Abstract:
A method of calibrating a projection particle beam lithography system, comprises the following steps which is embodied in a system provides a magnification reticle pattern of features and a magnification target pattern. Provide a rotation reticle pattern of features and a rotation target pattern, and a particle beam. Direct the particle beam through the magnification reticle pattern and scan its image over the magnification target pattern. Determine the distance between peaks of target patterns as indicated by particles backscattered from the magnification target pattern. Calculate the deviation from a standard for the distance between peaks of target patterns from the magnification target pattern and calculate the magnification deviation and use the magnification deviation to adjust the particle beam. Direct the particle beam through the rotation reticle pattern and scan its image over the rotation target pattern. Determine the distance between peaks of target patterns as indicated by particles from the rotation target pattern. Calculate the deviation for the distance between peaks of the rotation target pattern and calculate the rotation deviation. Then use the rotation deviation to adjust the rotational orientation of the particle beam.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to particle beam projection systems and more particularly to calibration of such systems. 
     2. Description of Related Art 
     See U.S. Pat. No. 5,763,894 of Enichen et al. for “Calibration Patterns and Techniques for Charged Particle Projection Lithography Systems” and U.S. Pat. No. 5,283,440 Sohda et al. for “Electron-Beam Writing System Used in a Cell Projection Method”. 
     In an EBPS (Electron-Beam Projection System) the size and orientation (rotation) of the projected cell or subfield must be adjusted in order for subfields or cells being formed to butt against the neighboring subfields or cells without gaps or an overlap between subfields or cells. 
     Previous calibration methods described in U.S. Pat. No. 5,763,894, supra, and U.S. Pat. No. 5,283,440, supra, have done this adjustment task by projecting an image formed by the reticle onto a matching target in the wafer plane, and the projected image is scanned over the matching target. The degree of matching is evaluated by measuring the peak signal strength of the backscattered electron signal or by measuring the width of the backscattered electron signal at a given threshold. The lenses that control the magnification and rotation of the subfields are stepped through a range of values and data is collected from the backscattered electron detector. The optimum adjustment is determined by the lens setting that maximizes the backscattered electron signal or minimizes the backscattered electron signal width. 
     The problem with the techniques of U.S. Pat. No. 5,763,894, supra, and U.S. Pat. No. 5,283,440, supra, is that for a single measurement it is impossible to determine the direction in which to make an adjustment. It is necessary to make enough trial adjustments in order to establish a maximum backscattered electron signal or a minimum backscattered electron signal width. A single measurement yields no information on the degree to which the adjustment has approached proximity to an optimum adjustment or in what direction an optimum can be approached. 
     SUMMARY OF THE INVENTION 
     In accordance with this invention, a method of calibrating a projection particle beam lithography system, comprises the following steps. Provide a magnification reticle pattern and a magnification target pattern. Provide a rotation reticle pattern and a rotation target pattern. Produce a particle beam. Direct the particle beam through the magnification reticle pattern and onto the magnification target pattern. The projected reticle pattern image is scanned over the magnification target using a calibrated deflection. Determine the distance between peaks of target patterns as indicated by particles backscattered from the magnification target pattern. Calculate the deviation from the ideal for the distance between peaks of a the backscatter signal and calculate the magnification deviation and use the magnification deviation to adjust the particle beam. Direct the particle beam through the rotation reticle pattern and onto the rotation target pattern. Scan the rotation reticle pattern image over the rotation target using a calibrated deflection. Determine the distance between peaks of the signal from the particles backscattered from the rotation target pattern. Calculate the deviation from the ideal for the distance between peaks of the backscatter signal and calculate the rotation value. Then use the rotation value to adjust the rotational orientation of the particle beam. 
     In accordance with another aspect of this invention, a method of calibrating a projection electron beam lithography system, comprises the following steps. Provide a magnification reticle pattern and a magnification target pattern. Provide a rotation reticle pattern and a rotation target pattern. Produce an electron beam. Demagnify the electron beam. Orient the electron beam. Direct the electron beam through the magnification reticle pattern and onto the magnification target pattern. Scan the image of the magnification reticle pattern over the magnification target elements with a calibrated scan. Determine the distance between peaks of the signal produced by secondary electrons or electrons backscattered from the magnification target pattern. Calculate the deviation from the distance between peaks of an ideal signal and calculate the magnification deviation and use the magnification deviation to adjust the electron beam. Direct the electron beam through the rotation reticle pattern and onto the rotation target pattern. Scan the image of the rotation reticle pattern over the rotation target elements with a calibrated scan. Determine the distance between peaks of the signal produced by secondary electrons or electrons backscattered from the rotation target pattern. Calculate the deviation from the distance between peaks of an ideal signal and calculate the rotation deviation, then use the rotation deviation to adjust the electron beam and using the rotation value to adjust the rotational orientation of the electron beam. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The foregoing and other aspects and advantages of this invention are explained and described below with reference to the accompanying drawings, in which: 
     FIG. 1A shows a calibration target T in accordance with this invention for use on a projection system to calibrate the subfield magnification with a square subfield. FIG. 1B shows a table of the dimensions of the elements of the target of FIG.  1 A. 
     FIG. 2A shows a magnification calibration reticle R with a pattern of openings comprising features matching the pattern of the alignment elements on the magnification target T. FIG. 2B shows a table of the dimensions of the elements of the magnification calibration reticle. 
     FIG. 3 shows the desired signal, i.e. the signal which is expected to be produced when the reticle image is scanned over the target of FIGS. 1A and 2A if the beam is properly adjusted and calibrated. 
     FIG. 4A shows a rotation target T in accordance with this invention for use on a projection system to calibrate the subfield magnification with a square subfield. FIG. 4B shows a table of the dimensions of the elements of the target of FIG.  4 A. 
     FIG. 5A shows a rotation calibration reticle R with a pattern of openings comprising features matching the pattern of the alignment elements on the rotation target T. FIG. 5B shows a table of the dimensions of the elements of the rotation calibration reticle. 
     FIG. 6 shows the desired signal, i.e. the signal which is expected to be produced when the reticle image is scanned over the target T of FIGS. 4A and 5A if the beam is properly adjusted and calibrated. 
     FIG. 7 schematically illustrates a projection electron beam lithography system in accordance with this device. 
     FIG. 8A shows a schematic block diagram of a process for manufacture of a semiconductor chip employing the tool of this invention for manufacture of a semiconductor chips. FIG. 8B shows a flow chart of lithography steps which are dominant steps in the wafer processing steps of FIG.  7 A. 
     FIG. 9A is a flow chart showing the steps leading to adjustment of the magnification in accordance with this invention. 
     FIG. 9B is a flow chart showing the steps leading to adjustment of the rotation in accordance with this invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     In accordance with this invention patterns on a reticle or reticles at the mask plane and patterns on the target or targets at the wafer plane are provided and used to measure the magnification and rotation of the subfield directly thereby speeding up the calibration process. 
     FIG. 1A shows a magnification calibration target T for use on a projection system to calibrate the subfield magnification with a square subfield with a size of 250 μm by 250 μm. The composition of the material of the alignment elements HZ 1 , HZ 2  HZ 3 , and HZ 4  on the magnification calibration target T is a high atomic number metal element such as gold, tantalum, or tungsten which provides strong backscattering of electrons or secondary electrons, which backscattered electrons or secondary electrons are detected easily with the backscatter detectors  50  seen in FIG. 7 which preferably are photodiodes. The alignment, backscattering elements HZ 1 , HZ 2  HZ 3 , and HZ 4  are elongated rectangular members formed on the top surface of the magnification calibration target T. Backscattering elements HZ 1 , HZ 2  HZ 3 , and HZ 4 , which are proximate to and parallel to the periphery of the magnification calibration target T, will produce backscattered electrons or secondary electrons when scanned by the image of a pattern on the magnification reticle. 
     FIG. 1B shows a table of the dimensions of the elements of the magnification calibration target T of FIG.  1 A. Thus, it can be seen that the backscattering elements HZ 1 , HZ 2  HZ 3 , and HZ 4  are 150 μm long and 6 μm wide are formed 16 μm from the periphery of the 250 μm×250 μm square area magnification calibration target T. The backscattering elements HZ 1  and HZ 3  are spaced 206 μm apart, backscattering elements HZ 2  and HZ 4  are also spaced 206 μm apart ,and backscattering elements HZ 1 , HZ 2 , HZ 3 , and HZ 4  are all centered along the sides of the magnification calibration target T. 
     FIG. 2A shows a magnification calibration reticle R with a pattern of imaging features in the form of openings OR 1 , OR 2  OR 3 , and OR 4  matching the pattern of the alignment elements HZ 1 , HZ 2  HZ 3 , and HZ 4  on the magnification calibration target T. The imaging feature openings OR 1 , OR 2  OR 3 , and OR 4  are elongated, rectangular windows proximate to and parallel to the periphery of the reticle R. This reticle can be fabricated using a stencil mask technology where the imaging feature openings OR 1 , OR 2 , OR 3  and OR 4  are openings in the silicon membrane. The imaging feature openings can be substituted for by imaging features implemented with SCALPEL technology (J. A. Liddle et al. “The Scattering with Angular Limitation in Projection Electron-Beam Lithography (SCALPEL) System Jpn J. Appl. Phys. Vol. 4 6663 (1995)) where OR 1 , OR 2 , OR 3  and OR 4  are areas of a thin membrane which produce relatively little scattering of the beam within a region of material which produces a high degree of scattering of the beam on a thin membrane. The pattern should be in the region of low scattering with the background having the high scattering material. SCALPEL is further described in U.S. Pat. No. 5,316,879 of Berger et al and U.S. Pat. No. 5,079,112 of Berger et al. 
     FIG. 2B shows a table of the dimensions of the elements of the magnification reticle R. The dimension in parentheses in the (target) column are the size of the transmitted image in the target plane using a reduction of 4:1 in the projection optics as shown in FIG.  7 . The pattern is designed so that when the image produced by the reticle R is reduced 4:1 by the projection optics and is scanned over the target T, for a scan in the x direction in FIG. 2A, the right-hand bar HZ 3  is scanned first and then the left-hand bar HZ 1  is scanned second producing the two peaks P 1  and P 2  illustrated on curve SA 1  in FIG.  3 . 
     It can be seen that the imaging feature openings OR 1 , OR 2  OR 3 , and OR 4  are 600 μm long and 24 μm wide are formed 32 μm from the periphery of the 1,000 μm×1,000 μm square area magnification calibration target R. The imaging feature openings OR 1  and OR 3  are spaced 888 μm apart. The imaging feature openings OR 2  and OR 4  are also spaced 888 μm apart. The imaging feature openings OR 1 , OR 2  OR 3 , and OR 4  are all centered along the sides of the magnification calibration target T. 
     The scan described above results in a signal SA 1  with the two pulses P 1  and P 2  shown in FIG. 3 are generated by backscattered electrons or secondary electrons in response to the electron beam which can be used in the method described by FIG.  8 A. FIG. 3 shows the desired signal SA 1 , i.e. the signal which is expected to be produced an ideal scan as described above if the beam is properly adjusted and calibrated. The distance D between the peaks of the two pulses P 1  and P 2  can be measured using standard techniques such as multiple clip levels or a moment calculation. The nominal distance between the two pulses P 1  and P 2  is designed to be 16 μm. In cases in which the actual distance between two pulses P 1  and P 2  is the nominal distance of exactly 16 μm, then there is no deviation. Any deviation from the nominal value indicates a magnification deviation. The magnification deviation is given by the deviation from nominal divided by the distance of the centerlines of the openings (for example as shown below 228 μm) on the reticle R scaled by the demagnification factor of the projection optics. 
     The distance D between the peaks for the aspect of the method of this invention as illustrated by FIGS. 1A,  2 A and  3  is the Peak Distance−16 μm. 
     “Magnification Deviation” is defined as follows:                Magnification Deviation     =         Magnification Peak Distance     -     16                 μm         Distance of centerlines of openings               (   1   )                                
     Using the specific values given in the examples of FIGS. 1A,  1 B,  2 A,  2 B and  3  the Magnification Deviation is as follows:                Magnification Deviation     =           Magnification Peak Distance     -     16                 μm       )       228      μm               (   2   )                                
     This result can be used to determine the correction to be applied to correct any error in magnification caused by the magnification deviation. This result yields both the sign and magnitude of the correction required to make the subfield the correct size. If the peak distance is smaller than nominal the subfield is too small. Conversely, if the peak distance is larger than nominal, the subfield is too large. The value of the magnification deviation in the y direction in FIG. 2A is determined by scanning in the y direction as will be well understood by those skilled in the art. 
     Referring to FIG. 4A, a variation of the technique of FIGS. 1,  2  and  3  and FIG. 9A can be used to measure the rotation of the subfield. FIG. 4A shows a rotation calibration target T adapted for determining rotation with a pattern of short backscattering stripes HZ 5 , HZ 6 , HZ 7 , and HZ 8  perpendicular to the adjacent periphery of the target T. The short backscattering stripes HZ 5 , HZ 6 , HZ 7 , and HZ 8  are four sets of short, parallel rectangles formed on the top surface of the target T proximate to and perpendicular to the adjacent periphery of the target T. 
     Referring again to FIG. 4A the elements HZ 6 , HZ 7 , HZ 8  and HZ 5  are spaced along the top right, bottom and left sides respectively of the target T with an alignment obtained simply by rotating the elements in consecutive rotations from the elements HZ 6  in the top row. It can be seen that the backscattering elements HZ 5 , HZ 6 , HZ 7 , and HZ 8  which are 25 μm long and 6 μm wide, are formed 1 μm from the periphery of the 250 μm×250 μm square area rotation calibration target T. Along the top edge of target T, there are seven upright backscattering elements HZ 6  which are spaced apart by a distance L 8  of 31 μm along the edges of the target T with the first element HZ 6  being spaced a distance L 9 =8 μm from the right edge of the target T. 
     The tip end of each element HZ 5 , HZ 6 , HZ 7 , and HZ 8  is located near the edge of rotation calibration target T, spaced only 1 μm from the edge of the target T. The twenty-eight (four groups of seven) backscattering elements HZ 5 , HZ 6 , HZ 7 , and HZ 8  are spaced 31 μm apart in each group of seven of those elements. 
     FIG. 5A shows a rotation calibration stencil reticle R with the imaging feature openings OR 5 , OR 6 , OR 7 , and OR 8  therethrough in a pattern corresponding to the rotation portion of target T of FIG.  4 A. In this embodiment, the image produced by the rotation portion of reticle R is scanned over the rotation portion of target T. At the bottom of the subfield the image from imaging feature openings OR 8  in FIG.  5 A and the bars HZ 8  in FIG. 4A come into coincidence first. Then the image from imaging feature openings OR 6  in FIG. 5A the bars HZ 6  in FIG. 4A at the top of the subfield come into coincidence second. This results in the two peaks P 1 ′ and P 2 ′; shown in FIG.  6 . Imaging feature openings OR 5 , OR 6 , OR 7 , and OR 8  are elongated rectangular windows through the reticle R proximate to and perpendicular to the adjacent periphery of the reticle R. 
     Alternatively, in place of the stencil reticle described above, a reticle using a SCALPEL (SCattering with Angular Limitation in Projection Electron-beam Lithography) design, as described above can be used. 
     FIG. 5B shows a table of the dimensions of the elements of the rotation reticle R, and the table is structured as the table in FIG. 2B above. The dimension in parentheses in the (target) column are the size of the transmitted image in the target plane using a reduction of 4:1 in the projection optics as shown in FIG.  7 . The pattern is designed so that when the rotation image produced by the rotation reticle R is reduced 4:1 by the projection optics and is scanned over the target T, for a scan in the x direction in FIG. 5A, the bottom bars HZ 8  are scanned and then the top bars HZ 6  are scanned second. 
     Referring again to FIG. 5A, the elements OR 6 , OR 7 , OR 8 , and OR 5  are spaced along the top, right, bottom and left sides respectively of the reticle R with an alignment obtained simply by rotating the elements in consecutive rotations from the elements HZ 6  in the top row. It can be seen that the rotation calibration imaging feature openings OR 5 , OR 6 , OR 7 , and OR 8  are 100 μm long and 24 μm wide are formed LN=62 μm from the periphery of the LA×LA=1,000 μm×1,000 μm square area rotation calibration reticle R. The imaging feature openings OR 5 , OR 6 , OR 7 , and OR 8  are spaced a distance LH of 124 μm along the edges of the rotation calibration reticle R with the first spaced distance LN=62 μm from the edge of the target T and the tip end each imaging feature openings OR 5 , OR 6 , OR 7 , and OR 8  is spaced only LK=4 μm from the edge of the rotation calibration reticle R. The rotation calibration, imaging feature openings OR 5 , OR 6 , OR 7 , and OR 8  are spaced with a periodicity of 124 μm. 
     FIG. 6 shows the desired signal SA 2  with pulses P 1 ′ and P 2 ′, i.e. the signal which is expected to be produced when the image of the reticle R is scanned by a ±15.5 μm calibration scan, as described above if the beam is properly adjusted and calibrated. Based on the patterns on the rotation reticle R and the rotation target T the distance between the pulses P 1 ′ and P 2 ′ in FIG. 6 is 15 μm. Any deviation from that value is due to rotation of the subfield. The distance DR between the peaks P 1 ′ and P 2 ′ can be determined using standard techniques. 
     One component of the Rotation Deviation for the aspect of the method of this invention as illustrated by FIGS. 4A,  5 A and  6  is the Rotation Peak Distance−15 μm. 
     The Rotation Deviation ratio is defined by the equation as follows:                Rotation Deviation     =         Rotation Peak Distance     -     15      μm         Distance between the rows of bars               (   3   )                                
     Using the specific values given in the examples of FIGS. 4A,  4 B,  5 A,  5 B and  6  the Rotation Deviation is as follows:                Rotation Deviation     =         Rotation Peak Distance     -     15      μm         223                   μm   .                 (   4   )                                
     This result can be used to determine the correction to be applied to correct any error caused by the rotation deviation. The sign (+/−) of the result indicates the direction of the rotation deviation. A positive (+) result represents a counter-clockwise rotation deviation of the image of the reticle with respect to the wafer target. A negative (−) result indicates a clockwise rotation deviation of the reticle image with respect to the wafer target. 
     Practical Application 
     FIG. 7 is a schematic diagram which illustrates an electron beam lithography system LS controlled by a conventional electron beam lithography system computer CS through connections to cable CB which are cut away for convenience of illustration. The lithography system LS includes an electron gun  12  (which emits electron beam  52 ) condenser lenses  14 , illumination shaping aperture  16 , blanking plates  20 , blanking aperture  22 , mask deflection yoke  24 , mask  26 , mask stage  30 , post deflection yoke  32 , reduction lens  34 , rotation/magnification correction lenses  36 , objective lens  40 , wafer  42 , target T, wafer stage  44 , transmission detector  46  and backscatter detectors  50 . In operation of system LS, electron gun  12  emits electron beam  52  directed through illumination shaping aperture  16 , which forms the beam  52  into a particular cross-sectional shape. The shaped beam  52  is then positioned by the mask deflection yoke  24  onto either mask  26  or reticle R, which further forms the cross-sectional shape of the beam  52 . 
     In accordance with a preferred embodiment of the invention, salient elements of a projection lithography system LS are shown in FIG.  7 . The reticle R and the mask  26  are both supported on the mask stage  30 , with the reticle R being permanently mounted on mask stage  30 , aside from the location of mask  26 , to be used with different masks  26 . In a similar manner, the target T and the wafer  42  are both supported on the wafer stage  44 , with the target T being permanently mounted on the wafer stage  44 , aside from the location of the wafer  42  for use with wafers  42  placed on the wafer stage  44 . 
     Once the final shape of the electron beam  52  is determined, under the control of computer system CS, the correction lenses  36  may be used to adjust the rotation, magnification, and focus of the electron beam  52 . Electron beam  52  is then incident on either target T or wafer  42 , which are supported by wafer stage  44 . The lens  34  would be adjusted once and all small corrections would be made through correction lenses  36 . Wafer  42  is coated with an electron sensitive resist material, and the electron beam 2  exposes that resist to a pattern dictated by the illumination aperture  16  and the mask  26 . Transmission detector  46  is used to detect and to generate signals representing the intensity of the electrons passing through the wafer  42  or the target T. A set of backscatter photodiodes  50  is provided to detect and to generate signals representing the intensity of the secondary electrons or electrons scattered upward from the target T or the wafer  42 . 
     The flow chart of FIG. 9A shows the steps leading to adjustment of the magnification as a function of magnification deviation in accordance with this invention. FIG. 9B is a flow chart showing steps that lead to adjustment of rotation as a function of rotation deviation in accordance with this invention. At this point in FIG. 7, referring to FIG. 9A, in step SM there were scans of the magnification of the first, reticle image over the first target; and referring to FIG. 9B, in step SR there were scans of the rotation of the second, reticle image over the second target. 
     Referring again to FIG. 7, the backscattered electrons or secondary electrons produce signals from backscatter photodiodes  50  which are received by backscatter diode detector BD which passes signals along to the signal conditioner SC. Then the conditioned signals pass into analog-to-digital converter AD (digitizers) and from there to the computer system CS for determining the distance between peaks. Referring again to FIGS. 9A and 9B in blocks DB and DB′ respectively it is indicated that at this stage, the backscatter signal is detected (detector BD) and digitized (analog-to-digital converter AD). 
     Presently “multiple clip levels” OR “moment calculation” are performed in the computer system CS in FIG. 7, but they can be done in dedicated digital hardware as will be well understood by those skilled in the art. 
     Referring again to FIGS. 9A and 9B, the computer system CS determines the distance between peaks (Peak Distance) in steps DD and DD′ respectively. 
     Then the output passes to the computer system which controls the lithography system LS. 
     In step MD, in FIG. 9A, the value of Magnification Deviation is calculated according to equation (1) above. 
     In step RD, in FIG. 9B, the value of Rotation Deviation is calculated according to equation (1) above. 
     Referring to FIG. 9A step AM, Magnification is adjusted in by computer system CS. 
     Referring to FIG. 9B step AR, Rotation is adjusted in by computer system CS. 
     Conventional or standard elements may be used in system LS. In addition, as will be understood by those of ordinary skill in the art, system LS may be provided with additional or different elements depending on the intended use of the system. Also, it may be noted that, typically, the magnification lens in system LS is used to reduce the size, or to demagnify, the electron beam  52 . The present invention may be used both in charged particle projection lithography systems in which the size of the electron beam  52  is decreased and in such system in which the size of the electron beam  52  is increased. Thus, the term “magnification” is used herein, and in the appended claims, to mean either increasing or decreasing the size of the electron beam  52 . 
     The reticle R of FIGS. 1A (located next to mask  26 ) and the target T (located next to wafer  42 ) are used during a calibration procedure in accordance with this invention before exposure of the wafer. 
     The system of FIG. 7 can be employed as a semiconductor manufacturing tool as will be well understood by those skilled in the art of semiconductor manufacturing. As an example, FIG. 8A shows a schematic block diagram of a process for manufacture of a semiconductor chip. FIG. 8A shows an example of a flow chart of semiconductor fabrication method to which the apparatus of this invention can be applied easily employing the calibration method of this invention. The semiconductor fabrication method comprises mainly a wafer production step P 10  (or wafer preparation step) which produces a finished wafer in step P 11 , a mask production step P 20  (or mask preparation step) which produces a finished reticle, mask in step P 21 , a wafer processing step P 12 , an assembly step P 40  yielding a chip P 41  and an inspection step P 42 . Each step comprises several substeps as will be well understood by those skilled in the art. Among these main steps, the wafer processing step P 12  is a most important step to achieve the specified finest pattern width and registration limit. In this step, the designed circuit patterns are stacked successively on the wafer from step P 11  and many operative semiconductor chips like memory devices or MPC are formed on the wafer from step P 11 . 
     The wafer processing steps P 12  comprises a step of thin film formation wherein a dielectric layer for insulation is formed or a metal layer for lead lines and for electrodes is formed. An oxidization step can be employed to oxidize the thin film or the wafer substrate. A lithography step P 31  involves use of the reticle/mask P 21  to form a photoresist or other resist pattern to process the thin film or wafer substrate selectively, a selected set of process steps P 32  including etching the thin film or wafer substrate and implanting ions or impurities into the thin film or wafer substrate using the resist pattern from step P 31  as a mask. There is the conventional resist stripping step to remove the resist from the wafer and chip inspection step. As indicated at P 34 , the wafer processing steps P 30  are repeated as many times as necessary to make a semiconductor chip be operable as designed, as will be well understood by those skilled in the art. 
     FIG. 8B shows a flow chart of lithography steps P 31  of FIG. 8A which are dominant steps in the wafer processing steps P 12 /P 30 . Lithography steps P 31  comprise a resist-coat step P 311  in which the wafer substrate is coated with resist on circuit elements formed in a previous steps. An exposure step P 312  then exposes the wafer coated with resist through the reticle/mask of step P 21  employing a deflector in accordance with this invention. A resist development step P 313  follows for developing the resist exposed in exposure step P 312  followed by a resist annealing step P 314  performed to enhance durability of the resist pattern produced in step P 313 . 
     While this invention has been described in terms of the above specific embodiment(s), those skilled in the art will recognize that the invention can be practiced with modifications within the spirit and scope of the appended claims, i.e. that changes can be made in form and detail, without departing from the spirit and scope of the invention. Accordingly all such changes come within the purview of the present invention and the invention encompasses the subject matter of the claims which follow.