Patent Number: 047926880
Section: description

DETAILED DESCRIPTION FIG. 1 illustrates, in block diagram form, a particle beam lithography system 10 for processing a workpiece 12, such as a semiconductor wafer or mask. This particle beam lithography system 10 also includes a differentially pumped seal apparatus 14 of this invention, hereinafter simply called "the seal apparatus", mounted at the output of a beam column 16. The beam column 16 includes an electron or ionized particle source, demagnification optics and projection and deflection optics which generate a finally focused beam 20 and may also include illumination and shaping optics when a shaped beam is utilized. A central tube 22 (shown in phantom) is within the column 16 and is traversed by the beam 20 and maintained at a high vacuum by a high vacuum pump 24 coupled to the column 16. The beam 20 passes through the seal apparatus 14 and impinges on the workpiece 12. The workpiece 12 is supported and held in position on a movable stage 26 which is translated in an X-Y direction by an X and Y axis drive system 30 and the position of the stage is sensed by X and Y position sensors 32 which are typically laser interferometers. The X and Y axis define a horizontal plane while the Z axis coincides with the axis of the beam. The complete lithography system 10 further includes a computer (controller), and associated electronics which controls the beam, the drive system, the vacuum system, the wafer handling system and stores pattern data and provides beam control signals. The relationship between the seal apparatus 14 and the workpiece 12 is illustrated in FIG. 2. The seal apparatus 14 includes a plurality of conically shaped sleeves 34, 36 and 40, partially shown in FIG. 2, which terminate in a generally planar tip 42 positioned, during processing, slightly above the workpiece 12. The position of the tip 42 relative to the workpiece 12 is referred to as a gap G and is important to the operation of the sealing apparatus 14 and the graded seal obtained thereby. As mentioned above, the seal apparatus 14 has increased vacuum conductance, provides a gap on the order of 12 to 15 microns, + or -3 microns, which is smaller than that used in the prior art, and a high vacuum on the order of 10.sup.-6 Torr which is lower than that of the prior art. As shown, the sleeves 34, 36 and 40 define a plurality of apertures. The first aperture 44 is annular and coupled to a first stage vacuum pump 46 which reduces the pressure around the two inner sleeves to a low vacuum level on the order of 1.0 Torr. The second aperture 48, inside the first aperture 44, is annular and coupled to a second stage vacuum pump 50 which reduces the pressure to an intermediate vacuum level on the order of 10.sup.-3 Torr. The third and central aperture 52 is coupled to a second high vacuum pump 54. This aperture 52 is maintained at a high vacuum corresponding to the vacuum in the central tube 22 which is on the order of 10.sup.-6 Torr and the beam 20 is scanned over the region of the workpiece 12 within the central aperture 52 as the workpiece 12 moves relative to the aperture. The construction of the seal apparatus 14 which accomplishes the reduction in vacuum and smaller gap size is shown in detail in FIGS. 3-7. The seal apparatus 14 is shown assembled in FIGS. 4-7 while the individual elements of the seal apparatus 14 are shown separately in FIG. 3. As shown, the seal apparatus 14 comprises three sectors of a circular cylinder (shown as a right circular cylinder) designated herein as a rough port nozzle R (of approximately 180 degrees), a medium port nozzle M (of approximately 90 degrees) and a high port nozzle H (of approximately 90 degrees). The term "approximate" is used herein to signify that any one of the nozzle sectors may vary in its angular extent so long as the total of 360 degrees for a circular cylinder is maintained and the terms "rough", "medium" and "high" are used to describe the degree of vacuum in each nozzle. When assembled, as in FIGS. 4-7, the seal apparatus 14 defines a circular, apertured, top 56 which is relatively thin as compared to an integral depending cylinder 58 of a lesser outer diameter. The latter terminates in the apertured sleeve 34 which is frustoconical in form and integral with the depending cylinder 58. As most clearly shown in FIG. 3, the rough port nozzle R is 180 degree sector of essentially three parts; a relatively flat top part 56 R with a depending cylindrical part 58 R, both of 180 degrees, and the frustoconical sleeve 34 of 360 degrees as shown in FIGS. 6 and 7. This sleeve 34 extends slightly below the depending cylindrical part 58 R, as at 60, is relatively flat and thin and with its aperture 44, being the largest of the three apertures, has its center on the center line of the seal apparatus 14. The wall of the depending cylindrical part 58 R is provided with a relatively large, radially oriented, channel 62 opening into the area of the sleeve 34 (see FIGS. 5 and 6). As will be apparent from the further description herein, this large channel 62 provides direct and unimpeded access to the aperture 44 when the seal apparatus is fully assembled. The top of sleeve 34 is also provided with an alignment ring or rib 64 of 180 degrees which is used to hold the other nozzles in place during assembly of the seal apparatus 14. The medium port nozzle M, shown separately in FIG. 3, is of essentially four parts although only a 90 degree sector. This nozzle M has a relatively flat top part 56 M with a depending cylindrical part 58 M and an inner circular integral cylinder part 66 which terminates in sleeve 36 which is also frustoconical with its aperture 48 on the center line of the seal apparatus 14. Cylindrical part 66 is thin walled and of a diameter less than the diameter of the depending cylindrical part 58 M to fit within the inner wall of the depending cylindrical part 58 R of the rough port nozzle R. The aperture 48 is on the center line of the seal apparatus 14 and is smaller than the aperture of the rough port nozzle R and concentric with the frustoconical sleeve 34 of the rough port nozzle R, when assembled. The inner cylindrical part 66 has a cut away portion 70, the width and depth of which will allow the high port nozzle H to be inserted therein. The wall of the depending cylindrical part 58 M is provided with a relatively large, radially oriented, channel 72, opening into the inner cylinder 66, to provide direct and unimpeded access to the aperture 48. The bottom wall of the depending cylindrical part 58 M has a downwardly extending ring 74 whose inner diameter is larger than the aligning ring 64 on the rough port nozzle R to facilitate assembly. The high port nozzle H, shown separately in FIG. 3, is also a sector of 90 degrees and essentially three parts; a top part 56 H with a depending cylindrical part 58 H and the conical sleeve part 40 of 360 degrees. This sleeve part 40 has the highest degree of taper and terminates in aperture 52 which is the smallest of the three apertures. The depending cylindrical part 58 H is also provided with a relatively large, radially oriented, channel 76 directly accessing the aperture 52. The bottom wall of the depending cylindrical part 58 H has a downwardly extending ring 80 whose inner diameter is larger than the aligning ring 64 on the rough port nozzle R to facilitate assembly. As in the prior art, the seal apparatus 14 is assembled and brazed to connect the nozzle sectors together. When the medium port nozzle M is placed on the aligning bar 64 so that the conical sleeve 36 is concentric with the conical sleeve 34 of the rough port nozzle R, the cylindrical inner sleeve part 66 is spaced from an inner cylindrical wall 82 of the depending cylindrical part 58 R thereby forming a rough vacuum chamber of 360 degrees which communicates with sleeve aperture 44 of 360 degrees and the relatively large radial channel 62. Thereafter, the high port nozzle H is placed on the aligning bar 64 in the cutaway 70, so that the conical sleeve 40 is in alignment with the other conical sleeves. Thus assembled, the inside vertical cylindrical wall 84 of the inner cylindrical part 66 forms, with the outside wall 86 of the conical sleeve 40, a tapered medium vacuum chamber of 270 degrees which communicates with sleeve aperture 48 and with the relatively large channel 72. The medium vacuum chamber is tapered due to the disposition of the walls 84 and 86. With the high port nozzle in place, the tapered high vacuum chamber of 360 degrees is formed by the inner wall 90 of the sleeve 40 which is in communication with sleeve aperture 52 of 360 degrees and with the relatively large channel 76. From the foregoing, it can be seen that air entering the rather restricted sleeve apertures and narrow gap will immediately enter passages which are large both horizontally and vertically as shown in FIG. 7 by arrows 92 thus producing a high vacuum conductance which, with a gap less than used in the prior art, increases the vacuum within the sealing apparatus and permits smaller vacuum pumps to be used. It should be apparent that, while the prior art seal apparatus is higher, (about 1.2 inches) and wider (about 3.25 inches) than the seal apparatus of this invention (which is 0.5 inches high and 1.34 inches wide), each port and passageway of the seal apparatus of this invention is higher than the prior art seal apparatus because the ports and pathways of the prior art seal apparatus are vertically stacked and some of the height is taken up by the thickness of the nested upper and lower plate members. Also, while only three port nozzles R, M and H are shown as the preferred embodiment, more than three nozzles may be designed utilizing the teachings of this invention; the only limitation being the balance of the vacuum conductance obtainable and the size of the passageways and channels within a 360 degree structure. When there is shown or described what is presently considered the preferred embodiment of the invention, it will occur to those skilled in the art that various changes and modifications may be made therein without departing from the scope of the invention as defined in the appended claims.