JP2005235604A - Electron gun and electron beam system using it - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electron gun which reduces heat dissipation from a cathode and to provide an electron beam system using it. <P>SOLUTION: The electron gun includes the cathode, a means to heat the cathode and a cathode holder to hold the cathode, wherein at least a portion of the cathode holder which comes into contact with the cathode includes a supporter of a small contact area. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an electron gun used in an electron beam apparatus such as an electron beam exposure apparatus or an electron microscope, and an electron beam apparatus using the same.

  In recent years, research and development of electron beam exposure apparatuses capable of exposing finer semiconductor integrated circuits have been actively conducted. In particular, an apparatus that shrinks and transfers a pattern such as an electronic circuit formed on a mask called an EB (electron beam) reticle onto a wafer by a projection lens of an electron optical system has attracted attention. The exposure area (field) of this apparatus is about 250 μm on the wafer, which is very large compared to other EB (electron beam) exposure apparatuses. Therefore, an electron gun with high emittance that can uniformly illuminate the field is required. As a gun with high emittance, a technology to heat a large-diameter tantalum single crystal by electron bombardment has been proposed (High emittance source for PREVAIL projection lithography system, J. Vac. Sci. Technol. B 17 (6), 2856 (1999).). As shown in FIG. 2, this electron gun has a cathode 101 having a polished (111) face of a tantalum single crystal having a diameter of 10 mm and a filament 103 for heating the back surface of the cathode 101 to emit thermoelectrons 105. The cathode 101 is fixed to the cathode holder 102, and the cathode holder 102 is fixed to the lens barrel via the insulator 107. Further, the filament 103 is fixed to the filament fixing portion 108, and the fixing portion 108 is fixed to the cathode holder 102 via the insulator 110. 111 and 113 are aperture plates for cutting excess thermoelectrons from the cathode holder 102.

  As a heating method of the cathode, first, the tungsten filament 103 is energized and heated by applying a voltage of Vf, and the thermoelectrons 104 are emitted. This voltage is usually around 20V. A voltage of Vb is applied to the back surface of the filament 103 and the cathode 101, and the thermoelectrons 104 from the filament 103 are accelerated to the back surface of the cathode 101 and bombarded. The bombardment voltage Vb is usually about 3 kV. The bombarded electrons are finally absorbed by the back surface of the cathode 101 while converting kinetic energy into thermal energy. An acceleration voltage (Vacc) of −100 kV is applied to the cathode 101, and the thermoelectrons 105 emitted from the cathode when heated are directed toward the illumination optical system 106, which is a ground potential, and are accelerated downward. . Thereafter, a reticle (not shown) is illuminated by a lens system (not shown).

In order to provide sufficient emissions from the tantalum cathode, the tantalum must be heated to about 1700 ° C. On the other hand, the tantalum cathode is mechanically held by the cathode holder 102. Therefore, heat is dissipated to the surroundings by heat conduction from the cathode holding portion. If the heat dissipation is large, more bombardment energy, that is, a larger amount of thermionic electrons must be given to the cathode, and the efficiency of heat utilization becomes worse. When a large amount of heat is generated in a vacuum, the cathode holder locally becomes hot and melts, and there are problems of thermal expansion, softening due to heat, deformation of the member due to recrystallization, and thermal deterioration of the member. In addition, if the heat dissipation is large, a wider part must be heated, and an increase in the volume of the heated part leads to an increase in the heat capacity, and it takes a long time to heat and cool it. That is, the thermal time constant increases. This means that it takes time to operate the apparatus or that it takes time to bring down the apparatus due to maintenance (for example, about half a day), and the total productivity is lowered. Further, when a wide portion of the cathode is heated, heat is transferred to the cathode holder accordingly, so that the temperature of the cathode holder rises. Therefore, the part where the temperature of the cathode holder becomes high must use a heat-resistant material such as a refractory metal, and the size of the cathode holder may need to be increased. It becomes. Further, refractory metals such as tungsten are expensive materials, and are very difficult to machine, leading to high cost of parts. Furthermore, in order to generate a large amount of heat, the load on the power source for heating also increases, leading to an increase in the size of the power source, an increase in noise, and an increase in cost.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide an electron gun with reduced heat dissipation from the cathode and an electron beam apparatus using the electron gun.

    A first means for solving the problem includes a cathode, a means for heating the cathode, and a cathode holder for holding the cathode, and the cathode holder has a contact area at least in a portion in contact with the cathode. An electron gun having a small support.

  In this means, since the support body having a small contact area is disposed at the portion where the cathode and the cathode holder are in contact with each other, the contact thermal conductivity is reduced, and the heat dissipation through the portion can be reduced. Heat dissipation in vacuum is only contact heat conduction and heat transfer by radiation, and keeping one factor small is effective in improving heat utilization efficiency. Therefore, the cathode can be efficiently heated with less bombardment energy. Moreover, since there is little heating, the thermal load with respect to a member can be reduced and the thermal expansion of a member, a thermal deformation, and deterioration by heat can be prevented. In addition, the cathode holder can be made smaller, the amount of refractory metal used can be reduced, and the cost can be greatly reduced. Moreover, the heating part can be reduced in size, the thermal time constant can be shortened, and the productivity of the apparatus can be improved. Furthermore, the power load can be reduced, and the cost and noise can be reduced.

  The support may be integrated with the cathode holder, or may be disposed separately between the cathode holder main body and the cathode, as will be described later.

    In this case, the support is preferably a paper made of fibers of a high melting point material.

  Since the paper made of fibers is thread-like and has a small contact area, it is possible to reduce heat dissipation from the cathode.

  In this case, it is preferable that the high melting point material fiber is made of carbon.

  Carbon has good electrical conductivity, and can be used as a drain for bombardment electrons (thermoelectrons) incident on the back surface of the cathode or to supply emission electrons (thermoelectrons) emitted from the cathode surface from the holder.

  In this case, it is preferable that the high melting point material fiber is made of ceramic.

  Ceramic is an insulator, but since it has electrical conduction at high temperatures, it is also used as a drain for bombardment electrons (thermoelectrons) incident on the backside of the cathode, or for holding emission electrons (thermoelectrons) emitted from the cathode surface. It is possible to supply from.

  It is preferable to further have means for electrically connecting the cathode and the cathode holder. In some cases, the cathode holder and the cathode must be electrically connected. In such a case, if the support 8 has poor electrical conductivity, it may be electrically connected separately.

The second means for solving the problem includes a cathode, a means for heating the cathode, a cathode holder for holding the cathode, and a holder contact member for making mechanical contact with the cathode holder, In the electron gun, the cathode holder and the holder contact member are mechanically connected via a support having a small contact area.
The cathode holder is also heated by heat from the cathode and filament. Therefore, it is necessary to reduce the propagation of heat from the cathode holder to a member (for example, an insulating insulator) that is in mechanical contact with the cathode holder. In this case, heat dissipation can be prevented by arranging a support having a small contact area. As this support, it is possible to use a paper made of a fiber having a high melting point, and it is possible to use carbon or ceramic as a material.
Further, when these electron guns are used in an electron beam apparatus, it is possible to provide an apparatus with high accuracy and low cost.

  As described above, according to the present invention, since the support having a small contact area is brought into contact with the cathode, it is possible to reduce heat dissipation from the cathode.

  FIG. 1 is a diagram showing a schematic configuration of an electron gun used in an electron beam apparatus according to an embodiment of the present invention. The configuration of the electron gun is substantially the same as that of the conventional electron gun shown in FIG. 2, but the filament fixing part 108 and the insulator 110 are omitted for convenience of explanation.

  The cathode 1 is fixed to the cathode holder 2 via the support 8, and the cathode holder 2 is fixed to the insulator 7 via the support 10. Reference numeral 6 denotes an illumination optical system, 3 denotes a filament, 4 denotes thermoelectrons emitted from the filament, and bombardment electrons for heating the cathode. The voltage Vf applied to the filament, the voltage Vb applied between the filament and the cathode, and the voltage Vacc applied between the cathode and the anode 11 are the same as those described in the prior art.

It is known that carbon paper made of carbon fiber and ceramic paper made of paper made of ceramic fibers reduce contact thermal conductivity (CV Madhusudana,
Thermal Contact Conductance, P94, Springer). Carbon paper has been attracting attention as a fuel cell electrode material that has recently been studied as a fuel for automobiles. The reason is the large surface area of the carbon paper. A large surface area means that the unevenness of the surface is very large, and conversely means that the contact area is small. Therefore, the contact thermal conductivity can be reduced. In FIG. 1, by using this carbon paper as the support 8, heat dissipation due to contact can be reduced. Since the cathode holder 2 also serves as a peripheral electrode, it must be electrically connected to the cathode 1. In this respect as well, since carbon has good electrical conductivity, it is convenient to use as a drain for bombardment electrons incident on the cathode back surface or to supply emission electrons emitted from the cathode surface from the holder. Furthermore, the melting point of carbon is as high as 3500 ° C or higher, much higher than 1800 ° C, the temperature at which the cathode emits sufficient thermoelectrons, and there is no concern about melting due to heat.

Similarly, ceramic paper can be used as the support 8 for thermal insulation. Ceramic is an insulator, but begins to show electrical conduction at high temperatures. Therefore, it is convenient to use as a drain for bombardment electrons incident on the back surface of the cathode or to supply emission electrons emitted from the cathode surface from the holder. In addition, when further electric conduction is required, as shown in FIG. 1, if the cathode is fixed to the holder 2 with a metal screw 9, electrons can flow in and out through the metal screw 9. However, in this case, heat insulation is deteriorated because heat is dissipated through the screw 9. Therefore, it is preferable to determine the material and shape of the screw 9 in consideration of the amount of electrons flowing in and out and the amount of heat conduction. In addition, as long as it does not require the function of fixing and is only electrically connected, a means (wire or the like) for electrically connecting the cathode 1 and the cathode holder 2 may be used instead of screws.

  Since the heat resistance of ceramic is about 1000 ° C., for example, when used for an electron gun in which the temperature near the center of the cathode is as high as 1800 ° C., the heat resistance is low. Therefore, it is also possible to increase the size of the cathode to some extent and adapt to a portion where the temperature is lowered (that is, a portion where heat resistance is sufficiently maintained). The actual electron gun has a more complicated shape, and there are a number of mechanical contact points in the part far from the cathode, and there is a part where current inflow and outflow do not occur so much. Therefore, for example, as shown in FIG. 1, it is possible to use a support 10 made of ceramic paper between the insulating insulator 7 that electrically insulates the holder from the ground potential and the holder 2. Since such a position is far from the cathode 1, it can be used at a heat-resistant temperature. As the material of the support 10, it is possible to use the above-described carbon paper or other materials having a small contact area.

  The electron gun in this embodiment can be applied to electron beam apparatuses such as an electron beam exposure apparatus and an electron beam microscope, and is particularly effective when an electron gun whose cathode is at a high temperature is used.

It is a figure which shows the outline of the electron gun by embodiment of this invention. It is the schematic which shows the conventional electron gun.

Explanation of symbols

1 ... cathode 2 ... cathode holder 3 ... filament 7 ... insulator 8 ... support 9 ... metal screw

Claims (10)

An electron gun comprising: a cathode; means for heating the cathode; and a cathode holder for holding the cathode, wherein the cathode holder has a support having a small contact area at least in a portion in contact with the cathode.   2. The electron gun according to claim 1, wherein the support is a paper made of a fiber of a high melting point material.   3. The electron gun according to claim 2, wherein the fiber of the high melting point material is made of carbon.   3. The electron gun according to claim 2, wherein the fibers of the high melting point material are made of ceramic.   5. The electron gun according to claim 1, further comprising means for electrically connecting the cathode and the cathode holder. A cathode, a means for heating the cathode, a cathode holder that holds the cathode, and a holder contact member that makes mechanical contact with the cathode holder, the cathode holder and the holder contact member having a contact area An electron gun characterized in that it is mechanically connected via a small support.   7. The electron gun according to claim 6, wherein the support is a paper made of fibers of a high melting point material.   8. The electron gun according to claim 7, wherein the fiber of the high melting point material is made of carbon.   8. The electron gun according to claim 7, wherein the fibers of the high melting point material are made of ceramic.   An electron beam apparatus using the electron gun according to claim 1.

Images