JPH07335531A - Adjusting method of electron beam lithography system - Google Patents

Abstract

PURPOSE:To optically adjust an electron beam lithography system with high accuracy without using any objective aperture by measuring a plurality of positions in a pattern formed on a sample by a beam containing the pattern under different focus conditions and adjusting an electron optical system in the direction in which each variation, etc., becomes smaller. CONSTITUTION:A plurality of positions in a pattern formed on a sample by a beam containing the pattern are measured under different focus conditions. Then an electron optical system is adjusted in the direction in which each variation, relative variation between the positions, or both of each variation and relative variation becomes smaller. The adjustment of the electron optical system is performed against the correcting amount of the astigmatism associated with the selection of the pattern, correcting amount of the focal point associated with the selection of the pattern, intensity of the aligner of an electron$ mirror, positions of apertures 13 and 14, etc. For example, a correcting device 15 which corrects such abberation as the astigmatism, curvature of field, etc., which occurs in a transferring lens section 16 is corrected by installing the correcting section 15 to the lens section 16.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electron beam drawing apparatus adjusting method using a collective figure irradiation method.

[0002]

2. Description of the Related Art FIG. 2 shows electron trajectories in an electron beam drawing apparatus using the collective figure irradiation method when there is no aberration when selecting a figure. That is, in FIG. 2, it is assumed that no aberration occurs in the transfer lens 3 due to the off axis due to the figure selection. Since the off-axis is reduced by the reduction lens 6, the amount of aberration in the reduction lens 6 and the objective lens 8 is small. On the other hand, FIG. 3 shows electron trajectories when the aberration is generated in the electron beam deflected from the center to the outside by the transfer lens 3 provided in the latter stage in accordance with the figure selection. The dotted line shows the electron orbit when aberration is taken into consideration. Since the image plane of the second aperture 5 is determined by the position of the second aperture and the selected figure, it is not directly affected by the aberration in the transfer lens unit. Therefore, the off-axis of the image plane is shown in FIG.
It is the same as the case shown in. However, the aberration in the transfer lens portion changes the incident angle of the electron beam on the second aperture, and increases the off-axis at the central portion of the lens (particularly the objective lens). That is, a large aberration appears at the crossover. Therefore, as for the aberration of the transfer lens portion, an off-axis aberration is likely to occur in the lower lens portion due to the change of the electron trajectory accompanying it. Also, note in FIG. 3 that the electrons that form images at different points on the second aperture 5 are affected by different amounts of off-axis. That is, the electrons passing on the axis of the aperture 5 are less likely to be affected by the aberration, and are more affected to the off-axis of the aperture 5. As a result, the electron trajectories in the objective lens 8 of the electrons reaching each point on the aperture 5 are greatly different. For this reason, it becomes difficult for the electron beams from all points in the collective figure to pass through the center of the lens. Since the electron beam passing off the axis of the objective lens 8 causes a reduction in the resolution of the drawing apparatus, it is impossible to uniformly transfer a collective figure in the above state.

In the conventional collective figure irradiation method, Takemoto et al.
As clarified in the lower part of the proceedings of the 0th Joint Lecture Meeting on Applied Physics on page 552, the aberration associated with the above figure selection should be maximized by using the current amount on the sample passing through the objective aperture as a monitor. Is adjusted by.

[0004]

In the above adjusting method, if the objective aperture is large, the sensitivity to aberrations is low, and even minute aberrations cannot be completely corrected. Further, since the center of the objective diaphragm and the center of the lens do not necessarily coincide with each other in consideration of manufacturing accuracy, it cannot be said that maximizing the transmitted current is optically optimal.

An object of the present invention is to realize more accurate optical adjustment without using the above-mentioned objective diaphragm.

[0006]

SUMMARY OF THE INVENTION The above object is to provide a method of adjusting an electron beam drawing apparatus capable of performing a collective figure irradiation method, in which a plurality of positions in a figure on a sample by a figure beam irradiated on the sample are determined. Measured under different focus conditions, the amount of astigmatism correction associated with figure selection, and figure selection in the direction of reducing each variation or the relative variation between multiple positions, or both This is achieved by adjusting the amount of focus correction, the aligner strength of the electron mirror body, the position of the aperture, and the like of the electron optical system.

Achieved by defining a plurality of positions within the illuminated figure by the center of gravity of a defined area within the illuminated figure, and wherein the graphic beam is formed by two or more independent apertures provided in the aperture. It is achieved by

Further, the above-mentioned electron optical system is adjusted by an electrostatic astigmatism corrector or a focus corrector, and one of the correctors also serves as a deflector for selecting a figure.

That is, first, a plurality of positions in the irradiation figure are measured, and the distances between the plurality of positions change with the focus change when an aberration occurs due to the figure selection. The electron optical system is adjusted in the direction of reducing the amount of change, which enables highly accurate adjustment. Further, reducing the absolute change amount is effective in adjusting the axis of the entire irradiation figure. The position can be defined at a specific pattern edge or the center of a specific pattern, but the method of defining it from the center of gravity of a determined area is particularly effective. As the electro-optical element to be adjusted, a corrector for correcting the astigmatism and focus of the crossover, a position of an anaylor defining the optical axis, or the position of the aperture are mainly considered.

In order to make these adjustments, it is also effective to use a dedicated aperture figure, and a figure having a plurality of independent apertures (two or more and at most four, a small number of apertures is good) is used. Good. In the case of a figure with four openings,
If the two directions are arranged so that they do not overlap each other, the adjustment becomes easy.

[0011]

As shown in FIG. 1, the aberration generated in the transfer lens section is corrected by installing a corrector 15 in the transfer lens section for correcting aberrations such as astigmatism and field curvature generated in the transfer lens section. Correction is possible. Note that these correctors may be electrostatic correctors or electromagnetic correctors. By correcting the aberration generated in the electron beam by these correctors, it becomes possible to reduce the off-axis in the objective lens. Since the aberration that mainly affects the crossover is corrected, it is effective to dispose the corrector at a position farther from the crossover (close to the mask and its image plane).

FIG. 4 shows an enlarged view of the vicinity of the sample surface (the wafer to be drawn or the calibration mark on the stage) shown in FIG. Since the axis in the objective lens is different depending on the position of the image, the incident angle on the sample surface is different, and the distance between the two points in FIG. Therefore, the astigmatism and the image plane in the transfer lens unit can be corrected by adjusting the distance between the two points so as not to change as much as possible with respect to the change in the focus condition. As a result, the off-axis in the objective lens is suppressed, and finally the aberration generated in the objective lens is reduced. Further, FIG. 4 also shows that if the axes in the irradiation figure are different, the dimension of the figure is likely to change due to the error in focus. Furthermore, by reducing the absolute position change of the image position, the axis of the irradiation figure can be adjusted to the lens center.

The distance between the two points can be obtained by defining the position at the specific pattern edge, the center of the specific pattern, or the like. However, a method of defining the position from the center of gravity of a determined area is available. Especially effective. The reason is,
Since the resolution deteriorates when the focus is changed, the rise of the beam profile becomes slow, and there is a fear that the accuracy may be deteriorated due to the level fluctuation of the detection signal in the conventionally used methods such as edge detection. Therefore, a method of defining a position from many coordinates is effective, such as a method of obtaining the center of gravity of a pattern or a method of detecting a mark by a correlation method. Further, in order to perform these adjustments with high accuracy, it is effective to use a dedicated aperture figure instead of the device pattern used for drawing. Specifically, a figure having a plurality of independent openings (two or more and a small number of at most about 4 is preferable) is preferable because it is easy to measure the position of each opening. At this time, if the openings do not overlap in the X and Y directions, the plurality of openings can be independently detected during one-dimensional scanning on the cross wire or the like. These openings need to have a certain size to obtain a detectable current amount, and it is difficult to provide five or more openings from these viewpoints.

In the above description, the off-axis aberration of the transfer lens in the latter stage is assumed, but there are also aberrations due to the off-axis passing of the figure selection deflector 4 or 17 and aberrations due to manufacturing errors of the figure selection deflector. And similarly affect the electron orbit. In order to reduce these, it is important to correct the astigmatism and focus as described above, but it is necessary to allow the electron beam to pass through the center of the transfer lens as much as possible by adjusting the anira or aperture position. It is effective because it reduces the occurrence itself.

[0015]

Embodiments of the present invention will now be described with reference to the drawings. FIG. 1 is a view showing an electron optical system in a first embodiment of an electron beam drawing apparatus for performing collective figure irradiation, FIG. 5 is a view showing an aperture of the first embodiment, and FIG. 6 is a beam profile of the first embodiment. FIG. 7 is a diagram showing the position dependence of the aperture, FIG. 8 is a diagram showing the aperture in the second embodiment of the present invention, FIG. 9 is a diagram showing the beam profile of the second embodiment, and FIG. FIG. 11 is a diagram showing an effect of astigmatism correction, FIG. 11 is a diagram showing an aperture in the third embodiment of the present invention, FIG. 12 is a diagram showing a gold dot image, and FIG. 13 is an electron optical system in the fourth embodiment of the present invention. FIG.

First Embodiment In FIG. 1 showing the electron optical system in the first embodiment of the present invention, the second aperture 20 is arranged as shown in FIG.
A variable molding was placed in the center and two adjustment marks were placed on the periphery.
It is formed by arranging in two corners of m-square. The parts separated by broken lines become collective figures. In the present embodiment, the adjustment is performed using the two-point mark at the upper right of the first position, but the same method can be applied by using marks at other positions regardless of the graphic arrangement position. 1 μm for each of the above two marks
The adjustment is made by measuring the center coordinates of the corners. First, a cross wire or a cross heavy metal mark on a light element substrate is one-dimensionally scanned in the X and Y directions to obtain a beam profile.

FIG. 6 shows the beam profile of the two-point mark. (A) shows the case where the excitation is optimized and the focus is focused on the detection surface, and (b) shows the case where the objective lens is strongly excited. In the case of strong excitation, the beam edge becomes slow. From the center of gravity of each opening, the relative distance of the opening at each excitation is obtained. The change in excitation of this relative distance is changed. As the simplest method, the center of gravity was calculated by summing the product of the coordinates of the measurement points and the signal strength within a predetermined range and talking by summing the signal strength. In FIG. 6, the distance is shorter in the case of strong excitation. Besides, the present invention can be applied if a position is defined, for example, the position is obtained from the edge of the profile.

FIG. 7 shows the result of the change in the relative distance due to the change in focus obtained by changing the mechanical origin position of the aperture. The amount of change in both X and Y becomes the minimum when the moving distance is 300 μm. Therefore, the aperture is located at the center of the electron optical system at the position where the moving distance is 300 μm. By moving the origin position of the aperture to the center of the transfer lens in this way, it is possible to reduce the influence of off-axis in the lens and reduce the difference in relative distance in the figure. As a result, it can be seen that the change in relative distance could be adjusted to 1/3. As a result, it is possible to prevent the drawing figure from being deformed, and the shot connection accuracy is improved from 0.05 μm to 0.03 μm. The resolution was 0.1 μm. In this example, the electron beam current density did not change with an accuracy of 1% regardless of the origin position of the aperture.

Second Embodiment Another layout of the aperture is shown in FIG. In this embodiment, a mark as shown in FIG. 8 is provided, which is 0.5 μm.
Four corner openings are arranged at an interval of 1 μm. This makes it possible to know the state of the electron orbit in the figure more accurately. The beam profile is as shown in FIG. 9, and the center of gravity of each is determined. In this embodiment, when the lens is strongly excited, the relative distance between A and B in the X direction is shortened, and C and D
The relative distance in the Y direction has been expanded. This indicates that astigmatism has occurred in the transfer lens unit. Astigmatism is caused by the manufacturing error of the deflector and the asymmetry of the lens. For this, the astigmatism corrector 30 (see FIG. 13) was used for correction. The astigmatism corrector can be corrected by both the electrostatic corrector and the electromagnetic corrector. In this embodiment, an electrostatic compensator was used. As a result, as shown in FIG. 10, the change in the relative distance between A and B in the X direction and the change in the relative distance between C and D in the Y direction changes according to the astigmatism correction amount, and becomes 1/10 before correction at the optimum value. And could be reduced. As a result, it was possible to improve the shot connection accuracy as in the first embodiment. Further, the astigmatism corrector is installed closer to the first or second aperture than the crossover image of the electron source formed at the deflection center of the figure selective deflection in order to correct the difference in aberration at each point on the aperture. It is effective to do. The four-point mark can be applied to measurement of the figure distortion of the figure beam. As a result, before adjustment, 0.05μ in 6 inch wafer
The dimensional accuracy error, which was m, could be reduced to 0.03 μm.

Third Embodiment Although the four-point mark shown in FIG. 11 is used in this embodiment, the four-point mark is 1 as in the first and second embodiments.
Even if the three-dimensional beam profile is obtained, the two marks overlap and the center of gravity of each mark cannot be obtained. Therefore, in this example, two-dimensional scanning was performed using 0.2 μm gold dots to obtain a two-dimensional backscattered electron image of the four-point mark shown in FIG. This makes it possible to obtain the position information of the four marks independently. Backscattered electron 2
Even in a three-dimensional image, the change in relative distance can be quantitatively obtained by obtaining the center of gravity of each point in two directions. In FIG. 12, it is conceivable that all the marks are isotropically moved outward and that curvature of field is generated in the crossover. The field curvature can be corrected by providing an electrostatic or electromagnetic corrector in the transfer lens. Alternatively, the two-dimensional information can be obtained by two-dimensionally scanning a fine hole with a graphic beam and monitoring the electrons transmitted through the hole. In this embodiment, the connection accuracy is 0.07 due to the focus correction.
It was possible to improve from μm to 0.03 μm.

Fourth Embodiment FIG. 13 is a diagram showing the electron optical system of the fourth embodiment. The transfer deflecting unit is provided with an eight-pole electrostatic deflector 30 for selecting a figure above and below the variable shaping electrostatic deflector 29. Are matched. Aberrations associated with figure selective deflection are 8
The correction is performed by applying a voltage to the electrostatic deflector 30 of the pole, that is, by using both the electrostatic deflector and the electrostatic astigmatism corrector. As a result, astigmatism correction by electrostatic correction that is not affected by response delay such as eddy current can be performed without increasing the place. Since the aberration changes depending on the position of the figure to be selected, it is necessary to dynamically correct the aberration in association with the figure selection. Since the value to be corrected can be obtained in advance by the method of the above embodiment or the like, it is important to shorten the time for setting the value. In this embodiment, since the astigmatism correction was performed by the electrostatic compensator, the correction was possible in 3 μs. Further, if the correction is performed in a place where the off-axis due to the figure selection is large, the position of the first aperture image on the second aperture is greatly moved due to the correction, which may be an obstacle to the correction. Therefore, it is advantageous that the astigmatism corrector 30 is also used as the upper deflector because it is less likely to be affected by this. Of course, the correction can be performed even if it is used also as the lower deflector. The same thing can be done with the electrostatic focus corrector, and a voltage for focus correction may be applied to the deflector.

In addition to the above-mentioned respective embodiments, the position and operating conditions of the electron gun, the inclination of the aperture, etc. can be considered as the electron optics adjusting method, and any of them can be adjusted by reducing the position change of the irradiation figure. become.

[0023]

As described above, the adjusting method of the electron beam drawing apparatus according to the present invention is the same as the adjusting method of the electron beam drawing apparatus capable of performing the collective figure irradiation method, and the sample shape beam irradiated on the sample is used. Astigmatism associated with figure selection in the direction of measuring multiple positions in a figure under different focus conditions and reducing the amount of change of each, the relative change between multiple positions, or both. By adjusting the amount of aberration correction and the amount of focus correction associated with figure selection, and the electron optical system such as the aligner strength and aperture position of the electron mirror body, the aberration that occurs at the crossover is measured and reduced. It is possible to realize accurate drawing.

[Brief description of drawings]

FIG. 1 is a diagram showing an electron optical system of a first embodiment in an electron beam drawing apparatus that performs collective graphic irradiation.

FIG. 2 is a diagram showing electron trajectories when a figure is selected when there is no aberration.

FIG. 3 is a diagram showing electron trajectories when a figure is selected when there is an aberration.

FIG. 4 is a diagram showing electron trajectories in the vicinity of the sample surface.

FIG. 5 is a diagram showing an aperture of the first embodiment.

6A and 6B are diagrams showing a beam profile of the first embodiment, wherein FIG. 6A is a diagram showing a case of an image formation state, and FIG. 6B is a diagram showing a case of strong excitation.

FIG. 7 is a diagram showing position dependence of an aperture.

FIG. 8 is a diagram showing an aperture according to a second embodiment of the present invention.

9A and 9B are diagrams showing a beam profile of the second embodiment, wherein FIG. 9A is a diagram showing a case of an image formation state, and FIG. 9B is a diagram showing a case of strong excitation.

FIG. 10 is a diagram showing an effect of astigmatism correction.

FIG. 11 is a diagram showing an aperture according to a third embodiment of the present invention.

12A and 12B are diagrams showing a gold dot image, FIG. 12A showing a case of an image formation state, and FIG. 12B showing a case of strong excitation.

FIG. 13 is a diagram showing an electron optical system in a fourth example of the present invention.

[Explanation of symbols]

 9, 27 Sample surface (wafer) 13, 14, 20, 21 Aperture 15 Astigmatism corrector 19, 30, 31 Figure selective deflector

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification number Internal reference number FI Technical indication location H01J 37/21 Z 37/305 B 9172-5E (72) Inventor Hiroyuki Ito Ichige Katsuta, Katsuta City, Ibaraki Prefecture 882 Address: Hitachi, Ltd., Measurement Instruments Division (72) Inventor: Shinichi Kato, 882, Ige, Katsuta-shi, Ibaraki Hitachi Ltd., Measurement Instruments Division

Claims (4)

[Claims] 1. An electron beam drawing apparatus adjusting method capable of performing a collective figure irradiation method, wherein a plurality of positions in a figure on a sample by a figure-shaped beam irradiated on the sample are set under different focus conditions. Astigmatism correction amount due to figure selection, focus correction amount due to figure selection in the direction of decreasing the change amount of each change amount or the relative change amount between a plurality of positions or both of them by measuring. A method for adjusting an electron beam drawing apparatus, which comprises adjusting an electron optical system such as aligner strength of an electron mirror body and position of an aperture. 2. The adjusting method for an electron beam drawing apparatus according to claim 1, wherein the plurality of positions in the irradiation figure are defined by the center of gravity of a predetermined area in the irradiation figure. 3. The method of adjusting an electron beam drawing apparatus according to claim 1, wherein the figure-shaped beam is formed by two or more independent openings provided in the aperture. 4. The electronic optical system is adjusted by an electrostatic astigmatism or focus corrector, and any one of the correctors is also used as a deflector for selecting a figure. A method for adjusting the electron beam drawing apparatus described.