JP2984308B2 - Field emission electron emitter - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Field of Industrial Application) The present invention relates to a micro-sized field emission electron emitter used for an SEM, a micro electron tube, a flat panel display and the like.

(Prior art) Micro-sized electron emitters are attracting attention as high-density electron current sources used in SEMs, micro-electron tubes, flat panel displays, etc.
Development competition is taking place for high stability. Micro-sized electron emitters that do not use a thermionic emission mechanism are roughly classified into a field emission type that emits electrons by field emission from the tip of a micro-sized conical or pyramid-shaped emitter, and a semiconductor that emits electrons from a semiconductor junction. There is a type.
Among them, the field emission electron emitter has an advantage in focusing an electron beam finely.

Micro-sized field emission electron emitters are roughly classified into Spindt type, which creates a micro-sized cone-shaped emitter by rotating evaporation at a pinhole in an insulator at an angle, and polygonal, using anisotropic etching of semiconductor. There is a Gray type that creates a conical emitter. In the field emission electron emitter, the most important factor is how to obtain a uniform and high electric field at the tip of the emitter. For that purpose, it is necessary to make a uniform and sharp tip electron emitter. From such a viewpoint, in particular, the Gray type is attracting attention as an important technology because it is possible to obtain a uniform and sharp-pointed electron emitter over a large area, supported by recent developments in semiconductor processing technology.

However, the gray-type field emission electron emitter shows saturation characteristics at a relatively small current density due to the conductivity of silicon, which is the material as the emission electron current increases, and the heating effect of the electron current concentrated at the tip of the emitter There is a weak point that melting of the tip of the emitter is caused by this.

As an improvement to compensate for these weaknesses, for example, a report by Busta et al. (HHBusta et.al, “Field Emission from Tu
ngsten-Clad Silicon Pyramids "IEEE Transaction
on Electron Device, Vol. 36, No. 11, (1989) pp. 267
As described in 9), there is a method of forming a refractory metal thin film on the surface of a silicon pyramid. FIG. 4 shows the Gr by this method.
1 shows a schematic view of a configuration and a manufacturing method of an ay-type field emission electron emitter. LPCVD (Low Pressure Chemistry) is applied to the surface of the silicon pyramid 2 made using anisotropic etching of silicon.
The refractory metal thin film 5 is formed by an ical vapor deposition method. Here, the refractory metal thin film 5 is
It has been reported that silicified ultrathin films of about 5 nm show better properties. By this method, the saturation current density is increased, and furthermore, the resistance of the emitter tip to fusion destruction is improved. However, the resistance of the tip of the emitter to melting destruction is not yet sufficient, and it is necessary to enlarge the shape of the tip of the emitter in order to obtain greater resistance, which causes a reduction in electron emission efficiency.

As described above, it has been difficult for the conventional gray-type field emission electron emitter to have sufficient resistance to the melt fracture at the tip without lowering the electron emission efficiency.

(Problems to be Solved by the Invention) The present invention has been made in view of such problems, and a field emission electron emitter which has improved electron emission efficiency and obtained sufficient resistance to melting breakdown at the tip of the emitter. The purpose is to provide.

(Means for Solving the Problems) A field emission electron emitter according to the present invention includes a semiconductor substrate, a weight-shaped semiconductor protrusion provided on the semiconductor substrate, and a height provided so as to cover the top of the weight. An electron emitting portion provided with a melting point metal, wherein a tip diameter of the electron emitting portion is equal to or smaller than a tip shape of the semiconductor protrusion.

That is, in the case of a gray field emission electron emitter,
An electron emitting portion using a high melting point metal thin film having a smaller tip diameter than the polygonal tip shape unevenly distributed near the tip of the polygonal cone is provided.

(Function) The field emission electron emitter of the present invention as described above can realize a field emission electron emitter having improved electron emission efficiency and sufficient resistance to melting breakdown at the tip of the emitter.

First, the improvement of the electron emission efficiency will be described. The electron emission efficiency of a field emission electron emitter is determined by the field strength at the tip. If the diameter of the tip and the distance to the anode are constant, the electric field strength is determined by the boundary conditions based on the surface material of the electron emitter. Comparing the case where the entire surface of the electron emitter is covered with metal and the case where only the vicinity of the tip is covered with metal as in the present invention, the latter has a higher electric field because the electric field is concentrated only near the tip. Therefore, the electron emission efficiency is improved.

Next, the resistance of the emitter tip to the melting destruction will be described. In a field emission electron emitter where the entire surface of the electron emitter is covered with metal, current flows through the surface metal and concentrates at the emitter tip causing meltdown of the tip. On the other hand, the saturation current of the field emission electron emitter in which only the vicinity of the tip is covered with metal as in the present invention is determined by the conductivity and shape of silicon. Since the current saturates before the metal tip near the tip melts, the tip is protected.
In addition, since the saturation current value is limited to the resistance value at the tip of silicon, the value of the saturation current is much larger than that of a field emission electron emitter made of a single material of silicon even with the same tip diameter.

(Example) A structure of a gray-type field emission electron emitter according to an example of the present invention will be described. FIG. 1 shows a schematic sectional view. As shown in the drawing, a silicon polygonal pyramid 2 as a semiconductor projection is formed on a silicon substrate 1. A refractory metal thin film 3 as an electron emitting portion is formed thereon so as to cover the apexes of the silicon pyramid 2. Here, the conditions required for the refractory metal thin film 3 are generally the following three points. First, its melting point is higher than silicon,
Second, the tip diameter (φ2) of the refractory metal thin film 3 is smaller than the tip diameter (φ1) of the silicon polygonal cone 2 (φ1> φ).
2) Third, the resistance of the high melting point metal is lower than that of silicon at the silicon-high melting point metal interface. Here, the resistance value means the product of the interface (contact) area and the specific resistivity of the material.

Next, the effect obtained by FIG. 1 will be described with reference to FIG. FIG. 1A shows a conventional example in which the entire surface of a silicon polygon 2 is covered with a high-melting point metal thin film 5, and FIG. 1 shows an embodiment of the invention covered with a thin film 3. In FIG. 2, the tip of the electron emission emitter and the counter electrode 4 are shown.
Relative positions were the same. In the drawing, the outline of the current flow 6 and the electric flux 7 are also shown.

First, the current flow 6 will be described. In FIG. 2 (A), the current flow 6 mainly flows on the surface of the electron emission emitter covered with the refractory metal thin film 5. For this reason, the saturation current value is equal to or larger than the value required for melting and breaking at the tip of the electron-emitting emitter, and melting may occur depending on conditions. On the other hand, in FIG. 2 (B), the current flow 6 flows through the inside of the polygonal pyramid 2 and further flows through the refractory metal thin film 3. Therefore, the saturation current value is determined by the conductivity and the shape of silicon, and does not lead to melting breakdown at the tip of the emitter.

Next, the electric flux 7 will be described. From the boundary condition of the electric field,
In FIG. 2 (B), the electric flux 7 is more concentrated near the tip than in FIG. 2 (A), and the tip of the electron emission emitter has a higher electric field. Therefore, the electron emission efficiency is improved.

3A to 3F are cross-sectional views illustrating an example of a method for manufacturing a field emission electron emitter according to one embodiment of the present invention.

First, an Si ₃ N ₄ film 8 serving as a mask for anisotropic etching of silicon is patterned to a predetermined size on a silicon substrate 1 (FIG. 3A). At this time, the silicon plane is set to be a (1,0,0) plane.

Then, using an etching solution (for example, a mixed solution of KOH, isopropyl alcohol, and H ₂ O), the silicon substrate 1
Then, a silicon polygonal pyramid 2 having a truncated octagonal pyramid shape is formed (FIG. 3B).

Subsequently, the surface of the silicon polygon 2 is smoothed with a light etching solution (for example, a mixed solution of diluted hydrofluoric acid and lactic acid) (FIG. 3 (C)).

Next, heat treatment (50 × 10 ⁻⁸ Torr or less) in a high vacuum (50 × 10 ⁻⁸ Torr or less)
(0 ° C. or higher) to clean the surface. Then, the counter electrode 4 made of, for example, a Si wafer is arranged in parallel with the silicon substrate 1 at a slight distance (on the order of several μm), and a reactive gas (for example, WF) ₆ ) Apply an appropriate voltage between the electrodes during the procedure.
The electric field is concentrated at the tip of the octagonal pyramid, and as a result, only the reactive gas near the tip is excited to form the gas excitation part 9, and the high melting point metal thin film 3 is deposited only near the tip of the octagonal pyramid (No. 3 (D)).

As a result of the deposition of the refractory metal thin film 3, the diameter near the tip gradually decreases, and the distance between the electrodes gradually decreases due to the generation of the deposited metal layer 10 on the counter electrode 4. The voltage gradually decreases (FIG. 3 (E)).

By this step, the tip (diameter φ) of the silicon polygonal spindle 2
1) The refractory metal thin film 3 (diameter φ2) is formed in the vicinity under the condition that the tip diameter is smaller (φ1> φ2), and the field emission electron emitter according to one embodiment of the present invention can be obtained (FIG. 3). (F)).

As another embodiment of the present invention, after the preparation of FIG. 3 (F), etching is performed using the refractory metal thin film 3 as a mask, and the shape of the electron emission emitter is processed into a more needle-like shape, thereby further concentrating the electric field. Examples can be given.

The embodiments of the present invention have been described above, but there are various other variations of the present invention without departing from the gist thereof.

[Effects of the Invention] According to the present invention, it is possible to provide a field emission electron emitter having improved electron emission efficiency and sufficient resistance to melting breakdown at the tip of the emitter.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view for explaining one embodiment of the present invention, and FIG.
FIG. 3 is a schematic sectional view for explaining the effect of the embodiment, and FIG.
FIG. 1 is a schematic sectional view illustrating an example of a manufacturing method according to an embodiment of the present invention, and FIG. 4 is a schematic sectional view illustrating a conventional technique. In FIG. 1 to FIG. 4, reference numerals 1 ... silicon substrate, 2 ... silicon polygonal pyramid (semiconductor projection), 3 ... high melting point metal thin film (electron emitting portion), 4 ... counter electrode, 5 ... ... High melting point metal thin film, 6 ... Current flow, 7
...... electric flux, 8 ...... Si ₃ N ₄ film, 9 ...... gas pumping unit, 10 ......
Represents the deposited metal layer.

Claims (2)

(57) [Claims] 1. A semiconductor substrate, a weight-shaped semiconductor projection provided on the semiconductor substrate, and an electron emission portion provided with a high melting point metal provided to cover a top portion of the weight. A field emission electron emitter, wherein a tip diameter of the electron emission portion is equal to or smaller than a tip diameter of the semiconductor protrusion. 2. The semiconductor device according to claim 1, wherein a resistance value of said electron emitting portion at a junction between said electron emitting portion and said semiconductor projection is smaller than a resistance value at a tip of said semiconductor projection.
A field emission electron emitter as described.