Patent Number: 
Section: description

An electrostatic multi-lens according to the present invention which has high charged beam position stability and lens focusing characteristics, and can minimize crosstalk between lenses, and its application method will be explained below. (Basic Structure of Lens) FIG. 1 shows the lens electrode structure of a resistor electrode lens 1 as an electrostatic lens according to the present invention. This resistor electrode lens 1 is comprised of a lens electrode substrate 10 formed of two high-resistance electrode substrates 2 and 3, an upper electrode substrate 7, and a lower electrode substrate 8. Each electrode substrate is formed with lens apertures 9 at the positions of beam axes 11 where charged beams pass. On each of the high-resistance electrode substrates 2 and 3, the lens apertures 9 are formed on a substrate made up of an insulator 4, and their inner walls are covered by a high-resistance layer 5. The high-resistance layer 5 is electrically connected to a wiring electrode 6 formed on the substrate of the insulator 4. The high-resistance electrode substrates 2 and 3 are bonded to each other to form the lens electrode substrate 10. The upper and lower electrode substrates 7 and 8 each made up of a low-resistor are respectively bonded to the upper and lower surfaces of the substrate 10. FIG. 4A is a sectional view of one lens of the resistor electrode lens 1 shown in FIG. 1. The electric field intensity distribution in the lens aperture 9 is formed by the potential of the wiring electrode 6 given by a lens control power supply 41, and the potential of the high-resistance layer 5 generated between the upper electrode substrate 7 and the ground potential of the lower electrode substrate 8. As can be seen from FIG. 4A, since the beam axis 11 of a charged beam which passes through the lens is surrounded by the high- and low-resistors, even if a scattered beam strikes the side wall in the lens, the charge is relieved via the high-resistance layer 5, thus preventing charge-up in the lens. Hence, position instability of the charged beam and deteriorated lens focusing characteristics can be prevented. Since the high-resistance layer 5 in each lens aperture of the resistor electrode lens 1 has an effect of shielding the influence of the electric fields of neighboring electrodes, it can prevent the influence of crosstalk of neighboring lens electric fields of the multi-lens. Furthermore, as shown in FIG. 1, the upper and lower electrode substrates 7 and 8, each of which is made up of a low-resistor material, are provided to the upper and lower surfaces of the lens electrode substrate 10 so as to suppress the influence of crosstalk between neighboring lenses due to the electric field distribution which extends from each lens aperture 9 to outside the lens. If T represents the thickness of each of the upper and lower electrode substrates 7 and 8, and D represents the diameter of the lens aperture 9, crosstalk between neighboring lens apertures 9 can be prevented by setting Txe2x89xa70.3D. A feature of the lens shape will be explained below. The structure of the resistor electrode lens 1 has a simple cylindrical shape, and can assure a broad effective area of the lens aperture 9 since it has no complicated shield electrode unlike in the prior art shown in FIG. 7. This means that not only the electric field distribution uniformity in the lens aperture 9 is improved to minimize lens aberrations of the electrostatic lens but also the mechanical required precision of the electrode shape can be relaxed. FIG. 2 shows an example of the resistor electrode lens 1 having a higher lens layout density. In the conventional electrostatic lens, since the lens apertures cannot be formed at nearby positions due to the presence of shield electrodes, lenses are laid out at intersections between lines X1, X2, and X3, and Y1, Y2, and Y3 in FIG. 2. By contrast, since the resistor electrode lens 1 of the present invention has no shield electrode, electrostatic lenses can also be laid out at the intersections between lines X1xe2x80x2 and X2xe2x80x2, and Y1xe2x80x2 and Y2xe2x80x2. This layout forms a face-centered structure, and can improve the layout density to twice or more that using the conventional electrostatic lenses. (Optimization of On-axis Electric Field Distribution) Another feature of the resistor electrode lens 1 lies in that the on-axis electric field distribution can be arbitrarily determined by changing the resistance of the high-resistance layer 5 in each lens aperture 9 along the direction of the beam axis, thus forming an electric field distribution suitable for the focusing characteristics of the electrostatic lens. FIG. 5 shows the surface potential of the high-resistance layer 5 required for obtaining a given focal length when the resistance of the high-resistance layer 5 of the resistor electrode lens shown in FIG. 4A is changed. This example shows the characteristics when the diameter of the lens aperture 9 is 160 xcexcm, the thickness of each of the high-resistance electrode substrates 2 and 3 is 300 xcexcm, the substrate thickness of each of the upper and lower electrode substrates 7 and 8 is 100 xcexcm, and the electrostatic lens forms a deceleration system. Lines a to c in FIG. 5 represent the positions and surface potentials of the high-resistance layer 5 corresponding to three different resistor distributions required for obtaining a focal length=1 m of an electron beam of 50 KeV. Line a represents a case wherein the high-resistance layer 5 has a constant resistance along the beam axis. Lines b and c represent cases wherein the high-resistance layer 5 has two different resistances along the beam axis. Line b represents a case wherein the resistance on the entrance and exit sides of the beam is nearly twice that on the wiring layer side of the lens center, and line c represents the case the resistance on the wiring layer side is nearly xc2xd that on the entrance and exit sides of the beam. The results of the beam focusing characteristics are 0.16 xcexcm in case of line a, 0.14 xcexcm in case of line b, and 0.23 xcexcm in case of line c. In these cases, a lens electric field formed by the resistance distribution of line b exhibits an optimal value. This results from a smooth on-axis potential gradient obtained by increasing the potential gradient on the entrance/exit side of the electrostatic lens, and lens aberrations, especially, spherical aberration can be improved. In this case, the high-resistance layer 5 has two different resistances along the beam axis. However, the layer 5 may have three or more different resistance values, or the resistance may change continuously to obtain the same effect. In general, when the high-resistance layer 5 is formed so that the resistance has a positive differential coefficient, the focusing characteristics of the electrostatic lens can be improved. As another example of adjusting the on-axis electric field distribution, a method of using a larger number of high-resistance electrode substrates and applying voltages that match the lens characteristics to the wiring electrodes of these substrates is available. FIG. 4B shows an example in which four high-resistance electrode substrates 4a to 4d are used compared to the lens shown in FIG. 4A. In this example, by adjusting potentials applied to the wiring electrodes of these substrates by lens control power supplies 41a to 41c, the electric field distribution in the lens aperture 9 can be optimized. (Temperature Control) The resistor electrode lens 1 of the present invention forms an electric field in each lens aperture 9 by applying a voltage across the high-resistance layer 5, and always supplies a constant small current to the high-resistance layer 5 when it is used. Hence, by preventing temperature rise due to heating of the high-resistance layer 5 by cooling and temperature control of the lens, the resistor electrode lens 1 can stably operate. FIG. 3A shows the cooling method of the resistor electrode lens 1, and FIG. 3B is a sectional view taken along line A-Axe2x80x2 of FIG. 3A. The resistor electrode lens 1 comprises a cooling plate 33 that surrounds the lens 1, a cooling rod 34 one end of which is connected to the cooling plate 33, a temperature sensor 35 provided on the cooling plate 33, and a temperature control unit 36 to which the other end of the cooling rod 34 is connected, and can be maintained at a given temperature. Especially, the cooling plate 33 can bring the upper and lower electrode substrates with high heat conductivity into thermal contact with each other to increase temperature uniformity, thus improving cooling efficiency. The lens heating condition is determined by conditions such as the resistance of a high-resistance material used, the lens shape, the lens voltage, and the like. For example, when the high-resistance layer 5 used shown in FIG. 1 has a resistivity of 108 xcexa9cm, if the high-resistance. electrode substrate 2 has a thickness of 500 xcexcm, the lens aperture 9 has a diameter of 100 xcexcm, the high-resistance layer 5 has a film thickness of 0.2 xcexcm, the number of lenses in the multi-lens is 5,000, and the voltage applied to the wiring electrode 6 is 1,000 V, a heat quantity of around 0.6 W is generated in the resistor electrode lens. The lower limit of the resistance corresponds to a maximum heat generation quantity of 100 W of the multi-lens of this example, and a resistivity of around 106 xcexa9cm or higher. The upper limit of the resistance must be a value that can avoid charge-up of the surface of the high-resistance layer 5 due to a scattered beam or the like, and does not influence the lens characteristics of a charged beam that passes through the lens, and a high-resistance material having a resistance of around 109 xcexa9cm or less can be used. (Composition Material) As materials that form the high-resistance electrode substrate 2 in FIG. 1, various ceramics (AiN, SiC, Al2O3, BeO) or glass materials as insulators can be used. The high-resistance layer 5 can be formed as a high-resistance film with high uniformity having a thickness of 20 nm to 1,000 nm by depositing a material containing silicon carbide, nitrogen compound, or the like by sputtering. As another method of forming the high-resistance layer 5, a method using cladglass used as a channel plate material is known. With this material, the layer 5 can be formed by controlling the resistance of the inner wall of the lens aperture 9 corresponding to a channel by heating it in a hydrogen-containing atmosphere to precipitate reduced metal lead. As a material of the wiring electrode 6, a transition metal such as W, Ta, or the like, Si or silicide-based material, or the like can be used. As a material of the upper and lower electrode substrates 7 and 8, a low-resistor material is used, and a metal substrate or an impurity-doped Si substrate may be used. (Applied Apparatus) FIGS. 8 to 10 show some application examples of multi-beam lithography schemes. FIG. 8 shows an example of a multi-beam scheme using one electron source. In this example, an electron beam 88 emitted by a single electron source 81 is collimated by a condenser lens 82, and is then split into a plurality of beams by a multi-aperture and blanker 83. These beams are focused at a predetermined position on a wafer 86 using a multi-lens 84, and a stage 87 and deflector 85 are synchronously scanned, thus attaining direct write. Since the resistor electrode lenses of the present invention can be laid out at a high density per unit area, the multi-lens 84 to which these lenses are applied can generate electron beams with uniform characteristics on the basis of a beam with a relatively narrow radiation angle range emitted by an electron gun. Hence, uniformity of the irradiated beam can be improved, and the beam current density can be increased. FIG. 9 shows an example of a multi-beam lithography scheme using multi electron sources. In this example, electron beams 88 emitted by electron sources 91 pass through a multi-aperture 92 and blanker 93, and are focused by a multi-lens 84 to strike a wafer 86. In this case, direct write is done by synchronizing scan of a stage 87 and the blanker 93. Since the degree of integration of the electron beams 88 in this scheme is determined not by the size of the multi electron sources 91 but by the size of each electrostatic lens, an electron beam lithography apparatus with high degree of beam integration and high productivity can be realized by applying the resistor electrode lens of the present invention to the multi-lens 84. FIG. 10 shows an example of a multi-beam scheme using a correction optical system like that described in Japanese Patent Laid-Open No. 9-245708. In this example, an electron beam 88 emitted by a single electron source 101 is collimated by a condenser lens 102, and is split into a plurality of beams by an aperture and blanker 103. After that, the beams are reduced by a reduction electron optical system 105 via an aberration correction multi-lens 104 that corrects lens aberrations of the reduction lens 105, and strike a wafer 86. With this method, a plurality of intermediate images of the light source are formed in a direction perpendicular to the optical axis of the reduction electron optical system 105, and aberrations produced upon projecting these intermediate images onto the wafer 86 in a reduced scale via the reduction electron optical system 105, especially, field curvature and the like, can be corrected in advance. Hence, the direct write range can be broadened without decreasing the resolution of the electron optical system, and the productivity of the lithography apparatus can be improved. When the present invention is applied to such apparatus, more multi beams are formed within the effective direct write range to further improve the productivity. Wiring of the wiring electrode of the high-resistance electrode lens applied to the multi-lens is formed in correspondence with the purpose of the multi-lens in each multi-beam scheme. For example, in the examples shown in FIGS. 8 and 9, it is preferable to allow independent control of lens power in combination with height correction such as the curvature or the like of the surface of the wafer 86. On the other hand, in the example shown in FIG. 10, it is preferable to have variable lens power at the center of the beam axis in consideration of correction of field curvature. Note that the wiring electrode 6 in FIG. 1 corresponds to a wiring example with variable lens power in a linear direction. As other application examples of the present invention, the present invention is not limited to electron beam applied apparatuses such as an electron beam microscope, electron beam distance measurement apparatus, and the like, but may be applied to charged beam applied apparatuses of an ion beam and the like. In such applications, a size reduction and high processing speed of the apparatus can be achieved. As described above, according to the resistor electrode lens of the present invention, a multi-lens which can prevent charge-up due to a scattered beam in the lens aperture, can improve lens focusing characteristics of the electrostatic lens, can prevent crosstalk due to electric fields of the multi-lens, and has a high degree of integration can be realized. Also, a compact charged beam applied apparatus with high productivity can be manufactured. (Device Manufacturing Method) An embodiment of a device manufacturing method using the aforementioned electron beam lithography apparatus or charged beam applied apparatus will be explained below. FIG. 11 shows the flow in the manufacture of a microdevice (a semiconductor chip such as an IC, LSI, or the like, liquid crystal panel, CCD, thin film magnetic head, micromachine, or the like). In step 1 (circuit design), the circuit design of a semiconductor device is made. In step 2 (generate exposure control data), exposure control data of the exposure apparatus is generated based on the designed circuit pattern. In step 3 (fabricate wafer), a wafer is fabricated using materials such as silicon, and the like. Step 4 (wafer process) is called a pre-process, and an actual circuit is formed by lithography using the exposure apparatus input with the exposure control data and the wafer. The next step 5 (assembly) is called a post-process, in which semiconductor chips are assembled using the wafer obtained in step 4, and includes an assembly process (dicing, bonding), a packaging (encapsulating chips), and the like. In step 6 (inspection), inspections such as operation tests, durability tests, and the like of semiconductor devices assembled in step 5 are run. Semiconductor devices are completed via these processes, and are delivered (step 7). FIG. 12 shows the detailed flow of the wafer process. In step 11 (oxidation), the surface of the wafer is oxidized. In step 12 (CVD), an insulating film is formed on the wafer surface. In step 13 (electrode formation), electrodes are formed by deposition on the wafer. In step 14 (ion implantation), ions are implanted into the wafer. In step 15 (resist process), a photosensitive agent is applied on the wafer. In step 16 (exposure), the circuit pattern is printed on the wafer by exposure using the aforementioned exposure apparatus. In step 17 (development), the exposed wafer is developed. In step 18 (etching), a portion other than the developed resist image is removed by etching. In step 19 (remove resist), the resist film which has become unnecessary after etching is removed. By repeating these steps, multiple circuit patterns are formed on the wafer. Using the manufacturing method of this embodiment, a semiconductor device with a high degree of integration, which is hard to manufacture in the prior art, can be manufactured with low cost. As described above, according to the present invention, charge-up caused by a scattered beam in the lens aperture can be prevented by a simple arrangement, and crosstalk between electrostatic lenses can be suppressed. Hence, a multi-lens type electrostatic lens which assures a stable beam position and lens characteristics, and has a high degree of integration can be provided. By changing the resistance of a high-resistance portion, the electric field distribution in the electrostatic lens can be adjusted, and the aberration characteristics of the electrostatic lens can be improved. Furthermore, since the electrode structure is simple, the manufacturing step can be simplified, and a multi-lens with low mechanical required precision can be manufactured. Also, since a multi-lens can be prepared by laying out electrostatic lenses at high density, an electron beam lithography apparatus and charged beam applied apparatus with high productivity can be realized. Hence, the productivity in the manufacture of devices using these apparatuses can be improved. As many apparently widely different embodiments of the present invention can be made without departing from the spirit and scope thereof, it is to be understood that the invention is not limited to the specific embodiments thereof except as defined in the appended claims.