Patent Number: 
Section: claims

1. A writing apparatus comprising:a selector unit responsive to receipt of input data of a pattern to be written by shots of irradiation of an electron beam, configured to select a current density of the electron beam being shot and a maximal shot size thereof based on the input data of the pattern to be written; and a writing unit configured to create an electron beam with the current density selected by said selector unit, shape the created electron beam into a shot size less than or equal to said maximal shot size in units of the shots, and shoot the shaped electron beam onto a workpiece to thereby write said pattern, wherein said selector unit is configured to select the current density and the maximal shot size in such a way that, even upon input of different pattern data, a beam current value for shooting onto the workpiece the electron beam as shaped to have its size being less than or equal to the maximal shot size is less than or equal to a preset value. 2. A writing apparatus, comprising:a selector unit responsive to receipt of input data of a pattern to be written by shots of irradiation of an electron beam, configured to select a current density of the electron beam being shot and a maximal shot size thereof based on the input data of the pattern to be written; anda writing unit configured to create an electron beam with the current density selected by said selector unit, shape the created electron beam into a shot size less than or equal to said maximal shot size in units of the shots, and shoot the shaped electron beam onto a workpiece to thereby write said pattern,wherein said selector unit is configured to select the current density and the maximal shot size so that a beam current value for writing become less than or equal to a beam current value to be set in accordance with the input data of the pattern to be written. 3. The apparatus according to claim 1, wherein said workpiece has a surface as virtually divided into a plurality of pattern-writing regions and wherein said selector unit is configured to select the current density and the maximal shot size in units of the regions. 4. The apparatus according to claim 3, wherein said selector units is configured to select the current density and the maximal shot size so that a beam current value for writing become less than or equal to a beam current value to be set in units of said regions. 5. The apparatus according to claim 1, wherein when a plurality of patterns are written on the workpiece, said selector unit is configured to select the current density and the maximal shot size on a per-pattern basis. 6. The apparatus according to claim 5, wherein said selector unit is configured to select the current density and the maximal shot size so that a beam current value for writing is less than or equal to a beam current value to be set per pattern. 7. A writing method comprising:analyzing a value of a writing time pursuant to a pattern data while using as variables a current density and a maximal shot size being in a relationship that a beam current value is less than or equal to a preset value;selecting, based on a result of said analyzing, a current density and a maximal shot size so as to be in a vicinity of a point of inflexion at which the writing time value changes in concavity; andshooting an electron beam onto a workpiece with the selected current density and a shot size less than or equal to said maximal shot size to thereby write thereon a pattern pursuant to said pattern data. 8. The method according to claim 7, wherein said beam current value is set based on the pattern data. 9. The method according to claim 7, wherein said beam current value is set based on an accuracy level as required for a pattern to be written. 10. The method according to claim 7, wherein said workpiece has a surface virtually divided into a plurality of pattern-writing regions and wherein said beam current value is determined in units of the regions. 11. The method according to claim 7, wherein when a plurality of patterns are written, said beam current value is set in units of the patterns. 12. A writing apparatus comprising:a selector unit responsive to receipt of input data of a pattern to be written through more than two electron beam shots, configured to select a current density of an electron beam being shot and a maximal shot area thereof based on the inputted data of the pattern to be written; and a writing unit configured to form the electron beam with the current density as selected by said selector unit, shape the formed electron beam to have a shot area less than or equal to said maximal shot area, and shoot the shaped electron beam onto a workpiece to thereby write said pattern,wherein said selector unit is configured to select the current density and the maximal shot area in a way such that, even when inputting different pattern data, a beam current value for shooting onto a workpiece the electron beam as shaped to have its area less than or equal to the maximal shot area is less than or equal to a preset value. 13. A writing apparatus, comprising:a selector unit responsive to receipt of input data of a pattern to be written through more than two electron beam shots, configured to select a current density of an electron beam being shot and a maximal shot area thereof based on the inputted data of the pattern to be written; and a writing unit configured to form the electron beam with the current density as selected by said selector unit, shape the formed electron beam to have a shot area less than or equal to said maximal shot area, and shoot the shared electron beam onto a workpiece to thereby write said pattern,wherein said selector unit is configured to select the current density and the maximal shot area so that a beam current value for writing is not greater than a beam current value to be set pursuant to the inputted data of the pattern to be written. 14. The apparatus according to claim 12, wherein said workpiece has a surface as virtually divided into a plurality of regions and wherein said selector unit is configured to select the current density and the maximal shot area in units of said regions. 15. The apparatus according to claim 14, wherein said selector unit is configured to select the current density and the maximal shot area so that a beam current value for writing is not greater than a beam current value as set in units of said regions. 16. The apparatus according to claim 12, wherein when more than two patterns are written onto said workpiece, said selector unit is configured to select the current density and the maximal shot area on a per-pattern basis. 17. The apparatus according to claim 16, wherein said selector unit is configured to select the current density and the maximal shot area so that a beam current value for writing is less than or equal to a beam current value to be set per pattern. 18. An apparatus for writing a prespecified pattern on a workpiece through more than two shots of an electron beam, comprising:means for variably shaping shot size of a shot; andmeans for varying a current density in accordance with each shot size so that a current value of a beam being shot onto the workpiece is less than or equal to a value as preset in each shot. 19. The apparatus according to claim 2, wherein said workpiece has a surface as virtually divided into a plurality of pattern-writing regions and wherein said selector unit is configured to select the current density and the maximal shot size in units of the regions. 20. The apparatus according to claim 19, wherein said selector units is configured to select the current density and the maximal shot size so that a beam current value for writing become less than or equal to a beam current value to be set in units of said regions. 21. The apparatus according to claim 2, wherein when a plurality of patterns are written on the workpiece, said selector unit is configured to select the current density and the maximal shot size on a per-pattern basis. 22. The apparatus according to claim 21, wherein said selector unit is configured to select the current density and the maximal shot size so that a beam current value for writing is less than or equal to a beam current value to be set per pattern. 23. The apparatus according to claim 13, wherein said workpiece has a surface as virtually divided into a plurality of regions and wherein said selector unit is configured to select the current density and the maximal shot area in units of said regions. 24. The apparatus according to claim 23, wherein said selector unit is configured to select the current density and the maximal shot area so that a beam current value for writing is not greater than a beam current value as set in units of said regions. 25. The apparatus according to claim 13, wherein when more than two patterns are written onto said workpiece, said selector unit is configured to select the current density and the maximal shot area on a per-pattern basis. 26. The apparatus according to claim 25, wherein said selector unit is configured to select the current density and the maximal shot area so that a beam current value for writing is less than or equal to a beam current value to be set per pattern.