JPH10172500A - Electron beam source, electron gun, electron beam plotting device, and pattern forming method using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To significantly improve device performance by applying a region limit type thermionic source to an electron beam application device of such type forming a mask on a sample. SOLUTION: An electron source 102 is made of two substances, and a center substance is an electron emission substance made of substances with their low work function. When a proper electric field and a temperature are imparted to an electron source, thermionic emission occurs with a substance with its low work function. Therefore, emission of an electron generated other than that actually used can be restrained. The emitted electron is applied to a first mask 103, and an image of the first mask 103 is formed on an aperture in a second mask 105 by two transfer lenses 104. A position on the second mask of the image of the aperture on the first mask 103 is determined by a deflector 113 between these two lenses. An electron passing through the second mask 105 is reduced by two reduction lenses and is projected on a wafer 109.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an electron beam source, an electron gun,
The present invention relates to an electron beam lithography apparatus and a pattern forming method using the same, and more particularly to a technique suitable for transferring a mask image onto a sample.

[0002]

2. Description of the Related Art The performance of an electron beam application apparatus largely depends on its electron source. For example, a triode thermoelectron gun capable of stably obtaining a large current is used in an industrial electron beam lithography apparatus. On the other hand, in the electron microscope, a field emission type electron gun having a small virtual light source diameter is used. On the other hand, as a new electron source, research has been conducted on a region-limited thermionic source composed of a substance having a large work function and a substance having a small work function. These works were performed by P, B, Swell, etc., in the proceedings of third, Farfarcon, Conference (1984).
163) and J. Dee, Peaushek et al. Are published in the Journal of Vacuum Science and Technology, B6 (1988), 1989. The feature of this electron source is that the energy width of electrons is smaller than that of a tripolar thermoelectron gun. However, this type of electron source has not been put to practical use yet.

[0003]

It is considered that the reason for this is that this electron source has been attempted to be applied to a point source type electron beam application apparatus. In the point source type electron beam application device, the field emission type electron source is an electron source which is more excellent in terms of energy width and light source diameter, and this has hindered practical use.

[0004]

As a result of exploring more effective use of this type of electron source, this electron source is applied to an electron beam application apparatus of the type that forms a mask image on a sample. Proved to be very effective. An example of an electron beam application apparatus that forms a mask image on a sample is described by Hayata et al. In Journal of Vacuum Science and Technology, B9 (1991), p. 2940. In this system, 10μA current is 105A / c
It must be obtained with m2sr brightness and uniformity within 5%.
This uniform distribution (angle dependence of electron emission) is important in an electron beam lithography apparatus using a mask image. Since the region-limited thermionic source has characteristics satisfying this requirement, it is possible to produce an electron beam application device having better performance than before because of the small energy width which is an advantage. Further, in the electron beam application apparatus of the type in which a mask image is formed on a sample, since the virtual light source of the electron source is enlarged, the Bellche effect which is a problem in the point source type electron beam application apparatus is small. This means that the small energy width of the region limited type thermoelectron source can be used effectively.

In order to obtain a more uniform current, each of the following structures is more preferable.

[0006] 1. The size of the small part of the uncoated work function is between 0.1 mmf and 1 mmf.

[0007] 2. The tip of the electron source must be between 0.2mm and 2mm.

[0008] 3. The difference in height between a substance having a large work function and a substance having a small work function is 10 μm or less.

4. The side of the electron source is composed of a material with a large work function.

The following structure is effective as a configuration of the electron gun.

5. Electrodes must be located at least 0.5 mm away from the tip of the electron source in the direction opposite to the anode.

Further, as a method of use, it is used at a temperature between 6.1650K and 1750K.

7. Only electrons emitted from less than 10% of the small unworked portion of the work function are used for writing.

An effective method for producing an electron source is as follows. Use a focused charged particle beam in defining a small portion of the uncoated work function.

9. A substance having a large work function coated with a substance having a small work function is removed by a chemical reaction.

Further, as an application to the system, there are: A system provided with a function of measuring the size of the virtual light source or the size of its image and a function of feeding it back to the electron optical system can be considered.

Hereinafter, these will be described in detail.

FIG. 1 shows a conceptual diagram of the present invention. This electron optical system is the same as that described by Hayata et al. In Journal of Vacuum Science and Technology, B9 (1991), p. 2940. The electron source 102 is composed of two substances. The central material is an electron emitting material 100 made of a material having a low work function. If a proper electric field and temperature are applied to the electron source, only the material having a low work function emits thermionic electrons. Therefore, emission of electrons other than electrons actually used can be suppressed. The emitted electrons irradiate the first mask 103. The image of the first mask is transferred to the second mask 10 by two transfer lenses 104.
5 formed on the aperture. In the case of the variable rectangular drawing apparatus, each of the two masks has a rectangular opening. In the case of the cell projection drawing apparatus, the second mask has various kinds of openings. The position of the aperture image on the first mask on the second mask is determined by the deflector 113 between the two lenses.
Is determined by The electrons that have passed through the second mask are reduced by the two reduction lenses, and finally the stage 110
It is projected on the upper sample 109. A deflector 114 in the objective lens defines the position of the electron beam on the sample. A mark 112 for electron beam measurement is also provided on the stage.
The present invention is not limited to this particular electron optical system, but may be various electron optical systems for mask transfer.

Since the region-limited type thermoelectron source has a uniform current angular distribution, it can be used as such a light source for mask irradiation. Further, the energy width is narrower than that of the conventional triode thermoelectron gun, and higher resolution than before can be realized. The energy width is 1 eV or less, which is considerably smaller than the conventional 2 to 3 eV.

Several methods are conceivable for obtaining an electron beam with better characteristics. First, the size of the uncovered portion having a small work function (electron emission region) is 0.1 mm.
It is effective that the distance is between f and 1 mmf. If the electron emission region having a low work function is too narrow, the electrostatic potential near the center is affected by the step of the coating material that does not emit electrons as shown in FIG. This is because a force acts to bend the off-axis electrons inward, and the angular distribution of the current increases with the angle. Conversely, if the electron emission region is too wide, the total emission current will be too large for the current used, causing discharge and contamination of the mirror. Typically, to use only electrons emitted from a region of about 20 μmf, it is close to one order of magnitude,
0.1 mmf is required. In other words, it is preferable to use only the electrons emitted from about 10% of the area of the electron emission region. The diameter of the tip of the electron source is also a large parameter. If the diameter of the tip becomes smaller, the center of the tip becomes farther from the step, and is less affected by the step shown in FIG. The effect becomes more remarkable than 2 mm. On the other hand, when the diameter is 0.2 mm or less, the current density angle distribution on the mask is easily affected by the current density distribution on the electron source surface. The current density angle distribution on the mask is the integral of the current density distribution on the electron source surface and the spread of electron emission from each point. This alleviates the influence of the non-uniformity of the current density distribution on the electron source surface due to the non-uniformity of the material. However, when the tip diameter is 0.2 μm, the electron emission angle with respect to the distance on the electron surface becomes large, and this relaxation effect cannot be expected. Therefore 0.2mm
Between 2 and 2 mm is effective in providing the tip diameter. Also,
The step is preferably suppressed to 10 μm or less.

Operating conditions are also important. Since the thermionic electron source operates at a high temperature, the electron-emitting substance evaporates. This causes a step with the non-electron-emitting substance to make the current angle distribution non-uniform. For example, LaB6 is 1 when used at 1750K.
Evaporates 8 μm per year. Therefore, it is desirable to use at a lower temperature than this condition. However, regarding the operating temperature, the electric field that can be applied to the electron source is limited in consideration of discharge,
1650K is required to obtain sufficient luminance.

Another problem caused by the evaporation of the electron source is a change in the virtual light source diameter (crossover diameter). Accordingly, it is necessary to adjust the electron optical parameters accordingly. For this purpose, it is desirable to add a function of measuring the virtual light source diameter and a function of feeding back the electron optical parameters to the electron beam lithography apparatus. The parameters to be changed are the excitation and voltage of the lens. There is also a method of providing a condenser lens for feedback between the electron gun and the transfer lens. However, as shown in Fig. 3, an electrode should be placed at a distance of 0.5 mm or more from the tip of the electron source, and the voltage should be changed. The method of adjusting by using is also effective. The reason for separating the electrodes by 0.5 mm or more is to prevent the added electrodes from impairing the uniformity of the current.
Therefore, the voltage applied to this electrode may be positive or negative with respect to the voltage of the electron source. When the crossover diameter increases, it is effective to apply a positive voltage. Since the change in the voltage of this electrode causes the change in the total current,
It is also necessary to adjust the anode voltage and the operating temperature. This electrode also has the effect of blocking non-rotationally symmetric electrostatic potentials due to the support of the electron source. If only the shielding effect is intended, the electrode and the electron source may be short-circuited.

The method of manufacturing the electron source also requires some contrivance. The most important thing is how to define the electron emission region. P, B, Swell, etc. mechanically do this, but mechanical methods can damage the surface of the electron emission region. Furthermore, it is difficult to produce an electron source having a finite diameter by their method. Therefore, etching using a focused ion beam and a chemical reaction is effective as a new method. The focused ion beam enables lithography on a three-dimensional sample such as an electron source. A simple method is to deposit a substance having a large work function that does not easily cause electron emission on the electron-emitting material, and remove the electron emission material only by sputtering using an ion beam where the electron emission is desired. Another method is shown in FIG. The electron emission material 402 is coated with the electron non-emission material 401. Further, an etching mask material 403 is coated thereon. The mask material is selectively removed with a focused ion beam (FIB). The electron non-emission material is etched using the mask material 403 as a mask. Finally, the mask material is removed. In this method, since the electron non-emission material can be chemically removed, damage to the surface of the electron emission material is minimized. The simplest manufacturing method is as follows. In this method, only the side of the electron source is coated. First, an electron non-emission material is deposited on the electron emission material. In this case, a deposition method having good covering properties such as a chemical vapor deposition method is used. Next, the electron non-emission material is mainly removed only from the upper surface by a strongly anisotropic removal method such as reactive dry etching. This method can also be applied to the mask material removal method, where the mask material is deposited by a deposition method with good coverage such as the chemical vapor deposition method, and the mask material is mainly removed only on the upper surface by a strong anisotropic removal method. Remove. In this method, the size of the electron emission region is determined by the thickness of the electron source, but the process is simplified because lithography is not required.

[0024]

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiment 1 FIG. 5 shows a structural diagram of a region-limited thermionic electron source. LaB6500 was used as an electron emission material, and carbon 501 was used as an electron non-emission material. The electron emission area is 0.15 mmf, and the tip is flat. The thickness of the electron non-emission material is 1 μm
Therefore, the level difference from the electron emission material is 1 μm. An electrode 503 is placed 0.5 mm behind the tip. FIG.
Shows the angle dependence of the current and the total current within the angle. From the figure 1
It can be seen that 5 μA is obtained with a uniformity of 5% or less. The operating temperature is 1700K and the accelerating voltage is 50kV. further,
The virtual crossover is 5 μm and the luminance is 5 * 105 A / cm2sr.

FIG. 7 shows a method of manufacturing an electron source. at first,
1 μm thick carbon 700 was deposited on LaB6701 by plasma enhanced chemical vapor deposition. Next, a silicon oxide film 703 having a thickness of 0.2 μm was also deposited by the plasma chemical vapor deposition method. The plasma-enhanced chemical vapor deposition method can be deposited on a poorly adherent carbon surface without any problem. In addition, a method such as a thermochemical vapor phase method or sputtering is also possible. Next, only the silicon oxide film in a limited area is removed using a focused ion beam. Furthermore, with the silicon oxide film as a mask by oxygen plasma,
Etch carbon. Finally, the silicon oxide film is removed with hydrofluoric acid. The advantage of the two-stage method is that the implantation of the focused ion beam into LaB6 and the sputtering of LaB6 can be avoided. Further, it is effective to perform high temperature heating in vacuum after carbon deposition. This allows
Graphitize carbon and increase work function.

FIG. 8 shows an electron optical mirror using this electron source. This mirror is for a lithography system having a cell projection function. 15 electron beams
The first mask 103 having an opening of 0 μm square is directly irradiated. This rectangular image is formed on the second mask 105.
FIG. 9 shows the arrangement on the second mask 105. A 125 μm square opening 901 for variable rectangular shape and many cell openings 902 are arranged. The position of the image of the first mask opening can be changed by the deflector. The image is reduced to 1/25 and is finally projected on the wafer 802 on the stage 110. The energy width of the electrons is 0.7 eV. This is smaller than the conventional 2 to 3 eV. Therefore, chromatic aberration is reduced.
When a 0.5 μm thick SAL601 resist is used,
A 9 μm line and space and a 0.07 μm hole could be drawn. When a conventional electron gun is used, they are 0.15 μm and 0.14 μm, respectively. Furthermore, by the combination of dry etching and cell projection, a hole and a wiring pattern of an LSI having a level of 0.1 μm could be formed. In particular, since the hole pattern has a small current, chromatic aberration mainly determines beam blur. Therefore, this electron source is particularly effective for hole patterns.

During the operation of the electron source, LaB6 evaporates but carbon hardly evaporates. Therefore, the step at the boundary between the two becomes large. This increases the crossover size and causes the electrons to converge inward. These phenomena are observed by detecting the reflected electrons from the mark 112 on the stage and changing the lens condition to focus on the mark. The crossover size can be adjusted by changing the voltage of the electrode behind the electron source. Increasing the voltage to a positive value reduces the crossover size. For example, 0
The crossover size of 5 μm at V is 4 μm at 200 V. After 6 months, the step is 10μm
As described above, the uniformity deteriorated.

Embodiment 2 FIG. 10 shows a region-limited thermionic source having another structure. The electron emission area is 0.1 mmf. The tip diameter is 0.2 mm. The step of the electron non-emission material is 4 μm. 5% even in this case
A current of 15 μA can be easily obtained with an error of 0.1mmf,
The reason why good results can be obtained even under the condition of 4 μm lies in the tip diameter of 0.2 mm. As a result, the position of the step is retracted from the tip of the electron source, and its influence is reduced. On the other hand, the uniformity of the LaB6 crystal is more likely to be affected by the current distribution on the mask.
If the tip diameter of the electron source is 0.1 mm, uniformity within 5% cannot be obtained. In an electron source having such a structure, a focused ion beam is particularly effective as a manufacturing method.

FIG. 11 shows an electron optical system in this example. In this optical system, the condenser lens 1200 is
And the first mask 103. This lens can control the irradiation condition of the electron to the mask. In this example, the second mask has a triangular opening 1201. As in the case of the first embodiment, the SAL601 resist is used and 0.3 is used.
A μm line and space was formed on the chromium. By etching chromium, a highly accurate reticle could be manufactured. The dimensional accuracy is 0.02 μm, which is smaller than the conventional 0.035 μm.

Embodiment 3 FIG. 12 shows a method of manufacturing a side-coated electron source. First, amorphous carbon 1300 is deposited. Then 1800
Heat in vacuum at K. This temperature is slightly higher than the operating temperature in the device. Therefore, further changes during operation can be prevented. Further, after depositing the silicon oxide film 1303, the silicon oxide film is removed by anisotropic etching. Then, carbon is etched using the silicon oxide film as a mask to obtain a side-coated electron source. The diameter of the electron source is 200 μm, and the electron emission area is sufficiently small.

The present invention is not limited to these embodiments. For example, although only LaB6 and carbon are used in the embodiment, other combinations of materials having different work functions may be used. W and W mixed with LaB6 and Re and Ir are also effective. Similarly, various implementation methods can be considered for the optical system and the resist.

[0032]

As described above, the performance of the device can be greatly improved by applying the region-limited thermionic source to an electron beam application device of a type that forms a mask image on a sample.

[Brief description of the drawings]

FIG. 1 is an electron beam drawing apparatus diagram to which the present invention is applied.

FIG. 2 is a diagram for explaining the influence of a step.

FIG. 3 is a view of a rear electrode.

FIG. 4 is a manufacturing process diagram of the electron source.

FIG. 5 is a structural diagram of an electron source according to the first embodiment.

FIG. 6 is an electron emission characteristic diagram of Example 1.

FIG. 7 is a manufacturing process diagram of the electron source according to the first embodiment.

FIG. 8 is a diagram of an electron beam drawing apparatus according to the first embodiment.

FIG. 9 is a mask diagram according to the first embodiment.

FIG. 10 is a structural diagram of an electron source according to a second embodiment.

FIG. 11 is a diagram of an electron beam drawing apparatus according to a second embodiment.

FIG. 12 is a manufacturing process diagram of the electron source according to the third embodiment.

[Explanation of symbols]

100--electron emitting material, 101--electron non-emitting material,
102-electron source, 103-first mask, 104-transfer lens, 105-second mask, 106-reduction lens, 107-objective lens, 108-objective aperture, 1
09-wafer, 110-stage, 111-electron detector, 112-mark, 113-deflector, 114
-Object deflector, 200-Electron emitting material, 201-Electron non-emitting material, 202-Anode electrode, 203-Electrostatic potential, 301-Back electrode, 401-Electron non-emitting material, 402-Electron emitting material, 403-Mask material , 700-amorphous carbon, 701
--LaB6, 702--graphite, 703--silicon oxide film, 800--resist, 801--deposited film, 900--first opening image, 901--125 μm square opening, 902--cell opening 1, 1000--LaB6,1
001—carbon, 1002—electron orbit, 1200—adjusting lens, 1201—second mask, 1202—resist, 1203—chrome, 1204—reticle plate, 1300—amorphous carbon, 130
1-LaB6, 1302-graphite, 130
3--Silicon oxide film.

Claims (11)

[Claims] 1. An electron beam lithography apparatus for transferring electrons transmitted through a mask onto a sample, wherein a region-limited thermoelectron source is used as an electron source, and a lithography method and pattern using the electron beam lithography apparatus. Forming method. 2. An electron beam lithography apparatus according to claim 1, further comprising a function of measuring the size of a virtual light source or the size of an image of the virtual light source and a function of feeding it back to an electron optical system. Drawing method and pattern forming method. 3. An electron beam lithography apparatus according to claim 1, wherein the size of the uncovered portion having a small work function is between 0.1 mmf and 1 mmf, and a lithography method and pattern formation using the same. Method. 4. The electron source according to claim 1, wherein the tip length of the electron source is 0.2 m.
A distance between m and 2 mm for an electron beam lithography apparatus, and a lithography method and a pattern forming method using the same. 5. An electron beam lithography apparatus according to claim 1, wherein a difference in height between a substance having a large work function and a substance having a small work function is 10 μm or less, and a drawing method and a pattern forming method using the same. . 6. An electron beam lithography apparatus and a lithography method using the electron beam lithography apparatus according to claim 1, wherein only electrons emitted from a portion having a small work function not covered by 10% or less are used. And a pattern forming method. 7. The method according to claim 1, wherein the temperature is from 1650K to 1750K.
An electron beam lithography apparatus characterized in that it is used at a temperature between the above, and a lithography method and a pattern formation method using the same. 8. An electron beam lithography apparatus according to claim 1, wherein said apparatus is used at 10-9 Torr, and a lithography method and a pattern formation method using said apparatus. 9. An electron gun using a region-limited thermoelectron source having a limited electron emission region, wherein an electron is provided at a distance of 0.5 mm or more from an end of the electron source in a direction opposite to an anode. A gun, an electron beam drawing apparatus equipped with the gun, a drawing method, and a pattern forming method. 10. An electron source characterized by using a converged charged particle beam when defining an uncoated small portion of a work function in a region limited type thermoelectron source having an electron emission region limited, and an electron source. On-board electron beam drawing apparatus, drawing method and pattern forming method. 11. An electron source equipped with an electron source having an electron emission region, wherein a high work function material coated with a low work function material is removed by a chemical reaction in a region limited type thermal electron source having a limited electron emission region. Line drawing apparatus, drawing method and pattern forming method.