JP2005079132A - Method for measuring astigmatism blur generation sensitivity in charged particle beam optical lithographic system and optical lithographic method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for measuring sensitivity to astigmatic blur of an astigmatic corrector, without being affected by astigmatic strain. <P>SOLUTION: In the method for measuring astigmatic blur sensitivity in a charged particle optical lithographic system having at least two sets of astigmatic correctors, setting of each astigmatic corrector for minimizing blurs in a specified direction is found, based on the astigmatic strain generation sensitivity of individual astigmatic correctors, while driving the astigmatic correctors in combination such that astigmatic strains can be neglected and then astigmatic blur sensitivity is measured based on the setting thus found. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a method for determining astigmatism blur generation sensitivity in a charged particle beam exposure apparatus, and an exposure method using the same.

  As the density of semiconductor devices increases, the pattern to be exposed and transferred from the reticle to the wafer in the manufacturing process is miniaturized. In order to expose and transfer such a fine pattern, the optical exposure transfer apparatus lacks the resolution, and the exposure transfer apparatus uses charged particle beams such as electron beams as an alternative to the optical exposure transfer apparatus. Development is underway.

  In a charged particle beam exposure apparatus, a charged particle emitted from a charged particle beam source is irradiated onto a reticle via an illumination optical system to illuminate, and a pattern formed on the reticle is irradiated onto a wafer via a projection optical system. Exposure transfer is performed by forming an image on the top.

  FIG. 2 shows an example of a charged particle beam exposure apparatus. The charged particle beam 2 emitted from the charged particle beam source 1 irradiates the shaping opening 4 with the first irradiation lens 3. The charged particle beam 2 that has passed through the shaping aperture 4 forms a shaping aperture image on the reticle 7 by the second irradiation lens 5 and the third irradiation lens 6. A pattern to be transferred is formed on the reticle 7, and the charged particle beam 2 that has passed through the reticle 7 is reticulated on the object 10 such as a resist on the wafer by the first projection lens 8 and the second projection lens 9. 7 images are formed. In a charged particle beam exposure apparatus, a reticle is usually divided into about 1 mm square, and is reduced and transferred to an exposure object by about 1/4. Therefore, the size of the image is about 0.25 mm square. Such an exposure area exposed at one time is called a subfield, and the subfields are connected to form an entire image, for example, a pattern of a semiconductor device.

  In such a charged particle beam exposure apparatus, the blur of the image projected on the object to be exposed 10 is adjusted by adjusting the focal position using the first projection lens 8, the second projection lens 9, or a dynamic focus corrector. This is done by adjusting astigmatism blur and astigmatism distortion by the astigmatism corrector SM. Astigmatism blur and astigmatism were determined by actual exposure or an aerial image sensor (AIS) to adjust the astigmatism corrector so that the amount of aberration is minimized according to the optical axis position or each deflection position. .

  However, as the required exposure transfer accuracy becomes higher, the exposure current changes depending on the aperture ratio in the subfield, and the blur due to the space charge effect (space charge blur) resulting from the change has become a problem. In order to cope with this, a method has been adopted in which the amount of space charge blur is calculated for each subfield by simulation and the focal position is changed as much as possible.

  The focus correction amount at this time is usually obtained by changing the height of the object to be exposed in advance (that is, by creating the same state as changing the focus position), and measuring the amount of blur of the image at that time, thereby obtaining unit blur. The amount of focus change per unit amount (focus correction sensitivity) is determined and can be obtained by multiplying the amount of blur determined by simulation by this focus correction sensitivity.

  However, when the exposure current changes, the astigmatism blur also changes due to the influence of the space charge effect. Therefore, in actual exposure, it is necessary to dynamically correct astigmatism blur as well as focus correction.

  As shown in FIG. 3, a typical astigmatism corrector uses four coils arranged at 90 ° intervals as shown in (a) as a first set of coils, as shown in (b). The four coils arranged at intervals of 90 ° in the direction deviated from this by 45 ° are used as a second set of coils, which are combined and arranged as shown in (c). (D) shows the AA sectional view in (c). In the figure, reference numerals 31a to 31d and 32a to 32d respectively show toroidal coils along the optical axis. Needless to say, the coils actually used are not limited to the toroidal type.

  The reference direction of the first coil (one of astigmatism blur correction directions) is set to 0 °. This direction does not necessarily coincide with the 0 ° direction based on the measurement pattern. The first set of coils is referred to as a 0 ° direction coil, and the second set of coils is referred to as a 45 ° direction coil. Of course, if the direction of astigmatism blur coincides with the direction of blur that can be corrected by the first set of coils, astigmatism correction can be performed using only the first set of coils. In this case, the description in this specification may be read while ignoring either set of coils (assuming that the current flowing through the coil is 0).

  Hereinafter, the astigmatism corrector, astigmatism blur, and distortion will be described. The correction components generated by the astigmatism corrector include astigmatism blur and astigmatism. Astigmatism blur is 0-90 ° blur, 45-135 ° blur, and astigmatism is anisotropic magnification. It is divided into non-orthogonality. When the astigmatism blur is changed in focus, the shape of the blur changes as described above, and the blur becomes a focal line at a specific focus position depending on the size of the astigmatism blur. There is a focal line position in the direction rotated by 90 ° with the previous focal line.

  The 0-90 ° direction blur is a blur that changes in the 0 ° direction and 90 ° direction of the coordinate system (normally the coordinates of the astigmatism blur measurement pattern described later) set by the blur due to astigmatism when the focus is changed. In the case of only 0-90 ° direction blur, the focal position that produces a 0 ° direction focal line (position where 90 ° direction blur is minimized) and the focal position that produces a 90 ° direction focal line (0 ° direction blur) Is defined as the difference (or half the difference). Similarly, the blur in the 45-135 ° direction is a blur that changes in the 45 ° direction and the 135 ° direction with respect to the coordinate system in which the astigmatism blur is set. It is defined by the difference (or half thereof) between the focal position that generates the focal line in the ° direction (position at which the 135 ° direction blur is minimized) and the focal position that generates the focal line in the 135 ° direction (position at which the 45 ° direction blur is minimized).

  The anisotropic magnification represents a deviation from the isotropic magnification with normal set coordinates, and the square is transformed into a rectangle. Non-orthogonality represents a deviation from orthogonality and transforms a square into a rhombus.

  In order to independently correct astigmatism blur and astigmatism at the time of exposure, at least two sets of astigmatism correction devices are provided. Operate with a combination of excitations.

Specifically, it is set as the following formula. Normally, one set of astigmatism correctors is operated with two sets of currents. However, the first astigmatism corrector first current causes astigmatism blur generation sensitivity in the 0-90 ° direction and 45-135 ° direction. Astigmatism blur generation sensitivity, anisotropic magnification generation sensitivity, and non-orthogonality generation sensitivity are (s11, s21, s31, s41), respectively. Similarly, the second current of the first astigmatism corrector, the second astigmatism The first and second current sensitivities of the aberration corrector are also (s12, s22, s32, s42), (s13, s23, s33, s43), (s14, s24, s34, s44), and the first astigmatism. When the exciting current of the corrector is (I1s1, I1s2) and the exciting current of the second astigmatism corrector is (I2s1, I2s2), astigmatism blur and astigmatism are obtained by the following equations (1). . S _0-90 is astigmatism blur in the 0-90 ° direction, S _45-135 is astigmatism blur in the 45-135 ° direction, AnisoMag is anisotropic magnification, and Ortho is non-orthogonal.

  The matrix in this equation is called the generation sensitivity matrix. The inverse matrix of the generation sensitivity matrix is called a correction sensitivity matrix, and is a matrix in the equation (2).

  As expressed by equation (2), when the correction value (S0-90, S45-135, AnisoMag, Ortho) to be set is applied to the correction sensitivity matrix from the right, the excitation current of each corrector can be calculated.

  In this example, the astigmatism corrector generates only 0-90 ° astigmatism blur, 45-135 ° direction astigmatism blur, anisotropic magnification, and non-orthogonality. There are focus lenses, deflectors, etc., which change the focus, magnification, rotation, exposure position. In consideration of changing them in the astigmatism corrector, a generation sensitivity matrix is created from these sensitivities, and an inverse matrix is created to determine the correction current amount of each corrector. However, for the sake of simplicity, the description here assumes that the astigmatism corrector generates only astigmatism blur and astigmatism distortion.

  Under these assumptions, in order to adjust astigmatism blur, anisotropic magnification, and non-orthogonality with an astigmatism corrector, it is necessary to obtain the aforementioned generation sensitivity matrix and correction sensitivity matrix. For this purpose, it is necessary to measure the sensitivity of each astigmatism corrector to astigmatism blur and astigmatism distortion. However, in the case of astigmatism blur, astigmatism is directional, and the astigmatism corrector is also composed of a combination of multiple coils. It has not been established whether to adjust the current flowing in the coil of the aberration corrector.

  In order to solve such a problem, the present inventor uses patterns oriented in directions of 0 °, 45 °, 90 °, and 135 °, respectively, with respect to the reference direction of the pattern, and sets the imaging plane. Slightly deviated from the normal focus position, current values to be passed through two sets of coil groups (0 ° direction coil and 45 ° direction coil) in which a focal line is formed for each pattern or two sets of electrode groups (0 ° direction electrode and 45 °). Invented a method for determining astigmatism blur generation sensitivity and astigmatism blur correction sensitivity using this value (referred to as “prior application invention”), and applied for a patent application. A patent application has been filed as 2002-276830.

  The prior invention will be described below. In this specification, the “positive focus position” means the position in the optical axis direction of the imaging plane where the minimum circle of confusion around the optical axis is formed when the imaging state is changed by a projection lens or the like (that is, , The position in the optical axis direction of the imaging plane where charged particles emitted from one point on the optical axis on the object surface are isotropically focused most.

  Usually, as a method for obtaining the normal focus position, a pinhole is formed on the optical axis of the object surface, the imaging plane is moved in the optical axis direction, and the beam blur in that direction is estimated by scanning in the X and Y directions, for example. A method is adopted in which the image plane position where the blur is minimized in each direction is found and the midpoint is set as the normal focus position.

  In the present specification and claims, the magnitude of astigmatism blur is converted into the magnitude of the focal position deviation in the optical axis direction. The absolute value of this two-component astigmatism blur is the absolute value of the amount of deviation from the normal focus of the image plane position that becomes the focal line when there is astigmatism, and any astigmatism blur is in the 0 ° direction. The 0 ° direction component and the 45 ° direction component are represented by the combination of the blur and the 45 ° direction blur. The 0 ° direction blur and the 0 ° direction blur with respect to the astigmatism blur (90 ° direction blur when the 0 ° direction blur becomes negative) ) And 45 ° direction blur (when the 45 ° direction blur is negative, it indicates that 135 ° direction blur has occurred). Naturally, when there is no astigmatism blur, both the 0 ° direction component and the 45 ° direction component are zero.

  In the present specification and claims, “astigmatism blur generation sensitivity” refers to the focal position that is generated when the current value or voltage value applied to the astigmatism corrector is changed by a unit amount. This means the amount of astigmatism blur. “Astigmatism blur correction sensitivity” refers to currents that flow through two sets of coils of an astigmatism corrector or two sets of electrodes to correct astigmatism blur corresponding to a defocus of unit length. This means the amount of change in voltage applied to.

  In the present specification and claims, the term “astigmatism generation sensitivity” refers to the magnitude of astigmatism generated when the current value or voltage value applied to the astigmatism corrector is changed by a unit amount. Means.

  First, the principle of the invention of the prior application will be described with reference to FIG. In the following description, the astigmatism corrector is described as being controlled by current, but the same idea can be applied when controlled by voltage. FIG. 4 shows how the astigmatism blur is caused by changing the current passed through the 0 ° direction coil (actually, the unit is assumed to be AT since the magnetic field is a problem) S1 and the current S2 passed through the 45 ° direction coil. It is the figure which showed whether it changes to. FIG. 4 shows an orthogonal coordinate system (S1-S2 coordinate system) in which the horizontal axis is the current S1 flowing through the first set of coils and the vertical axis is the current S2 flowing through the second set of coils. That is, this is a coordinate system for explaining excitation of the astigmatism corrector.

  However, in FIG. 4, the shape of the illustrated image is a shape (a shape on the xy plane) indicated by an orthogonal coordinate system (xy coordinate system) in which the reference direction of the measurement pattern is 0 °. . In FIG. 4, the figure is drawn so that the S1 axis and the x axis coincide with each other, and the S2 axis and the y axis coincide with each other. However, for the sake of easy understanding, this display is merely shown for convenience. . Since the xy coordinate system and the S1-S2 coordinate system are completely different, there is no particular meaning in displaying substantially the same display. Further, the origins of the S1-S2 coordinate system and the xy coordinate system do not need to coincide. Also, the circles shown by broken lines in FIG. 4 are on the S1-S2 plane.

  In this figure, it is assumed that the focal position is deviated from the normal focal position by Δh. In order to shift the focal position, the charged particle beam optical system may be operated to shift the focal position, but a simpler method can be realized by changing the height of the object to be exposed.

  Reference numeral 15 denotes a beam shape in a state where astigmatism blur does not occur.

  By changing S1 and S2, the beam shape changes as shown in the figure corresponding to the respective values of S1 and S2. In FIG. 4, each beam shape shows the beam shape in the (S1, S2) coordinates of the center point of the shape, that is, when the currents S1 and S2 are the values of the center point. Then, by adjusting S1 and S2, a focal line can be formed as shown in the figure.

  Of these focal lines, 11 is parallel to the x-axis, 12 is parallel to the y-axis, 13 is inclined 45 ° with respect to the x-axis, and 14 is inclined 135 ° with respect to the x-axis. In general, it is known that a set of S1 and S2 where a focal line is formed is on a circle centered at 15 in the (S1, S2) orthogonal coordinate system.

  The invention of the prior application finds a set of S1 and S2 that gives these focal lines 11 to 14, and based on this, the astigmatism blur generation sensitivity (the current value to be supplied to the astigmatism corrector or the voltage value to be applied is a unit quantity. Astigmatism blur amount converted to the focal position, and correction sensitivity (current flowing to the astigmatism corrector to correct the unit astigmatism blur amount converted to the focus position) Value or voltage value to be applied).

  That is, the coordinates of the focal point 11 where the focal line parallel to the x axis is formed (the point where the 90 ° direction blur is minimized) 11 are (S11, S21), and the focal point parallel to the y axis is formed (0 ° The coordinate of the point 12 where the directional blur is minimized (S21, S22), and the coordinate of the point where the focal line inclined 45 ° with respect to the x-axis (the point where the 135 ° directional blur is minimized) 13 is ( S13, S23), if the coordinates of the point at which the focal line tilted 135 ° with respect to the x-axis (the point where the 45 ° direction blur is minimized) 14 are (S14, S24), it will be clear from the figure. In addition, the current flowing through the 0 ° direction coil and the current flowing through the 45 ° direction coil from the state where there is no astigmatism at the same focal position as the measurement point,

By changing only astigmatism, the astigmatism blur in the 45-135 ° direction is not changed, and the astigmatism blur in the 0 ° -90 ° direction is corrected to minimize the astigmatism blur in the 0 ° direction. (12 states in FIG. 4). Conversely, if the signs of these equations are changed by the amount changed, astigmatism blur in the 90 ° direction can be minimized (state 11 in FIG. 4).

  Since this is a value when the focal position changes by Δh in the optical axis direction, when astigmatism blur is converted into a focal position deviation in the optical axis direction, astigmatism blur correction for defocus per unit length Sensitivity is as shown in equations (3) and (4), respectively. Here, the dimensions of the expressions (3) and (4) are expressed as, for example, [AT / mm] (in the case of voltage, expressed as V / mm).

  Expression (3) indicates that astigmatism blur correction sensitivity when correcting astigmatism blur in the 0-90 ° direction by the 0 ° direction coil (the direction in which astigmatism blur is generated in the 0 ° direction is positive). (4) is an astigmatism blur correction sensitivity when correcting astigmatism blur in the 0-90 ° direction by a 45 ° direction coil (direction in which astigmatism blur is generated in the 0 ° direction). Is positive).

  Similarly, the current flowing through the 0 ° direction coil and the current flowing through the 45 ° direction coil are respectively

By changing only astigmatism, the astigmatism blur in the 0-90 ° direction is not changed, and the astigmatism blur in the 45 ° -135 ° direction is corrected to minimize the astigmatism blur in the 45 ° direction. (State 14 in FIG. 4). Further, if the sign of the above equation is changed by an amount corresponding to the change, astigmatism blur in the 135 ° direction can be minimized (state 13 in FIG. 4).

  Since this is a value when the focal position changes by Δh in the optical axis direction, the astigmatism blur correction sensitivity with respect to the defocus per unit length is expressed by the equations (5) and (6), respectively. . Here, the dimensions of the equations (5) and (6) are expressed as [mm / AT], for example.

  Expression (5) is astigmatism blur correction sensitivity when correcting astigmatism blur in the 45-135 ° direction by the 0 ° direction coil (the direction in which astigmatism blur is generated in the 45 ° direction is positive). (6) is an astigmatism blur correction sensitivity (direction in which astigmatism blur is generated in the 45 ° direction) when the 45 ° -135 ° direction astigmatism blur is corrected by the 45 ° direction coil. Is positive).

  As described above, in the invention of the prior application, the amount of astigmatism blur is converted into the amount of change in the optical axis direction of the focal position. Therefore, when a certain astigmatism blur occurs on the image plane, the degree of the astigmatism blur is indicated by how much the focal position is deviated in the optical axis direction, and the correction sensitivity is expressed as a result. Astigmatism blur is corrected by applying.

The absolute value of astigmatism blur having two components is the absolute value of the amount of deviation from the normal focal point of the imaging plane position that becomes the focal line when there is astigmatism, and any astigmatism blur is in the direction of 0 degrees. This is expressed by combining blur and 45 degree direction blur. The 0 degree direction component and the 45 degree direction component are 0 degree direction blur with respect to the astigmatism blur (180 degree direction blur when 0 degree direction blur is negative). ), And 45 degree direction blur (if the 45 degree blur is negative, it indicates that 135 degree blur is occurring). Naturally, when there is no astigmatism blur, both the 0 degree direction component and the 45 degree direction component are zero. The astigmatism blur is corrected by applying the correction sensitivity for the astigmatism blur to the astigmatism blur. When the astigmatism blur in the 0-90 ° direction is converted into the optical axis position, Δh ₀ , and the astigmatism blur in the 45-135 ° direction converted into the optical axis position is Δh ₄₅ . In order to correct these, the change amount I _{0 of the} current flowing in the 0 ° direction coil and the change amount of the current flowing in the 45 ° direction coil are I ₄₅ .

Can be calculated from Moreover, it is clear that the quantities represented by the equations (3) to (6) are elements of the generation sensitivity matrix. Therefore, if measurement is performed on two sets of coils constituting one astigmatism corrector, it is possible to obtain an astigmatism blur among the elements of the generation sensitivity matrix.

  An example of a method for detecting a focal line is shown in FIG. The electron beam emitted from the electron gun illuminates the reticle by the illumination optical system, and forms an image of the reticle on the wafer stage by the projection optical system. In FIG. 5A, an astigmatism blur measurement mark is provided on a reticle (not shown), and an image 20 of the astigmatism blur measurement mark by the projection optical system is displayed on the target pattern 21 on the wafer stage. Scan by deflector or stage scan. A measurement signal such as a reflected electron signal is obtained from the target pattern 21 illuminated by the astigmatism blur measurement mark image 20.

  The astigmatism blur measurement mark image 20 has a uniform region 20a and a blur region 20b. The blur area 20b expands as the blur of the projection optical system increases, and the uniform area 20a contracts accordingly. The amount of blur is measured by scanning the image 20 of the astigmatism blur measurement mark and detecting a reflected electron signal or the like accordingly. The backscattered electron signal 22 is obtained by measuring the amount of backscattered electrons caused by the overlap of the target pattern 21 and the astigmatism blur measurement mark image 20 with a backscattered electron detector. The differentiated signal 23 is obtained by differentiating the reflected electron signal 22 or the like by a differentiation circuit or by software differentiation.

  FIG. 5B shows how the reflected electron signal 22 and the like change according to scanning. The region 30 where the astigmatism blur measurement mark image 20 and the target pattern 21 do not overlap at all becomes the region 31 where the astigmatism blur measurement mark image blur region 20b overlaps, and astigmatism blur measurement is performed. A region 32 that overlaps to the uniform region 20a of the image of the mark for use, and a region 33 that overlaps to the blur region 20b on the opposite side of the image of the astigmatism blur measurement mark, and an image of the astigmatism blur measurement mark Becomes a region 34 in which the astigmatism blur measurement mark image blur region 20b is omitted, and an astigmatism blur measurement mark image uniform region 20a disappears. Then, the blur region 20b on the opposite side of the image of the astigmatism blur measurement mark becomes a region 37 where the astigmatism blur measurement mark 20 is completely missing, and a region 38 where the astigmatism blur measurement mark 20 is completely missing.

A signal obtained by differentiating this signal is shown in FIG. The interval 26 between the position where the rising edge of the differential signal 23 falls below the 12% level 25 and the position where the differential signal 23 falls below the 88% level 24 is defined as a blur amount (blur). FIG. 5 (a) shows 0 ° of the pattern formed on the reticle. This is to detect the focal line that minimizes the blur in the direction (focal line 12 in FIG. 4). When detecting the focal line that minimizes the blur in the 45 °, 90 °, and 135 ° directions, Each of the scanning directions may be 45 °, 90 °, and 135 °, and a long rectangular target pattern and reticle pattern may be used in a direction perpendicular to the scanning direction.

  However, the method of the invention of the prior application is based on the premise that astigmatism can be ignored. That is, when the astigmatism corrector is adjusted, astigmatism usually changes in addition to astigmatism blur. If this cannot be ignored, an error occurs in the measurement of astigmatism blur generation sensitivity.

  This is shown in FIG. The reference numerals in FIG. 6 are the same as those shown in FIG. The pattern distortion at this time is shown superimposed on the focal line position in the figure. As can be seen from this, what is drawn as a focal line is not actually a focal line in the target pattern direction. In addition, although the figure is not attached | subjected, the position which gives only distortion of only an anisotropic magnification and only non-orthogonality is shown for reference (a rectangular shape is an anisotropic magnification at the center position) Only the non-orthogonal distortion at the center position is shown in the rhombus.)

  The reason why the lines are not in focus at 11, 12, 13, and 14 will be described. In this situation, the projected pattern is distorted. For example, when there is non-orthogonality, as shown in FIG. 7A, a long pattern such as an astigmatism blur measurement exposure pattern is used for measurement. The edge of will be rotated. Hereinafter, this is expressed as the inclination of the pattern. When blur is measured in this situation, the exposure pattern 40 scans on the target pattern 41 with an inclination, so that the edge of the exposure pattern enters the target pattern and the portion is measured as blur.

  That is, as can be seen from FIG. 7B showing the measurement signal, the image of the astigmatism blur measurement pattern is tilted from the region 50 where the image 40 of the astigmatism blur measurement pattern does not overlap at all. A part of the astigmatism blur measurement pattern becomes an area 51 where the blur part 40b of the image of the astigmatism blur measurement pattern overlaps the entire vertical direction. It becomes the area | region 53 where a part of inclined part of the like part 40a has overlapped. Therefore, not only astigmatism blur of each astigmatism corrector but also distortion is measured.

  Therefore, in FIG. 7C showing the differential value of the measurement signal, the interval 57 between the position where the rising edge of the differential signal 54 cuts off the 12% level 55 and the position where the differential signal 54 cuts off the 88% level 56 is measured as a blur amount. However, this blur amount is larger than the actual blur amount. Therefore, when the current value or voltage value of the astigmatism corrector in which the focal line is formed based on such a measurement result, an error is generated. There is a problem that the sensitivity to blurring of point aberration cannot be measured.

  The present invention has been made in view of such circumstances, and a method for measuring the sensitivity of an astigmatism corrector to astigmatism blur without being affected by astigmatism, and using this sensitivity It is an object to provide an exposure method for performing exposure.

  A first means for solving the above problem is a method for measuring astigmatism blur generation sensitivity in a charged particle beam exposure apparatus having at least two sets of astigmatism correctors, and each astigmatism corrector. Based on the astigmatism generation sensitivity of the astigmatism, find the setting of each astigmatism corrector that minimizes the blur in a specific direction while driving in combination with the astigmatism corrector so that astigmatism can be ignored Then, astigmatism blur generation sensitivity is measured based on this, and a method for measuring astigmatism blur generation sensitivity in a charged particle beam exposure apparatus (claim 1).

  In the prior invention, measurement was performed by individually driving an astigmatism corrector for measuring astigmatism blur generation sensitivity. In this means, two or more astigmatism correctors are driven, and based on the astigmatism generation sensitivity of each astigmatism corrector, thereby creating a condition in which astigmatism can be ignored, Under that condition, the setting of each astigmatism corrector that minimizes the blur in a specific direction is found, and the astigmatism blur generation sensitivity is measured based on the setting. Therefore, the astigmatism blur generation sensitivity can be measured with almost no influence of astigmatism distortion. As will be described later, astigmatism blur correction sensitivity can be obtained from the obtained astigmatism blur generation sensitivity.

  The second means for solving the above-mentioned problem is the first means, and the astigmatism blur generation of each astigmatism corrector together with the astigmatism generation sensitivity of each astigmatism corrector. Using the sensitivity, create a correction sensitivity matrix that can determine the strength of each astigmatism corrector that controls astigmatism blur and astigmatism, and combine astigmatism correctors so that astigmatism can be ignored based on it The astigmatism corrector setting that minimizes the blur in a specific direction is found and the measurement value of the astigmatism blur generation sensitivity is improved based on the setting. 2).

  In this means, astigmatism blur and astigmatism are controlled by using the astigmatism blur generation sensitivity of each astigmatism corrector and the astigmatism blur generation sensitivity of each astigmatism corrector. Create a correction sensitivity matrix that can determine the strength of each astigmatism corrector. Since the astigmatism blur generation sensitivity used for the correction sensitivity matrix at this time is provisional, it may be obtained using the prior application invention described above or obtained by simulation. Then, using this correction sensitivity matrix, a driving method of the astigmatism corrector that makes astigmatism negligible is found. In this way, it is possible to easily find a driving method of the astigmatism corrector that can ignore astigmatism.

  The third means for solving the above-mentioned problem is the first means or the second means, wherein the measurement is performed by changing the position of the measuring instrument for measuring the blur or by shifting the position of the focal point. (Claim 3).

  In this means, by changing the position of the measuring instrument for measuring the blur or shifting the focal position to generate astigmatism blur, and determining the driving state of the astigmatism corrector for correcting it, The astigmatism blur generation sensitivity is measured. Therefore, the astigmatism blur generation sensitivity can be measured by a simple method.

  A fourth means for solving the above problem is any one of the first to third means, which is more than the minimum number of data necessary for determining the astigmatism blur occurrence sensitivity. The data is obtained by measurement, and the astigmatism blur generation sensitivity is obtained by statistical means (claim 4).

  In this means, a large amount of data is collected, and the astigmatism blur occurrence sensitivity is obtained by statistical means. Therefore, even when there is an error in the measured value, the astigmatism blur occurrence sensitivity can be obtained accurately. .

  A fifth means for solving the above problem is a method of exposing and transferring an image of a reticle onto a wafer in a charged particle beam exposure apparatus, wherein any one of the first to fourth means is used. Using the astigmatism blur generation sensitivity determined by the measurement method of astigmatism blur generation sensitivity in a charged particle beam exposure system, adjust the astigmatism corrector to correct astigmatism blur for each subfield. An exposure method in a charged particle beam exposure apparatus, wherein exposure transfer is performed while the exposure transfer is performed (claim 5).

  In this means, exposure transfer is performed while adjusting the astigmatism corrector so as to correct the astigmatism blur for each subfield using the accurately obtained astigmatism blur generation sensitivity. Good exposure transfer is possible.

  As described above, according to the present invention, a method for measuring astigmatism blur generation sensitivity of an astigmatism corrector without being affected by astigmatism, and exposure using this sensitivity are performed. An exposure method can be provided.

Hereinafter, an example of an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a diagram for explaining an example of an embodiment of the present invention. In FIG. 1, the horizontal axis represents 0-90 ° astigmatism blur S _0-90 , and the vertical axis represents 45-135 ° astigmatism blur S _45-135 . The origin indicates a state in which astigmatism blur is corrected. Further, the astigmatism is also corrected.

  First, the astigmatism generation sensitivity and the astigmatism blur generation sensitivity for a single astigmatism corrector are obtained using the prior invention, etc., and from this, the generation sensitivity matrix represented by the above equation (1) and , A correction sensitivity matrix represented by equation (2) is obtained. In the equation (2), if AnisoMag = 0 and Ortho = 0,

The relationship becomes true. The exciting currents (I _1s1 , I _1s2 , I _2s1 , I _2s2 ) are changes.

As in the prior invention, the focal position is shifted by Δh from the normal focal position. Then, (S _0-90 , S _45-135 ) is changed around the excitation current of each coil of the astigmatism corrector obtained as S _0-90 = Δh and S _45-135 = 0 in the equation (8). The excitation current is changed so as to satisfy the condition of equation (8), and the combination of current values (I1s1, I1s2, where blur is minimized in the 0 ° direction by the method described in the description of the invention of the prior application. I2s1, I2s2). At this time, astigmatism distortion is much smaller than when sensitivity is measured by a single astigmatism corrector. Therefore, the distortion of the image of the astigmatism blur measurement pattern is small, and is hardly inclined with respect to the target pattern. Therefore, it is possible to determine the excitation condition of the astigmatism corrector when the focal line is formed with almost no influence of astigmatism.

Next, S _0-90 and S _45-135 are obtained by substituting the set of measured excitation currents into equation (1). If each element of the correction sensitivity matrix represented by equation (8) is accurate, S _0-90 obtained by substituting into equation (1) should be Δh, and S _45-135 should be zero. 1 and the point forming the focal line should be on the _S0-90 axis in FIG. 1, but actually, it is a slightly shifted position as shown by 16 in FIG. This amount of deviation is defined as (dS _0-90 , dS _45-135 ).

The same measurement, 90 °, 45 °, performed on 135 °, determine the set of excitation current focal line in each direction is formed, and S _0-90 are substituted into equation (1) S _{45- 135} is obtained, and (dS _0-90 , dS _45-135 ) is obtained from this. The obtained sets of (S _0-90 , S _45-135 ) are shown in FIG. 1 at positions 18, 17 and 19, respectively. The focal lines indicated by 16, 17, 18, and 19 are parallel to the y-axis of the pattern, 135 ° to the x-axis, parallel to the x-axis, 45 ° to the x-axis, and the S _0-90 axis. , S _45-135 is not related to the direction of the axis as described in FIG. However, the position of the center of the focal lines 16, 17, 18, 19 indicates the position in the coordinates (S _0-90 , S _45-135 ).

At that time, in order to prevent the generation of _astigmatism , (S _0-90 , S _45-135 ) substituted into the equation (2) is 90 ° (−Δh, 0), 45 ° (0, Δh). ), 135 ° (0, −Δh), and the reference values for _obtaining (dS _0-90 , dS _45-135 ) are also this value.

  Then, the relationship between these quantities

Can be written. This matrix is called an error matrix. The error matrix elements can be solved because there are eight unknowns and eight relational expressions. After all, the exact relational expression is

And the element of the matrix in equation (10) is accurate astigmatism blur generation sensitivity. or,

Is a correct generation sensitivity matrix, and a correct correction sensitivity matrix can be obtained by obtaining this inverse matrix.

  In the above description, when the 8 unknowns of the error matrix are obtained, when focal lines in the 0 °, 90 °, 45 °, and 135 ° directions are formed (90 ° direction, 0 ° direction, and 135 °, respectively). The excitation current value of the direction (when the 45 ° method blur is minimized) was determined and the equation was solved. However, the direction in which the focal line is formed is not limited to these directions.

Any direction may be used, but at this time, the position where the reference focal line is formed is on the circle of radius Δh, and is substituted into the equation (8) (S _0-90 , S _45-135). ). That is, when obtaining a set of current values that form a focal line in the θ direction, (Δh cos 2θ, Δh sin 2θ) is substituted into equation (8) to obtain a constraint condition for the set of current values. The focal line is detected in the θ direction, and the current value at that time is substituted into the equation (1) to obtain the actual (S _0-90 , S _45-135 ), and (Δhcos2θ, Δhsin2θ) ) To determine (dS _0-90 , dS _45-135 ).

  Furthermore, instead of finding a set of current values at which focal lines are formed in many directions or at several levels of height, and solving the equation, the error matrix may be obtained by a statistical method such as the least square method. Good. In this way, an accurate measurement result can be obtained even when there is an error in the measurement value.

  Also, if each astigmatism corrector is good, and it can be determined that the astigmatism blur generation ability by the two currents of the astigmatism corrector is the same and the direction is also rotated by 45 °, then there are 4 variables. Therefore, even if the measurement is 4 points, the sensitivity can be calculated accurately using a statistical method.

  Hereinafter, an example of a charged particle beam exposure method using the astigmatism blur correction sensitivity which is an inverse matrix of the astigmatism blur generation sensitivity thus obtained will be described. In this exposure method, the Coulomb effect is corrected for each subfield in consideration of the aperture ratio of the pattern for each subfield. That is, the focal position and astigmatism blur of the projection optical system are changed for each subfield so as to correct the Coulomb effect. The focal position shift amount and the astigmatism blur correction amount due to the Coulomb effect are obtained in advance by calculation. Then, only the value obtained by multiplying each correction amount by the focus correction sensitivity and the astigmatism blur correction sensitivity, the current flowing through the focus position corrector, the current flowing through the 0 ° direction coil of the astigmatism corrector, and the 45 ° direction coil The current flowing through the lens is changed to correct defocusing and astigmatism blur caused by the Coulomb effect.

  At the same time, the amount of astigmatism generated along with the change in the deflection position and the change in the focal position are also taken into account for simultaneous correction. In this way, a good imaging pattern with small astigmatism can be obtained.

It is a figure for demonstrating one example of embodiment of this invention. It is a figure which shows the example of a charged particle beam exposure apparatus. It is a figure which shows the example of an astigmatism correction device. It is a figure which shows the principle of prior invention. It is a figure which shows the example of the method of detecting a focal line. It is a figure explaining that an astigmatism gives an error to the measurement of astigmatism blur generation sensitivity. It is a figure explaining that an astigmatism gives an error to the measurement of astigmatism blur generation sensitivity.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Charged particle source, 2 ... Charged particle beam, 3 ... 1st irradiation lens, 4 ... Molding opening, 5 ... 2nd irradiation lens, 6 ... 3rd irradiation lens, 7 ... Reticle, 8 ... 1st projection lens, 9 ... second projection lens, 10 ... exposed object, 16 ... focal line parallel to y-axis, 17 ... focal line tilted by 135 [deg.] With respect to x-axis, 18 ... focal line parallel to x-axis, 14 ... x-axis Focal line tilted at 45 ° to

Claims (5)

A method for measuring astigmatism blur generation sensitivity in a charged particle beam exposure apparatus having at least two sets of astigmatism correctors, wherein astigmatism distortion is determined based on the astigmatism generation sensitivity of each astigmatism corrector. Astigmatism blur occurrence sensitivity is found based on the setting of each astigmatism corrector that minimizes the blur in a specific direction while driving in combination with astigmatism correctors so that can be ignored. A method for measuring astigmatism blur generation sensitivity in a charged particle beam exposure apparatus. The method for measuring astigmatism blur generation sensitivity in the charged particle beam exposure apparatus according to claim 1, wherein the astigmatism generation sensitivity of each astigmatism corrector and the astigmatism of each astigmatism corrector are as follows. Creates a correction sensitivity matrix that can determine the strength of each astigmatism corrector that controls astigmatism blur and astigmatism, and corrects astigmatism so that astigmatism can be ignored. Charging characterized by finding the setting of the astigmatism corrector that minimizes the blur in a specific direction while driving in combination, and increasing the accuracy of the measurement of astigmatism blur generation sensitivity based on that setting A method for measuring astigmatism blur generation sensitivity in a particle beam exposure apparatus. 3. The method for measuring astigmatism blur generation sensitivity in the charged particle beam exposure apparatus according to claim 1 or 2, wherein the measurement is performed by changing a position of a measuring instrument for measuring blur or by shifting a focus position. A method for measuring astigmatism blur generation sensitivity in a charged particle beam exposure apparatus. 4. The method for measuring astigmatism blur generation sensitivity in the charged particle beam exposure apparatus according to claim 1, wherein the data is larger than a minimum number of data necessary for determining the astigmatism blur generation sensitivity. The astigmatism blur generation sensitivity in a charged particle beam exposure apparatus, wherein the astigmatism blur generation sensitivity is determined by a statistical means. 5. A method for exposing and transferring an image of a reticle onto a wafer in a charged particle beam exposure apparatus, wherein the astigmatism blur generation sensitivity in the charged particle beam exposure apparatus according to claim 1. Charged particles characterized in that exposure transfer is performed while adjusting the astigmatism corrector so as to correct astigmatism blur for each subfield using the astigmatism blur generation sensitivity determined by the measurement method of An exposure method in a line exposure apparatus.

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