Patent Publication Number: US-3876883-A

Title: Method and system for focusing and registration in electron beam projection microfabrication

Description:
United States Patent Broers et al.  
 METHOD AND SYSTEM FOR FOCUSING AND REGISTRATION IN ELECTRON BEAM PROJECTION MICROFABRICATION Inventors: Alec Nigel Broers, Purdys Station;  
 Marcus Barry Heritage, Katonah, both of NY.  
 Assignee: International Business Machines Corporation, Armonk, NY.  
 Filed: Dec. 28, 1973 Appl. No.: 429,438  
  Related US. Application Data Continuation-impart of Ser. No. 267,844. June 30, 1972. abandoned.  
 Foreign Application Priority Data Primary Examiner-James W. Lawrence Assistant livaminer-B. C. Anderson Attorney, Agent, or Firm-Graham S. Jones, ll; John J. Goodwin [57] ABSTRACT A method and system for improved focusing and registration in an electron beam device including an electron beam source, condenser lenses, deflection coils,  
  r- 28, 1 3 United Kingdom 14834/73 projection lenses, a mask and a target. The deflection June 4, 1973 Japan 48-62080 il are l cated between econd and final condenser June 6, 1973 France ..73.2l785 lenses and deflect the focused electron beam onto a June 23, 1973 Germany 2332091 projection mark on the mask and onto a i il i 0.5. CI. 250/492; 250/398; 250/491 F P 9; :9 target pmvde super&#39;mpmd rm. Cl. H0lj 37/00 &#39;mages PurPOses- Field of Search 250/492, 491, 398, 31 l,  
 250/396 18 Claims, 18 Drawing Figures Y GENERATOR BLANKING 3 ARPL  I; 2 26 IIAIIuAL 21L 1 x GENERATOR ADJ. csT  
  cuRRERr M30 x AMPLITUDE AND vARIARLE orrsEr O\ CONTROLS,56 F 65 l l 62 l x CURRENT AMPLIFIER l J 5 T l Y AMPLITUDE AND I vARIAIILE OFFSET norms, as L Q Q 59 54 efi Y CURRENT AMPLIFIER i- Y VIDEO ADJ. r  
 mSPLAY PWR SPLY o o ADJ. 0ST 51 cuRRERr Wm PIIIR SPLY mm PHOTOMULTIPLIER PMHMUAPR 8i975 3,876,883  
 sum 3 0f 4 FIG. 70  
 FIG. 7A  
 FIG.7B FIG. 70  
 FIG. 8C  
 FIG. 8D  
 SHEET 0f 4 FIG 8A FIG. 88  
 FIG. 9C  
 FIG.9D  
 FIG. 9A  
 FIG.9B  
 METHOD AND SYSTEM FOR FOCUSING AND REGISTRATION IN ELECTRON BEAM PROJECTION MICROFABRICATION CROSS REFERENCE TO RELATED APPLICATION This application is a continuation&#39;in-part of copending patent application Ser. No. 267,844, filed on June 30, 1972 now abandoned.  
 BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to electron optical projection systems for microfabrication and methods of focusing and registration therefor, and use thereof.  
 2. Prior Art Electron beams such as used in electron beam tubes have been focused by lenses and deflected by magnetic fields in the prior art. A typical example of such a sys tem is described in US. Pat. No. 2,991,361 issued July 4, 1961 to Karl-Heinz Herrmann.  
  Another example of focusing an electron beam is set forth in US. Pat. 3,3 19,1 10, Electron Focus Projection &amp; Scanning System, issued May 9, 1967 to Kurt Schlesinger.  
  A distinction of the present invention over the prior art is the provision of a registration hole in a mask and a registration mark on a target which is used in combination with a deflection coil for providing radiation focused to form an image of the hole upon the registration mark on the target and employing such registration in an electron beam projection system to prepare for exposure of the entire target.  
  US Pat. No. 3,118,050 issued to J. S. Hetherington Jan. 14, 1964 shows an electron beam system with a microfabrication target and without a beam deflection system. The source of electrons passes through a single variable focus condenser or collimating type of magnetic lens. The lens floods the beam at once over all of the area of a projection mask having fiducial notches in the edge thereof through which rays of the electron beam may pass. The condenser type lens has an adjustable D.C. supply connected to opposite ends of the coil, which apparently can be adjusted to collimate the electrons passing through the lens. A focusing system including a pair of magnetic lenses is located between the mask and the work piece holder. The focusing lenses are also connected to adjustable D.C. supplies. The holder includes spaces for workpieces, and around the periphery of such spaces are fiducial notches each containing a terminal insulated from the holder. A balanced pair comparator circuit is employed to help to register the holder, while the holder is moved by adjusting of micrometer screws, until the balanced pair indicates proper positioning. The only means for viewing the position of the work holder and work is through a binocular microscope. The balanced pair and the binocular microscope are totally independent means for measuring the position of the holder via the balanced pair and the work as well, via the optical microscope.  
  No prior art has been found however, which deals with the problem of locating thespecific orientation of the work in the holder relative to a mask to be used. In addition an optical microscope type of sensor does not provide sufficient magnification for the small kinds of microcircuits being developed in electronics today. Also, any radiation projected by Hetherington floods the entire surface of the workpiece causing radiation exposure of the entire surface of the workpiece when the workpiece has not yet been registered. This is unacceptable in cases where the radiation must be shielded from the workpiece until after it has been registered in the proper position. Furthermore, Hetherington does not indicate how the radiation is to be applied during registration other than to say the beam is directed at the work and that the beam varies up to a maximum voltage, a maximum pulse rate and a maximum current, and that intensity can be varied. No suggestion is made as to how the beam can be prevented from performing work upon the workpiece during holder registration. Thus, Hetherington registers only the holder and thus fails to register the work itself, and apparently exposes the workpiece to harmful radiation, prior to alignment.  
  In addition none of the prior art suggests scanning a pencil beam focused upon a mask with windows through the mask onto a workpiece.  
 SUMMARY OF THE INVENTION An object of the present invention is an improvement to an electrorioptical projection system wherein a projection pattern is focused and accurately registered on an unexposed wafer.  
  Another object of the present invention is to provide an electron beam projection system including a set of deflection coils located proximate to condenser lenses to focus and deflect the electron beam onto registration marks.  
  The foregoing and other objects, features, and advantages of the present invention will be apparent from the following more particular description of a preferred embodiment of the invention as illustrated in the accompanying drawings.  
 BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 shows in a schematic manner the imaging portion of an electron beam column for optical projection and control circuits therefore in accordance with the principles of the present invention.  
  FIG. 2 is an illustration of superimposed registration images for the cases where the marks and thereby their images are similarand dissimilar.  
  FIG. 3 is a plan view of a mask for an electron beam projection microfabrication system.  
  FIG. 4 is a video display of a semiconductor wafer target registration mark with a shadow of a registration grid projected by the electron beam from a mask, with both images out of focus.  
  FIG. 5 is a view similar to FIG. 4 with the shadow grid in focus.  
  FIG. 6 is a view similar to FIG. 5 with the wafer also in focus.  
  FIG. 7 (A-D) is a set of video displays of projections of four registration windows in a mask upon a single wafer where excessive scale causes a mismatch of registration.  
  FIG. 8 (A-D) is a set of video displays of the marks in FIG. 7 (A-D) after the scale has been readjusted, by reducing magnification in the projection system.  
  FIG. 9 (A-D) is a set of video displays of the marks in FIG. 8 (A-D) after registration has been realigned.  
 DESCRIPTION OF A PREFERRED EMBODIMENT In electron projection optics, as in light optics, the function of the condenser lens system is to illuminate the projection mask and then collect all the electron beams passing through the mask and focus them into the entrance pupil of the projection lens system.  
  Because of the extreme tolerances required in the fabrication of microcircuits by electron beam projection optics, it is very important that the electron image of the mask be focused and that the projection mask and the target wafer be registered with respect to each other. In the past, electron beam tube projection systems have been used in the fabrication of microcircuits on semiconductor wafers in a manner similar to the way light optics in microcircuit cameras are used to photographically reproduce circuit patterns contained on light masks onto semiconductor wafers.  
  Some examples of the use of electron beam projection technology in the fabrication of microcircuits are described in the publication Electron Optical Microminiaturization of Stencils by H, Koops, G. Mollenstedt and R. Speidel, Optik 28 (5) pgs. 518-531 (1968/69) and an Electron Imaging System For the Fabrication of Integrated Circuits by T. W. OKeeffe, .I. Vine and R. M. Handy, Solid State Electronics, Pergamon Press 1969, Vol. 12, pp. 841-848. These publications discuss the use of electron beam optics in microminiaturization and are hereby incorporated by reference. Accordingly, the fundamentals of electron beam tube operation including electron beam sources, magnetic lenses, focusing, deflection systems and the like are presumed to be known to those of described skill in the art and will not be explained or describe in unnecessary detail in the present disclosure.  
  An embodiment of the present invention is shown schematically in FIG. 1. The structure of FIG. 1 is capable of illuminating a suitable projection mask with electrons and imaging the mask onto a semiconductor target wafer to fabricate a microcircuit in a manner described in the prior art. In FIG. 1, however, an additional mode of operation is shown and will be described wherein the electron beam optics can be operated in a scanning and in a preliminary focusing and registration mode, as well.  
  Referring to FIG. 1, an electron beam tube microcircuit fabrication structure 24 is shown in the focusing and registration mode, also referred to as the probe mode. The structure 24 evacuated to about Torr includes a conventional electron beam gun 28 of about KV which produces beams of electrons, for example, from a tungsten cathode. The electron beam is directed through blanking electrodes 25, 26 aperture 27 a first magnetic condenser lens 30 powered by adjustable constant current power supply 70 and a second magnetic condenser lens 32 powered by adjustable constant current power supply 71 which lenses focus the electron beam. In the present invention, prior to the final condenser lens 38 powered by adjustable constant current power supply 72, a set of orthogonal X deflection coils 34 and Y deflection coils 36 are positioned in a plane which is an image of aperture 44 through lenses 38 and 42. During registration rather than have the electron beam impinge the entire projection mask 40, the condenser lens system is readjusted to provide a pinpoint focus upon mask 40. The deflection coils 34 and 36 are energized by waveforms adapted to cause the electron beam to be directed through the final condenser lens 38 in such a direction that the electron beam is focused at a specific location on projection mask 40 at which there is located a unique registration pattern in the form of a hole 41 of a selected configuration.  
  In light beam projection systems for microcircuit fabrication, the projection mask is usually a transparent substrate on which the desired circuit is graphically layed out using light opaque material. In electron beam projection systems, the projection mask such as 40 in FIG. 1 and FIG. &#39;3 with circuit apertures 39 and registration mark apertures 41 can be analogous to light optics. Here the mask is preferably a photolithographically manufactured very thin (0.2 mil thick) selfsupporting, electro-formed grid, or pattern of copper gold or nickel which forms the electron opaque sections where desired. The grid is formed on a substrate and then lifted off it to produce the self-supporting foil. The electron beam is to pass through the openings in the mask and impinge on the target wafer thereby exposing the upper surface of the target wafer, which may be silicon or silicon oxide coated with an electron sensitive resist, with the desired circuit pattern. Yet again, it may be a cathode mask such as described in the aforementioned reference of OKeeffe et al. where now the mask itself is the source of electrons for the projec tion mode of operation. The mask 40 is rotatably mounted to be turned by worm gear 78.  
  In circuit fabrication, it is important that the projection mask be properly registered and aligned with the target wafer. In the embodiment of the present invention illustrated in Flg. 1, the deflection coils (or plates) 34 and 36 are provided to deflect the electron beam over the mask 40 and wafer 48 when a deflection current (or voltage) is applied to the coils. The value of the deflection current is a function of the type of deflection coils employed, the geometry of the projection system and the design of the magnetic lenses. This will vary from system to system and the deflection current in a given system can be determined by one having ordinary skill in electron beam technology. In the general case, including projection systems without a physical aperture, one or two sets of orthogonal coils may be positioned above, within or after the lens 38 previous to the mask such that the direction of the principal ray of the spot focused at the mask plane is such that the ray passes through the center of the effective entrance pupil of the projection optics.  
  In FIG. 1, the lens 38 previous to the mask focuses the electron beam at the plane of the mask. The focused spot, which is smaller than any dimension of the registration mark is scanned by the coils 34 and 36 over a registration hole configuration 41 in the mask 40. This may be any of the three types of mask described except that when the cathode mask is used, the accelerating electrostatic potential of the electron gun 28 is thesame as the electrostatic potential of the cathode mask. The focused beam that passes through the registration hole 41 then passes on through the projection optics, which consists of the projection lens 42 powered by constant current power supply 73, aperture 44 shifting deflection coils 79 and 80 associated with aperture 44 powered by variable supplies 74, for shifting the focus point transversely a small amount and final projection lens 46 powered by variable supply 76, and onto the target wafer 48 where another registration mark is located. The projection mask 40 and target wafer 48 are in alignment when the images of the registration marks on the wafer surface are superimposed with the shadow images 41 in FIG. 2 of the registration mark mask openings 41.  
  The aforesaid is accomplished in the following manner. A signal, which may take the form of backscattered electrons detected by the electron detector 50, is amplified and displayed by a video display 52 scanned in synchronism with the deflection coils 34 and 36. The scanning system includes X generator 55 and Y generator 54, which respectively drive X and Y amplitude and variable offset control units 56 and 58 having X and Y control knobs 62 and 64 respectively for amplitude which are shown mechanically ganged by line 93 for display magnification control and X and Y offset control knobs 63 and 65 respectively. Outputs are provided from X and Y units 56 and 58 to X and Y current amplifiers 57 and 59 connected to coils 34 and 36 respectively. Separate outputs from control units 56 and 58 are connected to the scanning input circuits of video display 52. Electron detector 50 comprises an electron scintillator receiving electrons 66 and a light pipe connecting the scintillator to a photo multiplier 51 which drives video amplifier 53 to control the intensity of video display 52. Knobs 62, 63, 64 and 65 make it possible for the beam to be adjusted to scan certain portions of the large mask 40 shown in cross section by reducing the amplitude, or the entire mask 40 and all apertures therein with larger amplitude control settings. The zero offset can be used to adjust the beam location for work in any given small area when a small amplitude signal is applied. In general, the signal may be detected by any of the methods known to those skilled in the art of scanning electron microscopy. Assuming that the surface of target wafer 48 is coincident with the projection image plane, video display 52 will produce two superimposed images one of the surface of target wafer 48 with the registration mark and any other surface feature perfectly focused. The second image will be a shadow image of mask 40 due to the chopping of the electron beams in the mask plane by the mask itself. It is to be noted that because the projection optics shown in FIG. I remain the same in both the pro jection mode and the focusing mode as shown, the correspondence between the two superimposed video images is the same as between the mask and its projected image except that dimensions appearing the same in both video images are in fact related by the projection magnification.  
  Alignment of mask 40 to target wafer 48 is achieved with reference to FIG. 2 by using registration patterns 41 or 41A in mask 40 and shaped marks 43 on target wafer 48 which may. but need not be similar in shape to the holes in the mask. FIG. 2 shows examples of a similar hole pattern 41 and mark 43 and a dissimilar hole pattern 141&#39; and mark 143, both examples being shown superimposed to indicate mask and wafer alignment. Registration of mask and wafer is complete when the video output shows the images of both marks superimposed as shown in FIG. 2 for all registration points on the object. The ultimate limit on the accuracy of registration is determined by the size of the electron beam probe in the image plane, which itself is only limited by the edge resolution in the projection optics. Any displacement in the mask from its appropriate conjugate plane results in a defocusing of the mask shadow image. Similarly, displacement of the wafer results in a defocusing of the wafer image. Thus, the wafer 48 and the mask 40 can be focused one to the other as appropriate and also the two can be accurately registered.  
 Focusing and Registration Procedure To achieve correct focusing of the beam upon the mask and the wafer (workpiece) as well as correct registration, three separate conditions must be satisfied. l The mask and wafer planes must be conjugate with respect to projection lenses 42 and 46 (i.e. the mask and wafer are in focus on the video display because the scanning beam is in focus as it reaches each of those planes.) (2) The demagnification of the projection system must be maintained to a very high degree of accuracy. (3) The mask and wafer must be aligned in both X and Y translations and rotation.  
  Satisfaction of the above conditions is obtained by the procedures outlined below. FIGS. 4-9 (D) show video displays with a mesh grid alignment mask and a cross marked on the substrate in various stages of adjustment. The image of the mesh grid is superposed upon the image of the cross on the wafer plane.  
 First Condition Step: Focusing To satisfy the first condition above, the objective is to correct the defocussing.  
  Step (la) is to adjust the current to condenser coil 38 until the mask grid image in FIG. 4 is in focus as in FIG. 5.  
  Step (lb) is to adjust current in projection coil 46 to focus the larger image of the wafer marking 96 as in FIG. 6.  
 Demagnification Adjustment Now the mask and wafer planes are both in focus. However, the projection demagnification if inaccurate must be adjusted. If it is inaccurate, then the result will be similar to that shown in FIG. 7, (A-D) where the mask size projected onto the wafer is too small. While mask projection 41A is aligned with its wafer mark, wafer marks 96B and 96D are both too high relative to the mask projections and wafer marks 96C and 96D are too far to the right of their corresponding mask projections. Thus, it is obvious that the mask demagnification must be changed to achieve similar relative positioning of all marks. Thus, the next step is to adjust current to the demagnification coils 42 and 46 from power supply units 73 and 76, so that the grid image remains focussed but the display shows similar relative positioning of all marks. Since the mark projections 41A&#39;,41B,41C and 41D are widely spaced on the projection onto the wafer the scale can be adjusted to an extremely high order of accuracy. Of course, the scan of the coils 34 and 36 must look at each one of those registration patterns alone without scanning the intermediate areas. A problem has arisen as shown in FIG. 8 (AD) in the course of demagnification, since marks 96A and 41A are no longer aligned correctly because as the whole pattern shrank, for example, 96A moved up away from 96D while 96D moved towards 96A and a correct position.  
 Alignment The alignment of the mask image and wafer can be adjusted in X, Y and rotation. The rotation is handled mechanically either by turning worm gear 78 attached to the support for mask 40 or by worm 91 attached to turn the table 92 supporting wafer 48.  
  While X, Y alignment is originally adjusted by knobs on micrometer drives 82, 83 to move intermediate support tables 84, 85, now deflection coils 79, 80 can be supplied a slightly different current by power supplies 74, 75 respectively to align the grids with the crosses properly as shown in FIG. 9 (AD). Note that the above steps may be required to be performed in a cyclical sequence of iterations of correction to achieve proper alignment.  
 Exposure After the alignment step, the work is in position ready for exposure of the work through the mask and now the electron beam can expose the work piece in the desired kind ofa way by flooding or scanning as de sired through the mask. Note, that the registration marks 43 on the wafer are made initially, with an extra thickness layer if required to prevent subsequent operationssuch as etching from removing them, as for example where photo resist is being developed to provide windows for etching, which windows would expose the marks for etching also. See Hatzakis U.S. Pat. No. 3,519,788.  
  An added feature of the invention is that the probe mode of operation as shown in FIG. 1 can be used to determine if any aberrations exist in the projection optics. When optimum focusing of both the shadow image of the mask opening and the wafer surface has been achieved, the relative difference in definition of the wafer surface features and the shadow image across the field of view gives an indication of the defocusing effect of coma, astigmatism and field curvature in the projection optics. Similarly comparing the distortion of the shadow image, if any exists, with that of the surface features of the wafer, can yield the projection distortion coefficient.  
  When the X or Y generator 54, 55 is retracing, a signal on line 97 or 98 respectively operates blanking amplifier 90 via line 99 to operate blanking electrodes to deflect the electron beam away from the aperture in aperture 27. Amplifier 90 can be operated manually also for timing of exposures in projection mode.  
  Variation in the configuration of the projection optics using magnetic lenses is possible and the structure is not necessarily limited to that shown in the drawings. For example, the final condenser lens and the first projection lens can be merged into one single field lens with the mask situated in the center of the focusing field. Under these circumstances, it is necessary to introduce an additional lens between the second condenser lens and the field lens in order to focus the probe at the mask plane. Except for this difference, all other operations in the probe mode are similar to those described. In general, the required size of the intermediate source image (after second condenser lens 32) in the projection and the probe modes will be different. Thus, it is expected that the changes in strength of the first and second condenser lenses will be required when switching form one mode to the other. Again, the changes in lens strengths are within the skill of workers in electron beam technology.  
  While the invention has been particularly shown and described with reference to a preferred embodiment, it will be understood by those skilled in the art that the foregoing and other changes in form and details may be made therein without departing form the spirit and scope of the invention.  
 What is claimed is:  
  l. A method for operating an electron beam wafer exposure system including a target whose position is adjustable, a source of an electron beam, a projection mask for said target having a registration hole therein, means for focusing said beam on said mask, means for scanning said focused beam across said mask, means for projecting radiation from said beam in the image form through said mask onto said target, means for sensing beam radiation projected onto said target, means for displaying a scanned input connected to receive the output of said means for sensing for display, means for providing scanning signals having outputs connected to drive said means for scanning and said means for displaying in synchronism, wher&#39;eby radiation projected onto said target through said mask is displayed upon said display, said target having a registration mark thereon, the steps comprising focusing said beam substantially only upon said registration hole in said mask, viewing said display, adjusting the position of said target until the display shows that said beam is focused upon said hole, and then broadening the focus of said beam to cover substantially all of said mask.  
  2. In a method for focusing and registration of an electron beam projection system including a source of an electron beam, a projection mask having a unique pattern of registration electron beam windows therein, an adjustable focal length condenser lens system located between said electron source and said projection mask including electron lenses for collecting said electron beam from said source and directing said beam onto said projection mask, a target wafer having a unique registration marks on the surface thereof, a projection lens system located between said projection mask and said target wafer for collecting electron beams passing through said projection mask and directing them onto said target wafer, a deflection system located between said source and said mask for scanning said electron beam across said mask, said deflection system cooperating with said condenser lens system to scan the focus of said electron beam across the plane of said projection mask at one of said registration windows and said projection lens system operating to focus the portion of said electron beam passing through a said window in said mask onto the surface of said target wafer, and electronic detection means for sensing the image projected through said mask onto said wafer, the improvement comprising, focusing said electron beam into a pencil point beam upon a point upon said projection mask, scanning said pencil point beam to hit a registration window in said mask, viewing said detection means to determine whether said electron beam is directed towards said registration mark on the surface of said target wafer, and adjusting the position until said beam is directed towards said mark, and then changing the focus of said condenser lens system to adjust said beam to flood said projection mask and to project through all of the windows therein upon said target wafer.  
  3. A method for operating an electron beam wafer exposure system including a target whose position is adjustable, a source of an electron beam, a projection mask for said target having plural widely spaced registration holes therein, first means for focusing said beam on said mask, means for scanning said focused beam across said mask, means for projecting radiation from said beam in the image form through said mask onto aaid target, means for sensing beam radiation projected onto said target, means for displaying a scanned input connected to receive the output of said means for sensing for display, means for providing scanning signals having outputs connected to drive said means for scanning and said means for displaying in synchronism, whereby radiation projected onto said target through said mask is displayed upon said display, said target having a registration mark thereon, the steps comprising focusing said beam substantially only upon said registration holes in said mask, viewing said display. adjusting the scale relative the position of said beam of said target until the display shows that said beam is generally focused upon said holes, adjusting the scale of the projection of said mask to match the spacing of said registration marks upon said target, adjusting the alignment of the projection through said holes upon said registration marks and then broadening the focus of said beam to cover substantially all of said mask.  
  4. A method in accordance with claim 3 wherein said first means is adjusted to focus said beam upon said mask by adjusting the control of said first means to yield a focused image of the scanned portion of said mask upon said display, and adjusting said means for projection to focus said beam passing through said mask upon said target, prior to adjusting scale and alignment of said projection.  
  5. A focusing and registration system for an electron beam projection system comprising:  
 a source of an electron beam,  
 a projection mask having a unique pattern of registration electron beam windows therein,  
 a condenser lens system located between said electron source and said projection mask including electron lenses for collecting said electron beam from said source and focusing said beam onto a point on said projection mask,  
 a target wafer having a unique registration mark on the surface thereof,  
 a projection lens system located between said projection mask and said target wafer for collecting electron beams passing through said projection mask and directing them onto said target wafer,  
 a deflection system located between said source and said mask for scanning said electron beam across said mask, said deflection system cooperating with said condenser lens system to scan the focus of said electron beam across the plane of said projection mask at one of said registration windows and said projection lens system operating to focus the portion of said electron beam passing through a regis tration window in said mask onto the surface of said target wafer,  
 and electronic detection means for sensing the image projected through said mask onto said wafer.  
  6. A focusing and registration system according to claim 5 wherein said projection mask has holes therein in a predetermined pattern, one of said holes being a unique registration hole.  
  7. A focusing and registration system according to claim 5 further including a projection aperture located in said projection lens system and where a first and second pair of deflection elements are located in said condenser lens system in a plane conjugate to the plane of said projection aperture through all projection lenses between &#39;said aperture and said mask and at least one condenser lens.  
  8. A focusing and registration system according to claim 5 wherein said detection means is an electron detector responsive to electrons scattered from the surface of or collected by said target wafer.  
  9. A focusing and registration system according to claim 5 wherein said condenser lens system includes a first magnetic condenser lens, a second condenser lens and a final condenser lens and wherein said deflection system is located between said second condenser lens and said final condenser lens.  
  10. A focusing and registration system according to claim 5 wherein said projection lens system includes a first magnetic projection lens and a final magnetic projection lens, said aperture being located between said first and final projection lenses and said projection mask being located between said condenser lens system and said first projection lens.  
  11. A focusing and registration system according to claim 5 wherein said first and. second pair of deflection elements are first and second deflection coils arranged orthogonally with respect to each other.  
  12. A focusing and registration system according to claim 6 wherein said registration hole in said projection mask and said registration mark on said target wafer have the same geometrical shapes.  
  13. A focusing and registration system according to claim 6 wherein said registration hole in said projection mask and said registration mark on said target wafer are dissimilar in geometric shape.  
  14. A focusing and registration system according to claim 8 wherein said electron detection means includes an electron detector responsive to electrons from the surface of said target wafer and a video display means connected to said electron detector for visually displaying the projected image of said registration window in said projection mask on said target wafer and the image of said registration mark on the surface of said target wafer.  
  15. A focusing system for an electron beam projection system comprising:  
 a source of an electron beam,  
 a projection mask having a unique pattern of windows therein,  
 a condenser lens system located between said electron source and said projection mask including an electron lens for collecting said electron beam from said source and focusing said beam onto a point on said projection mask,  
 a target,  
 a projection lens system including at least one lens and an aperture located between said projection mask and said target for collecting the portion of said electron beam passing through said projection mask and directing it onto said target,  
 a deflection system for scanning said electron beam across said mask, including deflection elements located between said source and said projection mask, said deflection system cooperating with said condenser lens system to scan the focus of said electron beam across the plane of said projection mask across at least one of said windows and said projection lens system operating to focus said elec tron beam passing through said window in said mask onto a point on the surface of said target.  
  16. A focusing and registration system for an electron beam electrical circuit manufacturing system comprisa source of an electron beam,  
 a projection mask having a unique registration pattern of windows therein.  
 a condenser lens system located between said electron source and said projection mask including electron lenses for collecting said electron beam from said source and focusing said beam onto a point on said projection mask,  
 a target electrical circuit material,  
 a projection lens system including at least one lens and an aperture located between said projection mask and said target wafer for collecting said electron beam passing through said projection mask and directing said beam onto said target material,  
 a deflection system for scanning said electron beam across said mask located in said condenser lens system in a plane conjugate to the plane of said aperture through all projection lenses between said aperture and said mask and at least one condenser lens, said deflection system cooperating with said condenser lens system to focus and scan said electron beam in the plane of said projection mask across at least one of said registration windows and operating with said projection lens system to focus the portion of said electron beam passing through said window in said mask onto a point on the surface of said target material.  
 17. An electron beam wafer exposure system including,  
 a target,  
 a source of an electron beam,  
 a projection mask for said target,  
 means for focusing said beam on said mask.  
 means for scanning said focused beam across said mask,  
 means for projecting radiation from said beam in the image formed by said mask onto said target.  
 means for sensing beam radiation projected onto said target,  
 means for displaying a scanned input having a radiation input connected to receive the output of said means for sensing for display and having position inputs for receiving scanning signals,  
 means for providing scanning signals having outputs connected to drive said means for scanning and said position inputs of said means for displaying in synchronism. 1  
 whereby radiation projected onto said target through said mask is displayed upon said display.  
  18. In a method for focusing and registration of an electron beam projection system including a source of an electron beam, a projection mask having a unique pattern of registration electron beam windows therein, an adjustable focal length condenser lens system located between said electron source and said projection mask including electron lenses for collecting said electron beam from said source and directing said beam onto said projection mask, a target wafer having a unique registration mark on the surface thereof, a projection lens system located between said projection mask and said target wafer for collecting electron beams passing through said projection mask and directing them onto said target wafer, a deflection system located between said source and said mask for scanning said electron beam across said mask, said deflection system cooperating with said condenser lens system to scan the focus of said electron beam across the plane of said projection mask at one of said registration windows and said projection lens system operating to focus the portion of said electron beam passing through a said window in said mask onto the surface of said target wafer, and electronic detection means for sensing the image projected through said mask onto said wafer, the improvement comprising, focusing said electron beam into a pencil point beam upon a point upon said projection mask, scanning said pencil point beam to hit a registration window in said mask, viewing said detection means to determine whether said electron beam is directed towards said registration mark on the surface of said target wafer, and adjusting the deflection of the beam until said beam is directed through said window towards said mark, adjusting power to said condenser lens system to focus said mask as presented upon said display;  
 adjusting power to said projection lens system to focus the image of said target wafer upon said display; adjusting the scale of the projection of said mask shown upon said display to match the spacing of the images of said registration windows with corresponding registration marks upon said target as shown upon said display; adjusting the alignment of the projection through of said windows upon said marks; and then changing the focus of said condenser lens system to adjust said beam to flood said projection mask and to project through all of the windows therein upon said target wafer.