JPH0522330B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a point cathode that requires a high-intensity electron beam, and more particularly to a point cathode with improved electron emissivity characteristics and lifetime.

Conventionally, cathodes used in lithography, such as photosensing semiconductors, require extremely small electron beams, so a cathode made of tungsten or the like with a sharp tip is heated to a high temperature, and then a high voltage is applied to create a needle. Obtaining an electron beam of .

However, if tungsten itself is used as a cathode, it has a high work function and poor electron emission, so it must be operated at _high temperatures and has a short lifespan. It is considered to use compounds. A cross-sectional view of a point cathode using this LaB ₆ is shown in FIG. In Figure 1, for example 5 of LaB ₆
The cathode portion has one end of a mmφ rod with a sharp tip of 5 μφ to 10 μφ, and 2 is carbon that holds the cathode portion 1. This LaB ₆ is highly reactive with ordinary metals, so it cannot be held by ordinary metals, so it is held by pressing with carbon. 3 is a heater for raising the temperature of the cathode part 1, and a coil made of tungsten wire is arranged around the cathode part 1. If an anode is disposed opposite to the sharp end of the cathode and a high voltage is applied, electrons are emitted from the sharp end of the cathode part 1 and a thin needle-shaped electron beam can be obtained. But this LaB ₆
Even though the work function of the cathode is low, it is higher than that of barium, etc., and has the disadvantage that the desired electron emission cannot be obtained unless the cathode temperature is raised to a high temperature of 1600°C or higher. Moreover, this LaB ₆ cannot be heated directly, but instead is heated indirectly by placing a heater 3 around the cathode part 1, so that the heater 3 reaches a very high temperature, which has a significant adverse effect on other parts, such as shortening the life of the heater 3.
Furthermore, the cathode part 1 using this LaB ₆ must be supported with carbon 2 as described above, but carbon has weaker mechanical strength than metal, and as mentioned above, in order to hold the high-temperature cathode part 1, it is necessary to There is a drawback that the temperature of the carbon becomes very high due to conduction, the mechanical strength is further reduced, and the direction of the sharp end of the cathode part 1 is deviated.

Another drawback is that LaB ₆ is difficult to mold, making it difficult to form very thin sharp edges.
Also, depending on the crystal plane, there is a direction in which the electron beam is more likely to decrease during operation, and if the crystal plane changes, the direction of the electron beam tends to change.

The present invention was made in view of these drawbacks, and an object of the present invention is to provide a cathode that can obtain an extremely small electron beam at a relatively low temperature. Specifically, for example, a porous body is formed from the same kind of material by closely attaching it around a thin high-melting point metal rod such as a tungsten rod with one end sharpened, and the porous body is impregnated with an electron radioactive substance to form a porous body around it. By placing a heater in the porous body and heating the porous body, barium or the like leached from the porous body is caused to creep onto the sharp end of the high melting point metal rod, thereby lowering the work function of the sharp end of the high melting point metal rod. This will be explained in detail below with reference to the drawings.

FIG. 2 is a sectional view of a dotted cathode which is an embodiment of the present invention.

In Figure 2, 4 is a tungsten rod with an outer diameter of 5 mmφ, for example, and 5 is a tungsten rod with an outer diameter of 5 mmφ.
6 is an electron radioactive substance immersed in the porous body 5, and 7 is a heater for raising the temperature of the electron radioactive substance 6.

Various methods can be considered for producing this cathode, but in one example, tungsten powder is first sintered to form a porous body 5 having an outer diameter of 1 to 5 mm and a length of 0.2 to 2 cm. Next, in the center of the porous body 5,
A 2 mmφ hole is penetrated, and a tungsten rod with a thickness of 0.1 to 2 mmφ is inserted into the hole, and then sintered to make it stick tightly. The porous body 5 has already been sintered, but when it is sintered again, it contracts and comes into close contact with the tungsten rod. Next, one end of the tungsten rod is machined to make it thinner, and to make the tip even thinner, chemical polishing such as electrolysis or alkali melting is used to make the tip thinner.
Form into a sharp edge of 0.05-10μ. Next, in the same way as manufacturing a normal impregnated cathode, a pre-fired mixture of barium carbonate, calcium carbonate, aluminum oxide, etc., which are raw materials for electron radioactive substances, is applied to the surface of the porous body. Melt impregnation at approximately 1800°C in a reducing atmosphere or in vacuum. This cathode can be manufactured by connecting the opposite side of the sharp end of the cathode portion thus manufactured to the cathode side electrode, and arranging a heater spaced apart from the outer periphery of the porous body.

As another manufacturing method, for example, the porous body portion can be formed by directly molding tungsten powder around a tungsten rod and sintering it, and the other manufacturing methods can be the same as in the previous example. Regardless of which method is used, if a thin tungsten wire is used instead of a tungsten rod, the sharp end can be formed directly by chemical polishing without going through a machining process. Alternatively, the tip of the tungsten rod can be previously sharpened and brought into close contact with the porous body.

In the above embodiment, the material of the core rod and the porous body was explained using tungsten as an example, but other than tungsten, any metal with a high melting point such as molybdenum may be used.
Further, although an example has been described in which the outer shape of the porous body is circular, the shape of the electron beam is determined by the shape of the sharp end, so the outer shape of the porous body can be made into any shape.
Furthermore, it does not have to be the same length as the metal rod porous body, but it is sufficient if it is at least at the tip part that emits the electron beam.

As explained above, according to the present invention, even with a point cathode that requires a very narrow electron beam, sufficient electron emission can be obtained at a cathode temperature comparable to that of a normal impregnated cathode. Since there is no need to increase the height more than necessary, the lifespan can be extended, which has the effect of greatly contributing to the development of electronic technology such as lithography.

[Brief explanation of drawings]

FIG. 1 is a sectional view of a conventional point-shaped cathode, in which LaB ₆ is suspended with carbon, and FIG. 2 is a sectional view of a point-shaped cathode, which is an embodiment of the present invention. 4... High melting point metal rod, 5... Porous body of high melting point metal, 6... Impregnating agent of electron radioactive substance, 7... Heater.

Claims (1)

[Claims] 1. A hollow high-melting point metal rod or wire with one end sharpened to 0.05 to 10 μmφ, and a material made of the same kind of material as the high-melting point metal rod or wire, tightly attached to the periphery of the high-melting point metal rod or wire. It consists of a porous body impregnated with the porous body, an electron radioactive substance impregnated into the porous body, and a heating heater placed isolated around the porous body impregnated with the electron radioactive substance, A point cathode characterized by emitting electrons from the sharp end of a rod or wire.