JP3291096B2 - Beam control method for electron beam exposure apparatus - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a beam control method for an electron beam exposure apparatus, and more particularly to a beam control method for an electron beam exposure apparatus that generates an electron beam having a predetermined beam size by combining a plurality of slits.

[0002] In recent years, the degree of integration and functions of ICs have been increasingly improved, and they are expected to play a role as a core technology of technological progress in a wide range of industries such as computers, communications, and machines.

A major pillar of IC process technology is high integration by fine processing. Photolithography is said to have a limit of about 0.3 μm, but electron beam exposure enables fine processing of 0.1 μm or less with an alignment accuracy of 0.05 μm or less. Therefore, if an electron beam exposure apparatus that exposes 1 cm ² in about 1 second is realized, any lithography means cannot be followed regardless of fineness, alignment accuracy, quick turnaround, and reliability. Alternatively, a 4-gigabit memory or a 1-megagate LSI can be manufactured. However, at this time, a finer and more accurate electron beam pattern is required.

[0004]

2. Description of the Related Art FIG. 7 shows the configuration of an electron beam exposure apparatus. The electron gun 11 is LaB ₆ (lanthanum hexaborite)
A cathode 11a, a Wellnert (grid) 11b, an anode 11c, etc., and an accelerating voltage of 20 kV or 30 k
V accelerates and emits electrons.

The electron beam BM emitted from the electron gun 11
Are aligned by the alignment coil 12 and supplied to the first slit 14. The first slit 14 has a rectangular hole 14a, and shapes the cross section of the electron beam BM into a rectangular shape.

The electron beam BM formed into a rectangular shape by the first slit 14 is supplied to a first lens 15. The first lens 15 converges the supplied electron beam BM. First
The electron beam BM converged by the lens 15 is supplied to the slit deflector 16.

[0007] The slit deflector section 16 includes a slit deflector 16a and a slit return deflector 16b, and deflects the supplied electron beam BM. The electron beam BM deflected by the slit deflector 16 is applied to the second slit 17.

The second slit 17 has a rectangular hole 17a. The rectangular electron beam BM formed by the first slit 14 is formed into a rectangular electron beam BM of a predetermined size by using the hole. I do.

The electron beam BM whose cross-sectional shape is formed to a predetermined size by the second slit 17 is converted into an irradiation beam by the second lens 18, and is transmitted to the third lens 20 via a blanker 19 for controlling irradiation of the electron beam BM. And the fourth lens 21.

The third lens 20 and the fourth lens 21 constitute a two-stage reduction lens.
The size of M is reduced to about 1/100. Electron beam B
M passes through the round aperture 22 during reduction by the third lens 20 and the fourth lens 21. The round aperture 22 removes an electron which is largely shifted on the axis around the electron beam BM to be obtained. The electron beam BM output from the fourth lens 21 is supplied to the fifth lens 23.

The fifth lens 23 constitutes a projection lens, and further reduces the supplied electron beam BM and projects it on a sample (silicon wafer) 24. The electron beam BM projected on the sample 24 is deflected by the main deflector 25 and the sub deflector 26 and is controlled so as to be projected on a predetermined position on the sample 24.
7. The focus beam shape and the like are controlled by the stig coil 28 and the like.

The electron beam BM is supplied directly to the Faraday cup 29. The Faraday cup 29 detects the electrons of the electron beam BM via the ammeter 33, and the ammeter 33 measures the current of the electron beam.

An alignment coil 12 and a refocus coil 13 are provided at various points in the middle of the passage of the electron beam BM to control the optical axis and the like. Electron gun 11, slit deflector 16, blanker 19, main deflector 25, sub deflector 26, focus coil 27, stig coil 28, first to fifth lenses 1
5, 18, 20, 23 and the Faraday cup 29 are connected to a drive control device 30 via an ammeter 33. The drive control device 30 supplies a drive control signal to each section, performs an exposure operation, and is detected by the Faraday cup 29,
The drive control signal is corrected and controlled based on the current value measured by the ammeter 33.

FIG. 8 is a view for explaining an operation of forming an electron beam by the first slit 14 and the second slit 17. As shown in FIG. 8, the electron beam BM emitted from the electron gun 11 passes through the rectangular hole 14 a of the first slit 14, obtains a rectangular first slit image 31, and is formed on the second slit 17.

The second slit 17 shields a part of the first slit image 31 and forms the second slit image 3 having a small beam size.
2 is output. At this time, the beam sizes are the first and second
The position of the first slit image 31 on the second slit 17 is determined by controlling the positional relationship of the slits 14 and 17 at the time of input and the driving voltage of the slit deflector 16.

At this time, the beam to be formed does not always have the desired beam size due to the mounting accuracy of the first slit 14 and the second slit 17 and the influence of the adjustment of the alignment coil 12 at the upper part of the column. Then, after mechanically adjusting the rotation of the first slit 14 and the second slit 17 to obtain a correct beam size, the voltage applied to the slit deflector 16 was corrected.

FIGS. 9, 10 and 11 are explanatory diagrams of the operation of the beam correction operation control method by the conventional drive control device 30. FIG. First, an electron beam is generated by the electron gun 11 and irradiates the silicon wafer 24. At this time, the electron beam BM
Is detected by the Faraday cup 29 and the ammeter 3
The current density J of the electron beam BM is measured by detecting the current value in Step 3 (Step S2-1). FIG.
(A) shows the electron beam size when the reference current density J is measured. For example, the electron beam size is set to a relatively large size of 3 μm × 3 μm, the current at this time is detected,
Calculate the current density J.

Next, based on the current density J measured in step S2-1 and the beam size at that time, current values Ix ₀ and Iy ₀ which are the references in the X and Y directions of the beam are calculated (step S2-). 2).

Next, the number of adjustments is determined (step S2-3). If the adjustment is not completed even after the predetermined number of adjustments have been made in step S2-3, the processing is terminated. If the adjustment is within the predetermined number of times, the processing described below is executed until the predetermined number of times is reached.

Next, the slit deflector 16 is controlled to generate an elongated beam in the X direction as shown in FIG. 10B, and the current value Ix in the X direction is detected by the Faraday cup 29 and the ammeter 33. (S2-4).

[0021] The detected current value Ix detected by the Faraday cup 29 and an ammeter 33 is compared with a reference current value Ix _0, determines whether or not within the tolerance the difference is predetermined (step S2-5). In step S2-5, and controls the next slit deflector portion 16 when the difference between the detected current value Ix and a reference current value Ix ₀ is within the permissible range, elongated in the Y direction as shown in FIG. 10 (C) A beam is generated, and the current value Iy in the Y direction is detected by the Faraday cup 29 and the ammeter 33 (step S2-6).

The detected current value I detected in step S2-6
y and the reference current value Iy. To determine whether the difference is within a predetermined allowable range (step S2-
7).

If the difference between the detected current value Iy and the reference current value Iy ₀ is within the allowable range in step S2-7, the adjustment is terminated (step S2-8).

In step S2-5, the detected current value Ix
The difference between the reference current value Ix ₀ compares the magnitude relation between the detected next current value Ix and a reference current value Ix ₀ when not within the allowable range (step S2-9).

In step S2-9, (detected current value Ix)
If> (reference current value Ix ₀ ), the slit offset correction coefficient OX in the X direction is reduced by an arbitrary amount (step S2-10). If (detected current value x) <(reference current value x ₀ ) in step S2-9, the slit offset correction coefficient X in the X direction is increased by an arbitrary amount (step S2-11).

In step S2-7, the detected current value Iy
The difference between the reference current value Iy ₀ compares the magnitude relation between the detected next current value Iy and the reference current value Iy ₀ when not within the allowable range (step S2-12).

In step S2-12, (detected current value I
When y)> (reference current value Iy ₀ ), the slit offset correction coefficient X in the Y direction is reduced by an arbitrary amount (step S2-13). If (detected current value Iy) <(reference current value Iy ₀ ) in step S2-12, the slit offset correction coefficient X in the Y direction is increased by an arbitrary amount (step S2-14).

By repeating steps S2-4 to S2-14, the detected current values Ix and Iy and the reference current value Ix
₀ , Iy ₀ is set within the allowable range, and the adjustment process ends.

If the difference does not fall within the allowable range even if steps S2-4 to S2-14 are repeated a predetermined number of times, the correction cannot be performed as it is, so that the correction processing is terminated and the input adjustment of the apparatus is performed. Do.

At this time, after mechanically adjusting the rotation of the first slit 14 and the second slit 17 in order to obtain a correct beam size, the voltage applied to the slit deflector 16 is corrected based on, for example, equation (1). Was.

Vx = A (Sx-Ox) + B (Sy-SOy) + Hx (Sx-SOx) (Sy-SOy) + Ox (1) Vy = D (Sx-Ox) + C (Sy -SOy) + Hy (Sx-SOx) (Sy-SOy) + Oy where Sx, Sy: input beam size SOx, SOy: voltage applied to slit deflector is 0
A, C: slit expansion correction coefficient B, D: slit rotation correction coefficient Hx, Hy: slit trapezoidal correction coefficient Ox, Oy: slit offset correction coefficient In equation (1), for example, the slit offset correction coefficient is It can be obtained by the following method.

First, a current density J at a large beam size such as 3 × 3 μm is determined in advance, and this is set as a reference current density. An Ox adjustment beam size is a narrow beam (for example, 0.1 × 3 μm) in the X direction, and an Oy adjustment beam size is a thin beam (for example, 3 × 0.1 μm) in the Y direction.
m), and an ideal current value at each beam size is calculated. Assuming that the current distribution in the 3 × 3 μm beam is uniform, ideal current values Iox and Ioy
Is the reference current density J multiplied by each beam size. In the case of the above beam size, Iox = Ioy = J × 0.1 × 3.0. Next, a beam having an Ox adjustment beam size is emitted, and the current value Ix is measured. If Ix> Iox, the slit size is larger than the desired slit size, so it is sufficient to gradually reduce Ox (FIG. 11).
(B)), if Ix <Iox, on the contrary, Ox may be reduced (FIG. 11C). The same adjustment is made for Oy. Ox adjustment Oy adjustment is performed alternately, and Ox, O
When the difference between the measured current value and the ideal current value falls within the allowable range for both y and the state becomes an appropriate state as shown in FIG. 11A, the adjustment ends.

[0033]

However, in the beam control method of the conventional electron beam exposure apparatus, since the current distribution of the electron beam is made uniform and the slit size for setting the shape of the electron beam is corrected, the electron beam exposure is performed. If the current distribution of the electron beam is uneven due to the mounting accuracy of the electron gun, the usage of the device, etc., the reference current value will be different from that of the target size, and correct correction cannot be performed. There was a problem that a beam size could not be obtained.

For example, when the current distribution of the beam changes linearly in the X direction, the slit size in the Y direction is correctly adjusted, but in the X direction, the current value is smaller than a value proportional to the slit size. Because it is not measured,
The offset coefficient of the slit size in the X direction is greatly corrected. If a fine beam pattern such as 0.2 × 0.2 μm is to be obtained with the corrected slit size, a beam elongated in the X direction is obtained. And the accuracy is not satisfactory.

The present invention has been made in view of the above points, and it is an object of the present invention to provide a beam control method for an electronic exposure apparatus capable of controlling an electron beam having a required beam size.

[0036]

FIG. 1 shows the principle of the present invention. In a first procedure 1, a current of the electron beam is detected by the detection unit, and a current density distribution of the electron beam is obtained according to the detected detection current of the electron beam.

In a second procedure 2, a reference current value of an electron beam having a target size is calculated based on the current density distribution obtained in the first procedure 1.

In a third procedure 3, the slit deflector is controlled according to the target size, and the current value of the electron beam at that time is detected by the current detecting means.

The fourth step is to compare the reference current value calculated in the second step 2 with the detected current value detected in the third step 3, and calculate the difference between the reference current value and the detected current value. , The slit deflector is controlled to obtain an electron beam having a target size.

[0040]

According to the present invention, since the current density distribution of the electron beam is obtained and the reference current value is obtained based on the obtained current density distribution, the reference current value can be set to a value corresponding to the actual electron beam. Therefore, a value close to the current value obtained according to the size of the target electron beam is obtained.
Actually obtained current value By performing beam correction so as to approach the reference current value, the actual size of the electron beam can be corrected to the target size. For this reason, finer exposure can be performed.

[0041]

FIG. 2 is a diagram for explaining the operation of an embodiment of the present invention. In this embodiment, the configuration of the electron beam exposure apparatus is the same as that of FIG. 7, and the operation of the drive control device 30 is different.
The description of the configuration is omitted.

First, an electron beam is generated by the electron gun 11, and the electron beam is sequentially scanned in the X and Y directions, whereby the electrons are directly detected by the Faraday cup 29 sequentially, and the current value is measured by the ammeter 33. Then, the current distribution of the electron beam is measured (step S1-1). The current value can be measured by a backscattered electron detector, but it is preferable to use a Faraday cup for accurate current detection.

FIG. 3 is a diagram for explaining the operation of measuring the current distribution in the backscattered electron detector. 10 on a silicon wafer 24.
An electron beam having a relatively large beam size of 3 μm × 3 μm square as shown in FIG. Silicon wafer 2
4 is provided at a predetermined position with a mark M made of tantalum, which is about 0.2 to 0.5 μm square and easily reflects electrons, and sequentially scans the electron beam in the xy directions,
The current distribution is obtained by sequentially detecting the electrons corresponding to the mark M by the backscattered electron detector and storing them.

Next, from the current distribution measured in step S1-1 and the target beam size, the current values Ix ₀ and Iy ₀ as the reference in the X and Y directions of the target size are calculated (step S1-3). ).

Next, a function approximated to the current distribution obtained in step S1-1 is obtained (step S1-2). FIG.
FIG. 5 is a diagram for explaining how to obtain an approximate function.

For example, when the beam has the intensity of an electronic signal as shown in FIG. 4A, the characteristic in the X direction is a linear function, so that the current density J is a linear function J = aS + b.
-It is approximated by (2). Here, J indicates current density, S indicates beam size, and a and b indicate constants.

In the case where the current density distribution is uniform as shown in FIG. 5A, the reference current I can be obtained by I = J × S, and has the characteristics as shown in FIG. FIG.
(C) the current density distribution is not uniform, as shown, the reference current value if it is approximated to a function as shown in equation (2) is ∫Jds = ∫ (aS + b) dS = aS 2/2 + b ·
S... (3) are obtained, and characteristics are obtained, for example, as shown in FIG.

The reference current value is obtained by substituting the target beam size S into equation (3).

Here, the reference current value is obtained using the equation (3) in the X direction and the Y direction.

Next, the number of adjustments is determined (step S1-4). If the adjustment is not completed even after the predetermined number of adjustments have been made in step S1-4, the process ends. If the adjustment is within the predetermined number of times, the process described below is executed until the predetermined number of times is reached.

Next, the slit deflector 16 is controlled to generate an elongated beam in the X direction as shown in FIG. 10B, and the current value Ix in the X direction is detected by the Faraday cup 29 and the ammeter 33. (S1-5).

[0052] The detected current value Ix detected by the Faraday cup 29 and an ammeter 33 is compared with a reference current value Ix _0, determines whether or not within the tolerance the difference is predetermined (step S1-6). In step S1-6, and controls the next slit deflector portion 16 when the difference between the detected current value Ix and a reference current value Ix ₀ is within the permissible range, elongated in the Y direction as shown in FIG. 10 (C) A beam is generated, and the current value Iy in the Y direction is detected by the Faraday cup 29 and the ammeter 33 (step S1-7).

The detected current value I detected in step S1-7
y and the reference current value Iy, and it is determined whether or not the difference is within a predetermined allowable range (step S1-
8).

If the difference between the detected current value Iy and the reference current value Iy ₀ is within the allowable range in step S1-8, the adjustment is terminated (step S1-9).

In step S1-6, the detected current value Ix
The difference between the reference current value Ix ₀ compares the magnitude relation between the detected next current value Ix and a reference current value Ix ₀ when not within the allowable range (step S1-10).

In step S1-10, (detected current value I
When x)> (reference current value Ix ₀ ), the slit offset correction coefficient X in the X direction is reduced by an arbitrary amount (step S1-11). When (detected current value Ix) <(reference current value Ix ₀ ) in step S1-10, the slit offset correction coefficient X in the X direction is increased by an arbitrary amount (step S1-12).

In step S1-8, the detected current value Iy
The difference between the reference current value Iy ₀ compares the magnitude relation between the detected next current value Iy and the reference current value Iy ₀ when not within the allowable range (step S1-13).

In step S1-13, (detected current value I
y)> (reference current value Iy₀), Slip in the Y direction
The offset correction coefficient X is reduced by an arbitrary amount.
Step S1-14). Also, in step S2-12, (detection)
Output current value y) <(reference current value y) ₀) In the Y direction
Increase the slit offset correction coefficient Y by an arbitrary amount
(Step S1-15).

By repeating steps S1-5 to S1-15, the detected current values Ix and Iy and the reference current value Ix
₀ , Iy ₀ is set within the allowable range, and the adjustment process ends.

If the difference does not fall within the allowable range even if steps S1-5 to S1-15 are repeated a predetermined number of times, the correction cannot be performed as it is, so that the correction processing ends and the input adjustment of the apparatus is performed. Do.

FIG. 6 is a diagram for explaining the operation of another embodiment of the present invention. This embodiment also has the same configuration as that of FIG. 7 and the operation of the drive control device 30 is different, so that the description of the configuration is omitted.

In FIG. 6, the same steps as those in FIG. 2 are denoted by the same reference numerals, and description thereof will be omitted.

In this embodiment, map data is created without approximating the current density distribution by a function, and the reference currents Ix ₀ and Iy ₀ are obtained based on the map data. In this case, similarly to the first embodiment, a dot mark on the sample (a tantalum dot mark on a silicon wafer; a size of about 0.2 to 0.5 μm square) is two-dimensionally scanned with a beam in the x and y directions. ,
An electronic signal g _d (x, y) is obtained (step S3-
1).

The current value Id at the beam size (3 μm × 3 μm) used in the measurement in step S3-1 is measured (step S3-2).

G measured in step S3-1_d(X,
y) and the sum に わ た る g over x and y _d(X, y),
With the current value Id obtained in step S3-2, the current density
Data is given by σ (x, y) = (Id / Σg_d(X, y)). G_d(X, y) ... Calculated by equation (4) (step S3-3).

The map data σ (x, y) obtained in steps S3-1 to S3-3 is used as a current density distribution. When calculating the current value I (SX, SY) of the beam size (SX, SY), the scanning step of step S3-1 is performed by ΔX, Δ
When Y, I (SX, SY) = Σ (σ (x, y) · ΔX · ΔY) (The sum is taken over 0 ≦ x ≦ SX and 0 ≦ y ≦ SY.)
Required by

The reference current values Ix ₀ ,
Using Iy ₀ , the slit offset is calculated in the same manner as in FIG.

As described above, according to the above-described embodiment, the current density distribution of the electron beam is obtained, and the reference current values Ix ₀ and Iy ₀ as the reference for correction are obtained based on the obtained current density distribution. A current value corresponding to a beam of a target size in the current density distribution of the beam can be obtained as a reference current value.Therefore, by performing correction so that the measured current value approaches the reference current value, A beam of a target size can be reliably obtained. In this embodiment, the current value of the electron beam is detected by the Faraday cup 29 and the ammeter 33. However, the present invention is not limited to this, and a similar effect can be obtained by using a backscattered electron detector.

[0069]

As described above, according to the present invention, the current distribution of an electron beam of a predetermined size is measured, and a reference current value of an electron beam of a target size is determined according to the measured current distribution. Since the correction is performed based on the current value, there is a feature that accurate correction corresponding to the target size and the current distribution can be performed.

[Brief description of the drawings]

FIG. 1 is a principle diagram of the present invention.

FIG. 2 is an operation explanatory diagram of one embodiment of the present invention.

FIG. 3 is an explanatory diagram of an operation of a main part of one embodiment of the present invention.

FIG. 4 is an operation explanatory diagram of another main part of one embodiment of the present invention.

FIG. 5 is an operation explanatory diagram of another main part of one embodiment of the present invention.

FIG. 6 is an operation explanatory diagram of another embodiment of the present invention.

FIG. 7 is a configuration diagram of an electron beam exposure apparatus.

FIG. 8 is an operation explanatory view of a main part of the electron beam exposure apparatus.

FIG. 9 is a diagram illustrating an operation of an example of the related art.

FIG. 10 is an explanatory diagram of an operation of a main part of a conventional example.

FIG. 11 is an operation explanatory diagram of another main part of a conventional example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 1st procedure 2 2nd procedure 3 3rd procedure 4 4th procedure 11 Electron gun 14 1st slit 14a Slit hole 16 Slit deflector part 17 2nd slit 17a Slit hole 29 Faraday cup 30 Drive control device 33 Current Total

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-62-234323 (JP, A) JP-A-54-135998 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01J 37/04 H01J 37/09 H01L 21/027

Claims (3)

(57) [Claims] 1. An electron beam generator for generating an electron beam, a first slit for forming an electron beam generated by the electron beam generator into a rectangular shape, and a rectangular shape formed by the first slit. A second slit for cutting out a rectangular electron beam of a predetermined size from the
A slit deflector that deflects the electron beam formed by the slit, projects the electron beam on the second slit, and sets the size of the electron beam in accordance with the amount of deflection of the electron beam, and cuts out by the second slit. A beam control method for an electron beam exposure apparatus, comprising: detecting means for detecting a current of the detected electron beam, wherein the detecting means detects a current of the electron beam, and the detecting means detects a current of the electron beam. A first procedure (1) for obtaining a current density distribution of an electron beam; and a second procedure for obtaining a reference current value of an electron beam having a target size based on the current density distribution obtained in the first procedure (1). Step (2): controlling the slit deflector according to the target size, and detecting a current value of the electron beam at that time by current detection means. Order (3) and a reference current value and the third calculated by the second procedure (2)
Comparing the detected current value detected in the procedure (3) of the above, and controlling the slit deflector according to the difference between the reference current value and the detected current value to obtain an electron beam of a target size. A beam control method for an electron beam exposure apparatus, comprising the step (4). 2. The second procedure (2) approximates the current distribution measured in the first procedure (1) with a function approximating the current distribution, and calculates a target beam size based on the function. 2. The method according to claim 1, wherein a corresponding reference current value is calculated. 3. The second procedure (2) forms a current density distribution map of the electron beam based on the current distribution of the electron beam of a predetermined size measured in the first procedure (1). 2. The beam control method for an electron beam exposure apparatus according to claim 1, wherein a reference current value of an electron beam having a target size is obtained based on a current density distribution map.