EP0107686B1 - Method and device for producing photons in the ultraviolet wavelength range - Google Patents

Abstract

Method and device for the production of photons (7), in the ultraviolet wavelength range, comprising the implantation in a solid matrix of inert or respectively matrix-insoluble gas ions, the excitation of the gas imprisoned (2) in the solid matrix, and the emission of said photons (7) by the excited gas, as well as in particular the ionic bombardment of a surface of the solid matrix by low energy ions of at least one gas such as afore-mentioned, and the low energy electronic bombardment (4) of the solid matrix with emission of the photons (7).

Description

The present invention relates to a process for the production of photons, in the range of ultraviolet wavelengths, comprising the implantation in a solid matrix of ions of inert gas or respectively insoluble with respect to the matrix, l excitation of the trapped gas in the form of extended defects of the solid matrix, and the emission of said photons by the excited gas, as well as to a device for the implementation of this process.

Common light sources for the near, far, and extreme ultraviolet wavelength ranges are generally discharge sources where light is produced by passing an electrical discharge through a capillary containing noble or other gases at pressures included between 10 and a few tens of thousands of Pa. For He, a commonly used gas, a continuous emission spectrum results from the formation in the discharge and the subsequent radiative decay, of excited helium molecules He ₂ ^*.

Another important source of radiation in this spectrum range is the synchrotron, which is a complicated and expensive installation, accessible only in a few places in the world.

It has also been envisaged to use the fluorescence of liquid helium as a source of radiation in the ultraviolet range, but this process requires cryogenic cooling, therefore at very low temperatures, as well as differential pumping, and its implementation is therefore very costly (see CM Surko, RE Packard, GJ Dick and F. Reif, Spectroscopic Study of the luminescence of liquid helium in the vacuum ultraviolet, in Physical Review Letters, Vol. 24, N ° 12, (1970), p . 657 et seq.).

It is also known to prepare solid matrices having wide defects, such as vacancy agglomerates, or bubbles containing an inert gas or insoluble with respect to the matrix. One obtains, for example, such a matrix with microbubbles of helium by bombardment by means of energetic He ions. The AI / He matrix has been the subject of studies in optical absorption and electronic energy loss spectroscopy (see JC Rife, SE Donnelly, AA Lucas, JM Gilles and JJ Ritsko, Optical absorption and electron-energy -loss spectra of helium microbubbles in Aluminum, Physical Review Letters, vol. 46, n ° 18 (1981), p. 1220 et seq.).

It has also been observed that a solid matrix bombarded with high-energy helium ions (200-600 keV) emits, from a certain dose of He, a continuous spectrum in the ultraviolet range (see RS Bhattacharya , KG Lang, A. Scharman and KH Schartner, Continuous emission in the vacuum ultraviolet under energetic inert gas ion bombardment of aluminum, in J. Phys. D, vol. 11 (1978), p. 1935 et seq.). It should be noted that the implantation of high energy helium ions is a relatively expensive process and that, since the helium ions are implanted at great depth in the matrix, the intensity of the emission of ultraviolet rays is low.

It will also be noted that the interaction between a hot plasma, as encountered in deuterium-tritium fusion reactors, and the solid surface of the walls of the reactor, is described by R. Behrish et al., Trapping of low-energy helium ions in niobium, in Journal of Nuclear Materials, volume 56, n ° 3, pages 365-367, North Holl. Publishing Company, Amsterdam (NL).

³He(d, p) ⁴He dans laquelle un deutéron (d) de 5LI keV transforme un atome ^cHe en isotope ⁴He avec émission d'un proton (r) de 3,5 MeV qui est détecté. La mesure du courant de protons donne accès à la quantité d'³He implantée. Le résultat central de ces mesures est présenté sous forme de courbes de capture donnant la quantité d'³He retenue par le solide en ;onction de la dose d'ions ³He⁺ implantés et pour plusieurs énergies d'implantation. La conclusion des auteurs est que le maximum de concentration d'He implanté à basse énergie dans le Nb est situé entre 50 et 100 % atomique et que le processus de saturation est atteint lorsqu'un atome d'³He s'échappe par diffusion pour chaque nouvel ion ³He' implanté. Aucune réémission substantielle d'³He n'est observée pour la dose critique qui provoque le cloquage superficiel, ce qui entraîne certaines implications pour les modèles de cloquages.To this end, low energy ions (with energies from 1 to 15 keV) of the ³ He isotope are implanted in a monocrystalline solid of Nb at various doses. The amount of ³ He actually captured and retained by the target is then determined by means of the reaction.

³ He (d, p) ⁴ He in which a deuteron (d) of 5LI keV transforms a ^c He atom into a ⁴ He isotope with emission of a proton (r) of 3.5 MeV which is detected. Measuring the proton current gives access to the quantity of ³ He implanted. The central result of these measurements is presented in the form of capture curves giving the quantity of ³ He retained by the solid in; anointing of the dose of implanted ³ He ⁺ ions and for several implantation energies. The authors conclude that the maximum concentration of He implanted at low energy in Nb is between 50 and 100 atomic% and that the saturation process is reached when a ³ He atom escapes by diffusion to each new ³ He 'ion implanted. No substantial ³ He reemission is observed for the critical dose that causes surface blistering, which has certain implications for blistering models.

Finally, we have also already studied the emission of far ultraviolet radiation (1,000-1,300 Å) from argon gas excited by an electron beam of 250 keV, the beam being pulsed in order to characterize the time dependence of the emission. fluorescent (v. Physical Review A, volume 5, n ° 3, March 1972, Inst. of Phys. New York (US), N. Thonnard et al., Time-dependent study of vacuum-ultraviolet emission in Argon, pages 1110 -1121). The bombarded argon sample is contained in gaseous form in a reaction cell where the gas is constantly replaced by pumping. The gas pressure varies between 1,333 and 133,322 Pa (between a few tens of torr and 1,000 torr). As for the emission of rare gases observed in discharges, sparks, microwave sources or proton bombardment, the spectra observed by electron bombardment consist of resonant transpositions from the first excited atomic state plus an emission of molecular continuum at longer wavelengths. The authors discuss the mechanisms of excitation energy transfers and the kinetics of molecular reactions based on the time course of fluorescence intensities.

The object of the present invention is to point of a process and a device for producing photons in the range of ultraviolet wavelengths which are simple and inexpensive while giving results comparable to discharge sources.

To this end, according to the invention, ion bombardment of a surface of the solid matrix is carried out with low-energy ions of at least one gas as mentioned above, so as to obtain implantation over a depth not exceeding not some 10- ¹ m (thousands of A) of gas in the solid matrix, and then an electron bombardment, of an energy lower than or equal to 20 keV, of the solid matrix, with excitation of the trapped gas and emission of photons above. According to one embodiment of the invention, the method comprises the implantation of gas ions by one face of a solid matrix in mass and the electron bombardment of this same face with emission of the aforementioned photons induced from this face. .

According to another embodiment of the invention, the method comprises the implantation of gas ions in a solid lamellar matrix with a thickness less than 1 fJ.m, and the above-mentioned electronic bombardment of one of the faces of this matrix with emission of the aforementioned photons induced from the other face of the matrix.

According to the invention, there is also provided a device for implementing the method according to the invention, comprising a vacuum envelope, a solid matrix in which are implanted ions of at least one inert gas or respectively insoluble vis -with respect to the matrix, this matrix being mounted on a support inside the vacuum envelope, as well as an output for the photons produced provided in the envelope, this device being characterized in that it includes an electron production device capable of subjecting the matrix to electronic bombardment with an energy less than or equal to 20 keV and an electrical connection connecting the matrix to the outside making it possible to measure the electric current in the matrix, the ions aforementioned gas is implanted to a depth not exceeding a few 10- ¹ m (thousands of a).

Other details and particularities of the invention will emerge from the description given below, without implied limitation and with reference to the attached drawings.

• FIG. 1 schematically illustrates a device implementing a method for producing photons according to the invention.
• FIG. 2 schematically illustrates a device implementing an alternative embodiment according to the invention.
• FIG. 3 shows, in more detail, a view partially in axial section through a device according to the invention.
• FIG. 4 represents the fluorescence spectrum obtained by the use of a device according to the invention. The units plotted on the abscissa represent the wavelengths of the fluorescence spectrum and on the ordinate plots are arbitrary emission intensity units.

In the figures, identical or analogous elements are designated by the same references.

The device illustrated in FIG. 1 comprises a solid matrix 1 which is prepared by implantation of low energy He ions in an Al sheet with a thickness less than 1 f.Lm. A He ion bombardment at low energy, in the range of 5 keV, allows the implantation of a high concentration (locally greater than 10 atomic%) of He at a depth of tens to 10- ¹ m ( thousands of A). Helium naturally agglomerates in the gaps in the matrix produced by bombardment and forms large defects, such as gap agglomerates or microbubbles 2 which remain stable at room temperature and can withstand temperature rises of up to at a few hundred ° C, for example up to 300 ° C.

The device illustrated in FIG. 1 also includes a device for producing low-energy electrons 3, such as an electronic gun, this device projecting an electron beam 4 onto one of the faces 5, called the rear face, of the matrix 1. The electrons in the electron beam 4 have an energy less than or equal to 20 keV, preferably between 1 and 5 keV. In this case, fluorescence of the target is induced from the front face 6 of the matrix, the emission of photons being represented by the arrows in wavy lines 7.

There is shown in this FIG. 1, in broken lines, an alternative embodiment, in which the lamellar matrix 1 is in the form of a continuous strip, wound at one end in a reserve roll 20 and at its other end in a discharge roller 21. In this way, if the part of the matrix subjected to electronic bombardment is accidentally altered, after a certain period of operation, the matrix can be moved in the direction of arrow 22, by rotating said rollers 20 and 21, and bring before the electron beam a new part of the matrix not yet subjected to electron bombardment. This movement can be carried out manually or automatically, and it can be continuous or intermittent during the operation of the device according to the invention.

In the device illustrated in FIG. 2, the matrix is a bulk substrate 8. The implantation of the He ions is carried out in the same manner as for the lamellar matrix 1, proceeding so as to obtain a maximum concentration of microbubbles 2 of He at a depth, preferably less than 5. 10- ¹ m (5000 A). In this case, the electron gun 3 projects a beam of low energy electrons on the same surface as that by which the He ions were implanted, and a fluorescence of the target is then induced through this surface 9, the emission of photons being represented by the arrows in wavy lines 10. We therefore have in this last case what will be called electronic bombardment of the front face of the matrix, as opposed to electronic bombardment of the rear face of the matrix illustrated in FIG. 1.

The device illustrated in FIG. 3 represents in a more detailed way a device implementing an electronic bombardment of the front face of the matrix.

This device according to FIG. 3 comprises an envelope 11 maintained under vacuum in which the matrix 8 is mounted on a support 12 which can be cooled by a cooling circuit 13, for example with water, in the event of use. of the high intensity device. An electron gun 3 emitting a low energy electron beam of adjustable intensity is mounted on the envelope so as to direct this beam on the matrix. The angle of incidence between the beam and the plane of the matrix is calculated so that the emitted photons can propagate through the exit opening 14 formed at one of the front ends of the envelope 11. This end is provided with a flange 15 which is used to connect the device according to the invention to an apparatus in which ultraviolet light will be used.

An electrical connection 16 makes it possible in particular to measure the electronic current in the matrix. An electronic screen 17 can be provided in the outlet opening 14 intended to prevent any exit of electrons through this opening, this electronic screen 17 then also being connected to the outside by an electrical connection 18.

The casing 11 is maintained under vacuum, either by a pumping device, not shown, connected to the casing by the flange connection 19, or by the pumping device now holding the vacuum device, not shown, connected to the flange 15 .

The matrix material must meet two main conditions: the insolubility of the gas in the matrix and relatively low absorption by the matrix of the gas emission continuum. The material of the matrix must preferably have optical properties such that the depth of escape of the photons produced is compatible with the depth of implantation. Therefore, the penetration depth of the electron beam need not exceed this photon escape depth, and electron energies in the range of 0.1 to 20 keV are sufficient, even for surface bombardment. before, with a relatively grazing incidence. This property of the photon source makes it possible to avoid the high costs necessary for carrying out high energy ionic and electronic bombardments, such as those used in known methods and devices. Excitement can notably be produced by the use of a low energy electronic gun.

As matrix material, materials chosen from the group comprising metals, such as Sn, Mg, AI, semiconductors, such as Si, Ge or certain insulators, such as LiF, NaCl, can advantageously be used.

As the emission depth of the source is very small, the source is substantially planar and the surface and the shape of the source can be simply adjusted by structuring the electron beam. By concentrating the beam, an effectively point source can be obtained; by scanning or spreading the beam, it is possible to obtain an extended source compatible, for example, with the slit geometry used in certain spectroscopic work. In addition, a time-varying fluorescence intensity can easily be obtained by modulating the electron beam in pulses, which allows the use of the source in servo-control techniques (of the “lock in •” type). The duration of existence of the fluorescence is less than 10 nsec.

According to a nonlimiting example of implementation of the method according to the invention, a source of photons based on AI / He is prepared in the manner described above and implemented according to the invention under an electron bombardment having an energy of 3 800 V. This source produces, as can be seen from FIG. 4, a continuous spectrum of fluorescence which extends from 5.8 to 9 10-8 m (from 580 to 900 A), which is similar to that that we get with conventional discharge sources. The production of photons from the matrix was compared with the synchrotron source SURF II and this comparison indicates an efficiency greater than or equal to 10- ⁴ photons per electron. With sufficient electronic current, the brightness can reach that obtained by discharge lamps.

Unlike conventional discharge sources, there is the possibility, using the method according to the invention, of developing a multi-gas composite source in order to extend the width of the spectral band by 5.8 to 30. 10-8 m (from 580 to 3000 A). Indeed, it is obvious that in addition to helium, other gases inert with respect to the matrix can be used, for example rare or other gases, such as Ne, Ar, ...., H ₂ , N ₂ , ... If we implant in the matrix of ions of several of these gases, we can thus obtain said composite multi-gas source.

The applications of a photon source according to the invention are numerous. It can be used in any application where discharge sources are now used, for example for photoelectron spectroscopy in the ultraviolet, for studies of reflectivity, adsorption and photoconductivity. etc.

• a) détecteurs de particules, par la détection de la fluorescence induite dans le dispositif par le passage de particules chargées ;
• b) lithographie de contact dans l'ultraviolet, par implantation d'un circuit intégré au moyen d'un faisceau d'ions de gaz inerte sur un masque sous forme de film mince et par impression ultérieure du circuit, par placement du film en contact avec un revêtement photorésistant, sensible aux photons UV, et par bombardement avec un faisceau électronique pour activer la fluorescence aux ultraviolets ;
• c) source d'émission stimulée d'ultraviolets extrêmes (laser à excimère), grâce au choix d'un mécanisme de pompage approprié et d'une cavité résonnante appropriée.

In addition to the use of the device according to the invention as a simple means of producing photons in the range of near, far and extreme ultraviolet rays, the source according to the invention can be incorporated into a large number of new, more complex systems. Among others, we can cite:

• a) particle detectors, by detecting the fluorescence induced in the device by the passage of charged particles;
• b) contact lithography in the ultraviolet, by implantation of an integrated circuit by means of a beam of inert gas ions on a mask in the form of thin film and by subsequent printing of the circuit, by placing the film in contact with a photoresist coating, sensitive to UV photons, and by bombardment with an electron beam to activate ultraviolet fluorescence;
• c) source of stimulated emission of extreme ultraviolet light (excimer laser), thanks to the choice of an appropriate pumping mechanism and an appropriate resonant cavity.

The methods and devices according to the invention have the advantage of not requiring differential pumping, gas replacement and cryogenic cooling. In addition, they are very easy to implement and flexible in operation. The source according to the invention offers the advantage of a brightness, which can vary by six orders of magnitude or more, by modification of the intensity of the electron beam. It allows a specific geometry by concentration. Finally, its implementation is relatively inexpensive.

It should be understood that the present invention is in no way limited to the embodiments described above and that many modifications can be made without departing from the scope of this patent.

Claims (24)

1. Method for producing photons (7), in the UV-wavelength range, comprising planting in a solid matrix, ions from a gas which is inert or insoluble relative to the matrix, excitating the captive gas (2) in the solid matrix, and radiating said photons (7) by the excitated gas, characterized in that it comprises performing an ionic bombardment of one surface from the solid matrix with low-energy ions from at least one gas as defined above, in such a way as to obtein a planting over a depth which does not exceed a few 10-⁷ m (thousands A) of gas (2) in the solid matrix, and thereafter an electronic bombardment (4), of an energy which is lower thai or equal to 20 keV, of the solid matrix, with excitating of the captive gas and emission of said photons (7).

2. Method according to the claim 1, characterized In t' at it comprises planting. of gas ions through the one side (9) of a mass solid matrix (8), and performing the electronic bombardment (4) of this same side with emission of said photons (10) being induced from this side (9).

3. Method according to the claim 1, characterized in that it comprises planting of gas ions in a laminated solid matrix (1) with a thickness smaller than 1 wm, and performing said electronic bombardment (4) of the one side (5, 6) of this matrix (1) with emission of said photons (7) being induced from the other side of the matrix (1

4. Method according to any one of the claims 1 or 3, characterized in that it comprises intermittently or continuously moving the matrix (1, 8) in which the gas ions have been planted, from a supply position to a bombardment position where same undergoes said electronic bombardment, then to a discharge position, the matrix (1, 8) being in the shape of a continuous substrate.

5. Method according to any one of the claims 1 to 4, characterized in that the ionic bombardment is performed with ions from said gas or gases having an energy allowing to obtain a high gas concentration in the form of extended faults (2) of the matrix (1, 8), over the above-mentioned depth.

6. Method according to the claim 5, characterized in that the energy of said gas ions is in the range of 5 keV.

7. Method according to any one of the claims 1 to 6, characterized in that it comprises planting in the matrix (1, 8) of ions from a plurality of gases which are inert or insoluble relative to the matrix.

8. Method according to any one of the claims 1 to 7, characterized in that it comprises planting ions from rare gases, particularly helium.

9. Method according to any one of the claims 1 to 8, characterized in that the electronic bombardment (4) is performed with electrons having an energy which is comprised between 1 and 5 keV.

10. Method according to any one of claims 1 to 9, characterized in that it comprises during the electronic bombardment (4) focalizing an electron beam on the matrix (1, 8) so as to form a pinpoint source of photons (7, 10).

11. Method according to any one of claims 1 to 9, characterized in that it comprises during the electronic bombardment (4) scanning the matrix with an electron beam so as to form an extended source of photons (7, 10).

12. Method according to any one of claims 1 to 9, characterized in that it comprises during the electronic bombardment (4) spreading an electron beam so as to form an extended source of photons (7, 10).

13. Method according to any one of claims 1 to 12, characterized in that it comprises during the electronic bombardment (4) modulating the intensity of the electron beam so as to form a varying-intensity source of photons (7, 10).

14. Method according to any one of claims 1 to 13, characterized in that the matrix (1, 8) being used is from a material having a low absorption of the continuous emission spectrum of the excitated gas, contained inside the matrix.

15. Method according to the claim 14, characterized in that the matrix (1, 8) being used is from a material selected in the group comprising metals, such as Sn, Mg, Al, semi-conductors, such as Si, Ge, or insulating materials, such as LiF, NaCl.

16. Device with a solid matrix (1, 8) into which are planted ions from at least one gas which is inert or insoluble relative to the matrix, for the production of photons in the UV-wavelength range according to any one of claims 1 to 15, comprising a vacuum enclosure (11), this matrix being mounted on a support (12) inside the vacuum enclosure, as well as an outlet (14) for the resulting photons, provided in the enclosure, said device being characterized in that it comprises a low-energy electron-producing apparatus (3) capable of subjecting the matrix to an electronic bombardment of an energy whim is lower than or equal to 20 keV and an electronic connection (16) connecting the matrix to the ouside allowing to measure the electric current in the matrix, said gas ions being planted over a depth which does not exceed a few 10^-7 m (thousands A).

17. Device according to the claim 16, characterized in that it comprises a mass solid matrix (8) the one surface of which contains planted-in gas ions, the electron-producing apparatus (3) being so arranged as to perform said electronic bombardment of this surface, with emission of said induced photons from this surface.

18. Device according to the claim 16, characterized in that it comprises a laminated solid material (1) with a thickness smaller than 1 µm, the electron-producing apparatus being so arranged as to perform said electronic bombardment of the one side of the matrix, with emission of said induced photons from the other side of the matrix.

19. Device according to any one of claims 16 or 18, characterized in that it comprises a matrix (1, 8) in the shape of a continuous substrate, movable inside the enclosure in an intermittent or continuous way between a supply position, a matrix-bombardment position, and a discharge position.

20. Device according to any one of claims 16 to 19, characterized in that it comprises a cooling circuit (13) for the matrix support (12).

21. Device according to any one of claims 16 to 20, characterized in that the enclosure (11) has a connecting flange (15) about the outlet (14) for the resulting photons, to mount a vacuum apparatus on the device, and in that possibly the device has across this outlet, an electron screen (17) connected to the outside.

22. Device according to any one of claims 16 to 21, characterized in that the electron-producing apparatus (3) with low-energy, is an electron gun generating electrons having an energy lower than or equal to 5 keV.

23. Device according to any one of claims 16 to 22, characterized in that it comprises a vacuum pump connected to the vacuum endps-ure.

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