JPH0130247B2 - - Google Patents

Description

[Detailed Description of the Invention] This invention relates to lanthanum hexaboride (LaB ₆ ).
This article relates to an electron gun using a single crystal chip.

In recent years, electron guns using LaB ₆ single crystal chips have come to be used in electron beam equipment such as electron beam exposure equipment. This is largely due to advances in LaB ₆ single crystal manufacturing technology and advances in stable heating technology for single crystal chips. Although this electron gun has the advantages of high brightness and long life, there are still problems to be solved as described below.

(1) The crossover diameter created by the emitted electron beam is unstable with respect to chip temperature, bias voltage, and operating time.

(2) To make the crossover shape circular,
The chip heating temperature must be increased until the evaporation rate of LaB ₆ increases, or the bias voltage must be increased until the electron emission is nearly cut off in a region where the temperature is not raised that high.

(3) The intensity distribution (emission pattern) of the emitted electron beam is a flower pattern, as is well known.
In order to make this circular, as in (2), the heating temperature or bias voltage must be increased.

(4) When the chip is heated to high temperatures, LaB ₆ evaporates accumulate on the inner surface of the Wehnelt, making the operation of the electron gun unstable.

In view of the above points, this invention makes it possible to obtain an electron beam with a circular cross-over shape and circular emission pattern without particularly increasing the heating temperature and bias voltage of the chip, and therefore enables longer life operation. The purpose of the present invention is to provide an electron gun using a LaB ₆ single crystal chip.

This invention was derived from an analysis of the state of electron emission from a conventionally used LaB ₆ single crystal chip. First, the conventional LaB ₆ single crystal chip will be explained. Figure 1 shows the shape of the chip.
One end of the square prism is a square pyramid, and the tip of this square pyramid is machined into a conical shape, and the electron beam is emitted from the conical tip.

Figures 2a, b, and c show the emission patterns of the emitted electron beam when the axes of the chip shown in Figure 1 are set to [100], [110], and [111], respectively. . These patterns depend on the chip heating temperature and bias voltage. For example, when the axis of the chip is set to [100], the emission pattern, that is, the pattern shown in Fig. 2a, changes depending on the heating temperature and bias voltage as shown in Figs. 3a and 3b. Here, the heating temperature is T ₁ 1300℃,
T ₂ 1400℃, T ₃ 1500℃, T ₄ 1600℃.
The bias voltage strongly depends on the geometry of the electron gun, but V ₁ <V ₂ <V ₃ < ₄ .

Electron beam equipment generally has multiple apertures on the electron beam path to prevent beam scattering, but as shown in Figure 3, for example, when the heating temperature is T ₃ and the bias voltage is V ₃ , there are 4 locations where the axis of the electron beam can be aligned. There are several. FIG. 4 is an example showing how the apertures are aligned in that case. 41 is the aperture, 42 ₁ ~
42 ₄ is an emission pattern projected onto the aperture plane, and 43 is a crossover image. As is clear from the figure, there are four locations where the axis of the aperture 41 can be aligned. However, in reality, the four electron beams have different intensities,
It is necessary to overlap the largest one. This operation is very tedious and often results in incorrect alignment.

As is clear from FIG. 3, if the heating temperature or bias voltage of the chip is made sufficiently high, the electron beams overlap to form a circular emission pattern, making it easy to align the apertures. However, as mentioned above, increasing the heating temperature of the chip until the emission pattern becomes circular will make the electron gun unstable and shorten its life. Furthermore, if the bias voltage is increased until the emission pattern becomes circular, sufficient brightness will not be obtained.

Next, Figures 5a, b, and c are crossover images of the emitted electron beam when the axes of the chip shown in Figure 1 are set to [100], [110], and [111], respectively. They correspond to the emission patterns of FIG. 2a, b, and c, respectively. These crossover shapes also depend on the chip heating temperature and bias voltage. The situation is shown in FIGS. 6a and 6b, corresponding to FIGS. 3a and 3b, when the chip axis is set to [100]. As is clear from the figure, the spots in the crossover image are separated into four when the heating temperature and bias voltage are low, and become one when the heating temperature or bias voltage is raised sufficiently.

In an electron beam exposure apparatus, the diameter of the crossover is defined by A in FIG. 6a. The relationship between this diameter A, chip heating temperature, and bias voltage is shown in FIGS. 7a and 7b, respectively. Typical operating conditions for an electron gun in an electron beam exposure system are an accelerating voltage of 20kV.
The brightness is 1×10 ⁶ A/cm ² str, the crossover is a single spot, and the chip heating temperature is as low as possible. For example, from FIG. 6, the following conditions are given: heating temperature T ₃ 1500° C. bias voltage V ₃ . However, it is very difficult to actually find such conditions and requires a long time of setting operations. Moreover, the heating temperature is the optimum condition.
T ₃ , bias voltage V ₃ changes with time, 3
Re-adjustment is required about once a day. The fact that the crossover diameter varies depending on the heating temperature or bias voltage of the chip is also disadvantageous for electron beam exposure apparatuses that require a precise electron beam diameter.

The above problems can be solved by other crystal orientations [110],
The chips that selected [111] also exist in the same way, although there are some differences in characteristics.

Based on the above experimental data, the inventors
The number of spots constituting the crossover and the angles formed by the spots with respect to each other were compared with the stereo projection diagram of the LaB ₆ single crystal. In the LaB ₆ single crystal chip, the number of spots constituting the crossover and the angles formed by each other were compared. It was confirmed that the electron beam was emitted from the crystal plane with the crystal orientation (see Figure 5c). Therefore, in this invention, the tip of the LaB ₆ single crystal chip is provided with a crystal plane having a crystal orientation of [310], a crystal orientation within a range of 15° from this, or a crystal orientation equivalent to these (hereinafter referred to as {310} plane). )
It is characterized by emitting electrons from this crystal plane.

FIG. 8 shows the shape of a LaB ₆ single crystal chip according to an embodiment of the present invention. In this embodiment, the axis of the single crystal chip was selected to be [310], and a conical apex with a half apex angle of 70° was formed at the tip. [310]
The equivalent direction to [310] is 25°51′,
It appears at 36°52′, 53°8′, 72°33′, 84°16′, and 90°0′.
Here, among the axial orientations equivalent to the chip's axial orientation [310], the minimum angle between the two axial orientations is [310], and the angle in that case is 25°51'. Furthermore, LaB ₆ has a cubic crystal structure, and the axial direction and both directions are perpendicular to each other.

Therefore, if the angle formed by the two axes is smaller than 25°51', i.e., the half apex angle of the tip is larger than 64°9', for example a 70° conical chip, the top of the tip will be only {310} plane (here (310)
Since a {310} plane equivalent to the (310) plane does not appear on the slope, a single spot beam of electrons is emitted only from the top.

The heating temperature and bias voltage dependence of the electron beam emission pattern of this LaB ₆ single crystal chip was evaluated, and the results were as shown in FIGS. 9a and 9b. As is clear from the comparison with the conventional example, the emission pattern was circular regardless of the heating temperature and bias voltage. As shown in FIGS. 10a and 10b, it was confirmed that the cross-over shape was circular regardless of the heating temperature and bias voltage.

In this embodiment, the axis of the single crystal chip was selected to be [310], but instead of this, various crystal orientations equivalent to [310], that is, <310> crystal orientation may be selected. Also, the half apex angle was set to 70°, but
If processed to have a half apex angle larger than 64°9′,
Since the crystal plane that emits electrons, that is, the {310} plane, appears only at the top, it is possible to obtain an electron beam whose emission pattern and crossover shape are circular regardless of the heating temperature and bias voltage, as in the above embodiment. can.

In the above embodiment, since the tip of the chip is conical, a strong electron beam is emitted from the tip {310}
In addition to the surface, there is also a surface from which the electron beam is not emitted, and by defining the tip angle, multiple {310}
It was important that the surface be processed so that no surface was exposed, in order to prevent the formation of multiple spots.

Now, the feature of the present invention is to provide an electron gun having a chip shape processed so as to make effective use of the {310} plane from which a strong electron beam can be obtained.

Next, as another embodiment according to the present invention, the tip of the chip is entirely surrounded by a slope made of {310} plane so that there is no surface where the beam is not radiated. An example will be described in which a large amount of electron beam is obtained from a sloped portion consisting of a surface. Chip shapes of some embodiments are shown in FIGS. 11 to 14. 11th
In the figure, the axis of the single crystal chip is set to [111], and the slopes of the tip are (310), (301), (103), (013),
This is an example of showing (031) and (130) sides. Figure 12 shows an example in which the axis of the single crystal chip is set to [100], and the (310), (301), (310), and (301) planes are formed on the slopes of the tip. The 13th is the axis of the single crystal chip.
100>, and on the slope of the tip (130), (10
3), (130), and (103) sides are shown. Figure 14 shows an example in which the axis of the single crystal chip is set to [110], and the (310) and (130) planes are formed on the slopes of the tip. In Figures 11 to 13, the top is a point,
In FIG. 14, the top is a line. In either case, all the slopes at the tip end are {310} planes, so
Uniform and strong electron emission is performed from the tip of the chip, especially from the {310} plane near the top line or point where the electric field is concentrated, and the electron emission from each {310} plane is combined to produce the desired radiation. becomes an electron beam.
That is, the electron beam is not dependent on normal heating temperatures and bias voltages, and provides a crossover image of a substantially circular emission pattern and a single spot.

FIG. 15 shows yet another embodiment that actively utilizes the {310} plane. In other words, this is an example in which the axis of the single crystal chip is chosen to be [310], and a flat (310) plane perpendicular to the axis of the chip is formed at the tip.
According to this embodiment, the tip of the chip has a conical shape and a flat surface consisting of a (310) plane perpendicular to the axial direction [310] of the chip is formed. Intense electron radiation takes place, so that in this embodiment, as in the previous embodiment, the electron emission is independent of the heating temperature and bias voltage.
An electron beam is obtained that provides a circular emission pattern and a single spot crossover image.
A similar electron beam can be obtained by selecting the {310} plane, which includes a plane equivalent to (310), as the flat surface of the tip. Also, in this case, only the flat surface of the tip {310}
It may be a plane, or it may be composed of {310} planes up to the slope.

As described above, in this invention, the {310} plane is exposed at the tip of the LaB ₆ single crystal chip, and electrons are emitted from this plane, which allows for lower heating temperatures and lower bias voltages than in the past. An electron beam is obtained which gives a circular emission pattern and a single spot crossover image. Further, since the electron gun according to the present invention can easily align the axis of the electron beam and can operate at low temperatures, it has a long life and has little change over time. In addition, the brightness of the electron beam emitted from this electron gun is {100}
It is about twice as large as that of a LaB ₆ single crystal chip with a {110} plane at the tip. Therefore, the electron gun according to the present invention is very useful for use in various electron beam equipment such as electron beam exposure equipment.

[Brief explanation of drawings]

Figure 1 shows the shape of a LaB ₆ single crystal chip in a conventional electron gun, and Figures 2 a to c show the radiation when the chip axes are set to [100], [110], and [111], respectively. Figures 3a and 3b show the heating temperature and bias voltage dependence of the emission pattern, and Figure 4 shows the alignment of the electron beam and aperture in a conventional electron gun. Figures 5a to 5c show the axes of the LaB ₆ single crystal chip in Figure 1 at [100],
Figures 6a and b showing crossover images of emitted electron beams when [110] and [111] are selected.
7 is a diagram showing the heating temperature and bias voltage dependence of the crossover image, FIGS. 7a and 7b are also diagrams showing the heating temperature and bias voltage dependency of the crossover image diameter, and FIG. Figures 9a and 9b are diagrams showing the shape of the LaB ₆ single crystal chip in this example, and Figures 9a and 9b are diagrams showing the heating temperature and bias voltage dependence of the electron beam emission pattern produced by an electron gun using this chip. a, b
Similarly, FIGS. 11 to 15 are diagrams showing the heating temperature and bias voltage dependence of a crossover image, and FIGS. 11 to 15 are diagrams showing the shape of a LaB ₆ single crystal chip in another embodiment of the present invention.

Claims (1)

[Claims] 1. In an electron gun using a lanthanum hexaboride single crystal chip, the axis of the single crystal chip is <310>
An electron gun characterized in that a flat surface perpendicular to the chip axis is formed on the tip cone-shaped part of the single crystal chip, and an electron beam is emitted from this flat surface. 2 In an electron gun using a lanthanum hexaboride single crystal chip, the axis of the single crystal chip is <310>
The tip of this single crystal chip is formed into a conical shape with a half apex angle larger than 64°9', and a rounded apex is formed at the tip, and an electron beam is emitted from this apex. An electron gun characterized by: 3. In an electron gun using a lanthanum hexaboride single crystal chip, all the slopes at the tip of the single crystal chip are {310} planes, and the electron beam is emitted from the slopes. Characteristic electron gun.