| 主权项 |
1. A method of making axial alignment of a charged particle beam by a charged particle beam system having an astigmatic correction lens including a first pair of coils and a second pair of coils, the first pair of coils consisting of first and second coils which are located on opposite sides of the axis of the charged particle beam, the first and second coils having opposite coil surfaces having magnetic poles of a first polarity, the second pair of coils consisting of third and fourth coils which are located on opposite sides of the axis of the charged particle beam, the third and fourth coils having opposite coil surfaces having magnetic poles of a second polarity different from the first polarity, the second pair of coils being angularly spaced from the first pair of coils, said method comprising the steps of:
obtaining first to sixth sets of image data while varying currents flowing through the first to fourth coils according to first to sixth sets of conditions; and then calculating the values of the currents through the first to fourth coils for correcting the position of the axis of the charged particle beam passing through the astigmatic correction lens based on the first to sixth sets of image data, wherein electric current J flowing through each of the first to fourth coils is the sum I+i(J=I+i), where I is a first component of the current J for correcting astigmatism and i is a second component of the current J for correcting the position of the axis of the charged particle beam; wherein under the first set of conditions, the first components (I's) through the first to fourth coils are equal to each other and equal to a given current value I1, the second currents (i's) through the first and second coils, respectively, are current values +i1 and −i1, respectively, which are equal to each other in absolute value but opposite in sign, and the second currents (i's) through the third and fourth coils, respectively, are current values +i2 and −i2, respectively, which are equal to each other in absolute value but opposite in sign; wherein under the second set of conditions, the first components (I's) through the first to fourth coils are equal to each other and equal to a current value I2 different from the given current value, the second components (i's) through the first to fourth coils are current values +i1, −i1, +i2, and −i2, respectively, which are the same as the current values of the second components through the first to fourth coils, respectively, under the first set of conditions; wherein under the third set of conditions, the first components (I's) of the first to fourth coils are equal to the given current value I1 flowing under the first set of conditions, the second components (i's) through the first and second coils are current values +i1 and −i1, respectively, which are the same as the current values of the second components through the first and second coils, respectively, under the first set of conditions, and the second components (i's) through the third and fourth coils are current values +i1 and −i3, respectively, which are equal to each other in absolute value but opposite in sign and which are different in absolute value from the second component through the third coil under the first set of conditions; wherein under the fourth set of conditions, the first components (I's) through the first to fourth coils are current value I2 which is the same as the current value of the first component through the first coil under the second set of conditions, the second components (i's) through the first to fourth coils are current values +i1, −i1, +i3, and −i3, respectively, which are the same as the current values of the second components through the first to fourth coils, respectively, under the third set of conditions; wherein under the fifth set of conditions, the first components (I's) through the first to fourth coils are the given current value I1 flowing under the first set of conditions, the second components (i's) through the first and second coils, respectively, are current values +i4 and −i4, respectively, which are equal to each other in absolute value but opposite in sign and which are different in absolute value from the second component through the first coil under the first set of conditions, the second components (i's) through the third and fourth coils, respectively, are current values +i2 and −i2, respectively, which are the same as the current values of the second components through the third and fourth coils, respectively, under the first set of conditions; and wherein under the sixth set of conditions, the first components (I's) through the first to fourth coils, respectively, are current value I2 identical with the current value of the first component through the first coil under the second set of conditions, the second components (i's) through the first to fourth coils, respectively, are current values +i4, −i4, +i2, and −i2, respectively, which are the same as the current values of the second components through the first to fourth coils, respectively, flowing under the fifth set of conditions, and adjusting the currents in the first to fourth coils to correspond to the calculated values. |
