Patent Number: 
Section: claims

1. A multi charged particle beam writing method comprising:converting, for each shot of beams of multiple charged particle beams, a respective first gray scale value of each beam of the multiple charged particle beams, which is obtained by dividing an individual irradiation time period of the each beam by a quantization unit, into respective data of binary numbers of a predetermined digit number set in advance;dividing a maximum irradiation time period per shot of beams of the multiple charged particle beams into a plurality, being the predetermined digit number, of first irradiation time periods, each of which is calculated by multiplying a corresponding second gray scale value of a plurality of second gray scale values by the quantization unit, where the plurality of second gray scale values are gray scale values defined in decimal numbers converted from each digit value of data of binary numbers of the predetermined digit number;dividing a plurality of second irradiation time periods, which are a part of the plurality of first irradiation time periods into a plurality of third irradiation time periods;dividing irradiation of each beam of the multiple charged particle beams by using the plurality of third irradiation time periods and remaining undivided plurality of first irradiation time periods, into first irradiation steps which are irradiation steps of the plurality of third irradiation time periods and second irradiation steps which are irradiation steps of the remaining undivided plurality of first irradiation time periods; andirradiating, for each group of a plurality of groups in the each shot of beams, a target object, in order, with the multiple charged particle beams such that the plurality of groups are respectively composed of combination of at least two irradiation steps of first irradiation steps and second irradiation steps and the plurality of groups continue in order. 2. The method according to claim 1, wherein “b” number of the plurality of second irradiation time periods corresponding to a reference irradiation time T′ that satisfies an equation (3) and an equation (4) are divided, where a combination number “m” of the at least two irradiation steps, a digit number “n” being the predetermined digit number, a quantization unit Δ, and a first irradiation time period Ti of an i-th digit of data of binary numbers in “n” number of the plurality of first irradiation time periods are used in the equation (3) and the equation (4), anda number of irradiation time periods is increased from the digit number “n” by a number “a” corresponding to the reference irradiation time T′ that satisfies the equation (3) and the equation (4), by dividing the plurality of second irradiation time periods.                              T          ′                =                                            (                                                2                  n                                -                1                            )                                                      (                                  n                  +                  a                                )                            /              m                                ⁢          Δ                                    (        3        )                                          T          ′                >                                            ∑              i                              Ti                >                                  T                  ′                                                      ⁢                                                  ⁢            Ti                                a            +            b                                              (        4        )             3. The method according to claim 2, wherein, in the plurality of first irradiation time periods, a number of first irradiation time periods Ti being greater than the reference irradiation time period T′ are defined as “b” number of the plurality of second irradiation time periods, and the “b” number of the plurality of second irradiation time periods are divided into the plurality of third irradiation time periods so that the number of irradiation time periods is increased from the “n” number of the plurality of first irradiation time periods by the number “a”, andeach first irradiation step of the plurality of third irradiation time periods and each second irradiation step of remaining undivided plurality of first irradiation time periods are assigned to one of the plurality of groups so that a total irradiation time of each group is closer to the reference irradiation time T′. 4. The method according to claim 3, wherein the irradiation of the beam concerned is divided into respective irradiation steps of a plurality of irradiation time periods that configure the plurality of groups where a part of irradiation time periods of the at least two irradiation steps that configure at least one group of the plurality of groups is divided into a plurality of fourth irradiation time periods, and a part of the plurality of fourth irradiation time periods is assigned to other group. 5. The method according to claim 1, further comprising:setting an initial value for a combination number “m” and an irradiation time increased number “a” which indicates that “n” plurality of irradiation time periods is increased by “a”, where “n” is a digit number; andcalculating a reference irradiation time T′ by solving a following equation (3) using the combination number “m”, the digit number “n”, the number “a” and a quantization unit Δ.                              T          ′                =                                            (                                                2                  n                                -                1                            )                                                      (                                  n                  +                  a                                )                            /              m                                ⁢          Δ                                    (        3        )             6. The method according to claim 5, further comprising:determining whether a calculated reference irradiation time T′ satisfies a following equation (4) by using the number “a”, a first irradiation time Ti of an i-th digit of binary numbers in “n” number of the plurality of first irradiation time periods, where “n” is the digit number, and number “b” indicating a partial number of irradiation time periods to be divided, in the “n” number of the plurality of first irradiation time periods.                              T          ′                >                                            ∑              i                              Ti                >                                  T                  ′                                                      ⁢                                                  ⁢            Ti                                a            +            b                                              (        4        )             7. The method according to claim 6, further comprising:changing the number “a” when the reference irradiation time T′ does not satisfy the equation (4); andcalculating the reference irradiation time T′ again using a changed number “a”. 8. The method according to claim 6, further comprising:dividing “b” number of the plurality of second irradiation time periods Ti, each of which is greater than the reference irradiation time T′, in the “n” number of the plurality of first irradiation time periods, “n” being the digit number, into the plurality of third irradiation time periods so that a number of irradiation time periods is increased from the plurality of first irradiation time periods by the number “a”. 9. A multi charged particle beam writing apparatus comprising:a stage configured to mount a target object thereon and to be continuously movable;an emission unit configured to emit a charged particle beam;an aperture member, in which a plurality of openings are formed, configured to form multiple beams by letting a region including a whole of the plurality of openings be irradiated with the charged particle beam and letting portions of the charged particle beam respectively pass through a corresponding opening of the plurality of openings;a plurality of blankers configured to respectively perform blanking deflection of a corresponding beam in the multiple beams having passed through the plurality of openings of the aperture member;a blanking aperture member configured to block each beam having been deflected to be in a beam-off state by the plurality of blankers; anda deflection control unit configured to control a corresponding blanker of the plurality of blankers such thata maximum irradiation time period per shot of beams of the multiple beams is divided into a plurality, being a predetermined digit number set in advance, of first irradiation time periods, each of which is calculated by multiplying a corresponding second gray scale value of a plurality of second gray scale values by a quantization unit, where the plurality of second gray scale values are gray scale values defined in decimal numbers converted from each digit value of data of binary numbers of the predetermined digit number,a plurality of second irradiation time periods, which are a part of the plurality of first irradiation time periods, are divided into a plurality of third irradiation time periods,irradiation of each beam of the multiple charged particle beams by using the plurality of third irradiation time periods and remaining undivided plurality of first irradiation time periods is divided into first irradiation steps of the plurality of third irradiation time periods and second irradiation steps of the remaining undivided plurality of first irradiation time periods, anda target object is irradiated, in order, with the multiple charged particle beams such that a plurality of groups are respectively composed of combination of at least two irradiation steps of the first irradiation steps and the second irradiation steps and the plurality of groups continue in order, for each group of a plurality of groups in the each shot of beams. 10. The apparatus according to claim 9, further comprising:a bit processing table generation unit configured to generate a bit processing table, which shows a relation between a place value “k” of bit data and an irradiation time corresponding to the place value “k”, by using the plurality of third irradiation time periods and the remaining undivided plurality of first irradiation time periods. 11. A multi charged particle beam writing apparatus comprising:a stage for mounting a target object thereon and being continuously movable;an emission means for emitting a charged particle beam;an aperture means, in which a plurality of openings are formed, for forming multiple beams by letting a region including a whole of the plurality of openings be irradiated with the charged particle beam and letting portions of the charged particle beam respectively pass through a corresponding opening of the plurality of openings;a plurality of blankers for respectively performing blanking deflection of a corresponding beam in the multiple beams having passed through the plurality of openings of the aperture member;a blanking aperture member for blocking each beam having been deflected to be in a beam-off state by the plurality of blankers; anda deflection control means for controlling a corresponding blanker of the plurality of blankers such thata maximum irradiation time period per shot of beams of the multiple beams is divided into a plurality, being a predetermined digit number set in advance, of first irradiation time periods, each of which is calculated by multiplying a corresponding second gray scale value of a plurality of second gray scale values by a quantization unit, where the plurality of second gray scale values are gray scale values defined in decimal numbers converted from each digit value of data of binary numbers of the predetermined digit number,a plurality of second irradiation time periods, which are a part of the plurality of first irradiation time periods, are divided into a plurality of third irradiation time periods,irradiation of each beam of the multiple charged particle beams by using the plurality of third irradiation time periods and remaining undivided plurality of first irradiation time periods is divided into first irradiation steps of the plurality of third irradiation time periods and second irradiation steps of the remaining undivided plurality of first irradiation time periods, anda target object is irradiated, in order, with the multiple charged particle beams such that a plurality of groups are respectively composed of combination of at least two irradiation steps of the first irradiation steps and the second irradiation steps and the plurality of groups continue in order, for each group of a plurality of groups in the each shot of beams.