Wafer alignment method for dual beam system
A gradient charged particle beam apparatus capable of moving highly accurately to a specific position by eliminating influences of warp inside a wafer surface is provided. A portion 46 having a mark 47 for aligning visual field alignment positioned in advance to the same horizontal and the same height as a stage plane as a reference point is arranged on a wafer holder. A height of an observation point on a sample is adjusted to the height of the mark 47 and the visual field of a gradient column is brought into conformity with the visual field of a vertical column by use of a known offset between the gradient column and the vertical column at that time.
1. An alignment method in a charged particle beam apparatus including a stage capable of moving inside an XY plane and in a Z axis direction perpendicular to said XY plane while holding a sample, a first column having an optical axis parallel to said Z axis and a second column having an optical axis inclined to said Z axis, said method comprising steps of:
moving said stage inside the XY plane and positioning a first known mark on a sample to the visual field center of said first column;
moving said stage by an offset between the visual field of said first column and the visual field of said second column;
observing said first known mark by said second column and determining a deviation amount from the visual field center;
determining a height deviation of the sample from a reference height on the basis of said deviation amount;
moving said stage by the height deviation in the Z axis direction and adjusting a sample surface provided with said first known mark to said reference height and determining a position of said first known mark;
moving said stage inside the XY plane while fixing in said Z direction and positioning to a second known mark on the sample; and
determining a position of the second known mark by said second column and achieving Die alignment.
2. An alignment method as defined in claim 1 , further comprising steps of:
moving said stage inside the XY plane while fixing in said Z direction and positioning to a third known mark on the sample; and
determining a position of the third known mark by said second column and achieving Die alignment.
3. An alignment method as defined in claim 2 , further comprising steps of:
moving said stage inside the XY plane while fixing in said Z direction and positioning to a fourth known mark on the sample; and
determining a position of the fourth known mark by said second column and achieving Die alignment.
4. An alignment method as defined in claim 1 , wherein said first column is a scanning electron microscope and said second column is a focused ion beam apparatus.
5. An alignment method in a charged particle beam apparatus including a stage capable of moving inside an XY plane and in a Z axis direction perpendicular to said XY plane while holding a sample, an optical microscope having an optical axis parallel to said Z axis, a first column having an optical axis inclined at 45° with respect to said Z axis inside a YZ plane and a second column having an optical axis inclined at 45° with respect to said Z axis inside an XZ plane, said method comprising steps of:
moving said stage inside the XY plane and positioning a first known mark on a sample to the visual field center of said optical microscope;
moving said stage by a difference between the stage coordinates of said first known mark by said optical microscope and the stage coordinates of said first known mark by said first column;
observing said first known mark by said first column and calculating a deviation amount ΔY from the visual field center in the Y direction;
moving said stage by −√2·ΔY in the Z axis direction and adjusting the sample surface on which said first known mark is disposed to a reference height and determining a position of said first known mark;
moving said stage inside the XY plane while fixing in said Z direction and positioning to a second known mark on the sample; and
determining a position of the first known mark by said first column and achieving Die alignment.
6. An alignment method as defined in claim 5 , further comprising steps of:
moving said stage inside the XY plane while fixing in said Z direction and positioning to a third known mark on the sample; and
determining a position of the third known mark by said second column and achieving Die alignment.
7. An alignment method as defined in claim 5 , further comprising the steps of:
moving said stage inside the XY plane while fixing in said Z direction and positioning to a fourth known mark on the sample; and
determining a position of the fourth known mark by said second column and achieving Die alignment.
8. An alignment method as defined in claim 5 , wherein said first column is a scanning electron microscope and said second column is a focused ion beam apparatus.