JPH06251693A - Manufacture of electric field emission cold cathode - Google Patents

Abstract

PURPOSE:To provide a method of manufacturing an electric field emission cold cathode capable of manufacturing the electric field emission cold cathode sharper than sharpness, limited by lithography, and excellent in uniformity and reproducibility of emitter shape with high aspect ratio. CONSTITUTION:In a method of manufacturing an electric field emission cold cathode having a sharp point end with high aspect ratio, an SiO2 layer 12 is formed on an Si substrate 11 of face orientation (100) and worked by photolithography, to form an etching mask 13. Next by etching the Si substrate 11 with a solution of tetramethyl ammonium hydroxide, an octagonal pyramid-shaped emitter 15, surrounded by a face {112}, is formed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a field emission cold cathode used in vacuum microelectronic devices and the like, and more particularly to a method for manufacturing a field emission cold cathode utilizing solution etching.

[0002]

2. Description of the Related Art In recent years, using fine processing technology for semiconductors,
Research is underway to realize micron-sized, microintegratable vacuum microelectronic devices, and application to flat-panel image display devices, ultra-high-speed microwave devices, power devices, electron beam devices, etc. is underway. .

The key part of this vacuum microelectronics element is a field emission cold cathode (microemitter) that emits electrons by an electric field. As a promising method for producing this, gray (HFGray) has been proposed. There is also a method of utilizing anisotropic etching of Si. Hereinafter, this method will be briefly described with reference to FIG.

First, as shown in FIG. 5 (a), Si (1
00) Layer 5 serving as an etching mask material on the wafer 51
2 (Si0 ₂ , Si ₃ N ₄ ) is formed. Then, FIG.
As shown in (b), for example, a 2.4 μm square square etching mask 53 is formed by lithography and etching, and anisotropic etching (KOH 15% solution,
Si under the mask 53 is processed into a conical shape 54 by a liquid temperature of 40 ° C. for 13 minutes. Thereafter, as shown in FIG. 5C, SiO ₂ or the like to be the insulating layer 55 and a metal layer to be the gate metal layer 56 are sequentially deposited. Finally, FIG. 5 (c)
As shown in, the mask 53 above the emitter is removed by ultrasonic cleaning or the like to form the micro-emitter 57.

This micro-emitter 57 is actually S
It has an octagonal pyramid shape surrounded by the i {212} plane. For example, when using a 2.4 μm square mask,
The diameter of the bottom surface of the emitter is about 1.3 μm, the aspect ratio (the ratio of the height to the radius of the bottom surface) is about 1.0, and the radius of curvature of the tip of the emitter is about 70 ± 40 nm.
There is a variation of about 60%.

On the other hand, the characteristics required for the emitter of the vacuum microelectronic device include a high aspect ratio, uniformity and reproducibility of the emitter shape, and sharpness of the tip of the emitter. Generally, in a vacuum microelectronic device, an anode electrode is arranged to face the emitter, and the anode has a positive potential with respect to the emitter. In order for this electron emission to occur at a low voltage, the aspect ratio of the emitter must be high and the tip must be sharp. Further, in order to obtain stable performance as a vacuum microelectronic device, it is necessary that the emitter shape is uniform and the reproducibility is good.

However, the conventional method for manufacturing a field emission cold cathode as described above has the following problems. That is, since the aspect ratio of the emitter is kept at about 1.0 by etching with the KOH solution, it is extremely insufficient as a field emission cold cathode, and it is difficult to cause field emission at a low voltage.

Further, in the etching using KOH, since the etching speed is high, it is difficult to control the etching time so that the etching is completed in the state where the tip of the emitter is sharpest. For this reason, the tip shape of the emitter has a large variation, and the sharpness and shape reproducibility are lacking, and there are problems that the field emission rate is nonuniform or lowered, and further the yield is deteriorated. In order to slow down the etching rate, it is sufficient to lower the KOH concentration, but then the side reaction product of Si and KOH will remain on the surface, making it difficult to lower the etching rate.

Further, in order to sharpen the tip of the emitter, it is desirable to reduce the size of the mask, but the limit is limited by the resolution of lithography. for that reason,
There is a drawback that it is not possible to manufacture a sharp emitter.

Furthermore, in the semiconductor microfabrication process, alkali metals deteriorate the characteristics of electronic devices, so it is desirable not to use them as much as possible. However, K
Since OH contains potassium ions, there is a problem that, when the expensive equipment for the microfabrication process is shared with other Si semiconductor devices, the contamination in the equipment and other electronic devices cannot be ignored. .

[0011]

As described above, in the conventional field emission type cold cathode manufacturing method, there is a limit due to the nature of the etching solution in order to obtain an emitter with a high aspect ratio, and the tip should be sharp. However, there is a problem in that it is not possible to obtain an emitter having a high aspect ratio and a sharp tip, because the resolution of lithography is limited. Further, the uniformity and reproducibility of the emitter shape are very low, and there have been problems such as reduction in field emission efficiency, non-uniformity, and reduction in yield. In addition, there was a concern about contamination of other Si processes with potassium ions.

The present invention has been made in consideration of the above circumstances, and an object thereof is to have a high aspect ratio,
It is an object of the present invention to provide a method for manufacturing a field emission cold cathode which is excellent in uniformity and reproducibility of the emitter shape and which can manufacture a field emission cold cathode having a sharpness higher than the sharpness limited by lithography.

[0013]

The essence of the present invention resides in that a tetraalkylammonium hydroxide solution is used in place of the KOH solution which has been conventionally used as an anisotropic etching solution.

That is, according to the present invention, in a method for manufacturing a field emission type cold cathode having a sharp tip and a high aspect ratio, an etching mask having a desired size is formed on a Si substrate having a plane orientation of {100}, and then the Si substrate is formed. Is etched with a tetraalkylammonium hydroxide solution to form a conical shape. Here, the plane orientation is {100}
Within 5 °, it can be used because it has the same property even if it is slightly inclined. Here, the following are preferred embodiments of the present invention. (1) Use a square or circular mask as an etching mask.

(2) By the above etching, Si {11
Form an octagonal pyramid-shaped field emission cold cathode surrounded by the 2} plane. The Si plane here is also 5 ° from the {112} plane
If it is within the range, it has the same property even if it is slightly inclined,
Can be used.

[0016]

The inventors of the present invention repeated various studies and experiments using various solutions as the anisotropic etching solution capable of obtaining an emitter shape with a sharp tip and a high aspect ratio.
We have found that tetraalkylammonium hydroxide is the most desirable.

The tetraalkylammonium hydroxide solution has a higher etching rate in the {111} crystal axis direction under the mask than the conventionally used KOH solution, so that the size of the mask is restricted by the lithography technique. On the other hand, it is possible to obtain an emitter having a smaller radius at the base of the emitter and a sharper tip. Moreover, since the etching rate for Si is relatively low and the etching time can be easily controlled, it becomes possible to obtain a field emission cold cathode having excellent height and uniformity of the tip shape with good reproducibility. Therefore, KOH is used as the Si etching liquid.
A field emission type cold cathode having a high aspect ratio can be obtained, and the field emission efficiency can be significantly improved, as compared with the case of being manufactured using.

Further, since the tetraalkylammonium hydroxide solution does not contain an alkali metal such as potassium ion, which causes contamination of the Si semiconductor microfabrication process and device, it does not pollute other Si processes with potassium ion. There is no invitation.

[0019]

The details of the present invention will be described below with reference to the illustrated embodiments.

FIG. 1 is a sectional view showing a manufacturing process of a field emission cold cathode according to the first embodiment of the present invention. First,
As shown in FIG. 1A, a SiO ₂ layer 1 having a thickness of about 0.1 μm is formed on a Si (100) wafer 11 by dry oxidation.
Form 2. Next, a resist is applied on this, a 2.4 μm square pattern is created by a stepper, and then the SiO ₂ layer 12 is etched by a NH ₄ / HF mixed solution, as shown in FIG. Square Si
The O ₂ mask 13 is formed.

Next, after removing the resist, the wafer 11 is etched at a liquid temperature of 30 ° C. for 38 minutes using a 22% tetramethylammonium hydroxide solution as an etching solution, and as shown in FIG. A cone-shaped emitter prototype was completed under the mask 13. Then 5 in acetone
The mask 13 on the upper part of the emitter was removed by ultrasonic cleaning for 1 minute to obtain an emitter 15 as shown in FIG. Here, the tetramethylammonium hydroxide solution is
The etching rate in the (111) crystal axis direction under the mask is higher than that of KOH, and the {112} plane is generally likely to appear.

The emitter obtained by the above steps is S
It has an octagonal pyramid shape surrounded by i {112} planes, the bottom surface has a diameter of about 0.85 μm, the aspect ratio is about 2.0, and the radius of curvature of the emitter tip is 50 ± 10 nm.
The variation in the radius of curvature was ± 60% in the case of KOH, which was significantly improved to about ± 20%.

As described above, according to the present embodiment, the aspect ratio of 1.0 produced by the conventional method is greatly improved to 2.0. Further, regarding the uniformity and reproducibility, the variation of the tip shape of ± 60% in the past is reduced to 20% according to the present embodiment, which is greatly improved. Regarding the sharpness, a value equal to or higher than the conventional value was obtained. Furthermore, in the method of this embodiment, since no alkali metal is contained, there is no risk of contamination of the Si semiconductor fine processing equipment and other devices.

That is, by using tetramethylammonium hydroxide as the Si etchant, the aspect ratio is high and the emitter shape is uniform and reproducible.
It is possible to manufacture a field emission cold cathode having a sharpness higher than the sharpness limited by lithography, and it is extremely effective for use as an emitter of various microelectronic devices.

Next, a second embodiment of the present invention will be described. In this embodiment, first, as shown in FIG. 2A, a Si (100) wafer (p-type, 5 Ωcm) 21 is
A SiO ₂ layer 22 having a thickness of about 0.1 μm is formed by dry oxidation. Then, a resist is applied on this, and a 2.4 μm square pattern is formed by a stepper,
The SiO ₂ layer 22 was etched with a mixed solution of NH ₄ and HF, and a square SiO ₂ mask 23 was obtained as shown in FIG.

Next, after removing the resist, the wafer 21 is etched at a liquid temperature of 30 ° C. for 65 minutes using a 5% tetramethylammonium hydroxide solution as an etching solution, and as shown in FIG. A conical emitter prototype was formed on the bottom. Thereafter, as shown in FIG. 2D, a SiO ₂ layer 25 serving as an insulating layer was formed by CVD, and a Mo layer 26 serving as a gate metal layer was vacuum-deposited thereon. Finally, the mask 23 was removed by ultrasonic cleaning in acetone for 5 minutes to obtain an emitter 27 as shown in FIG.

The emitter obtained through the above steps has an octagonal pyramid shape surrounded by Si {112} planes as in the first embodiment, the bottom diameter is 0.95 μm, and the aspect ratio is approximately. 1.8, the radius of curvature of the tip of the emitter is about 60 ± 20 nm, and the variation is ±± for KOH.
Compared to 60%, it was reduced to about ± 30% and improved. In this embodiment, as in the first embodiment, the aspect ratio and the uniformity of the tip shape are remarkably improved as compared with the case of using the KOH solution.

Next, a third embodiment of the present invention will be described.
Since the basic steps of the method of this embodiment are the same as those of the second embodiment, FIG. 2 will be referred to as a process chart.

First, a Si ₃ N ₄ layer 32 having a thickness of about 0.1 μm is formed on a Si (100) wafer 31 by dry oxidation (FIG. 2A). A resist is coated on this, a circular pattern with a diameter of 2.4 μm is created by a stepper, and then the Si ₃ N ₄ layer 32 is etched by a NH ₄ / HF mixed solution to obtain a circular Si ₃ N ₄ mask 33. (Fig. 2 (b)).

Next, after removing the resist, the wafer 31 is etched for 15 minutes at a liquid temperature of 30 ° C. using a 35% tetramethylammonium hydroxide solution as an etching solution to form a cone-shaped emitter prototype 34 under the mask 33. (Fig. 2 (c)). After that, a SiO ₂ layer 35 to be an insulating layer is formed by CVD, and Ta to be a gate metal layer is formed thereon.
The layer 36 is vacuum-deposited (FIG. 2 (d)), and finally the mask 33 is removed by ultrasonic cleaning in acetone for 5 minutes to remove the emitter 3
7 was obtained (FIG. 2 (e)).

The emitter obtained by the above steps has a bottom diameter of 0.92 μm and an aspect ratio of about 1.85.
The radius of curvature of the tip of the emitter is approximately 70 ± 20 nm, and the variation is ± 30% compared to ± 60% in the case of KOH.
%, Which was small and improved. In this embodiment, as in the first embodiment, the aspect ratio and the uniformity of the tip shape are remarkably improved as compared with the case of using the KOH solution.

In the following, the emitters prepared by changing the concentration and the solution temperature of the tetramethylaluminum hydroxide solution by the same method as the above-described manufacturing method are used in Examples 4 to 1
It was set to 6. Example 4 ... concentration 15%, solution temperature 30 ° C Example 5 ... concentration 5%, solution temperature 25 ° C Example 6 ... concentration 15%, solution temperature 25 ° C Example 7 ... concentration 22%, solution temperature 25 ° C Example 8 ... concentration 35%, solution temperature 25 ° C. Example 9 ... concentration 5%, solution temperature 40 ° C. Example 10 ... concentration 15%, solution temperature 40 ° C. Example 11 ... concentration 22%, solution temperature 40 ° C. Example 12 ... Concentration 35%, solution temperature 40 ° C. Example 13 ... concentration 5%, solution temperature 60 ° C. Example 14 ... concentration 15%, solution temperature 60 ° C. Example 15 ... concentration 22%, solution temperature 60 ° C. Example 16 ... concentration 35 %, Solution temperature 60 ℃

FIG. 3 shows the relationship between the aspect ratio of the emitter and the concentration of the tetramethylammonium hydroxide solution obtained when changing the solution temperature of the tetramethylammonium hydroxide solution obtained from Examples 1 to 16. . The aspect ratio of the emitter is expressed with reference to the aspect ratio of 1.0 of the emitter created by the conventional method. The etching time is such that the aspect ratio and the tip shape are optimal at each solution concentration and solution temperature.

When the solution temperature is 30 ° C., the aspect ratio is 1.8 when the solution concentration is 5%, the aspect ratio is 1.95 when the solution concentration is 15%, and the aspect ratio is 2.0 when the solution concentration is 22%. Is 35%, the aspect ratio is 1.85.
Thus, in all the examples, the aspect ratio was remarkably improved as compared with the conventional method, and the maximum aspect ratio was obtained especially at the solution concentration of 22%.

Similarly, when the solution temperature is 25 ° C., the aspect ratio is 1.7 to 1.9, when the solution temperature is 40 ° C., the aspect ratio is 1.6 to 1.75 and the solution temperature is 60 ° C. In this case, the aspect ratio was 1.5 to 1.66, which was much higher than the conventional example in any of the examples.

As described above, the method of the present invention using the tetramethylammonium hydroxide solution has a higher emitter aspect ratio than the case of using the conventional KOH.
It was possible to manufacture a higher performance field emission type cold cathode having excellent shape reproducibility and uniformity.

Next, a flat panel image display device using the field emission type cold cathode according to the present invention will be described with reference to FIG. The same parts as those in FIG. 2 are designated by the same reference numerals, and detailed description thereof will be omitted.

The flat panel image display device 40 of this embodiment is
Si (100) substrate 21 having a large number of emitters 27 formed
Is placed on another substrate 41 serving as a base (hereinafter referred to as a cold cathode plate 42), and a transparent electrode (anode electrode) layer 44 made of a phosphor 43 and ITO is sequentially laminated to face this. The glass face plates 45 thus formed are arranged at a predetermined interval, and these constitute a vacuum housing.

As shown in FIG. 4, on the cold cathode plate 42, a Si (100) substrate 21 which also serves as a cathode electrode and a gate electrode layer 26 are formed as a network intersecting with each other, and at each intersection thereof. A cold cathode forming region 46 forming each pixel is set. Each cold cathode forming region 46 corresponding to one pixel has a large number, for example, 1
It has 00 emitters 27. The phosphor layer 43 formed on the glass face plate 45 is composed of a red light emitting phosphor layer 43a, a green light emitting phosphor layer 43b, and a blue light emitting phosphor layer 43c corresponding to each pixel. It is provided corresponding to each cold cathode forming region 46. Each phosphor layer 43a, 43b, 43c
Are sequentially and repeatedly formed in the horizontal direction.

Using the flat panel image display device 40 as described above, 40 V is applied between the gate and the cathode in accordance with the pixel signal.
When the pixel was driven by applying a voltage of 2 V and a voltage of 250 V between the anode and the cathode, it was possible to obtain a good image with excellent emission luminance of pixels and little variation in luminance between pixels.

In the flat panel image display device of this embodiment, since the emitter 27 having excellent shape uniformity as described above is used, it is possible to stably obtain an image with little variation in emission brightness. Further, since the field emission cold cathode used here is excellent in electron emission efficiency, it contributes to low voltage driving and reduction of power consumption.

The present invention is not limited to the above embodiments. In the examples, only tetramethylammonium hydroxide solution was used as the anisotropic etching solution for Si, but any solution containing this as a main component may be used. Furthermore, the conditions such as the concentration of the tetramethylammonium hydroxide solution and the liquid temperature may be appropriately determined according to the specifications. Further, other tetraalkylammonium hydroxide, for example, tetraethylammonium hydroxide solution or tetrabutylammonium hydroxide solution may be used as a single etching solution, or these etching solutions may be mixed and used. Furthermore, the etching mask is SiO ₂ or Si ₃ N
_The number is not limited to ₄ , but may be any as long as a sufficient selection ratio with respect to Si can be obtained.

Further, the silicon substrate is not limited to one having a (100) main surface, and other {100} plane orientations, for example, (01
It may be 0), (-100), (0-10) or the like. Further, in the embodiment, an example in which the field emission cold cathode according to the present invention is applied to a flat panel image display device has been described, but the field emission cold cathode according to the present invention is not limited thereto, and, for example, an ultrafast microwave element, power It can be applied to various electronic devices such as elements and electron beam devices. In addition, various modifications can be made without departing from the scope of the present invention.

[0044]

As described above, according to the method for producing a field emission cold cathode of the present invention, by using tetramethylammonium hydroxide as an etching solution for Si,
Since a sharp emitter with a high aspect ratio and excellent shape reproducibility and uniformity can be stably obtained, a high-performance field-emission cold cathode that excels in field emission rate and greatly suppresses its variation is provided. It can be realized with good reproducibility. Further, since the etching solution does not contain potassium ions, there is also an effect that there is no contamination with respect to other Si process lines.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a manufacturing process of a field emission cold cathode according to a first embodiment of the present invention.

FIG. 2 is a cross-sectional view showing a manufacturing process of a field emission cold cathode according to a second embodiment of the present invention.

FIG. 3 is a diagram showing a relationship between an emitter aspect ratio improvement rate and a concentration of a tetramethylammonium hydroxide solution based on the first to sixteenth examples of the present invention.

FIG. 4 is a perspective view showing a configuration of a main part when the present invention is applied to a flat panel image display device.

FIG. 5 is a cross-sectional view showing a manufacturing process of a conventional field emission cold cathode.

[Explanation of symbols]

11, 21, 31 ... Si (100) single crystal substrate 12, 22 ... SiO ₂ thermal oxide film 13, 23 ... Etching SiO ₂ mask 14, 24, 34 ... Embossed convex portion 15, 27, 37 ... Emitter 25, 35 ... SiO ₂ insulating layer 26, 36 ... Gate electrode layer 32 ... Si ₃ N ₄ thermal oxide film 33 ... Etching Si ₃ N ₄ mask 40 ... Flat plate image display device 41 ... Substrate which is a base of a cold cathode plate 42 ... Cold cathode plate 43 ... Phosphor layer 43a ... Red light emitting phosphor layer 43b ... Green light emitting phosphor layer 43c ... Blue light emitting phosphor layer 44 ... Anode electrode layer 45 ... Glass face plate

Claims (1)

[Claims] 1. A method comprising: forming an etching mask on a Si substrate having a plane orientation of {100}; and etching the substrate with a tetraalkylammonium hydroxide solution to form a conical shape. Method for manufacturing field emission cold cathode.