JPH09260256A - Charged particle beam aligner - Google Patents

Abstract

PROBLEM TO BE SOLVED: To accurately and rapidly judge the cleaning time of contaminant stuck on an optical system. SOLUTION: This equipment consists of the following; a first and a second shaping apertures 22, 25 which shape an electron beam casted from an electron gun 1 in a desired form, a projection lens 24, a shaping deflector 23 and an objective 27. In this case, after the beam is deflected on a first position on the second aperture 25 for a constant time with the shaping deflector 23, the beam is deflected on a second position. The beam current value in the second deflection position is measured, and the cleaning time of the shaping deflector 23 is judged from changing amount of the measured beam current value.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a charged beam exposure apparatus for drawing a fine pattern such as LSI on a sample surface.

[0002]

2. Description of the Related Art An electron beam exposure apparatus using an electron beam is used as a means for exposing a fine pattern on the surface of a semiconductor substrate. Among the electron beam exposure apparatuses, a variable shaped beam type electron beam exposure apparatus that forms a beam of an arbitrary shape by changing the beam size is
It has a feature that the throughput is remarkably high.

In a variable shaped beam type electron beam exposure apparatus, it is necessary to adjust the beam size so that the set beam size and the actual beam size match. The beam size can be adjusted, for example, by the method described in JP-A-63-23756.

However, it is known that the beam size deviates from the set beam size during exposure. This is inside the electron optical lens barrel (hereinafter referred to as EOS [Electron
This occurs because electric charge is accumulated in the optical system (hereinafter referred to as “optical system”) (hereinafter referred to as “charge-up”) and the trajectory of the charged beam is changed (so-called beam drift). More specifically, when charge-up occurs in the shaping deflector for controlling the beam size, beam drift occurs, the position of the electron beam image on the second shaping aperture changes, and the actual beam size shifts. . This means that the offset amount for adjusting the actual size to the set beam size changes as a function of time (hereinafter referred to as offset drift).

This offset drift changes greatly in a short time and is composed of a short cycle offset drift that saturates and a long time offset drift that drifts over a long time. The influence of this offset drift on the drawing pattern becomes more remarkable as the pattern becomes finer. For example, when the offset drift amount is 0.01 μm (on the sample surface), 2% (0.0
Although the error is 1 / 0.5), the error is 10% (0.01 / 0.1) in the drawing pattern of the 0.1 μm rule.

If charge-up occurs in the objective deflector or in the resist on the surface of the sample, the beam size does not change but the beam irradiation position changes. In order to eliminate such beam irradiation position error,
The beam irradiation position is measured at regular intervals during patterning, and the beam deflection amount is adjusted by the amount of position drift,
A reduction in drawing accuracy is prevented (see, for example, JP-A-5-304080).

This method is effective when the beam drift occurs relatively slowly, but it is difficult to correct the drift for a short time. Therefore, before writing a pattern, dummy irradiation is performed in which the beam is irradiated to a place deviated from the object to be irradiated and a desired pattern is drawn for a time period in which the beam drift is relatively stable.

However, since this method is not effective for the beam drift that changes the beam size, there is a drawback in that the actual beam size during writing cannot be controlled correctly. That is, the beam size measured during beam adjustment changes due to offset drift.
In addition, there is a problem that the beam size during writing is unknown even if the time becomes stable.

The offset drift is caused by charge-up of the contaminant layer adhering to the electrode of the EOS, particularly the electrostatic deflector, and the potential change of the electrode surface due to the charge-up. This contaminant layer adheres due to the interaction between the residual hydrocarbon molecules in vacuum and the electron beam. Although this contaminant is large and small, it is a problem common to all devices using a charged beam. As a method of removing this carbon, for example, there is a method proposed in Japanese Patent Application No. 06-313715. This method uses a strong oxidation process by downflow using a mixed gas of CF ₄ and O ₂ to remove contaminants adhering to the electrode surface. By removing contaminants, offset drift due to charge-up of contaminants can be eliminated.

However, even if the contaminants are removed from the electrode surface by the above-mentioned method, the contaminants are again present on the electrode surface due to the interaction between the hydrocarbon molecules remaining in the vacuum and the electron beam depending on the usage time thereafter. Adhere to. Then, offset drift due to charge-up of contaminants is induced. Therefore, it is necessary to regularly clean the electrode surface.

In order to carry out cleaning, the operation of the apparatus must be stopped. Including the cleaning process and the subsequent adjustment confirmation process, the equipment must be stopped for about 3 to 5 days. However, such a stoppage of the device causes an increase in cost in manufacturing a product, which is not desirable.

However, if the contaminants are not washed, the offset drift due to the contaminants on the electrode surface increases quadratically with time, degrading the drawing pattern accuracy.
If drawing is continued in the state where the pattern accuracy is deteriorated, the yield will be reduced, and enormous damage will occur if the post-process is included.

That is, frequent cleaning shortens the operating time of the apparatus and increases the manufacturing cost. In addition, if the cleaning is not performed, the yield is reduced and the manufacturing cost is increased. Therefore, it is necessary to make an accurate decision on the implementation of cleaning.
In order to determine whether cleaning is to be performed, it is necessary to actually perform writing and determine from the state of the writing pattern, or to measure the beam current amount with a Faraday cup etc. and determine the offset drift amount from the change in beam current value. is there.

In the former judgment method, the state of offset drift cannot be judged before drawing, and it takes about two days for development processing after drawing, observation with a scanning electron microscope, etc., and therefore the judgment takes time. Also, due to factors such as process factors, the decision timing was often incorrect. On the other hand, if the change in the beam current value is monitored as in the latter case, a warning or the like is issued before drawing, so that the above problem does not occur. However, there is a problem that the measurement result of the beam current value and the actual drawing pattern do not match, and the cleaning time cannot be accurately determined.

[0015]

As described above, conventionally, since the contaminants attached to the optical system of the electron beam exposure apparatus cause the beam drift, it is necessary to regularly clean the optical system. It was not possible to judge the time accurately and quickly. That is, there is a problem that it takes a long time to make a judgment based on the drawing pattern. In addition, the change of the beam current value has a problem that a result different from the actually obtained drawing pattern is obtained. The problem of determining the cleaning time of contaminants is not limited to the electron beam exposure apparatus, and can be similarly applied to the ion beam exposure apparatus. An object of the present invention is to provide a charged beam exposure apparatus that can accurately and quickly determine the cleaning time for cleaning contaminants attached to an optical system.

[0016]

[Means for Solving the Problems]

(Structure) The charged beam exposure apparatus of the present invention is structured as follows. (1) In a charged beam exposure apparatus including a charged beam generator that generates a charged beam and an optical system that includes a deflector that deflects the charged beam generated by the charged beam generator, a deflector of the optical system. By the first charged beam
Is deflected to a second position for a certain period of time and then the physical quantity of the charged beam at the second position is measured, and the measured change amount of the physical quantity is compared with a preset value. And (2) A charged beam generator that generates a charged beam, first and second shaping apertures that shape the charged beam generated by the charged beam generator into a desired shape, and are provided between these apertures. A projection lens for projecting the image of the first shaping aperture onto the second shaping aperture, a shaping deflector for varying the optical overlap of the first and second shaping apertures, and shaping by the shaping deflector. The charged beam is deflected to the first position on the second aperture for a certain period of time by the objective lens for projecting the focused beam onto the sample and the shaping deflector, and then to the second position. Current value measuring means for measuring the current value of the charged beam at the position, and current value comparing means for comparing the amount of change in the measured current value with a preset value. (3) A charged beam generator for generating a charged beam, a means for shaping the beam generated by the charged beam generator into a desired shape, and an objective lens for focusing the shaped beam on a sample. An objective deflector for deflecting the shaped beam to a desired position on the sample, and the objective deflector deflecting the charged beam to a first position on the sample for a certain period of time and then to a second position, It comprises a position measuring means for measuring the position of the beam at the second position and a position comparing means for comparing the measured change amount of the beam position with a preset value. (4) The current value measuring means changes the first position to two or more positions and performs a plurality of measurements. (5) In (2), the second position is a position where a line beam is formed in which the shape of the beam is greatly different in aspect ratio. (6) The position measuring means changes the first position to two or more places and performs a plurality of measurements. (7) In (3), the first position is near the apex of the deflectable area of the objective deflector. (8) In (3), in order to measure the irradiation position of the beam, the second position is measured using the reflected electrons of the beam.

(Operation) Offset drift was experimentally measured using an electron beam drawing apparatus EX-8D (manufactured by Toshiba). The offset drift was evaluated by measuring the beam current with a Faraday cup. Specifically, after adjusting the beam size, the beam is deflected so that the transmission current value at each position (Type-1 to Type-5) on the second shaping aperture shown in FIG. It is deflected to each position until the charge-up is sufficient within (180 seconds is set here). After that, the electron beam image S1 as shown in FIGS.
X line beam for drift measurement (1μm × 0.01μ
m) and Y line beams (0.01 μm × 1 μm) were deflected, and the time change of the current value of each line beam was measured. The current value of the line beam changes abruptly when the widthwise dimension of the short side changes. Therefore, the drift can be easily observed by measuring the current change.
The drift in the Y direction can be measured with the line beam, and the drift in the X direction can be measured with the Y line beam.

Typical measurement results are shown in FIGS. 9, 10, 11, and 12. (A) to (e) of FIG. 9 and FIG.
Time variation of beam current value after deflection from each Type into an X-line beam, (a) to (e) of FIGS.
FIG. 4 is a diagram showing a change over time in a beam current value after deflecting a beam from each Type to a Y line. 11 and 1
In No. 2, when the type-1 is deflected to the Y line beam, the beam current value does not change. In all other cases, the beam current greatly increases in a short cycle (about 100 seconds), and then the current value saturates and stabilizes. On the other hand, when the beam is deflected from each Type to the X-line beam as shown in FIGS. 9 and 10, the beam current value increases in all the Types, and then becomes saturated and stable. However, Type
In the case of e-1, the initial increase amount is smaller than that of the other types.

Next, FIG. 13 shows a change in the voltage applied to the shaping deflector when deflecting each type into an X and Y line beam by a vector. Here, in FIG.
Is the change in applied voltage when deflecting from each Type to the X line beam, and FIG. 13B is the change in applied voltage when deflecting from each Type to the Y line beam. Also, FIG.
4 shows the coordinate system in FIG. 13 together with the shaping aperture 25 and the objective deflector 23. However, although the actual deflector is configured with 8 poles, it is shown with 4 poles for simplification of description.

In the case of Type-1 for both X and Y lines, the vector amount is small. On the other hand, in other types, the vector amount is large. When compared with FIGS. 9, 10, 11, and 12, it was noticed that there is a strong correlation between the change in the applied voltage of the deflection voltage and the change amount of the beam current value in a short time.

When the beam is deflected from Type-1 to a line beam, the voltage applied to the deflector changes little and does not change much from the position of the line beam. Therefore, the beam current value is close to that measured without deflection. Can be said. If the beam current value is simply measured without deflection, the measured value does not change. However, since it is deflected during actual drawing,
It can be seen that when the beam is not deflected, the amount of change in the beam current value and the actual writing pattern do not match.

That is, the offset drift strongly depends on the previous history of beam deflection, and depends on the previous history and the amount of change in the deflection voltage. For example, when the deflection is performed from Type-1 to the Y line, the beam current value does not change. When the cleaning time is determined in this state, it is determined that there is no offset drift and there is no need for cleaning. However, it can be seen that when the beam is deflected from Type-5 to the Y line, the beam current value changes greatly and the beam size changes. If drawing is performed in this state, the accuracy of the formed pattern decreases, which becomes a problem.

A remarkable representation of this problem is shown in FIGS. Here, a is the beam current value before cleaning, and b is the beam current value after cleaning. FIG. 15 shows changes over time in the beam current value when deflected from Type-1 to a line beam by using electrodes before and after cleaning. There is no initial increase in the beam current value between before cleaning and after cleaning, and the difference between before cleaning and after cleaning does not appear significantly. Therefore, when the offset drift is evaluated by deflecting from Type-1 to the line beam, it is determined that there is no offset drift, and it is determined that the electrode cleaning process is not necessary.

FIG. 16 is a diagram showing the change over time in the beam current value when the same electrode as that used in the measurement of FIG. 15 is used, and before and after cleaning, the beam current is deflected from Type-5 to a line beam. Here, a is the beam current value before cleaning, and b is the beam current value after cleaning. The beam current value before cleaning has an initial increase, and it is judged that cleaning of the electrode is necessary. Further, it can be seen that the cleaning eliminates the initial increase in the beam current value, and the cleaning eliminates the offset drift.

As described above, since the change in the beam current value greatly differs depending on the history, if the cleaning time is judged only by measuring the change in the current value, the judgment will be erroneous. Since the actual drawing is performed while deflecting each type, it is not possible to judge the cleaning time by simply measuring the beam current value. However, by deflecting each type into a line beam and observing the temporal change in the beam current value after that, it is possible to observe the change in the beam current value in a state close to that during actual writing.

As described above, the proper cleaning time can be determined by deflecting each type into a line beam and setting the cleaning time when the amount of change in beam current value exceeds a certain level.

[0027]

BEST MODE FOR CARRYING OUT THE INVENTION

(First Embodiment) FIG. 1 is a schematic view showing the outline of an electron beam exposure apparatus according to the first embodiment of the present invention. Here, a chamber for housing an optical system and the like, an exhaust system, etc. are omitted. An optical system 2 that focuses, deflects, and shapes the electron beam is provided below the electron gun 1 (charged beam generator) that generates the electron beam. A sample 3 to be exposed is set below the optical system 2 on a movable stage 4 which is movable. Further, on the movable stage 4, a Faraday cup (current value measuring means) 5 for measuring the current value of the electron beam,
A beam size measurement mark table 6 is provided. Also,
By moving the movable stage 4, the irradiation position of the electron beam can be selected from the sample 3, the Faraday cup 5, or the mark stand 6 for measuring the electron beam size.

Further, the Faraday cup 5 has a cleaning determination device (current value comparison means) which compares the amount of change in the current value measured by the Faraday cup 5 with a preset reference value and determines whether or not it is in the cleaning time. 7 is connected.

Next, the detailed structure of the optical system 2 will be described. A condenser lens 21 for adjusting the current density of the electron beam is provided below the electron gun 1. Further, a first shaping aperture 22 for limiting the electron beam is provided below it. Further, a shaping deflector 23 that deflects the electron beam is provided below it. A projection lens 24 and a second shaping aperture 25 are provided. A reduction lens 26 is provided below the objective lens 2 below the reduction lens 26.
7 and the objective deflector 28 are provided.

Further, the pattern data memory 30 for storing the data of the size of the electron beam and the position of irradiating the sample.
Are connected to send a data signal to the pattern data decoder 31 and the drawing data decoder 32. The pattern data decoder 31 calculates the voltage applied to the shaping deflector 23 from the data of the pattern data memory 30, and controls the beam shaping amplifier 33 which applies the voltage to the shaping deflector 23. Further, the drawing data decoder 32 calculates the voltage applied to the objective deflector 28 from the data of the pattern data memory 30 and controls the objective deflection amplifier 34 which applies the voltage to the objective deflector 28.

Here, the actual exposure will be described. The electron beam emitted from the electron gun 1 has its current density adjusted by the condenser lens 21 of the electron gun, and is uniformly irradiated on the first shaping aperture 22. Aperture 22
The electron beam shaped by
An image is formed on the shaping aperture 25. A shaping deflector 2 provided between the first shaping aperture 22 and the projection lens 24.
3 controls the degree to which the electron beam formed by the first shaping aperture 22 overlaps the second shaping aperture 25, and changes the size of the electron beam.

The electron beam images shaped by the first and second shaping apertures 22 and 25 are reduced by the reduction lens 26, and further formed on the sample 3 by the objective lens 27. The position of the electron beam image projected on the sample 3 is determined by the objective deflector 28.

Next, the determination of the cleaning time will be described with reference to FIG. FIG. 2 is a diagram showing the position of the electron beam image S1 on the second shaping aperture 25. When the electron beam image S1 formed by the first forming aperture 22 is deflected to the line beam Type-L, the Faraday cup 5 is irradiated with the electron beam, and the electron beam value is adjusted so that it can be measured.

The electron beam images shaped by the first shaping aperture are Type-L, Type-2, Type-L, T.
type-3, Type-L, Type-4, Type-
The light is deflected in the order of L, Type-5, and Type-L for 20 seconds each. At that time, from Type-2 to Type-5
The beam current value when deflected to L is measured by the Faraday cup 5.

FIG. 3 is a diagram showing the change over time of the beam current value when the electrode surface of the shaping deflector is not dirty.
In the section of the arrow in the figure, the state is deflected to Type-2 to 5. It can be seen that when the surface of the electrode is not dirty, the difference ΔI between the maximum value and the minimum value of the beam current value changes little and the offset drift amount during drawing is small.

Further, FIG. 4 shows the line beams T from Type-2 to 5 when the surface of the shaping deflector electrode is dirty.
It is a figure which shows the time change of the beam current value after deflecting to yp-L. The measurement was performed in the same manner as the measurement in FIG. It can be seen that when the electrode surface of the shaping deflector is dirty, the difference ΔI between the maximum value and the minimum value of the beam current is large, and an offset drift occurs during writing.

That is, the change amount ΔI of the electron beam value can be small when the offset drift has not occurred, and the change amount ΔI can be large when the offset drift has occurred. Therefore, the actual cleaning time is determined when the change amount ΔI of the beam current exceeds a certain reference value.

After the above measurement, the cleaning determination device 7 compares the change amount ΔI of the beam current value with the reference value, and if the change amount ΔI is equal to or larger than the reference value, determines that it is the cleaning time. In this way, by obtaining the amount of change in current after setting the line beam L from Type-2 to Type-5, it is possible to perform evaluation under the same conditions as in actual writing.

In the present embodiment, the time for deflecting the type-2 to 5 and the line beam Type-L is set to 20 seconds, but the time interval may be set as necessary.
This set time depends on the quality of contaminants on the electrode surface.

The reference value of the beam current for determining the cleaning time may be set according to the accuracy of the target drawing pattern. By measuring the change in the beam current value in consideration of the beam history as in the present embodiment, the offset drift amount can be evaluated in a state close to the actual drawing, and the cleaning time of the shaping deflector can be determined. You can make an accurate judgment.

(Second Embodiment) In this embodiment, an apparatus for determining the cleaning time of the objective deflector 28 will be described with reference to FIGS.
This will be described with reference to FIG. FIG. 5 is a diagram showing the deflectable area of the objective deflector and the deflection position of the beam current value before drift measurement,
FIG. 6 is a diagram showing an example in which the deflectable region and the deflection position before the drift measurement are deflected to the drift measurement position. In addition, in FIGS. 5 and 6, the region indicated by a square is a region in which the electron beam can be deflected by the objective deflector.

Deflection is performed near the vertices P1, P2, P3, P4 of the deflectable area by the objective deflector, and is deflected until the electrode surface of the objective deflector is sufficiently charged up at each point.
After that, it is deflected to the measurement position M shown in FIG. 6, the irradiation position of the electron beam is obtained, and the cleaning time of the electrode of the objective deflector can be judged from the fluctuation of the irradiation position of the electron beam.

The beam position is measured, for example, by the following method. The mark base 6 is moved to the drift measurement position M, and a heavy metal for beam size measurement is installed on the mark base, and after deflecting from each point P1 to 4 to the measurement point M,
The beam is finely scanned on the measurement position M, the reflected electrons from the heavy metal on the mark base 6 are detected, and the position of the drift measurement position M is measured. Then, this measurement is repeated for a predetermined time.
When there is a drift, the measured position of the position M varies depending on the measurement time. Here, the position of the measurement position M is measured instead of measuring the irradiation position of the beam, but if the irradiation position of the beam changes, the measured measurement position M changes. Therefore, by measuring the position of the drift measurement position M, the beam irradiation position can be measured. Similar to the first embodiment, the actual judgment is to judge whether or not the cleaning time is reached by comparing the amount of change in position with the set reference value.

The measuring point M is not limited to the position shown in FIG. 6, and the measuring point may be provided at any position. The important point is that after deflecting to the maximum position of the deflectable area, it is deflected to the measurement point and the position is measured.

Although the electron beam is used as the charged particle beam in the above embodiment, a charged beam such as an ion beam may be used. In addition, without departing from the gist of the present invention,
Various modifications are possible.

[0046]

The charged beam exposure apparatus according to the present invention measures the beam current value or the beam irradiation position while deflecting the beam in a state close to the actual writing, thereby providing an optical system (forming deflector or objective deflector). The cleaning time can be determined quickly and accurately.

[Brief description of drawings]

FIG. 1 is a diagram showing a schematic configuration of an optical system of an electron beam exposure apparatus according to a first embodiment.

FIG. 2 is a diagram showing a deflection position of an electron beam image on a second shaping aperture of the optical system of FIG.

FIG. 3 is a diagram showing a time change of a beam current value in the case of a deflector after cleaning.

FIG. 4 is a diagram showing a time change of a beam current value in the case of a deflector before cleaning.

FIG. 5 is a diagram showing a relationship between an objective deflection area and a deflection position before drift measurement.

FIG. 6 is a diagram showing an example in which an objective deflection region and a deflection position before drift measurement are deflected to a drift measurement position.

FIG. 7 is a diagram showing each Type at a position on the second shaping aperture of the electron beam image.

FIG. 8 is a diagram showing a line beam.

FIG. 9 is a diagram (1) showing a change over time in the beam current value when each Type is deflected into an X-line beam.

FIG. 10 is a diagram (2) showing a time change of the beam current value when each Type is deflected into an X-line beam.

FIG. 11 is a diagram (1) showing a time change of a beam current value when each Type is deflected into a Y line beam.

FIG. 12 is a diagram (2) showing a time change of the beam current value when each Type is deflected to a Y line beam.

FIG. 13 is a diagram showing an applied voltage when deflecting each type into a line beam.

FIG. 14 is a diagram showing a coordinate system of applied voltage vectors of a deflector.

FIG. 15 is a diagram showing a time change of a beam current value when deflected from Type-1 to a line beam before and after cleaning.

FIG. 16 is a diagram showing a time change of a beam current value when deflected from Type-5 to a line beam before and after cleaning.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Electron gun (charged beam generation part) 2 ... Optical system 3 ... Sample 4 ... Movable stage 5 ... Faraday cup (current value measuring means) 6 ... Beam size measurement mark stand 7 ... Cleaning judging device (current value comparing means) 21 ... Condenser lens 22 ... 1st shaping aperture 23 ... Molding deflector 24 ... Projection lens 25 ... 2nd shaping aperture 26 ... Reduction lens 27 ... Objective lens 28 ... Objective deflector 30 ... Pattern data memory 31 ... Pattern data decoder 32 ... Drawing data decoder 33 ... Beam shaping amplifier 34 ... Objective deflection amplifier

Claims (3)

[Claims] 1. A charged beam exposure apparatus comprising: a charged beam generator for generating a charged beam; and an optical system including a deflector for deflecting the charged beam generated by the charged beam generator. The deflector deflects the charged beam to the first position for a certain period of time and then to the second position, measures the physical quantity of the charged beam at the second position, and presets the amount of change in the measured physical quantity. Charged beam exposure apparatus, characterized in that it is compared with the measured value. 2. A charged beam generator for generating a charged beam, and first and second shaping apertures for shaping the charged beam generated by the charged beam generator into a desired shape.
A projection lens provided between these apertures for projecting the image of the first shaping aperture onto the second shaping aperture and a shaping deflector for varying the optical overlap of the first and second shaping apertures. An objective lens for projecting the beam shaped by the shaping deflector onto a sample; and a second deflecting the charged beam to a first position on the second aperture for a predetermined time by the shaping deflector.
Current value measuring means for deflecting the charged beam to the second position and measuring the current value of the charged beam at the second position, and current value comparing means for comparing the measured change amount of the current value with a preset value. A charged particle beam device comprising: 3. A charged beam generator for generating a charged beam, means for shaping the beam generated by the charged beam generator into a desired shape, and an objective for imaging the shaped beam on a sample. A lens, an objective deflector for deflecting the shaped beam to a desired position on the sample, and the objective deflector for deflecting the charged beam to a first position on the sample for a certain time and then to a second position. However, it is provided with position measuring means for measuring the position of the beam at the second position and position comparing means for comparing the measured change amount of the beam position with a preset value. Charged beam exposure device.