JPH09293477A - Charged beam adjusting method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To accurately focus electron beams and enhance the drawing accuracy of a fine pattern. SOLUTION: An electron beam drawing device irradiates an aperture mask having the pecified opening shape with electron beams 101 to generate open- shaped beams, and deflects the beams to draw a pattern in the desired position on a sample 109. The relation between the beam size and the distance between a plurality of fine marks arranged in the scanning direction of the beams is suitably selected, the electron beams 101 are scanned on at least two marks, the intensity of a reflected electron signal obtained by scanning is used as an evaluation function, the evaluation function is measured while a focal point position is varied, the relation between the evaluation function and the focusing point position is applied to a secondary function, and the focal point position becoming the external value of the secondary function is used as the optimum focal point position to adjust the focal point of the beam.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a charged beam drawing technique for drawing a fine pattern such as ULSI on a sample surface, and more particularly to a charged beam adjusting method for adjusting the focus position of the charged beam.

[0002]

2. Description of the Related Art Conventionally, an electron beam drawing apparatus has been used for drawing a desired fine pattern on a sample surface such as a semiconductor wafer. In this type of electron beam writer,
A mechanism for measuring the intensity distribution of the electron beam and adjusting the focus position of the electron beam on the sample surface is generally provided.

For example, when a single fine mark provided on a part of the sample stage is scanned with an electron beam to detect backscattered electrons, an intensity distribution reflecting the shape of the electron beam can be obtained. The beam width from 10% to 90% of the crest value of the intensity distribution is defined as the beam resolution, and the beam resolution is measured while changing the excitation position of the objective lens to change the focal position of the electron beam. Quadratic function as a function of excitation or focus position of
If we find the extrema of the quadratic function that minimizes the beam resolution,
The optimum focus position on the sample surface can be obtained.

In recent years, as the drawing pattern has become finer and the depth of focus has become shallower, it has become necessary to improve the precision in adjusting the focal position of the electron beam. The intensity distribution of the electron beam obtained by the method described in the related art is a convolution pattern of a beam shape and a fine mark shape. Therefore,
The smaller the mark size, the more accurate the beam shape can be measured.

However, when the mark size is reduced, the reflected electron signal is weakened, the S / N ratio is reduced, the measurement error is increased, and the focus position cannot be adjusted with high accuracy. In addition, when the beam shape is not symmetrical and the behavior of noise causes a large variation in the measured value of the beam resolution, the focus position cannot be adjusted accurately. Further, when the drawing pattern size is about 0.1 μm, the intensity distribution at the interface portion of the beam shape and the shoulder portion has a delicate influence on the drawing pattern, so the focus position is adjusted using the beam resolution as an evaluation function. Then, there is a problem that the fine pattern shape is greatly adversely affected.

[0006]

As described above, conventionally, it is necessary to measure the intensity distribution of the beam in order to adjust the focus position of the electron beam. However, in order to measure the beam intensity distribution with high accuracy, the mark size is made small. Then, the S / N ratio becomes small, and highly accurate focus position adjustment cannot be performed. Further, due to the asymmetry of the beam shape and the influence of noise, the measured value of the beam resolution varies, and there is a problem that the focus position cannot be adjusted accurately.

The above problem is not limited to the electron beam writing apparatus that draws a pattern by using an electron beam, and the same applies to an ion beam writing apparatus that draws a pattern by using an ion beam.

The present invention has been made in consideration of the above circumstances, and it is an object of the present invention to adjust the focal position of the charged beam with high precision, which can contribute to improvement of drawing precision of a fine pattern. It is to provide a method of adjusting a charged beam.

[0009]

[Means for Solving the Problems]

(Structure) In order to solve the above problem, the present invention employs the following structure. That is, according to the present invention, in a method of adjusting a charged beam for adjusting a focal position of the charged beam, at least two fine marks arranged at a predetermined interval are scanned by the charged beam, and a reflected electron obtained by the scanning is obtained. Alternatively, the secondary electron signal is detected, the intensity distribution of the charged beam is measured, and the focus position of the charged beam is adjusted based on the measured intensity distribution.

Here, preferred embodiments of the present invention include the following. (1) A plurality of marks are arranged along the beam scanning direction,
All mark intervals are the same. (2) A plurality of marks are arranged along the beam scanning direction,
The distance between each mark shall be gradually increased or decreased. (3) Marks are classified into a plurality of mark groups, each mark group has the same mark interval, and different mark groups have different mark intervals. (4) When adjusting the focus position of the charged beam, use marks with a mark interval that causes the largest change in the measured intensity distribution with respect to the change in the focus position. (5) When adjusting the focus position of the charged beam, the intensity distribution of the beam is measured while changing the charged beam size, and the change in the measured intensity distribution is the largest beam size with respect to the change in the focus position. Use a charged beam. (6) Using the measured charged beam intensity distribution as an evaluation function,
The evaluation function is measured while changing the focus position, the relationship between the evaluation function and the focus position is applied to a quadratic function, and the focus position that is the extreme value of the quadratic function is set as the optimum focus position.

Further, according to the present invention, by irradiating an aperture mask having a predetermined aperture shape with a charged beam, a beam having the aperture shape is generated, and the beam is deflected to be drawn at a desired position on a sample. The beam drawing apparatus is characterized in that a mark group in which at least two fine marks are aligned in the deflection direction of the charged beam is provided in a part of the sample table.

Here, it is characterized in that the intervals of the respective fine marks in the mark group are all the same. Further, it is characterized in that at least two sets of mark groups in which the intervals between the fine marks are slightly changed between the mark groups are provided in a part of the sample table. Further, at least one or more sets of mark groups in which the intervals between the fine marks in the mark group are slightly changed are provided in a part of the sample table.

Further, it is characterized in that the fine marks are dot-shaped or line-shaped. In addition, the shape of the fine mark is
It is characterized in that it is convex or concave with respect to the base around the mark. Further, it is characterized in that the gap between the fine marks is about the same as the beam size. (Operation) In the present invention, an appropriate relationship is selected between the beam size and the interval between a plurality of fine marks aligned in the scanning direction of the beam, and at least two fine marks are charged with a charged beam. The intensity distribution of the charged beam is obtained by scanning and detecting reflected electrons or secondary electrons obtained when the fine mark is irradiated with the charged beam. Then, the S / N ratio of backscattered electrons and secondary electron signals becomes large, so that the measurement accuracy can be improved and the focus position of the charged beam can be adjusted with high accuracy, which contributes to the improvement of the drawing accuracy of the fine pattern. Is possible.

Further, using the obtained intensity distribution as an evaluation function,
The evaluation function is measured while changing the focus position, the relationship between the evaluation function and the focus position is applied to a quadratic function, and the focus position that is the extreme value of the quadratic function is used as the optimum focus position to adjust the focus position. Therefore, this evaluation function includes information on the shoulders and interfaces of the beam in addition to the beam resolution, and the sensitivity of the evaluation function to changes in the focus position is higher than that when the conventional beam resolution is used as the evaluation function. Accurate focus position adjustment can be performed.

FIG. 13 compares the rate of change of the evaluation function when the focus position is changed between the case of the conventional method and the case of the present invention. In the case of the present invention, the rate of change of the evaluation function is large, especially when the focus position deviates from the optimum focus position, as compared with the conventional method, so that the error due to the fitting of the quadratic function can be reduced. Therefore, by using the charged beam adjusting method according to the present invention, it is possible to realize a highly accurate drawing pattern.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The details of the present invention will be described below with reference to the illustrated embodiments. FIG. 1 is a schematic configuration diagram showing an electron beam drawing apparatus used in an embodiment of the present invention. In the figure, 100 is an electron gun, 101 is an electron beam emitted from the electron gun 100, 102 is a deflection control circuit for controlling the position of the beam, 103 is a deflection amplifier, 104 is a deflector, 10
5 is an objective lens, 106 is a backscattered electron detector, 107 is a circuit for processing backscattered electron signals, 108 is a movable stage, 1
Reference numeral 09 is a sample such as a wafer, 110 is a fine mark stand, and 111
Is a stage position control circuit, and 112 is a control computer. Further, 113 is a backscattered electron obtained when the fine mark on the fine mark stand 110 is scanned by the electron beam 101.

The electron beam is focused on the sample by the objective lens 105 and can be positioned at an arbitrary position on the sample by the deflector 104. The sample 109 such as a wafer and the fine mark table 110 can be selected by moving the movable stage 108, and the positions thereof can be accurately controlled by a stage position control circuit 111 including a laser length measurement system.

FIG. 2 shows definitions of three types of beam sizes. The beam size A is the full width at half maximum of the electron beam intensity distribution, the beam size B is the width of the 100% portion of the peak value, and the beam size C is the width of the interface of the intensity distribution. 11 is the left side edge of the beam, 12 is the right side edge, 1
3 is called the beam interface and 14 is called the beam shoulder.

In the intensity distribution of FIG. 2, it is the inclination of the edge 11 or 12 of the beam that reflects the beam resolution. Conventionally, the focus position is adjusted using this as an evaluation function. On the other hand, in the present embodiment, in order to measure the change in the beam shape due to the change in the focus position, in addition to the change in the inclinations of the edges 11 and 12 of the beam, the interface 13 of the beam is changed.
And the intensity change of the shoulder 14 of the beam is captured with high sensitivity. (First Embodiment) First, a first embodiment of the present invention will be described.

As shown in FIG. 3, on the fine mark base 110, columnar marks 21 of the same size manufactured by the lithography process are arranged in a matrix at the same intervals m. Of the marks shown in FIG. 3, the electron beam 10 passes over two marks 22 and 23 that are laterally adjacent to each other.
When the scanning is continuously performed at 1, the intensity distribution of the reflected electrons as shown in FIG. 4 is obtained. At this time, the relationship between the lateral beam size (defined in FIG. 2) and the distance m between the marks 22 and 23 is B <m <A as shown in FIG. The beam size in the vertical direction is set to the same value as that in the horizontal direction.

Since the size of the mark interval m is fixed,
Depending on the size of the electron beam 101, the intensity distribution as shown in FIG. 4 may not be obtained. In this case, the intensity distribution may be measured while changing the beam size of the electron beam 101, and the beam size with which the intensity distribution similar to that in FIG. 4 is obtained may be used.

When the excitation of the objective lens 105 is changed to change the focal position of the electron beam, 31, 32, 33 in FIG.
The intensity distribution changes as shown in. Intensity distribution 33,3
The beam resolution decreases in the order of 2, 31 and the peak value of the intensity distribution increases. Here, as shown in FIG.
Beam deflection position t1, centered on the peak value of the intensity distribution
By setting t2, a value S _N obtained by normalizing the integrated value S of the intensity of the portion equal to or larger than the threshold value It between t1 and t2 by the total integrated value of the intensity distribution is used as the evaluation function.

In FIG. 7, the intensity distribution is measured while changing the focal position to obtain the integrated value S, and the standardized integrated value S _N is calculated.
And the focal position are applied to a quadratic function (y = ax ² + bx + c). Extreme value of quadratic function (-b / 2a)
Then, the focus position can be adjusted by determining the focus position at this time as the optimum focus value.

The relationship between the beam size and the mark interval is C <m
When <B, the intensity distribution has a concave shape as shown in FIG. Beam deflection positions t3 and t4 are provided, and from t3 to t
A value obtained by standardizing the integrated value S of the intensity between 4 and the total integrated value of the intensity distribution can be used as the evaluation function. In this case, the relationship between the focus position and the evaluation function can be approximated by a downward convex quadratic function, and the focus position can be adjusted with the focus position at the extreme value of the quadratic function as the optimum focus position. .

In the present embodiment, the beam sizes in the horizontal direction and the vertical direction are the same, but by changing the beam size in the vertical direction and the vertical position of the electron beam when scanning the fine mark, the mark 22 is changed. Also, the electron beam may be applied to the upper mark row or the lower mark row in which the marks 23 are lined up to increase the reflected electron signal amount and increase the S / N ratio to improve the accuracy. (Second Embodiment) Next, a second embodiment of the present invention will be described.

FIG. 9 is a diagram showing a fine mark arrangement for explaining the second embodiment of the present invention. According to the method described in the first embodiment, if the beam size cannot be changed arbitrarily as in the electron beam apparatus of the batch exposure method, the optimum beam size for measuring the intensity distribution cannot be obtained.

Therefore, in the present embodiment, a plurality of mark groups M1 (mark intervals ml) in which the mark intervals are slightly different,
M2 (mark interval m2) and M3 (mark interval m3) are prepared (the mark interval is the same in one mark group). Then, the electron beam 10 passes over the marks of each mark group.
1, the intensity distribution is measured by scanning at 1, and the optimum mark group for performing the focus position adjustment shown in the first embodiment is selected,
The optimum focus position can be obtained by the method described in the first embodiment. (Third Embodiment) Next, a third embodiment of the present invention will be described.

FIG. 10 is a diagram showing the arrangement of fine marks for explaining the third embodiment of the present invention. As shown in FIG. 10, the mark spacing is ml <m2 <m3 <m4 <m.
5 <m6 <m7 to changing little by little as <m _x Place,
By scanning the mark row with the electron beam 101, the optimum relationship between the mark interval and the beam size for mark detection can be easily selected.

When the marks shown in FIG. 10 are continuously scanned by the electron beam having the shape shown in FIG. 2, the mark intervals ml to m7 and the beam sizes A to C defined in FIG. The intensity distributions shown in FIGS. 11A to 11G are obtained. Similar to the description of the first embodiment, FIG.
The focus position can be adjusted by the method described in the first embodiment using the intensity distribution of (c) or the intensity distribution of FIG. 11 (e). (Fourth Embodiment) Next, a fourth embodiment of the present invention will be described.

In the first to third embodiments, a dot-shaped columnar mark is used as a mark for observing the intensity distribution, but when the dot mark has a small S / N ratio, it is shown in FIG. As shown, the line marks 25 may be arranged in a grid pattern, and the electron beams may be scanned over the line marks 25 to intensify the reflected electron signal for detection. The shape of the intensity distribution obtained when scanning the line mark with the electron beam is the same as the shape of the intensity distribution obtained when scanning the dot-shaped columnar mark. Therefore, the line mark interval is L1 =
If L2 = L3 = ..., Focus position adjustment can be performed by the same method as in the first embodiment.

If line marks having a mark interval of L1 = L2 = L3 = ... Are set as one mark group and a plurality of mark groups having slightly different mark intervals are used,
The focus position can be adjusted by the method of the second embodiment. Furthermore, by using line marks having a mark interval of L1 <L2 <L3 <..., Focus position adjustment can be performed by the same method as in the third embodiment. (Other Embodiments) In the first to fourth embodiments, the electron beam scans the fine mark once to obtain the intensity distribution, but the same position is scanned twice or more to perform the average addition process. The accuracy can be further improved by. Furthermore, in the first and second embodiments, the accuracy can be further improved by scanning three or more marks continuously at one time and performing the average addition process.

Although the fine marks described in the above embodiments are convex columnar dot marks or line marks with respect to the base around the fine marks, a concave hole mark or a concave groove line mark is used. Also, since the intensity distribution similar to that of the convex mark can be obtained, the same effect as that of the above-described embodiment can be obtained.

The scanning direction of the electron beam in the above-described embodiment is not limited to the horizontal direction described in the above embodiment, but the electron beam may be scanned in the vertical direction using the fine mark rows in the vertical direction to adjust the focus position. good. Further, not only the reflected electrons but also the secondary electrons may be used for the detection.

Although the present embodiment has been described with respect to the adjustment of the focal position of the electron beam, the present invention is not limited to this, and a charged beam exposure device such as an ion beam drawing device, and further, a laser beam is scanned or a light beam is irradiated. It is also applicable when detecting a mark image. Further, it can be applied to beam astigmatism adjustment.

In carrying out this embodiment, it is premised that the scanning direction of the beam and the arrangement direction of the marks are the same. Therefore, before performing the focus adjustment, it is necessary to perform the rotation correction of the deflection position by the deflection position control circuit 102 that controls the deflection position of the electron beam. The rotation correction of the deflection position can be performed by changing the balance of the voltage applied to each electrode of the deflector. Alternatively, the fine mark stand 11
It is also possible to rotate 0 to match the arrangement direction of the marks with the scanning direction of the beam. In addition, various modifications can be made without departing from the scope of the present invention.

[0036]

As described above in detail, according to the present invention, at least two fine marks are scanned with a charged beam,
The reflected electron or secondary electron signal obtained by the scanning is detected to measure the beam intensity distribution, and the focus position of the beam is adjusted based on the measured intensity distribution, so that the focus position of the charged beam can be accurately adjusted. It is possible to match them, and it is possible to contribute to improvement of drawing accuracy of a fine pattern.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram showing an electron beam writing apparatus used in an embodiment of the present invention.

FIG. 2 is a diagram showing the definition of beam size.

FIG. 3 is a view showing a fine mark array arranged at the same intervals.

FIG. 4 is a diagram showing an intensity distribution obtained by scanning two fine marks with an electron beam while changing the focal position.

FIG. 5 is a diagram showing a relationship between a space between two fine marks and a beam size.

FIG. 6 is a diagram showing an example of a method of obtaining an integrated value S for obtaining an optimum focus position.

FIG. 7 is a diagram showing a relationship between a focus position for obtaining an optimum focus position and an integrated value.

FIG. 8 is a diagram showing an example of a method for obtaining an integrated value S for obtaining an optimum focus position.

FIG. 9 is a diagram showing an example in which a plurality of mark groups having the same mark interval are arranged.

FIG. 10 is a diagram showing an example in which a plurality of marks are arranged with different mark intervals.

FIG. 11 is a diagram showing an intensity distribution obtained when the mark rows having different intervals are continuously scanned with an electron beam.

FIG. 12 is a view showing an example in which line-shaped fine marks are arranged in a grid pattern.

FIG. 13 is a diagram showing a comparison of the rate of change in the evaluation function between the conventional method and the method according to the present invention.

[Explanation of symbols]

 11 ... left edge of beam 12 ... right edge of beam 13 ... interface of beam 14 ... shoulder of beam 21, 22, 23 ... fine columnar mark 25 ... fine line mark 31, 32, 33 ... intensity distribution of reflected electron signal 100 ... Electron gun 101 ... Electron beam 102 ... Deflection control circuit 103 ... Deflection amplifier 104 ... Deflector 105 ... Objective lens 106 ... Reflection electron detector 107 ... Circuit for processing reflected electron signal 108 ... Movable stage 109 ... Sample 110 ... Fine mark stand 111 ... Stage position control circuit 112 ... Control computer 113 ... Backscattered electron

Claims (6)

[Claims] 1. An intensity distribution of the charged beam is obtained by scanning at least two fine marks arranged at a predetermined interval with a charged beam and detecting backscattered electrons or secondary electron signals obtained by the scanning. A method for adjusting a charged beam, which comprises measuring and adjusting a focus position of the charged beam based on the measured intensity distribution. 2. The method of adjusting a charged particle beam according to claim 1, wherein a plurality of the marks are arranged along the beam scanning direction, and the intervals between the marks are gradually lengthened or shortened. 3. The mark is classified into a plurality of mark groups,
2. The method of adjusting a charged particle beam according to claim 1, wherein each mark group has the same mark interval, and different mark groups have different mark intervals. 4. When adjusting the focus position of the charged beam, the intensity distribution of the beam is measured while changing the size of the charged beam, and the change of the measured intensity distribution becomes the largest with respect to the change of the focus position. 2. The method for adjusting a charged beam according to claim 1, wherein a charged beam having a beam size is used. 5. A mark having a mark interval with which the change in the measured intensity distribution is the largest with respect to the change in the focus position is used when adjusting the focus position of the charged beam. Method for adjusting the charged beam. 6. The intensity distribution of the measured charged beam is used as an evaluation function, the evaluation function is measured while changing the focus position, and the relationship between the evaluation function and the focus position is applied to a quadratic function to obtain the 2. The method of adjusting a charged particle beam according to claim 1, wherein a focal position that is an extreme value of the next function is set as an optimum focal position.