Patent Application
20080231192
This application is based upon and claims the benefit of priority from prior Japanese Patent Application No. 2007-071089, filed Mar. 19, 2007, the entire contents of which are incorporated herein by reference.
1. Field of the Invention
This invention relates to an electron beam drawing apparatus which draws an LSI pattern on a specimen using an electron beam.
2. Description of the Related Art
In an electron beam drawing apparatus, an electrostatic deflector composed of a plurality of deflecting electrodes is used to deflect an electron beam. The deflector is for deflecting an electron beam by an electric field generated between the deflecting electrodes by applying to the deflecting electrodes a potential generated by a deflection amplifier.
One end of a coaxial cable is connected to the output end of the deflection amplifier. The other end of the coaxial cable is connected to the deflecting electrodes. Normally, since the deflecting electrodes are electrically connected only to the coaxial cable, it is conceivable that capacitive loads are connected to the tip of the coaxial cable in an equivalent circuit. Therefore, the signal input from the deflection amplifier to the deflecting electrode is almost totally reflected by the deflecting electrode and returns to the deflection amplifier with a specific time delay corresponding to the length of the coaxial cable, and again reflected by the deflection amplifier, which causes so-called ringing phenomenon. This phenomenon makes it difficult for the deflection amplifier to operate at high speed.
To overcome this problem, a method of connecting a coaxial cable connected to a terminating resistance to the deflecting electrodes apart from the coaxial cable connected to the deflection amplifier in order to suppress the reflection of the signal at the deflecting electrodes to achieve a high-speed operation has been proposed (e.g., JP-A H11-273603 (KOKAI)). Moreover, a method of connecting the coaxial cable connected to the deflection amplifier to the coaxial cable connected to a terminating resistance and then coupling the central conductor of the coaxial cable with the deflecting electrodes at the connections has been proposed (e.g., JP-A H11-176719 (KOKAI)). However, either method has the following problem: two coaxial cables have to be connected to one deflecting electrode, which makes the configuration complex.
According to an aspect of the invention, there is provided an electron beam drawing apparatus which forms a pattern by selectively applying an electron beam emitted from an electron source to a specimen, the electron beam drawing apparatus comprising: an electrostatic deflector which deflects the electron beam by an electric field and which includes an external cylinder provided more downstream than the electron source and kept at the ground potential, and a plurality of deflecting electrodes which are provided in the external cylinder and to each of which a deflecting voltage is applied; a coaxial cable unit including a plurality of coaxial cables which are connected to the deflecting electrodes, respectively, and each of which includes a central conductor and a tubular outer conductor surrounding the central conductor coaxially, one end of the central conductor passing through the external cylinder and being connected to corresponding one of the deflecting electrodes and one end of the outer conductor being connected to the external cylinder; and a resistive element which is connected between the central conductor and the outer conductor or the external cylinder in the vicinity of a junction between the central conductor and corresponding one of the deflecting electrodes and a resistance of which is set to a value for obtaining impedance matching the coaxial cable.
According to another aspect of the invention, there is provided an electron beam drawing apparatus which forms a pattern by selectively applying an electron beam emitted from an electron source to a specimen, the electron beam drawing apparatus comprising: an electrostatic deflector which deflects the electron beam by an electric field and which includes an external cylinder provided more downstream than the electron source and kept at the ground potential and a plurality of deflecting electrodes which are provided in the external cylinder and to each of which a deflecting voltage is applied; a coaxial cable unit having a plurality of coaxial cables which are connected to the deflecting electrodes, respectively, and each of which includes a central conductor and a tubular outer conductor surrounding the central conductor coaxially, one end of the central conductor passing through the external cylinder and being connected to corresponding one of the deflecting electrodes and one end of the outer conductor being connected to the external cylinder; and a resistive element which is connected between each of the deflecting electrodes and the outer conductor or the external cylinder in the vicinity of a junction between the central conductor and the corresponding one of the deflecting electrodes and which is formed into a tube whose diameter is almost the same as that of the outer conductor and a resistance of which is set to a value for obtaining impedance matching the coaxial cables.
According to still another aspect of the invention, there is provided an electron beam drawing apparatus which forms a pattern by selectively applying an electron beam emitted from an electron source to a specimen, the electron beam drawing apparatus comprising: an electrostatic deflector which deflects the electron beam by an electric field and which includes an external cylinder provided coaxially with respect to an axis of the electron beam and more downstream than the electron source and kept at the ground potential and a plurality of deflecting electrodes which are provided in the external cylinder so as to be symmetrical with respect to the axis of the electron beam and to each of which a deflecting voltage is applied; a coaxial cable unit having a plurality of coaxial cables which are connected to the deflecting electrodes, respectively, and each of which includes a central conductor and a tubular outer conductor surrounding the central conductor coaxially, one end of the central conductor passing through the external cylinder and being connected to corresponding one of the deflecting electrodes and the outer surface of one end of the outer conductor being connected to the external cylinder; and a resistive element which is inserted between the inner surface of one end of the outer conductor and the central conductor and which has its resistance set to almost the same as that of the characteristic impedance of the coaxial cable unit and which has the central conductor passing through its central part and has its outer surface formed into a ring making contact with the outer conductor.
Hereinafter, referring to the accompanying drawings, embodiments of the invention will be explained in detail.
As shown in
An electron beam emitted from the electron gun 11 at an accelerating voltage of 50 kV is condensed by condenser lenses 12a, 12b which are so excited that a crossover image coincides with a deflection fixed point of a shaping deflector 13b and is applied to a first shaping aperture 14a. A rectangular hole is made in the first shaping aperture 14a. A first forming beam passed through the aperture 14a has a rectangular cross-sectional shape.
The shaped electron beam shaped by the first shaping aperture 14a is focused by a projection lens 12c so excided that the image of the first shaping aperture 14a is formed on a second shaping aperture 14b and is applied to the second shaping aperture 14b. Here, the irradiated position on the second shaping aperture 14b can be changed by the shaping deflector 13b. In the second aperture 14b, openings of various shapes have been made. A beam is caused to pass through in a desired position of the second shaping aperture 14b, which enables an electron beam of a desired cross-sectional shape to be obtained.
The electron beam passed through the second shaping aperture 14b is focused by a reduction lens 12d and an objective lens 12e and reaches the surface of the specimen 15 placed on the specimen stage 16. At this time, the electron beam is deflected by an objective deflector 13c and reaches the desired position on the specimen 15.
In an external cylinder 21 provided coaxially with the axis of the electron beam, four deflecting electrodes 22 are arranged symmetrically with respect to the beam axis. These deflecting electrodes 22 are secured to the inner surface of the external cylinder 21 by a deflecting electrode fixing member 23 made of insulating material. The external cylinder 21, deflecting electrodes 22, and deflecting electrode fixing member 23 constitute an electrostatic deflector 20.
The external cylinder 21 has only to be basically a cylindrical body provided coaxially with the axis of the electron beam. In the first embodiment, to make the shield more reliable, disk members for closing the openings in the top surface and the bottom surface of the cylindrical body are provided. In the upper and lower disk members, holes to allow the electron beam to pass through are made.
Connected to the electrostatic defector 20 is a coaxial cable 30 which is composed of a central conductor 31 and an outer conductor 32 coaxially surrounding the conductor 31 and which is for supplying a deflecting voltage from a deflection amplifier (not shown). Specifically, a through hole is made in the side face of the external cylinder 21 of the electrostatic deflector 20. One end of the central conductor 31 of the coaxial cable 30 passes through the through hole and is connected to the deflecting electrode 22. The diameter of the through hole in the external cylinder 21 is made almost the same as the outer diameter of the outer conductor 32. One end of the outer conductor 32 is inserted into the hole in the external cylinder 21. One end side of the outer conductor 32 of the coaxial cable 30 is connected to the external cylinder 21 at the through hole part. A space between the central conductor 31 of the coaxial cable 30 and the outer conductor 32 is set as to be empty or is filled with dielectric material.
At the tip portion of the coaxial cable 30, a ring-shaped resistive element 41 is provided between the central conductor 31 and outer conductor 32. Specifically, the ring-shaped resistive element 41 is inserted into the outer conductor 32. The resistive element 41 has its central hole part connected to the central conductor 31 and its outer surface connected to the outer conductor 32. The resistance of the resistive element 41 is designed to be equal to the characteristic impedance of the coaxial cable 30, for example, 50 ohms. In the vicinity of the junction between the external cylinder 21 and the outer conductor 32 of the coaxial cable 30, a cooling pipe 42 is provided so as to surround the external cylinder 21.
Although the coaxial cable 30 using a metal pipe as the outer conductor 31 is preferable, the one using a metal mesh as the outer conductor 31 may be used. Fluorine resin is used as the dielectric material of the coaxial cable 30 and nonmagnetic copper material is used as the central conductor 31. The central conductor 31 which generates less gas and uses no nonmagnetic material is favorable. If the characteristic impedance of the coaxial cable 30 is Z ohms, it is often the case that reflection can be virtually neglected at a reflectivity coefficient of 10% or less. To meet this condition, it is desirable that the difference between the characteristic impedance of the coaxial cable 30 and the resistance of the resistive element 41 should be ±20% or less.
For example, the surface of a low-dielectric insulating material, such as fluorine resin, covered with a conductive film, such as a metal film or carbon film, can be used as the resistive element 41. The resistivity distribution at this time can be so designed that a part closer to the periphery of the resistive element 41 has a larger resistance, localizing the distributed heat source in the peripheral part, which facilitates cooling.
The deflecting electrodes 22 of the electrostatic deflector 20 are virtually isolated from the external cylinder 21 in the places excluding the junction with the central conductor 31 of the coaxial cable 30. Specifically, the deflecting electrode fixing member 23 as a mechanical support part is made of an insulating material or high-resistivity element whose resistance is sufficiently higher than 50 ohms. When this state is considered using an equivalent circuit diagram, it can be approximated by a circuit which includes resistance RL whose resistance is the same as ZC and capacitance Cd for the external cylinder 21 of the deflecting electrode 22 connected in parallel with lines whose characteristic impedance is Zc as shown in
Here, in a region of frequency f where the expression RL<<1/(Cd2πf) holds, Cd can be ignored and the load can be regarded as RL and therefore the signal is not reflected. On the other hand, even in such a high-frequency region as satisfies the expressions L1Cd>>1/(2πf)2 and L1/RL>>1/(2πf), although the load resistance can be regarded as RL, it is not taken into account here because the frequencies in such a region are very high.
For example, if of the sides of one deflecting electrode 22, the dimensions of the part facing the external cylinder 21 connected to the ground are 5 mm×20 mm and the clearance between the part and the external cylinder 21 is 0.2 mm, the capacitance between the deflecting electrode 22 and the external cylinder 21 is about 5 pF. Suppose the capacitance between adjacent deflecting electrodes 22 is designed to be lower than about 5 pF and the capacitance of the deflecting electrode 22 is set to Cd=5 pF. Moreover, if inductance L1=10 pH, this gives 1/(2π(L1Cdf)−0.5)=22.5 GHz and R1/(2πL1)=1.6 GHz. Therefore, the effect of the inductance can be practically ignored. If f=100 MHz, the effect of the inductance can be ignored, giving 1/(Cd2πf)=318 ohms. The amplitude reflectivity is as low as 8%.
For such an approximation to hold, the central conductor 31 connecting the resistive element 41 and the deflecting electrode 22 should be shorter. Making the central conductor longer increases the frequency dependency of the impedance in the high-frequency region, which impairs the high-speed response. The analysis made by the inventor of the invention has shown that, when the rise time of the pulse from the deflection amplifier was set longer than L1/Rd and CdR1, the rise of the voltage applied to the deflecting electrode 22 almost coincided with the rise of the pulse from the deflection amplifier, which made the reflection very small. In the above example, since L1/R=0.1 ps and CdR1=250 ps, the rise time of the deflection amplifier is set to, for example, about 1 ns. In this case, too, the response is determined statically with an accuracy of 1.5×10−5 in about 11 ns.
The resistive element 41 is not necessarily provided between the central conductor 31 and the outer conductor 32. As shown in
Furthermore, as shown in
Furthermore, the leakage of the magnetic field outside the coaxial cable can be reduced by providing a resistive material and a resistivity distribution so as to make the current flow in the resistive element 41 symmetrical with respect to the central conductor 31 as shown in
The place in which the deflecting electrode 22 is fixed is set sufficiently away from the place where the coaxial cable 30 is connected and the junction of the central conductor 31 with the deflecting electrode 22 is bended slightly. By doing this, the influence of the expansion and contraction of the central conductor 31 caused by a temperature change in the resistive element 41 can be absorbed, which enables the mounting accuracy to be maintained. Making the central conductor 31 of bendable material enables the expansion and contraction of the central conductor 31 to be absorbed more efficiently.
As described above, with the first embodiment, one end of the central conductor 31 of the coaxial cable 30 is caused to pass through the external cylinder 21 and is connected to the deflecting electrode 22 of the electrostatic deflector 20, one end of the outer conductor 32 of the coaxial cable 30 is connected to the external cylinder 21, and the resistive element 41 is provided between the central conductor 31 and the outer conductor 32 in the vicinity of the junction of the central conductor 31 with the deflecting electrode 22. With this configuration, the reflection of the signal at the deflecting electrode 22 can be suppressed, which makes it possible to realize a high-speed operation of the electrostatic deflector 20. In this case, the configuration can be simplified-without increasing the number of coaxial cables 30 connected.
Furthermore, as shown in
The second embodiment differs from the first embodiment in the place where the resistive element is inserted. Specifically, in the second embodiment, the resistive element 45 is provided between the deflecting electrode 22 and the outer conductor 32 in the vicinity of the junction of the central conductor 31 with the deflecting electrode 22. The resistive element 45 has a cylindrical body whose diameter is almost the same as that of the outer conductor 32 of the coaxial cable 30. The resistance of the resistive element 45 is designed to be equal to the characteristic impedance of the coaxial cable 30, for example, 50 ohms.
Since the deflecting electrode 22 has the same potential as that of the central conductor 31, even if the resistive element 45 is provided between the deflecting electrode 32 and the outer conductor 32, the equivalent circuit is the same as in the first embodiment. However, since the resistive element 45 is provided in a place farther away from the junction of the central conductor 31 with the deflecting electrode 22, the high-speed response deteriorates. Therefore, the junction of the resistive element 45 with the deflecting electrode 22 should be close to the junction of the central conductor 31.
Furthermore, as shown in
As described above, even if the resistive element 45 is provided between the deflecting electrode 22 and the outer conductor 32 or the external cylinder 21, not between the central conductor 31 and the outer conductor 32, this produces the same effect as that of the first embodiment. Moreover, in the second embodiment, the resistive element 45 may be used as the fixing member for the deflecting electrode 22, which provides the advantage of eliminating the deflecting electrode fixing member 23.
The third embodiment is such that the coaxial cable 30 is configured to be installed on or removed from the electrostatic deflector 20 and the resistive element 41 is secured to the coaxial cable 30.
As shown in
As shown in
Accordingly, in the state of
The fourth embodiment is such that the coaxial cable 30 is configured to be installed on or removed from the electrostatic deflector 20 and the resistive element 41 is secured to the external cylinder 21.
As shown in
As shown in
Accordingly, in the state of
(Modification)
The invention is not limited to the above embodiments. The configuration of the optical system of the electron beam drawing apparatus is not restricted to that of
Furthermore, the shape and material of the resistive element may be changed suitably according to the specification. Moreover, the position in which the resistive element is provided is not restricted to the places shown in the embodiments. The resistive element may be provided in any position in the vicinity of the junction between the central conductor and the deflecting electrode. In addition, the damping resistance may be a part of the electrode in the vicinity of the junction of the central conductor, provided that the damping resistance is in parallel with the resistive element in an equivalent circuit. For example, the junction member 25 may be made of a resistive material in
Additional advantages and modifications will readily occur to those skilled in the art. Therefore, the invention in its broader aspects is not limited to the specific details and representative embodiments shown and described herein. Accordingly, various modifications may be made without departing from the spirit or scope of the general inventive concept as defined by the appended claims and their equivalents.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2007-071089 | Mar 2007 | JP | national |
