JPH11186130A - Beam edge blur amount measuring method and refocus amount determining method, stencil mask used for these methods, charged particle beam exposure method and apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a more appropriate refocus value. SOLUTION: Formed on a stencil mask 40A as a block pattern for simultaneous exposure are a slit aperture 41 to measure the edge defocusing quantity σa of the charge particle beam and an aperture 42 formed with enough clearance to ignore elements other than the Coulomb interaction of δa and that the charged particle beam passes at the same time with the aperture 41. The stencil masks 40A and 40B are used to measure the edge defocusing quantity of the charged particle beam that has passed through the aperture 41 for each of the masks. The refocus value of the charged particle beam is determined so that the edge fading is minimal. Based on the refocus value determined for the total aperture area of each of the stencil makes 40A and 40B, linear approximation is obtained for the relationship of the refocus value to the aperture area of a required block pattern on the stencil mask.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for measuring a beam edge blur amount and a method for determining a refocus amount in charged particle beam exposure, a stencil mask used in these methods, and a charged particle beam exposure method and apparatus.

[0002]

2. Description of the Related Art In a charged particle beam exposure apparatus, in order to draw a finer pattern, blurring of a beam edge, that is, blurring of an edge portion of a mask pattern projected image on a sample is performed.
It is necessary to reduce as much as possible. FIG. 5 shows a schematic configuration of a conventional charged particle beam exposure apparatus.

[0003] Between a charged particle gun 10 and a semiconductor wafer 11 as an object to be exposed, a forming aperture 1 is formed along an optical axis.
2, a mask 13 and an angle stop 14 are arranged. A two-dot chain line is an enlarged vertical cross section of a charged particle beam emitted from one point of the charged particle gun 10, for example, an electron beam (hereinafter, the charged particle beam is an electron beam) in a direction perpendicular to the optical axis. 15 so that the electromagnetic lens 2
1 to 25 are arranged. The electromagnetic lens 21 is an electromagnetic lens 21A arranged so as to sandwich the formed diaphragm 12 up and down.
And an electromagnetic lens 21B. The electromagnetic lens 22 is an electromagnetic lens 22 that is disposed so as to sandwich the mask 13 up and down.
A and an electromagnetic lens 22B.

[0004] A shaping deflector 26 is arranged between the shaping diaphragm 12 and the mask 13, a blanking deflector 27 is arranged between the mask 13 and the angle diaphragm 14, and charged particles are stored in the objective lens 25. A main deflector 28 and a sub deflector 29 for beam scanning are arranged. The electron beam emitted from the charged particle gun 10 is applied to the rectangular aperture 1 of the forming aperture 12.
2a, the cross section of which is formed into a rectangular shape, and the forming deflector 2
6, the rectangular image is formed on the mask 13, and the logical product of the rectangular image and the rectangular aperture 13a passes through the rectangular aperture 13a. Thereby, the cross section of the electron beam is made a variable rectangle according to the amount of deflection by the shaping deflector 26. The electron beam is further limited in its angle through the circular aperture 14a of the angle stop 14, and is then deflected by the main deflector 28 and the sub deflector 29 so that the variable rectangle is reduced and projected to a desired position on the wafer 11. Is done.

[0005] Coulomb repulsion acts between the electrons in the beam, resulting in blurring of the projected image on the wafer 11.
In order to correct this, a refocus coil 30 is arranged below the mask 13 so that its axis coincides with the optical axis AX. The beam current passing through the rectangular aperture 12a is constant, and the amount of refocus for blur correction is almost proportional to the current of the beam passing through the rectangular aperture 13a.
A current Ir proportional to the area where the rectangular aperture 13a and the image of the forming aperture 12 at this position overlap, that is, a current Ir corresponding to the amount of deflection by the forming deflector 26, is supplied to the refocus coil 30 as a refocus amount. Is done.

When a stencil mask is used as the mask 13, the refocus correction is performed similarly. In order to determine the refocus amount, conventionally, the beam edge blur amount has been measured as follows. That is, as shown in FIG. 6A, a knife edge of a tantalum film Ta having a higher electron reflectivity and a higher secondary electron emission rate than silicon Si is formed on a silicon Si wafer 11. The beam is scanned by the sub deflector 29 shown in FIG. 5 so that the projected image BS crosses the knife edge of the tantalum film Ta. At this time, reflected electrons and / or secondary electrons from the irradiation point are detected by the electron detector 31.
And 32. Then, the electron detectors 31 and 32
6B, which is the sum of the outputs S1 and S2 of FIG. This electron detection amount S is differentiated with respect to the beam scanning position X to obtain a waveform DS as shown in FIG.
Is obtained, and the distance at which the maximum value DS0 changes from 90% to 10% is obtained as the beam edge blur amount δ. The beam scanning position X is determined by the relationship with the voltage applied to the sub deflector 29.

Conventionally, the refocusing amount Ir for minimizing the beam edge blurring amount δ is changed to the projected image B having different areas.
S, the area of the variable rectangle and the refocus amount I
r is linearly approximated, and based on the linear approximation, the refocus amount I
r had been determined.

[0008]

However, the beam edge blur δ includes a component that is not proportional to the aperture area due to the increase in the size of the projection image BS, in addition to the Coulomb interaction, Even if the refocus amount Ir determined in this way is used, the beam edge blur amount δ
Cannot be minimized, which is an obstacle to miniaturization of patterns.

Even if the beam edge blurring amount δ is measured for a specific block pattern without performing the above-mentioned linear approximation, the above problem occurs for the same reason as described above. For example, in a line-and-space block pattern as shown in FIG. 7A, the current density profile on a line perpendicular to the longitudinal direction of the line pattern on the sample is shown in FIG.
become that way. Electrons in the beam passing through the aperture shown in FIG. 7A vary in direction and speed. Even in the same direction, if the speed is different, the force received from the electromagnetic field and the transit time are different, so that the irradiation point on the sample is different. For this reason, some of the electrons in the beam that have passed through the aperture 132 are irrespective of the Coulomb interaction,
To contribute. Therefore, even if the beam edge blur δ is measured for the profile end E1, the beam edge blur δ due to only the Coulomb interaction cannot be accurately measured, and the above problem occurs.

In view of the above problems, an object of the present invention is a beam edge blur amount measuring method and a refocus amount determining method capable of determining a more appropriate refocus amount, and a stencil used in these methods. A mask and a charged particle beam exposure method and apparatus are provided.

[0011]

According to the stencil mask of the present invention, a line-shaped first opening for substantially measuring an edge blur amount of a charged particle beam;
And a second opening through which the charged particle beam passes at the same time as the first opening, wherein a component other than the Coulomb interaction of the edge blur amount is formed to be negligible. It is formed as a block pattern for simultaneous exposure.

When the amount of edge blur of the charged particle beam passing through the first line-shaped opening is substantially measured using the stencil mask, the first opening and the second opening have a Coulomb with the amount of edge blur. Since the components other than the interaction are negligiblely separated, the effect is obtained that the edge blur amount is substantially based only on the Coulomb interaction. According to a second aspect of the present invention, the edge blur of the charged particle beam passing through the first opening is substantially measured using the stencil mask of the first aspect.

According to a third aspect of the present invention, in the second aspect, the charged particle beam is an electron beam, and the portion on the sample where the electron reflectivity or the secondary electron emission rate changes rapidly is irradiated with the electron beam. The electron beam is scanned over the sample so that a point passes therethrough, the amount of reflected electrons or secondary electrons from the electron beam irradiation point is detected, and the edge is detected based on the detected amount or the differential value of the detected amount. The amount of blur is substantially measured.

According to a fourth aspect of the present invention, there is provided a method of determining a refocus amount.
Using the stencil mask of claim 1, the amount of edge blur of the charged particle beam passing through the first opening is substantially measured, and the amount of refocus with respect to the charged particle beam is minimized so that the amount of edge blur is minimized. decide. According to this refocus amount determination method, since the beam edge blur amount is almost based only on the Coulomb interaction, the refocus amount for Coulomb interaction correction is determined for an arbitrary opening pattern of the mask based on this relationship. By doing so, it is possible to reduce the amount of beam edge blur compared to the related art, and this greatly contributes to miniaturization of the exposure pattern.

According to a fifth aspect, the first opening and the second opening are provided.
2. A stencil mask according to claim 1, wherein a plurality of block patterns having different total opening areas from the openings are formed, and for each of the plurality of block patterns, edge blurring of the charged particle beam passing through the first opening. Measuring the amount substantially, determining the amount of refocus for the charged particle beam that minimizes the amount of edge blur, and determining the amount of refocus for the total aperture area of each of the plurality of block patterns. Based on this, the relationship between the opening area of an arbitrary block pattern on the stencil mask and the refocus amount is linearly approximated.

According to a sixth aspect of the present invention, there is provided a method of determining a refocus amount.
The stencil mask according to claim 1, wherein the charged particle irradiation area on the second opening is changed, and the edge blur amount of the charged particle beam passing through the first opening is substantially changed for each charged particle irradiation area. The edge blur amount is minimized, the refocus amount for the charged particle beam is determined, and based on the refocus amount determined for each of the plurality of charged particle irradiation areas, an arbitrary value on the stencil mask is determined. The relationship of the refocus amount to the opening area of the block pattern is determined.

According to this method, a plurality of refocus amount determining blocks are formed on the stencil mask only by changing the irradiation position of the charged particle beam with respect to one refocus amount determining block mask formed on the stencil mask. There is an advantage that the same result as in the case of forming these masks and using them can be obtained. According to a seventh aspect of the present invention, in any one of the fourth to sixth aspects,
The charged particle beam is an electron beam, and the electron beam is scanned on the sample so that the electron beam irradiation point passes through a portion on the sample where the electron reflectivity or the secondary electron emission rate changes abruptly. The amount of reflected electrons or secondary electrons from the point is detected, and the blur amount is substantially measured based on the detected amount or the differential value of the detected amount.

In the charged particle beam exposure method according to claim 8,
Exposure is performed by correcting the focus of the charged particle beam with the refocus amount determined by the refocus amount determination method according to any one of claims 4 to 7. In the charged particle beam exposure apparatus according to claim 8, a stencil mask according to claim 1, and an optical system configured to irradiate a block pattern on the stencil mask with a charged particle beam and reduce and project the block pattern onto a sample; A deflector for scanning the charged particle beam on the sample.

[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIGS. 1A and 1B show a stencil mask 4 used in a beam edge blur amount measuring method.
4A and 4B show block patterns of 0A and 40B. The hatched portion is the substrate portion.

The stencil mask 40A is used in place of the rectangular mask 13 shown in FIG. 5, and a charged particle beam is applied to a rectangular area including the apertures 41 and 42, and the images of the apertures 41 and 42 are simultaneously reduced on the wafer 11. Projected. The aperture 41 as a line-shaped opening corresponds to, for example, a wiring pattern. Reduce magnification of 1
/ M, for example, 1/60, the line width of the aperture 41 is, for example, 0.1 M μm.

When the aperture 42 is brought closer to the aperture 41, as described above with reference to FIG.
The blur of the electron beam that has passed through will include something other than Coulomb interaction due to the effect of part of the electron beam that has passed through aperture 42. Therefore, the aperture 41
The aperture 42 is formed at a distance more than a distance where such an effect can be ignored (hereinafter, this is referred to as a non-weighted distance). The base member width between the apertures 41 and 42 is, for example, 0.4 M μm. The width of the aperture 42 is, for example, 4.0 M μm.

The images of the apertures 41 and 42 on the wafer 11 are projected images BS1 and B2 shown in FIG.
It becomes like S2. As in the case of FIG.
As shown in (A), on a silicon Si wafer 11,
A knife edge of a tantalum film Ta having an electron reflectance and a secondary electron emission rate higher than silicon Si is formed in advance. FIG.
The beam is scanned by the sub-deflector 29 to cause the projected image BS to cross the knife edge of the tantalum film Ta. At this time, FIG. 2B shows the sum of the outputs S1 and S2 of the electron detectors 31 and 32. ) Is determined. This electron detection amount S is differentiated with respect to the beam scanning position X, and FIG.
A waveform DS as shown in (C) is acquired, and the maximum value DS1 of the portion corresponding to the edge of the projection image BS1 is 90% to 10%.
% Is obtained as the beam edge blur amount δa.

In order to increase the measurement accuracy of δa, the longitudinal direction of the projected image BS1 is made parallel to the knife edge of the tantalum film Ta, and the scanning direction of the projected image BS1 is made perpendicular to the longitudinal direction. In the differential waveform DS, the projected image BS
Assuming that a distance at which the maximum value DS2 of the portion corresponding to the edge of No. 2 changes from 90% to 10% is δax, δa <δa
x. This is because the beam edge blur δa hardly includes the effect of a part of the electron beam passing through the aperture 42, and is almost based only on the Coulomb interaction. On the other hand, the beam edge blur δax Is
This is because the aperture 42 is wide, and the influence of a part of the electron beam passing near the edge of the aperture 42 is included.

On the other hand, since the Coulomb interaction in the electron beam mainly occurs at the crossover point of the two-dot chain line 15 in FIG. 5, the separation between the apertures 41 and 42 is caused by the blur on the wafer 11 due to the Coulomb interaction. Does not affect That is, the component based on the Coulomb interaction included in the beam edge blur δa is the same as that of δax, and depends on the block pattern opening area Aa = A1 + A2.

Therefore, the beam edge blur δa is measured for determining the refocus amount Ir. Refocus amount I
r, the beam edge blur amount δa is reduced to the minimum value δa.
Find Ir = Ir1 that is min. Next, FIG.
In the same manner as described above, a stencil mask 40B is used to search for a minimum beam edge blur amount δbmin corresponding to the minimum beam edge blur amount δamin, and the refocus amount Ir at this time is obtained as Ir2.

The stencil mask 40B is formed with the same shape as the aperture 41 of the stencil mask 40A, and an aperture 43 having an area A3 different from the aperture 42. The block pattern opening area Ab is A1 +
A3. The aperture 43 is separated from the aperture 41 by an unheavy distance or more for the same reason as described above. FIG.
As shown in (C), two points (Aa, δamin) and (Aa
b, δbmin) to approximate the refocus amount Ir for an arbitrary block pattern opening area A.

Since the minimum values δamin and δbmin of the beam edge blur amounts are almost based only on the Coulomb interaction, the refocus amount Ir for Coulomb interaction correction is determined for an arbitrary block pattern based on this relationship. Thus, the beam edge blur amount δ can be reduced as compared with the related art. Thereby, it becomes possible to expose a finer pattern than ever before.

Since the beam edge blur amount δb is determined by the block pattern opening area Ab, the stencil mask 40B shown in FIG. 1B is used instead of the stencil mask 40B shown in FIG.
A stencil mask 40C, 40D or 40E having a block pattern opening area Ab as shown in FIG. The area of the aperture 43A of the stencil mask 40C is A3, and the apertures 431 to 43 of the stencil mask 40D.
6, the total area is A3, and the area of the aperture 43B of the stencil mask 40E is also A3. An aperture 41 is formed in each of the stencil masks 40C, 40D, and 40E, and apertures 43A, 431, and 43E are formed.
Each of B is separated from the aperture 41 by an unheavy distance or more.

Next, a method of determining a refocus amount according to another embodiment of the present invention will be described with reference to FIG. In this method, one block pattern is used, and the same result as when two or more block patterns are used is obtained. That is,
As shown in FIG. 4A, an image 12I of the aperture 12a in FIG. 5 is formed on the stencil mask 40A, and the edge blur δ of the electron beam passing through the aperture 41 is measured in the same manner as in the above embodiment. Then, the refocus amount that minimizes this is determined.

Next, the image 12I of the aperture 12a on the stencil mask 40A is shown by the deflector 26 in FIG.
The aperture 42 and the image 121 are shifted as shown in FIG.
In the same manner as described above, the edge blur amount δ of the electron beam passing through the aperture 41 is measured, and the refocus amount that minimizes the edge blur amount is determined.

Thus, the same relationship as in FIG. 1C is obtained. According to this method, one refocus amount determination block mask is formed on the stencil mask, and only by changing the electron beam irradiation position on the stencil mask, a plurality of refocus amount determination block masks are formed. Has the advantage that the same result as in the case of using is obtained.

The present invention includes various other modifications. For example, it is a matter of course that the approximate straight line in FIG. 1C may be obtained by the least square method based on three or more measurement points. Also, the aperture 41 may be narrow enough that the above-mentioned effect on the beam edge blur amount δ can be ignored.
It does not need to correspond to the actual wiring pattern.

Further, in the above embodiment, the case where the line-shaped opening is one aperture 41 has been described, but the line-shaped opening may be constituted by a plurality of apertures interrupted on the same straight line, for example. Good. Since the beam edge blur amount is used not only for determining the refocus amount but also for calculating the proximity effect in exposure, the beam edge blur amount measuring method of the present invention alone has technical significance.

The beam edge sharpness may be measured using the above-described stencil mask to substantially measure the beam edge blur amount according to the present invention.

[Brief description of the drawings]

FIGS. 1A and 1B are diagrams showing a block pattern of a stencil mask used in a beam edge blur amount measuring method according to an embodiment of the present invention, and FIGS. FIG. 3 is a diagram showing a relationship with an amount.

FIG. 2 is an explanatory diagram for measuring a beam edge blur amount using the block pattern of FIG.

FIG. 3 is a diagram showing a modified example of the block pattern of FIG.

FIG. 4 is an explanatory diagram of a method of obtaining the relationship of FIG. 1C using one block pattern according to another embodiment of the present invention.

FIG. 5 is a schematic configuration diagram of a conventional charged particle beam exposure apparatus optical system.

FIG. 6 is an explanatory diagram of a conventional beam edge blur amount measurement.

FIG. 7 is an explanatory diagram of a problem in the related art.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 11 Wafer 12a, 13a Rectangular aperture 13 Mask 29 Sub-deflector 30 Refocus coil 31, 32 Electron detector 40A-40E Stencil mask 41-43, 132, 43A, 43B, 431-436
Aperture S Electron detection amount δa, δb Beam edge blur δamin, δbmin Minimum beam edge blur Si Si Ta Tantalum film BS, BS1, BS2 Projected image

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁶ Identification code FI H01J 37/04 H01J 37/04 A H01L 21/30 541R

Claims (9)

[Claims] 1. A line-shaped first opening for substantially measuring an edge blur amount of a charged particle beam; and a first opening portion such that components other than the Coulomb interaction of the edge blur amount are negligible. A stencil mask, wherein the stencil mask is formed so as to be spaced apart from the second opening through which the charged particle beam passes simultaneously with the first opening as a block pattern for simultaneous exposure. 2. A beam edge blur amount measuring method, wherein the edge blur amount of a charged particle beam passing through the first opening is substantially measured using the stencil mask according to claim 1. 3. The charged particle beam is an electron beam, and the electron beam is scanned on the sample so that an electron beam irradiation point passes through a portion on the sample where the electron reflectance or the secondary electron emission rate changes abruptly. Detecting an amount of reflected electrons or secondary electrons from the electron beam irradiation point, and substantially measuring the edge blur amount based on the detected amount or a differential value of the detected amount. Item 2. The beam edge blur amount measuring method according to Item 2. 4. Using the stencil mask of claim 1, substantially measuring an edge blur amount of the charged particle beam passing through the first opening, and minimizing the edge blur amount.
A method for determining a refocus amount, comprising determining a refocus amount for a charged particle beam. 5. The stencil mask according to claim 1, wherein a plurality of block patterns having different total opening areas of the first opening and the second opening are formed. Substantially measuring an edge blur amount of the charged particle beam passing through the first opening, and determining a refocus amount for the charged particle beam that minimizes the edge blur amount; A method of linearly approximating the relationship between the refocus amount and the opening area of an arbitrary block pattern on a stencil mask based on the refocus amount determined for the total opening area. 6. The stencil mask according to claim 1, wherein the charged particle irradiation area on the second opening is changed, and for each charged particle irradiation area, the edge of the charged particle beam passing through the first opening is changed. Measuring the amount of blur substantially, determining the amount of refocus for the charged particle beam that minimizes the amount of edge blur, based on the amount of refocus determined for each of the plurality of charged particle irradiation areas, A method of determining a refocus amount, wherein a relation between a refocus amount and an opening area of an arbitrary block pattern on a stencil mask is determined. 7. The charged particle beam is an electron beam, and the electron beam is scanned on the sample so that an electron beam irradiation point passes through a portion on the sample where the electron reflectivity or the secondary electron emission rate changes abruptly. Detecting an amount of reflected electrons or secondary electrons from the electron beam irradiation point, and substantially measuring the blur amount based on the detected amount or a differential value of the detected amount. 7. The method for determining a refocus amount according to any one of 4 to 6. 8. A charged particle beam, wherein the exposure is performed by correcting the focus of the charged particle beam with the refocus amount determined by the refocus amount determining method according to claim 4. Exposure method. 9. A stencil mask according to claim 1, an optical system for irradiating a block pattern on the stencil mask with a charged particle beam to reduce and project the block pattern onto a sample, and applying the charged particle beam to the sample. A charged particle beam exposure apparatus, comprising: a deflector that scans on the charged particle beam.