JP2002246303A - Method of adjusting focal point and electron beam lithography system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of adjusting focal point, by which the focal point of a beam including a beam having an arbitrary shape can be adjusted with high accuracy, and to provide an electron beam lithography system which can write a pattern with high accuracy. SOLUTION: The lens value of an objective lens 8 is set in a plurality of stages, by using an objective lens driving circuit 21 or a dynamic focal point corrector 22, and the focal point of the lens 8 is adjusted to the lens value at which positional deviation δr of a mark on the surface 28 of a sample becomes minimal, by scanning the deviation of the axis of the lens 8 using a deflection control circuit 14, while the angle θ of incidence on the lens 8 is changed under different conditions and measuring the positional deviation δr by means of mark position detecting mechanisms 16 and 18.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electron beam lithography apparatus in the field of semiconductor manufacturing and the like, and more particularly to a method of adjusting the focus of an electron beam having an arbitrary cross-sectional shape and an electron beam lithography apparatus.

[0002]

2. Description of the Related Art In the field of semiconductor manufacturing, an electron beam lithography apparatus has been demonstrated to be useful in pattern production functions for mask originals such as light exposure and the like, and for direct drawing of small-quantity multi-products, especially for trial production of advanced devices. . The electron beam lithography apparatus projects and scans an electron source image and a beam shaping aperture image on a sample surface to form a fine pattern. In particular, in the latter variable shaping method, the beam shape is controlled by a rectangular shaping aperture and a shaping deflector, and the pattern is efficiently formed by reducing and projecting the beam onto the sample surface. For this reason, the variable shaping method achieves a higher writing speed than the point beam method for transferring the electron source image. Furthermore, in recent years, a partial batch exposure method for forming and transferring a repetitive pattern as a batch exposure aperture in advance has been put to practical use, and has dramatically improved the drawing speed and achieved higher precision.

Under such circumstances, the design rule of semiconductor devices has been reduced to 100 nm or less, and it is important to improve the accuracy of focus correction in order to stably maintain fineness. Conventionally, beam blur has been measured by mark scanning and waveform blur. For example, in the case of a Gaussian beam, the half value width of the scanning waveform or the differential waveform is quantified as the rising edge of the primary differential waveform or the peak value of the secondary differential waveform in the case of a simple rectangular beam, and the optimal focus position is obtained. .

The dynamic focus (dynamic focus adjustment) is described in, for example, JP-A-2000-22816.
No. 4 discloses such a technique.

[0005]

However, the above-mentioned system using differentiation has the following problems. The first point is that advanced signal processing such as differential processing is required, processing time is long, and differential processing is weak against noise. Second, in the case of a batch transfer beam having a complicated shape, it is difficult in principle to quantify beam blur. For example, in the case of a circular aperture or an angle figure, it is difficult to extract a beam blur with a normal beam scanning waveform. Further, from the viewpoint of beam positioning accuracy, a beam imaging position shift due to a focus shift becomes a problem.

SUMMARY OF THE INVENTION An object of the present invention is to provide a focus adjusting method or an electron beam writing apparatus which enables highly accurate beam focus adjustment.

Another object of the present invention is to provide a focus adjustment method for realizing high-precision beam focus adjustment including a beam having an arbitrary shape or an electron beam lithography apparatus capable of high-precision pattern writing.

[0008]

A first feature of the present invention is a method of adjusting the focus of an electron beam drawing apparatus,
Setting the objective lens to a plurality of different lens values; changing the incident angle under these lens values to scan on the calibration mark; and detecting the beam position on the sample stage in these scans And a step of determining a lens value that minimizes a beam position shift caused by a change in the incident angle, and a step of setting the determined lens value as a lens value of the objective lens.

A second feature of the present invention is that, in the electron beam lithography apparatus, means for setting the objective lens to a plurality of different lens values, and under each of these conditions, the angle of incidence by the axis adjusting deflecting means. Means for scanning the calibration mark to detect the beam position on the sample stage, and means for setting the objective lens with a lens value that minimizes the displacement of the beam position caused by a change in the incident angle. It is prepared.

By measuring the displacement in this way, it is possible to set a desired optimum lens value without using complicated differentiation processing or the like. Focusing is possible by measuring the position of an arbitrary pattern. Furthermore, even if there is some beam axis deviation, the beam irradiation position deviation can be minimized.

Other features of the present invention will become apparent from the following description of embodiments.

[0012]

FIG. 1 is a diagram showing the overall configuration of a variable-shaped electron beam lithography apparatus according to one embodiment of the present invention.
In FIG. 1, an electron beam emitted from an electron source 1 passes through a first forming aperture 2 having a generally rectangular shape, and a shaped lens 3 is formed.
Thereby, an image is formed on the second forming opening 4. Second forming opening 4
A rectangular aperture or the like is arranged, and the shape of the first rectangular aperture image position is controlled by the shaping deflector 5 to generate a shaping beam 6. The formed shaping beam 6 is reduced to several tenths by a reduction lens 7 and is incident on an objective lens 8. The objective lens 8
An image of the shaped beam 6 is formed on the sample stage 9. The sample stage drive system 10 and the objective deflector 11 sequentially move the shaping beam 6 to the drawing position, irradiate the beam, irradiate the beam, and LS on the drawing sample.
Draw an I pattern. The control computer 12 adjusts the beam shape according to the drawing data by the shaping / deflection drive system (control circuit) 1.
3. The irradiation position is driven and controlled via the objective deflection control circuit 14 and the sample stage control circuit 15. In the batch exposure method, a desired shape opening is further selected by the molding deflection drive system 13. The backscattered electron detector 16 detects electrons reflected from the calibration mark 17 arranged on the sample stage 9. The signal processing circuit 18 performs beam scanning on the mark 17 by the objective deflector 11 and detects a beam position and the like from the obtained signal waveform. 19 is an axis adjusting deflector, and 20 is a drive circuit thereof.
The objective lens drive circuit 21 adjusts the lens value of the objective lens 8 and adjusts the focus. In addition, a dynamic focus corrector 22 for performing focus adjustment at a higher speed and a driving circuit 23 thereof are provided.
Any of these may be used.

FIG. 1 omits a beam blanking function for controlling the irradiation dose, a sample stage coordinate measuring mechanism, and a sample for simplification. Although FIG. 1 shows a variable-shaped electron beam lithography apparatus, it is obvious that the present invention can also be applied to a Gaussian (point) beam in principle. In that case, in FIG. This is an optical system in which the molding optical system is omitted.

FIG. 2 is a principle diagram of the present invention, schematically showing the objective lens imaging relationship in the configuration shown in FIG. The coordinate axes are Z axis in the axial direction of the objective lens 8 and XY on a plane perpendicular to the Z axis.
Take the axis. An on-axis beam 25 entering the objective lens 8 from an object point 24 on the Z axis converges on an on-axis imaging point 26 by the action of the objective lens 8. Similarly, the off-axis beam 27 inclined at an off-axis incident angle θ from the object point 24 is also converged on the image point 26 by the lens action. If the lens value (lens strength) of the objective lens 8 is insufficient, the imaging point 26 moves farther. Therefore, equivalently, the sample surface 28 in FIG. It is equal to approaching the sample surface 29 by h. Therefore, the sample arrival point 26 of the on-axis beam 25
On the other hand, the sample arrival point of the off-axis beam 27 is shifted by δr on the XY coordinate plane. This shift disappears when the lens value of the objective lens 10 is appropriately increased by using the objective lens drive circuit 18 or the dynamic focus corrector 22, and 1
Can converge to a point. In the present invention, this focusing is realized by the following method.

That is, while changing the beam incident angle θ using the axis adjusting deflector 19, the sample arrival point is detected by scanning using the objective deflector 11, and the on-axis beam arrival point 2 is detected.
The lens value of the objective lens 8 that minimizes the deviation δr from 6 is obtained as the output of the objective lens driving circuit 18 or the correction value by the dynamic focus corrector 22. The conditions obtained in this way are the optimum lens values. Beam displacement δr
Can be measured by a normal mark position detection function using the backscattered electron detector 16 and the signal processing circuit 19.

The above is the basic principle of one embodiment of the present invention. More specifically, first, the on-axis beam 25 that has passed through the object point 24 of the objective lens in FIG. If the lens value of the objective lens 8 is appropriate, also in the case of the off-axis beam 27 deflected by the angle θ using the axis adjusting deflector 19 having the fulcrum at the objective lens object point 24, the lens action of the objective lens 8 also causes It should converge to the sample imaging point 26. Therefore, the axis adjusting deflector 19 scans while changing the incident angle θ in a predetermined plurality of stages, and determines the arrival points of the beams 25 and 27 on the sample surface 28 at this time by the reflected electron detector 16 shown in FIG.
If it is detected by the above, the lens value of the objective lens 8 that minimizes the deviation δr of the sample arrival point, that is, the output value of the objective lens drive circuit 18 or the output value of the correction control circuit 23 to be given to the dynamic focus corrector 22 is obtained. Can be.

In general, electrons passing through the object point 24 converge on an image point 26 if the incident angle θ is small and the paraxial assumption is satisfied. If the incident angle θ is increased, a change in the beam trajectory and a change in blur at the image forming point 26 become large due to the influence of spherical aberration and the like proportional to the cube of the convergence angle. For this reason, it is usually desirable that the opening angle of the on-axis beam 25 be about the same. That is, the output value of the correction circuit 23 to the drive circuit 21 of the objective lens 8 and the dynamic focus corrector 22 is changed, and the displacement δr is measured at the incident angles θ = 0 and θ = θ,
Find the minimum output value.

In order to maintain the correction accuracy of this embodiment, an angle deflecting function for scanning the incident angle θ without changing the position of the object point 24 is required. This can be achieved by using the axis adjusting deflector 19 as shown in FIG. 2 and making the object point 24 coincide with the deflection center point passing on the axis in the deflector as viewed from the emission side. Under this condition, the deflection angle θ can be changed without changing the position of the object point 24. However, even if the position of the object point 24 does not exactly coincide with the deflection center of the axis adjusting deflector 19, focus correction can be performed by measuring the displacement δr under a plurality of imaging conditions and minimizing the variation.

The object point 24 is located at the center of the axis adjusting deflector 19.
When it is difficult to dispose the shaft adjusting deflector 19, an axis adjusting deflector 19 is arranged at a stage subsequent to the object point 24 side, and a return deflector is further added at a later stage to perform two-stage deflection. It is possible to move the deflection center point out of the range. That is,
In this case, the axis adjusting deflector 19 includes a first axis adjusting deflector, and a second axis deflector which is deflected back to the first axis adjusting deflector with the electron source image or the formed aperture image as a fulcrum. It has an axis adjusting deflector.

According to this embodiment, by measuring the displacement, a desired optimum lens can be set without using complicated differentiation processing or the like. In addition, focusing can be performed by measuring the position of an arbitrary pattern. Further, it can be seen that even if there is some beam axis deviation, the beam irradiation position deviation can be minimized.

FIG. 3 is a principle diagram of field curvature correction according to a second embodiment of the present invention, schematically showing the image forming relationship by the objective lens in the configuration shown in FIG. The figure shows an example of so-called field curvature in which the image forming point shifts to the lens side due to the beam deflection. When the beam is deflected at a large angle as in an electron beam lithography apparatus, since the focal point deviates from the plane of the sample projection plane 28 due to the curvature of field, the image forming position is adjusted by the focus corrector 22.
Need to be fixed. The same method as that of FIG. 2 can be applied to the field curvature correction.

In FIG. 3, focusing is accurately performed on the central axis of the objective lens 8, that is, with the objective deflection amount R = 0.
A thick solid line 25 in the figure is an on-axis beam, and the objective deflector 1
1 and XY from the center of deflection on the sample surface 28.
A case where the landing point 26 is deflected by R on the coordinate plane is shown. However, similarly to FIG. 2, the on-axis beam 25 is deflected by the angle θ by the
When the off-axis beam is indicated by 7, the deflection image point (field curvature store) 30 is formed above the sample surface 28 by δ _Z due to the influence of the field curvature aberration that is the deflection aberration. Therefore, on the sample surface 28, the droplet lands on the imaging point 31 which is also shifted from the imaging point 26 by δr.

Also in this embodiment, the field curvature is corrected by changing the electromagnetic field strength of the drive (control) circuit 18 of the objective lens 8 or the dynamic focus corrector 22 depending on the deflection coordinates (X, Y). . The dynamic focus corrector 22 is particularly suitable for use when the electrical load on the main lens is large and high-speed operation is not possible.

In the concrete measurement of the correction amount, a value that minimizes the deviation δr at a plurality of representative points in the deflection area is obtained as in the case of FIG. According to the present embodiment, the off-axis beam after performing the focus adjustment is corrected as indicated by a dashed line 32,
It has landed on the correct imaging point 26 on the sample surface 28. The deflection-dependent formula of the measured correction amount, that is, the focus correction formula is approximated by a second-order polynomial of X and Y as follows.

FIG. 4 illustrates a specific example of the shift δr when the axis is shifted in the X-axis direction in FIG. 3 using a two-dimensional map of an XY coordinate plane on the sample surface 28. In the figure, a broken line 32 is an ideal image formation point, and a solid line 33 is an actual image formation point due to field curvature. The displacement amount δr (δX, δY) is given by δX = A ₀ + A ₁ X + A ₂ Y + A ₃ X ² + A ₄ XY + A ₅ Y ² +
_{··· δY = B 0 + B 1} X + B 2 Y + B 3 X 2 + B 4 XY + B 5 Y 2 +
... can be represented by In FIG. 4, the δr distortion shape is 2 for X and Y.
It has the following curve. According to the theory of geometric aberration, the defocus δZ due to the curvature of field of a rotationally symmetric system has a relationship with the deflection amount R as follows: δZ = KcR ² = Kc (X ² + Y ² ). Further, the displacement amount δZ is a minute amount, and can be considered as a straight line from the image surface to the sample surface. Therefore, when the displacement amount δZ is a quadratic expression of X and Y, the displacement amount δr can be approximated by a quadratic expression. Since the focus correction sensitivity is also considered to be linear, it can be seen that the output of the focus corrector 22 for correcting the displacement amount δZ can be approximated by a second-order X, Y polynomial.

In the above embodiment, the objective lens 8 for forming a beam image on the sample surface 28, the means 21 or 22 for adjusting the focal point of the objective lens 8, and the objective lens disposed in front of the objective lens 8 Axis adjusting / deflecting means 19 for controlling the angle of incidence θ of the beam to the beam 8; an objective deflector 11 for deflecting the beam image to a desired position on the sample surface 28; and an objective deflection control means 14 for controlling the objective deflector 11 An electron beam comprising: a sample stage 9 on which a writing sample is mounted; and a beam detecting means 16 for detecting a transmitted or reflected beam generated by scanning the calibration mark 17 on the sample stage 9 using the objective deflector 11. In the drawing apparatus, means for setting the objective lens 8 to a plurality of different lens values by using the focus adjusting means 21 or 22 and input / output by the axis adjusting / deflecting means 19 under these respective conditions. Means 16 and 18 for detecting the beam position on the sample stage 9 by scanning the calibration mark 17 by changing the angle θ, and the lens value for minimizing the beam position shift δr caused by the change of the incident angle θ Is set to the objective lens 8.

FIG. 5 is a flowchart showing a correction processing procedure according to one embodiment of the present invention, and shows the case of FIG.
First, in step 501, the lens strength (lens value) of the objective lens 8 is controlled by the drive (control) circuit 18 of the objective lens 8 or the correction control circuit 23 of the dynamic focus corrector 22.
Is set to Oi (i = 1 to n). In this state, in step 502, the output of the drive circuit 20 to the axis adjusting deflector 19 is changed to set the incident angle θi (i = 1 to m), and then in step 503, the beam position δri is measured. This is measured m times, ie, δr ₁ ,... Δri,... Δrm. If it is determined in step 506 that the measurement of all the predetermined n lens values O ₁ ,... Oi,... On is completed, the process proceeds to step 507, and the optimum objective lens value Oopt is calculated as follows.

For example, assuming that the lens value of the objective lens 8 is O, the displacement amount δr can be approximated by δr = K ₀ + K ₁ O + K ₂ O ² +. As apparent from FIG. 2, K ₂ thereafter can be approximated by zero. In this case, the displacement amount δr is obtained at a plurality of points, the coefficient is obtained by the least square method, and the optimal objective lens value Op
t becomes Oopt = K ₀ / K ₁ . When correcting the curvature of field, approximations are further approximated by quadratic expressions of deflection coordinates X and Y from FIGS.

The focus adjusting method of the electron beam lithography apparatus according to the present embodiment includes a step of setting the objective lens 8 to a plurality of n different lens values Oi (i = 1 to n), and a step under each of these setting conditions. Then, the incident angle θ is changed to θi (i = 1 to m) by the incident angle changing means 19 so that the objective deflector 1
Scanning the calibration mark 17 using the step 1 and detecting the beam position on the sample stage 9 in these scans, and the deviation δr of the beam position caused by the change in the incident angle θ is minimized. A step of determining the lens value Oopt and a step of setting the determined lens value Oopt as the lens value of the objective lens 8 are included.

According to this focus adjusting method, a high-resolution beam focus adjusting method for an electron beam lithography apparatus can be realized. Since the focus is directly corrected so as to minimize the beam position shift, high-precision positioning is possible. The speed can be increased as compared with the method of analyzing and evaluating beam blur, and the beam focusing method in the collective cell exposure method including an arbitrary figure shape beam is possible.

[0031]

According to the present invention, it is possible to provide a highly accurate beam focus adjusting method for an electron beam lithography apparatus and an electron beam lithography apparatus capable of performing a highly accurate pattern writing.

[Brief description of the drawings]

FIG. 1 shows the overall configuration of a variable-shaped electron beam lithography apparatus according to one embodiment of the present invention.

FIG. 2 is a principle diagram of a first embodiment of the present invention, schematically showing an image forming relationship by an objective lens in the configuration in FIG.

FIG. 3 is a principle diagram of field curvature correction according to a second embodiment of the present invention, schematically showing an image forming relationship by an objective lens in the configuration in FIG. 1;

FIG. 4 is an explanatory diagram of the present invention showing an example of a position shift of a field curvature beam.

FIG. 5 is a control processing flowchart according to an embodiment of the present invention.

Claims (10)

[Claims] 1. An objective lens for forming a beam image on a sample surface, means for adjusting the focal point of the objective lens, and means for controlling the angle of incidence of the beam on the objective lens, which is disposed before the objective lens. An objective deflector for deflecting a beam image to a desired position on a sample surface, means for controlling the objective deflector, a sample stage on which a writing sample is mounted, and calibration on the sample stage using the objective deflector. Means for detecting a transmitted or reflected beam generated by scanning a mark, comprising the steps of: setting the objective lens to a plurality of different lens values; Scanning the calibration mark by changing the incident angle by the incident angle changing means under setting conditions; and detecting the beam position on the sample stage in these scans. And a step of determining a lens value that minimizes the deviation of the beam position caused by a change in the incident angle, and a step of setting the determined lens value as a lens value of the objective lens. A focus adjusting method for an electron beam writing apparatus. 2. An objective lens for forming a beam image on a sample surface, means for adjusting the focal point of the objective lens, and an axis adjustment disposed before the objective lens and controlling an incident angle of the beam to the objective lens Deflection means, an objective deflector for deflecting the beam image to a desired position on the sample surface, an objective deflection control means for controlling the objective deflector, a sample stage on which a writing sample is mounted, and the objective deflector An electron beam lithography apparatus comprising: a beam detection unit that detects a transmitted or reflected beam generated by scanning a calibration mark on the sample stage. The objective lens is set to a plurality of different lens values using the focus adjustment unit. Means for detecting the beam position on the sample stage by changing the angle of incidence by the axis adjusting / deflecting means and scanning the calibration mark under these respective conditions. Electron beam lithography apparatus, wherein a lens value deviation of the beam position caused by the change of the incident angle is minimized and means for setting the objective lens. 3. The apparatus according to claim 2, wherein said focus adjustment means comprises:
An electron beam writing apparatus, comprising: an objective lens driving circuit; and a dynamic focus correction unit, wherein the lens value setting unit is configured using the dynamic focus correction unit. 4. An objective lens for forming an electron source image for generating an electron beam or a shaping aperture image for shaping an electron beam on a sample surface, an objective lens driving circuit for adjusting a focus of the objective lens, and the objective lens An axis adjusting deflector that is arranged in front of the lens and controls the angle of incidence on the objective lens; an axis adjusting deflection control circuit that controls the axis adjusting deflector; and an object that deflects the beam image to a desired position on the sample surface. A deflector, an objective deflection control circuit for controlling the objective deflector, a sample stage on which a drawing sample and a calibration mark are mounted, a stage control circuit for positioning the sample stage, and a calibration on the sample stage by the objective deflector. In an electron beam lithography apparatus comprising a beam detector for detecting a transmitted or reflected beam generated by scanning a mark with a beam, the output of the axis adjusting deflector is varied to calibrate the mark. Means for scanning the laser beam to detect a beam position shift on the sample surface, and setting the lens value of the objective lens to a lens value at which the beam position shift based on varying the output of the axis adjustment deflector is minimized. An electron beam lithography apparatus characterized by comprising means for performing. 5. An electron beam lithography apparatus according to claim 4, wherein the center of said beam axis adjusting deflector is arranged at the position of an electron source or a shaped aperture image formed on said sample surface. 6. An axis adjusting deflector according to claim 4, wherein said axis adjusting deflector supports said electron source image or shaped aperture image with respect to said first axis adjusting deflector. An electron beam lithography apparatus comprising: a second swing-back axis adjusting deflector that is angle-deflected. 7. A means according to claim 4, wherein said means for variably controlling said axis adjusting deflector at a plurality of representative points in a deflection area, and a change in a displacement amount at said plurality of representative points are minimized. An electron beam lithography apparatus comprising: means for setting an output of the objective lens driving circuit at a focal point. 8. The objective lens according to claim 4, further comprising a dynamic focus corrector disposed in said objective lens, and a focus correction circuit for controlling said dynamic focus corrector. An electron beam writing apparatus, wherein the means for setting a value performs correction using the focus correction circuit. 9. The focus correction value according to claim 4, wherein the position shift amount is measured with respect to a plurality of focus correction values, and a focus correction value that minimizes the position shift amount is approximated by a polynomial of a focus correction output. An electron beam lithography apparatus comprising means for determining. 10. An electron beam writing apparatus according to claim 4, wherein the optimum focus correction amount is approximated by a second-order polynomial of deflection coordinates.