JPH0415609B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to semiconductor integrated circuit manufacturing technology, and particularly to improvements in electron beam lithography equipment for mask production and direct lithography.

[Technical background of the invention and its problems]

BACKGROUND ART Recently, electron beam lithography systems have been used to form fine patterns on samples such as semiconductor wafers and masks. There are many performances required of an electron beam lithography system, and one of them is an important problem regarding the electron beam itself, which contributes to actual lithography. In other words, if the electron beam is unstable, it becomes impossible to perform patterning as designed, and high-precision drawing cannot be performed. One aspect of the stability of the electron beam is the life of the cathode of the electron gun, and there is usually performance deterioration over time, i.e., a decrease in the beam current and a change in the beam diameter, until the resist is sufficiently exposed. ability is lost.

The causes of changes in beam current and beam diameter are in the cathode itself, and in particular in various physical properties in the cathode tip region where electrons are emitted. The present inventors conducted research on single-crystal lanthanum hexaboride (LaB ₆ ), which has a brightness more than 10 times that of tungsten, and found the following facts as a result. First, the electron emission of the LaB ₆ cathode has crystal orientation anisotropy, and furthermore, the long-term characteristics change over time is that when the LaB ₆ cathode is used at high temperatures of 1500 [℃] or higher, it evaporates and the tip shape changes. It's for a reason. This tendency is particularly strong when the conventionally used tip is spherical and has a small semi-longitudinal curvature of 15 [μm]. In addition, when the shape of the cathode tip is small, the electric field of the anode is concentrated in a narrow area and high brightness can be obtained, but this has the disadvantage that the beam tends to become multi-beam.
The range of bias, temperature, etc. that satisfies the writing conditions is narrow. Therefore, the beam characteristics change due to slight fluctuations in bias or temperature, and stability is still insufficient. The reason why the beam tends to become multiple beams is because the cathode tip is spherical, and because a crossover image is not formed at an aperture position in the middle of the optical system.

[Purpose of the invention]

An object of the present invention is to provide electron beam lithography that can reduce dependence of electron gun brightness, beam current, beam diameter, etc. on bias and cathode temperature, improve beam stability, and make beam intensity distribution uniform. The goal is to provide equipment.

[Summary of the invention]

The gist of the present invention is to provide a cathode shape that makes it difficult to form multiple beams, and to realize an optical system that selects only a part of the multi-beams and eliminates the drawbacks of the multi-beams. be.

First, in order to create a cathode shape that is unlikely to form multiple beams, the tip of the cathode, which was conventionally spherical, is processed into a flat surface. When the tip of a single-crystal LaB ₆ cathode is spherical, there are various orientations of the spherical tip. Furthermore, since electron emission usually has crystal anisotropy, electron emission is not uniformly performed from the entire region of the spherical surface. For this reason, the number of electron beams obtained is not one but a plurality, which tends to result in multi-beams.

FIGS. 1 a to 1 c are schematic diagrams showing crossover images obtained when the tip is spherical and the axis orientations are <100>, <110>, and <111>, respectively. Although there are multiple beams in any axial direction, these multiple beams can be converged into one by the space charge effect by increasing the Wehnelt bias of the electron gun. However, in this case, the bias range under usable conditions becomes narrower, and the brightness further deteriorates due to the space charge effect. Also,
Even if the cathode temperature is increased, it is possible to converge the beam into a single beam due to the space charge effect in the same way as described above, but in this case, the high temperature causes intense evaporation and shortens the life of the cathode. On the other hand, if the cathode tip is machined into a flat surface, there is only one axial orientation, and as a result, even if the bias is shallow and the cathode temperature is low, there is only one beam, which widens the usable range of bias and cathode temperature. . However, in this case, it is necessary to select a direction in which electron emission is likely to occur as the axial direction.

As for the axial orientation of the LaB ₆ cathode, it has been confirmed through experiments by the present inventors that <100> or <310> is the orientation in which electron emission is most likely to occur. In reference photos (1) to (4), the diameter of the tip plane is 150 [μm], and the axis directions are <100>, <110>, <111>, and <310, respectively.
＞ shows the electron emission intensity distribution from the LaB ₆ cathode. As is clear from these, the directions where electron emission is likely to occur are shown in reference photos (1) and (4).
100> and <310>, and it can be seen that in <110> and <111> shown in reference photos (2) and (3), almost no electrons are emitted from their plane regions.

On the other hand, when the cathode tip is flat, the electric field concentrates on the surrounding edges, resulting in a high electric field, making it easier for electrons to be emitted from these edges. This tendency is particularly strong when the tip plane area is narrow, and in addition to electrons from the center, multiple beams appear around it.
This may result in multiple beams.
In order to avoid this, the inventors of the present invention have conducted extensive research and found that it is only necessary to select a portion of the crossover image using the aperture. In other words, it has been found that by selecting a portion of the crossover image using an aperture mask having an aperture of a desired diameter, a single beam can always be obtained. In practice, it was most effective to magnify the crossover image and place an aperture at the magnified imaging position to allow only the central portion of the central beam to pass through.

The present invention focuses on these points and produces single crystal LaB ₆
In an electron beam lithography system that uses an optical system to irradiate the sample surface with an electron beam emitted from an electron gun using a cathode and forms an image of the electron gun crossover on the sample surface, the axial direction of the cathode is set to <100.
> or <310>, the tip of the cathode is processed into a flat surface, and an aperture mask is provided to select only the central portion of the crossover image.

〔Effect of the invention〕

According to the present invention, the axis orientation of the single-crystal LaB ₆ cathode is set to <100> or <310>, where electron emission is likely to occur, and the cathode tip is processed to be flat, so the Wehnelt bias cannot be made too deep. It is possible to combine the beams into one beam without increasing the cathode temperature too much. Therefore, dependence of the brightness of the electron gun, beam current, beam diameter, etc. on bias and temperature can be reduced, and beam stability can be improved. Furthermore, since only the central portion of the beam is selected using an aperture mask, the peripheral portion of the crossover image is cut out, making it possible to make the beam intensity distribution uniform. Furthermore, even in the case of multiple beams, it can be taken out as a single beam, so the beam stability can be further improved. Therefore, when drawing patterns on semiconductor wafers, masks, etc.
It is possible to improve drawing accuracy.

FIGS. 2 and 3 are diagrams showing the bias dependence of brightness and beam current, respectively, and FIGS. 4 and 5 are diagrams showing the temperature dependence of brightness and beam current, respectively. Note that the solid line in the figure shows the multi-beam state, and the broken line shows the case where only the central beam is selected by the aperture mask. Moreover, these are the results using a single-crystal LaB ₆ cathode with an axial orientation of <310> and a tip plane diameter of 50 [μm]. It can be seen from FIG. 2 that by using an aperture mask, the bias dependence of brightness is reduced. Similarly, FIG. 3 shows that the bias dependence of the beam current, FIG. 4 shows that the brightness depends on the cathode temperature, and FIG. 5 shows that the dependence of the beam current on the cathode temperature becomes small.

[Embodiments of the invention]

FIG. 6 is a schematic configuration diagram showing an electron beam lithography apparatus according to an embodiment of the present invention. In the figure, 1 is a single-crystal LaB ₆ cathode, 2 is a Wehnelt electrode, and 3 is an anode, which constitute an electron gun 4. As shown in FIG. 7, the cathode 1 has a flat tip 1a, and its axial direction is <100
> is set.

Electrons emitted from the electron gun 4 create a crossover image P below the anode 3, and an alignment coil 5 is disposed at this position. A magnifying lens 6 and an aperture mask 7 are arranged below the alignment coil 5. The diameter of the crossover image P is about 20 [μm], and this image P is enlarged about five times by the lens 6 and focused at the position of the aperture mask 7. The aperture diameter of the aperture mask 7 is formed to be 100 [μm] or less, and even if there are multiple crossover images P, only the central portion of one central beam is selectively passed through the aperture mask 7. ing. The beam passing through the aperture mask 7 is irradiated onto a sample surface 10 via an electron lens 8 and a deflector 9.

With such a configuration, it is possible to reduce the dependence of the aforementioned brightness, beam current, etc. on bias and cathode temperature, and of course, it is possible to measure beam stability. Further, since the beam on the aperture mask 7 is expanded using the magnifying lens 6, the aperture shape of the aperture mask 7 can be made large enough to be easily manufactured.

Note that the present invention is not limited to the embodiments described above, and can be implemented with various modifications without departing from the gist thereof. For example, the size of the aperture diameter of the aperture mask may be determined as appropriate depending on the size of the crossover to be obtained. Furthermore, if the aperture diameter of the aperture mask can be made as small as the electron gun crossover, it is possible to remove the magnifying lens by arranging the aperture mask at the crossover position. In addition, the shape of the single crystal LaB ₆ cathode is
The tip plane area may be rectangular as shown in FIGS. 8a and 8b.

[Brief explanation of drawings]

Figure 1 a to c are single crystals with spherical tips, respectively.
A schematic diagram showing the crossover image with respect to the axial direction of the LaB ₆ cathode, Figure 2 is a characteristic diagram showing the relationship between brightness and bias, Figure 3 is a characteristic diagram showing the relationship between beam current and bias, and Figure 4 is a characteristic diagram showing the relationship between beam current and bias. FIG. 5 is a characteristic diagram showing the relationship between brightness and cathode temperature, FIG. 5 is a characteristic diagram showing the relationship between beam current and cathode temperature, and FIG. 6 is a schematic configuration diagram showing an electron beam lithography apparatus according to an embodiment of the present invention. , FIG. 7 is a perspective view showing the main structure of the above embodiment, and FIGS. 8a and 8b are schematic views showing a modified example. 1... Single crystal LaB ₆ cathode, 2... Wehnelt electrode, 3... Anode, 4... Electron gun, 6...
Magnifying lens, 7...Aperture mask.

Claims (1)

[Scope of Claims] 1. In an electron beam lithography apparatus that irradiates an electron beam emitted from an electron gun onto a sample surface using an optical system and forms a crossover image produced by the electron gun on the sample surface, A single crystal lanthanum hexaboride whose axial direction is <100> or <310> and whose tip is flattened is used as the cathode, and the periphery of the crossover image is cut and only the central part is selected and passed through. An electron beam lithography apparatus comprising an aperture mask having an aperture. 2. The electron beam lithography apparatus according to claim 1, wherein the aperture mask is placed at a position where the crossover image is formed. 3. Claim 1, wherein the aperture mask is disposed at a position where the crossover image is enlarged and formed by a lens.
The electron beam lithography apparatus described in Section 1.