JP5772424B2 - Plasma light source - Google Patents

Description

  The present invention relates to a plasma light source for EUV radiation.

  Lithography using an extreme ultraviolet light source is expected for fine processing of next-generation semiconductors. Lithography is a technique for forming an electronic circuit by exposing a resist material to light and a beam by reducing and projecting them onto a silicon substrate through a mask on which a circuit pattern is drawn. The minimum processing dimension of a circuit formed by photolithography basically depends on the wavelength of the light source. Therefore, it is essential to shorten the wavelength of the light source for next-generation semiconductor development, and research for this light source development is underway.

The most promising next generation lithography light source is an extreme ultra violet (EUV) light source, which means light in a wavelength region of about 1 to 100 nm. Hereinafter, the light in this region is called plasma light or simply EUV.
Since plasma light (EUV) has a high absorptivity with respect to all substances and a transmissive optical system such as a lens cannot be used, a reflective optical system is used. In addition, the optical system in this region is very difficult to develop and exhibits reflection characteristics only at a limited wavelength.

  Currently, a Mo / Si multilayer reflector having a sensitivity of 13.5 nm has been developed, and if a lithography technique combining light of this wavelength and the reflector is developed, it is expected that a processing dimension of 30 nm or less can be realized. ing. Development of a lithography light source with a wavelength of 13.5 nm is an urgent task for realizing further microfabrication technology, and radiation from a high energy density plasma has attracted attention.

  Light source plasma generation can be broadly classified into a laser irradiation (LPP: Laser Produced Plasma) method and a gas discharge (DPP: Discharge Produced Plasma) method driven by a pulse power technique. DPP has the advantage that the input power is directly converted into plasma energy, so that it has an advantage in conversion efficiency as compared with LPP, and the apparatus is small in size and low in cost.

  Patent Documents 1 to 3 have already been disclosed as gas discharge (DPP) type light source plasma generation means.

JP 2010-147231, “Plasma light source and plasma light generation method” JP 2011-54729 A, “Plasma Light Source” JP2011-54730, "Plasma light source"

  The plasma light sources disclosed in Patent Documents 1 to 3 have a structure in which plasma is confined between a pair of opposing coaxial electrodes, and a planar discharge (current sheet) that develops from two coaxial electrodes is coaxial. The plasma is contained by colliding at the center between the electrode-like electrodes and changing the current path.

FIGS. 1A and 1B are schematic diagrams of changing current paths. FIG. 1A shows a state immediately before changing, and FIG. 1B shows a state immediately after changing.
As shown in this figure, immediately before switching (A), a sheet discharge 2 is performed between the center electrode b and the guide electrode c in each coaxial electrode a, and immediately after switching (B). The tubular discharge 4 needs to be performed between the two central electrodes b in the two coaxial electrodes a. In this figure, 3 is plasma.

  However, as a result of actually producing and testing such a plasma light source, it is difficult to change the current path, and it is desired to stabilize the operation of changing the current path and further improve the output, stability and reliability of the plasma light source. was there.

  The present invention has been developed to satisfy such a demand. That is, the object of the present invention is to increase the stability of changing the current path for connecting the planar discharge generated in the two coaxial electrodes to the tubular discharge between the coaxial electrodes, the output of the plasma light source, the stability, An object of the present invention is to provide a plasma light source capable of improving reliability.

According to the present invention, a pair of coaxial electrodes disposed opposite to each other, and a discharge environment holding device that supplies a plasma medium in the coaxial electrodes and maintains a temperature and pressure suitable for plasma generation,
The coaxial electrode includes a rod-shaped center electrode extending on a single axis, a tubular guide electrode that surrounds the center electrode at a predetermined interval, and a center electrode and a distal end portion of the guide electrode. It consists of a ring-shaped insulator that insulates,
The center electrode is located on the axis, and the tip portions thereof are opposed to each other with a space therebetween.
Further, a discharge voltage having a reversed polarity is applied to the end portions of the pair of center electrodes to generate a sheet discharge between the center electrode and the guide electrode, respectively, and the pair of center electrodes are generated by the sheet discharge. A plasma light source comprising a plasma control device that forms a single plasma at an intermediate position between them, and then forms a plasma confining magnetic field by confining the plasma by switching the planar discharge to a tubular discharge between a pair of central electrodes Because
A plasma light source is provided, comprising: a connecting conductor that directly and directly couples the tip portions of the pair of guide electrodes, wherein only a central portion of the connecting conductor is grounded.

According to the apparatus of the present invention, since the connecting conductor for electrically directly connecting the tip portions of the pair of guide electrodes is provided, and only the central portion of the connecting conductor is grounded, the current path is changed. Before and after, the tip portions of the pair of guide electrodes are always fixed at the same potential (ground potential).
Therefore, before and after current path switching, a potential relationship is established in which the potential difference between the center electrodes is in the forward direction of the current and the potential difference between the guide electrodes is zero, and current switching is likely to occur.

In other words, at the “change time”, the pair of center electrodes maintain the polarity (+ or −) of the applied discharge voltage, respectively, and there is a forward potential difference in the change direction for both planar discharges. In addition, since the tip portions of the pair of guide electrodes are always fixed at the same potential (ground potential), the connection is smoothly changed.
Therefore, the stability of changing the current path can be improved, and the output, stability, and reliability of the plasma light source can be improved.

It is a schematic diagram of the connection of a current path. 1 is an embodiment diagram of a plasma light source according to the present invention. FIG. It is a figure which shows the electrical potential relationship immediately before the conventional change. It is a figure which shows the electric potential relationship just before the change by this invention.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. In addition, the same code | symbol is attached | subjected to the common part in each figure, and the overlapping description is abbreviate | omitted.

FIG. 2 is a diagram showing an embodiment of a plasma light source according to the present invention.
In this figure, the plasma light source of the present invention includes a pair of coaxial electrodes 10 and a discharge environment holding device 20.

The pair of coaxial electrodes 10 are disposed opposite to each other with the symmetry plane 1 as the center.
Each coaxial electrode 10 includes a rod-shaped center electrode 12, a tubular guide electrode 14, and a ring-shaped insulator 16.

  The rod-shaped center electrode 12 is a conductive electrode extending on a single axis ZZ. The center electrode 12 has an outer peripheral surface that is axisymmetric with respect to the axis ZZ.

The tubular guide electrode 14 is preferably configured to be rotationally symmetric with respect to the axis ZZ, and surrounds the center electrode 12 at a predetermined interval and holds a plasma medium therebetween. The plasma medium is preferably Xe, Sn, Li or the like.
The shape of the guide electrode 14 is not limited to rotational symmetry, and may be a rectangle, for example.
An insulating plate 26 is sandwiched between the guide electrode 14 and the vacuum chamber 22 (see FIG. 2), and the guide electrode 14 is insulated from the vacuum chamber 22.

The ring-shaped insulator 16 is a hollow cylindrical electrical insulator positioned between the end portions of the center electrode 12 and the guide electrode 14, and electrically insulates between the center electrode 12 and the end portions of the guide electrode 14. .
The insulator 16 is preferably rotationally symmetric with respect to the axis ZZ, but the present invention is not limited to this shape, and electrically insulates between the center electrode 12 and the end portions of the guide electrode 14. As long as it is other shapes, such as a rectangle.

  The center electrodes 12 of the pair of coaxial electrodes 10 described above are located on the same axis line ZZ, and the tip portions thereof are opposed to each other with a space therebetween.

The discharge environment holding device 20 supplies a plasma medium into the coaxial electrode 10 and holds the coaxial electrode 10 at a temperature and pressure suitable for plasma generation. The temperature suitable for plasma generation is, for example, 0 to 300 ° C., and the pressure suitable for plasma generation is, for example, a vacuum degree of 1 to 10 × 10 ⁻⁶ torr.
The discharge environment holding device 20 can be constituted by, for example, a vacuum chamber 22, an exhaust device 24, a gas supply system, a temperature controller, and a plasma medium supply device. The vacuum chamber 22 and the exhaust device 24 are essential, but the gas supply system, temperature controller, and plasma medium supply device are not essential.

In FIG. 2, the plasma light source of the present invention further includes a plasma control device 30.
The plasma control device 30 applies a discharge voltage having a reversed polarity to the end portions of the pair of center electrodes 12 to generate a sheet discharge 2 between the center electrode 12 and the guide electrode 14, respectively. 2, a single plasma 3 is formed at an intermediate position between the pair of center electrodes 12, and then the planar discharge 2 is changed into a tubular discharge 4 (see FIG. 1) between the pair of center electrodes 12. It has a function of forming a magnetic field that can contain.
The “intermediate position” for forming the plasma 3 is not limited to the symmetry plane 1 and may be a position other than the midpoint of the center electrode 12 tip.

  In FIG. 2, the plasma control device 30 includes a connecting conductor 32, a positive voltage source 34, a negative voltage source 36, and a timing control device 40.

The connecting conductor 32 electrically directly couples the tip portions of the pair of guide electrodes 14.
In this example, the connecting conductor 32 is a conductor having a low electrical resistance, for example, a metal wire, a rod, a plate, or the like made of a conductor such as gold or copper, and both ends of the pair of guide electrodes 14 are opposed to each other. Are connected by brazing or the like. The number of the connecting conductors 32 is not limited to one and may be plural.
The electrical resistance of the connecting conductor 32 is preferably as small as possible, and the potential of the pair of coaxial electrodes 10 is statically the same potential, and preferably transiently less than 10% of the applied voltage.
Moreover, the structure of the connection conductor 32 is not limited to this example, For example, you may electrically couple | bond the front-end | tip part of a pair of guide electrode 14 directly. Further, the pair of guide electrodes 14 may be replaced with a single guide electrode 14, and a necessary opening (for example, an opening for gas or light) may be provided in a part thereof.

  In this example, only the central part of the connecting conductor 32 is grounded, and the terminal part of the guide electrode 14 is kept at a floating voltage.

The positive voltage source 34 accumulates energy in the discharge capacitor 37b, and applies a positive discharge voltage higher than the ground voltage (0 V) to the central electrode 12 on one side (left side in the figure).
The negative voltage source 36 stores energy in the discharge capacitor 37b, and applies a negative discharge voltage lower than the ground voltage (0 V) to the other center electrode 12 (right side in the figure).

  The timing control device 40 controls the application timing of the positive voltage source 34 and the negative voltage source 36.

  In FIG. 2, the positive voltage source 34 and the negative voltage source 36 each have a high voltage power storage device 37 and a trigger switch 38.

  Each of the high voltage power storage devices 37 includes a high voltage power source 37a and a discharge capacitor 37b, and charges the discharge capacitor 37b with a predetermined high voltage. The predetermined high voltage (charging voltage) is preferably a positive voltage or a negative voltage of 10 to 15 kV.

  The trigger switch 38 includes a high voltage pulse generator 38a and a gap switch 38b. The trigger switch 38 outputs a high voltage pulse from the high voltage pulse generator 38a and operates the gap switch 38b. In this example, resistors R1 and R2 are provided to protect the gap switch 38b.

The timing control device 40 outputs a pulse signal to the high voltage pulse generator 38a, operates the high voltage pulse generator 38a by this pulse signal, and operates the gap switch 38b.
By the operation of the gap switch 38b, the gap switch 38b is short-circuited, and a high voltage charged in the discharging capacitor 37b is applied to each coaxial electrode 10.

In FIG. 2, the end portions of the pair of guide electrodes 14 are not directly grounded (grounded) but are grounded via a connecting conductor 32.
One end of the discharge capacitor 37b of the positive voltage source 34 is connected to the end of the guide electrode 14, and the other end is applied to a positive (+) high voltage higher than the ground voltage.
One end of the discharge capacitor 37b of the negative voltage source 36 is connected to the end of the guide electrode 14, and the other end is applied to a negative (−) high voltage lower than the ground voltage.
The high voltage of the positive voltage source 34 and the negative voltage source 36 is preferably a positive voltage or a negative voltage of 10 to 15 kV.

  Further, the timing control device 40 includes a timer (not shown) for setting a time difference between pulse signals output to the respective high voltage pulse generators 38a, and controls the timing at which the discharge voltage is applied to each coaxial electrode 10. It can be done.

In FIG. 2, a residual resistance R and a floating inductance L (not shown) exist between the trigger switch 38 and the center electrode 12. The current waveform when the voltage is applied is determined by the applied voltage V, the floating inductance L, the capacitance C1 of the discharging capacitor 37b, the resistors R1 and R2, and the residual resistor R.
In the present invention, the current waveform at the time of voltage application is a sine wave of period T, and the quarter period (T / 4) is preferably 0.5 to 3 μs, and preferably 1 to 2 μs. Is particularly preferred.

  FIG. 3 is a diagram showing a potential relationship immediately before the conventional connection change. In this figure, (A) is a schematic diagram of a conventional plasma light source, and (B) is a diagram corresponding to (A) and showing a potential relationship immediately before switching.

FIG. 3A is different from the plasma light source of the present invention described above in the following points.
(1) The terminal portions of the pair of guide electrodes 14 are grounded (grounded).
(2) One end of the discharging capacitor 37b of the positive voltage source 34 and the negative voltage source 36 is grounded.
(3) The connecting conductor 32 of the present invention is not provided, and the tip portions of the pair of guide electrodes 14 are not electrically connected.

FIG. 3B shows the positive voltage source side (points A +, B +, C +, D +) and the negative voltage source side (points A−, B−, C−, D−) of FIG. The voltage is shown.
In FIG. 3B, since the points D + and D− are grounded (earthed), they are fixed at the same potential (grounded potential).
In this case, since the voltage at the tip (B +) of the center electrode 12 on the positive voltage source side is higher than the voltage at the tip (B−) of the center electrode 12 on the negative voltage source side, the voltage from the point B + to the point B− It is possible to change the current.

On the other hand, as shown in FIG. 1B, after changing the current, from the tip (C−) of the guide electrode 14 on the negative voltage source side to the tip (C +) of the guide electrode 14 on the positive voltage source side. Current needs to flow.
However, in the example of FIG. 3B, since the voltage of C− immediately before the change is lower than the voltage of C +, the change of the current in this direction is difficult to occur.

  FIG. 4 is a diagram showing a potential relationship immediately before the connection change according to the present invention. In this figure, (A) is a schematic diagram of the plasma light source of the present invention, and (B) is a diagram corresponding to (A) and showing a potential relationship immediately before switching.

FIG. 4B shows a positive voltage source side (points A +, B +, C +, D +) and a negative voltage source side (points A−, B−, C−, D−) of FIG. The voltage is shown.
In FIG. 4B, the tip portions (points C + and C−) of the guide electrode 14 are electrically directly coupled by the connecting conductor 34, and only the central portion of the connecting conductor 34 is grounded (grounded). Therefore, the point C + and the point C− are fixed to the same potential (ground potential).
In this case, since the voltage at the tip (B +) of the center electrode 12 on the positive voltage source side is higher than the voltage at the tip (B−) of the center electrode 12 on the negative voltage source side, the voltage from the point B + to the point B− It is possible to change the current.

  On the other hand, as shown in FIG. 1B, after changing the current, from the tip (C−) of the guide electrode 14 on the negative voltage source side to the tip (C +) of the guide electrode 14 on the positive voltage source side. Although the current needs to flow, in the example of FIG. 4B, the potential at the point C + and the point C− immediately before the switching is the same potential, so that the switching of the current in this direction can be easily performed.

As described above, according to the apparatus of the present invention, the connecting conductor 32 that directly couples the front ends of the pair of guide electrodes 14 is provided, and only the central portion of the connecting conductor 32 is grounded. The front ends of the pair of guide electrodes 14 are always fixed at the same potential (ground potential) before and after changing the current path.
Therefore, before and after current path switching, a potential relationship is established in which the potential difference between the center electrodes 12 is in the forward direction of the current and the potential difference between the guide electrodes 14 is zero, and current switching is likely to occur.

That is, at the “change time point”, the pair of center electrodes 12 maintain the polarity (+ or −) of the applied discharge voltage, and the potential difference in the forward direction in the change direction is connected to both planar discharges 2. In addition, the tip portions of the pair of guide electrodes 14 are always fixed at the same potential (ground potential).
Therefore, the stability of changing the current path can be improved, and the output, stability, and reliability of the plasma light source can be improved.

  In addition, this invention is not limited to embodiment mentioned above, is shown by description of a claim, and also includes all the changes within the meaning and range equivalent to description of a claim.

1 symmetry plane, 2 planar discharge, 3 plasma, 4 tubular discharge,
10 coaxial electrode, 12 center electrode, 14 guide electrode, 16 insulator,
20 discharge environment holding device, 22 vacuum chamber,
24 exhaust device, 26 insulating plate,
30 plasma control device, 32 connecting conductors,
34 positive voltage source, 36 negative voltage source,
37 high voltage power storage device, 37a high voltage power supply, 37b discharge capacitor,
38 trigger switch, 38a high voltage pulse generator,
38b Gap switch, 40 timing control device

Claims (2)

A pair of coaxial electrodes arranged opposite to each other, and a discharge environment holding device that supplies a plasma medium in the coaxial electrodes and maintains a temperature and pressure suitable for plasma generation,
The coaxial electrode includes a rod-shaped center electrode extending on a single axis, a tubular guide electrode that surrounds the center electrode at a predetermined interval, and a center electrode and a distal end portion of the guide electrode. It consists of a ring-shaped insulator that insulates,
The center electrode is located on the axis, and the tip portions thereof are opposed to each other with a space therebetween.
Further, a discharge voltage having a reversed polarity is applied to the end portions of the pair of center electrodes to generate a sheet discharge between the center electrode and the guide electrode, respectively, and the pair of center electrodes are generated by the sheet discharge. A plasma light source comprising a plasma control device that forms a single plasma at an intermediate position between them, and then forms a plasma confining magnetic field by confining the plasma by switching the planar discharge to a tubular discharge between a pair of central electrodes Because
A plasma light source, comprising: a connecting conductor that directly and electrically couples the tip portions of the pair of guide electrodes, wherein only a central portion of the connecting conductor is grounded. The plasma control device comprises:
A positive voltage source for applying a positive discharge voltage higher than the ground voltage to one central electrode;
A negative voltage source for applying a negative discharge voltage lower than the ground voltage to the other central electrode;
The plasma light source according to claim 1, further comprising: a timing control device that controls application timing of the positive voltage source and the negative voltage source.