JPS6276620A - Charged beam exposure device - Google Patents

Abstract

PURPOSE:To improve the accuracy of exposure and the exposure throughput by performing the focus adjustment on a sample fast and highly accurately in controlling the excitation current of the electromagnetic lens so that the inclination of the mark on a deflection co-ordinates is at a specified inclination which is determined based on the height position of the measured sample. CONSTITUTION:In a Z-position sensor, it is arranged that a detection output corresponding to the Z-position of the surface to be detected since the position of the light irradiated on a position detector 35 differs with the height position of the surface to be detected. A set angle theta0 is calculated on the basis of the measured Z-position z to an arbitrary wafer 12. Then, a sample stage 11 is transferred to move a reference mark 18 to just under an optical mirror cylinder. Under this condition, the inclination angle theta of the reference mark 18 is measured to compare then angle theta with the set angle theta0. Then, if theta>theta0, the current in an auxiliary coil 24 is increased to measure the inclination angle thetaof the reference mark 18 again. On the other hand, if theta<theta0, the current in the auxiliary coil 24 is decreased to measure the inclination angle theta of the reference mark 18.

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field of the Invention) The present invention relates to a charged beam exposure apparatus, and more particularly to a charged beam exposure apparatus in which an electromagnetic lens focusing and alignment mechanism is improved.

[Technical background of the invention and its problems]

In recent years, various electron beam exposure devices have been used to form fine patterns on samples such as semiconductor wafers and mask substrates, but these devices require focusing between an optical system and the sample. In electron beam direct writing, the following method is used for focusing. That is, the height of the wafer (2 positions) is measured by a Z sensor, and the lens current is corrected with an excitation kN current proportional to the difference Δ2 from the height 20 of the reference surface to perform focusing on the wafer.

However, this type of device has the following problems. That is, an electromagnetic lens is generally used as a lens for focusing an electron beam, and there is so-called hysteresis between the excitation current of this lens and the magnetic field strength. Therefore, the current must be reset after changing the lens current in a certain sequence, and this setting takes a lot of time. Furthermore, even with this method, there is still a problem in that there is no way to finally confirm that the effects of hysteresis have been completely avoided.

Note that the above problem is not limited to electron beam exposure apparatuses, but also applies to ion beam exposure apparatuses that use ion beams to form a desired pattern on a sample.

[Purpose of the invention]

The present invention has been made in consideration of the above circumstances, and its purpose is to provide a charged beam exposure apparatus that can focus on a sample at high speed and with high precision, and that can improve exposure accuracy and exposure throughput. Our goal is to provide the following.

[Summary of the invention]

The gist of the present invention is to control the excitation current of the electromagnetic lens by detecting the amount of rotation of the beam trajectory.

As described above, there is hysteresis between the excitation current of the electromagnetic lens and the magnetic field strength, and it is extremely difficult to control the excitation current and set the magnetic field strength to a predetermined value. However, there is a proportional relationship without hysteresis between the magnetic field strength and the amount of rotation of the beam. The amount of beam rotation can be easily measured by irradiating a beam onto a reference mark on a sample and detecting the reflected beam. Therefore, by controlling the excitation current so that the beam rotating wheel reaches a predetermined value, it is possible to set the magnetic field strength to a predetermined value.

The present invention focuses on such points, and focuses a charged beam emitted from a charged beam source with an electromagnetic lens, and scans the sample with a deflector to expose a desired pattern on the sample. The exposure apparatus includes means for measuring the height position of the sample surface, and a means for scanning a reference mark with a charged beam using the deflector, detecting a secondary image from the mark, and detecting a mark on the deflection coordinates. and means for controlling the excitation current of the electromagnetic lens so that the measured slope becomes a predetermined slope determined based on the measured height position of the sample. This is what I did.

〔Effect of the invention〕

According to the present invention, it is possible to focus on a sample at high speed and with high precision without being affected by hysteresis, and not only the beam resolution but also the beam position error can be reduced.

Therefore, exposure precision and exposure throughput can be significantly improved.

[Embodiments of the invention]

First, before explaining embodiments, the basic principle of the present invention will be explained.

The principle of the present invention is to control the excitation current by detecting the rotation of the beam trajectory caused by excitation of the lens and indirectly measuring changes in the lens magnetic field.

Generally, the beam rotation mθ is expressed as: Here, e is the charge of the electron, m is the mass of the electron, ■ is the heating voltage, B (z) is the magnetic field distribution on the axis of the lens, and a and b are the positions on the axis, for example, the object point.

Corresponds to the image point. The distribution shape of B(z) is determined by the shape of the lens, usually the Bohr diameters Di, D2 and the gap size S. In other words, B(Z) is B(Z)-Bo-E(Z)...
・Represented by ■. Here, E(Z) is the maximum value of the normalized distribution function, BaG, tB(Z). E(Z) is a function of only C1, D2, and S.

So changes approximately in proportion to the lens excitation current 1'O, but Bo and In do not correspond one-to-one due to hysteresis. However, since the rotation amount θ of the beam is , Ba is 1
It corresponds to 1:1. Focusing of the wafer is performed as follows by utilizing this property.

That is, the rotation angle change Δ with respect to the focal position shift Δ2 is calculated in advance.
Find θ. Next, the rotation angle θ at that time is measured by focusing on the reference plane. Focusing is completed by measuring the deviation Δ2 of the Z-direction position of the wafer from the reference plane and controlling the excitation current so that the rotation angle is θ−θ+Δθ.

The measurement of θ is performed by determining the positions of two marks on the reference plane using a normal registration function.

For example, Boer Dt-40 shoes, D2-10111゜5
When using a =10111III lens at a focal length of approximately f~19M, Δθ-1.71 for ΔZ-50μm!
It is 1 rad.

If the distance between the two mark positions is L-250am (which is the smaller deflection field), the movement of the mark position by Δθ is L-Δθ-250X 1.7 X 10"3-0.42
It becomes 5 μm. Position detection accuracy is 0.25~0.05μ
m, so the focusing accuracy is in this case. On the other hand, the dependence of the beam resolution Δ on Δ2 is −Ten 0.
002 Δ2 Therefore, when this method is used, the resolution reduction due to the focusing error is only 5.9 x O,002 - 0,01 μm, which is a negligible value.

In contrast, in conventional methods, excitation of the lens introduces an error of up to 3×10 4 due to hysteresis.

Since this corresponds to a resolution of 0.05 μm, it is an error that cannot be ignored. Also, this error corresponds to 0.051 rad in terms of rotation amount, and the resulting beam position deviation is 250 Xo, 5 will occur.

Hereinafter, one embodiment of the present invention will be described with reference to the drawings.

FIG. 1 is a schematic diagram showing an electron beam exposure apparatus according to an embodiment of the present invention. In the figure, 11 is a sample stage movable in the X-Y direction, 12 is a semiconductor wafer, 13 is a wafer cassette that accommodates the wafer 12, and 14 is the stage 1
1 is a cassette holder attached to the wafer cassette 13 for holding the wafer cassette 13; 15 is a reference surface table; 16 is a Faraday cup having a knife around the opening; and 18 is a reference mark for detecting the beam scanning direction.

21 to 25 constitute an electron optical lens barrel;
21 is a main deflector that largely deflects the beam; 22 is a sub-deflector that deflects the beam at high speed; 23 is an objective lens main coil; 24 is an auxiliary coil for focusing; and 25 is a backscattered electron detector. Note that an electron gun, a blanking plate, various lenses, etc. (not shown) are arranged above these.

3), ~, 35 constitute a two-position sensor,
3) is a semiconductor laser, 32 is a slit, 33 and 34 are mirrors, and 35 is a position detector such as a PSD. In this two-position sensor, the position detector 35
Since the positions of the incident light are different, detection outputs corresponding to two positions on the detection surface can be obtained.

Further, 40 is a CPU for performing various controls, calculations, etc.;
1 is a memory, 42 is an arithmetic processing circuit that measures two positions from the detection output of the position detector 35, and 43 is a backscattered electron detector d.
44 is an arithmetic processing circuit that measures the inclination angle of the mark from the detection output of the backscattered electron detector 25;
5 (45a.

~, 45d) is a D/A converter, 46 (468, ~).

46d) is an amplifier.

In this device, the main deflector 23 positions the electron beam in a subfield obtained by dividing the deflection field into small areas, and the sub deflector 24 scans the beam at this position to draw a pattern.

By sequentially changing the positions of the subfields, patterns are drawn for each subfield.

Next, a focusing method using this apparatus configured as described above will be explained.

First, in order to obtain the set inclination angle θ of the mark based on the Z position of the wafer 12, the following preprocessing is performed. That is,
The sample stage 11 is moved so that the Faraday cup 16 on the reference surface table 15 is positioned directly below the electron optical column. In this state, scan the naifetsuji with an electron beam,
The current in the auxiliary coil 24 is roughly varied to focus the beam onto the knife. That is, focusing with respect to the reference surface table 15 is performed by changing the coil current so that the detection output of the Faraday cup 16 is maximized. If the beam is a variable shaped beam, it can be scattered around the opening of the AU coarse particle Faraday cup 16 of about 0.1 .mu.m instead of the knife, and focused using the reflected electron signal.

Next, the sample stage 11 is moved so that the reference mark 18 is positioned directly below the electron optical lens barrel.

In this state, the second position IZa of the mark 18 (the surface of the reference surface table 15) is measured using the two sensors, the arithmetic processing circuit 42, and the like. Next, the mark 18 is scanned with an electron beam to form the arm 18a or 1 of the mark 18, as shown in FIG.
The tilt angle θ8 in the main deflection field of 8b is determined.

Next, as shown in FIG. 3, an opening 5 with a knife is opened.
The sample stage 11 is moved so that the wafer 12 having the marks 1 and 52 is located directly below the electron optical column.

In this state, the 7th position +122 of the wafer 12 is measured, and the inclination angle θ2 of the mark 52 is further measured. Next, opening 5
The knife No. 1 is focused in the same manner as before, and in this state, the inclination angle θ2' of the mark 52 is determined again. At this time, if ΔZ-22-26 Δθ-θ2'-θ2, then the inclination angle θ of the mark 18 is θ-θB+Δθ. In other words, if the current of the auxiliary coil 24 is set so that the measured inclination angle θ of the reference mark 18 becomes θ8+Δθ with respect to the 7th position Nz2 of the wafer 12, the focus will be adjusted to the surface of the wafer 12. . Therefore,
In order to focus on an arbitrary wafer, it is sufficient to measure the Z position 2 of the wafer and set the auxiliary coil current so that θ-θ8+Δθ □ ...■△2.

Here, the actual focusing method after performing the above preprocessing will be explained in more detail with reference to the flowchart of FIG.

First, the Z position 2 of an arbitrary wafer 12 is measured using the Z sensor or the like. Measured Z position! Based on z, 8 set angles are calculated from the formula (2) above. Next, the sample stage 11 is moved to move the reference mark 18 directly below the optical table. In this state, the inclination angle θ of the reference mark 18 is measured, and this angle θ is compared with the set angle θD. If θ>θG, the auxiliary coil current is increased and the inclination angle θ of the reference mark 18 is measured again. On the other hand, if θ is less than θa, the auxiliary coil current is decreased and the inclination angle θ of the reference mark 18 is measured again. By repeating the above process, focusing is completed when θ=θ. In this state, if the sample stage 11 is moved so that the wafer 12 is positioned below the optical barrel,
The surface of wafer 12 will be in focus.

As described above, according to this embodiment, the inclination angle θ of the reference mark 18 is determined from the set angle θ determined from the 7th position Nz of the wafer 12.
By controlling the coil current so that it becomes 0,
The wafer 12 can be reliably focused. In this case, since the rotation angle of the beam is controlled to a desired value by feedback looseness, focusing can be performed to a large amount Iα regardless of the hysteresis of the lens. Furthermore, after measuring the seven positions 2 on the wafer 12, it is only necessary to control the lens current so that the inclination angle O of the reference mark 18 becomes θa, which has the advantage that focusing can be completed in a relatively short time. be.

Note that the present invention is not limited to the embodiments described above. For example, the shape of the fiducial mark is not limited to a cross shape, but may have at least one straight line. Furthermore, it goes without saying that the present invention can be applied not only to those using two stages of main and sub-deflection, but also to ordinary electron beam exposure apparatuses. Furthermore, the Z sensor is not limited to the configuration shown in FIG. 1, but can be modified as appropriate as long as it can measure the height position of the sample with respect to the electron optical VL tube.

It is also possible to apply the present invention to an ion beam haze optical device that uses an ion beam instead of an electron beam. others,
Various modifications can be made without departing from the spirit of the invention.

[Brief explanation of drawings]

FIG. 1 is a schematic configuration diagram showing an electron beam exposure apparatus according to an embodiment of the present invention, FIG. 2 is a schematic diagram showing the principle of measuring the inclination angle of a reference mark, and FIG. FIG. 4, which is a plan view showing the arrangement of marks and openings, is a flowchart for explaining the operation of this embodiment. 11... Sample stage, 12... Wafer (sample),
15... Reference surface stand, 16... Faraday cup, 1
8... Reference mark, 21.22... Deflector, 23.
...Objective lens main coil, 24...Auxiliary coil, 25
... Backscattered electron detector, 3). ~, 35...Z sensor, 40...CPU, 41...memory, 42.44.
...Arithmetic processing circuit. Applicant's representative Patent attorney Takehiko Suzue Figure 2 Figure 3 Figure 4

Claims (3)

[Claims] (1) In a charged beam exposure apparatus that focuses a charged beam emitted from a charged beam source using an electromagnetic lens and deflects it onto a sample using a deflector to expose a desired pattern on the sample, the height of the sample surface is means for measuring the position of the mark on the deflection coordinate; means for scanning the reference mark with a charged beam using the deflector and detecting a secondary beam from the mark to measure the inclination of the mark on the deflection coordinate; and means for controlling the excitation current of the electromagnetic lens so that the tilt of the electromagnetic lens is a predetermined tilt determined based on the measured height position of the sample. Device. (2) The charged beam exposure apparatus according to claim 1, wherein the reference mark is provided on a sample stage on which the sample is placed. (3) The charged beam exposure apparatus according to claim 1, wherein the electromagnetic lens whose excitation current is controlled is an objective lens disposed at the bottom of a charged beam optical column.