JP4939565B2 - Electron beam exposure system - Google Patents

Description

The present invention relates to electronic beam exposure apparatus.

  In the mass production stage of semiconductor memory device manufacturing, an optical stepper with high productivity has been used. However, in the production of memory devices after 1G and 4GDRAM having a line width of 0.2 μm or less, exposure instead of the optical exposure method is used. As one of the techniques, an electron beam exposure method with high resolution is expected.

  Conventional electron beam exposure methods have centered on a single beam Gaussian method and a variable shaping method. Since these electron beam exposure methods have low productivity, they have been used for mask drawing, ultra-LSI research and development, and exposure of small-volume production ASIC devices.

  As described above, the problem for mass production of the electron beam exposure method has been how to improve productivity. Recently, a partial batch transfer method has been proposed as one method for solving this problem. As shown in FIG. 8 (a), these variable formation type or partial batch transfer type exposure apparatuses include an electron gun 20 including an electron source 7b, a Wehnelt electrode 8, a ground electrode 9, and an aperture 10a, a deflector 13, An illumination device 21 including illumination lenses 11a and 11b and an aperture 10b (or electron beam mask 15), and a projection lens 12 that projects an electron beam that has passed through the electron beam mask 15 onto a wafer 16 on a stage 17 through a deflector 14. A projection lens system 22. In particular, the partial batch transfer type exposure apparatus can reduce the number of exposure shots by making the repeated portion of the memory circuit pattern into a cell of several μm, thereby improving the drawing productivity.

  On the other hand, ensuring the exposure line width accuracy as well as the productivity of the exposure apparatus is an important element for practical use as an exposure apparatus. Therefore, the uniformity of the irradiation intensity in the exposure area is 0.5% in the entire exposure area. It is required to: In order to obtain an irradiation electron beam with high uniformity, an aperture 10b shields an electron beam in an opening angle region of several mrad with good characteristics from among several tens of mrad emitted from an electron gun. And extracted as an irradiation beam (see FIG. 8B).

  In recent years, a method for further increasing the exposure area has been proposed in order to further improve productivity. For example, an electron beam transfer method using an electron beam scattering mask: SCALPEL (SDBerger et. Al. “Projection electron beam lithography: A new approach.” J. Vac. Sci. Technology B9, 2996, (1991)) This is one exposure method of high-speed electron beam exposure. In this method, since the exposure area is 2500 times or more larger than the conventional variable forming method and cell exposure method, the influence of the electron-electron interaction due to the Coulomb effect can be reduced. It is possible to carry out exposure with an order of magnitude higher than the above, and high productivity can be expected. However, this electron beam exposure method requires a highly uniform irradiation intensity in a wide exposure region. As the irradiation current increases, the amount of electron beam that shields the electron beam generated from the electron source with the electron gun and the aperture in the column increases.

  On the other hand, in an electron beam mask transfer apparatus using an arc beam (refer to Japanese Patent Application No. 283814), the width of the exposure area is several mm, which is about 6 times larger than the transfer exposure (SCALPEL). High-speed exposure is possible by scanning exposure of the mask and wafer, but in order to uniformly illuminate a wide area, part of the peripheral beam of the electron beam emitted from the electron gun is exposed as a ring-shaped or arc-shaped beam. Used for irradiation beams. In particular, when an electron beam radiated uniformly from an electron gun is used, the use efficiency of the emitted electron beam is about 1/1000, and most of the generated electron beam is shielded by the electron gun and the aperture in the column. The problem that I said occurred.

  In the conventional exposure method, the irradiation beam is small, and it was not a problem if electrons were shielded by an electron gun or an aperture electrode in the middle of the column. However, in the high-productivity exposure method, the irradiation beam on the wafer The exposure was performed with a current of several tens of μA, which is one digit greater than that of the conventional exposure method, and the electron current shielded by the aperture electrode was a large value of several mA.

  Therefore, the conventional method of shielding a radiated electron beam with a beam shielding electrode in the middle not only raises the temperature of the shielding electrode and the problem of dissolution of the electrode, but also raises the temperature inside the column or scatters the shielded electrons. The charge-up phenomenon in the above leads to the deterioration of the beam position accuracy, which is important for the exposure performance, so it is difficult to increase the irradiation current and improve the throughput. Furthermore, since the power load of the electron generator is larger than that of the conventional electron generator, it is difficult to stabilize the power supply and reduce the price.

  An object of the present invention is to reduce an electron beam shielded by an aperture for shaping an electron beam from a thermal electron source.

In order to achieve the above object, the present invention provides an electron beam exposure apparatus that simultaneously exposes a plurality of exposure areas with a plurality of electron beams,
An electron gun that includes a thermionic source and an electrode that forms a crossover of electrons emitted from the thermionic source, and emits an electron beam from the crossover ;
An aperture that blocks a part of the electron beam emitted from the electron gun and forms an irradiation electron beam that irradiates each of the exposure regions; and
Electron emission surface of the thermionic source comprises a plurality of effective irradiation area, an irradiation restricted region disposed between the effective irradiation area of the plurality of, effective irradiation area of said plurality of, from the irradiation restricted area, High electron emission efficiency
The plurality of irradiation effective regions include the irradiation electrons so that a part of each of the plurality of electron beams emitted from the plurality of irradiation effective regions is shielded by the apertures and the irradiation electron beams are shaped by the apertures. It is characterized by being arranged in association with each of the exposure areas irradiated with a beam.

  (Operation) In the invention as described above, an irradiation effective area and an irradiation limiting area having different electron emission efficiencies are provided on the electron emission surface of the thermionic source of the electron gun, and the irradiation effective area is defined as an effective electron emission area contributing to exposure. The irradiation limited region is a region that does not directly contribute to exposure and emits an electron beam shielded by an electron gun or an aperture electrode in the column if not limited. Thereby, the irradiation utilization efficiency of a radiated electron can be raised. Furthermore, since the amount of electron beam irradiated to the aperture electrode in the column is greatly reduced, problems such as a rise in column temperature due to electron beam irradiation, charge-up in the column, and melting of the aperture can be solved. Further, by taking out only the necessary beam into the column, it is possible to prevent the beam resolution performance from being deteriorated due to the electron-electron interaction.

  The present invention can reduce the electron beam shielded by the aperture that shapes the electron beam from the thermionic source.

It is the figure which showed the shape of the electron source provided with the irradiation effective area | region and the irradiation limited area | region in the electron emission surface of the electron beam illuminating device by embodiment of this invention. It is a figure explaining the example of a manufacturing method for forming an irradiation limited area | region in the electron emission surface of the electron source of the electron beam illuminating device by embodiment of this invention. It is a figure for demonstrating the electron gun characteristic when the electron source of the electron beam illuminating device by embodiment of this invention is applied to an exposure system, (a) is the track | orbit of the electron discharge | released from the electron emission surface of the electron source The electron gun characteristics when the electron source shown in FIG. 1A is applied are schematically shown. It is the figure which showed the example of the electron beam mask transfer exposure apparatus provided with the electron beam illumination apparatus which irradiates the planar electron beam by embodiment of this invention. It is a figure which shows an angle distribution characteristic when the electron source which formed the ring-shaped irradiation effective area | region as shown in FIG.1 (b) in the electron emission surface is used for an electron gun. It is a figure which shows an angle distribution characteristic when the electron source which formed the ring-shaped irradiation effective area | region in FIG. 1 (e) in the concave electron emission surface was used for the electron gun. It is the figure which showed the example of the electron beam mask transfer exposure apparatus provided with the electron beam illumination apparatus which irradiates the arc-shaped electron beam by embodiment of this invention. It is a figure which shows an example of the conventional electron beam exposure apparatus.

  Hereinafter, the electron beam illumination apparatus of the present invention will be described in detail.

(Principle explanation)
First, the principle of electron beam illumination will be described with an example.

  The electron beam emitted from the electron emission surface of the electron source is accelerated and focused by an electron gun to form a crossover (see FIG. 3A described later). In the electron beam exposure apparatus, a certain angle component of the electron beam diverging from the crossover is taken out as an irradiation electron beam for irradiating the irradiation region on the wafer. Since the position of the electron emission surface of the electron source substantially corresponds to the angular component of the beam diverging from the crossover, the irradiation electron beam contributing to the exposure can be associated with the electron emission surface position of the thermal electron source. .

  Therefore, on the electron emission surface, the effective electron emission region contributing to the exposure is set as the irradiation effective region of the electron emission surface, and does not directly contribute to the exposure, and if not limited by an electron gun or an aperture electrode in the column. The area that emits the shielded electron beam was defined as an irradiation limited area. Further, by providing a difference in electron emission efficiency between the irradiation effective region and the irradiation limited region on the electron emission surface, it is possible to increase the irradiation utilization efficiency of the emitted electrons.

  Specifically, a difference is provided in the electron generation efficiency between the irradiation effective region and the irradiation limited region by providing a difference in the work function of the thermionic emission surface.

  The current density of electrons emitted from the thermionic source is derived from the Richardson equation.

[Equation 1]
J = AT ² exp (-W / kT)
J: Current density A: Richardson equation constant T: Thermal cathode absolute temperature W: Cathode surface work function k: Boltzman constant Therefore, on the electron emission surface, the work function of the irradiation effective region with high electron emission efficiency is Wa, If the work function of the irradiation limited region with low efficiency is Wb, the difference between the work functions of both regions is

[Equation 2]
ΔW = Wb−Wa The ratio R of electron emission efficiency in both regions is

[Equation 3]
R = J _b / J _a = exp (−ΔW)
Can be shown.

As an example, a boride compound (in this example, LaB ₆ was used) as a material with high electron emission efficiency in the irradiation effective region of the electron emission surface, and carbon was used as a material with low electron emission efficiency in the radiation limited region. In this case, LaB ₆ (lanthanum boride) is approximately 2.7 eV and carbon is approximately 4.7 eV, so the difference between the work functions of both regions is

[Equation 4]
ΔW = (W _C −W _LaB6 ) = 2.0 eV
The ratio of electron emission efficiency in both regions is

[Equation 5]
R = J _C / J _LaB6 = 0.14
Thus, an effective difference can be made in the electron emission efficiency between the irradiation effective region and the irradiation limited region. Moreover, since carbon is a stable material that does not react with LaB ₆ even at high temperatures, an apparatus with high thermal stability can be provided.

  As yet another example, a case where a refractory metal is used as a thermionic source will be described. In particular, when Th-W represented by a monoatomic layer cathode material is used as the material of the irradiation effective region of the electron emission surface and carbon is used as the surface material of the irradiation limited region, the work function of Th-W is 2.63 eV, and the difference between the work functions of both regions is

[Equation 6]
ΔW = (W _C −W _Th−W ) = 1.4 eV
The ratio of electron emission efficiency in both regions is

[Equation 7]
R = J _C / J _Th-W = 0.07
Thus, it can be seen that it is effective even when a refractory metal material is used as a thermionic source.

Further, even when a high melting point material of Th-W (work function 2.63 eV) and W (work function 4.5 eV) is applied to the irradiation effective region and the irradiation limited region material, ΔW is 1.87 eV, which is effective. Combination. Other combinations of monoatomic cathodes include materials other than Th-W, such as Zr-W (work function 3.14 eV), Th-W ₂ C (work function 2.18 eV), Cs-W (work function). 1.4 eV), Ba-W (work function 1.63 eV), or the like can be used.

  Further, instead of W, a high melting point material of Pt (work function 5.3 eV) or Pd (work function 4.8 eV) can be used.

  That is, it can be seen that in order to make the ratio of electron emission efficiency 0.4 or less, the work function difference ΔW of the electron emission surface should be set larger by 1.0 eV or more.

(Embodiment)
Next, the structure of the electron emission surface according to the present invention adapted to the exposure region of the electron beam exposure method, its characteristics, and an example of an application apparatus will be described with reference to the drawings.

  FIG. 1 is a diagram showing the shape of an electron source having an irradiation effective region and an irradiation limiting region on the electron emission surface in accordance with the electron beam exposure method, and FIGS. 1 (a) to (d) and (h) ) Shows an example in which the irradiation restricted region 1 is formed on a flat electron emission surface. FIGS. 1E to 1G show examples in which the electron emission surface is processed to form concave and curved shapes. The shape of the irradiation effective region 2 excluding the irradiation limited regions 1 having various shapes shown in these drawings is a circular shape in a plane in FIG. 1A, a ring shape in a plane in FIG. 1B, and a straight line in a plane in FIG. (D) is in-plane double line, (e) is in-concave ring shape, (f) is in convex curve ring shape, (g) is in concave curve ring shape, (h) is multi-plane shape in plane It has become.

  Among the electron sources having various electron emission surface shapes as described above, the exposure method shown in FIG. 1A is suitable for an exposure method using a planar beam as an exposure beam. In addition, the electron source having the ring-shaped irradiation effective region 2 shown in FIGS. 1B, 1E, 1F, and 1G is suitable for the exposure method using an arc beam. The electron source in FIG. 1C having the linear irradiation effective area 2 is suitable for an exposure method in which the aspect ratio of the exposure area is different. Furthermore, the electron source shown in FIGS. 1D and 1H in which the irradiation effective areas 2 are discretely arranged is suitable for an exposure method in which a plurality of exposure areas are exposed simultaneously by using multiple electron beams. .

FIG. 2 is a diagram for explaining an example of a manufacturing method for forming an irradiation limiting region on the electron emission surface, and here, shows a case where the irradiation limiting region of the electron source shown in FIG. 1B is formed. A LaB ₆ single crystal (100) having a surface size of 0.5 to 2 mmφ is used as a material for the irradiation effective region of the electron source. The irradiation limited region can be formed by a method similar to a semiconductor process, as shown in FIGS. That is, the resist 4 is applied to the surface of the LaB ₆ single crystal 3, patterned into a desired irradiation limited region shape, and then the low electron emission efficiency material on the LaB ₆ 3 surface and the resist pattern portion 5 from which the resist has been removed. Then, the resist pattern portion 5 is peeled off.

  In particular, in the step shown in FIG. 2D, carbon is coated on the electron emission surface as the formation of the irradiation restricted region. As a method for forming the surface material of the electron source, any of a vacuum vapor deposition method, a sputtering method, an ion plating method, and a CVD (Chemical Vapor Deposition) method may be used. The thickness of the coating film may be very thin because the purpose is to change the work function of the electron emission surface. For example, sufficient thickness can be obtained with a thickness of several nanometers to several tens of nanometers. . Since this thickness does not disturb the distribution of the electrostatic field formed on the electron emission surface of the electron source, the electron trajectory of the emitted electrons is not affected.

As another surface formation method, a work function can be increased by implanting low energy carbon ions of about 60 keV into the surface of LaB ₆ . This method of modifying the electron emission surface by ion implantation is particularly stable because the surface state is stable. Among the surface formation methods, particularly stable and long-life characteristics can be obtained, and the irradiation effective region and the irradiation limited region can be obtained. Since no step is generated at the boundary, the boundary does not affect the electron trajectory of the emitted electrons.

  FIG. 3 is a diagram for explaining electron gun characteristics when the electron source is applied to an exposure method. FIG. 3A schematically shows the trajectory of electrons emitted from the electron emission surface of the electron source. The electron source 7a is a planar electron source, and electrons emitted from the surface are accelerated and focused by the Wehnelt electrode 8 and the ground electrode 9 constituting the electron gun 20 to form a crossover CO and have a certain radiation angle. Radiated from the electron gun 20. Thereafter, an irradiation beam used for electron beam exposure is formed by shielding with an electron gun and an aperture electrode in the column in order to obtain a highly uniform region from the emitted electron beam.

  FIG. 3B shows electron gun characteristics when the electron source shown in FIG. 1A is used as the electron source for surface exposure. As the electron radiation beam used for the surface exposure, a radiation electron beam having a good characteristic of several mrad from the central axis is used in order to increase the uniformity of the electron beam irradiation intensity in the exposure region. The angular distribution characteristics of emitted electrons when there is no conventional irradiation restricted region are indicated by dotted lines in FIG. This is because a radiation half angle with a half intensity distribution has an opening angle of about 50 mrad. On the other hand, in the electron source of the present invention, by providing an irradiation limited region on the electron emission surface, the radiation half angle is set to about 10 mrad as shown by the angle distribution characteristic shown by the solid line in FIG. I can do it.

  FIG. 4 shows an example of an electron beam mask transfer exposure apparatus using the planar electron beam. The exposure apparatus shown in this figure has an electron gun 20, an aperture 10 a for obtaining a highly uniform intensity region from a radiated electron beam, illumination lenses 11 a and 11 b, a rectangular shape on an electron beam mask 15 that is shielded. A projection lens 12a that limits the size of the electron beam that has passed through the electron beam mask 15 by the aperture 10e and projects it onto the wafer 16 on the stage 17 while forming a rectangular aperture 10c that forms the electron beam SB. , 12b and a projection lens system 22. In this exposure apparatus, the electron beam EB incident on the illumination device 21 is restricted at the electron gun 20 by providing an irradiation restriction region on the electron emission surface of the electron source (see FIG. 3B). Accordingly, since the amount of electron beam irradiated to the aperture 10c in the column can be greatly reduced, problems such as temperature increase in the column, charge-up in the column, and melting of the aperture can be solved. I can do it.

  FIG. 5 shows angular distribution characteristics when an electron source 7a in which a ring-shaped irradiation effective region as shown in FIG. In this figure, the solid line indicates the characteristic of the present invention, and the dotted line indicates the conventional characteristic. In the conventional method, a radiation electron beam is formed by cutting out a radiation electron beam in a ring shape from electrons emitted from the entire electron emission surface. On the other hand, in the present invention, by providing an irradiation limited region on the flat crystal surface that forms a ring-shaped irradiation effective region on the electron emission surface of the electron source, a radiated electron beam that does not contribute to exposure inside the ring It can be restricted at the electron emission surface, not the aperture in the column.

  FIG. 6 shows angular distribution characteristics when the concave shape shown in FIG. 1E is used on the electron emission surface of the electron source as a method for further improving the efficiency of the ring-shaped irradiation electron beam. Yes. As the characteristics of the concave electron source, by increasing the electric field around the electron emission surface, the influence of the space charge effect can be reduced and the current density can be increased. The dotted line in FIG. 6 shows the angular distribution characteristic from an electron source that does not have an irradiation restricted region. The solid line represents the angular distribution characteristic when the electron source having the irradiation limited region on the concave electron emission surface shown in FIG. In this way, by forming the ring-shaped irradiation effective region on the outermost surface of the concave electron emission surface, it is possible to improve the utilization efficiency of the emitted electrons from the electron gun.

  FIG. 7 shows an example of an electron beam mask transfer exposure apparatus using the arc-shaped beam. The exposure apparatus shown in this figure includes an electron gun 20, an aperture 10 a for obtaining a highly uniform intensity region from the radiated electron beam, illumination lenses 11 a and 11 b, and a circular shield on the electron beam mask 15. An illumination device 21 configured by an arc-shaped aperture 10d that forms an arc-shaped electron beam CB, and a projection lens 12a that limits the size of the electron beam that has passed through the electron beam mask 15 by the aperture 10e and projects it onto the wafer 16 on the stage 17. , 12b and a projection lens system 22. In this apparatus, the arc-shaped beam CB on the mask surface formed by the illumination device 21 is configured such that an image of the arc-shaped aperture 10d is formed on the electron beam mask surface. Since the projection lens system 22 can significantly reduce the curvature of field by using an arc-shaped beam, the width of the exposure area (the length of the arc beam) when the planar electron beam shown in FIG. 4 is used. Can be increased by 10 times or more, and as a result, high-speed electron beam writing can be performed with a large current irradiation beam. In this method, the amount of the electron beam incident on the illumination lens can be significantly reduced by using the ring-shaped beam shown in FIGS. 5 and 6, so that the amount of the electron beam applied to the arc-shaped aperture 10d in the column can be reduced. It can be greatly reduced. Accordingly, it is possible to solve problems such as temperature rise in the column due to electron beam irradiation, charge up in the column, and melting of the aperture.

  Note that the present invention is not limited to the mask transfer method, but also in a multi-beam exposure method in which a plurality of exposure areas are simultaneously exposed using a plurality of beam bundles, (d), FIG. As shown in (h), it is effective for the same reason to discretely provide irradiation effective regions on the electron emission surface of the electron source.

  As described above, according to the present invention according to the embodiment, in a high-speed electron beam exposure apparatus having a wide exposure area, the use efficiency of a radiated electron beam generated from an electron source is excellent, and the amount of shielding beam is reduced. The charge-up inside is reduced and the beam position accuracy is improved. Furthermore, the temperature rise due to the shielding beam is reduced, the thermal stability of the electron gun and the column is improved, and the problem of melting of the shielding electrode is solved. From this, a large irradiation current can be input to the exposure region, so that an improvement in throughput can be expected. Further, since the power load of the electron generator can be reduced, the device cost can be reduced.

1 irradiation restricted area 2 illuminated effective region 3 LaB ₆ single crystal 4 resist 5 resist pattern portion 6 low electron emission efficiency material 7a electron source 8 Wehnelt electrode 9 ground electrode 10a, 10b, 10e aperture 10c rectangular aperture 10d arcuate aperture 11a first Illumination lens 11b Second illumination lens 12a First projection lens 12b Second projection lens 15 Electron beam mask 16 Wafer 17 Stage EB Electron beam SB Rectangular beam CB on mask surface Arc beam on mask surface

Claims (3)

An electron beam exposure apparatus that simultaneously exposes a plurality of exposure areas with a plurality of electron beams,
An electron gun that includes a thermionic source and an electrode that forms a crossover of electrons emitted from the thermionic source, and emits an electron beam from the crossover ;
An aperture that blocks a part of the electron beam emitted from the electron gun and forms an irradiation electron beam that irradiates each of the exposure regions; and
Electron emission surface of the thermionic source comprises a plurality of effective irradiation area, an irradiation restricted region disposed between the effective irradiation area of the plurality of, effective irradiation area of said plurality of, from the irradiation restricted area, High electron emission efficiency
The plurality of irradiation effective regions include the irradiation electrons so that a part of each of the plurality of electron beams emitted from the plurality of irradiation effective regions is shielded by the apertures and the irradiation electron beams are shaped by the apertures. An electron beam exposure apparatus, wherein the electron beam exposure apparatus is arranged in association with each of the exposure areas irradiated with a beam. The electron beam exposure apparatus according to claim 1, wherein each of the plurality of irradiation effective regions has a linear shape. The electron beam exposure apparatus according to claim 1, wherein each of the plurality of irradiation effective areas has a dot shape.

Images