JP2006054270A - Extreme-ultraviolet light generator - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an extreme-ultraviolet light generator wherein the damages to the collector due to debris can be effectively suppressed. <P>SOLUTION: The extreme ultraviolet light generator comprises a discharge gas inlet path 10 for supplying a discharge gas into a capillary 11C; a capillary structure 11 with the coaxial cylindrical capillary 11C arranged at the center, and the peripheral part, formed of an insulator; and an anode 12 and a cathode 13 which are connected to both sides of the capillary 11C. There are provided a nozzle 17 and a diffuser 18 arranged above the axis of the capillary 11C, arranged near the capillary 11C a debris-shielding mechanism which sends out a curtain gas from the nozzle 17 and collects it by the diffuser 18. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an extreme ultraviolet light (EUV) generator using a discharge generation plasma system.

  As one of methods for generating extreme ultraviolet light (EUV) having a wavelength of about 10 nm to 13 nm, a method using a discharge generated plasma method (discharge produced plasma, hereinafter referred to as “DPP method”) is known. Yes.

  FIG. 5 shows an example of a typical conventional DPP type extreme ultraviolet light generator, and particularly shows a partial cross-sectional view around the discharge part. In the figure, xenon gas (Xe), for example, is introduced from a discharge gas introduction path 100 into a capillary 101C disposed at the center of a capillary (thin tube) structure 101 made of an insulator such as ceramics. When a high voltage is applied to the cathode 103, plasma is generated between both electrodes through the inside of the capillary, and extreme ultraviolet light is generated. Since the capillary 101C serving as the discharge part becomes high temperature, the cooling water introduction port 104, the cooling water discharge port 105, and the cooling water circulation passage 106 are provided inside the apparatus to circulate the cooling water. The extreme ultraviolet light radiates at a constant condensing angle α (more precisely, a solid angle) and is collected by a condensing system (not shown) provided with a condensing mirror or the like. Since extreme ultraviolet light is easily absorbed and attenuated by a neutral gas, the light condensing system is placed under a high vacuum.

  For example, Patent Document 1 discloses an extreme ultraviolet light source, and the structure of the discharge portion is considered to be substantially the same as the above configuration.

  The extreme ultraviolet light generators according to the present invention are all premised on discharge generated plasma (DPP), but unlike this, Patent Document 2 discloses laser generated plasma (laser produced plasma, hereinafter “ Nozzle structure used in an extreme ultraviolet light generator of “LPP system”) is disclosed. This will be described later.

JP 2003-288998 A JP 2001-319800 A

  The problem with the above-mentioned conventional DPP type extreme ultraviolet light generator is that the capillary structure becomes extremely hot due to discharge, so that part of the capillary structure evaporates and harmful dust (debris) is generated. Impinging on and collecting on the collector), damaging the mirror and significantly reducing the reflectivity.

  This invention makes it a technical subject to provide the extreme ultraviolet light generator which makes it possible to suppress effectively the damage of the collector by debris.

  In the first extreme ultraviolet light generator 1 according to the present invention, a discharge gas introduction path 10 for supplying a discharge gas to a capillary 11C and a coaxial cylindrical capillary 11C are arranged in the center and the periphery thereof is made of an insulator. The capillary structure 11 and an anode 12 and a cathode 13 connected to both ends of the capillary 11C are provided. A nozzle 17 and a diffuser 18 are provided on the axial front of the capillary 11C, and curtain gas is sent from the nozzle 17. A debris shield mechanism for collecting the curtain gas by the diffuser 18 is provided in the vicinity of the capillary 11C.

  The second extreme ultraviolet light generator 20 according to the present invention includes a first gas flow passage 24 having an annular cross section, a nozzle 21 having a second gas flow passage 25 inside thereof, and the first and second portions. And a diffuser 22 provided so as to face the gas flow path, and the nozzle 21 and the diffuser 22 are configured as discharge electrodes. Since this apparatus discharges using a nozzle and a diffuser as electrodes, it is not necessary to use a discharge tube for main discharge as in the prior art, and debris generation can be effectively reduced.

  In this apparatus, it is preferable that the nozzle 21 and the diffuser 22 are coaxially arranged, and further includes a preliminary ionization mechanism 23 on the axis thereof and in the vicinity of one end of the nozzle. If it does in this way, a plasma jet will be formed in the 2nd gas flow passage through which discharge gas circulates, and main discharge can be started reliably.

According to the first extreme ultraviolet light generator according to the present invention, the debris generated in the discharge part is effectively removed.
Moreover, according to the 2nd extreme ultraviolet light generator which concerns on this invention, curtain gas and discharge gas cannot interfere easily, and it is easy to take pressure matching. In addition, since the light is condensed from the radial direction with respect to the axial direction of the capillary structure, a wide condensing angle can be obtained. Therefore, more extreme ultraviolet light can be sent out to a condensing system (illumination optical system) in which an exposure apparatus or the like is installed.

(First embodiment)-Dynamic gas curtain system-
As a first embodiment, there is a method of removing debris by providing a debris shield mechanism using curtain gas such as helium in front of the discharge part on the axis.

  FIG. 1 shows an example of a DPP type extreme ultraviolet light generator showing one of the embodiments of the present invention, and particularly shows a partial cross-sectional view around a discharge part. The structure of the discharge part itself can adopt the same structure as the conventional one, but is characterized in that a debris shield mechanism is provided to prevent the debris from diffusing into the condensing system.

  In FIG. 1, a discharge gas, for example, xenon gas (Xe), is introduced from a discharge gas introduction path 10 into a capillary 11C disposed at the center of a capillary (thin tube) structure 11 made of an insulator. When a high voltage is applied to 12 and the cathode 13, plasma is generated between both electrodes through the inside of the capillary, and extreme ultraviolet light is generated. Since the capillary 11C serving as the discharge portion becomes high temperature, the cooling water introduction port 14, the cooling water discharge port 15, and the cooling water circulation passage 16 are provided inside the apparatus to circulate the cooling water and cool it.

  Furthermore, a nozzle 17 and a diffuser 18 are provided in front of the capillary 11C on the axis, and a debris shield mechanism is provided that sends out curtain gas such as helium gas from the nozzle 17 and collects the curtain gas by the diffuser 18. The diffuser is used such that it is always evacuated by a vacuum pump (not shown) such as a turbo molecular pump (TMP).

  The nozzle 17 needs to be able to send out the curtain gas at a high speed, and the diffuser 18 is provided with faces having different slopes so that the pressure is converted between the nozzle side and the pump side. It is preferable that the configuration be This is because with such a configuration, the pressure can be recovered by the diffuser, and high-speed gas can be continuously recovered even by a pump having a small exhaust capacity.

  By continuously flowing the curtain gas, a gas curtain 19 serving as a debris shield is formed. Since this gas curtain 19 is provided in contact with the condensing system exhausted to a high vacuum, it is necessary to keep the curtain gas flowing at a certain high speed. For example, the flow rate of curtain gas can take various values depending on conditions, but it is considered that at least several times the speed of sound (speed of about Mach 5) is necessary. The curtain gas is preferably a gas that does not absorb EUV light, for example, an inert gas such as helium gas.

  These debris shield mechanisms are provided so that the gas curtain is perpendicular to the axial direction of the discharge part, and the gas curtain 19 is, for example, a columnar shape (19a) having a certain width as shown in FIG. Alternatively, it is preferable that the shape of the nozzle and the diffuser is devised to form a planar sheet shape (19b) as shown in FIG. Moreover, what completely blocks debris in a wider range than the solid angle of EUV radiation is preferable.

  With the configuration described above, even if debris is generated in the discharge part, the gas curtain 19 can prevent the debris from being mixed into the light collecting system.

Second Embodiment-Double Coaxial Nozzle Method-
In the method described in the first embodiment, when a gas curtain is provided in the vicinity of the discharge portion in order to increase the condensing angle, a discharge gas (xenon gas or the like) and a curtain gas (helium gas or the like) are generated. Interference and pressure matching become very difficult, and conversely, if the distance between the gas curtain and the discharge part is increased, the width of the gas curtain must be increased in order to obtain a large condensing angle. This consumes a large amount of curtain gas and makes it difficult to design a nozzle for generating a wide and stable uniform gas curtain. Thus, the system described in this embodiment has been conceived.

  FIG. 3 shows an example of a DPP-type extreme ultraviolet light generator according to the second embodiment of the present invention, and particularly shows the periphery of the discharge part. The structure of the discharge part adopts a novel configuration completely different from the conventional one. FIG. 3A shows a front view of the apparatus, and FIG. 3B shows a partial cross-sectional view thereof.

  The extreme ultraviolet light generator 20 shown in FIGS. 3A and 3B includes a nozzle 21 having first and second gas flow passages 24 and 25 through which two kinds of gas pass, and these two kinds. A pre-ionization discharge tube 23 is provided near one end of the nozzle 21 (on the discharge gas introduction side) as necessary.

  4A shows an XX sectional view in FIG. 3B, and FIG. 4B shows a YY sectional view in FIG. 3B. As shown in FIGS. 3 and 4, the nozzle 21 is substantially cylindrical and has a first gas flow passage 24 having a circular cross section cut perpendicular to the central axis of the cylinder, A cylindrical second gas flow passage 25 including a central axis is provided on the inner peripheral portion.

  The respective gases introduced from the curtain gas introduction port 24a and the discharge gas introduction port 25a pass through the gas flow passages 24 and 25 and are discharged from the opposite gas discharge ports 24b and 25b.

  On the other hand, these two kinds of gases are recovered from the gas recovery port 26a by the diffuser 22 installed facing the nozzle 21 in the positional relationship as shown in FIG. The recovered gas passes through the gas flow passage 26 and is exhausted from the gas discharge port 26b. In such a system in which gas flows coaxially and in the same direction, the gas can be supplied and the exhaust system can be stably operated with a relatively small vacuum pump.

-About the mechanism of discharge-
Unlike the DPP method using a conventional capillary, in this embodiment, the nozzle 21 and the diffuser 22 each serve as an electrode. First, the discharge gas and the curtain gas are allowed to flow from the nozzle 21 to adjust the central portion to a predetermined pressure while forming a cylindrical gas curtain on the outside. The flow rate of the curtain gas is, for example, about Mach 5, and the flow rate of the discharge gas is such that the internal pressure becomes a predetermined discharge pressure (for example, 66.5 Pa (0.5 Torr) to 665 Pa (5 Torr)). In this way, when a high-speed gas flow is formed around the periphery, a decrease in the gas density at the center can be suppressed.

  In this state, for example, when a voltage is applied to both ends of the both electrodes using a predetermined discharge circuit with the nozzle 21 as a cathode and the diffuser 22 as an anode, a high-temperature and high-density pinch plasma P between the nozzle 21 and the diffuser 22 is applied. And extreme ultraviolet light is emitted in a radial direction (that is, in all directions perpendicular to the central axis) with respect to the central axis of the nozzle and the diffuser. In addition, since the nozzle 21 and the diffuser 22 are used as electrodes, it is necessary to be made of a conductive member such as metal. Although the distance between the two electrodes varies depending on the discharge conditions, for example, the distance between the electrodes may be about 10 mm at the end.

  When performing high-frequency pulse discharge by the above-described discharge mechanism, the discharge tube does not exist (corresponding to the discharge tube is a cylindrical high-speed gas flow), so that the discharge is difficult to start. Therefore, in order to increase the discharge starting efficiency, it is preferable to provide a preliminary ionization discharge mechanism (a preliminary ionization discharge tube and a preliminary ionization circuit) if necessary, and to provide the preliminary discharge tube 23 in the vicinity of the discharge gas inlet 25a of the nozzle 21. In this way, since the discharge gas forms a plasma jet in a straight line on the central axis of the nozzle, it is possible to reliably start discharge (referred to as “main discharge” with respect to preliminary discharge).

  Specifically, when a DC discharge tube is provided as a preionization discharge tube and a pulse voltage is applied to the discharge electrodes of the main discharge circuit (both ends of the nozzle 21 and the diffuser 22), the main discharge pinch plasma generates a pulse discharge of at least about 10 kHz. It can be carried out. Of course, while the frequency is low, the preliminary ionization discharge and the main discharge may be synchronized and both may be pulse discharges.

  In this way, since the discharge gas is confined in the cylindrical space formed by the curtain gas and the high-temperature and high-density pinch plasma is generated, the gas curtain functions as a discharge tube. That is, since a discharge tube such as a capillary structure is not required, the occurrence of debris generated from the discharge part is suppressed, and even if debris occurs from the main discharge part for some reason, the gas curtain Since it is completely wrapped, there is no worry that debris leaks out from the discharge part to the outside (condensing system).

  Furthermore, since the emitted light is radiated in all directions in the radial direction with respect to the central axes of the nozzle and the diffuser, the light collection angle is extremely large. Further, since the gas curtain at the sonic level completely surrounds the discharge gas, there is almost no interference between the discharge gas and the gas curtain.

  Furthermore, since the curtain gas flows at a high speed such as Mach 5, for example, a cooling effect of the electrode part (nozzle 21 and diffuser 22) is also expected, and therefore, it is considered that not much debris generated from the electrode is generated.

  As described above, in the case of laser-produced plasma (LPP method), a nozzle having two gas flow passages having a structure similar to that of the second embodiment of the present invention is known (see above). Patent Document 2), a gas flow passage having an annular cross section (“second channel” in the same document) is for limiting the lateral expansion of the first gas flow that flows through the central portion, and the present invention. It is not for producing a gas curtain. In the case of the LPP method, in order to generate plasma, a laser must be irradiated from the outside, and a nozzle and a diffuser are not used as electrodes. In the case of the LPP method, a preliminary ionization mechanism is not necessary. Furthermore, since it is excited by a laser, the problem of debris generation is not as serious as the DPP method.

  According to the extreme ultraviolet light generator according to the present invention, the generation of debris can be significantly suppressed as compared with the conventional case. In particular, the extreme ultraviolet light generation apparatus described in the second embodiment proposes a completely new discharge generation plasma generation method different from the conventional one, and not only minimizes the generation of debris but also wide condensing. In the sense that a corner can be obtained, its technical significance is extremely large.

FIG. 1 shows an example of a DPP-type extreme ultraviolet light generator showing one embodiment of the present invention, and particularly shows a partial cross-sectional view around a discharge part. FIG. 2 is a schematic diagram showing how debris generated together with extreme ultraviolet light from the capillary 11C is blocked by the gas curtain 19. As shown in FIG. (A) shows the columnar gas curtain 19a, and (b) shows the flat gas curtain 19b. FIG. 3 shows an example of a DPP type extreme ultraviolet light generator according to the second embodiment of the present invention, and particularly shows the structure around the discharge part. (A) is the front view of an apparatus, (b) has shown sectional drawing. 4A shows an XX sectional view in FIG. 3B, and FIG. 4B shows a YY sectional view in FIG. 3B. An example of a typical conventional DPP type extreme ultraviolet light generator is shown, and in particular, a partial cross-sectional view around a discharge portion is shown.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Extreme ultraviolet light generator 10 which concerns on 2nd Embodiment 10 Discharge gas introduction path 11 Capillary (thin tube) structure 11C Capillary 12 Anode 13 Cathode 14 Rejected water inlet 15 Cooling water discharge port 17 Nozzle 18 Diffuser 20 1st implementation Extreme ultraviolet light generator 21 nozzle (electrode)
22 Diffuser (electrode)
23 Pre-ionization discharge tube 24 1st gas flow path 25 2nd gas flow path

Claims (3)

A discharge gas introduction path for supplying a discharge gas to the capillary; a capillary structure in which the capillary is disposed at the center and made of an insulator; and an anode and a cathode connected to both ends of the capillary. An extreme ultraviolet light characterized in that a nozzle and a diffuser are provided in front of the capillary axis, and a debris shield mechanism is provided in the vicinity of the capillary for sending out curtain gas from the nozzle and collecting the curtain gas with the diffuser. Generator. A first gas flow passage having an annular cross section, a nozzle having a second gas flow passage inside thereof, and a diffuser provided facing the first and second gas flow passages. And the extreme ultraviolet light generator characterized by comprising the said diffuser as a discharge electrode. 3. The extreme ultraviolet light generator according to claim 2, wherein the nozzle and the diffuser are arranged coaxially, and further include a preionization mechanism on the axis thereof and in the vicinity of one end of the nozzle.

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