Patent Number: 
Section: description

The invention is described below in the context of representative embodiments. However, it will be understood that the invention is not limited to those embodiments. Also, the invention is described in the context of using an electron beam as an exemplary charged particle beam. However, it will be understood that the general principles set forth herein are applicable with equal facility to other types of charged particle beams, such as an ion beam. Reference is made first to FIG. 3, depicting certain general aspects of an electron-beam microlithography apparatus used for step-and-repeat projection-transfer of a pattern from a reticle to a suitable substrate (e.g., semiconductor wafer). FIG. 3 especially shows certain details of the xe2x80x9celectron-optical systemxe2x80x9d of the apparatus, including the focusing system and a system for controlling operation of the electron-optical system. An electron gun 1 is situated at the extreme upstream end of the electron-optical system. The electron gun 1 emits an electron beam that propagates downstream of the electron gun generally in the direction of an xe2x80x9coptical axisxe2x80x9d AX (i.e., Z-direction). The electron beam propagating from the electron gun 1 to a reticle 10 is termed an xe2x80x9cillumination beam,xe2x80x9d and the portion of the electron-optical system arranged along the axis AX between the electron gun 1 and the reticle 10 is termed the xe2x80x9cillumination-optical system.xe2x80x9d The illumination-optical system comprises two condenser lenses 2, 3 that converge the illumination beam at a crossover C.O.1 situated at a blanking aperture 7. A xe2x80x9cbeam-shapingxe2x80x9d aperture 4 (generally rectangular in profile) is situated downstream of the second condenser lens 3. The beam-shaping aperture 4 transmits only a portion of the illumination beam sufficient to illuminate a single subfield (exposure unit) of the pattern defined on the reticle 10. For example, in this embodiment, the beam-shaping aperture 4 trims the illumination beam to a square transverse profile with dimensions slightly greater than 1 mm per side to illuminate a (1 mm)-square subfield on the reticle 10. An image of the beam-shaping aperture 4 is formed by an illumination lens 9 on the surface of the reticle 10. A blanking deflector 5 is situated either downstream or upstream of the beam-shaping aperture 4. The blanking deflector 5 deflects the illumination beam as required to be incident on a non-transmissive portion of the blanking aperture 7. Whenever the illumination beam is xe2x80x9cblankedxe2x80x9d in this manner, it does not pass through the blanking aperture 7 and thus is not incident on the reticle 10. A subfield-selection deflector 8 is situated downstream of the blanking aperture 7. The subfield-selection deflector 8 mainly scans the illumination beam left and right in FIG. 3 (i.e., the X-direction) so as to illuminate the subfields on the reticle 10 in a sequential manner. The magnitude of lateral beam deflection imparted by the subfield-selection deflector 8 is within the optical field of the illumination-optical system. Another component of the illumination-optical system is the illumination lens 9 situated downstream of the deflector 8. The illumination lens 9 collimates the illumination beam before the beam is incident on the reticle 10. The illumination lens 9 also forms the image of the beam-shaping aperture 4 on the reticle 10. It will be understood from the foregoing that the optical components of the illumination-optical system guide and shape the illumination beam as the beam propagates from the electron gun 1 to the reticle 10. The reticle 10 is depicted in FIG. 3 as a single subfield located on the optical axis AX. However, it will be understood that an actual reticle contains a plurality (typically many thousands) of subfields extending in the X-Y plane perpendicular to the optical axis AX. The reticle 10 typically defines the entire pattern for a layer of a chip (die) to be formed on a substrate (xe2x80x9cwaferxe2x80x9d) 15. As noted above, the subfield-selection deflector 8 deflects the illumination beam laterally within the optical field of the illumination-optical system. To allow exposure of subfields located outside the optical field, the reticle 10 is mounted to a reticle stage 11 that is movable in the X- and Y-directions. This movement is imparted by respective linear motors denoted generally by the reference numeral 11b.  Situated below the reticle 10 (between the reticle 10 and the substrate 15) are various components of an xe2x80x9cimaging-optical system,xe2x80x9d described below. As particles of the illumination beam are transmitted through an illuminated subfield on the reticle 10, they become a xe2x80x9cpatterned beamxe2x80x9d (also termed an xe2x80x9cimaging beamxe2x80x9d) that passes through the imaging-optical system to the wafer 15. The patterned beam carries an image of the illuminated subfield. The imaging-optical system includes a first (or reticle-side) electromagnetic projection lens 12 and a second (or wafer-side) electromagnetic projection lens 14. As the patterned beam passes through the projection lenses 12, 14, the image carried by the beam is xe2x80x9cdemagnified,xe2x80x9d projected onto, and formed at a predetermined location on the wafer 15. To be imprintable with the image, the upstream-facing surface of the wafer 15 is coated with a suitable resist. As the patterned beam is incident on region of the wafer surface, corresponding to the particular subfield being illuminated, a demagnified latent image of the subfield is formed at the region, thereby completing xe2x80x9ctransferxe2x80x9d of the image of the subfield. By xe2x80x9cdemagnifiedxe2x80x9d is meant that the image as formed on the wafer 15 is smaller (typically by a xe2x80x9cdemagnification ratioxe2x80x9d factor 1/X, wherein X usually is 2 to 10) than the corresponding subfield on the reticle 10. As the patterned beam propagates through the imaging-optical system, a crossover C.O.2 is formed at a point on the axis AX at which the axial distance between the reticle 10 and the wafer 15 is divided according to the demagnification ratio. A xe2x80x9ccontrast aperturexe2x80x9d 18 normally is provided at the crossover C.O.2. The contrast aperture 18 blocks scattered particles of the patterned beam, thereby preventing the scattered particles from propagating to the wafer 15 on which the particles otherwise would expose the resist and cause blur of the images formed on the wafer. The wafer 15 is mounted on an electrostatic wafer chuck 16 situated on a wafer stage 17 that is movable in the X- and Y-direction. This movement is imparted by respective linear motors denoted generally by the reference numeral 17b. During exposure, the reticle stage 11 and wafer stage 17 are scanned synchronously in mutually opposite directions to allow a plurality of aligned subfields in a chip pattern to be exposed sequentially. Furthermore, both stages 11, 17 are provided with respective position-measuring systems comprising laser interferometers for measuring the respective stage positions with extremely high accuracy. Hence, the position of the patterned beam as incident on the wafer 15 can be controlled with high accuracy. Energization of each of the lenses 2, 3, 9, 12, 14 and of each of the deflectors 5, 8 is controlled by a controller 21 via individual coil power supplies 2a, 3a, 9a, 12a, 14a, and 5a, 8a, respectively. Similarly, the linear motors 11b, 17b of the reticle stage 11 and wafer stage 17, respectively, are controlled by the controller 21 via respective stage drivers 11a, 17a. Further similarly, the wafer chuck 16 is operated in a controllable manner by the controller 21 via a chuck driver 16a. Hence, by accurate stage positioning and operation of the illumination- and imaging-optical systems, the demagnified images of the reticle subfields are formed and xe2x80x9cstitched togetherxe2x80x9d accurately on the wafer 15, thereby achieving transfer of the entire chip pattern onto the wafer 15. As well understood in the art, the electron gun 1, illumination-optical system, imaging-optical system, the reticle stage 11 and the wafer stage 17 are situated inside a vacuum chamber (not shown) that is evacuated by a vacuum pump (not shown). The vacuum chamber and electron-optical components enclosed therein is referred to as the xe2x80x9ccolumn.xe2x80x9d Details of the wafer-side electromagnetic projection lens 14 and the reticle-side electromagnetic projection lens 12 are shown in FIGS. 1 and 2, respectively. FIG. 1 is an enlarged elevational section of the lower right portion of the wafer-side projection lens 14 and its vicinity. The wafer-side projection lens 14 comprises a magnetic pole 19 that is rotationally symmetrical about the axis 27 and has a xe2x80x9cCxe2x80x9d radial section opening toward the axis 27. Conductive windings 20 are configured as a coil situated inside the magnetic pole 19. The magnetic pole 19 is made of a ferromagnetic material such as Permalloy or soft iron. The coil windings 20 are energized with an electrical current to cause the magnetic pole 19 to produce a magnetic field. The magnetic pole 19 also serves as a shield that blocks inward incursion of external magnetic fields. Along the inside diameter of the magnetic pole 19 is a ferrite stack 22 comprising alternating rings of an insulator material 22a and a ferrite material 22b stacked vertically in the figure (i.e., in the direction of the optical axis 27). The ferrite stack 22 is a magnetic shield that blocks outward escape of the deflection magnetic fields produced by deflection coils 23-25 (described later). Situated radially inward of the ferrite stack 22 are the deflection coils 23-25, which function to correct aberrations and the like of the wafer-side projection lens 14. The deflection coils 23-25 are stacked in the vertical (axial) direction in the figure. The respective downstream-facing surfaces of the wafer-side projection lens 14, of the ferrite stack 22, and of the deflection coil 25 are all xe2x80x9ccoveredxe2x80x9d by a rotationally symmetrical xe2x80x9clowerxe2x80x9d first vacuum wall 26. The lower first vacuum wall 26 desirably is made of an insulator material such as ceramic or plastic. A rotationally symmetrical xe2x80x9clowerxe2x80x9d second vacuum wall 28 extends in an upstream direction from and is attached to the xe2x80x9cupperxe2x80x9d surface of the peripheral edge of the lower first vacuum wall 26. The outside of the wafer-side projection lens 14 substantially is xe2x80x9ccoveredxe2x80x9d by the lower second vacuum wall 28, which desirably is made of soft iron or a material such as Permalloy or Permendur. The downstream end of the lower second vacuum wall 28 extends radially toward the axis 27 and defines a gland (groove) 28aconfigured to hold an elastomeric O-ring 29 or analogous sealing member. The O-ring 29 forms a circumferential seal where the lower first vacuum wall 26 contacts the lower second vacuum wall 28. A liner tube 30 extends in the optical-axis direction (vertical direction in the figure) and is attached circumferentially to the lower first vacuum wall 26 at an inside edge 26b of the lower first vacuum wall 26. The inside edge 26b defines a ring-shaped gland (groove) 26a configured to hold an elastomeric O-ring 31 or analogous sealing member. Thus, the O-ring 31 forms a circumferential seal between the inside edge 26b of the lower first vacuum wall 26 and the downstream end of the liner tube 30. A wafer Z-position sensor (not shown, but known in the art) is disposed to direct a light beam (and receive a reflected light beam) at a shallow angle (grazing-incidence angle) upward from the surface of the wafer 15. The incident and reflected light beams propagate within defined respective zones 32. The reflected beam is detected and processed in a manner yielding information concerning the axial height position of the wafer 15. As a result of the configuration described above, the space located radially inward from the wafer-side projection lens 14 is shielded magnetically by the magnetic pole 19 from magnetic fields generated by electrical current flowing in conductors located outside the column, by movements of conductive bodies within or outside the column, and by movements of the linear motor 17b actuating the wafer stage 17. These various magnetic fields are termed simply herein xe2x80x9cstray magnetic fields.xe2x80x9d The area situated in a gap between the downstream-facing surface of the wafer-side projection lens 14 and the wafer 15 is affected easily by stray magnetic fields (generated by, e.g., the linear motor 17b) because this area is outside the effective electromagnetic lens-effect range of the wafer-side projection lens 14. If the patterned beam propagating through this area were to be affected adversely by a stray magnetic field, then the irradiation position of the patterned beam on the upstream-facing (sensitive) surface of the wafer 15 would be affected correspondingly, leading to undesired variations in exposure position on the wafer surface. The effects of stray magnetic fields can be suppressed by narrowing this gap, but some gap must be present to provide the zone 32 in which the Z-sensor light beam can propagate without obstruction. The magnitude of variation in position of the patterned beam on the sensitive surface of the wafer 15 can be expressed as a product of the magnitude of the stray magnetic field and the axial distance from the sensitive surface of the wafer 15 to the location of the stray magnetic field. I.e., the magnitude of variation in beam position is proportional to this axial distance. Hence, if a strong stray magnetic field were present directly on the sensitive surface of the wafer 15, then the axial distance would be zero and no beam-position variation would be exhibited. But, the effect of a stray magnetic field is significant upstream from the sensitive surface. Therefore, it is important to shield against stray magnetic fields in the region from the xe2x80x9clowerxe2x80x9d (downstream-facing) surface of the wafer-side projection lens 14 to near the sensitive surface of the wafer 15. In view of the above, and according to this embodiment, a first magnetic shield 33 is attached to the xe2x80x9clowerxe2x80x9d (downstream-facing) surface of the lower first vacuum wall 26. As discussed above, the magnitude of variation of beam position caused by a stray magnetic field is proportional to the axial distance from the sensitive surface of the wafer 15 to the location where the stray magnetic field is generated. Therefore, a shield against the stray magnetic field must function effectively from the location of the shield upstream wafer 15 to a location adjacent the sensitive surface of the wafer 15, without obstructing the zone 32 for the light beam for the Z-position sensor. Hence, in this embodiment, the first magnetic shield 33 is disposed so that a xe2x80x9clowerxe2x80x9d surface 33e of the first magnetic shield 33 is adjacent as close as possible to the zone 32 without obstructing the zone 32. For example, the first magnetic shield 33 is close to the zone 32 at two places in a radial direction, while maintaining a slight clearance between the first magnetic shield 33 and the zone 32. In this embodiment, the first magnetic shield 33 is a three-layer clad structure in which a copper layer 33h is sandwiched between two ferromagnetic (e.g., Supermalloy) layers 33f, 33g that are each 0.5 xcexcm thick. Structuring the first magnetic shield 33 in this way as a multilayer structure that includes at least two ferromagnetic body layers 33f, 33g having a nonmagnetic body layer 33h therebetween is equivalent to using a thick ferromagnetic body, and provides a strong shielding effect. In this embodiment, the first magnetic shield 33 is rotationally symmetrical about the optical axis 27. In this regard, by way of example, the first magnetic shield 33 in this embodiment includes an upturned-lip portion 33a (having an L-shaped elevational section) and a shallow xe2x80x9cconicalxe2x80x9d part 33b connected to the L-shaped part 33a. The shallow conical part 33b actually has a 3-dimensional profile of a truncated cone, and has an xe2x80x9cinnerxe2x80x9d (or xe2x80x9cfirst axis-facingxe2x80x9d as referred to in the claims) surface 33c that is conical. By adjusting the magnetic-field parameters of the wafer-side projection lens 14 to integrate the magnetic field produced by the lens with the magnetic field produced by the first magnetic shield 33, aberrations are canceled that otherwise would occur if the first magnetic shield 33 were not axially symmetrical about the optical axis 27. Furthermore, third-order and fifth-order aberrations, for example, that ordinarily would not be cancelled even with the inner surface 33c of the first magnetic shield 33 being conical nevertheless can be cancelled by suitably adjusting the energization parameters of the wafer-side projection lens 14. Energization parameters include respective electrical energizations of the deflection coils 23-25. A xe2x80x9cshielding ratioxe2x80x9d S (a measure of shield xe2x80x9cstrengthxe2x80x9d) of a cylindrical magnetic shield, made of a ferromagnetic material, against a stray magnetic field is defined by the following Equation (1): S=xcexct/2Rxe2x80x83xe2x80x83(1) wherein t is the thickness of the magnetic shield, R is the inside diameter of the magnetic shield, and xcexc is the permeability of the magnetic shield. Equation (1) indicates that, for a cylindrical magnetic shield, the shielding ratio S can be increased by decreasing the inside diameter R of the magnetic shield or by increasing either the thickness t or the permeability xcexc of the shield. But, as the inside diameter of the magnetic shield is reduced, increased eddy currents are created in the magnetic shield in response to the magnetic fields generated by deflector(s) (e.g., deflector coils 23-25) used to correct electromagnetic lens aberrations, etc. The eddy currents produce corresponding delays in the time constant of the deflector(s). Therefore, in this embodiment, the inside diameter (measured at the edge 33d) of the first magnetic shield 33 is slightly greater than the inside diameter of the ferrite stack 22. With such a configuration, the first magnetic shield 33 efficiently shields against stray magnetic fields without causing a delay in the time constant of the deflection coils 23-25. The configuration of the first magnetic shield 33 described above also allows stray magnetic fields created between the wafer-side projection lens 14 and the wafer 15 to flow smoothly from the first magnetic shield 33 to the lower second vacuum wall 28. This effect provides further shielding against stray magnetic fields. As shown in FIG. 3, the reticle-side projection lens 12 is disposed upstream of the wafer-side projection lens 14. FIG. 2 is an enlarged elevational section of the xe2x80x9cupperxe2x80x9d right portion of the reticle-side electromagnetic projection lens 12 and its vicinity. The reticle-side projection lens 12 comprises a magnetic pole 6 that is rotationally symmetrical about the axis 27 and has a xe2x80x9cCxe2x80x9d radial section opening toward the axis 27. The magnetic pole 6 is made of a ferromagnetic material such as Permalloy or soft iron. Conductive windings 13 are configured as a coil situated inside the magnetic pole 6. The magnetic pole 6 also serves as a magnetic shield that blocks inward incursion of external magnetic fields toward the axis. Inward of the reticle-side projection lens 12 is situated a first ferrite stack 34 made of alternating rings of an insulator material 34a and of a ferrite material 34b. The rings are stacked in the xe2x80x9cverticalxe2x80x9d (axial) direction. The first ferrite stack 34 functions as a shield that blocks the deflection magnetic field produced by a first deflector coil 35 (described later) from leaking outward. The first deflector coil 35 is situated radially inwardly of the first ferrite stack 34 and serves to correct aberrations, etc., in the reticle-side projection lens 12. A second ferrite stack 36 is disposed upstream of the reticle-side projection lens 12, and comprises alternating rings made of an insulator material 36a and rings made of a ferrite material 36b stacked in the xe2x80x9cverticalxe2x80x9d (axial) direction. Inward of the second ferrite stack 36 is a second deflector coil 37 that also serves to correct aberrations, etc., in the reticle-side projection lens 12. The upstream-facing surface of the second ferrite stack 36 and of the second deflection coil 37 are xe2x80x9ccoveredxe2x80x9d by an xe2x80x9cupperxe2x80x9d first vacuum wall 38 made of a material that is non-magnetic and non-metallic. A rotationally symmetrical xe2x80x9cupperxe2x80x9d second vacuum wall 39, extending xe2x80x9cdownwardxe2x80x9d in the figure (i.e., in the axial direction), is attached at the peripheral lower edge 38c of the upper first vacuum wall 38. Thus, the upper second vacuum wall 39 effectively extends over and xe2x80x9ccoversxe2x80x9d the outside diameter of the reticle-side projection lens 12. The upper second vacuum wall 39 is made of a ferromagnetic material. The upstream-facing edge of the upper second vacuum wall 39 defines a ring-shaped gland (groove) 39a extending downward in the figure. The gland 39a is configured to receive an elastomeric O-ring 40 or analogous sealing member. The O-ring 40 forms a seal at the area of contact of the peripheral lower edge 38c of the upper first vacuum wall 38 with the upper second vacuum wall 39. An upstream end of the tube-shaped liner tube 30 (that extends cylindrically in the optical-axis direction, or vertical direction in the figure) is attached circumferentially to the upper first vacuum wall 38 at an inner edge 38b of the upper first vacuum wall 38. Thus, the upstream end of the liner tube 30 is attached to the upper first vacuum wall 38 of the reticle-side projection lens 12, and the downstream end of the liner tube 30 is attached to the lower first vacuum wall 26 of the wafer-side projection lens 14. On the upstream end of the liner tube 30, the inner edge 38b of the upper first vacuum wall 38 defines a ring-shaped gland (groove) 38a in which is placed an elastomeric O-ring 41 or analogous sealing member. The O-ring 41 forms a seal between the inner edge 38b of the upper first vacuum wall 38 and the outer diameter of the upstream end of the liner tube 30. The liner tube 30 desirably is configured as a cylinder having an axis that is coincident with the optical axis 27. Midway in an axial direction from the projection lens 12 to the projection lens 14, the liner tube defines a circular ledge 30a where the inside diameter of the liner tube 30 abruptly narrows. The ledge 30a supports the contrast aperture 18. A reticle Z-position sensor (not shown, but known in the art) is disposed to direct a light beam (and receive a reflected light beam) at a shallow angle (grazing-incidence angle) downward (in the figure) from the surface of the reticle 10. The incident and reflected light beams propagate within a defined zone 42. The reflected beam is detected and processed in a manner yielding information concerning the axial height position of the reticle 10. Hence, the reticle-side Z-position sensor is a so-called xe2x80x9cgrazing-incidencexe2x80x9d-type sensor. The space situated radially inwardly from the reticle-side projection lens 12 is blocked magnetically by the magnetic pole 6 against external stray magnetic fields. Notwithstanding this blocking, the area between the reticle 10 and the upstream-facing surface of the reticle-side projection lens 12 is affected easily by stray magnetic fields (such as from the linear motors 11b of the reticle stage 11) because this area is outside the effective electromagnetic lens-effect range of the reticle-side projection lens 12. If the patterned beam were to be affected by a stray magnetic field, then the beam position on the sensitive surface of the wafer 15 would exhibit unwanted variation. Effects of stray magnetic fields can be suppressed by narrowing the gap between the reticle and the projection lens 12. (However, this approach has limitations because the gap still must allow for the zone 42 used by the light beam of the Z-position sensor.) The magnitude of variation of the beam position is a function of the product of the field strength of the stray magnetic field and the axial distance from the downstream-facing surface of the reticle 10 to the location where the stray magnetic field is created. That is, the magnitude of the variation in beam position is proportional to that distance. Similar to the wafer-side projection lens 14, it is desirable to block incursion of stray magnetic fields from a region extending from the downstream-facing surface of the reticle 10 to the upstream-facing surface of the reticle-side projection lens 12. To such end, the FIG. 2 embodiment includes a second magnetic shield 43 fastened to the upper second vacuum wall 39. The variation of beam position also is proportional to the axial distance from the downstream-facing surface of the reticle 10 to the location where a stray magnetic field is created. Hence, shielding against stray magnetic fields is desirable in this region without interfering with the zone 42 in which the beam of the Z-position sensor propagates. To such end, in this embodiment, the second magnetic shield 43 is disposed so that its upstream-facing surface is adjacent the zone 42 without actually being in the zone. I.e., the upstream-facing surface of the second magnetic shield 43 and the zone 42 are immediately adjacent to each other with a slight clearance therebetween. Similar to the first magnetic shield 33, the second magnetic shield 43 desirably has a multilayer structure (not shown) that includes at least two layers of a ferromagnetic material with a layer of a non magnetic material sandwiched between them. Such a shield 43 works at least as well as using a thicker shield made only of a ferromagnetic shield material. In this embodiment, the second magnetic shield 43 is rotationally symmetrical about the optical axis 27. More specifically, the second magnetic shield 43 comprises a cylindrical portion 43a and a conical portion 43b connected to the cylindrical portion 43a. The conical portion 43b actually is configured as a truncated cone. Hence, the xe2x80x9cinnerxe2x80x9d (or xe2x80x9csecond axis-facingxe2x80x9d as referred to in the claims) surface 43c of the second magnetic shield 43 (i.e., the surface inclined toward the optical axis 27) has a conical shape. By adjusting the parameters of the magnetic field generated by the projection lens 12 to integrate the lens field with the magnetic shield, it is possible to cancel aberrations that otherwise would occur if the magnetic shield were not axially symmetrical at least about the optical axis 27. Third-order and fifth-order aberrations that cannot be cancelled even with the inner surface 43c of the second magnetic shield 43 having a conical shape can be cancelled by adjusting the energization parameters of the reticle-side projection lens 12 (e.g., the energization parameters of the second deflection coil 37), including the second magnetic shield 43. Also, as discussed above regarding the first magnetic shield 33, in this embodiment the inside diameter (at the inner edge 43e of the second magnetic shield 43) is slightly greater than the inside diameter of the second ferrite stack 36. With such a configuration, the second magnetic shield 43 efficiently shields against stray magnetic fields (e.g., from the linear motors 11b of the reticle stage 11) without causing any delay in the time constant of the second deflection coil 37. By configuring and placing the second magnetic shield 43 as described above, stray magnetic fields created between the reticle 10 and the reticle-side projection lens 12 flow smoothly from the second magnetic shield 43 to the upper first vacuum wall 38, thereby preventing inward incursion of such fields. FIG. 4 is a flowchart of steps in a process for manufacturing a microelectronic device such as a semiconductor chip (e.g., an integrated circuit or LSI device), a display panel (e.g., liquid-crystal panel), a charge-coupled device (CCD), a thin-film magnetic head, or a micro-machine, for example. In step S1, the circuit for the device is designed. In step S2, a reticle for a layer of the circuit is fabricated. During this step, local resizing of pattern elements can be performed to correct for, e.g., proximity effects and space-charge effects. In step S3, a wafer (or other suitable substrate) is fabricated from a material such as silicon. Steps S4-S13 are directed to wafer-processing steps, also termed xe2x80x9cpre-processxe2x80x9d steps. In the pre-process steps, the circuit pattern defined on the reticle is transferred onto the wafer by microlithography. More specifically, step S4 is an oxidation step for oxidizing the surface of the wafer. Step S5 involves chemical vapor deposition (CVD) for forming an insulating layer on the wafer surface. Step S6 is an electrode-forming step for forming electrodes on the wafer (typically by vapor deposition). Step S7 is an ion-implantation step for implanting ions (e.g., dopant ions) into the wafer. Step S8 involves application of a resist (exposure-sensitive material) to the wafer. After the wafer is coated with the resist, the wafer is mounted to the surface of an electrostatic wafer chuck according to the invention, as described above. Step S9 involves exposing the resist-coated wafer using CPB microlithography so as to imprint the resist with the reticle pattern, as described elsewhere herein. Step S10 involves exposing the resist as required to a reticle pattern using optical microlithography. Either before or after the CPB microlithography step S9, an auxiliary exposure can be performed to correct for proximity effects from backscattered charged particles. Step S11 involves developing the exposed resist on the wafer. Step S12 involves etching the wafer to remove material from areas where developed resist is absent. Step S13 involves resist stripping, in which remaining resist on the wafer is removed after the etching step. By repeating steps S4-S13 as required, circuit patterns as defined by successive reticles are formed superposedly on the wafer. Step S14 is an assembly step (also termed a xe2x80x9cpost-processxe2x80x9d step) in which the wafer that has been passed through steps S4-S13 is formed into semiconductor chips. This step can include, e.g., assembling the devices (dicing and bonding) and packaging (encapsulation of individual chips). Step S15 is a testing and inspection step in which various operability and qualification tests of the device produced in step S14 are conducted. Afterward, in step S16, devices that successfully pass step S15 are finished, packaged, and shipped. Whereas the invention has been described in connection with a representative embodiment, it will be understood that the invention is not limited to that embodiment. On the contrary, the invention is intended to encompass all modifications, alternatives, and equivalents as may be included within the spirit and scope of the invention, as defined in the appended claims.