Patent Number: 
Section: description

A representative embodiment of a xe2x80x9cscattering aperturexe2x80x9d according to the invention is shown in FIGS. 1(a)-1(b). Turning first to FIG. 1(b), the scattering aperture 4 comprises a plate 4A made of a CPB-scattering material. The plate 4A defines aperture segments (xe2x80x9cvoidsxe2x80x9d) 4B that, in FIG. 1(b), collectively define essentially a ring-shaped aperture. The plate 4A can be silicon that is several micrometers thick. The aperture segments 4B are produced by micro-machining a silicon wafer using conventional techniques as used in semiconductor manufacturing. Turning now to FIG. 1(a), a charged particle beam 1 is incident on the scattering aperture 4 situated at a crossover plane A. Particles of the beam 1 passing through the void segments 4B become the transmitted hollow beam 2. Particles of the beam 1 that impact the plate 4A are scattered as they pass though the plate 4A and become the xe2x80x9cscattered beamxe2x80x9d 2xe2x80x2. The transmitted hollow beam 2 passes readily through a blocking aperture 5 located downstream of the scattering aperture 4. Most of the scattered beam 2xe2x80x2 is blocked by the blocking aperture 5. Specifically, the scattered beam 2xe2x80x2 is absorbed by the blocking aperture 5. The blocking aperture 5 defines a central void 5a and is situated between the scattering aperture 4 and the reticle 13. The blocking aperture 5 desirably is formed of a material that can withstand high temperatures (at least several hundred degrees C) and is several mm or more thick. The central void 5a has a diameter sufficiently large so as not to impede passage of the transmitted hollow beam 2. As can be seen in FIG. 1(a), some of the scattered beam 2xe2x80x2 xe2x80x9cleaksxe2x80x9d through the void 5a in the blocking aperture 5. However, the number of charged particles of the scattered beam 2xe2x80x2 leaking through is relatively small. Also, because the leaking particles are scattered, they pose no significant problem to pattern transfer. Furthermore, the number of such scattered particles reaching the reticle 13 can be reduced to substantially zero by adding one or more additional particle-absorbing apertures between the annular scattering aperture 4 and the reticle 13. An exemplary embodiment of a CPB microlithography system (e.g., electron-beam system) comprising the scattering aperture 4 and blocking aperture 5, as described above, is shown in FIG. 2. Components in FIG. 2 that are the same as described above have the same respective reference numerals and are not described further. An electron beam 1 is produced by an electron-beam source 6 (e.g., electron gun). The beam 1 passes through illumination lenses 7, 8 between which is a field-limiting aperture 9. A first beam crossover 10 is situated just downstream of the source 6. Downstream of the second illumination lens 8 is a current-limiting aperture 11. After passing through the current-limiting aperture 11, the beam 1 passes through the scattering aperture 4, the blocking aperture 5, and a third illumination lens 12 to the reticle 13. (The components located between the source 6 and the reticle 13 collectively are termed the xe2x80x9cillumination-optical system.xe2x80x9d) Electrons passing through the reticle 13 pass through first and second projection lenses 14, 15, respectively, to the wafer 16. Between the first and second projection lenses 14, 15 is a contrast aperture 17. (The components located between the reticle 13 and the wafer 16 collectively are termed the xe2x80x9cprojection-optical system.xe2x80x9d) The electron beam 1 emitted from the source 6 passes through the illumination lenses 7, 8 to the scattering aperture 4. The field-limiting aperture 9, which restricts the optical field illuminated by the beam 1 and shapes the beam, is situated at a position that is conjugate with the electron-emission surface in the electron source 6, with respect to the lens system consisting of the illumination lenses 7, 8. An image of the first crossover 10 is formed at the scattering aperture 4 by the illumination lenses 7, 8, as shown in FIG. 1(a). In other words, the scattering aperture 4 is disposed at a crossover position A of the illumination-optical system. The current-limiting aperture 11 is disposed upstream of the scattering aperture 4. The current-limiting aperture 11 pre-clips the edges of the electron beam 1 that were spread at the crossover, thereby alleviating the thermal load on the scattering aperture 4. The hollow beam 2 transmitted through the scattering aperture 4 forms an image of the electron-emission surface of the source 6 on the reticle 13 by means of the third illumination lens 12. The third illumination lens 12 achieves uniform illumination of the irradiated region of the reticle 13. The size and profile of the irradiated region is determined by the field-limiting aperture 9, which is disposed at an axial position that is conjugate with the reticle 13, with respect to the lens system consisting of the illumination lenses 8 and 12. As discussed above, most of the scattered electron beam 2xe2x80x2 from the scattering aperture 4 is absorbed by the blocking aperture 5. An image of the irradiated region (e.g., subfield) on the reticle 13 is formed on the wafer 16 by means of the projection lenses 14, 15. The contrast aperture 17 blocks particles of the beam 2 that were scattered by the reticle 13 (which can be a membrane type or a scattering-stencil type). Since the beam 2 is hollow before it irradiates the reticle 13 in this embodiment, Coulomb effects are reduced, thereby reducing image defocusing and distortion on the wafer 36, without having to reduce beam current. Consequently, this embodiment advantageously increases image resolution and pattern-transfer accuracy without decreasing throughput. In actual practice, image focal-point shift is reduced to less than several micrometers and image distortion is maintained at less than several nanometers. As noted above, although not shown in FIG. 2, multiple apertures may be disposed above the reticle 13 (but downstream of the apertures 4, 5) to block passage of particles in the scattered beam 2xe2x80x2 that were not absorbed by the blocking aperture 5. Exemplary alternative embodiments 40, 41 of the scattering aperture 4 are shown in FIGS. 3(a)-3(b), respectively, which are similar to FIGS. 8 and 9, respectively, of the JP Hei 11-297610 reference cited above. In FIG. 3(a), two half-ring-shaped void segments 40B, defined by the plate 40A, collectively define an essentially annular void. In FIG. 3(b), multiple small round void segments 41B, arranged in a bolt circle, collectively define an essentially annular void. Other configurations of void segments are also possible so long as the resulting scattering aperture effectively scatters particles of the beam incident within a central circular area having a first radius and transmits particles of the beam incident within an area outside the central region and having a first radius greater than the radius of the central region but also having a second radius greater than the first radius. The beam-transmitting area is surrounded by a beam-scattering area. Alternatively to a plate with voids, the scattering aperture 4 can be configured as a ring-shaped (or analogous segmented-ring-shaped) opening 42 in a layer 43 of a CPB-scattering material on a thin, relatively CPB-transmissive membrane 45 (see FIGS. 3(c)-3(d)). The charged particle beam passes with little or no scattering through the opening 42 (and supporting CPB-transmissive membrane 45 (arrow 46), but is blocked (highly scattered, arrow 47) by the CPB-scattering material 43. The respective materials and thicknesses of the CPB-scattering material 43 and membrane 45 are similar to materials and thicknesses that would be used in a so-called xe2x80x9cscattering-membranexe2x80x9d reticle as known in the art. Although this alternative configuration exhibits, with respect to the beam passing through the opening 42, greater dispersion of beam energy than exhibited by passage of the beam through actual voids, this alternative configuration (FIGS. 3(c)-3(d)) allows the opening 42 to be a complete ring (donut-shaped profile) as shown. Under some conditions, the beam passing through a scattering aperture 4 with a full-ring opening 42 (rather than a segmented-ring void such as shown in FIG. 1(b), 3(a), or 3(b)) exhibits less aberration. Since particles of the hollow beam 2 that are scattered (by passage through the scattering aperture 4) are absorbed by the downstream blocking aperture 5, neither the scattering aperture 4 nor the blocking aperture 5 reach high temperatures during use. Therefore, the scattering aperture 4 can be formed from a material such as silicon that is micro-machined easily. Also, the blocking aperture 5 can be made with a relatively large thickness. As a result, the problems inherent to the apparatus disclosed in JP Hei 11-297610 are solved while exploiting the advantages of that apparatus. The thermal load on the scattering aperture 4 can be alleviated further by passing the beam through a current-absorbing aperture before the beam enters the scattering aperture 4. Semiconductor devices can be manufactured having high resolution and high transfer accuracy using an apparatus according to the invention. Whereas the invention has been described in connection with a representative and alternative embodiments, it will be apparent that the invention is not limited to those embodiments. On the contrary, the invention encompasses all modifications, alternatives, and equivalents as may be included within the spirit and scope of the invention, as defined by the appended claims.