JP2000164501A - Charged particle beam exposure system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a charged particle beam exposure system for validly removing theoretically removable blur or distortions in actuality. SOLUTION: A pattern formed on a reticule 2 is reduced and transferred to a wafer 3 by a first projecting lens 4 and a second projecting lens 5. A deflector 7 is used for transferring the pattern of a part which is not present on an optical axis 1, and a dynamic focusing coil 8 and a stigmater 9 are used for correcting blurs or distortions caused by the deflection. One stigmater 9 is arranged at the reticule 2 side with a scatter aperture 6 face interposed, and one stigmater 9 is arranged at the wafer 3 side so that the symmetry of electromagnetic fields tends to be ensured, and any blur or distortion left without being completely corrected can be reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for forming a pattern formed on a reticle (including a mask, the same in the present specification) using a charged particle beam such as an electron beam on a sensitive substrate such as a wafer. The present invention relates to a charged particle beam exposure apparatus for exposing and transferring the image, and more specifically, by appropriately selecting the arrangement and size of a stigmeter for dynamic correction,
The present invention relates to a charged particle beam exposure apparatus capable of effectively removing blur and distortion.

[0002]

2. Description of the Related Art In recent years, fine processing techniques for semiconductors have been progressing year by year. Current exposure apparatuses mainly use light, but in order to carry out further fine processing, a shorter wavelength of light is required. However, there is a limit to shortening the wavelength, and although an exposure apparatus using X-rays has been considered, it has not been put to practical use at the present time because it is not easy to manufacture a reticle. Against this background, electron beam transfer and exposure have attracted attention.
Various proposals have been made for optical systems in electron beam exposure, and MOL (Moving Objective Lens) (E. Goto, et al.
Optik 48, 255 (1977)), VAL (Variable Axis Len
s) (HC Pfeiffer and GO Langner, J. Vac.
echnol. 19, 1058 (1981)), VAIL (Variable Axis)
ImmersionLens) (MA Sturans, et al, J. Vac. Sc
i. Technol. B8, 1682 (1682)) and the like.

[0003]

However, the above M
Even in the OL, VAL, and VAIL optical systems, when a fine pattern on a reticle is actually exposed and transferred onto a wafer by an electron beam, distortion and blur due to geometrical aberrations in the electron optical system are extremely large and can be used. Not something.

On the other hand, the present inventor has proposed a method of reducing distortion and aberration by using six deflectors in a two-stage lens and optimizing the inner diameter, angle, exciting current, position, etc. of each deflector. And filed an application in 1997 as Patent Application No. 60881 (prior application invention). However, of those blurs and distortions, those that can be theoretically removed by dynamic correction were ignored.

[0005] That is, in the invention of the prior application, very excellent optical characteristics can be obtained, but in the case of the advanced invention alone, large blur and distortion remain when dynamic correction is not performed. Conventionally, when performing dynamic correction, two stig meters and a dynamic focus coil 3 are used.
It is reported that one is needed.

[0006]

However, in the above-described optical system, if only a stigmator and a dynamic focus coil are arranged in a dark cloud, the third and fifth order aberrations which can be theoretically removed by dynamic correction can be obtained. Even so,
There is a problem that it is difficult to perform correction so that it is practically sufficiently small.

For example, in order to realize exposure of a pattern having a minimum line width of 100 nm or less, it is desirable that the blur is 100 nm or less and the distortion is 10 nm or less. Further, when a smaller minimum line width is required, it is necessary to reduce the blur and distortion to smaller values. In particular, it is required to reduce distortion in nm units. Further, if the blur and distortion can be reduced by 1 nm by performing the dynamic correction, other required accuracy such as the stage positioning accuracy can be relaxed accordingly.

The present invention has been made in view of such circumstances, and it is an object of the present invention to provide a charged particle beam exposure apparatus capable of effectively removing blur and distortion that can be theoretically removed even in reality. And

[0009]

A first means for solving the above problem is to reduce or enlarge a pattern formed on a reticle to 1: M on a sensitive substrate by using a charged particle beam. A charged particle beam exposure apparatus that performs exposure transfer and has six deflectors for transferring a pattern on a reticle surface off the optical axis onto a sensitive substrate off the optical axis. A charged particle beam exposure apparatus, wherein one is arranged on the reticle side and one is arranged on the sensitive substrate side across the aperture surface.

In an exposure transfer optical system of a charged particle beam exposure apparatus, a lens or the like is arranged point-symmetrically with respect to the center of the aperture with an aperture interposed therebetween, and an electromagnetic field formed by the lens or the like moves a point with respect to the center of the aperture. It is designed to be formed symmetrically. This is because by doing so, it is easy to reduce blur, distortion, and aberration of the image.

The inventor pays attention to this point, and even in the case of disposing the stigmator, by preventing the symmetry of the electromagnetic field with respect to the center of the aperture from being destroyed, the blur or distortion of the image that can be theoretically removed can be reduced. An experiment was conducted on the assumption that it could be removed even by an actual charged particle beam exposure apparatus. As a result, as described later, by disposing one stigmometer on the reticle side and one on the sensitive substrate side with the aperture surface interposed therebetween, it is possible to reduce the electromagnetic field rather than to dispose two stigmators on one side of the aperture. It has been proved that since the symmetry is easily ensured, it is possible to reduce blurs and distortions that cannot be completely corrected.

A second means for solving the above-mentioned problem is as follows.
The first means, wherein the two stigmeters are arranged at positions that are 1: M point-symmetric with respect to the aperture center (Claim 2). .

By arranging the two stigmeters in this manner, it has been proved that the symmetry of the electromagnetic field can be more easily ensured, and as will be described later, the blur and distortion remaining without being completely corrected can be reduced.

A third means for solving the above-mentioned problem is as follows.
In the first means, the two stigmeters are arranged at a point symmetrical with respect to the aperture center at a point of 1: M, and the size (inner diameter / outer diameter / length) of the reticle-side stigmeter ) And the size ratio of the wafer-side stig meter is set to 1: M (claim 3).

By arranging the two stigmeters in this way and by providing a symmetrical size, the symmetry of the electromagnetic field can be more easily ensured. It has been proved that the distortion can be further reduced.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments according to the present invention and comparative examples will be described below in detail with reference to FIGS. Here, an electron beam exposure apparatus will be described as an example. In the following description. The optical axis
The description will be made on the assumption that the z-axis is the origin of the wafer surface and the reticle direction is negative. The lens barrel length (distance from the reticle surface to the wafer surface) is 400 mm, the beam opening angle is 6 mrad, the forming beam size is 0.25 mm square, and the maximum main deflection position on the wafer surface is
It was 2.375 mm x 0.375 mm. Also, the beam energy is reduced to 10
At 0 keV, the energy spread of the electron beam was 5 eV, and the aperture position was -80 mm.

FIG. 1 is a schematic view of an optical system according to an embodiment of the present invention and a comparative example. In FIG. 1, 1 is an optical axis, 2 is a reticle, 3 is a wafer, 4 is a first projection lens, and 5 is a second projection lens.
A projection lens, 6 is an aperture, 7 is a deflector, 8 is a dynamic focus coil, and 9 is a stigmator. This optical system reduces the pattern on the reticle 2 to ウ ェ ハ and transfers the pattern onto the wafer 3.

The first projection lens used in this embodiment and the comparative example had a pole piece interval of 120 mm and a pole piece inner diameter of 280 mm, and was arranged so as to have a center at a position of z = -240 mm.
The second projection lens has a size of the first projection lens 1/4, that is, a pole piece interval of 30 mm, and a pole piece inner diameter of 70 mm.
, And was installed so as to have a center at the position of z = -40 mm. That is, the arrangement and size of the first projection lens and the second projection lens are determined so as to be 4: 1 point-symmetric with respect to the center of the aperture.

A description will be given of the result before dynamic correction when such a lens field is optimized using six deflectors.
The six deflectors are arranged from the reticle side toward the wafer side.
fa1, defa2, defa3, defb3, defb2, defb1. Each of the deflectors was a toroidal coil type deflector having a shape as shown in FIG. FIG. 2 shows an x-axis direction deflector, and a y-axis direction deflector obtained by rotating the one shown in FIG. 2 by 90 ° is used. As shown, the inner radius of the deflector is R1, the outer radius of the deflector is R2,
The length of the deflector is L, and the shape of such a deflector is (R1,
R2, L).

In this embodiment, defb1 = defb2 =
defb3 = (26, 32, 8) (unit: mm), and the center position of each deflector is z (defa1) =-328mm z (defa2) =-272mm z (defa3) =-148mm z (defb3 ) =-63 mm z (defb2) =-32 mm z (defb1) =-18 mm As a result of optimizing the excitation current of the deflector, blurring is 2290 nm before dynamic correction and distortion is 470 nm, but most of these are due to dynamic correction, theoretically blurring 60 nm and distortion 4.
Reduced to 2nm.

The dynamic correction was performed using a toroidal coil stigmeter. The shape of the stig meter is shown in FIG. FIG. 3 shows a stigmeter for dynamic correction in the x-axis direction. As the stigmeter for dynamic correction in the y-axis direction, the one shown in FIG. 3 rotated by 90 ° is used. The dynamic focus coil is
((Diameter 207mm, position -110mm), (diameter 207mm, position -100
mm) and (diameter 51.75 mm, position -75 mm)).

As shown in the drawing, the inner radius of the stig meter is R1, the outer radius of the stig meter is R2, the length of the stig meter is L, and the shape of such a stig meter is represented by (R1, R2, L). I will. Then, a stig meter stigb on the wafer side from the aperture 6 and a stig meter on the reticle side are stiga.

In the first embodiment, stigb = (26, 3
2, 8) (the unit is mm), and the size of the stiga is four times that (104, 128, 32). And the setting position (center) of stigb is z (stigb) =-47mm, and the setting position (center) of stiga
Was set to zz (stiga) = − 212 mm. That is, in this embodiment, the stigmeters on the reticle side and the wafer side and their sizes are point-symmetric with respect to the center point of the aperture at 4: 1.

Under these conditions, by optimizing the position of the stig meter, the exciting current and the exciting current of the dynamic focus coil, aberrations that can be theoretically removed by dynamic correction can be practically almost completely removed. As a result, a blur of 60 nm due to aberration and a distortion of 4.1 nm were realized.

In the second embodiment, stiga = (52, 6
4, 16), stigb = (26, 32, 8), z (stiga) = -212m
m, z (stigb) =-It was arranged at the position of 47 mm. That is, in the second embodiment, unlike the first embodiment, the installation position of the stig meter has a point symmetry of 4: 1 with respect to the center position of the aperture. Not kept. In the second embodiment, as in the first embodiment, the excitation current of the stig meter and the excitation current of the dynamic focus coil were optimized. As a result, the blur caused by the aberration was 60 nm, which was the same as that of the first embodiment, but the distortion was 7.0 nm, which was worse than that of the first embodiment.

In the third embodiment, stiga = (52, 6
4, 16), stigb = (26, 32, 8), z (stiga) =-300m
m, z (stigb) =-It was arranged at the position of 47 mm. That is, in the second embodiment, each stig meter is arranged separately on the wafer side and the reticle side with an aperture interposed therebetween. However, unlike the first and second embodiments, each stig meter is different from the other. The symmetry of size and position is not maintained.
In the third embodiment, as in the first and second embodiments, the excitation current of the stig meter and the excitation current of the dynamic focus coil were optimized. As a result, the blur due to aberration is 63 nm, the distortion is 7.3 nm, and the second
It was worse than the example of

As a comparative example, two stigmeters of stiga = (52, 64, 16) were arranged at positions of Z (stiga) = − 300 and Z (stigb) = − 180 on the reticle side from the aperture. . Also in this comparative example, as in the first embodiment, the excitation current of the stig meter and the excitation current of the dynamic focus coil were optimized. As a result, the blur due to the aberration is 74 nm, the distortion is 41 nm,
It was significantly worse than in the two examples.

In the present invention, a toroidal deflector and a stigmometer are used, but a saddle-type deflector and a stigmometer may be used. Also, the combination is not limited.

[0029]

As described above, in the invention according to the first aspect of the present invention, one stigmometer is provided on the reticle side and one is provided on the sensitive substrate side with the aperture surface interposed therebetween.
By arranging two stig meters, symmetry of the electromagnetic field can be easily ensured compared to arranging two stig meters on one side of the aperture, so that blurring and distortion can be reduced.

According to the second aspect of the present invention, the installation positions of the two stigmeters are point-symmetric with respect to the center of the aperture at a ratio of 1: M. And distortion can be reduced.

In the invention according to claim 3, in addition to this, the size of the two stigmeters is 1: M point symmetric with respect to the center of the aperture, so that the symmetry of the electromagnetic field is further secured. Blur and distortion,
It can be even smaller.

According to each of these inventions, the minimum line width of the pattern that can be realized can be reduced, and the specifications required for the positioning accuracy of the stage and the like can be relaxed accordingly. Exposure transfer of a high-density pattern can be performed.

[Brief description of the drawings]

FIG. 1 is a schematic diagram of an optical system according to an embodiment of the present invention.

FIG. 2 is a diagram illustrating an outline of a shape of a deflector according to an embodiment of the present invention.

FIG. 3 is a diagram showing an outline of a shape of a stig meter in the embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Optical axis 2 ... Reticle 3 ... Wafer 4 ... 1st projection lens 5 ... 2nd projection lens 6 ... Aperture 7 ... Deflector 8 ... Dynamic focus coil 9 ... Stigmeter

Claims (3)

[Claims] 1. A charged particle beam exposure apparatus for exposing and transferring a pattern formed on a reticle on a sensitive substrate by reducing or enlarging the pattern to 1: M by using a charged particle beam, the reticle being off the optical axis. In a device having six deflectors for transferring a surface pattern onto a sensitive substrate off the optical axis, a stigmeter for dynamic correction is provided on the reticle side and one on the sensitive substrate side across the aperture surface. A charged particle beam exposure apparatus, wherein: 2. The charged particle beam exposure apparatus according to claim 1, wherein the two stigmeters are arranged at a point that is 1: M point-symmetric with respect to the aperture center. Characterized particle beam exposure equipment. 3. The charged particle beam exposure apparatus according to claim 1, wherein the two stigmeters are arranged at a position that is 1: M point-symmetric with respect to the aperture center, and a reticle-side stigm is provided. A charged particle beam exposure apparatus characterized in that the ratio of the size of the meter (inner diameter / outer diameter / length) to the size of the wafer-side stig meter is 1: M.