JPH09246146A - Method and apparatus for electron-beam lithography - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the deflection response characteristic of an electron beam caused by a deflection delay or by an advance factor by a method wherein a correction waveform as the difference between a first waveform at a time when an electron beam is deflected on a mask and a second waveform at a time when the electron beam is deflected to an edge part on the mask is added to a deflection control signal. SOLUTION: An electron beam 1 is deflected toward a point A4 on a mark from a point A0 at a prescribed distance from the mask, and a first waveform B2 is obtained. Then, the electron beam is deflected to the jump starting point AO, a sufficient time which does not affect a deflection delay is awaited, the electron beam is then deflected to an edge part A2 on the mark, and a second waveform C2 as a mark edge waveform is obtained. When the second waveform C2 is subtracted from the first waveform B2, a third waveform (a response delay waveform) C3 is obtained. The third waveform C3 is added to a deflection waveform, and the magnitude and the polarity are controlled so as to reduce the third waveform C3 to a minimum. Then, the time elapsed until the deflection waveform at this time reaches the point A4 on the mark is shortened.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electron beam drawing apparatus, and more particularly to a deflection control circuit for an electron beam drawing apparatus.

[0002]

2. Description of the Related Art Improving throughput in an electron beam drawing apparatus is an important issue. In order to improve the throughput, deflection control of the electron beam writing apparatus is performed by setting the position of the writing field with a highly accurate electromagnetic deflection system and deflecting the electron beam within the writing field with a high-speed electrostatic deflection system. Has been adopted. This makes it relatively fast,
High-precision drawing is possible. An example of the deflection system of such an electron beam drawing apparatus is shown in FIG. In the figure,
(1) is an electron beam, (16) is a wafer, (2a) is an electromagnetic deflector, and (4a), (3a), and (15) are main field data designated by the drawing control unit to the electromagnetic deflector. A DA converter for giving and a main deflection amplifier, and (2b) is an electrostatic deflector for the sub field, which is controlled by the DA converter of (4b) and the sub deflection amplifier of (3b). (2
c) is an electrostatic deflector for the sub-subfield, (4c)
It is controlled by the DA converter and the sub-deflection amplifier (3c). An example of the numerical values of the main field, subfield, and subfield is 5000μ as shown in the figure.
m, 500 μm, 80 μm. The electromagnetic deflection system determines the position of the sub-field and the sub-field electrostatic deflection system determines the position of the sub-subfield. Drawing is performed by electrostatically deflecting the sub-subfield at high speed.

An electromagnetic deflection system having a large deflection region has a narrow frequency band and poor response characteristics because the deflection coil for deflecting the beam is an inductive load. The response time of electromagnetic deflection is extremely long, for example, 50 to 100 μsec.
For this reason, the electrostatic deflector cannot be deflected until the output of the electromagnetic deflection amplifier reaches a predetermined value, resulting in dead time for drawing. In addition, the deflection response time of the sub-deflection of the electrostatic deflection system that determines the pattern writing shot period is, for example, 100 nanoseconds, which is a major factor in reducing the throughput of the electron beam writing apparatus. Many methods have been proposed in the past for improving these problems.

For example, a method of shortening the deflection response time by adding a correction signal whose amplitude, delay, or polarity is controlled according to the deflection signal input to the deflection amplifier (Japanese Patent Laid-Open No. 7-106964), or electromagnetic Corrects the delay in electromagnetic deflection response time by detecting the difference between the deflection waveform to be applied to the deflection coil and the actual deflection current waveform, and adding a correction signal waveform that minimizes the difference to the electrostatic deflector. There is a method (Patent Publication 4-32530).
In addition, as a method of reducing the effect of eddy currents due to electromagnetic deflection, a conductor is installed near the deflection coil, the eddy current generated in the conductor is detected by the deflection magnetic field, and the current that flows in the deflection coil is detected based on the detected output. Method of applying feedback (Japanese Patent Laid-Open No. Sho 6)
0-74618) or a correction circuit for simulating an electron beam irradiation position deviation error caused by an eddy current with an electric circuit, and the correction circuit corrects the current supplied to the electromagnetic deflector (Japanese Patent Laid-Open No. 3-44916). )and so on.

[0005]

In the above-mentioned conventional techniques, the movement of the electron beam on the sample such as the wafer is not directly measured. There are a method of correcting the deflection response delay by detecting a deflection current (magnetic field), and a method of generating a correction signal for simulatingly correcting the deflection response delay to correct the deflection response delay. Therefore,
The actual movement of the electron beam and the effect of correction were unknown.
Therefore, the effect of the correction is to draw the result and to
There is a problem that it cannot be understood unless observed with a (scanning electron microscope) or the like. This requires a lot of time and effort to confirm the effect of the correction. Particularly in the case of an electromagnetic deflection system, the influence of the eddy current on the electron beam greatly differs depending on the material, shape, or position of the structure near the electromagnetic deflection coil, resulting in overshoot or undershoot. Moreover, it changes intricately depending on the direction and size of the deflection. The reason is that there are a plurality of locations where eddy currents are generated and they interfere with each other in a complicated manner. Alternatively, there is a change in the position of the electron beam due to a long-term change in the magnetic domain of the ferrite core, called a magnetic aftereffect, or crosstalk in an electric circuit. For these reasons, as a practical problem, it was difficult to produce an optimum correction signal, so that the blanking signal, that is, the signal for turning on the beam could not be advanced.

[0006] The present invention solves the above problems,
This was done to reduce the throughput of the electron beam lithography system. It improves the deflection response characteristics of the electron beam due to all deflection delay (or advance) factors such as eddy current, magnetic aftereffect, electric circuit, etc. It is an object of the present invention to provide a method and a device that enable highly accurate drawing.

[0007]

According to the present invention, a first waveform obtained when an electron beam is deflected on a mark from a position separated from the mark by a predetermined distance and a position separated by the predetermined distance again A second waveform obtained when the electron beam is deflected to the edge portion of the mark as a starting point is acquired in synchronization with each deflection, and a third waveform which is a difference between the two waveforms is stored as a correction waveform, The stored correction waveform is read in synchronization with the deflection of the electron beam and added to the deflection control signal to correct the deflection response delay of the electron beam.

A method of correcting the electron beam deflection response according to the present invention will be described with reference to FIG. In the figure, as shown in the deflection (B) on the mark, the electron beam (1) having a certain area is deflected (jumped) from a point A0, which is a predetermined distance from the mark, toward A4 on the mark. To do. A deflection waveform (B1) shows an example of the deflection control signal waveform at this time and the position of the electron beam. At first, it reaches the target position vicinity a4 at high speed, and then slowly reaches the final position A4. Alternatively, it reaches A4 rapidly and converges with damping vibration. Although these states change intricately depending on the transfer characteristics of the deflection circuit, they are shown by broken lines for ease of explanation. When the electron beam reaches A1, reflected electrons are generated from the mark and a first waveform (waveform on the mark: B2) is obtained. Here, the delay or vibration of the first waveform does not appear because the size of the reflected electrons does not change even if the beam position on the mark changes, because the surface of the mark is flat.

Next, the electron beam is applied to the above jump start point A.
After being deflected to 0 and waiting for a sufficient time without the influence of the deflection delay, this time, it is deflected to the edge portion A2 of the mark. The positional relationship between the beam and the mark in this case is shown in mark edge deflection (C). At this time, the second waveform (mark edge waveform: C2) is obtained. This is a waveform that reflects the beam position change due to the deflection waveform (C1). Therefore, when the second waveform (C2) is subtracted from the first waveform (B2), the third waveform (response delay waveform: C
3) is obtained. The third waveform (C3) represents the response delay of the deflection control signal. In other words, it is possible in this way to measure how the beam is deflected on the target, which is one of the objects of the invention. In addition,
Even if vibration occurs in the detection system of the first waveform (B2), the vibration that appears in the first waveform (B2) and the vibration that appears in the second waveform (C2) are the same, so there are two signals. It is canceled by subtracting and no vibration appears in the output. Of course, when vibration occurs in the deflection signal waveform, it is measured as a vibration waveform. When the third waveform (C3) is added to the deflection waveform and the magnitude and polarity are controlled so that the third waveform (C3) is minimized, the deflection waveform at that time is the fourth waveform (deflection response waveform: C4). ),
This means that the conventional time t4 required to reach the point A4 on the mark is shortened to the time t3. That is, conventionally, t
Although drawing had to be started after waiting until 4, it can be shortened to t3 in the present invention.

The deflection response characteristic changes depending on the magnitude of deflection. Generally, if the deflection amount is small, the response time becomes short. By arranging the deflection distance to an arbitrary value from the minimum to the maximum, the relationship between the deflection distance and the correction condition is obtained, and by interpolating between these points, the response time is finely corrected. The electromagnetic deflection system is complicated. This is because the eddy current, the magnetic aftereffect, or the characteristics of the deflection circuit interfere intricately as described above. It is not possible to determine the third waveform (C3) for all possible deflection distances. Therefore, in the present invention, the present invention is applied only to the case where the frequency of repetitions in which the magnitude of the deflection is determined is high. Fig. 2 shows an example.
(1), (2), (3). For example, adjacent subfields are adjacent jumps in which step deflection is performed from left to right in the order shown in (1), such as 1 to 2, 2 to 3, and 10 as shown in (2). There are cases such as a non-adjacent jump from 1 to 11 and a simultaneous XY jump from the upper right end position of the main field to the lower left position of the next main field as shown in (3). In the present invention, the correction conditions for minimizing the deflection response delay for each of (1), (2), and (3) are obtained and stored in advance. Then, at the time of drawing, the response characteristic of electromagnetic deflection can be corrected by reading and correcting the third waveform stored in accordance with the deflection condition in synchronization with the deflection.

Further, the beam-on timing of the blanking signal can be advanced based on this correction signal.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 3 shows an embodiment of the present invention.
The deflection circuit section (3) and the deflector (2) detect the waveform on the mark when the electron beam (1) whose origin is a predetermined distance from the mark is deflected onto the mark by the detector (17). To do. The detected mark waveform is the deflection start time t.
The signal waveform memory (5) whose address is incremented at a timing of 0 and at a predetermined time cycle is stored. After that, the electron beam is deflected to the above-mentioned position apart from the mark by a predetermined distance, and after waiting for the time until settling, this time it is deflected to the mark edge portion and the resulting mark edge waveform is stored in the signal waveform memory (6). The difference between these two stored mark waveforms is obtained and stored as a correction waveform in the correction waveform memory (7) at the address corresponding to the address of the signal waveform memory. After that, the electron beam is deflected again from the position apart from the mark by a predetermined distance to the edge portion of the mark. However, in this case, the correction waveform stored in the correction memory (7) is read by using the deflection start timing (t0) as a trigger, and is processed by the correction signal control unit (10) to be added to the deflection waveform. The resulting mark edge waveform is compared with the already stored mark edge waveform, and the above deflection and correction are repeated until the difference becomes minimum. The optimum correction waveform thus obtained is stored in the correction memory (7) as the final correction waveform. Further, these operations are performed even when the predetermined distance is changed. Although the operations detailed above are very time-consuming, they are automatically performed by the control computer. The frequency of obtaining the correction waveform does not have to be set each time drawing is performed. Normally, it is sufficient to do it during the initial adjustment of the system.

At the time of drawing, at the timing of the start of deflection, that is, at time t0, the correction waveform stored in the correction waveform memory (7) at the address corresponding to the deflection size is read out and added to the deflection circuit section (3). . This makes it possible to correct the response delay of the deflection.

(Embodiment 1) In the present embodiment, the basic device configuration and operation will be described by taking as an example a case where it is applied to a sub-sub electrostatic deflection system that greatly affects the throughput of an electron beam drawing apparatus. This will be described with reference to FIGS. 4, 5, and 6. First, in FIG. 4, the drawing control unit (15) controls the beam size setting unit (13) to set the size of the beam (1) by the deflector (12). In the case of this embodiment,
The size was 1 μm. The reason will be described later. After that, the drawing controller (15) gives predetermined deflection data to the DA converter (4c), converts it into a voltage by the sub-sub-deflection amplifier (3c), and the electron beam (1) by the sub-sub-electrostatic deflector (2c). Deflect. The relationship between the beam and the mark and the signal waveform at this time are shown in the mark deflection (B) and waveform diagram of FIG. In the case of the above-mentioned example, the sub-subfield is 8
0 μm. The sub-sub-deflection amplifier (3c) outputs the beam to the A
Deflection waveform (B1) when deflecting 80 μm from 0 to A4
At a slew rate of about 20 nanoseconds (a
It has characteristics that reach 4). The position error of (a4) is about 0.2% (0.16 μm). Approximately 80 nanoseconds then 0.005 μm drawing tolerance (A4)
To reach.

Here, the mark is a wire stretched in a cross shape on the groove. The detector (17) is a metal plate at the bottom of the groove, which is insulated from other parts. In other words, the fact that the current stops flowing when the electron beam hits the wire is used. In principle, backscattered electrons can also be used, but due to the fact that the intensity of backscattered electrons changes if there is unevenness on the mark surface, and there is currently no sensor that can detect changes of 100 nanoseconds or less. The drawing controller (15) is a DA converter (4
At the same time as outputting the deflection data trigger to c), the memory address control unit (14) is operated. The memory address control unit (14) generates a clock signal at the timing of the deflection data trigger. An example of the oscillation frequency of this clock signal is 500 MHz. The AD converter (9) is operated in synchronization with this oscillation frequency, the mark signal waveform converted into a voltage by the amplifier (8) is sampled, converted into a digital code and stored in the signal waveform memory (5). At this time, the memory address is incremented by the memory address control unit (14) in a cycle of 2 nanoseconds (500 MHz). The counter runs for at least 100 nanoseconds after t0.
The 80 nanosecond slow change in the deflection waveform (B1)
It is exponential, but when approximated to a straight line, the change is 0.16 μm in 80 nanoseconds. That is, when sampling is performed at a cycle of 2 nanoseconds, it is possible to detect the mark waveform with an accuracy of 0.004 μm.

In this way, the waveform stored in the signal waveform memory (5) becomes the mark waveform (B2). The response delay (or vibration) that appears in this mark waveform is not due to deflection. The characteristics of the mark signal detection system including the amplifier (8) are mainly dominant. The reason is,
This is because the signal strength does not change even if the position of the beam changes after the beam is placed on the mark. By the way, the amplitude of this waveform corresponds to the beam size and is 1 μm.
The larger the beam size is, the more preferable the signal S / N is, but a high-speed AD converter (9) having a bit number proportional to the beam size is required. Currently available high-speed AD converters have an 8-bit resolution. On the other hand, in the case of the present embodiment, the required accuracy is 0.005 μm, and therefore the beam size is 1 μm.

Subsequently, the drawing controller (15) starts the operation mode of the mark edge deflection (C) of FIG. The drawing control unit (15) outputs a deflection data trigger to the DA converter (4c) and at the same time operates the memory address control unit (14). The process from the start of deflection to the acquisition of the mark edge waveform (C2) is the same as in the above-described mark deflection (B). The obtained mark edge waveform (C2) is stored in the signal waveform memory (6). Although not shown, a method of detecting a mark position by scanning a mark with an electron beam in an electron beam drawing apparatus is well known. Although detailed description is omitted, the beam can be easily deflected to the edge portion of the mark by the conventional technique.

When the above operation is completed, the drawing control unit (1
5) obtains the difference between the waveform of the signal waveform memory (5) and the two waveforms of the signal waveform memory (6). By taking the difference, a correct response delay waveform (C3) that is not affected by the amplifier (8) or the AD converter (9) can be obtained. Then, the response delay waveform (C3) is stored in the correction waveform memory (7) of the corresponding address.

Subsequently, the drawing controller (15) again performs the mark edge deflection as shown in FIG. However, in this case, a trigger is given to the memory address control section (14) at the timing when the deflection data of the position A2 is given to the DA converter (4c). The memory address controller (14) is 500
Correction waveform memory (7) at a frequency of 2 nanoseconds in MHz
The response delay waveform (3) stored in is read out, and the DA converter (11) and the correction signal control unit (10) control the size and polarity thereof and add it to the sub-sub deflection amplifier (3c). The resulting mark waveform is stored in the signal waveform memory (6). The drawing controller (15) obtains a response delay waveform (D2), for example, by taking a difference from the waveform of the signal waveform memory (5) already stored. This procedure is repeated until it becomes minimum as shown by the response delay waveform (D3), and the correction waveform at that time is stored in the correction waveform memory (7). When the response characteristic of the amplifier (8) is equal to that of the sub-sub-deflection amplifier, the deflection response time up to t3 is 20 ns for the deflection and the slew rate of the amplifier as shown in the corrected deflection waveform (D4). About 4
It is 0 nanoseconds, which is less than half that of the conventional method. Here, the amplifier (8) changes the output slowly like the deflection, but the beam size is 1 μm and the error after 20 nanoseconds is 0.2%, so the error is neglected to be 0.002 μm. it can. The S / N of the mark waveform is extremely bad in relation to the beam current. Actually, the S / N is improved by repeating the deflection a number of times and averaging.

In the case of the electrostatic deflection system, the magnitude of deflection and the response delay are almost proportional. Therefore, the optimum correction amount corresponding to an arbitrary deflection distance can be obtained by changing the deflection amount and performing the above-described operation. At the time of drawing, the contents of the correction waveform memory thus obtained and stored are corrected in real time at the timing of the drawing pattern data given to the DA converter (4c). Then, the magnitude of the correction is controlled according to the deflection distance.

(Embodiment 2) The correction waveform may not be added in some cases depending on the characteristics of the sub-sub deflection amplifier. An example of such a case is shown in FIG. Dedicated deflection amplifier (3) for correcting the signal of the correction signal control unit (10)
d) and the electrostatic deflector (2d) are used to correct the response delay of the sub-sub-deflection. Others are the same as in the first embodiment described above.

(Embodiment 3) As described above, when a current flows through the electromagnetic deflection coil, an eddy current transiently flows by electromagnetic induction in a structure or the like in the vicinity thereof. In many cases, the magnetic field due to the eddy current acts so as to prevent the deflection of the electron beam. That is, the deflection response characteristic is deteriorated by the eddy current. Alternatively, a change in the position of the electron beam due to a long-term change in the magnetic domain of the ferrite core, which is called a magnetic aftereffect, and crosstalk in an electric circuit are factors that reduce the deflection speed and accuracy.
Therefore, as a practical problem, it is difficult to create an optimum correction signal. FIG. 8 shows an embodiment in which the present invention is applied to the above problems of the electromagnetic deflection system. If the response delay of the electromagnetic deflection system is corrected to the electromagnetic deflection system, an eddy current is generated due to the correction deflection, and it may be difficult to perform ideal correction. In the present embodiment, in order to avoid the above-mentioned inconvenience, the electromagnetic deflection system is delayed by the electrostatic deflection system. Other configurations and operations are the same as those in the first embodiment, and therefore the description thereof is omitted.

[0023]

As described above, in the method and apparatus for correcting the electron beam deflection delay according to the present invention, the deflection response delay is measured by measuring the mark signal when the electron beam is deflected to the mark. Can be measured, and the deflection delay of the electron beam can be corrected by superimposing it on the deflection signal of the electron beam based on the obtained response delay waveform. As a result, for example, in an electron beam drawing apparatus, it is possible to create a high-speed and high-precision semiconductor device.

[Brief description of drawings]

FIG. 1 is a diagram showing a basic operation of a method and apparatus for correcting an electron beam deflection response delay according to the present invention.

FIG. 2 is a diagram showing a configuration of a deflection system of an electron beam drawing apparatus and a state of deflection.

FIG. 3 is a diagram showing an embodiment of the present invention.

FIG. 4 is a basic configuration diagram of a first embodiment according to the present invention.

FIG. 5 is a first diagram for explaining the operation of the first embodiment.

FIG. 6 is a second diagram for explaining the operation of the first embodiment.

FIG. 7 is a basic configuration diagram of a second embodiment according to the present invention.

FIG. 8 is a basic configuration diagram of a third embodiment according to the present invention.

[Explanation of symbols]

1 ... electron beam 2 2, 12 ... deflector 3 ... deflection circuit (amplifier) 4 ... D / A converter 5, 6 ... waveform memory 7 ... corrected waveform memory 8 ... amplifier 9 ... A / D converter 10 ... correction signal control unit 11 ... D / A converter 13 ... beam size setting unit 14 ... memory address control unit 15 ... drawing control unit.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yasuko Goto 1-280 Higashi Koigokubo, Kokubunji City, Tokyo Inside the Central Research Laboratory, Hitachi, Ltd.

Claims (8)

[Claims] 1. A step of obtaining a first waveform obtained when an electron beam is deflected onto a mark starting from a position distant from the mark by a predetermined distance, and an electron beam starting from a position distant from the mark by a predetermined distance. The step of obtaining a second waveform obtained when the mark is deflected to the edge portion of the mark; the step of obtaining and storing a third waveform by taking the difference between the first waveform and the second waveform; The third waveform is added to the deflection control signal of the electron beam to obtain the fourth waveform.
And a step of determining a blanking signal of the beam from the fourth waveform, the electron beam drawing method. 2. A mark signal waveform 1 obtained when an electron beam is deflected onto a mark from a position distant from the mark by a predetermined distance, and an electron beam from the mark again from the position distant by the predetermined distance from the mark. The mark signal waveform 2 obtained when deflected to the edge portion is acquired in synchronization with each deflection, the difference between the two waveforms is obtained and stored as a correction waveform, and the stored correction waveform is deflected by the electron beam. A method for correcting a deflection response delay of an electron beam, which comprises: reading in synchronization with the deflection control signal and adding the deflection control signal to the deflection control signal to correct the deflection response delay of the electron beam. 3. An electron beam drawing method, wherein the third waveform according to claim 1 is obtained for each specific deflection distance, and the deflection response characteristic of the electron beam is corrected based on the obtained waveform. . 4. A third method according to claim 1, wherein the deflection distance is changed.
Is obtained, a correction waveform at an arbitrary deflection distance is obtained based on the waveform, and the deflection response characteristic of the electron beam is corrected based on the obtained correction waveform. 5. The first and second waveforms according to claim 1, which are obtained for each deflection by repeating deflection at the same distance, are averaged and stored, and based on the waveforms that are averaged and stored. The electron beam drawing method according to claim 1, wherein the third waveform according to claim 1 is obtained. 6. When deflecting using an electromagnetic deflector, an electron is characterized in that the deflection delay due to the electromagnetic deflector is corrected by applying the third waveform according to claim 1 to the electrostatic deflector. Line drawing method. 7. An electron source, an electron optical system for controlling an electron beam from the electron source, mark means provided on a sample stage, deflecting means for deflecting and irradiating the mark means with an electron beam, and the mark. And a means for calculating and calculating the waveform of the electron beam drawing apparatus. 8. A means for automatically obtaining the position of the mark based on a mark signal obtained by scanning the electron beam on the mark, and deflection of the electron beam starting from a position separated by a predetermined distance from the mark. And a means for measuring the mark signal waveform 1 obtained in accordance with the deflection control signal, and a mark signal waveform 2 obtained by deflecting the mark signal waveform 1 to the edge portion of the mark again starting from the position separated by the predetermined distance. And a means for storing the difference between the two waveforms as a correction waveform, and the stored correction waveform is read in synchronization with the deflection start signal of the electron beam to obtain the deflection response characteristic. An electron beam drawing apparatus provided with a means for correcting deflection so as to be improved and a means for automatically performing these.