JP2005310448A - Forming method of projection structure, projection structure, and electron emitting element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To form a projection structure in which thin projections are alignedly arranged regularly. <P>SOLUTION: A plate board 1 made of a diamond is prepared, and RCA cleaning is applied to the plate board 1. Raw materials of SiH<SB>4</SB>or the like are decomposed using plasma at a plate board temperature of around 530°C to accumulate a a-Si membrane 3 on the plate board 1. A resist is coated onto the a-Si membrane 3, and the resist is minutely processed with electron beam exposure or photolithography to form a resist pattern 4. Size of the resist pattern 4 is controlled by ashing. Etching is conducted using the resist pattern as a mask on the a-Si membrane by dry etching by using CF<SB>4</SB>gas to form a Si mask 5. The resist pattern 4 is removed with a sulfuric acid based solution. By using minutely processed Si mask 5, the etching is conducted on the plate board 1 made of the diamond in an oxygen gas added with a slight amount of CF<SB>4</SB>to form the projection 2 of more minute size than that of the mask. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a method for forming a protrusion structure, a protrusion structure, and an electron-emitting device.

An electron-emitting device such as an electron gun uses a protrusion structure in which protrusions are formed on a substrate containing carbon such as diamond. In order to form such a protrusion structure, as described in Non-Patent Document 1, an Al film is first formed on a diamond substrate. Next, a dot-like pattern is formed on the Al film by photolithography. Further, using the formed pattern as a mask, the diamond substrate is etched to form a protruding structure on the substrate.
Yoshiki Nishibayashi, Yutaka Ando, Hiroshi Furuta, Koji Kobashi, Kiichi Meguro, Takahiro Imai, Takashi Hirao, Kenjiro Oura; SEI Technical Review, September 2002 issue

  However, since Al is a material that is difficult to finely process, the pattern cannot be processed with a fine size. For this reason, each of the protrusions formed by the above method has a width of 300 nm square or more, and it is impossible to form a protrusion structure in which protrusions having a width of 300 nm or less are regularly arranged. there were.

  In view of such circumstances, the present invention provides a method for forming a protrusion structure in which a thin protrusion is arranged, a protrusion structure in which a thin protrusion is arranged, and an electron-emitting device in which the thin protrusion is arranged. Is to provide.

  The present invention includes (a) a first step of forming a Si film on a substrate made of a material containing carbon, and (b) etching the Si film to form a Si mask having a plurality of patterns arranged on the substrate. A second step of forming, and (c) a third step of etching the substrate using a Si mask to form a plurality of protrusions on the substrate.

  According to said structure, a mask can be formed from Si film which is easy to carry out microfabrication, and a processus | protrusion can be formed.

In the present invention, the Si film is preferably an amorphous Si film.
According to the above configuration, the Si mask can be formed from the amorphous Si film (a-Si film) having very good uniformity in microfabrication.

In the present invention, each pattern preferably has a maximum width of 300 nm or less.
According to the above configuration, a protrusion having a root diameter of 300 nm or less can be formed using a Si mask having a width of 300 nm or less.

In the present invention, the ratio (H / W) between the height H and the maximum width W of each pattern is preferably 0.5 or more.
According to said structure, protrusion with small variation in height can be formed. Further, it is possible to form a protrusion having a small tip diameter.

In the present invention, the TTV (Total Thickness variation) of the substrate is preferably 50 nm or less.
According to said structure, a projection with small variation in height can be formed by forming a projection on a flat substrate having a TTV of 50 nm or less.

In the present invention, the substrate is preferably made of diamond.
According to said structure, the protrusion structure of a diamond can be formed.

  The present invention is a projection structure comprising (a) a substrate made of a material containing carbon, and (b) a plurality of projections formed on the substrate, wherein the plurality of projections are arranged on the substrate. The tip of each projection is thinner than the base of the projection, the width of the tip of each projection is 100 nm or less, and the width of the base of each projection is 300 nm or less.

  According to the above configuration, since the protrusions are regularly arranged on the substrate, the current is uniformly dispersed and a large current can be output. Further, since the protrusion has a tapered shape, the tip diameter is 100 nm or less, and the root diameter is as thin as 300 nm or less, the emission current density can be increased.

In the present invention, the protrusions are preferably provided on the substrate at a density of 4 pieces / μm ² or more.
According to the above configuration, the emission current density can be set to, for example, 100 mA / mm ² or more.

In the present invention, the protrusion structure may be made of diamond.
According to said structure, characteristics, such as a negative electron affinity which a diamond has, can be utilized.

The present invention is an electron-emitting device including (a) a substrate made of a material containing carbon, and (b) a plurality of protrusions formed on the substrate, wherein the plurality of protrusions are arranged on the substrate. The tip of each projection is thinner than the base of the projection, the width of the tip of each projection is 100 nm or less, and the width of the base of each projection is 300 nm or less.
According to said structure, it can be set as the electron emission element in which the fine protrusion was formed compared with the conventional electron emission element.

  According to the method for forming a protrusion structure of the present invention, a protrusion can be formed by forming a mask from a Si film that is easily finely processed. Further, according to the protrusion structure of the present invention, since the protrusions are regularly arranged on the substrate as compared with the conventional protrusion structure, the current is uniformly distributed and a large current can be generated. Further, since the protrusion has a tapered shape, the tip diameter is 100 nm or less, and the root diameter is as thin as 300 nm or less, the emission current density can be increased. Furthermore, according to the electron-emitting device of the present invention, an electron-emitting device in which fine protrusions are formed as compared with the conventional electron-emitting device can be obtained.

Embodiments of the present invention will be described below with reference to the accompanying drawings.
FIG. 1 is a view showing a part of the protruding structure according to the present embodiment. As shown in FIG. 1, the protrusion structure 10 according to the present embodiment includes a substrate 1 made of diamond and a plurality of protrusions 2 formed on the substrate 1. In the example of FIG. 1, the substrate 1 is made of diamond, but a diamond-like carbon (DLC) film, an amorphous carbon nitride (a-CN), an amorphous carbon (a-C) film, a carbon nanotube (CNT) / SiC film, It may be made of a material containing carbon such as a graphite / SiC film. The protrusions 2 are arranged on the substrate 1. In the protrusion 2, the tip of the protrusion 2 is thinner than the root of the protrusion 2. The width _{W 1} of the distal end of the projection 2 is 100nm or less. The width _{W 2} of the base of the projections 2 are 300nm or less, more preferably 200nm or less. Then, the width _{W 1} of the distal end of the projections 2 is less than half of the base width. The center of the base of each projection 2 and the center of the tip are arranged with an accuracy of 10% or less of each width. Further, the aspect ratio of the protrusion (height / width of the protrusion) is set to 1 or more. The protrusions 2 are provided on the substrate 1 with a density of 4 pieces / μm ² or more.
As described above, since the fine protrusions are provided at a high density, the emission current density of the protrusion structure of the present embodiment is high. In addition, the sharp protrusion is a protrusion that is accurately in the center. The arrangement of the protrusions is more accurate than the conventional arrangement. And the height of each minute protrusion becomes uniform compared with the conventional one.

  FIGS. 2A to 2G are views showing a process for forming a protruding structure according to this embodiment. First, as shown in FIG. 2A, a substrate 1 made of diamond is prepared, and the substrate 1 is subjected to RCA cleaning.

Next, as shown in FIG. 2B, a source material such as SiH ₄ is decomposed on the substrate 1 using plasma at a substrate temperature of about 530 ° C. (600 ° C. or less), and amorphous silicon (a-Si) is obtained. ) Deposit film 3;

  Next, as shown in FIG. 2C, a resist is applied on the a-Si film 3, and the resist is finely processed by electron beam exposure or photolithography to form a resist pattern 4.

  Next, as shown in FIG. 2D, the size of the resist pattern 4 is controlled by ashing. Unless the resist size is reduced by 50% or more from the original resist size, the variation will not be so much.

Then, as shown in FIG. 2E, the Si mask 5 is formed by etching the a-Si film by dry etching using CF ₄ gas using the resist pattern 4 as a mask.

  Next, as shown in FIG. 2F, the resist pattern 4 is removed with a sulfuric acid-based solution. Note that the resist is not necessarily removed. This is because the resist is removed in a short time because the process of etching the next diamond is a process of removing the carbon material.

Finally, as shown in FIG. 2 (g), the substrate 1 made of diamond is etched in an oxygen gas to which a small amount of CF ₄ is added using a finely processed Si mask 5 so that the tip is the mask size. The projection 2 having a smaller size is formed. The formed diamond protrusion is, for example, a tall protrusion having a narrow tip and an aspect ratio of 2 or more.

  In view of the above-mentioned problems, the present inventor has found that Si is used as a mask for diamond for obtaining very fine protrusions. Si is a material that is easy to micro-process compared to Al and the like. Al is difficult to pattern when the size is smaller than 50 nm. This is related to the fact that Al has low resistance to resist developer. On the other hand, Si has high resistance to a resist developer. Therefore, patterning processing finer than that of Al becomes possible. Therefore, the advantage of Si becomes more prominent when the mask size is 50 nm or less.

Further, the present inventor has found that Si is durable against etching of diamond mainly using oxygen and can be a sufficient mask. Moreover, Si material can have electroconductivity. When electron beam drawing is used for microfabrication, it is more convenient for the conductive material to be less susceptible to the effects of charge-up than the insulating material. Even when the drawing size is reduced, the accuracy is improved. Furthermore, Si can be dry-etched with a CF ₄ gas. This is practically advantageous as compared with the case where the etching can be performed only by changing the composition ratio of the gas for etching diamond and the harmful chlorine gas must be used.

  Note that the Si film used for the mask is preferably an amorphous Si (a-Si) film. This is because amorphous Si does not have grain boundaries and therefore has excellent uniformity when etching a diamond substrate. The amorphous silicon material can be formed at a temperature of about 300 ° C. When oxygen is present at a temperature exceeding 600 ° C., the surface is damaged, but if the temperature is as low as 300 ° C., residual oxygen in the synthesis chamber is not affected so much as to be damaged.

  Although a Si film having a μm size can be produced, in order to form sharp protrusions, a Si film having a thickness of 500 nm or more must be formed. That is, the film thickness of the Si film is almost determined by the size of the mask to be formed on the substrate. When forming a mask having a diameter of 200 nm or less, a Si film having a thickness of 300 nm or less may be used. For example, a Si film having a thickness of 75 nm is formed with a mask having a diameter of 50 nm.

  The effect of the Si mask of the present invention is exhibited in a mask having a very small size of less than 80 nm. That is, even in the case where only 80 nm resist can be processed by microfabrication, it can be reduced to about 50 nm by over-etching. Up to this point, the same technique can be applied to the entire conventional mask material such as Al. However, it is difficult to reduce the size of an 80 nm Al mask by overetching to 20 nm. This is because the time until etching is short when processing a very fine size even at a normal etching rate. In addition, it is difficult to control in units of seconds (for example, within 5 seconds), and it is necessary to control at levels of 75% and 80%. On the other hand, in the Si film, a very thin layer can be oxidized by low-temperature oxidation, and a method of oxidizing the surface and sides of the mask and performing wet etching on the oxidized portion can be used. That is, the size reduction can be controlled by the thickness of the oxide layer and does not require time control in seconds. This is because the liquid such as BHF can automatically stop shrinking because a very large etching rate difference is obtained between the oxide film and the Si film. In particular, in a-Si, the grain boundary is not oxidized and does not shrink non-uniformly. Further, a-Si formed at a low temperature contains hydrogen and can be oxidized at a low temperature by extracting hydrogen, for example, by oxidizing in plasma. Therefore, it was found that it is very compatible with diamond that is weak against oxygen at high temperatures.

3A is a plan view showing the arrangement of the pattern of the Si mask according to the present embodiment, and FIG. 3B is a diagram showing each pattern of the Si mask, and FIGS. These are figures which show the other aspect of Si mask. As shown in FIG. 3A, the Si mask 5 of this embodiment is arranged on the substrate 1. As shown in FIG. 3B, the maximum width W of each pattern of the Si mask 5 is set to 300 nm or less. The ratio (H / W) between the height H and the maximum width W in each pattern of the Si mask 5 is 0.5 or more.
Each pattern of the Si mask 5 is not limited to that shown in FIG. 3B. For example, a cylindrical shape as shown in FIG. 3C or a cylindrical tip as shown in FIG. Can be applied, such as those with rounded corners, water droplets as shown in FIG. 3 (e), and those with H / W of 1 or more as shown in FIG. 3 (f).

  When diamond is etched using such a Si mask, a very sharp tip with a sharp tip can be formed, and even though the overall width is smaller than 300 nm, it is formed with very good positional accuracy. I knew it was possible. The aspect ratio (H / W) of the Si mask pattern is preferably 0.5 or more, more preferably 1 or more.

  For example, if the diameter of the pattern of the a-Si mask is 45 nm and a diamond protrusion is formed, a protrusion having a root diameter of 45 nm and a tip diameter of 10 nm or less can be formed. For example, such fine protrusions can form 11 to 25 protrusions in a 1 μm square. Furthermore, in the method of the present embodiment, it is possible to make 100 protrusions.

  In the method of the present embodiment, a large selection ratio between diamond and Si can be obtained, so that a protrusion having a very high aspect ratio can be formed. Even if etching is stopped so that the mask remains at the tip of the protrusion, it is possible to form a mask with a very small mask size of 100 nm or less. Therefore, the tip is naturally smaller than the mask size, so that a very small tip can be formed, and the height variation also varies. It can be made as small as the surface roughness of the substrate.

Next, the reason why it is important to increase the density of protrusions on the substrate will be described below. When protrusions with a diameter of 1 μm are formed, the height of the protrusions is at least 2 μm, and the density of protrusions is at most 250,000 pieces / mm ² in consideration of the protrusion interval. This is 25 mA / mm ^{2 where the} current that can be stably output from one is 0.1 μA. Considering that the emission current density in the conventional material including the hot cathode material was about 100 mA / mm ² , this is a little insufficient. However, when protrusions having a diameter of 300 nm or less are formed, the protrusion interval can be set to 500 nm, and the protrusion density can be increased to 1000000 pieces / mm ² or more. As a result, the current density becomes 100 mA / mm ² or more, and a material higher than the conventional material can be formed. Therefore, the formation of four or more protrusions within a 1 μm square can form a meaningful device with this as a boundary. Until now, no method for forming protrusions having such a density has been proposed. Furthermore, if the diameter is 200 nm or less, the number is 6.25 or more in 1 μm square, which is clearly effective.

  Here, the protrusion structure of this embodiment is a protrusion with a high aspect ratio, and is arranged with regularity. This is because a low aspect ratio of 1 or less generates a large capacitance between the structure having a gate electrode and the substrate, and hinders high-frequency operation. Also, when the gate is fabricated by self-alignment, it is difficult to make a hole around the emitter if the gate is short. Also, a random arrangement of protrusions is not preferable. This is because random items cannot prevent local concentration of current values (cannot design uniform dispersion of currents), and do not make much sense when trying to output a large current.

  In order to form the protruding structure as described above, it can be obtained by processing diamond by dry etching containing oxygen using a Si mask.

  In order to realize fine protrusions, the flatness of the substrate is preferably good. For example, since the height of the protrusion can be 1 μm or less, the flatness (TTV) of the substrate is preferably 100 nm or less, more preferably 50 nm or less, and still more preferably 20 nm or less. . A substrate having such flatness is easier to form if it is a single crystal, but it may be a polycrystal.

  Furthermore, since the protrusion itself needs to reach the tip without disappearance of carriers, it is preferably a single crystal. In the projections of the past size, the single crystal is preferable to the polycrystal because the grain boundary is included in the projection, but the projection of the present invention is very small. It does not matter. However, the reason why it is preferable to use a polycrystal having a grain size larger than the size of the protrusion is due to the above reason. For the same reason, a highly oriented polycrystalline diamond other than a single crystal is preferred to a randomly oriented polycrystalline, and a heteroepitaxial substrate is even more preferred.

  In addition, even if the substrate for forming the protrusions in this embodiment is not a diamond substrate, a carbon-based material having very high flatness (100 nm or less, more preferably 50 nm or less, and even more preferably 20 nm or less), for example, It can be applied to diamond-like carbon (DLC) film, amorphous carbon nitride (a-CN), amorphous carbon (a-C) film, carbon nanotube (CNT) / SiC film, graphite / SiC film and the like.

  4A to 4C are perspective views showing the structure of the electron-emitting device of this embodiment. The electron-emitting device 100 shown in FIG. 4A shows a case where the substrate 1 is a conductive material. 4B shows a case where the substrate 1 is an insulating material. In this case, the cathode electrode 11 is provided. Further, the electron-emitting device 100 shown in FIG. 4C is provided with a gate electrode 12.

A high-pressure synthetic single crystal diamond substrate (100) and a CVD polycrystalline diamond wafer substrate flattened to a few nm or less by polishing are prepared, and plasma CVD is performed thereon as shown in order from the top of the process shown in FIG. An a-Si film was formed by the method. The conditions for film formation were LPCVD, temperature 525 ° C., SiH ₄ (He dilution 50%): 200 sccm, N ₂ : 150 sccm, pressure 0.29 Torr (38.7 Pa).

  The film thickness is as shown in FIG. Thereafter, a negative resist for electron beam exposure was applied thereon, and electron beam exposure was performed to perform dot-like patterning. The reason for using the negative type was that the dot pattern had a smaller area than other parts, so that the time was shortened. If there is no problem with time, a positive type can be used. The resist pattern was formed using an electron beam exposure apparatus at an acceleration voltage of 50 kV.

The size of the resist dots was slightly controlled by ashing. The ashing conditions were as follows: use gas O ₂ : 50 sccm, pressure 0.6 Torr (80.0 Pa), and RF power 140 W. After a resist having a desired size was formed, the mask was patterned with CF ₄ gas. Etching conditions were RIE for SiO ₂ , working gas CF4: 20 sccm, and chamber pressure 25 mTorr (3.3 Pa). The size of the diameter can be controlled by controlling the time of side etching.

The etching is stopped at an appropriate time, and the resist is removed by SH (H ₂ SO ₄ : H ₂ O ₂ = 500: 167), which is a sulfuric acid-based solution, and is completed. Note that the resist is not necessarily removed. This is because the resist is removed in a short time because the process of etching the next diamond is a process of removing the carbon material.

6A to 6C are electron micrographs of the a-Si mask according to this embodiment. It was confirmed by SEM (= scanning electron microscope) that the formed mask was trapezoidal (conical frustum) as shown in FIG. FIG. 6 shows a photograph from the top and a photograph from the side. A mask with a size of 45 nm could be formed.
FIG. 7 shows an example of processing diamond using this as a mask. FIGS. 7A to 7D are electron micrographs showing the protrusion structure according to the present embodiment. It was confirmed that protrusions having a very high aspect ratio of 4 to 5 were formed.

  Furthermore, the individual protrusions are almost the same height. According to the rough measurement, it is 5% or less. More simply, since the mask size for the tip (lower layer) is 45 nm, if etching is stopped with a reduction of 50%, the tip diameter becomes 20 nm and the tip height variation is Consistent with flatness. Since we used a flat substrate having a flatness of 2 nm at the maximum, assuming that the height of the protrusion is about 250 nm, the height variation is about 2/250, 0.8%.

FIG. 5 shows the result of the experiment. The reduction ratio of the tip diameter is small with respect to the mask diameter, and the height variation is small when the tip diameter is kept large. The reduction ratio of the tip diameter with respect to the mask diameter. The one with a larger diameter and smaller tip diameter cannot be stopped well, and the height variation is slightly higher. It is advantageous to select a mask size close to the final tip diameter and increase the mask thickness (increase the mask aspect ratio) because the height variation can be reduced and the tip diameter can be reduced.
An example of a (1/3) mask with a small H / W is shown at the bottom of FIG. In this case, the formed protrusion has a large tip diameter. Further, when the etching is performed, the tip is reduced, but the size of the protrusion is also reduced, and the controllability of the shape of the formed protrusion is not good. Thus, a mask having a large H / W of 0.5 or more is preferable to a mask having a small H / W.

  It should be noted that the protrusion structure forming method, protrusion structure, and electron-emitting device of the present invention are not limited to the above-described embodiments, and various modifications can be made without departing from the scope of the present invention. It is.

It is a figure which shows a part of protrusion structure which concerns on this embodiment. (A)-(g) is a figure which shows the formation process of the protrusion structure which concerns on this embodiment. (A) is a top view which shows the arrangement | sequence of the pattern of Si mask of this embodiment, (b) is a figure which shows each pattern of Si mask, (c)-(f) is other than Si mask It is a figure which shows the aspect of. (A)-(c) is a perspective view which shows the structure of the electron-emitting element of this embodiment. It is a figure which shows an experimental result. (A)-(c) is an electron micrograph of the a-Si mask which concerns on this embodiment. (A)-(d) is an electron micrograph which shows the protrusion structure which concerns on this embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Substrate, 2 ... Protrusion, 3 ... Amorphous Si (a-Si) film, 4 ... Resist pattern, 5 ... Si mask, 10 ... Projection structure, 11 ... Cathode electrode, 12 ... Gate electrode, 100 ... Discharge element .

Claims (10)

A first step of forming a Si film on a substrate made of a material containing carbon;
Etching the Si film to form a Si mask having a plurality of patterns arranged on the substrate;
Etching the substrate using the Si mask to form a plurality of protrusions on the substrate;
A method for forming a protruding structure, comprising:   The method for forming a protrusion structure according to claim 1, wherein the Si film is an amorphous Si film.   The method for forming a protrusion structure according to claim 1, wherein each pattern has a maximum width of 300 nm or less.   4. The protrusion according to claim 1, wherein a ratio (H / W) between the height H and the maximum width W of each of the patterns is 0.5 or more. 5. Structure formation method.   5. The method for forming a protruding structure according to claim 1, wherein the substrate has a TTV (Total Thickness Variation) of 50 nm or less.   The method for forming a protrusion structure according to claim 1, wherein the substrate is made of diamond. A substrate made of carbon-containing material;
A plurality of protrusions formed on the substrate;
A protrusion structure comprising:
The plurality of protrusions are arranged on the substrate,
The tip of each protrusion is thinner than the base of the protrusion,
The width of the tip of each protrusion is 100 nm or less,
A protrusion structure characterized in that the base width of each protrusion is 300 nm or less. The protrusion structure according to claim 7, wherein the protrusions are provided on the substrate at a density of 4 pieces / μm ² or more.   The protrusion structure according to claim 7, wherein the protrusion structure is made of diamond. A substrate made of carbon-containing material;
A plurality of protrusions formed on the substrate;
An electron-emitting device comprising:
The plurality of protrusions are arranged on the substrate,
The tip of each protrusion is thinner than the base of the protrusion,
The width of the tip of each protrusion is 100 nm or less,
An electron-emitting device characterized in that the base width of each protrusion is 300 nm or less.

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