JPWO2008084537A1 - Electron gun and electron beam exposure apparatus - Google Patents

Abstract

An electron gun with improved brightness and an electron beam exposure apparatus with improved throughput by using the electron gun are provided. An electron gun comprising an electron source comprising lanthanum hexaboride (LaB6) or cerium hexaboride (CeB6), a suppressor electrode and an acceleration electrode, wherein the tip of the electron source is the suppressor electrode and the acceleration electrode. The electron source has an electron emission region and an electron emission restriction region, and the electron emission restriction region is a side surface of the electron source other than the electron emission surface of the electron source tip, Covered with carbon. The electron source may have a cylindrical shape with a tip portion having a diameter of 10 μm to 100 μm, and the tip portion of the electron source protrudes from the upper surface of the suppressor electrode by 2.5 mm or more. The distance between and may be 5 mm or less. [Selection] Figure 3

Description

  The present invention relates to an electron gun used in a lithography process for manufacturing a semiconductor device, and an electron beam exposure apparatus provided with the electron gun.

  In recent years, in an electron beam exposure apparatus, in order to improve throughput, a variable rectangular opening or a plurality of mask patterns are prepared in a mask, and these are selected by beam deflection and transferred and exposed on a wafer. As one of exposure methods using such a plurality of mask patterns, an electron beam exposure apparatus that performs partial batch exposure has been proposed. In partial collective exposure, the pattern is transferred to the sample surface as follows. That is, a beam is irradiated to one pattern region selected by beam deflection from a plurality of patterns arranged on the mask, and a beam cross section is formed into a pattern shape. Further, the beam that has passed through the mask is deflected back by a subsequent deflector, reduced to a fixed reduction rate determined by the electron optical system, and transferred to the sample surface.

By the way, in such an exposure apparatus, increasing the brightness is important for improving the throughput. In addition, since the aperture angle can be made small without impairing the current density due to the improvement in luminance, an improvement in resolution can be expected by reducing aberrations, which is particularly effective for fine patterns. In a conventional electron beam exposure apparatus, a hot cathode made of lanthanum hexaboride (LaB ₆ ) is used. The luminance is about 10 A / cm ² / sr / V, but from the above viewpoint, the luminance is twice or more.

As means for improving the angular current density, it has been proposed that the tip of an electron emitting cathode such as LaB ₆ is disposed between the control electrode and the extraction electrode and the electron emitting cathode is operated in a temperature limited region (Patent Document 1). ). This method increases the current density on the axis and improves the brightness, but on the other hand, the electron emission cathode side surface is outside the control electrode, so that the electron emission from there cannot be suppressed, and as a result There is a problem that the surplus current becomes large.
JP 2001-325910 A

  The present invention has been made in view of the problems of the prior art, and an object thereof is to provide an electron gun with improved luminance and an electron beam exposure apparatus with improved throughput by using the electron gun.

The above-described problem is that an electron source composed of lanthanum hexaboride (LaB ₆ ) or cerium hexaboride (CeB ₆ ), an electron gun composed of a suppressor electrode and an acceleration electrode, the tip of the electron source is connected to the suppressor electrode The electron source is disposed between the acceleration electrode, the electron source has an electron emission region and an electron emission restriction region, and the electron emission restriction region is a side surface of the electron source other than the electron emission surface of the electron source tip. The problem is solved by an electron gun characterized by being covered with carbon.

  In the electron gun according to this aspect, the electron source may have a cylindrical shape with a tip portion of 10 μm to 100 μm in diameter. In addition, the electron source includes a tip portion having a cylindrical shape with a diameter of 10 μm to 100 μm, an intermediate portion having a tapered side surface having a bottom surface having a larger area than the upper surface and the upper surface, and a maximum cross-sectional portion perpendicular to the axial direction. The length is longer than the diameter of the tip and is a cylinder or prismatic body having a shape of 2 mm or less. The upper surface of the intermediate portion and the end surface facing the electron emission surface of the tip are the same surface, and the bottom of the intermediate portion And the end surface of the main body portion may be the same surface, and the tip portion, the intermediate portion, and the main body portion may be integrated with the same central axis. The tip of the electron source may protrude from the upper surface of the suppressor electrode by 2.5 mm or more, and the distance between the tip of the electron source and the acceleration electrode may be 5 mm or less.

  In the present invention, the electron source is composed of a main body portion and a tip portion having an electron emission surface. The electron emission surface has a diameter of 10 μm to 100 μm, and the area of the electron emission surface is reduced. This makes it possible to increase the electric field strength and facilitate electron emission.

  Further, a tapered portion is provided between the cylindrical portion of the tip portion of the electron source and the main body portion. By configuring the electron source in this way, it is possible to lengthen the cylindrical portion that emits electrons as much as possible, and to increase the mechanical strength while suppressing the reduction of the electric field strength. .

  In the electron gun according to the above aspect, the tip of the electron source protrudes from the upper surface of the suppressor electrode by 2.5 mm or more, and the distance between the tip of the electron source and the acceleration electrode is set to 5 mm or less. While suppressing, it becomes possible to make the electron radiance from the restricted electron emission surface more than twice the conventional one.

It is a block diagram of the electron beam exposure apparatus which concerns on this invention. It is a block diagram of the electron gun which concerns on this invention. It is a block diagram of the electron source and electrode which concern on the electron gun of FIG. FIG. 4A is a diagram showing a luminance change when the amount of protrusion from the suppressor of the electron source is changed in the configuration of the electron source and the electrode according to the electron gun of FIG. FIG. 4B is a diagram showing a change in luminance when the distance between the tip of the electron source and the acceleration electrode is changed in the configuration of the electron source and the electrode according to the electron gun of FIG. 5A to 5C are cross-sectional views showing the shape of the tip of the electron source.

  Embodiments of the present invention will be described below with reference to the drawings.

First, the configuration of the electron beam exposure apparatus will be described. Next, the configuration of the electron gun will be described, and the configuration of the electron source which is a characteristic part of the present invention in the electron gun will be described. Next, a method for forming a region for limiting electron emission on the surface of the electron source will be described. Finally, the effect when the electron gun of this embodiment is used will be described.
(Configuration of electron beam exposure system)
FIG. 1 shows a configuration diagram of an electron beam exposure apparatus according to the present embodiment.

  The electron beam exposure apparatus is roughly divided into an electron optical system column 100 and a control unit 200 that controls each part of the electron optical system column 100. Among these, the electron optical system column 100 includes an electron beam generation unit 130, a mask deflection unit 140, and a substrate deflection unit 150, and the inside of the vacuum portion is decompressed.

  In the electron beam generator 130, the electron beam EB generated from the electron gun 101 is converged by the first electromagnetic lens 102, then passes through the rectangular aperture 103 a of the beam shaping mask 103, and the cross section of the electron beam EB is rectangular. To be shaped.

  Thereafter, the electron beam EB is imaged on the exposure mask 110 by the second electromagnetic lens 105 of the mask deflection unit 140. The electron beam EB is deflected to a specific pattern Si formed on the exposure mask 110 by the first and second electrostatic deflectors 104 and 106, and the cross-sectional shape thereof is shaped to the shape of the pattern Si.

  Although the exposure mask 110 is fixed to the mask stage 123, the mask stage 123 is movable in a horizontal plane, and the deflection range (beam deflection region) of the first and second electrostatic deflectors 104 and 106 is set. In the case of using the pattern S in the portion exceeding, the pattern S is moved into the beam deflection region by moving the mask stage 123.

  The third and fourth electromagnetic lenses 108 and 111 arranged above and below the exposure mask 110 play a role of forming an image of the electron beam EB on the substrate W by adjusting their current amounts.

  The size of the electron beam EB that has passed through the exposure mask 110 is reduced by the fifth electromagnetic lens 114 after being returned to the optical axis C by the deflection action of the third and fourth electrostatic deflectors 112 and 113.

  The mask deflection unit 140 is provided with first and second correction coils 107 and 109, which correct beam deflection aberrations generated by the first to fourth electrostatic deflectors 104, 106, 112, and 113. Is done.

  Thereafter, the electron beam EB passes through the aperture 115a of the shielding plate 115 constituting the substrate deflecting unit 150, and is projected onto the substrate W by the first and second projection electromagnetic lenses 116 and 121. As a result, the pattern image of the exposure mask 110 is transferred to the substrate W at a predetermined reduction ratio, for example, a reduction ratio of 1/10.

  The substrate deflecting unit 150 is provided with a fifth electrostatic deflector 119 and an electromagnetic deflector 120, and the electron beam EB is deflected by these deflectors 119 and 120, and an exposure mask is formed at a predetermined position on the substrate W. The pattern image is projected.

  Further, the substrate deflection unit 150 is provided with third and fourth correction coils 117 and 118 for correcting the deflection aberration of the electron beam EB on the substrate W.

  The substrate W is fixed to a wafer stage 124 that can be moved in the horizontal direction by a driving unit 125 such as a motor. By moving the wafer stage 124, it is possible to expose the entire surface of the substrate W.

  On the other hand, the control unit 200 includes an electron gun control unit 202, an electron optical system control unit 203, a mask deflection control unit 204, a mask stage control unit 205, a blanking control unit 206, a substrate deflection control unit 207, and a wafer stage control unit 208. Have. Among these, the electron gun control unit 202 controls the electron gun 101 to control the acceleration voltage of the electron beam EB, beam emission conditions, and the like. Further, the electron optical system control unit 203 controls the amount of current to the electromagnetic lenses 102, 105, 108, 111, 114, 116 and 121, and the magnification and focus of the electron optical system in which these electromagnetic lenses are configured. Adjust the position. The blanking control unit 206 controls the voltage applied to the blanking electrode 127 to deflect the electron beam EB generated before the start of exposure onto the shielding plate 115, and before the exposure, the electron beam EB is applied onto the substrate. Is prevented from being irradiated.

The substrate deflection control unit 207 controls the voltage applied to the fifth electrostatic deflector 119 and the amount of current to the electromagnetic deflector 120 so that the electron beam EB is deflected to a predetermined position on the substrate W. To. The wafer stage control unit 208 adjusts the driving amount of the driving unit 125 to move the substrate W in the horizontal direction so that the desired position on the substrate W is irradiated with the electron beam EB. The above-described units 202 to 208 are controlled in an integrated manner by an integrated control system 201 such as a workstation.
(Configuration of electron gun)
FIG. 2 shows a configuration diagram of the electron gun 101. The electron gun 101 includes an electron source 20, a heating element 22 for heating an electron source made of carbon, a support 23, a suppressor electrode 24, and an acceleration electrode 21. As the electron source 20, for example, single crystal LaB ₆ or CeB ₆ is used.

  In the electron gun 101 configured as described above, the electron gun control unit 202 keeps applying the electron source heating current to the electron source heating heating element 22 to heat the electron source 20 to keep the electron source 20 at a constant temperature. In this state, an electric field is applied between the electron source 20 and the acceleration electrode 21 to extract an electron beam having a predetermined energy from the electron source 20, and a substrate coated with a resist that fixes the electron beam on the wafer stage 124 is applied. Electron beam exposure is performed by irradiating W.

  Here, the voltage applied to the suppressor electrode 24 is 0 to −0.5 kV, and the voltage applied to the acceleration electrode 21 is +50 kV. These voltages are values with respect to the potential of the electron source 20, and since the electron source 20 is normally -50 kV with respect to a true earth ground, it is a value obtained by adding -50 kV.

  In this embodiment, electrons are emitted by applying a strong electric field while heating the electron source 20. For this reason, it is possible to prevent gas molecules from adsorbing to the surface of the electron source 20, and it is possible to prevent a decrease in luminance of the electron beam.

In addition, it is preferable that the tip of the electron source protrudes from the upper surface of the suppressor electrode by 2.5 mm or more and the distance between the electron source tip and the acceleration electrode is 5 mm or less because the luminance can be increased.
(Configuration of electron source)
Below, the structure of the electron source 20 used by this embodiment is demonstrated.

  FIG. 3 is a cross-sectional view showing a part of the electron source 20 and electrodes constituting the electron gun 101.

  The tip of the electron source 20 is disposed so as to be positioned between the suppressor electrode 24 and the acceleration electrode 21. A zero or negative voltage is applied to the suppressor electrode 24 with respect to the electron source 20 and functions to shield electrons emitted from portions other than the tip of the electron source 20.

  The tip of the electron source 20 is formed in a cylindrical shape, and the periphery is covered with carbon 30. The carbon 30 is formed on the surface of the electron source 20 by, for example, a CVD method. At the tip of the electron source 20, the material of the electron source 20 is exposed, and the exposed portion is flattened (20a). The surface from which electrons are emitted is preferably 10 μm to 100 μm in diameter, and usually 40 μm.

Further, the thickness of the carbon covering the periphery of the electron source 20 is desirably 5 μm. Since the coated carbon 30 has a work function larger than that of LaB ₆ or CeB ₆ used in the electron source 20, electron emission from other than the electron emission surface can be suppressed.

  Next, the positional relationship between the electron source 20, the suppressor electrode 24, and the acceleration electrode 21 will be described.

FIG. 4 shows the luminance when the protrusion amount (x1) of the tip of the electron source 20 from the suppressor electrode 24 and the distance (x2) between the tip of the electron source 20 and the acceleration electrode 21 shown in FIG. 3 are changed. In both cases, the suppressor electrode hole diameter was 2.5 mm, the electron emission surface diameter at the tip of the electron source was 0.08 mm, the acceleration electrode 21 hole diameter was 2 mm, and the potential of the acceleration electrode 21 with respect to the electron source 20 was +50 kV. As the electron source 20, a LaB ₆ single crystal was used.

FIG. 4A shows the result of fixing the distance (x2) between the tip of the electron source 20 and the accelerating electrode 21 to 5 mm. By setting the protrusion amount (x1) to 2.5 mm or more, the luminance can be improved. It can be seen that a doubled 20 A / cm ² / sr / V can be achieved. FIG. 4B shows the luminance when the distance (x1) between the tip of the electron source 20 and the suppressor electrode 24 is fixed to 2.5 mm and the distance between the tip of the electron source 20 and the acceleration electrode 21 is changed. FIG. As shown in FIG. 4B, as a result of fixing the protrusion amount (x1) to 2.5 mm, the distance (x2) between the tip of the electron source 20 and the acceleration electrode 21 is set to 5 mm or less. It can be seen that.

  Next, the shape of the electron source 20 will be described.

  As described above, the tip portion of the electron source 20 is cylindrical, and a diameter portion equivalent to the electron emission surface is required to some extent, but in order to give strength, a shape as shown in FIG. 5 was examined.

FIG. 5A shows an example of the shape of the electron source. As shown in FIG. 5A, the electron source includes a main body portion 52 and a tip portion 51. The tip portion 51 has a cylindrical shape with a diameter of 10 μm to 100 μm, and the main body portion 52 has a cylindrical or prismatic shape in which the maximum length of the cross section perpendicular to the axial direction is longer than the diameter of the tip portion and is 2 mm or less. The main body 52 and the tip 51 are integrated with the same central axis.

  FIG. 5B is an example of another electron source shape. As shown in FIG. 5B, the electron source is composed of a tip end portion 53 a, a truncated cone portion 53 b, and a main body portion 54. The tip 53a of the electron source has a cylindrical shape with a diameter of 10 μm to 100 μm. Further, the upper surface of the truncated cone portion 53b and the end surface facing the electron emission surface of the distal end portion 53a are the same surface. The main body 54 has a columnar or prismatic shape in which the maximum length of the cross section perpendicular to the axial direction is longer than the diameter of the tip 53a and 2 mm or less, and the bottom surface of the truncated cone 53b and the end surface of the main body 54 are the same. It is a surface. The tip 53a, the truncated cone 53b, and the main body 54 are integrated with the same central axis.

  FIG. 5C is an example of another electron source shape. As shown in FIG. 5C, the electron source includes a tip end portion 55 a, an intermediate portion 55 b, and a main body portion 56. The tip 55a of the electron source has a cylindrical shape with a diameter of 10 μm to 100 μm. The intermediate portion 55b has a top surface and a bottom surface having a larger area than the top surface, and has a tapered side surface. The intermediate portion 55b has a side surface that gradually becomes thinner toward the upper surface, and the upper surface of the intermediate portion 55b and the end surface facing the electron emission surface of the tip portion 55a are flush with each other. The main body 56 has a cylindrical or prismatic shape in which the maximum length of the cross section perpendicular to the axial direction is longer than the diameter of the tip 55a and 2 mm or less, and the bottom surface of the intermediate portion 55b and the end surface of the main body 56 are flush with each other. It is said. Further, the front end portion 55a, the intermediate portion 55b, and the main body portion 56 are integrated with the same central axis.

  In the structure of FIG. 5C, the side surface is gradually narrowed from the main body portion 56 toward the tip end portion 55a by applying the truncated cone portion 53b of FIG. 5B.

  Thus, in this embodiment, the electron source is comprised from the main-body part and the front-end | tip part which has an electron emission surface. The electron emission surface has a diameter of 10 μm to 100 μm, and the area of the electron emission surface is reduced. This makes it possible to increase the electric field strength and facilitate electron emission.

  Further, in the electron source described with reference to FIG. 5C, a tapered portion is provided between the cylindrical portion of the tip portion of the electron source and the main body portion. By configuring the electron source in this way, it is possible to lengthen the cylindrical portion that emits electrons as much as possible, and to increase the mechanical strength while suppressing the reduction of the electric field strength. .

As for the electron source described with reference to FIG. 5, the surface other than the electron emission surface is covered with a material (carbon) different from the material of the electron source (LaB ₆ or CeB ₆ ) as in the electron source of FIG. To.
(Method of forming a region for limiting electron emission on the surface of the electron source)
Next, a method for forming the region for limiting the electron emission in the electron source 20 will be described.

Here, the electron source having the structure shown in FIG. 3 is taken as an example, and a case where a single crystal of LaB ₆ is used as the electron source 20 will be described.

First, a LaB ₆ single crystal is processed so that the tip has a cylindrical shape with a diameter of 10 to 100 μm.

Next, in order to form a region that restricts electron emission, carbon 30 is coated on the surface of the LaB ₆ single crystal. This coating may be any method such as a CVD method, a vacuum deposition method, or a sputtering method. At this time, the thickness of the coating film may be a thickness that can sufficiently change the work function of the electron emission surface (make it larger than LaB ₆ ) and prevent evaporation of the LaB ₆ material. When carbon is used, it is preferable that the thickness of the carbon is 2 μm to 10 μm, considering that carbon reacts with oxygen and evaporates as CO ₂ .

Next, the tip of the electron source 20 is polished together with the coated film.
(effect)
As described above, in the present embodiment, since a large electric field can be applied to the exposed tip portion of the electron source 20, high-intensity electron emission can be achieved from the electron emission surface, and the electron gun is used as an electron beam exposure apparatus. By using this, high throughput can be realized.

  Further, since the opening angle can be made small without impairing the current density, an improvement in resolution can be expected by reducing aberrations, which is particularly effective for fine patterns.

  In addition, since the electron emission from the side surface of the electron source can be completely suppressed, degassing due to the electron beam irradiation around the electrode portion can be suppressed, and the problem that the vacuum is deteriorated can be avoided.

Further, since the exposed surface of LaB ₆ is practically only the center part of the tip of the electron gun, evaporation of the electron source 20 is suppressed, and substances such as LaB ₆ and CeB ₆ constituting the electron source 20 adhere to the back surface of the suppressor. Can be prevented. If these substances adhere to the back side of the suppressor, the deposits can become whiskers and can trigger micro discharges. In that case, when the electron beam exposure apparatus is used, a phenomenon that the amount of the electron beam and the irradiation position are not stable occurs. Therefore, even if the deformation of the electron source 20 of the electron gun 101 is small, the electron beam exposure apparatus cannot be used stably in a state where a minute discharge occurs.

Claims (5)

In an electron gun consisting of lanthanum hexaboride (LaB ₆ ) or cerium hexaboride (CeB ₆ ), a suppressor electrode and an acceleration electrode,
A tip of the electron source is disposed between the suppressor electrode and the acceleration electrode;
The electron source has an electron emission region and an electron emission restriction region,
The electron gun is characterized in that the electron emission restriction region is a side surface of the electron source other than the electron emission surface of the electron source tip and is covered with carbon. 2. The electron gun according to claim 1, wherein the electron source has a cylindrical shape with a tip portion having a diameter of 10 μm to 100 μm. The electron source includes a tip portion having a cylindrical shape with a diameter of 10 μm to 100 μm, an intermediate portion having a tapered side surface having a bottom surface wider than the upper surface and the upper surface, and a maximum length of a cross-sectional portion perpendicular to the axial direction. Is formed of a cylindrical or prismatic main body that is longer than the diameter of the tip portion and is 2 mm or less in length, and the upper surface of the intermediate portion and the end surface facing the electron emission surface of the tip portion are the same surface, and the bottom surface of the intermediate portion and the 2. The electron gun according to claim 1, wherein the end surface of the main body portion is the same surface, and the tip portion, the intermediate portion, and the main body portion are integrated with the same central axis. The tip of the electron source protrudes 2.5 mm or more from the upper surface of the suppressor electrode, and the distance between the tip of the electron source and the acceleration electrode is 5 mm or less. The electron gun according to the item. An electron beam exposure apparatus comprising the electron gun according to claim 1.

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