Patent Application
20090057571
1. Field of the Invention
The present invention relates to a charged-particle beam lithography apparatus and a device manufacturing method.
2. Description of the Related Art
An electron beam lithography apparatus as a type of charged-particle beam lithography apparatuses has conventionally been developed with an aim at increasing the throughput. An improvement in throughput requires increasing the exposure beam current, which faces a problem attributed to the Coulomb effect. The Coulomb effect has the demerit of blurring a convergent electron beam due to the repulsive force between electrons, resulting in degradation in resolution. For this reason, the resolution and the throughput have a trade-off relationship.
To increase the exposure beam current while suppressing aberration due to the Coulomb effect to a considerable degree, a method of decreasing the average density of the exposure beam current to some extent is available. This method reduces the Coulomb effect by decreasing the current density by irradiating an exposure region (subfield) as relatively large as about several hundred micrometers square, thus maintaining a given throughput.
Another method sets a relatively large convergent angle of an electron beam on the sample surface. This method applies a decelerating electric field between the projection lens and the sample. It is expected to reduce the aberration of the projection lens, and to suppress a decrease in resist sensitivity and heat generation and deterioration of the sample surface by irradiating the sample surface with a charged-particle beam at low speed.
Japanese Patent Laid-Open No. 2000-232052 discloses a scheme which reduces aberration by a decelerating electric field. The scheme disclosed in Japanese Patent Laid-Open No. 2000-232052 applies decelerating electric fields between the transfer mask and the projection optical system, and between the projection optical system and the wafer in an electron beam exposure apparatus.
Although the method of decreasing the average density of the exposure beam current is applied to an electron beam exposure apparatus, it requires a transfer mask, which entails an additional cost.
In the method of setting a relatively large convergent angle of an electron beam, geometrical aberration increases as the exposure area (angle of view) increases. To attain high resolution, the aberration performance of the projection lens must meet a strict demand. Still worse, a disturbance of the decelerating electric field occurs due to factors associated with, for example, the shape of the sample surface and a member disposed on the stage, so parasitic aberration and a positional shift of the charged-particle beam occur. The scheme disclosed in Japanese Patent Laid-Open No. 2000-232052 may cause a disturbance of the decelerating electric field due to factors associated with, for example, the shapes of the wafer surface and its vicinity and a member disposed on the stage, so parasitic aberration occurs, resulting in degradation in resolving performance.
It is an object of the present invention to provide a charged-particle beam lithography apparatus which attains a high throughput while suppressing blurring of a charged-particle beam due to the Coulomb effect.
According to the present invention, there is provided a charged-particle beam lithography apparatus which comprises a projection system which projects a charged-particle beam, and images a pattern on a substrate with the projected charged-particle beam, wherein the projection system comprises a symmetrical magnetic doublet lens configured to generate a magnetic field, and an electro-static lens configured to generate an electric field superimposed on the magnetic field, and the electro-static lens includes an electrode configured to apply, on at least a pupil plane of the symmetrical magnetic doublet lens, a potential to accelerate the charged-particle beam which has entered the symmetrical magnetic doublet lens.
According to the present invention, it is possible to provide a charged-particle beam lithography apparatus which attains a high throughput while suppressing blurring of a charged-particle beam due to the Coulomb effect.
Further features of the present invention will become apparent from the following description of exemplary embodiments with reference to the attached drawings.
A charged-particle beam lithography apparatus according to an embodiment of the present invention will be described below with reference to the accompanying drawings. The lithography apparatus according to the present invention includes, for example, an imaging apparatus and exposure apparatus.
The second cylindrical electrode 20 is disposed between a central position 14 of the upper magnetic lens 12 in the vertical direction and a central position 17 of the lower magnetic lens 15 in the vertical direction in the symmetrical magnetic doublet lens. The strength of a magnetic field formed by the upper magnetic lens 12 and lower magnetic lens 15 is a maximum at the two central positions 14 and 17. The second cylindrical electrode 20 has a length defined such that its upper end is located higher than the lower end of the upper magnetic lens 12, and its lower end is located lower than the upper end of the lower magnetic lens 15. The second cylindrical electrode 20 lies on a pupil plane 18 of the symmetrical magnetic doublet lens and its vicinity. As is obvious from
δ ∝ Lc×I/(V1.5×α) (1)
where Lc is the distance between the object plane and the image plane, I is the beam current of a charged-particle beam, V is the acceleration potential of the charged-particle beam, and α is the convergent half-angle on the image plane.
An electron gun serving as the electron generation source can decrease the blurring δ by highly accelerating an electron beam, but this method has several demerits. Applying a high-accelerated (high-energy) electron beam on a photosensitive substrate lowers the effective sensitivity of the photosensitive material. High acceleration by an electron gun requires a large-size electron optical lens, resulting in increases in the optical path length Lc and the blurring δ in expression (1). A high-accelerated electron scatters over a wider region on the photosensitive substrate, resulting in an increase in proximity effect. On the other hand, when the potential of the second cylindrical electrode 20 is raised as in the present invention, the term of the acceleration potential V in equation (1) rises. Since the blurring δ due to the Coulomb effect then decreases, there is no problem as in the above-described case in which an electron gun highly accelerates an electron beam.
In this embodiment, the projection lens is an optical system formed by a symmetrical magnetic doublet lens. In an optical system of this type, the magnetic field strength and full width at half maximum of the magnetic field distribution of the upper magnetic lens 12 and lower magnetic lens 15 have preset ratios. Since an anisotropic component of optical aberration is canceled, this optical system is suited to a relatively large angle of view.
When an electro-static lens with an electric field superimposed on a magnetic field generated by a symmetrical magnetic doublet lens, it is necessary to set the lengths and disposition of cylindrical electrodes of the electrostatic lens so as not to degrade the aberration characteristic of the symmetrical magnetic doublet lens. The central position of a gap 22 between the first cylindrical electrode 19 and the second cylindrical electrode 20 is matched with that 14 of the gap between the magnetic poles of the upper magnetic lens 12. In addition, the central position of a gap 23 between the second cylindrical electrode 20 and the third cylindrical electrode 21 is matched with that 17 of the gap between the magnetic poles of the lower magnetic lens 15.
The ratio between a distance L1 from the upper end of the second cylindrical electrode 20 to the pupil plane 18 of the symmetrical magnetic doublet lens, and a distance L2 from the lower end of the second cylindrical electrode 20 to the pupil plane 18 of the symmetrical magnetic doublet lens is set to satisfy:
L2/L1=M (2)
M is the magnification of the symmetrical magnetic doublet lens.
When the second cylindrical electrode 20 is disposed to satisfy expression (2), the rotation angles of images of the upper magnetic lens 12 and lower magnetic lens 15 become equal to each other. Since the images do not rotate under this condition, no anisotropic aberration occurs. This prevents degradation in the optical characteristic of the symmetrical magnetic doublet lens.
A device manufacturing method using the above-described charged-particle beam lithography apparatus will be exemplified next.
Devices (e.g., a semiconductor integrated circuit device and liquid crystal display device) are manufactured by a pattern imaging step of imaging a pattern on a substrate using the charged-particle lithography apparatus according to the above-described embodiment, a developing step of developing the substrate on which the pattern is imaged in the pattern imaging step, and other known steps (e.g., etching, resist removal, dicing, bonding, and packaging steps) of processing the substrate developed in the developing step.
While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions.
This application claims the benefit of Japanese Patent Application No. 2007-229454, filed Sep. 4, 2007, which is hereby incorporated by reference herein in its entirety.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2007-229454 | Sep 2007 | JP | national |
