JP2005235605A - Electron gun and electron beam system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve the problem that a filament and a cathode are not electrically insulated in a satisfactory manner. <P>SOLUTION: In an electron gun having the cathode and the filament to heat the cathode by thermion, the cathode and the filament are insulated by an insulator including boron nitride. <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.

  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 perform sufficient emission (thermal electron emission) from the tantalum cathode 101, tantalum must be heated to about 2000 ° C. The filament 103 that generates bombardment electrons for heating tantalum is also heated to about 2000 ° C. in order to obtain sufficient electrons. When the heated ones are mechanically held together, the holding part becomes one place, and heat dissipation due to heat conduction is small. However, a bombardment voltage of 3 kV is applied between the cathode 101 and the filament 103. Therefore, both must be electrically insulated. For that reason, both of them are held in separate mechanical structures via insulators 110 such as ceramics. However, since ceramic exhibits electrical conductivity at high temperatures, it is difficult to achieve good insulation.

  Further, since each of the cathode 101 and the filament 103 has two mechanical contacts, there is a problem that heat dissipation due to heat conduction from the cathode 101 and the filament 103 is large, and heat utilization efficiency is poor.

Another problem is the exchange of the cathode 101 and the filament 103. Since the filament 103 and the cathode 101 are used at high temperatures, they have problems such as evaporation, deformation, and recrystallization due to heat, and are not permanently usable, and must be replaced every predetermined period. At the time of replacement, the filament 103 and the cathode 101 are not integrated into one unit, so that the replacement work takes time. That is, the downtime of the apparatus is increased. However, if the downtime of the apparatus becomes long, the total productivity of the apparatus decreases, so it is desirable that the maintenance can be completed in a short time.

  Furthermore, it is ideal that the cathode 101 and the filament 103 are positioned and fixed in advance. When the filament 103 is attached to the cathode 101 while being offset, the heated electrons from the filament 103 are biased toward the cathode 101 and a temperature deviation occurs in the cathode 101. The uneven temperature causes the uneven emission of electrons, and the illumination uniformity decreases. Conventionally, as described above, the filament 103 and the cathode 101 are independently fixed from the viewpoint of electrical insulation. That is, the filament 103 and the cathode 101 are aligned through a large number of mechanical members, and the positioning accuracy of each is poor. Furthermore, the cathode 101 must be positioned relative to the anode 112 acting as an electrostatic lens. Conventionally, since the cathode 101, the filament 103, and the anode 112 are fixed independently of each other, it is difficult to align them on the same axis.

  The present invention has been made in view of the above problems, and a first object thereof is to provide an electron gun and an electron beam exposure apparatus in which a filament and a cathode are electrically insulated well. It is a second object of the present invention to provide an electron gun and an electron beam exposure apparatus that have a short down time and a high alignment accuracy between the cathode and the filament.

  Therefore, according to the present invention, first, in an electron gun having a cathode and a filament for heating the cathode with thermoelectrons, the cathode and the filament are insulated by a insulator containing boron nitride. Provide an electron gun.

  Although it is possible to use ceramics such as alumina as insulation, ceramic is generally an insulator at room temperature, but begins to show electrical conductivity at high temperatures, so it is not suitable as an insulating material for parts used at high temperatures. It is. It is also conceivable to use SiC having a higher sintering temperature (2000 ° C. to 2300 ° C.) than ceramics such as alumina as another material that can withstand high temperatures. However, since SiC is a semiconductor, there is some electrical conduction at room temperature, and the volume resistivity further decreases at higher temperatures. When the volume resistivity decreases, there is a problem that the leakage current from the filament to the cathode increases. When a leak occurs, the bombardment current cannot be measured correctly, and it becomes difficult to operate the electron gun accurately.

  In contrast, in the present invention, boron nitride is used as a material for electrically insulating the filament and the cathode. Boron nitride has a sintering temperature as high as 3000 ° C and can be used in vacuum at a temperature of about 2200 ° C. There is little outgas even at high temperatures, and a high degree of vacuum can be maintained. For this reason, even if the insulator temperature rises due to heat conduction or heat radiation from a high-temperature cathode or filament, the electrical insulation can be maintained.

  The filament, the cathode and the insulator are preferably unitized.

  By unitizing, the positional relationship between the filament and the cathode can be adjusted and fixed. Accordingly, the positioning accuracy is improved because the unit and the anode need only be aligned with the anode or the like.

  It is preferable to further include a mount for detachably mounting the unit.

By making the unit detachable, the filament and the cathode can be exchanged in a short time.
Further, by using an electron beam apparatus equipped with the above-described electron gun, a highly accurate apparatus can be configured.

  As described above, in the present invention, since the cathode and the filament are insulated by the insulator made of boron nitride, it is possible to fix the both in a high temperature electron gun while being well insulated. In addition, by unitizing the cathode and the filament, it is possible to provide an electron gun with a short downtime and a high alignment accuracy between the cathode and the filament.

  FIG. 1 is a schematic configuration diagram of an electron gun used in an electron beam exposure apparatus showing an embodiment of the present invention.

  The cathode 1 is fixed to a tungsten cathode holder 2, and the cathode holder 2 is fixed to a insulator 4 made of boron nitride (BN) with screws 13. The end of the filament 3 is electrically connected and fixed to two electrodes (receptacles) 5, and the receptacle 5 passes through the insulator 4 and has a socket at the end opposite to the filament 3. The two electrodes (plugs) 7 are plugs such as banana plugs, and each plug is electrically connected by being inserted into the socket of the receptacle 5. The two plugs 7 are inserted into the high-pressure plug board 8 and are electrically connected to the cables 17 and 18. The feed-through is constituted by the plug 7, the plug board 8, and the plug 9 described later. Cables 17 and 18 are each connected to a voltage source. The cathode 1, cathode holder 2, insulator 4, filament 3, and receptacle 5 constitute a cathode unit, and the cathode unit is detachably fixed to a metal cathode mount 12. An electrode (plug) 9 is connected to the cathode mount 12 via a connector, the opposite end of the plug 9 is connected to a cable 19 via a high-voltage plug board 8, and the cable 19 is connected to a voltage source. The Reference numeral 10 denotes a vacuum partition, which together with the high-pressure plug board 8 constitutes a vacuum chamber of an electron gun. An exhaust cable 11 exhausts the inside of the electron gun. The cathode mount 12 is electrically insulated from the anode 16 by the insulator 14. Reference numeral 6 denotes an illumination optical system.

  The principle of electron beam emission is the same as in the prior art, and a voltage of Vf = 20 V is applied to the tungsten filament 3 to emit thermal electrons. A voltage of Vb = 3 kV is applied between the filament 3 and the cathode 1, and thermoelectrons are bombarded on the back surface of the cathode 1, whereby the cathode is heated and thermoelectrons are emitted from the surface of the cathode 1. The cathode 1 is applied with an acceleration voltage Vacc = -100 kV, and the anode 16 is at ground potential. Accordingly, the thermoelectrons 15 emitted from the cathode 1 are accelerated downward toward the illumination optical system 6.

  In FIG. 1, a cathode 1 and a filament 3 are fixed by a insulator 4 made of boron nitride. If it does in this way, the cathode 1 and the filament 3 which become high temperature will be confined in one cavity. If it does in this way, heat radiation will be confined in a cavity and heat will be hard to escape outside by heat radiation. For this reason, the use of a unit not only reduces the mechanical support points, but also has an advantage of easily confining heat radiation.

When the filament 3 and the cathode 1 are exchanged, the electrode 7 is first removed from the connector after the vacuum leak, and then the unit of the filament 3 and the cathode 1 is pulled out. The positional relationship between the cathode 1 and the filament 3 can be accurately fixed and fixed to the insulator 4 in advance. Therefore, when the cathode unit is fixed to the cathode mount 12 of the electron gun, only the positional relationship between the cathode unit and the anode 16 needs to be aligned, the replacement time is shortened, and the total positioning accuracy is improved. The cathode unit only needs to be held by one mechanical contact, and by reducing the contact area of that portion, heat dissipation due to contact heat conduction is reduced and thermal efficiency is improved. Moreover, since the filament and the cathode are positioned through a few mechanical structures, the alignment accuracy is improved.

  The electron gun in this embodiment can be applied to an electron beam apparatus such as an electron beam exposure apparatus and an electron beam microscope. When an electron gun whose cathode or filament is at a high temperature of 2000 ° C. or higher is used. It is particularly effective.

Schematic showing an electron gun according to an embodiment of the present invention Schematic showing the structure of a conventional electron gun

Explanation of symbols

1 ... cathode 2 ... cathode holder 3 ... filament 4 ... insulator

Claims (4)

An electron gun having a cathode and a filament for heating the cathode with thermoelectrons, wherein the cathode and the filament are insulated by a insulator containing boron nitride.   The electron gun according to claim 1, wherein the filament, the cathode, and the insulator are unitized.   The electron gun according to claim 2, further comprising a mount for detachably mounting the unit.   An electron beam apparatus comprising the electron gun according to claim 1.

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