JP2002175977A - Method and equipment for electron beam writing - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electron beam writing equipment, which can reduce the influence by manufacturing errors of a mask, making the writing with reduced chromatic aberration and high resolution possible, to eliminate such a problem found in the conventional rectangular beam decomposition or collective figure irradiation method that these methods exclusively use a thermoelectron gun, from which a large current can be obtained, however, the thermoelectron gun generates a wide range of energies and thereby chromatic aberrations are increased, which turns into a cause for restrictions on the resolution. SOLUTION: As a source of electrons, an electron beam from a source of photoelectrons is used. The electron beam from the source of photoelectrons is once enlarged to be irradiated on a mask, and then an image on the mask is reduced to be projected on a sample.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electron beam writing apparatus, and more particularly to a high-speed and high-accuracy electron beam writing method and apparatus.

[0002]

2. Description of the Related Art In a conventional electron beam drawing apparatus, a pattern is decomposed into a point beam or a rectangular beam for drawing. A relatively new approach is to increase throughput by forming complex shaped electron beams, as described in Journal of Vacuum Science and Technology, B9, Vol. 6, pp. 2940-2943. Attempts have also been made to call the collective figure irradiation method. In these variable shaping and collective figure irradiation methods, a thermoelectron gun that can exclusively obtain a large current is used.

[0003]

However, the thermionic gun has a problem that the energy width becomes large, the chromatic aberration increases, and this is a limiting factor of the resolution. In addition, the emittance is not so large, and the amount of current that can uniformly irradiate the mask is limited.

[0004]

The present invention is characterized in that an electron beam from a photoelectron source is used as an electron source, and the photoelectron source is temporarily enlarged when irradiating a mask. The mask image is used for actual drawing. One of the features of the photoelectron source is that the energy width is small. 2 for thermal electron gun
While there is an energy width of ３3 eV, a beam with an energy width of 1 eV or less is obtained with the photoelectron source. This alone can greatly reduce chromatic aberration.

[0005] Another feature of the photoelectron source is that the emittance can be increased by increasing the size of the excitation light. However, photoelectrons do not have good uniformity in the angular distribution of electrons emitted from one point, so to effectively use the increase in emittance due to the increase in the area of the electron source, use an optical system that places a mask near the photoelectron source image. Irradiation is desirable. Conversely, it is also effective to shift the mask position slightly back and forth from the photoelectron source image position in order to reduce the non-uniformity of the photoelectron source surface and the excitation light source. As another means, there is a method in which a deflector is provided between the photoelectron source and the mask, and the electron beam is scanned and averaged on the mask for writing.

[0006] Photoelectrons are emitted relatively concentrated in the front. The half aperture angle when accelerating to 50 kV is about 1 mrad. Considering the aberration in the objective lens, the half aperture angle on the sample surface is considered to be about 4 mrad. Therefore, the electron source image is reduced to about 1/4. However, in practice, in order to form a transferred image of the mask, the requirement of processing accuracy for the mask becomes extremely strict in 1/4. Therefore, high-precision mask transfer can be achieved by irradiating the mask with the photoelectrons once (which requires twice or more times) and irradiating the mask image with a large reduction in the subsequent stage. Further, by making the photoelectron source size smaller than the mask size, the total amount of current from the photoelectron source can be reduced.

In a typical thermoelectron source, the mask opening irradiation current (maximum current used for writing) is 10 μA or less for a total current of 100 μA or more, and the ratio is 1/10 or less. In a thermionic source, a crossover is formed in a low-speed region by a Wehnelt electrode, so that this large total current causes an increase in the energy width due to the Coulomb effect. It is possible to reduce this ratio by using a photoelectron source, and it is effective for high-resolution drawing to set the ratio of the mask opening irradiation current to the total current to 1/5 or more and 30 μA or less for the total current. is there.

Another feature of photoelectrons is that the size of the electron source can be controlled at high speed by using a plurality of excitation light sources. To take advantage of this feature, the electron emission area may be changed according to the size of the opening of the mask to be irradiated. Thus, when the sizes of the collective figures in the collective figure irradiation method are different, the collective figures can be densely arranged by changing the mask irradiation area. Further, there is a possibility that a uniform current distribution cannot be obtained on the mask at the same excitation light intensity due to the state of the photoelectron surface and the non-uniformity of the extraction acceleration electric field. Therefore, a plurality of excitation light sources whose intensity can be individually controlled, a photoelectron source, an optical system for enlarging the same, an optical system for forming an image of a mask irradiated with photoelectrons on a sample, and a current density distribution of the mask image. And a means for feeding back the intensity of the excitation light, a uniform irradiation current distribution can be obtained by controlling the intensity of the excitation light.

[0009]

(Embodiment 1) FIG. 1 shows an apparatus configuration according to an embodiment of the present invention. Electrons are emitted from the photoelectron surface 101 by the excitation light 100. Light from a GaAs laser is transmitted as an excitation light through an optical fiber and condensed on a photoelectron surface. For the photoelectron surface, a GaAlAs thin film obtained by evaporating Cs in a vacuum was used. As another method, a combination of an excimer laser and Au can be considered.

The emitted electron beam is accelerated to 50 kV, expanded by two lenses 103 and 104, and projected on a first mask 106. The magnification is 6.25 times. The reason why the electron source image is used for projection onto the mask is to obtain uniform irradiation. Photoelectrons have poor uniformity in the angular distribution of electrons emitted from one point, so that only a part of the angular distribution can be used, resulting in poor efficiency. If the electron source image is used, the uniform irradiation area can be enlarged by increasing the size of the electron source. However, in this case, the uniformity of the electron emission surface becomes a problem. Therefore, in the present embodiment, the focal point is shifted by 10 mm and the averaging is performed.

As the first mask 106, a mask having a rectangular opening of 150 μm square formed in silicon having a thickness of 5 μm was used.
Since the 50 kV electrons are scattered and pass through the mask 106, they do not reach the sample 116 if a scattering stop is provided at the subsequent stage. Although the sample on the stage 117 is a silicon substrate for LSI in this embodiment, the same applies to a GaAs substrate for a communication element and a reticle substrate. The aperture image of the first mask 106 is projected onto the second mask 109 by the two transfer lenses 107 and 108. The electrons that have passed through the opening on the second mask 109 are reduced by the first reduction lens 114 and imaged on the sample by the objective lens 115. The reduction ratio from the first and second masks onto the sample is 25.

FIG. 2 shows an arrangement of openings in the second mask 109. Each area surrounded by a thick solid line is a collective figure opening area 204, which is 150 μm square. A first mask opening image 205 of the same size as the second mask 109 is formed.
Formed on top. The position of the first mask opening image 205 can be changed by the first deflector 110, and various collective figures 202 on the second mask 109 can be selected. In the center is a 125 μm square opening 201 for variable molding. The size of the opening used for drawing is larger than the electron source. Although a deflector for variable shaping is not shown, it can be further provided between the first and second transfer lenses.

The half aperture angle of electrons extracted from the photoelectron source at an acceleration voltage of 50 kV is about 1 mrad. On the other hand, in order to suppress the aberration of the objective lens, it is necessary to set the half-opening angle of the objective lens to about 4 mrad, and to use electrons as effectively as possible, the electron source image from the photoelectron source is reduced to 1/4.
About. On the other hand, from the viewpoint of manufacturing a mask, the smaller the reduction ratio from the mask, the better. Assuming that the processing accuracy of the mask is about 50 nm, the reduction ratio is 10 and 5 nm, and
At a minimum, this level of reduction is required.

In this embodiment, the reduction ratio is 25. The enlargement rate of the electron source is 2.5 at the reduction rate of 10, and 25 at the reduction rate, respectively.
Is 6.25. Thus, it can be seen from the characteristics of the electron source and the processing accuracy of the mask that it is desirable to irradiate the mask with the electron source enlargement system.

In this embodiment, the size of the electron emission surface is 30 μm.
m angle, emission current is 15 μA, emission angle is 1 mra
d. Therefore, the brightness is 5.3 × 10 ⁵ A / cm ² st.
r. Therefore, the maximum current used for writing is 6.7 μA
Is about 0.45 for the total emission current. If the total emission current is 30 μA or less and the ratio of the mask opening irradiation current to the total current is 1/5 or more, the Coulomb effect can be sufficiently suppressed. Also, unlike a thermionic electron source, there is no need to restrict the emission area by the Wehnelt electrode,
The crossover can be formed after the electrons are sufficiently accelerated. In practice, it is desirable to form a crossover after accelerating to 10 kV or more. Due to these effects, the energy width was 1 eV or less. Thereby, the chromatic aberration of the lens and the deflector is reduced.

As a result of applying a resist on an LSI substrate with silicon as a base and forming a pattern, a resolution of 50 nm was obtained in both the variable molding method and the collective figure irradiation method.
The result of drawing with a conventional thermoelectron gun was only a resolution of 80 nm, and a large improvement in resolution was obtained. Thereafter, by processing the material of the lower layer of the resist, the LSI
The required circuit pattern was obtained. Although the maximum irradiation size on the sample is 5 μm square in this embodiment, the size can be increased by increasing the irradiation area of the excitation light, which is also a great advantage of the present invention.

(Embodiment 2) FIG. 3 shows the configuration of an electron beam writing apparatus according to a second embodiment of the present invention. In this embodiment, electrons are emitted from the photoelectron surface 101 by a plurality of excitation lights 300. The excitation light transmits light from a GaAs laser through an optical fiber and condenses it on a photoelectron surface. On the photoelectron surface 101, a GaAlAs thin film
s was deposited in a vacuum. Here, the excitation light 3
00 is arranged in a 30 × 30 array within a 30 μm square, and the size of one light source is 2 μm square. Uniformity is achieved.

Further, an electrostatic deflector 305 for scanning electrons on the mask is provided. When the demand for uniformity is more severe, drawing is performed while scanning this deflector. This deflector has a crossover position 506 as the center of deflection. Other optical systems are basically the same as those in the first embodiment,
In this embodiment, the deflection control unit 302 and the photoelectric control unit 301 are further connected to the graphic information storage unit 303 by a signal line 304.

The advantages of these control systems will be described with reference to FIG. FIG. 4 is an opening arrangement diagram of the second mask 109 according to the second embodiment. As in the case of the first embodiment, a variable molding
Although there is a rectangular opening 401 of 25 μm square, the size of the peripheral collective figure opening area 404 is variable according to the size of the opening 402. This is possible because the size of the photoelectron source can be changed according to the size of the collective figure. That is, in this embodiment, by turning off a light source unnecessary for aperture irradiation, the irradiation area on the mask can be reduced. Since the electron sources are arranged at a pitch of 0.25 μm on the sample, it can be controlled in units of 1 μm or less even when the portions where the light sources overlap are taken into account.

In order to improve the controllability, it is possible to further increase the number of light source arrays. The fact that the collective figures can be densely arranged as shown in FIG. 4 has the effect of increasing the number of collective figures, considering that there is a limit to the deflection range on the second mask 109 by the first deflector. This contributes to an improvement in throughput. As a result of drawing a logic LSI having a gate of 70 nm, a throughput of 3 wafers / hour can be obtained with an 8-inch wafer. On the other hand, in the conventional collective figure method, the number of collective figures is small and the throughput is only 2 pieces / hour.

(Embodiment 3) FIG. 5 shows an apparatus configuration for explaining another embodiment of the present invention. The first crossover image 506 was formed in the same manner as in Example 2 except that the first transfer lens was not used and the extraction and the electrostatic lens having only the anode electrode were used. Various methods are conceivable for the optical system up to the irradiation of the first mask, and irradiation by strengthening the electrostatic lens is also possible unless vertical incidence on the mask is an absolute condition.

A Faraday cup 501 and an ammeter 502 for measuring the current density distribution of the mask image are provided. The mask image is scanned on the Faraday cup by the objective deflector 503 to measure the current density. These are controlled by the current density distribution measurement unit 504. The current density distribution can be substituted by another method such as a combination of a backscattered electron detector and a heavy metal mark. 30 × 3 to make the current density distribution as uniform as possible from the data obtained by the current density distribution measurement unit
The intensity of the 0 excitation light is adjusted.

FIG. 6 shows the result. This is a current density distribution represented by contour lines. Use area 5 before adjustment
Up to 96% of the contour lines were observed within the μm square, but only 99% of the contour lines became visible after adjustment by increasing the intensity of the excitation light in the peripheral portion. Further, if local non-uniformity exists, it can be eliminated by defocusing the electron source image as described above.

Since it is expected that the surface condition of the electron source will gradually change, it is desirable to make these adjustments periodically. In this embodiment, the adjustment is performed every time immediately before the lot drawing. This makes it possible to reduce deterioration in dimensional accuracy due to non-uniformity of current distribution. As a result of drawing a 70-nm gate logic LSI, it has become possible to reduce the dimensional uniformity on an 8-inch wafer from ± 15 nm to ± 7 nm.

[0025]

As described above, according to the present invention, a photoelectron source having small energy dispersion can be applied to a mask transfer drawing apparatus, and a high-resolution and high-speed drawing apparatus can be obtained.

[Brief description of the drawings]

FIG. 1 is a schematic cross-sectional view illustrating a device configuration according to a first embodiment of the present invention.

FIG. 2 is a plan view of a second mask according to the first embodiment of the present invention.

FIG. 3 is a schematic cross-sectional view illustrating a device configuration according to a second embodiment of the present invention.

FIG. 4 is a plan view of a second mask according to a second embodiment of the present invention.

FIG. 5 is a schematic cross-sectional view illustrating a device configuration according to a third embodiment of the present invention.

FIG. 6 is a measurement diagram showing a current density distribution of Example 3 of the present invention.

[Explanation of symbols]

Reference numeral 100: excitation light, 101: photoelectric surface, 102: extraction electrode, 103: first transfer lens, 104: second transfer lens, 105: transfer aligner, 106: first mask, 1
07: first transfer lens, 108: second transfer lens, 10
9 second mask, 110 first deflector, 111 second deflector, 112 third transfer lens, 113 fourth transfer lens, 115 first objective lens, 116 sample, 117
Stage 119: ray trace of electron source image, 120: ray trace of crossover image, 201: rectangular opening for variable shaping, 202: collective figure opening (figure shape opening), 203: aperture for beam adjustment, 204: collective figure opening area , 205 ...
First mask image, 300: multiple excitation lights, 301: light source control unit, 302: deflector control unit, 303: graphic information storage unit, 304: signal line, 305: mask deflector for scanning, 401: variable shaping Rectangular opening, 402 ...
Collective figure opening, 404: Collective figure opening area, 405: First mask opening image and / or electron source image, 501: Faraday cup, 502: Ammeter, 503: Object deflector, 504: Current distribution measurement unit, 505 ... Anode electrode, 506: First crossover image.

 ──────────────────────────────────────────────────の Continuing on the front page (72) Inventor Akika Tanimoto 1-280 Higashi Koigakubo, Kokubunji City, Tokyo Inside the Central Research Laboratory of Hitachi, Ltd. F-term in the Central Research Laboratory (Reference) 2H097 BB01 CA16 LA10 5C030 CC01 CC07 CC10 5C034 BB01 BB02 BB05 5F056 AA04 AA06 FA02 FA03 FA07

Claims (15)

[Claims] In an electron beam writing apparatus capable of performing a variable shaping method or a batch figure irradiation method, an electron beam from a photoelectron source having a size smaller than the maximum aperture of a mask used for writing is irradiated on the mask, and an image of the mask is formed. An electron beam writing method, wherein a photoelectron source is temporarily enlarged when projecting onto a sample. 2. An electron beam writing apparatus capable of performing a variable shaping method or a batch pattern irradiation method, irradiates an electron beam from a photoelectron source onto a mask, and once the image of the mask is projected onto a sample, the photoelectron source is once turned on. An electron beam lithography method characterized in that the magnification is twice or more. 3. An electron beam writing apparatus capable of performing a variable shaping method or a batch figure irradiation method, irradiating an electron beam from a photoelectron source onto a mask and projecting an image of the mask onto a sample. An electron beam writing method, wherein the ratio of the amount of emission current to the maximum current used for writing is 1/5 or more, or the amount of emission current from the photoelectron source is 30 μA or less. 4. An electron beam lithography system capable of performing a variable shaping method or a collective pattern irradiation method, irradiates an electron beam from a photoelectron source onto a mask and projects a plurality of photoelectron sources when projecting an image of the mask onto a sample. An electron beam writing method characterized by using the excitation light of (1). 5. An electron beam writing apparatus capable of performing a variable shaping method or a batch figure irradiation method, irradiating an electron beam from a photoelectron source onto a mask and projecting the mask image onto a sample. An electron beam writing method, wherein the electron beam writing method is provided closer to an electron source image than a crossover image. 6. An electron beam writing method according to claim 1, wherein the mask is irradiated with an electron beam from a photoelectron source and an image of the mask is projected onto a sample to be irradiated. An electron beam drawing method characterized by drawing while scanning photoelectrons. 7. An electron beam writing method according to claim 1, wherein an electron emission area is changed according to a size of an opening of a mask to be irradiated. 8. An electron beam writing apparatus capable of performing a variable shaping method or a batch figure irradiation method, irradiating an electron beam from a photoelectron source onto a mask and projecting an image of the mask onto a sample. An electron beam writing method, characterized in that the current density on a mask is made uniform by making the excitation light intensity distribution non-uniform. 9. An electron beam writing apparatus capable of performing a variable shaping method or a batch figure irradiation method, a photoelectron source having a size smaller than the maximum aperture of a mask used for writing, an optical system for enlarging the same, and a mask irradiated with photoelectrons. An electron beam lithography apparatus having an optical system for forming an image of a sample on a sample. 10. An electron beam writing apparatus capable of performing a variable shaping method or a batch figure irradiation method, comprising:
An electron beam lithography apparatus having an optical system that magnifies the image by a factor of two or more and an optical system that forms an image of a mask irradiated with photoelectrons on a sample. 11. An electron beam writing apparatus capable of performing a variable shaping method or a batch figure irradiation method, comprising: a plurality of excitation light sources;
An electron beam lithography system comprising a photoelectron source, an optical system for enlarging the photoelectron, and an optical system for forming an image of a mask irradiated with photoelectrons on a sample. 12. An electron beam lithography system capable of performing a variable shaping method or a batch figure irradiation method, wherein a plurality of excitation light sources whose intensity can be individually controlled, a photoelectron source, an optical system for enlarging the same, and photoelectrons are irradiated. An electron beam lithography apparatus having an optical system for forming an image of a mask on a sample, a unit for measuring a current density distribution of the mask image, and a unit for feeding back the intensity of excitation light. 13. An electron beam writing apparatus capable of performing a variable shaping method or a batch figure irradiation method, comprising: a plurality of excitation light sources;
An electron beam lithography system comprising a photoelectron source, an optical system for enlarging the photoelectron, and an optical system for forming an image of a mask irradiated with photoelectrons on a sample. 14. An electron beam writing apparatus capable of performing a variable shaping method or a batch figure irradiation method, comprising: a photoelectron source, an optical system for enlarging the photoelectron source, a deflector for raster scanning between the photoelectron source and the mask, and a photoelectron. An electron beam lithography apparatus having an optical system for forming an image of an irradiated mask on a sample. 15. An electron beam writing apparatus capable of performing a variable shaping method or a batch figure irradiation method, comprising: a plurality of excitation light sources;
A deflector control unit for selecting information on a figure of a mask to be irradiated in an electron beam lithography apparatus having a photoelectron source, an optical system for enlarging the same, and an optical system for forming an image of a mask irradiated with photoelectrons on a sample; An electron beam writing apparatus having a signal line to be sent to an electron source control unit.