JPH0125403Y2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to an electron beam source in which thermionic emission from various parts of the emission surface is uniform.

Recently, electron beam exposure equipment has been attracting attention as a means of manufacturing LSI devices and VLSI devices. especially,
It is equipped with a plurality of slit plates having polygonal holes and a deflection system placed between each of the slit plates to deflect the electron beam that has passed through the holes in the upper slit plate. ) variable area electron beam exposure equipment that attempts to obtain an electron beam with a cross section of
It is considered promising because it is significantly superior in terms of drawing speed and accuracy, as the pattern is written in one shot or by connecting multiple beams (referred to as area exposure) with a cross-section that corresponds to the size and shape of the pattern. has been done. Now, in such a variable area electron beam exposure system, it is necessary to make the current density distribution of each square beam uniform, so an electron beam source with a cathode with a wide electron emission surface (referred to as the emission surface) is desired. . However, conventional electron beam sources heat a rod-shaped cathode material and emit thermoelectrons from the emission surface of the material. It became difficult to make the heating temperature uniform over the entire surface, and it was not possible to make the amount of thermionic electrons emitted from each part of the emission surface uniform. Even if a beam with a predetermined shape and size and cross section is created from the electron beam emitted from such an emission surface,
Since the emitted electron density differs depending on the location on the emission surface, it is difficult to obtain a beam with a uniform current density. In such cases, in order to draw a pattern directly on the sample, if the beam is irradiated onto the resist surface coated on the sample and developed, for example, when using a positive resist, the current density may be lower than the sensitivity of the resist. The area where the beam hit will remain as it is,
When a beam having a current density higher than the sensitivity is applied, a portion near the edge of the pattern is developed together with the pattern due to the proximity effect (see Japanese Patent Application No. 51-133898). Therefore, pattern drawing accuracy is significantly reduced.

The present invention was made in view of the above points, and includes a hot cathode having a flat electron emitting surface and an electron emitting member that becomes thicker toward the center, and a hot cathode having an electron emitting member that becomes thicker toward the center. The object of the present invention is to provide a novel electron beam source, which is equipped with a means for passing an electric current, and has a uniform amount of thermionic electrons emitted from each part of the electron emitting surface of the hot cathode.

FIG. 1 shows a hot cathode section of an electron beam source showing an embodiment of the present invention. The hot cathode part has a hollow cylindrical part 1, an electron emitting member 2, and a central metal column 3 standing upright from the member at the center of the member. Both are made of metals such as tantalum. Basically, there is no need to generate heat in the central metal column 3 and the hollow cylindrical portion 1, so when the three portions are made of the same material as in this embodiment, the central metal column 3 and the hollow cylindrical portion 1 are It is desirable that the cross-sectional area of these parts be sufficiently large so that the resistance of the hollow cylindrical part 1 is small. In addition, in order to avoid a situation where the resistance of the central metal column 3 becomes excessive and only the center of the electron emitting surface is heated,
The cross-sectional area of the central metal column 3 and the cross-sectional area of the hollow cylindrical portion 1 are made the same. Although not shown outside the cathode part, there is a heating power source for passing a heating current I between the central metal column 3 and the outer peripheral wall to heat the member, and an anode disposed below the electron emitting member 2. (not shown) and an acceleration power source for accelerating thermoelectrons emitted from the electron emitting surface E of the member is provided between the member and the member. Now, the shape of the electron emitting member 2 is set as follows.

FIG. 2a is a view of the electron-emitting member 2 viewed from below, that is, a view showing the electron-emitting surface E, FIG. 2b is a view of the member viewed from the side, and FIG. 2c is a view of FIG. 2b. It is an enlarged view of the part. For example, the amount of heat C per unit area between r and r+dr from the center of the electron emission surface is given by the heating current I, the current density J, the resistivity of the bottom part ρ, and the thickness of the bottom part h: The calorific value per unit volume is ρJ ² = ρ
(I/2πrh) ² , so C=2πrhdrρ(I/2πrh) ² /2πrdr=ρI ² /4π ² r ² h. In this formula ρI ² /4π ² r ² h, ρI ² and 4π ²
is a constant value. Therefore, in order to make the amount of heat generated at any part of the electron emission surface E constant, the shape of the member 2 should be set so that the value of r ² h is constant. The shape of the member set in this way is such that the electron emitting surface E is flat and the surface opposite to the electron emitting surface is h∝
It is formed into a curved surface symmetrical about the central axis in accordance with the formula 1/r ² .

In this way, the electron emitting member is formed, and the central metal column 2
When a heating current is passed between the E and the outer peripheral wall, the amount of heat generated from each part of the electron emitting surface E of the member, that is, the amount of heat dissipated, becomes uniform, so the heating temperature is uniform over the entire surface of the electron emitting surface. The same amount of thermoelectrons can be emitted from each part of the electron emitting surface. Note that the direction in which the heating current is passed may be either from the metal column 3 to the hollow cylindrical portion 1 or from the hollow cylindrical portion 1 to the metal column 3.

Further, the end portion of the hollow cylindrical portion forming the side portion of the hot cathode portion may be divided into a sagging shape. Furthermore, a lead wire may be provided instead of the central metal pillar.

According to the present invention, it is possible to realize an electron beam source having a cathode portion in which the amount of thermionic electrons emitted from each part of the electron emission surface is uniform, thereby improving pattern drawing accuracy in electron beam exposure. Furthermore, the electron beam source of the present invention has an extremely simple construction.

[Brief explanation of drawings]

FIG. 1 is a hot cathode section of an electron beam source showing an embodiment of the present invention, FIG. 2 a is a bottom view of the electron emitting surface of the hot cathode section, and FIG. 2 b is the same electron emitting surface. FIG. 2c is a partially enlarged view of FIG. 2b. 1: Hollow cylinder part, 2: Electron emission member, 3: Central metal column, E: Emission part.

Claims (1)

[Scope of utility model registration request] An electron-emitting device comprising: a hot cathode consisting of a hollow cylinder having a flat electron-emitting surface at the bottom; a central metal column standing upright from the bottom along the central axis of the cylinder; and means for passing a current through the entire electron-emitting member. An electron beam source characterized in that the thickness of the electron emitting member changes depending on the distance from the center so that the temperature of the electron emitting surface is constant.