FR2883410A1 - PHOTON SOURCE COMPRISING A MULTICHARGED ION PLASMA SOURCE WITH ELECTRONIC CYCLOTRON RESONANCE. - Google Patents

Abstract

Provided is a photon source comprising an electron cyclotron resonance (ECR) multicharged ion plasma source that includes a vacuum cylindrical plasma chamber (CH), a guide (GD) for injecting microwaves into the chamber, a device (I) for injecting a gas into the chamber, a pumping system (P) for discharging the ionized gas resulting from the action of the microwaves on the gas (g), and a cylindrical magnetic structure (1, 2, 3a, 3b, 4) which surrounds the chamber (CH) and which produces at least two closed surfaces (S) aligned along the axis of the chamber and on which the magnetic field takes the value of the resonance field RCE, the photons being extracted by an opening (02) aligned with the axis of the chamber. The invention applies to EUV lithography.

Description

PHOTON SOURCE COMPRISING

  TECHNICAL FIELD AND PRIOR ART The present invention relates to a source of photons and, more particularly, to a source of photons comprising a source of ionic plasma multicharged at the electron cyclotron resonance ( RCE) more commonly referred to as RCE source.

  An application of the photon source according to the invention is, for example, the production of EUV photons (EUV for Extreme Ultra-Violet) that can be used for lithography.

  Different light sources are used for EUV lithography, such as, for example, laser plasmas (LPP), synchrotron light, discharge sources (Z-pinch, hollow cathode, capillary source). These EUV sources present, as the case may be, the following problems: pulsed operation and too low power for certain lasers; production of debris harmful to optics (mirrors); - high cost (lasers, synchrotron); - heavy pumping; - poor reproducibility and service life of the source.

  Recently a new type of EUV light source has been proposed (see reference [1]). It is a light source based on the de-excitation of multicharged ions. The disclosed light source includes an electron cyclotron resonance (ECR) multicharged ion plasma source. The plasma source includes a cavity in which a resonance magnetic field is distributed along an unclosed surface that intercepts the walls of the cavity. The light source produces photons with a wavelength of 13.5 nm from the deexcitation of Xelo + ions. Photons having such a wavelength advantageously make it possible to produce etches less than 65 nm (see abbreviated reference [1]). ).

  Compared to the light sources mentioned above, the use of an ECR source 15 has many advantages: - continuous and stable operation; - no debris at the exit; - no wear (very long use time due to lack of filament or cathode); low pressure (10-5-10-4 mbar) to limit the dimensions of the pumps and any vibrations; - low cost, if the magnetic structure is made of permanent magnets.

  Despite the advantages mentioned above, a major problem of such a photon source that produces photons from an ECR source is the very low power it emits. As will appear below, the invention does not have this disadvantage.

  The production of multicharged ions in an ECR source has been described in numerous patents and articles.

  Reference [2] describes the realization of an RCE source entirely of permanent magnets producing a strong Xelo + ion flux at the extraction to create an ion beam.

  Ionization of the gas to obtain multi-charged ions of the Xeq + type takes place stepwise, by electronic impact. It then follows: Xe (q1) + + e> Xeq + + e- + e- It appears that the following conditions must be established to obtain ions Xeq + a) a microwave power of frequencies typically between 2.45 GHz and 50 GHz is injected into a vacuum cavity located in a magnetic structure, producing the ionization of a gas or metal vapor, for example Xenon, which is introduced, moreover, into the cavity at a pressure between 10-5mbar and 10-9 mbar, b) the term Rq of production of the ion Xeq + is written: Rq = ne <Ve 6q-1, q> nq_1 where is the electron density, nq_l the density of ions Xe (q-1) + and <Ve aq_1, q> the product of the electron impact ionization cross section by the velocity of the electrons taking into account their energy distribution, c) the energy of the incident electrons must be sufficient to effect the ionization (a 2883410 4 400eV energy is optimal for obtaining Xelo + ions (Xe9 + + e-> Xe l + + e- + e-)), d) the transfer of energy from the microwave power injected into the electrons of the plasma occurs at a magnetic field location Bres such that the electron cyclotron resonance condition is established, c that is to say when there is equality between the pulsation of the high frequency wave (HF and the cyclotron pulsation of the electron: (OHF = (OCE = qe Bres / me (for example for f = 10 GHz , Bres = 0.36 T and for f = 14 GHz, Bres = 0E 5T) It follows from this that a particular magnetic configuration is necessary to obtain given ions in a RCE source.

  From this point of view, the French patents FR 2475798 and FR 2640411 also disclose that, in order to increase the magnetic confinement and, consequently, the lifetime of the ions and the electrons, the resonance magnetic field is distributed inside. of the plasma chamber, according to a closed surface on which it takes a substantially constant value BresÉ This closed surface, called the resonance surface, has no contact with the walls and is itself located inside a surface on which the magnetic field takes a Bd value substantially equal to twice the Bres value (Bd> _2xBres) This magnetic configuration with closed resonance surface is produced by the juxtaposition of an axial magnetic mirror produced, for example, by two solenoids or two crowns of permanent magnets and a multipole structure, for example a hexapole consisting of six magnets in alternating poles, the resulting magnetic field being the vector sum of the two axial and radial contributions.

  SUMMARY OF THE INVENTION The invention relates to a photon source comprising a source of electron cyclotron resonance (ECR) multicharged ion plasma. The photon source comprises: a vacuum cylindrical plasma chamber of axis AA, provided with an opening through which the photons are extracted from the chamber, at least one microwave injection guide for injecting microwaves in the chamber; - a gas injection device for injecting a gas into the chamber; a pumping system for pumping electrically neutral particles present in the chamber; and - a cylindrical magnetic structure which surrounds the chamber and which produces, inside the chamber, a magnetic field distributed according to at least two closed surfaces aligned along the axis AA, on which the magnetic field has a value substantially equal to the value of the electron cyclotron resonance field, these surfaces being separated from each other, without contact with the walls of the chamber and located inside an additional surface, without contact with the chamber, on which the magnetic field takes a a substantially constant value equal to or greater than twice the value (BRCE) of the electron cyclotron resonance field (IBI> -2 I BRcE) - According to a further characteristic of the invention, the magnetic structure comprises two transverse magnet hollow magnetic cylinders , the magnetization of a first hollow cylinder having a direction opposite to the magnetization of the second hollow cylinder, N multipolar hollow magnetic cylinders, N being a number greater than or equal to 2 and N-1 hollow magnetic cylinders with longitudinal magnetization, the two hollow magnetic cylinders with transverse magnetization, the N multipolar hollow magnetic cylinders and the longitudinal magnetic magnet N-1 hollow cylinders being aligned along the axis AA of the chamber, the N multipolar hollow magnetic cylinders and the N-1 hollow magnetic cylinders longitudinal magnetization being placed between the two hollow cylinders with transverse magnetization, a cylindrical multipole hollow magnetic core alternating with a longitudinally magnetized hollow cylinder, a first multipolar hollow magnetic cylinder adjacent to a first transverse magnet hollow magnetic cylinder and a second multipolar hollow magnetic cylinder adjacent to the second transverse magnet hollow magnetic cylinder.

  According to yet another characteristic of the invention, the N multipolar hollow magnetic cylinders are hexapoles of Halbach type.

  According to a further feature of the invention, the N multipolar hollow magnetic cylinders are quadrupole cylinders.

  According to yet another characteristic of the invention, the N multipolar hollow magnetic cylinders are hexapolar cylinders.

  According to yet another characteristic of the invention, the N multipolar hollow magnetic cylinders are octopole cylinders.

  According to yet another characteristic of the invention, the N multipolar hollow magnetic cylinders are dodecapolar cylinders.

  According to yet another feature of the invention, a hollow magnetic cylinder with additional longitudinal magnetization substantially surrounds the assembly consisting of N multipolar hollow magnetic cylinders and N-1 hollow magnetic cylinders longitudinal magnetization.

  According to yet another characteristic of the invention, the gas introduced into the chamber is Xenon whose pressure is between 10-5 mbar and 10 -4 mbar.

  In a multicharged ion RCE plasma source, the maximum density of energetic electrons and multicharged ions is located on or near the resonance surface (equimodule surface B = Bres). The maximum photon emission site is thus also on or near the Bres resonance surface.

  According to the invention, the increase of the photon flux along a particular axis is obtained by increasing the number of resonance surfaces along this axis. Unlike a conventional multi-charged ion source which comprises a single resonance surface, the multicharged ion source of the invention thus comprises a plurality of resonance surfaces substantially aligned along a given axis which make it possible to increase the power very substantially. issued according to this axis.

  In the context of the invention, the resonance surfaces of the magnetic field may be surfaces which do not close inside the chamber and which intercept the walls of the chamber or closed surfaces without contact with the walls of the chamber. bedroom. However, according to the preferred embodiment of the invention, the resonance surfaces of the magnetic field are closed surfaces without contact with the walls, because then the lifetimes of the ions and electrons are very substantially elongated.

  The power obtained along the axis of the chamber is advantageously substantially proportional to the number of closed resonance surfaces present in the chamber.

Brief description of the figures

  Other features and advantages of the invention will appear on reading a preferred embodiment with reference to the appended figures, among which: FIG. 1 represents an example of a source of EUV photons according to the invention; Figure 2 shows a sectional view of a first ring of magnets which participates in the photon source shown in Figure 1; - Figure 3 shows a sectional view of a second ring of magnets which participates in the source of photons shown in Figure 1; FIGS. 4a, 4b show, by way of example, sectional views of hexapolar magnetic structures which participate in the source of photons represented in FIG. 1; FIG. 5 represents a sectional view of a magnetic structure with longitudinal magnetization which participates in the source of photons represented in FIG. 1; FIG. 6 represents an improvement of the photon source represented in FIG. 1; FIG. 7 represents a sectional view of a magnetic structure with longitudinal magnetization which participates in the source of photons according to the improvement of FIG. 6.

  In all the figures, the same references 30 designate the same elements.

  DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION FIG. 1 represents an example of a source of photons according to the invention.

  The photon source includes an electron cyclotron resonance (ECR) multicharged ion plasma source. The electron cyclotron resonance multi-electron plasma source comprises a vacuum cylindrical plasma chamber CH, a microwave injection waveguide GD, a gas injection device I, a pump device P and a magnetic structure 1, 2, 3a, 3b, 4. An opening 02 is made in the chamber CH to allow the extraction of photons. Preferably, the opening 02 is substantially aligned with the axis AA of the chamber.

  The microwave injection guide GD injects microwaves into the CH chamber. The GD guide is equipped with an air / vacuum sealing window (not shown in the figure). The pressure at which the gas g is injected into the CH chamber by the device I is, for example, between 10-5 mbar and 10-4 mbar. The pumping system P makes it possible to evacuate the electrically neutral particles that are present in the chamber. The pumping rate is, for example, 300 liters per second.

  The cylindrical magnetic structure 1, 2, 3a, 3b, 4 surrounds the chamber CH and produces, within the chamber, a magnetic field distributed on a succession of closed surfaces S, on which the magnetic field has a substantially equal value to the value BRCE resonance field ECR, these closed surfaces S being substantially aligned along the axis AA of the chamber, independent of each other, without contact with the walls of the chamber CH and located within a closed surface E on which the magnetic field takes a substantially constant value, equal to or greater than twice the BRCE value of the resonance field OB 2 BRCE I) The curve V represents the variation of the magnetic field along the axis AA, to inside the CH room. It appears that this variation is substantially sinusoidal, its mathematical expression then writing: B (z) # Burin + B1 (l + sin (z)) (1), with -z a variable which parameterizes the displacement along the axis AA, and Bmin <BRCE <Bmax Burin + (2 x B1); B1 # 0 The diameter of the plasma chamber CH must be relatively large, limited by the internal diameter of the magnetic structure which produces the closed surfaces S globally included in the equimodule surface E. The chamber CH is a multimode circular cavity for the waves electromagnetic. Consequently, if the diameter of the chamber is smaller than the cut-off wavelength 1c of the fundamental mode of propagation in the cavity (mode TE11), no wave can propagate in the chamber.

  The table below gives, for four successive propagation modes, whose fundamental propagation mode TE11r the value of the cut-off wavelengths A: TE11 mode 2, 5cm TM01 3, 28cm TE21 4, 1cm TMll 5, 2cm By way of non-limiting example, in the case where the diameter of the chamber is equal to 4.4 cm, the wave can thus propagate according to TE11r TM01r TE21 modes and be absorbed by resonance on the different surfaces S (there there is no reflection of the wave at the entrance of the cavity).

  Rigorously, the propagation conditions mentioned above are verified for propagation in vacuum or in air. In the presence of plasma, the wave propagates differently.

  However, the experiment shows that, while respecting the condition according to which the diameter of the chamber is greater than the cut-off wavelength of the fundamental mode (Xc (TE11)), there is propagation of electromagnetic waves in the chamber, absorption of these waves by resonance and creation of plasma.

  According to the preferred embodiment of the invention, the plasma chamber CH is a hollow cylinder, for example non-magnetic stainless steel, or aluminum, or copper, double outer wall for the circulation of a cooling liquid.

  By way of non-limiting example, the outer diameter of the chamber may be equal to 4.80 cm, the internal diameter to 4.40 cm and the length to 61 cm.

  The microwaves injected into the chamber CH by the injection guide GD are emitted, for example, by a variable frequency transmitter centered on a frequency of 10 GHz, the adjustment of the frequency being carried out by optimizing the photon flux. products. The microwave power injected into the chamber is, for example, equal to 1 kW. By way of nonlimiting example, the waveguide GD can introduce the microwaves into the chamber through an opening 01 located opposite the opening 02 through which the photons are extracted from the chamber. According to other embodiments of the invention, the microwaves can be introduced in different places at a time, for example at each closed resonance surface.

  The cylindrical magnetic structure which surrounds the chamber CH is constituted, for example, by two transverse magnetization hollow magnetic cylinders 1 and 2, a set of multipole hollow magnetic cylinders 3a, 3b and a set of magnetic hollow magnetisation cylinders. longitudinal 4.

  By magnetic cylinder transverse magnetization is meant a magnetic cylinder whose magnetization intersects the axis of the cylinder perpendicular to this axis. Figures 2 and 3 illustrate such hollow cylinders. FIG. 2 illustrates a hollow magnetic cylinder with transverse magnetization whose magnetization m1 is directed towards the axis of the cylinder whereas FIG. 3 illustrates a hollow magnetic cylinder whose magnetization m 2 is directed outwards.

  Cylinders 1 and 2 are placed at both ends of the chamber. The cylinder 1 is placed, for example, on the side of an opening 01 through which the microwaves are introduced into the chamber and the cylinder 2 on the side of the opening 02 through which the photons are extracted from the chamber.

  Advantageously, the magnetic field lines diverge from the axis AA at the cylinders 1 and 2. It follows that the electrons and the ions are deviated from the axis AA at the output of the photon source, allowing this last to emit substantially only photons. The cylinders 1 and 2 preferably have identical ribs. The length of the cylinders 1 and 2 is equal, for example, to 11 cm, the outer diameter (D1, D2) to 30 cm and the internal diameter (dl, d2) to 5 cm.

  By multipolar magnetic cylinder is meant a cylinder having 2P poles alternately poles regularly distributed over a circumference, P magnets North-South alternating regularly with P magnets South-North orientation.

  The multipole magnetic cylinders can be, for example, magnetic quadrupole (P = 2), hexapolar (P = 3), octopole (P = 4) or dodecapolar (P = 6) magnetic cylinders. Figures 4a and 4b show sectional views of hexapolar cylinders.

  The hexapolar cylinder 3a shown in FIG. 4a is a magnetic hexapole which comprises six magnets regularly distributed on a circumference, a North / South orientation magnet alternating with a South / North orientation magnet.

  The hexapolar cylinder 3b shown in FIG. 4b is a Halbach-type hexapole which also comprises six magnets distributed regularly over a circumference, a North / South orientation magnet alternating with a south / north orientation magnet, intermediate magnets enabling the establishing transition magnetizations between a North / South orientation magnet and the South / North orientation magnet which follows it or precedes it.

  Longitudinal magnetization magnetic cylinder means a magnetic cylinder whose magnetization is in every point parallel to the axis of the cylinder. FIG. 5 represents the cross-sectional view of a longitudinally magnetized magnetic cylinder 4 whose magnetization m3 is parallel to the axis of the cylinder.

  By way of non-limiting example, the magnetic structure of the photon source shown in FIG. 1 comprises, between the two transversally magnetized hollow magnetic cylinders 1, 2 located at the two ends of the chamber, five hexapolar hollow magnetic cylinders 3a, 3b. and four longitudinal magnetic magnet hollow cylinders 4, the latter being regularly interposed between the five hexapolar hollow magnetic cylinders. The cylinders 1 and 2 are each in contact with a magnetic hexapole, Halbach type or not.

  By way of non-limiting example, the dimensions of the cylinders 3a, 3b and 4 are as follows.

  a) Cylinder 3a: - external diameter Dia = 15.8cm, - internal diameter d3a = 5cm, - length = 8cm.

  b) Cylinder 3b: - external diameter D3b = 15.8cm, - internal diameter d3b = 5cm, - length = 3cm.

  c) Cylinder 4: - external diameter D4 = 15.8 cm, - internal diameter d4 = 5 cm, - length = 3 cm.

  More generally, the magnetic structure of the photon source according to the invention comprises, between the two hollow magnetic cylinders with transverse magnetization 1 and 2, N multipolar hollow magnetic cylinders, N being a number greater than or equal to 2, and N -1 hollow magnetic cylinders with longitudinal magnetization regularly interposed between the N hollow hexagonal magnetic cylinders. The number of closed surfaces S is then equal to N. Advantageously, the more the number N is high, the more the number of photons collected along the axis AA of the chamber CH is high.

  The material constituting the magnetic cylinders is, for example, an iron-neodymium-boron alloy. Also by way of non-limiting example, the remanent field Br has a value substantially equal to 1.33 Tesla and the coercivity at 200C is substantially equal to 1360 kA / m.

  FIG. 6 represents an improvement of the source of photons represented in FIG. 1. In addition to the elements represented in FIG. 1, the magnetic structure of the photon source comprises an additional hollow magnetic cylinder 5 with longitudinal magnetization which substantially surrounds all magnetic cylinders 3a, 3b and 4. Figure 7 shows a sectional view of a longitudinal magnet magnet hollow cylinder m4. Fastening means are then provided for fixing the cylinder 5 on at least one of the magnetic cylinders 3a, 3b or 4. Thus, the additional cylinder 5 may comprise, on its inner face, protuberances to fix it on at least a hollow magnetic cylinder with longitudinal magnetization 6 whose outer diameter is then reduced (for example, outer diameter of 12cm instead of 15.8cm as indicated above). The additional cylinder 5 and one of the cylinders 4 may also constitute a single unitary structure. The cylinder 5 advantageously increases the intensity of the axial field in the center of the chamber. By way of non-limiting example, the dimensions of the additional longitudinal hollow magnet cylinder 5 may be: external diameter D5 = 28cm, internal diameter d5 = 16cm, length = 26cm.

  By way of non-limiting example, are given, below, the magnetic characteristics obtained, in the context of the invention, for a source of photons according to FIG.

  five closed elementary resonance surfaces S are present in the chamber CH, on which the magnetic field Bres is substantially 0, 36T, an equimodule surface E on which the field is substantially 0, 72T (2x0,36T) surrounding the five elementary closed surfaces S, the expression of the magnetic field B (z) along the axis AA of the chamber CH is written (see equation (1) above): B (z) = Bmin + B1 (l + sin (z) ), with Bmin = 0.31T, Bres = 0.36T, Bmax = 0.6T, B1 = 0.145T - the maximum magnetic field strength obtained at the ends of the chamber is substantially equal to 0.81T .

REFERENCES

  [1] "Permanent magnet ECR source for generation of EUV light", S.K. Hatho et al., Lithography Int. Sematech, Santa Clara, CA-USA, Source Workshop, February 22, 2004.

  [2] "An all-permanent magnet ECR source ion for the ORNL MIRF upgrade project", D. Hitz et al., 16 International Workshop on ECR Ion Sources ECRIS'04; September 26-30, 2004; Berkeley, USA.

Claims (9)

  1 photon source comprising an electron cyclotron resonance (ECR) multicharged ion plasma source, characterized in that it comprises: a vacuum cylindrical plasma chamber (CH), of axis AA, provided with an opening (02) by which the photons are extracted from the chamber, - at least one microwave injection guide (GD) for injecting microwaves into the chamber (CH), - a device (I) for injecting gas to inject a gas (g) into the chamber (CH), -a pumping system (P) for pumping electrically neutral particles present in the chamber, and - a cylindrical magnetic structure (1, 2, 3a, 3b, 4) which surrounds the chamber (CH) and which produces, inside the chamber, a magnetic field distributed according to at least two closed surfaces (S) aligned along the axis AA, on which the magnetic field has a value substantially equal to the value (BRCE) of the electron cyclotron resonance field (ECR), these surfaces (S) are nt separated from each other, without contact with the chamber walls (CH) and located inside an additional surface (E) without contact with the chamber (CH), on which the magnetic field takes a value substantially constant equal to or greater than twice the value (BRcE) of the electron cyclotron resonance field (IB? 2 BRcE). 2. Photon source according to claim 1, in which the magnetic structure (1, 2, 3a, 3b, 4) comprises two hollow magnetic cylinders with transverse magnetization (1, 2), the magnetization (ml) of a first cylinder. hollow (1) having a direction opposite to the magnetization (m2) of the second hollow cylinder (2), N multipolar hollow magnetic cylinders (3a, 3b), N being a number greater than or equal to 2 and N-1 hollow magnetic cylinders with longitudinal magnetization (4), the two hollow magnetic cylinders with transverse magnetization (1, 2), the N multipolar hollow magnetic cylinders (3a, 3b) and the N-1 hollow magnetic cylinders with longitudinal magnetization (4) being aligned according to the axis AA of the chamber, the N multipolar hollow magnetic cylinders (3a, 3b) and the N-1 hollow magnetic cylinders with longitudinal magnetization (4) being placed between the two hollow cylinders with transverse magnetization, a hollow multipolar magnetic cylinder alternating with a cylinder longitudinally magnetized recess hollow, a first multipolar hollow magnetic cylinder adjoining a first transverse magnet hollow magnetic cylinder and a second multipolar hollow magnetic cylinder adjacent to the second transverse magnet hollow magnetic cylinder.   3. Photon source according to claim 2 wherein the N multipole hollow magnetic cylinders 30 are Halbach type hexapoles (3b).   The photon source of claim 2 wherein the N multipolar hollow magnetic cylinders are quadrupole cylinders.   The photon source of claim 2 wherein the N multipole hollow magnetic cylinders are hexapolar cylinders.   6. Photon source according to claim 2 wherein the N multipolar hollow magnetic cylinders are octopole cylinders.   The photon source of claim 2 wherein the N multipole hollow magnetic cylinders are twelve-pole cylinders.   8. photon source according to one of claims 2 to 7, wherein a hollow magnet magnet with additional longitudinal magnetization (5) substantially surrounds the assembly consisting of N multipolar hollow magnetic cylinders (3a, 3b) and N-1 hollow magnetic cylinders with longitudinal magnetization (4).   9. Photon source according to any one of the preceding claims wherein the gas is Xenon introduced into the chamber (CH) at a pressure of between 10-5 mbar and 10-4 mbar.