatic potential of the object can be maintained at sufficiently low values ​​to minimize interference with the implantation of new ions and allow them to penetrate deep enough beneath the surface of the object.

[0015] According to one embodiment of the invention, the atmospheric pressure inside the vacuum chamber is between 10⁴ and 10⁻⁴ Pa, and preferably between 10⁻² Pa and 10⁻⁴ Pa.

[0016] According to one embodiment of the invention, a gas such as a noble gas is injected into the vacuum chamber. Indeed, due to the relatively high vacuum within the vacuum chamber in which the object to be treated is placed, it has been observed that the atoms and molecules remaining in this rarefied atmosphere are not always sufficient in number to guarantee satisfactory implementation of the ion implantation process. Therefore, as an alternative, the atmosphere of the vacuum chamber is enriched with a noble gas so that the ionization of this atmosphere produces electrons in greater quantities. Brief description of the figures

[0017] Other features and advantages of the present invention will become clearer from the following detailed description of an example embodiment of the ion implantation system, this example being given purely for illustrative purposes and not as a limitation, only in connection with the accompanying drawing in which: there figure 1 The already cited schematic view of an electron cyclotron resonance (ECR) ion source according to the prior art is shown; figure 2 The previously mentioned schematic view illustrates an ion beam at the output of the electron cyclotron resonance (ECR) ion source shown in the illustration. figure 1 ; there figure 3 is a schematic view of an installation for implanting single- or multi-charged ions onto the surface of an object to be treated according to the invention, and the figure 4 is a larger-scale view of the area surrounded by a circle on the figure 3which illustrates the phenomenon of recombination of free electrons in the atmosphere of the vacuum chamber with ions present on the surface of the object being treated. Detailed description of an embodiment of the invention

[0018] The present invention proceeds from the general inventive idea of ​​placing an object undergoing an ion implantation process in a vacuum chamber and illuminating it with ultraviolet radiation while simultaneously bombarding it with a beam of single- or multi-charged ions. As they propagate through the vacuum chamber, the photons of the ultraviolet radiation strip electrons from the atoms and molecules remaining in the rarefied atmosphere of the vacuum chamber. These free electrons then recombine with the ions present on the surface of the object being treated. It is thus possible to control the surface potential of the object being treated and to maintain this potential at a sufficiently low level so that the newly arriving ions are not excessively slowed down by the potential barrier and retain sufficient kinetic energy to penetrate deeply into the object being treated.

[0019] An ion implantation system according to the invention, enabling the implementation of the process, is schematically represented in the figure 3 Designated as a whole by the general reference numeral 18, this ion implantation installation comprises a vacuum chamber 20 within the sealed enclosure 22 of which is placed an object 24 intended to undergo an ion implantation process. The object 24 to be treated may be a solid mass or in powder form. It may be an amorphous or crystalline material, an insulator or electrical conductor, metallic or ceramic. If the object 24 to be treated is in powder form, it will preferably be agitated throughout the ion implantation process to ensure that the particles composing the powder are homogeneously exposed to the ion implantation beam.

[0020] An ion source 26, for example of the ECR electron cyclotron resonance type, is hermetically fixed to the enclosure 22 of the vacuum chamber 20, opposite a first opening 28 provided in this enclosure 22. This ion source 26, of a kind analogous to that of the ECR ion source described above, is oriented so that the beam of single- or multi-charged ions 30 that it produces propagates in the vacuum chamber 20 and strikes the surface of the object 24 to be treated. The single or multiple charged ions that strike the object to be treated 24 penetrate more or less deeply under the surface of this object 24 and gradually accumulate, thus giving rise to an electrostatic potential barrier which tends to slow down and repel the ions that arrive subsequently, which poses problems of inhomogeneity of the distribution of ions on and under the surface and in the thickness of the object 24 to be treated.

[0021] To remedy this problem, an ultraviolet radiation source 32 is also mounted in a sealed manner on the enclosure 22 of the vacuum chamber 20, opposite a second opening 34 provided in the enclosure 22. This ultraviolet radiation source 32 is oriented so that the ultraviolet radiation 36 that it produces propagates in the vacuum chamber 20 and falls on the surface of the object to be treated 24 at the same time as the ion beam 30 strikes the surface of this same object to be treated 24.

[0022] The vacuum within the sealed enclosure 22 of the vacuum chamber 20 is relatively high, typically between 10⁴ and 10⁻⁴ Pa, and preferably between 10⁻² Pa and 10⁻⁴ Pa. Nevertheless, despite the relatively high vacuum in the vacuum chamber 20, atoms and molecules remain in the atmosphere of this chamber 20. Photons from ultraviolet radiation 36 will remove electrons from these atoms and molecules, which will be attracted by the positive potential of the surface of the object being treated 24 and will recombine with the ions present on the surface of this object 24, thus neutralizing the electrostatic charges. The electrostatic potential of the object being treated 24 can therefore be maintained at sufficiently low values ​​to minimize interference with the implantation of new ions and allow them to penetrate sufficiently deep beneath the surface of the object being treated 24.

[0023] To improve the ion implantation process in the object to be treated 24, it may be possible to enrich the atmosphere of the vacuum chamber 20. For this purpose, the vacuum chamber 20 is equipped with an inlet valve 38 to which a gas source 40 is connected, for example, a noble gas such as argon or xenon. This inlet valve 38 opens near the object to be treated 24, so as to create locally, in the vicinity of the object to be treated 24, a slight overpressure of a noble gas richer in atoms.

[0024] By proceeding in this way, the atmosphere of vacuum chamber 20 is enriched and the number of electrons stripped from the atoms present in the atmosphere within vacuum chamber 20 is increased (see figure 4The recombination process between electrons in the vacuum chamber 20 and ions on the surface of the object being treated 24 is thus amplified, which makes it possible to lower the electrical potential of the object being treated even further. Indeed, it was observed, somewhat surprisingly, that the electrons stripped from the noble gas atoms by the photons of ultraviolet radiation, although they partially recombine with ionized noble gas atoms, or even with the ions of the ion implantation beam, still recombine in sufficient numbers with the positive charges present on the surface of the object being treated to significantly lower the electrostatic potential of the surface of the object being treated.

[0025] To further improve the ion implantation process in the object to be treated 24, a second ultraviolet radiation source 42 is used in the ion implantation setup according to the invention. This second ultraviolet radiation source 42 can be hermetically sealed onto the enclosure 22 of the vacuum chamber 20, or directly installed inside the vacuum chamber 20 and supported by a stand 44. The second ultraviolet radiation source 42 is oriented so that the ultraviolet radiation 46 it emits forms an angle of approximately 90° with the ultraviolet radiation 36 emitted by the first ultraviolet radiation source 32. With such an arrangement of the ultraviolet radiation sources 32, 42, it is possible to treat larger objects 24.

[0026] It goes without saying that the present invention is not limited to the embodiments just described and that various simple modifications and variants can be envisaged by a person skilled in the art without departing from the scope of the invention as defined by the attached claims.

[0027] It should be noted in particular that the present invention applies specifically to the surface treatment of sapphire objects (natural or synthetic) for the production of watch crystals. Thanks to the ion implantation system according to the invention, the amount of incident light reflected by such crystals is significantly reduced, which significantly improves the legibility of the information displayed by the indicator elements (hands, date, decorations) located beneath these crystals.

[0028] The present invention also applies to the surface treatment of crystalline or amorphous metallic objects or ceramics whose mechanical properties, in particular scratch resistance, are greatly improved when the ion implantation process with charge neutralization is applied to them.

[0029] The present invention also applies to the surface treatment of particles of a metallic or ceramic material in powder form. The metallic or ceramic powder particles obtained using the ion implantation system according to the invention are intended for the manufacture of bulk parts using powder metallurgy processes such as injection molding, better known by its Anglo-Saxon name Metal Injection Moulding or MIM, pressing, or additive manufacturing such as three-dimensional laser printing.

[0030] According to particular embodiments of the ion implantation installation according to the invention: The source of single- or multi-charged ions is of the electron cyclotron resonance (ECR) type; the ions are accelerated under a voltage between 7,500 volts and 40,000 volts; the material from which the ion beam is produced is chosen from nitrogen (N), carbon (C), oxygen (O), argon (Ar), helium (He), and neon (Ne); the dose of implanted ions is between 1 x 10¹⁴ ions.cm⁻² and 7.5 x 10¹⁷ ions.cm⁻², and preferably between 1 x 10¹⁶ ions.cm⁻² and 15 x 10¹⁶ ions.cm⁻²; the ion implantation depth is 150 nm to 250 nm; the metallic material is a precious metal chosen from gold and platinum; the metallic material is a non-precious metal chosen from magnesium, titanium, and aluminum. the particles of the metallic or ceramic powder are agitated throughout the entire ion implantation process;the particle size distribution of the metal or ceramic powder used is such that approximately 50% of all these particles have a size less than 2 micrometers, the size of the particles of the metal or ceramic powder used not exceeding 60 micrometers; the ceramic material treated by means of the ion implantation installation according to the present invention is a carbide, in particular a titanium carbide TiC or a silicon carbide SiC; the carbide-type ceramic material is bombarded with nitrogen ions N to form a carbonitride, in particular titanium carbonitride TiCN or silicon carbonitride SiCN; the ceramic material treated by means of the ion implantation installation according to the invention is a nitride, in particular a silicon nitride Si3N4;the ceramic material treated by means of the ion implantation installation according to the present invention is an oxide, in particular of zirconia ZrO 2 or of alumina Al 2 O 3; the oxide-type ceramic material is bombarded with nitrogen ions to form an oxynitride, in particular zirconia oxynitride ZrO(NO 3 ) 2, or even zirconium nitride ZrN if the ion bombardment is prolonged sufficiently long, or even alumina nitride AlO x N y; the oxide-type ceramic material is bombarded with carbon ions to form a carbonitride, in particular zirconia carbide ZrO 2 C, or even zirconium carbide ZrC; The oxide-type ceramic material is bombarded with boron ions to form an oxyboride, in particular zirconia boride ZrO₂B, or even zirconia boride ZrB₂ if the ion bombardment is prolonged sufficiently. The invention is defined by the claims. Nomenclature

[0031] 1. Electron Cyclotron Resonance (ECR) Multicharged Ion Source 2. Injection Stage 4. Volume of Gas to be Ionized 6. Microwave 8. Magnetic Confinement Stage 10. Plasma 12. Extraction Stage 14a. Anode 14b. Cathode 16. Mono- or Multicharged Ion Beam 18. Ion Implantation Facility 20. Vacuum Chamber 22. Airtight Enclosure 24. Object to be Treated 26. Ion Source 28. First Opening 30. Mono- or Multicharged Ion Beam 32. Ultraviolet Radiation Source 34. Second Opening 36. Ultraviolet Radiation 38. Inlet Valve 40. Gas Source 42. Second Ultraviolet Radiation Source 44. Base 46. Ultraviolet Radiation

Claims

1. An installation for implanting monoatomic or polyatomic ions in a surface of an object to be treated (24), this installation (28) comprising a vacuum chamber (20) in which the object to be treated (24) is placed, the installation (18) also comprising a source of ions (26) that injects a beam of monoatomic or polyatomic ions (30) into the vacuum chamber (20), this ion beam (30) being directed towards the surface of the object to be treated (24), the said ion source being arranged so that, when the installation is in operation, the monoatomic or polyatomic ions strike the object to be treated (24) and penetrate more or less deeply into the surface of this object to be treated (24) and gradually accumulate, thus creating an electrostatic potential barrier that tends to slow and repel the ions that subsequently arrive, the installation (18) also comprising a first source of ultraviolet radiation (32) arranged to function at the same time as the ion source (26) and to produce a first ultraviolet radiation (36), the said first source of ultraviolet radiation being oriented so that, when the installation is in operation, the first ultraviolet radiation (36) propagates in the vacuum chamber (20) and falls onto the surface of the object to be treated (24) at the same time as the ion beam (30) strikes the surface of this same object to be treated (24) so that the photons from the first ultraviolet radiation (36) strip the atoms and molecules present in the vacuum chamber (20) of the electrons which will be attracted by the positive potential of the surface of the object to be treated (24) and will recombine with the ions present on the surface of the object to be treated (24), so as to cancel out the electrostatic charges, the said installation further comprising a second source of ultraviolet radiation (42) arranged to illuminate the surface of the object to be treated (24) with a second ultraviolet radiation (46), the said second source of ultraviolet radiation being oriented so that, when the installation is in operation, the second ultraviolet radiation (36) propagates in the vacuum chamber (20) in a direction forming an angle of approximately 90° with the first ultraviolet radiation (36).

2. The installation for implanting monoatomic or polyatomic ions according to claim 1, in which the ion source (26) is of the electron cyclotron resonance type.

3. The installation for implanting monoatomic or polyatomic ions according to any of claims 1 or 2, comprising a source of gas (40) arranged to deliver gas into the vacuum chamber (20) via an inlet valve (38) to which the source of gas (40) is connected.

4. The installation for implanting monoatomic or polyatomic ions according to claim 3, in which the gas contained in the gas source (40) is a noble gas.

5. The installation for implanting monoatomic or polyatomic ions according to any of claims 1 to 4, in which the material from which the ion beam is produced is chosen among nitrogen N, carbon C, oxygen O, argon Ar, helium He and neon Ne.

6. The installation for implanting monoatomic or polyatomic ions according to any of claims 1 to 5, in which the ion source is arranged to produce an ion implantation dose in a range comprised between 1*1014 ions.cm-2 and 7.5.1017 ions.cm-2, and preferably between 1*1016 ions.cm-2 and 15*1016 ions.cm-2, the installation comprising a high-voltage source arranged to produce an acceleration voltage of the ions comprised between 7.5 kV and 40 kV.

7. The installation for implanting monoatomic or polyatomic ions according to any of claims 1 to 6, comprising means for generating a vacuum designed such that the atmospheric pressure inside the vacuum chamber (20) is comprised between 104 Pa and 10-4 Pa and preferably between 10-2 Pa and 10-4 Pa.