JP2018026516A - Multi charged particle beam lithography apparatus and adjustment method thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To perform automatic adjustment of aberration of an optical system with high accuracy when irradiating a multi-beam.SOLUTION: A multi charged particle beam lithography apparatus includes an aperture member 8 for forming a multi-beam by passing a charged particle beam through multiple apertures 80, a blanking plate 10 where multiple blankers performing blanking deflection of corresponding beams, out of the multi-beam, are arranged, a limitation aperture member 14 for shielding each beam deflected to become beam OFF state by the multiple blankers, a stage 22 on which a substrate 24 irradiated with the multi-beam is placed, a detector 26 for detecting reflection charged particles from the substrate 24, a feature amount calculation unit 51 for calculating the feature amount of an aperture image based on the detection value of the detector 26, and an aberration correction unit 40 for correcting aberration of a charged particle beam based on the feature amount.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a multi-charged particle beam drawing apparatus and an adjustment method thereof.

  With the high integration of LSI, the circuit line width of a semiconductor device has been reduced year by year. In order to form a desired circuit pattern on a semiconductor device, a reduction projection type exposure apparatus is used to form a high-precision original pattern pattern formed on quartz (a mask, or a pattern used particularly in a stepper or scanner is also called a reticle). )) Is reduced and transferred onto the wafer. A high-precision original pattern is drawn by an electron beam drawing apparatus, and so-called electron beam lithography technology is used.

  For example, there is a drawing apparatus using a multi-beam. By using a multi-beam, it is possible to irradiate many beams at one time (one shot) as compared with the case of drawing with one electron beam, so that the throughput can be greatly improved. In a multi-beam type drawing apparatus, for example, an electron beam emitted from an electron gun is passed through an aperture member having a plurality of holes to form a multi-beam, and blanking control of each beam is performed by a blanking plate to block the beam. The beam that has not been reduced is reduced by an optical system and irradiated onto a substrate placed on a movable stage.

  In the aperture member forming the multi-beam, holes of vertical m rows × horizontal n rows (m, n ≧ 2) are formed in a matrix at a predetermined arrangement pitch. Therefore, the shape (aperture image) of the entire multi-beam irradiated on the substrate is ideally rectangular. However, due to the influence of the spherical aberration of the optical system provided in the drawing device, the four outer peripheral sides of the beam shape become a shape that bulges outward or a shape that is concave inward.

  It was difficult to automatically adjust the spherical aberration by evaluating such a unique beam shape.

JP 2006-210503 A JP 2015-167212 A JP 2014-229481 A JP 2008-153209 A JP-T-2006-510184 JP 2012-104426 A JP 2005-302359 A

  It is an object of the present invention to provide a multi-charged particle beam drawing apparatus and an adjustment method thereof that can automatically and accurately adjust aberrations of an optical system when irradiating multi-beams.

  A multi-charged particle beam drawing apparatus according to an aspect of the present invention includes a discharge unit that emits a charged particle beam and a plurality of openings, and the charged particle beam passes through the plurality of openings to generate a multi-beam. The aperture member to be formed, a blanking plate on which a plurality of blankers for performing blanking deflection of the corresponding beams among the multi-beams, and the plurality of blankers were deflected so as to be in a beam OFF state. A limiting aperture member that shields each beam, a stage on which the substrate to which the multi-beam is irradiated, a detector that detects reflected charged particles from the substrate, and an aperture image based on the detection value of the detector A feature amount calculation unit that calculates a feature amount; an aberration correction unit that corrects an aberration of the charged particle beam based on the feature amount; It is those with a.

  In the multi-charged particle beam drawing apparatus according to one aspect of the present invention, the feature amount calculation unit generates an approximate figure that approximates the aperture image, and the aperture located at least one of the inside and the outside of the approximate figure The feature amount is calculated from the area of the image, and the aberration correction unit corrects the spherical aberration of the charged particle beam based on the feature amount.

  In the multi-charged particle beam drawing apparatus according to an aspect of the present invention, the feature amount calculation unit generates an approximate quadrangle that approximates the aperture image, the longer one of the diagonal lines of the approximate quadrangle, and the aperture image A ratio with the outer peripheral length is calculated as the feature amount, and the aberration correction unit corrects the spherical aberration of the charged particle beam based on the feature amount.

  In the multi-charged particle beam drawing apparatus according to one aspect of the present invention, the feature amount calculation unit calculates a standard deviation of illuminance in the aperture image as the feature amount, and the aberration correction unit charges based on the feature amount. Correct spherical aberration of particle beam.

  In the multi-charged particle beam drawing apparatus according to one aspect of the present invention, the feature amount calculation unit generates an approximate rectangle that approximates the aperture image, and calculates variations in lengths of four sides of the approximate rectangle as a first feature amount. The aberration correction unit corrects multi-beam astigmatism based on the first feature amount.

  In the multi-charged particle beam drawing apparatus according to an aspect of the present invention, the feature amount calculation unit generates an approximate quadrangle that approximates the aperture image, and uses the squareness of four interior angles of the approximate quadrangle as a second feature amount. The aberration correction unit calculates and corrects multi-beam astigmatism based on the second feature amount.

  In the multi-charged particle beam drawing apparatus according to one aspect of the present invention, the feature amount calculation unit generates an approximate rectangle that approximates the aperture image, and calculates variations in lengths of four sides of the approximate rectangle as a first feature amount. Then, the squareness of the four inner angles of the approximate quadrangle is calculated as a second feature amount, and the aberration correction unit corrects multi-beam astigmatism based on the first feature amount and the second feature amount. To do.

  An adjustment method of a multi-charged particle beam drawing apparatus according to an aspect of the present invention includes a step of emitting a charged particle beam, a step of forming the multi-beam by passing the charged particle beam through a plurality of openings of an aperture member, Irradiating the substrate placed on the stage with the multi-beam, detecting the reflected charged particles from the substrate, calculating the feature value of the aperture image based on the detected reflected charged particles, Correcting the aberration of the charged particle beam based on the feature amount.

  The adjustment method of the multi charged particle beam drawing apparatus according to one aspect of the present invention corrects the spherical aberration of the charged particle beam based on the feature amount.

  An adjustment method of a multi-charged particle beam drawing apparatus according to an aspect of the present invention generates an approximate quadrangle that approximates the aperture image, a first feature amount indicating variation in length of four sides of the approximate quadrangle, and the approximate quadrangle. And calculating the astigmatism of the multi-beam based on the first feature value and / or the second feature value, and calculating at least one of the second feature value indicating the squareness of the four interior angles. .

  According to the present invention, the aberration of the optical system when irradiating a multi-beam can be automatically adjusted with high accuracy.

1 is a schematic view of a multi-charged particle beam drawing apparatus according to an embodiment of the present invention. It is the schematic of an aperture member. (A)-(c) is a figure which shows the example of an aperture image. (A)-(c) is a figure which shows the calculation method of the feature-value of an aperture image. It is a flowchart explaining the calculation method of the rectangle which approximates an aperture image. It is a figure explaining how to obtain an approximate rectangle. It is a figure explaining how to obtain an approximate rectangle. It is a figure explaining how to obtain an approximate rectangle. It is a figure explaining how to obtain an approximate rectangle. (A) (b) is a figure explaining how to obtain an approximate rectangle. (A) (b) is a figure explaining how to obtain an approximate rectangle. It is a graph which shows the example of the relationship between an aperture image area ratio and an aberration correction lens voltage. (A)-(c) is a figure which shows the calculation method of the feature-value of an aperture image by another embodiment. It is the schematic of the multi charged particle beam drawing apparatus by another embodiment. It is a figure which shows the example of the shape change of the aperture image accompanying the change of an astigmatism correction coil value. It is a figure explaining the calculation method of the feature-value of an aperture image. It is a figure which shows the example of the calculation result of a 1st feature-value. It is a figure which shows the example of the calculation result of a 2nd feature-value.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 is a schematic diagram of a multi-charged particle beam drawing apparatus according to an embodiment of the present invention. In this embodiment, a configuration using an electron beam will be described as an example of a charged particle beam. However, the charged particle beam is not limited to the electron beam, and may be another charged particle beam such as an ion beam.

  The drawing apparatus includes a drawing unit W that draws a desired pattern by irradiating a substrate 24 to be drawn with an electron beam, and a control unit C that controls the operation of the drawing unit W.

  The drawing unit W includes an electron beam column 2 and a drawing chamber 20. In the electron beam column 2, there are an electron gun 4, an illumination lens 6, an aperture member 8, a blanking aperture array 10, a reduction lens 12, an alignment coil 13, a limiting aperture member 14, an objective lens 16, a deflector 18, and aberrations. A correction lens 40 is disposed.

  The aberration correction lens 40 is provided between the illumination lens 6 and the aperture member 8, and for example, a foil lens is used.

  An XY stage 22 and a detector 26 are arranged in the drawing chamber 20. A substrate 24 to be drawn is placed on the XY stage 22. The drawing target substrate 24 is, for example, a wafer, an exposure mask for transferring a pattern using a reduction projection type exposure apparatus such as a stepper or a scanner using an excimer laser as a light source, or an extreme ultraviolet exposure apparatus (EUV). included.

  The electron beam 30 emitted from the electron gun 4 illuminates the entire aperture member 8 almost vertically by the illumination lens 6. FIG. 2 is a conceptual diagram showing the configuration of the aperture member 8. In the aperture member 8, vertical (y direction) m rows × horizontal (x direction) n rows (m, n ≧ 2) holes (openings) 80 are formed in a matrix at a predetermined arrangement pitch. For example, 512 rows × 512 rows of holes 80 are formed. Each hole 80 is formed of a rectangle having the same size and shape. Each hole 80 may be a circle having the same diameter.

  The electron beam 30 illuminates the area containing all the holes 80 of the aperture member 8. As part of the electron beam 30 passes through the plurality of holes 80, multi-beams 30a to 30e as shown in FIG. 1 are formed.

  The arrangement of the holes 80 is not limited to the case where the vertical and horizontal directions are arranged in a lattice pattern as shown in FIG. For example, the holes adjacent in the vertical direction may be alternately arranged in a staggered manner.

  In the blanking aperture array 10, through holes are formed in accordance with the arrangement positions of the respective holes 80 of the aperture member 8, and blankers composed of two pairs of electrodes are arranged in the respective through holes. The electron beams 30a to 30e passing through the through holes are independently deflected by a voltage applied by the blanker. Each beam is blanked by this deflection. In this way, blanking deflection is performed by the blanking aperture array 10 on each of the multi-beams that have passed through the plurality of holes 80 of the aperture member 8.

  The multi-beams 30 a to 30 e that have passed through the blanking aperture array 10 are reduced in size and arrangement pitch by the reduction lens 12 and proceed toward the central hole formed in the limiting aperture member 14. The alignment coil 13 adjusts the optical axis so that the multibeam passes through the center of the hole of the limiting aperture member 14.

  The trajectory of the electron beam deflected by the blanker of the blanking aperture array 10 is displaced, the position of the electron beam is displaced from the hole of the limiting aperture member 14, and the electron beam is blocked by the limiting aperture member 14. On the other hand, the electron beam that has not been deflected by the blanker of the blanking aperture array 10 passes through the hole of the limiting aperture member 14.

  Thus, the limiting aperture member 14 shields each beam deflected so as to be in a beam OFF state by the electrode of the blanking aperture array 10. Then, the beam that has passed through the limiting aperture member 14 from when the beam is turned on to when the beam is turned off becomes a shot beam for one shot.

  The multi-beams 30a to 30e that have passed through the limiting aperture member 14 are focused by the objective lens 16 and become a pattern image having a desired reduction ratio. The beams (entire multi-beams) that have passed through the limiting aperture member 14 are deflected together in the same direction by the deflector 18 and irradiated onto the substrate 24. The detector 26 detects reflected electrons (secondary electrons) from the substrate 24.

  The multi-beams irradiated at a time are ideally arranged at a pitch obtained by multiplying the arrangement pitch of the plurality of holes 80 of the aperture member 8 by the desired reduction ratio described above. This drawing apparatus performs a drawing operation by a raster scan method in which shot beams are continuously irradiated in order, and when drawing a desired pattern, the necessary beam is controlled to be ON by blanking control according to the pattern. The When the XY stage 22 is continuously moving, the beam irradiation position is controlled by the deflector 18 so as to follow the movement of the XY stage 22.

  The control unit C includes a control computer 50, a storage device 52, a lens control circuit 54, a control circuit 56, and a signal acquisition circuit 58. The control computer 50 acquires drawing data from the storage device 52, performs a plurality of stages of data conversion processing on the drawing data, generates apparatus-specific shot data, and outputs the shot data to the control circuit 56. In the shot data, the irradiation amount and irradiation position coordinates of each shot are defined.

  The control circuit 56 controls each part of the drawing unit W to perform drawing processing. For example, the control circuit 56 calculates the irradiation time t by dividing the irradiation amount of each shot by the current density, and when the corresponding shot is performed, the control circuit 56 corresponds to the blanking aperture array 10 so that the beam is turned on only for the irradiation time t. A deflection voltage is applied to the blanker.

  Further, the control circuit 56 calculates the deflection amount so that each beam is deflected to the position (coordinates) indicated by the shot data, and applies the deflection voltage to the deflector 18. Thereby, the multi-beams shot at that time are deflected together.

  The multi-beam formed through the plurality of holes 80 of the aperture member 8 is irradiated onto the substrate 24. As described above, the aperture member 8 has holes 80 in the vertical (y direction) m rows × horizontal (x direction) n rows (m, n ≧ 2). Therefore, an image showing the shape of the entire multi-beam irradiated on the substrate 24 (hereinafter sometimes simply referred to as “aperture image”) is ideally like a multi-beam B1 shown in FIG. It becomes a rectangle (substantially a rectangle).

  However, in the multi-beam drawing apparatus, the aperture image is distorted due to the spherical aberration of the lens, and has a barrel shape in which the four sides of the outer periphery of the aperture image bulge outward as a beam B2 shown in FIG. Or a pincushion type shape in which the four sides of the outer periphery are recessed inward as in the beam B3 shown in FIG.

  In the present embodiment, a feature amount representing the feature of the aperture image is calculated, and the spherical aberration is adjusted based on the calculated feature amount. The control computer 50 obtains an aperture image based on the detection value of the detector 26 acquired through the signal acquisition circuit 58. The feature amount calculator 51 calculates the feature amount of the aperture image. The lens control circuit 54 controls the voltage applied to the aberration correction lens 40 based on the calculated feature amount, corrects the spherical aberration, and adjusts the aperture image to have a desired shape (rectangle).

  The feature amount calculation unit 51 generates a quadrangle that approximates the obtained aperture image, and among the aperture images, the area located inside the approximate rectangle, the area located outside the approximate rectangle, the inside of the approximate rectangle, and the aperture image The area etc. of the area | region which becomes outside is calculated | required, and these ratios are calculated as a feature-value.

  For example, as shown in FIG. 4A, in the substantially square beam B1, most of the aperture image is located inside the approximate rectangle R, and the area 61 located outside the approximate rectangle R is small. Further, there is no or almost no area inside the approximate rectangle R and outside the aperture image.

  As shown in FIG. 4 (b), the barrel beam B2 has many aperture images located inside the approximate rectangle R, like the substantially square beam B1 shown in FIG. The area of the region 62 located outside is larger than the area of the region 61 in FIG. There is no or almost no area inside the approximate rectangle R and outside the aperture image.

  As shown in FIG. 4C, in the pin cushion type beam B3, the area of the region 60 which is inside the approximate square R and outside the aperture image is larger than the substantially square beam B1 or the barrel type beam B2. The area of the aperture image located outside the approximate rectangle R is extremely small.

  As described above, in the substantially quadrangular beam B1, which is an ideal beam shape, the area 61 located outside the approximate quadrangle R is small, and the area inside the approximate quadrangle R and outside the aperture image is zero or zero. almost none. Therefore, the lens control circuit 54 corrects the aberration so that the area of the region located outside the approximate rectangle R is within the predetermined range, and the region inside the approximate rectangle R and outside the aperture image is equal to or less than the predetermined value. The voltage applied to the lens 40 is controlled to correct spherical aberration.

  Next, a calculation method of the rectangle R that approximates the aperture image will be described using the flowchart shown in FIG. The approximate rectangle R is determined by calculating four vertices.

  When the aperture image is obtained based on the detection value of the detector 26 acquired via the signal acquisition circuit 58, the feature amount calculation unit 51 has a point where the X coordinate and the Y coordinate on the contour of the aperture image are maximized, And the point which becomes the minimum is extracted. A point where the X coordinate is maximum is Xmax, a point where the X coordinate is minimum is Xmin, a point where the Y coordinate is maximum is Ymax, and a point where the Y coordinate is minimum is Ymin. When Xmax, Xmin, Ymax, and Ymin are uniquely determined (step S1_Yes), the interval between the extracted points is calculated (step S2).

  When all the calculated intervals are equal to or larger than the predetermined value (step S3_Yes), as shown in FIG. 6, Xmax, Xmin, Ymax, and Ymin can each be a vertex of a quadrangle that approximates the aperture image B10. Is determined (step S4).

  When the calculated interval is less than a predetermined value (for example, the length of one tenth of one side of the assumed rectangle) (step S3_No), two points that are less than the predetermined value are regarded as the same point. Consider it (step S5). For example, the interval between Xmax and Ymax shown in FIG. 7 is less than a predetermined value, and Xmax and Ymax correspond to the same vertex of a rectangle that approximates the aperture image B11. Since the two points are regarded as the same point, the number of vertices (= 4) necessary to determine the approximate quadrangle is insufficient, and the process proceeds to step S20. The processing after step S20 will be described later.

  Depending on the aperture image, Xmax, Xmin, Ymax, and Ymin may not be uniquely determined (step S1_No). For example, Xmin is not uniquely determined in the aperture image B12 shown in FIG.

  When Xmax or Xmin is not uniquely determined (step S10_Yes), a point with the maximum Y coordinate and a point with the minimum Y coordinate are extracted from a plurality of candidates (step S11). For example, in the example shown in FIG. 8, Xmin is not uniquely determined. Therefore, as shown in FIG. 9, a point Xmin_ymax where the Y coordinate is maximum and a point Xmin_ymin where the Y coordinate is minimum are selected from the candidates for Xmin. Extract

  Similarly, when Ymax or Ymin is not uniquely determined (step S12_Yes), a point with the maximum X coordinate and a point with the minimum X coordinate are extracted from a plurality of candidates (step S13).

  Next, one unselected point is selected from a plurality of extracted points on the contour of the aperture image (step S14). Then, the distance from the selected point to another extracted point is calculated (step S15). If the calculated distance is less than the predetermined value (step S16_Yes), one of the two points having the distance less than the predetermined value is deleted (step S17). If there is an unselected point (step S18_Yes), the process returns to step S14. The same processing is performed for all extracted points on the contour of the aperture image. When the number of extraction points remaining after the processing of steps S14 to S18 is four (step S19_Yes), the aperture image can be used as the approximate vertex of the quadrangle, and the approximate quadrangle is determined (step S4).

  For example, in the example shown in FIG. 9, since the distance from Ymax to Xmin_ymax is less than a predetermined value, one of them is deleted. As a result, four points Xmax, Xmin_ymin, Ymax (or Xmin_ymax), and Ymin remain on the contour of the aperture image B12, and an approximate quadrangle having these as vertices is determined.

  In step S17, instead of deleting one of the two points having a distance less than the predetermined value, an intermediate point on the outline of these two points may be newly extracted to delete the two points. For example, in the example shown in FIG. 9, an intermediate point between Ymax and Xmin_ymax on the contour of the aperture image B12 may be newly extracted to delete Ymax and Xmin_ymax.

  Depending on the aperture image, the number of remaining extracted points is 3 or less due to the point erasure in step S17 (step S19_No). For example, when the processes in steps S14 to S18 are performed on the aperture image B13 illustrated in FIG. 10A, Ymin and Xmin_ymin are combined into one point. Xmax and Ymax are combined into one point. Therefore, only three vertices of points P1, P2, and P3 remain as shown in FIG.

  In such a case, first, a straight line connecting the remaining vertices is drawn (step S20). For example, as shown in FIG. 11A, a straight line L1 passing through the points P2 and P3, a straight line L2 passing through the points P1 and P3, and a straight line L3 passing through the points P1 and P2 are drawn.

  Subsequently, the shortest distance from the point on the contour of the aperture image to the straight line drawn in step S20 is obtained. When a plurality of straight lines are drawn, the shortest distance among the shortest distances to each straight line is obtained. Then, the point where the shortest distance is maximum is regarded as a vertex (step S21). Steps S20 and S21 are repeated until the number of vertices reaches four. When the number of vertices becomes four (step S22_Yes), the aperture image can be made a quadrangular vertex that approximates the aperture image, and the approximate quadrilateral is determined (step S4).

  For example, the shortest distance to the straight lines L1, L2, and L3 shown in FIG. 11A is the maximum at the point P4 shown in FIG. 11B. A quadrangle whose vertices are points P1, P2, P3, and P4 is a quadrangle that approximates the aperture image B13.

  In this way, a quadrangle that approximates the aperture image is calculated, and the area of the aperture image located outside the approximate quadrangle and the area of the region inside the approximate quadrangle and outside the aperture image are obtained, and the aberration correction lens 40 is obtained. Is applied to control the spherical aberration.

  For example, the relationship between the ratio of the area of the aperture image located outside the approximate rectangle to the total area of the aperture image and the voltage applied to the aberration correction lens 40 tends to be as shown in FIG. Therefore, the lens control circuit 54 controls the voltage applied to the aberration correction lens 40 so that the area ratio becomes a desired value. Thereby, the spherical aberration can be automatically adjusted so that the aperture image becomes a square (substantially square). Note that the area ratio to be adjusted is determined separately based on drawing accuracy and the like. Further, since the area ratio increases as the applied voltage increases, it can be adjusted by binary search during automatic adjustment.

  As described above, according to the present embodiment, the feature amount of the aperture image is calculated using the approximate quadrature of the aperture image (beam shape), and the multi-beam is irradiated to adjust the spherical aberration based on the feature amount. The spherical aberration of the optical system can be automatically adjusted with high accuracy.

  In the above embodiment, the feature amount is the area located outside the approximate quadrangle of the aperture image, but the feature amount is not limited to this. For example, the ratio of the length of the diagonal of the approximate rectangle to the outer periphery (contour) of the aperture image may be used as the feature amount.

  FIGS. 13A, 13B, and 13C show diagonal lines DL1 and DL2 of an approximate square R of a substantially square beam B1, a barrel beam B2, and a pincushion beam B3. The barrel type beam B2 and the pincushion type beam B3 have a smaller ratio of, for example, the longer diagonal length to the outer peripheral length compared to the substantially square beam B1. The lens control circuit 54 adjusts the spherical aberration by controlling the voltage applied to the aberration correction lens 40 so that this ratio becomes large (so that it becomes a predetermined value or more).

  The standard deviation of the brightness (illuminance) distribution in the aperture image may be used as the feature amount. For example, the substantially square beam has a substantially uniform brightness in the aperture image and a small standard deviation. The barrel beam is dark at the center and bright at the outer periphery, and has a large standard deviation. The pincushion beam is bright at the center and darker toward the outer periphery, and has a large standard deviation. The lens control circuit 54 adjusts the spherical aberration by controlling the voltage applied to the aberration correction lens 40 so that the standard deviation becomes small (below a predetermined value).

  The spherical aberration adjustment method according to the present embodiment can also be applied when the aperture image has a shape other than a square. For example, when the shape of the aperture image is a rectangle, the aperture image is deformed based on the ratio of the long side to the short side, and the spherical aberration is adjusted according to the above embodiment. Alternatively, the spherical aberration is adjusted so that the standard deviation of illuminance becomes small.

  When the shape of the aperture image is circular, adjustment is made so that the ratio of the diameter of the aperture image to the outer peripheral length becomes small. Alternatively, the spherical aberration is adjusted so that the standard deviation of illuminance becomes small.

  In the above-described embodiment, the configuration for correcting spherical aberration using the aberration correction lens 40 has been described. However, in addition to the foil lens, for example, a combination of a grating lens and a correction lens, or a multipole electromagnetic field is used as the aberration correction lens. An aberration corrector may be used. The aberration correction lens can reduce the spherical aberration component of the beam by generating an axially symmetric electric / magnetic field by an electrostatic lens or a coil.

  As shown in FIG. 2, the aperture members 8 forming the multi-beams are formed with a matrix of holes 80 of vertical m rows × horizontal n rows at a predetermined arrangement pitch. The approximate quadrangle of the aperture image is ideally a rectangle, particularly a square when m = n. However, due to astigmatism, the aperture image may be distorted and the shape of the approximate rectangle may not be a square. In order to make the aperture image easy to see, the focus may be appropriately shifted only during adjustment.

  Therefore, as shown in FIG. 14, the astigmatism adjustment coils 42 and 44 for correcting (adjusting) the astigmatism of the multi-beams, and the excitation value (astigmatism correction coil value) for exciting the astigmatism adjustment coils 42 and 44 are obtained. A coil control circuit 59 to be controlled may be provided to perform astigmatism adjustment. The astigmatism adjustment coils 42 and 44 perform astigmatism adjustment in the first axis direction and the second axis direction (for example, the x axis direction and the y axis direction) orthogonal to each other in the horizontal plane.

  As shown in FIG. 15, when the astigmatism correction coil values of the astigmatism adjustment coils 42 and 44 are changed, the shape of the approximate quadrangle of the aperture image changes.

  The feature amount calculation unit 51 calculates a feature amount indicating the degree of square of the approximate rectangle of the aperture image. The coil control circuit 59 controls the astigmatism correction coil values set in the astigmatism adjustment coils 42 and 44 based on the calculated feature amount, corrects astigmatism, and the shape of the approximate quadrangle of the aperture image is square. Adjust so that

  A method for calculating the feature amount indicating the square degree of the approximate quadrangle of the aperture image will be described. The feature amount calculation unit 51 calculates an approximate rectangle of the aperture image based on the detection value of the detector 26 by the method described in the above embodiment. A square is a figure having the same length on all four sides and the same four interior angles (all at right angles). Therefore, the feature amount calculation unit 51 calculates at least one of the first feature amount indicating variation in the lengths of the four sides of the approximate rectangle and the second feature amount indicating variations in the angles of the four interior angles of the approximate rectangle. calculate.

  For example, the feature quantity calculation unit 51 calculates the standard deviation (or variance) of the lengths H1, H2, H3, and H4 of the four sides of the approximate rectangle shown in FIG. 16 as the first feature quantity. The setting change of the astigmatism correction coil value and the calculation of the first feature value are repeated so that the first feature value becomes smaller. FIG. 17 is a graph showing the relationship between the astigmatism correction coil values set in the astigmatism adjustment coils 42 and 44 and the calculated first feature amount. By setting the astigmatism correction coil values set in the astigmatism adjustment coils 42 and 44 to the values indicated by the broken lines in FIG. 17, the lengths H1, H2, H3, and H4 of the four sides of the approximate quadrangle become substantially equal.

Further, for example, the feature quantity calculation unit 51 calculates the sum of squares of the inner products of the _four interior angles θ ₁ , θ ₂ , θ ₃ , and θ ₄ as the second feature quantity for the approximate rectangle shown in FIG. The inner product square sum is calculated using the following equation.
(Cos θ ₁ ) ² + (cos θ ₂ ) ² + (cos θ ₃ ) ² + (cos θ ₄ ) ²

This second feature value indicates the squareness of the four interior angles θ ₁ , θ ₂ , θ ₃ , and θ _{4. When} the approximate rectangle is a square, the second feature value is zero. The setting change of the astigmatism correction coil value and the calculation of the second feature value are repeated so that the second feature value becomes smaller. FIG. 18 is a graph showing the relationship between the astigmatism correction coil value set in the astigmatism adjustment coils 42 and 44 and the calculated second feature amount. The astigmatism correction coil values set in the astigmatism correction coils 42 and 44, by the value indicated by the broken line in FIG. 18, four interior angles _{θ 1, θ 2, θ 3} , θ 4 is substantially 90 ° Become.

  Astigmatism adjustment may be performed by controlling the astigmatism correction coil value using both the first feature quantity and the second feature quantity. In this case, it can be adjusted so that the second feature amount is decreased by changing the first axis, and the first feature amount is decreased by changing the second axis.

  When the shape of the approximate quadrangle of the ideal aperture image is a rectangle, the astigmatism correction coil value is controlled so that the above-described first feature value becomes a predetermined value based on the ratio of the long side to the short side. When the shape of the approximate rectangle is other than a rectangle, for example, when it is a circle, the astigmatism correction coil value may be adjusted based on the ratio between the diameter of the aperture image and the outer circumference length. do it. The optical system may be adjusted so that the standard deviation (dispersion) of the illuminance of the aperture image is small.

  Instead of the aperture member 8 and the blanking aperture array 10, astigmatism adjustment may be performed by installing an adjustment plate provided with an opening. In this case, a feature amount corresponding to the opening provided in the adjustment plate is selected.

  Each function of the control computer 50 including the feature amount calculation unit 51 may be configured by hardware or software. When configured by software, a program for realizing at least a part of the functions of the control computer 50 may be stored in a recording medium such as a CD-ROM and read and executed by a computer. The recording medium is not limited to a removable medium such as a magnetic disk or an optical disk, but may be a fixed recording medium such as a hard disk device or a memory.

  Note that the present invention is not limited to the above-described embodiment as it is, and can be embodied by modifying the constituent elements without departing from the scope of the invention in the implementation stage. In addition, various inventions can be formed by appropriately combining a plurality of components disclosed in the embodiment. For example, some components may be deleted from all the components shown in the embodiment. Furthermore, constituent elements over different embodiments may be appropriately combined.

2 Electron beam column 4 Electron gun 6 Illumination lens 8 Aperture member 10 Blanking aperture array 12 Reduction lens 13 Alignment coil 14 Restriction aperture member 16 Objective lens 18 Deflector 20 Drawing chamber 22 XY stage 26 Detector 40 Aberration correction lens 42, 44 Astigmatism adjustment coil 50 Control computer 51 Feature quantity calculation unit 54 Lens control circuit 56 Control circuit 58 Signal acquisition circuit 59 Coil control circuit

Claims (10)

An emission part for emitting a charged particle beam;
A plurality of openings, and an aperture member that forms a multi-beam by passing the charged particle beam through the openings;
A blanking plate in which a plurality of blankers for performing blanking deflection of the corresponding beams among the multi-beams are disposed,
A limiting aperture member that blocks each beam deflected to be in a beam OFF state by the plurality of blankers;
A stage on which a substrate to be irradiated with the multi-beam is placed;
A detector for detecting reflected charged particles from the substrate;
A feature amount calculation unit for calculating a feature amount of an aperture image based on a detection value of the detector;
An aberration correction unit for correcting the aberration of the charged particle beam based on the feature amount;
A multi-charged particle beam drawing apparatus. The feature amount calculation unit generates an approximate figure that approximates the aperture image,
Calculating the feature amount from the area of the aperture image located on at least one of the inside and the outside of the approximate figure,
The multi charged particle beam drawing apparatus according to claim 1, wherein the aberration correction unit corrects spherical aberration of the charged particle beam based on the feature amount. The feature amount calculation unit generates an approximate rectangle that approximates the aperture image, calculates a ratio between a longer length of diagonal lines of the approximate rectangle and an outer peripheral length of the aperture image as the feature amount,
The multi charged particle beam drawing apparatus according to claim 1, wherein the aberration correction unit corrects spherical aberration of the charged particle beam based on the feature amount. The feature amount calculation unit calculates a standard deviation of illuminance in the aperture image as the feature amount,
The multi charged particle beam drawing apparatus according to claim 1, wherein the aberration correction unit corrects spherical aberration of the charged particle beam based on the feature amount. The feature amount calculation unit generates an approximate rectangle that approximates the aperture image, calculates a variation in length of four sides of the approximate rectangle as a first feature amount,
2. The multi-charged particle beam drawing apparatus according to claim 1, wherein the aberration correction unit corrects astigmatism of the multi-beam based on the first feature amount. The feature amount calculation unit generates an approximate rectangle that approximates the aperture image, calculates a squareness of four interior angles of the approximate rectangle as a second feature amount,
2. The multi-charged particle beam drawing apparatus according to claim 1, wherein the aberration correction unit corrects multi-beam astigmatism based on the second feature amount. The feature amount calculation unit generates an approximate quadrangle that approximates the aperture image, calculates a variation in length of four sides of the approximate quadrangle as a first feature amount, and determines the squareness of the four inner angles of the approximate quadrangle. Calculate as the second feature,
2. The multi-charged particle beam drawing apparatus according to claim 1, wherein the aberration correction unit corrects astigmatism of the multi-beam based on the first feature amount and the second feature amount. Emitting a charged particle beam;
The charged particle beam passes through a plurality of openings of the aperture member to form a multi-beam; and
Irradiating the substrate placed on the stage with the multi-beam;
Detecting reflected charged particles from the substrate;
Calculating a feature amount of an aperture image based on the detected reflected charged particles;
Correcting the aberration of the charged particle beam based on the feature amount;
A method for adjusting a multi-charged particle beam drawing apparatus comprising:   9. The method of adjusting a multi charged particle beam drawing apparatus according to claim 8, wherein spherical aberration of the charged particle beam is corrected based on the feature amount. An approximate quadrangle that approximates the aperture image is generated, and at least a first feature amount that indicates a variation in length of four sides of the approximate rectangle and a second feature amount that indicates the squareness of four internal angles of the approximate rectangle. Calculate either one,
The multi-charged particle beam drawing apparatus adjustment method according to claim 8, wherein multi-beam astigmatism is corrected based on the first feature amount and / or the second feature amount.

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