Patent Number: 047926880
Section: claims

1. A differentially pumped seal apparatus for use in a particle beam lithography system comprising, vacuum pumping means,  a plurality of nozzles each including a cylindrical part of a sector of a cylinder with horizontal conical sleeves each with a centrally located aperture therein and each with a gas channel located radially in said cylindrical part,  said nozzles together forming a cylinder and said conical sleeves forming concentric apertures and with chambers having zones of vacuum with the highest vacuum zone being in the centermost nozzle when said channels of each said nozzles are connected to said vacuum pumping means.  vacuum pumping means,  a rough port nozzle including a first cylindrical part of a sector of a cylinder with a horizontal conical sleeve with a centrally located aperture therein and with a gas channel located radially in said first cylindrical part,  a medium port nozzle including a second cylindrical part as a sector of a cylinder with a conical sleeve and a centrally located aperture therein and with a gas channel located radially in said second cylindrical part, and  a high port nozzle including a third cylindrical part as a sector of a cylinder with a conical sleeve and a centrally located aperture therein and with a gas channel located radially in said third cylindrical part,  said rough port nozzle, medium port nozzle and said high port nozzle together forming a cylinder with chambers having zones of vacuum with the highest vacuum being in the high port nozzle when said channels of each said rough port, medium port and high port nozzles are connected to said vacuum pumping means.  the improvement comprising in combination,  a differentially pumped seal apparatus for forming a graded seal between said beam column workpiece,  said apparatus comprising  a rough port nozzle configured as a sector of a cylinder and a rough vacuum pump, said rough port nozzle defining a sleeve with a rough vacuum chamber, said rough vacuum chamber being connected to said rough vacuum pump for producing a first vacuum area of a selected size on said workpiece when said workpiece is brought in close proximity with said apparatus, said rough vacuum chamber being connected to said rough vacuum pump by a channel formed in the wall of said rough vacuum chamber,  a medium port nozzle configured as a sector of a cylinder and a medium vacuum pump, said medium port nozzle defining a sleeve with a medium vacuum chamber, said medium vacuum chamber being connected to said medium vacuum pump for producing a second vacuum area of a selected size on said workpiece within said first vacuum area when said workpiece is brought in close proximity with said apparatus, said medium vacuum chamber being connected to said medium vacuum pump by a channel formed in the wall of said medium vacuum chamber,  a high port nozzle configured as a sector of a cylinder, said high port nozzle defining a sleeve with a high vacuum chamber, said high vacuum chamber being connected to said high vacuum pump for producing a third vacuum area of a selected size on said workpiece within said second vacuum area when said workpiece is brought in close proximity with said apparatus, said high vacuum channel being connected to said high vacuum pump by a channel formed in the wall of said high vacuum chamber,  said rough, medium and high port nozzles together forming a cylinder with three depending sleeves which form said first, second and third vacuum areas with the the third vacuum area being of highest vacuum, the second vacuum area surrounding said third vacuum area being of lesser vacuum and the first vacuum area surrounding both said second and third vacuum areas being of the lowest vacuum so that only that portion of the workpiece proximate said apparatus is subject to vacuum while the rest of the workpiece is at ambient pressure. 2. The seal apparatus as claimed in claim 1 having a high conductance wherein said chambers provide a rapid increase in volume immediately behind said apertures for the air entering said apertures and subjected to said vacuum means. 3. The seal apparatus as claimed in claim 2 wherein said plurality of nozzles comprise a rough port nozzle of 180 degrees of said cylinder, a medium port nozzle of 90 degrees of said cylinder and a high port nozzle of 90 degrees of said cylinder. 4. A differentially pumped seal apparatus for use in a particle beam lithography system comprising, 5. In a particle beam lithography system which includes at least a beam column, a stage movable in an X-Y plane for supporting a workpiece thereon, said stage being positioned so as to be impinged upon by said particle beam to form selected patterns on said workpiece surface and further including a high vacuum pump for maintaining high vacuum in said beam column for proper formation and operation of said particle beam,