JPH11260687A - Charged particle beam exposure method and charged particle beam exposure system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide charged particle beam exposure method, capable of transferring a pattern with high accuracy by reducing a distortion of a projection image. SOLUTION: In this method, charged particle beam exposure is made, in which patterns are formed in a plurality of subfields 51 provided in a mask 5, respectively, and electrons EB are sequentially irradiated to each subfield 51 to project and align an image of patterns on a wafer 11. In this case, the distortion of the image of the subfield 51 has previously been measured for each subfield 51, and based on the measurement values, the distortion of a image of the subfield 51 is corrected every subfield 51 by a dynamic correction system constituted by a focus correction coil 21 and a non-focus corrector 22 to be aligned. A distortion measurement of the image of the subfield 51, for example, has previously been measured by the use of an evaluating mask forming a distortion measuring pattern.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a charged particle beam exposure method and a charged particle beam exposure apparatus.

[0002]

2. Description of the Related Art Today, as semiconductors become more highly integrated, higher-resolution exposure apparatuses are required. In such a situation, charged particle beam exposure apparatuses typified by electron beams are larger. Interested. As one of such exposure apparatuses, there is an electron beam exposure apparatus for exposing and transferring a circuit pattern formed on a reticle (also referred to as a mask) onto a wafer with an electron beam.

FIG. 13 is a diagram schematically showing a schematic configuration of an electron beam exposure apparatus. An electron beam EB from the electron beam source 1 is shaped into a beam having a predetermined cross-sectional shape (for example, a square) by an aperture 3, focused by a condenser lens 2, and then a predetermined small area of a reticle 5 by a deflector 4 for field selection. 51 (called a sub-field). The electron beam EB that has passed through the reticle is deflected by a deflector 8 by a predetermined amount, and is then imaged at a predetermined position on the wafer 11 by the projection lenses 9 and 10 with a predetermined reduction amount. In addition, 17 and 18 are deflection amount setting devices.

The reticle 5 and the wafer 11 are mounted on a reticle stage 6 and a wafer stage 12 which are driven in x and y directions by driving devices 7 and 13, respectively. Detector 14,
15 respectively. The control of the entire exposure apparatus is performed by the main control system 16, and the deflectors 4, 8, the stages 6, 12, etc. are controlled based on the detection results of the position detectors 14, 15.

In an electron beam projection exposure apparatus, a subfield 51, which is a region that can be subjected to collective exposure, is very small compared to the entire circuit pattern. Therefore, the circuit pattern on the reticle 5 is formed by dividing it into a plurality of subfields. FIG.
FIG. 4 is a view for explaining exposure transfer of a reticle pattern onto a wafer 11 by an electron beam EB. Each subfield 5
1 is a boundary region 52 for blocking or diffusing the electron beam EB.
Are separated from each other. The electron beam EB that has passed through the subfield 51 located at a position (distance δ) away from the lens center axis AX is applied to the corresponding small area 111 on the wafer 11 outside the axis AX, and the pattern of the subfield 51 is applied to the small area 111. Is formed. By repeating such exposure transfer for each subfield, all patterns of the reticle 5 are exposed and transferred to the area 110 on the wafer 11.

On the reticle 5, each subfield 51 is separated by a boundary area 52.
An image of each subfield 51 exposed and transferred onto the wafer 11 (a region on the wafer obtained when a rectangular subfield region is projected by a projection optical system, and hereinafter referred to as a subfield image) is provided without gaps. The deflection amount of the electron beam EB is adjusted by the deflector 8 so as to be accurately connected.

[0007]

However, in the electron beam optical system used in the electron beam exposure apparatus, there is an aberration caused by deflecting the electron beam EB, and the aberration causes blur and distortion of the subfield image. Will happen. For example, as shown in FIG.
In the case of the pattern P which extends over the subfields a and 111b, the subfield images Q1 and Q2 are distorted and a gap is generated between adjacent subfields, and the pattern P is cut off (FIG. 15).
(b)) On the contrary, there is a problem that the subfield images Q1 and Q2 overlap with each other and the pattern line width of that portion deviates from the design value (FIG. 15C).

The electron beam optical system is composed of a focusing magnetic lens or an electrostatic lens, a magnetic type or an electrostatic type deflector, etc., but the processing accuracy in manufacturing these lenses and deflectors is high. Because there is a limit, the lens magnetic pole (electrode)
A deviation of the shape from a perfect circle and an error in the relative positions of the coils and electrodes of the deflector are inevitable. Furthermore, since an error occurs in the mounting position when the lens or deflector is mounted on the device, even if the magnetic lens or the like is excited as designed, the electromagnetic field formed on the electron beam trajectory deviates from the designed value. Become.

The aberration of an image due to an electron beam is determined by the shape of an electron beam orbit and the electromagnetic field passing through the orbit (HC
Chu and E. Munro, Optic61 (1982) 121-145), as described above, if a machining error or mounting position error occurs,
The deviation of the electromagnetic field actually formed from the designed value occurs, and the trajectory of the electron beam also deviates, thereby changing the aberration of the electron beam image and blurring or distortion of the subfield image formed on the wafer 11. Will also change. And
In the case where the change in distortion is large, the inconvenience shown in FIG. 15 occurs.

An object of the present invention is to provide a charged particle beam exposure method and a charged particle beam exposure apparatus capable of transferring a pattern with high accuracy by reducing distortion of a projected image.

[0011]

An embodiment of the present invention will be described with reference to FIGS. (1) Explaining in association with FIG. 1, the invention of claim 1 forms a pattern on each of a plurality of small areas 51 provided on a mask 5 and sequentially irradiates each small area 51 with a charged particle beam EB. Applied to the charged particle beam exposure method for projecting and exposing the image of the pattern on the sensitive substrate 11
The distortion of the image of the small region 51 projected above is measured in advance for each small region 51 and for each deflection position, and the distortion of the image of the small region 51 is determined based on the measured value. A small area 51 is obtained by a dynamic correction system including the point corrector 22.
The above object is achieved by performing exposure while correcting each time. (2) Explaining with reference to FIGS. 3 and 5, the invention according to claim 2 is the charged particle beam exposure method according to claim 1,
A plurality of strain measurement patterns 302 formed on the evaluation mask 30 are irradiated with a charged particle beam, and the strain measurement patterns 302
The distortion of the image of the small area is obtained by measuring the position of the image 402. (3) Explained in connection with FIG. 1, the invention of claim 3 is the charged particle beam exposure method according to claim 1 or 2, wherein the distortion of the image of the small area 51 is reduced by a linear distortion component and a higher-order distortion. And the distortion component to be corrected among the linear distortion component and the higher-order distortion component is calculated based on (a) the aberration term relating to the distortion component and (b) the excitation current of the focus correction coil 21. A linear form with the aberration correction term by the focus correction coil 21 or (c) the aberration correction term by the astigmatism corrector 22 calculated based on the excitation current of the astigmatism corrector 22;
The numbers of the focus correction coils 21 and the astigmatism correctors 22 are respectively determined so that the simultaneous equations having the linear form are satisfied, and the excitation currents of the focus correction coils 21 and the astigmatism correctors 22 are calculated from the simultaneous equations. Adjust the current. (4) The charged particle beam exposure method according to claim 1 or 2, wherein the line relating to the distortion component to be corrected is obtained from the equations (21) to (30) relating to the distortion correction of the image of the small area 51. Choose a form to form a system of equations,

(Equation 3) The numbers of the focus correction coils 21 and the astigmatism correctors 22 constituting the dynamic correction system are determined by Nc and Ns that satisfy the simultaneous equations.
And adjusting the respective exciting currents of the Nc focus correction coils 21 to ΔIc, j calculated from the simultaneous equations,
The respective exciting currents of the astigmatism correctors 22 are adjusted to ΔIs, j calculated from the simultaneous equations. However, equations (21)-
In (30), (a) β and γ are the position of the pattern in the small area image and the deflection position of the small area image. (B) f1 (γ), f2 (γ) and g1 (γ) to g3 ( γ) is the aberration coefficient of the aberration with respect to the distortion component, f1 (γ) and f2 (γ) are those relating to the linear distortion component calculated from the measurement values, g1
(γ) to g3 (γ) relate to the secondary distortion component calculated from the measurement value. (c) ΔWdc1, j (1) is the aberration correction coefficient of the focus correction coil 21 and relates to the linear distortion component. ) ΔWdc2, j (1) is an aberration correction coefficient of the astigmatism corrector 22 and relates to a linear distortion component. (E) ΔHdis1, j (3), ΔHdis2, j (3), ΔHdis
3, j (3) is an aberration correction coefficient of the astigmatism corrector 22,
(F) <> represents complex conjugate (5) The invention of claim 5 forms a pattern in each of a plurality of small areas 51 provided on a mask 5,
Is applied to a charged particle beam exposure apparatus for projecting and exposing a pattern image on the sensitive substrate 11 by sequentially irradiating the substrate with the charged particle beam EB, and distortion data of the image of the small area 51 projected on the sensitive substrate 11 is stored in advance. Storage unit 16b and correction means 16, 21, 22, 23 for correcting an image of a pattern projected and exposed on the sensitive substrate 11 for each small area 51 based on the distortion data stored in the storage unit 16b. In order to achieve the above object. (6) According to the invention of claim 6, a pattern is formed on each of the plurality of small areas 51 provided on the mask 5, and
Is applied to a charged particle beam exposure apparatus for projecting and exposing a pattern image on the sensitive substrate 11 by sequentially irradiating the substrate with the charged particle beam EB, and distortion data of the image of the small area 51 projected on the sensitive substrate 11 is stored in advance. The storage unit 16b, the dynamic correction system including the two focus correction coils 21 and the four astigmatism correctors 22, and the excitation current of the focus correction coil 21 and the astigmatism corrector 22 are represented by the following equation (31). ) To (40)

(Equation 4) ΔIc, j and ΔIs, j calculated from the simultaneous equations
The above-mentioned object is achieved by providing control means 16 and 23 for controlling the above. In the equations (31) to (40), (a) β and γ are the position of the pattern in the small area image and the deflection position of the small area image. (B) f1 (γ), f2 (γ) and g1 (γ) to g3 (γ) are aberration system coefficients of the aberration related to the distortion component, and f1 (γ) and f2 (γ) are related to a linear distortion component calculated from the measurement value.
(γ) to g3 (γ) relate to the secondary distortion component calculated from the measurement value. (c) ΔWdc1, j (1) is the aberration correction coefficient of the focus correction coil 21 and relates to the linear distortion component. ) ΔWdc2, j (1) is an aberration correction coefficient of the astigmatism corrector 22 and relates to a linear distortion component. (E) ΔHdis1, j (3), ΔHdis2, j (3), ΔHdis
3, j (3) is an aberration correction coefficient of the astigmatism corrector 22,
(F) <> represents a complex conjugate. In claim 6, two focus correction coils and four astigmatism correctors are used. Usually, one focus correction coil and one astigmatism corrector are added for the field curvature correction and the astigmatism correction. These are controlled by a common control system with the distortion correction corrector.

In the section of the means for solving the above-mentioned problems, which explains the configuration of the present invention, the drawings of the embodiments of the present invention are used to make the present invention easier to understand. However, the present invention is not limited to the embodiment.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS. FIG. 1 is a view showing one embodiment of a charged particle beam exposure apparatus according to the present invention, and is a schematic view showing a schematic configuration of an electron optical system of an electron beam exposure apparatus.
The same parts as those in FIG. 13 are denoted by the same reference numerals. One of the subfields of the mask 5 (indicated by reference numeral 51) is irradiated with an electron beam EB by an illumination optical system (not shown),
The electron beam EB that has passed through is formed by the projection lenses 9 and 10 on the wafer 11 as a sensitive substrate at a predetermined reduction rate.
At this time, of the electron beams EB that have passed through the mask 5, only those that have passed through the aperture of the scattering aperture 20 are imaged. Reference numerals 21 and 22 denote a focus correction coil and an astigmatism corrector which constitute a dynamic correction system, respectively. The dynamic correction system and the astigmatism corrector are based on correction data (described later in detail) stored in a storage unit 16b of the main control system 16. Is controlled by the application control system 23. Reference numeral 24 denotes a deflector control system for controlling the deflector 8, and both control systems 23 and 24 perform control based on control signals from the main control system 16.

Incidentally, 9a and 10a are projection lenses 9 and 10 respectively.
, And 9b and 10b are respective lens coils. The mark M is a mark provided on the wafer stage 12 and used at the time of distortion correction measurement of a subfield image, and 25 is a reflected electron detector for detecting electrons scattered by the mark M. The other configurations (illumination system and stage system) of the exposure apparatus are the same as those in FIG.

By the way, if exposure is performed without using the focus correction coil 21 and the astigmatism corrector 22, which are dynamic correction systems, distortion occurs in the subfield image formed on the wafer 11. That was mentioned above. FIG. 2 shows a typical example of such a subfield image distortion. In FIG. 2, a rectangular area A indicated by a broken line represents an ideal subfield image when there is no distortion, and an area B indicated by a solid line represents a subfield image when distortion occurs.
(A) shows the case where the size (magnification) of the subfield image B changes and increases, (b) shows the case where the vertical and horizontal sizes of the subfield image B change, and (c) shows the case where the subfield image B changes. (D) shows the case where the shape of the subfield image B is deformed into a rhombus, (e) shows the case where the subfield image B is distorted in a curve. Actually, the distortion of the subfield image occurs in a form in which these distortions are combined. Therefore, general subfield image distortion can be decomposed into distortion components shown in FIGS. 2 (a) to 2 (e). Therefore, in the present embodiment, the distortion of the subfield image is decomposed into the above-described distortion components, and the focus correction coil 2 serving as a dynamic correction system is decomposed.
1 and the astigmatism corrector 22 are used to correct the distortion of the subfield image.

Next, a correction method will be described. (A) Measurement of Subfield Image Distortion First, the distortion of the subfield image on the wafer 11 is measured using an evaluation mask. FIG. 3A is a diagram showing a part of the evaluation mask 30, where 31 is a subfield, and each subfield 31 is separated by a non-pattern area 32. In each subfield 31, a plurality of test patterns 302 are formed along the diagonal line. FIG. 3B is a detailed view of the test pattern 302. In each test pattern 302, alignment marks 303a and 303b (marks of a line and space pattern) used for position measurement are formed. The alignment mark 303a is a mark for measuring the position in the y direction, and the alignment mark 303b is a mark for measuring the position in the x direction.

The evaluation mask 30 is set on the mask stage 6 as shown in FIG. 4, and one of the subfields 31 is irradiated with an electron beam EB to form an image of the subfield 31 on the wafer stage 12. . FIG. 5B shows a subfield image formed on the wafer stage 12. Since the subfield image B is distorted with respect to the ideal subfield image A, a diagonal image (curve) of the subfield 31a is formed. 41a, 41b) also draw complicated curves instead of straight lines. Then, the image 4 of the test pattern 302
02 will be imaged on the curve 41.

Then, the distortion of the subfield image B is measured by measuring the position of each test pattern image 402 projected on the wafer stage 12. For example,
As shown in FIG. 4, the electron beam EB is applied to one of the subfields 3
1a, the wafer stage 12 is moved so that the mark M (line and space mark) is located at the projection position, and the image 4 of each test pattern 302 is
02 is detected. At this time, while deflecting the electron beam EB by the deflector 8, reflected electrons from the mark M are reflected by the reflected electron detector 2.
5, the test pattern image is detected, and the x and y positions of the wafer stage 12 at that time are detected by the position detector 15. The mark M is a mark composed of the same line and space as 303a and 303b. Usually, in order to increase the reflection efficiency of the electron beam,
The line portion is made of heavy metal or the like.

After the positions of the images 402 of all the test patterns 302 included in the subfield 31a are measured in this way, the next subfield 31b
And the wafer stage 12 is moved so that the mark M is positioned at the projection position of the image of the subfield 31b, and similarly, the positions of the images of all the test patterns 302 in the subfield 31b are measured. . The same measurement is performed for all subfields 3 of the evaluation mask 30.
1, the subfield image distortion is measured for each subfield 31. The number of the subfields 31 of the evaluation mask 30 does not need to be the same as the number of the subfields 51 of the mask 5, and may be any number that can cover the deflection range (view range) of the electron beam EB. The calculation of the position of the test pattern image is performed by the calculation unit 16a of the main control system 16 based on the detection signals of the position detectors 14, 15 and the backscattered electron detector 25, and is stored in the storage unit 16b for each subfield. You. Note that the test pattern 302
Are not limited to those shown in FIG. 3, but may be, for example, those shown in FIGS.

Here, a coordinate system on the wafer stage 12 is defined as shown in FIG. First, an XY coordinate system with the lens center axis AX as the coordinate origin is considered, and the coordinates of the center of the subfield image (the subfield image B viewed from the lens center axis AX).
) Is (X, Y). Further, considering the xy coordinates with the origin at the center of the subfield image, the coordinates of the pattern image P in the subfield image are represented by (x ′, y ′). When these coordinates are represented by complex coordinates, the subfield image position is represented by γ = X + iY, <γ> = X−iY, and the pattern position viewed from the center of the subfield image is β = x ′ + iy ′, <
β> = x′−iy ′. That is, the position of the pattern image in each subfield image is represented by β, <β>, γ, <γ>.

(B) Correction of Distortion Next, based on the obtained mask distortion measurement value, the distortion of each subfield image B is converted into a linear distortion component (the distortion shown in FIGS. 2 (a) to 2 (d)). Component) and other higher-order distortion components (distortion components shown in FIG. 2 (e)), and these distortions are corrected by primary and secondary transformations on coordinates β and <β>. . (B-1) Correction by Primary Transformation It is assumed that a subfield image B as shown in FIG. 5 is obtained when exposure is performed using the mask 30 shown in FIG. As described above, the image of the test pattern 402 is curve 4
1a and 41b (the diagonal lines of the ideal subfield image A are deformed), the curves 41a and 4b
Two straight lines 51a and 51b that are in contact at the position of the intersection of 1b are calculated from the strain measurement values. When a subfield image having the straight lines 51a and 51b as diagonal lines is considered, generally, the subfield image is rotated with respect to the ideal subfield image A as shown in FIG. (b) and Fig. 2 (d)
It is transformed into a rectangle or rhombus like. Therefore,
As shown in FIG. 7, the primary transformation of the subfield image in which the diagonal line of the ideal subfield image A and the straight lines 51a and 51b match (or almost match) is obtained.

Thereafter, primary conversion is performed so that the interval between the test pattern images 402 matches the ideal value, that is, the projection magnification of the subfield image matches that of the ideal subfield image A. However, since the interval between the test pattern images 402 differs depending on the position (β, <β>) in the subfield image due to the occurrence of distortion, the magnification is determined based on the measurement data of the test pattern image 402 near the intersection of the straight lines 51a and 51b. Calculate the primary transform. When the primary conversion for the magnification adjustment and the above-described primary conversion are collectively represented by one linear conversion equation φ (β, <β>), the subfield image B is expressed as 1
The subfield image B2 shown in FIG. 7 is obtained by performing conversion using the following conversion equation φ (β, <β>). Note that 52a, 52
b indicates a straight line after linearly converting the straight lines 51a and 51b.

(B-2) Correction by Secondary Transformation As can be seen from FIG. 7, the test pattern image 402 can be obtained by simply transforming the subfield image B into the primary form only because the entire subfield image is deformed at the same rate. They are still aligned along the curve (42a, 42b in FIG. 7). Therefore, these curves (higher-order curves) 42a and 42b are fitted to the quadratic curves 43a and 43b using the least squares method. At this time, the subfield image B2 in FIG. 7 is converted into a subfield image B3 shown in FIG.

Next, the quadratic curve 43 obtained by the least square method
a, 43b are diagonal lines 53 of the ideal subfield image A
a, 53b (which coincides with the above-described straight lines 52a, 52b) are subjected to the following secondary conversion. That is, when the quadratic curves 43a and 43b are represented by the above-described complex coordinates β and <β>, β is β + aβ2 + b <β>
2 is replaced. When such a quadratic transformation is performed, the quadratic curves 43a and 43b become straight lines, and a rectangular subfield image B4 (FIG. 8B) obtained by quadratic transforming the subfield image B3 in FIG. 8A. Diagonal lines 44a, 44b
Becomes Further, in order to correct the remaining higher-order magnification shift, a secondary transformation is performed to replace β with β + cβ <β>. Note that a, b, and c are complex number coefficients. Thus, 2
When the higher order components of distortion are corrected by the following transformation, a subfield image B5 very close to the ideal subfield image A is obtained as shown in FIG. 8C, and the test pattern image 402 is also a diagonal line of the rectangular subfield image B5. 45a and 45b are arranged along the upper side.

The above-described coefficients of the primary conversion and the secondary conversion are data for each deflection position γ, that is, for each subfield, and are input to the storage unit in advance. In the distortion correction method described above, the measured distortion of the sub-field image is decomposed into a linear component and a higher-order component and corrected by the primary conversion and the secondary conversion.
The correction may be made as disclosed in Japanese Patent Application Laid-Open No. 4 (1999) -1994.

(C) Correction of Distortion by Dynamic Correction System When the above-described distortion correction by the primary conversion and the secondary conversion is performed by the exposure apparatus, the dynamic correction system of the exposure apparatus (the focus correction coil 21, the astigmatism) This is performed by adjusting the exciting current of the compensator 22). Here, of the distortion components of the subfield image, (a) magnification and rotation components can be corrected by adjusting the excitation current of the focus correction coil 21 of the dynamic correction system, and (b) deformation into a rectangle or rhombus The component related to can be corrected by adjusting the exciting current of the astigmatism corrector 22 of the dynamic correction system. The higher-order component can be corrected by adjusting the quadratic curve distortion generated by the focus correction coil 21 and the astigmatism corrector 22 through the adjustment of the exciting current.

The astigmatism corrector 22 comprises two sets of quadrupoles which can be controlled independently as shown in FIG. 9. Each coil 220 has a current (Ia) as shown in FIG. 9 for the exciting currents Ia and Ib. -Ib, etc.). Therefore, the exciting current of the astigmatism corrector 22 is generally expressed in complex notation Is, j
(= Ia, j + i · Ib, j). In the following, 2
The excitation currents of the two focus correctors 21 are represented by ΔIc, j (where j =
1, 2), and the excitation currents of the four astigmatism correctors are represented by ΔIs, j
(However, ΔIs, j = ΔIa, j + i · ΔIb, j, and j =
1, 2, 3, 4).

At this time, the exciting current flowing through each focus correction coil and astigmatism corrector is determined by the following equations (41) to (45).

(Equation 5) Here, when the linear distortion caused by the primary conversion is corrected by the focus correction coil 21 and the astigmatism corrector 22, the excitation current ΔIc, j of the focus correction coil 21 and the excitation current ΔIs, j of the astigmatism corrector 22 are corrected. Is determined by equations (41) and (42). When correcting higher-order distortion by the second-order conversion, the excitation currents ΔIc, j and ΔIs, j are determined by the equations (43) to (45).

In equations (41) to (45), the first term represents distortion to be corrected, f1 (γ) and f2 (γ) are linear components of distortion data obtained by distortion measurement, g1 (γ), g2 (γ), g3
(γ) is a higher-order component and is a function of the deflection position γ. On the other hand, the second term is a correction term by the dynamic correction system, and acts so as to cancel the first term. ΔWdc1, j of the second term
(1), ΔWdc2, j (1) are coefficients of a portion proportional to β, <β> in the deviation amount of the approximate orbit of the electron beam generated by the dynamic correction system, and ΔHdis1, j (3), ΔHdis2, j (3), Δ
Hdis3, j (3) is a coefficient of the third-order distortion generated by the dynamic correction system, and these amounts are determined in advance theoretically or experimentally for the dynamic correction system used in the exposure apparatus.

By the way, the above equations (41) to (45)
, The coefficients f1 (γ), f2 (γ), g1 (γ) to g3 (γ), etc. are represented by complex numbers.
Consists of two expressions. As a result, equations (41) to (45) are
Actually, it is expressed as the following equations (46) to (55).

(Equation 6) That is, the excitation currents of the two focus correction coils 21 are determined from Expressions (46) and (47), and the excitation currents of the four astigmatism correctors 22 are determined from Expressions (48) to (55).

FIG. 10 is a block diagram for explaining the correction operation. The storage unit 16b of the main control system 16 stores the sub-field image distortion correction data d1 (f1 (γ), g1 in Equations (41) to (45)) at each deflection position related to the dynamic correction described above.
(γ), ΔWdc1, j (1), ΔHdis1, j (3))
And deflection position data d2. The deflection position data is data relating to the subfield image center position (X, Y) when the image of each subfield is projected on the wafer 12, and the position deviation of the subfield image is corrected by the deflector 8. This deflection position is calculated based on the strain measurement data.

When exposing each subfield, data d1 and d2 relating to the subfield to be exposed are read from the storage unit 16b into the calculation unit 16a, and the excitation current ΔIc of each focus correction coil 21 and astigmatism corrector 22 is read. , j, ΔI
s, j and the exciting current Id, j of each deflector 8 (where j =
1, 2, 3, 4, 5) are calculated, and the signals S (d1, d2),
S (d2) is transmitted to the dynamic correction shape control system 23 and the deflector control system 24. The control system 23 for the dynamic corrector outputs the signal S (d
1, d2), the excitation current of each focus correction coil 21 is represented by ΔI
The excitation current of each astigmatism corrector is controlled to ΔIs, j, and the deflector control system 24 controls each deflector 8 to the excitation current Id, j. In the present embodiment, the equations (46) to (5) are based on the distortion correction data d1 input to the storage unit 16b.
Although the excitation currents ΔIc, j and ΔIs, j are calculated by the calculation unit 16a using the above 5), the excitation currents ΔIc,
j and ΔIs, j may be stored in the storage unit 16b and controlled.

As a method of correcting the distortion of the subfield image, there are known (a) a method disclosed in Japanese Patent Laid-Open No. 9-129544 and (b) a method using a distortion mask. In this respect, the correction method of the present invention is superior. (A) In the method disclosed in Japanese Patent Application Laid-Open No. 9-129544, the average of the maximum value and the minimum value of distortion in a subfield image is regarded as distortion in the subfield, and the distortion is corrected using a deflector. doing. On the other hand, in the present embodiment, in addition to linear distortion, higher-order distortion is also corrected by the dynamic correction system using the quadratic transformation, so that distortion can be corrected with higher accuracy. (B) On the other hand, the method using a distortion mask is a method in which a distorted pattern is formed on the mask in advance so as to cancel the distortion of the subfield image due to the electron optical system. However, since the distortion of the subfield image differs for each exposure apparatus, a distortion mask must be prepared for each apparatus, and there is a disadvantage that the mask cannot be shared.

In the above-described embodiment, the position of the image 402 of each test pattern 302 is measured using the mark M on the wafer stage 12, but each test pattern image 402 is actually exposed on the wafer 11. Then, a test pattern may be printed and the pattern formed on the wafer 11 may be measured. Further, as shown in FIG. 3, the evaluation mask 30 is provided with a plurality of subfields 31 covering the visual field range, but only one subfield 31 on which the test pattern 302 is formed is formed on the evaluation mask 30. By moving the mask stage 6 in the x and y directions, the distortion of all subfields may be measured. In the above-described embodiment, the dynamic correction system is configured by the electromagnetic coil type focus correction coil and the astigmatism corrector. However, the dynamic correction system is configured by the electrostatic type astigmatism corrector and the focus corrector. You may. In this case, the above-described equations are not equations relating to current but equations relating to voltage.

In the correspondence between the embodiment described above and the elements of the claims, the test pattern 302 is a measurement pattern, the subfield 51 is a small area, the wafer 11 is a sensitive substrate, the main control system 16, Focus correction coil 2
1, the astigmatism corrector 22 and the control system 23 for the dynamic correction system constitute correction means, and the main control system 16 and the control system 23 for the dynamic correction system constitute control means.

[0036]

As described above, according to the present invention,
Exposure is performed while preliminarily measuring the image distortion of each small area of the mask and correcting the image distortion by a dynamic correction system for each small area based on the measured value, so that pattern distortion is small and highly accurate. It can be performed. For example, it is possible to correct a distortion of a projection image due to a manufacturing error (a processing error or an assembly error) of the projection optical system.

[Brief description of the drawings]

FIG. 1 is a diagram showing an embodiment of a charged particle beam exposure apparatus according to the present invention.

FIG. 2 is a diagram showing a typical example of distortion of a subfield image, and (a) to (e) show various types of distortion.

3A and 3B are views for explaining an evaluation mask 30; FIG.
FIG. 3 is a plan view of a subfield 31, and FIG. 3B is a detailed view of a test pattern 302.

FIG. 4 is a diagram illustrating a distortion measurement operation.

FIG. 5 is a diagram showing a distorted subfield image B.

FIG. 6 is a diagram illustrating a coordinate system.

FIG. 7 is a diagram illustrating a method for correcting a linear distortion component.

FIG. 8 is a diagram illustrating a method of correcting a higher-order distortion component;
(A) to (c) show various correction methods.

FIG. 9 is a detailed view of the astigmatism corrector 22.

FIG. 10 is a block diagram for explaining a correction operation.

FIG. 11 is a diagram showing a first modification of the evaluation mask.

FIG. 12 is a diagram showing a second modification of the evaluation mask.

FIG. 13 is a schematic diagram showing a schematic configuration of a conventional electron beam exposure apparatus.

FIG. 14 is a diagram illustrating exposure transfer.

15A and 15B are diagrams for explaining a pattern image. FIG. 15A shows a pattern image in the case of a normal subfield image, and FIGS.
(C) shows a pattern image when the subfield image is distorted.

[Explanation of symbols]

 Reference Signs List 5 mask 8 deflector 9, 10 projection lens 11 wafer 12 wafer stage 16 main control system 16a operation unit 16b storage unit 21 focus correction coil 22 astigmatism corrector 23 control system for dynamic correction system 24 control system for deflector 25 reflected electron Detector 30 Evaluation mask 31, 31a, 31b, 51 Subfield 302 Test pattern 402 Test pattern image A Ideal subfield image B, B2, B3, B4, B5 Subfield image EB Electron beam M mark

Claims (6)

[Claims] 1. A charged particle beam for forming a pattern on each of a plurality of small regions provided on a mask, sequentially irradiating each of the small regions with a charged particle beam, and projecting and exposing an image of the pattern on a sensitive substrate. In the exposure method, the distortion of the image of the small area projected on the sensitive substrate is measured in advance for each small area and for each deflection position, and the image distortion of the small area is measured based on the measurement value. A charged particle beam exposure method, wherein exposure is performed while correcting each small area using a dynamic correction system including a focus correction coil and an astigmatism corrector. 2. The charged particle beam exposure method according to claim 1, wherein the plurality of strain measurement patterns formed on the evaluation mask are irradiated with a charged particle beam to measure the position of the image of the strain measurement pattern. A charged particle beam exposure method, wherein the distortion of the image of the small area is obtained by performing the following. 3. The charged particle beam exposure method according to claim 1, wherein the image distortion of the small area is decomposed into a linear distortion component and a higher-order distortion component, and the linear distortion component and the higher-order distortion component are decomposed. With respect to the distortion component to be corrected among the distortion components, (a) an aberration term relating to the distortion component and (b) an aberration correction term calculated by the focus correction coil calculated based on the excitation current of the focus correction coil, or (c) the aberration correction term Form a linear form with the aberration correction term by the astigmatism corrector calculated based on the excitation current of the point corrector, the focus correction coil and the astigmatism corrector so that a simultaneous equation consisting of the linear form is established. A charged particle beam exposure method, wherein the number is determined respectively, and the exciting currents of the focus correction coil and the astigmatism corrector are adjusted to currents calculated from the simultaneous equations. 4. The charged particle beam exposure method according to claim 1, wherein a linear form relating to a distortion component to be corrected is selected from equations (1) to (10) relating to distortion correction of the image of the small area. Form the equation, The numbers of focus correction coils and astigmatism correctors constituting the dynamic correction system are set to Nc and Ns for establishing the simultaneous equations, and the respective excitation currents of the Nc focus correction coils are calculated from the simultaneous equations. ΔIc, j
A charged particle beam exposure method, wherein each excitation current of the astigmatism correctors is adjusted to ΔIs, j calculated from the simultaneous equations. In the equations (1) to (10), (a) β and γ are the position of the pattern in the small area image and the deflection position of the small area image. (B) f1 (γ), f2 (γ) and g1 (γ) to g3 (γ) are aberration system coefficients of the aberration related to the distortion component, and f1 (γ) and f2 (γ) are related to a linear distortion component calculated from the measurement value.
(γ) to g3 (γ) relate to the secondary distortion component calculated from the measured value. (c) ΔWdc1, j (1) is the aberration correction coefficient of the focus correction coil, and relates to the linear distortion component. ) ΔWdc2, j (1) is an aberration correction coefficient of the astigmatism corrector and relates to a linear distortion component. (E) ΔHdis1, j (3), ΔHdis2, j (3), ΔHdis
3, j (3) is an aberration correction coefficient of the astigmatism corrector, 2
(F) <> represents complex conjugate 5. A charged particle beam exposure for forming a pattern on each of a plurality of small regions provided on a mask, sequentially irradiating the small regions with a charged particle beam, and projecting and exposing an image of the pattern on a sensitive substrate. In the apparatus, a storage unit in which distortion data of the image of the small area projected on the sensitive substrate is stored in advance, and a pattern projected and exposed on the sensitive substrate based on the distortion data stored in the storage unit And a correction unit for correcting the image of each of the small areas for each of the small areas. 6. A charged particle beam exposure for forming a pattern in each of a plurality of small regions provided on a mask, sequentially irradiating the small regions with a charged particle beam, and projecting and exposing an image of the pattern on a sensitive substrate. In the apparatus, a storage unit in which distortion data of the image of the small area projected on the sensitive substrate is stored in advance, a dynamic correction system including two focus correction coils and four astigmatism correctors, The excitation currents of the focus correction coil and the astigmatism corrector are expressed by the following equations (11) to (20). ΔIc, j and ΔIs, j calculated from the simultaneous equations
A charged particle beam exposure apparatus, comprising: In the equations (11) to (20), (a) β and γ are the position of the pattern in the small area image and the deflection position of the small area image. (B) f1 (γ), f2 (γ) and g1 (γ) to g3 (γ) are aberration system coefficients of the aberration related to the distortion component, and f1 (γ) and f2 (γ) are related to a linear distortion component calculated from the measurement value.
(γ) to g3 (γ) relate to the secondary distortion component calculated from the measured value. (c) ΔWdc1, j (1) is the aberration correction coefficient of the focus correction coil, and relates to the linear distortion component. ) ΔWdc2, j (1) is an aberration correction coefficient of the astigmatism corrector and relates to a linear distortion component. (E) ΔHdis1, j (3), ΔHdis2, j (3), ΔHdis
3, j (3) is an aberration correction coefficient of the astigmatism corrector, 2
(F) <> represents complex conjugate