JPH0433096B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a field emitter used in an electron beam exposure machine and a device using a high-intensity electron beam.

Tungsten has been used as a material for conventional field emitters, and attempts have been made to use transition metal carbides.

However, when tungsten is used, since tungsten is an active metal, residual gas is adsorbed on the surface, and the adsorbed atoms diffuse and move onto the emitting surface. This changes the local work function of the radiation surface, causing fluctuations in the emitted computer beam. Typically, tungsten has the disadvantage that its radiation current varies by about 5%.

In addition, when using transition metal carbides, they are inert compared to tungsten in reacting with residual gas, but their activity is closely related to the number of carbon defects on the emitting surface, and the number of defects increases. As the number increases, the surface activity increases and the fluctuation range of the electron beam approaches the value for tungsten. In transition metal carbide MC _x (where M represents a transition metal), x is 0.5 to 0.96
Thermodynamically, there exists a region of non-stoichiometric ratios over
In general, crystals created in a state close to thermal equilibrium have a
20 atomic percent carbon defects are introduced.

The purpose of the present invention is to create a radiation surface that is more inert with respect to reaction with residual gas due to carbon defects inevitably introduced in transition metal carbides, and to provide a stable, high-brightness field emitter. .

The present inventors have found that a stable high-brightness field emitter can be obtained by reducing carbon defects in transition metal carbides by incorporating nitrogen and/or oxygen into solid solution.

Transition metal carbides, transition metal oxides, and transition metal nitrides all have the same rock salt crystal structure and have similar chemical bonds, so they form a solid solution with each other, and this solid solution reduces the number of carbon defects. I can do it.
Furthermore, the solid solution of oxygen lowers the work function of the radiation surface and has the effect of emitting electrons efficiently. In addition, the solid solution of nitrogen improves thermal conductivity and has the effect that flash heating for cleaning the radiation surface can be performed more efficiently.

Since the smaller the number of carbon defects, the more stable the radiation surface becomes, the general formula M _x O _y N _z (where M is V,
Represents a solid solution of transition metals of the group 1 or 2 or more. ), x+y+z=1
It is desirable that the value be close to 1, but it does not necessarily have to be 1 and can be stabilized by solid solution. Valid composition ranges are as follows.

0.5<x+y+z1 0.5x1, 0y0.5, 0z0.5 However, y and z are never 0 at the same time.
, V, group transition metals include Ti, Zr, Hf,
Examples include V, Nb, Ta, Mo, and W, and these may be used alone or as a solid solution.

Here, the reason for limiting x, y, and z is as follows. It is known that the NaCl type structure of carbide MC _x is stable within the composition range of 0.5<x1. This shows that the crystal is stable even if 50% of vacancies are created at carbon atom sites. Stable field emitters can be obtained by introducing oxygen or nitrogen atoms into these carbon vacancies. Therefore, the amount of oxygen atoms or nitrogen atoms introduced is at most 50%. In other words, 0y
0.5, 0z0.5. Also, oxygen and nitrogen
Not only can two atoms enter the carbon atom vacancy at the same time, but they can also enter to replace a carbon atom, and in this case, the limit of the carbon atom site, i.e., 0.5
<Receive x+y+z1.

In addition, a method for applying oxygen or nitrogen to carbon defects within the above range may be by introducing oxygen (or nitrogen) gas in a vacuum and heating at 1000°C,
The emitter may be exposed to oxygen (or nitrogen) gas at 1 atm and then heat treated at 1000° C. in vacuum. Furthermore, a similar effect can be obtained by dissolving oxygen (or nitrogen) gas in the crystal during crystal growth.

Next, Examples will be given to demonstrate the excellent effects of the field emitter of the present invention.

Comparative Example A TiC _0.96 single crystal whose composition was controlled by the floating zone method was prepared and cut out so that the <100>, <111>, and <110> axes coincided with the radiation axis. The tip was shaped to a radius of curvature of less than 0.1μ by electrolytic polishing, and the field emission was examined in an ultra-high vacuum of 10 ^-9 Pa.

The surface of the <100> chip had defects of more than 10 atomic percent. The emitted current change over time in this chip was as shown in FIG. As shown in Figure 1,
The radiation current from the surface fluctuated in steps and spikes, and also decreased with time.
This trend was also observed for <111> and <110> chips.

Example In the same manner as in the comparative example, <100>, <111>,
A chip of <110> was prepared, and after adsorbing oxygen and nitrogen in an atmosphere of 1 atm, it was annealed by heating at 1000°C for 10 minutes, and then field-treated in the same manner as the comparative example.
I looked into Emitsushiyoshi. The change in radiation current over time in this <100> chip was as shown in Figure 2. As this figure shows, the emitted current was extremely stable and remained stable even after 10 hours. This trend was also observed for <111> and <110> chips.

In practical terms, as a representative transition metal
I mentioned Ti, but Zr, Hr, V, Nb, Ta, Mo, W
Similar results can be obtained in .

As described above, the field emitter of the present invention exhibits an excellent effect in that the emitted current is extremely stable over a long period of time compared to conventional ones.

[Brief explanation of drawings]

FIG. 1 shows a time change diagram of the radiation current in a conventional field emitter having carbon defects of more than 10 atomic percent, and FIG. 2 shows a time change diagram of the radiation current in the field emitter of the present invention.

Claims (1)

[Claims] 1 The chemical composition of the material is the general formula MC _x O _y N _z (where M is V, a solid solution of one or more group transition metals, 0.5<x+y+z1, 0.5
It represents x1, 0y0.5, 0z0.5, but y and z are never 0 at the same time. ) A field emitter characterized by being made of a transition metal compound represented by: