JP2000277410A - Electron beam drawing equipment - Google Patents

Abstract

(57) [Summary] An electron beam lithography system using a sample stage continuous moving lithography system obtains a high-precision lithography pattern. When a deviation from the operating range of a tracking D / A converter is about to occur, a means for temporarily suspending a figure drawing position and resetting a tracking correction amount is provided. In the electron beam lithography apparatus according to the present invention, the moving amount of the sample stage when drawing a graphic on the continuously moving sample stage is likely to deviate from the operating range of the tracking D / A converter specified in advance. At this time, the drawing of the figure is suspended, and the figure drawing position data of the shaped electron beam is reset.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electron beam lithography apparatus mainly used in the semiconductor industry, and more particularly to an electron beam lithography apparatus which draws a figure by following an electron beam while continuously moving a sample stage. The present invention relates to a figure drawing method, which relates to a technique for increasing the accuracy of analog addition of a following deflection amount for following a sample stage.

[0002]

2. Description of the Related Art Generally, an electron beam writing apparatus for writing an LSI pattern forms an electron beam into a desired shape in accordance with pattern data (hereinafter abbreviated as a formed electron beam) and deflects the electron beam to a predetermined position. At the same time, control is performed to position the drawing portion of the sample in the deflection field. 2. Description of the Related Art In recent years, an electron beam lithography system has been constructed with a continuous movement lithography technique for writing the entire surface of a sample while continuously moving a sample stage along a predetermined path (hereinafter, referred to as a chip stripe) for the purpose of improving throughput. This is realized by detecting a moving amount of the sample stage that moves continuously during writing, and establishing a technique for feeding back the moving amount to the deflection signal of the shaped electron beam.

In this method, first, a moving speed of a sample stage is calculated from the sparse density of a writing pattern to create a speed table, and the table is continuously moved with reference to the table. On the other hand, the shaped electron beam always measures the amount of movement of the sample stage to determine the amount of follow-up deflection, and feeds this back to the main deflector to follow the sample stage, and draws by the sub-deflector. For this reason, the continuous moving drawing method does not waste the moving time of the sample stage, which is advantageous for increasing the throughput. A known example of this continuous moving drawing method is disclosed in Japanese Patent Application Laid-Open No. Sho 64-11328.

[0004] As a feedback method of the following deflection amount, there are a step following method performed by the main deflector and a method using analog addition performed by the sub deflector. As a method of feeding back the following deflection amount, Japanese Patent Application Laid-Open No. 6-196394 can be cited as a known example.

[0005]

At present, in the semiconductor industry such as the manufacture of LSIs, the greatest problems required of an electron beam lithography apparatus are improvement in lithography accuracy and throughput. To achieve this, it is essential to improve the control technology of the electron beam lithography system in addition to the electron beam technology and the resist technology.

As described above, in the continuous movement drawing method, a deviation from an initial value is always obtained by measuring the amount of movement of the sample table, and this deviation is added to a deflection position signal for graphic drawing to follow up. Configure a feedback loop. As a key device to realize this, without adding noise to the deflection position signal,
In addition, a tracking digital / analog converter (hereinafter, abbreviated as a tracking D / A converter) that generates a deviation amount with high accuracy is exemplified.

A D / A converter used for tracking deflection is required to have a high resolution of 14 to 16 bits or more in order to increase tracking accuracy. Also, the operation speed has been required to operate at a speed of several tens of MHz or more. This is due to the fact that the quantization unit of the writing data has become finer, the following deflection range has been widened from several tens of μm to several hundreds μm or more. Is required.

The problem with the tracking D / A converter is the presence of internal noise in the tracking feedback loop, which results in a deterioration in drawing accuracy. In particular, the tracking D / A converter employs a high-speed D / A converter, and is a spike noise caused by a slight difference between turn-on and turn-off times of internal logic circuits such as registers and analog switches. Hereinafter, this is called glitch noise.

The glitch noise is generated when the value changes from -1 to zero, or when the high-order bit such as 1/2 full scale is detected.
When the lower bits change and rise,
Glitch noise that is large from ns to several hundreds ns is likely to occur. The feature of glitch noise is that noise corresponding to the full scale of the D / A converter is instantaneously generated when all bits are inverted. When this glitch noise is mixed into the deflection signal of the figure drawing, one figure drawing time is several tens of times.
Since the time is from 00 ns to several μs, a position shift depending on glitch noise occurs. As a result, irregularities and irregular displacements occur in the drawing result, causing a serious problem.

In the semiconductor manufacturing industry in recent years, there is an increasing demand for drawing a pattern of 0.1 μm or less, and there is a tendency for higher precision to be achieved. Therefore, a misregistration of figure drawing due to glitch noise, which can be ignored in the past, has become apparent.
If this glitch noise is flattened by a filter or the like, a problem arises as a cause of causing a long positional displacement of several tens of nanometers.

In the case where a measure is taken using a sample and hold circuit, pedestal noise of the sample and hold circuit itself has become a problem. The pedestal noise is a kind of spike noise generated when the sample and hold circuit shifts from the sampling mode to the hold mode. Since it occurs every time the sample and hold is repeated, the occurrence frequency is much higher than the glitch noise. Therefore, high precision could not be completely realized.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problem, and has been described in accordance with a continuous-moving drawing method of a method for adding a follow-up deflection amount.
It is an object of the present invention to provide a high-accuracy and high-throughput electron beam lithography apparatus in which glitch noise of an / A converter is reduced.

[0013]

In order to achieve this object, an electron beam drawing apparatus according to the present invention comprises: a means for measuring and monitoring a figure drawing time during a single figure drawing; Means for measuring the amount of movement of the sample stage during the operation and storing the measured amount as the amount of movement within the figure drawing, and comparing the amount of movement within the figure drawing with a value of a preset allowable range, thereby determining whether the movement is within the allowable range. Means for judging whether or not, if the value deviates from the permissible range, the operation of drawing graphics is temporarily suspended,
The graphic drawing remaining time is obtained from the means for correcting and adding the graphic drawing position data (X, Y) using the latest sample stage position information and the means for measuring and monitoring the graphic drawing time, and the graphic drawing is executed again (re- (Referred to as graphic drawing) means. If a deviation phenomenon similar to the above occurs during the re-drawing of the graphic, the operation is performed so as to repeat the above-mentioned re-drawing of the graphic.

The D / A conversion means for the tracking correction data used when converting the tracking correction data and the graphic drawing data into analog signals and adding the same is provided with a plurality of different voltage values or current values. The following deflection signal is obtained using a D / A converter having means for selecting and switching any one of the reference values according to the sample stage movement data code from the reference value group composed of The sample stage following deflection is performed by adding the output signal of the sample and the drawing position signal (X, Y).

Further, in addition to the above-mentioned means, there is provided a means for initializing the follow-up correction amount and starting the graphic drawing when the movement amount in the graphic drawing exceeds the allowable range.

[0016]

FIG. 1 is an overall block diagram of an electron beam lithography apparatus according to the present invention.

An embodiment of the present invention will be described below with reference to FIG.

In the electron beam lithography apparatus of this embodiment, a main, sub and two-stage deflector is used as the shaped electron beam deflecting means.

First, the first-stage main deflector 16 deflects the shaped electron beam to the subfield origin position and fixes it.
The second-stage sub deflector 17 deflects the shaped electron beam in a subfield and draws a figure in the subfield. At this time, since the sample stage 19 is continuously moving during writing, the amount of follow-up deflection is calculated, added to the drawing data, and given to the deflector 17 so that the shaped electron beam follows the sample stage 19. I have.

In FIG. 1, the control computer 1 first sets a speed table in the sample stage controller 12. The speed table is a table in which the sparse density of the drawing figure pattern is previously flattened by a filter and converted into the moving speed of the sample table 19. In addition, based on the sample table moving speed and the graphic drawing time, an allowable range of the moving amount in the graphic drawing is calculated and set in the moving amount in the graphic drawing comparing means 10. Graphic patterns such as LSI
The data is converted into an image for the electron beam drawing apparatus and stored in the graphic data memory 2.

Next, when a drawing start command is issued from the outside to the control computer 1, the control computer 1 activates the sample stage control unit 12. The sample stage controller 12 moves the sample stage 19 to a predetermined chip stripe start position, and then continuously moves the sample stage 19 with reference to the speed table. Further, the control computer 1 activates a restoration unit 3 for reading the graphic data to be drawn from the graphic data memory 2 and a decomposing unit 4 for converting the graphic data into fine graphic data. The operation of the restoration unit 3 and the disassembly unit 4 gives the origin position of the subfield to the main deflection control circuit 5, and at the same time, the figure data, that is, the coordinates (X,
Y) and the size (W: width, H: height) are given to the sub-deflection control circuit 7 for drawing a figure, and drawing starts.

As described above, when the continuous writing is started, a signal for irradiating the blanker 18 with the shaped electron beam to the sample is given. The irradiation time of this figure drawing is determined from a resist material used in a semiconductor manufacturing process such as an LSI, a current density of a formed electron beam, and the like. Here, it is assumed to be 0.5 (us) in consideration of increasing the sensitivity of the resist. The amount of movement of the sample stage that moves within this figure drawing time (the amount of movement in figure drawing)
Is determined by the moving speed of the sample stage. Sample stage moving speed is 1
Assuming 0 (mm / s), the movement amount in the figure drawing is 5 (n
m). Assuming in this way, the amount of movement in the graphic drawing is 5
(Nm), and compares it with the actual movement amount to determine whether it is within the allowable range or beyond the range.

First, if the actual movement amount is within the allowable range,
The graphic drawing is not divided and is executed by one operation. The follow-up correction amount during that time is converted into an analog amount by the follow-up D / A converter, and the analog amount is added by the sub deflection analog circuit 8. By repeating the same operation one after another in this manner, writing is performed on the entire surface of the sample.

However, if the actual amount of movement exceeds the allowable range, it may deviate from the operating range of the tracking D / A converter, and normal tracking correction cannot be performed. In order to avoid this, it is necessary to correct the position data of the graphic drawing. First, the moving amount in figure drawing comparison means 10 immediately issues a deviation alarm to the sub deflection control circuit. Blanking control circuit 11 for simultaneously controlling the irradiation time of the shaped electron beam
Issue a suspend signal.

Next, the blanking control circuit immediately suspends the current graphic drawing and waits for restart. The sub-deflection control circuit 7 inputs the current coordinates of the sample stage 19 via the sample stage length meter 14 and the sample stage control unit 12, and corrects the position data of the graphic drawing. Thus, the graphic drawing position is moved to the allowable range by moving the graphic drawing position data. After making this setting, the blanking control circuit is restarted and graphic drawing is resumed.

According to the present invention, the number of D / A converters used for analog addition of the tracking correction amount can be satisfied with far less bits than the conventional number of bits. This is a great advantage in improving the accuracy of the electron beam lithography apparatus. For example, when covering 5 (nm) as described above, the resolution 1 (n)
m) / LSB, a D / A converter of 4 bits or less is sufficient. On the other hand, in the conventional method, the tracking range is 1 (u
Since m) to 100 (um) or more were required, a D / A converter of 11 to 18 bits was required at the same resolution.

Although there is a method of using a sample and hold circuit to prevent glitch noise of the D / A converter, there is still a problem with improvement in accuracy and realization. Noise of the sample and hold circuit itself (pedestal and
(Offset) is generated every time, and even a small noise equivalent to several LSBs is always generated and causes deterioration of accuracy.

One of the most effective solutions for realizing higher precision of the electron beam writing apparatus is to reduce the number of bits of the following D / A converter. This method is a method that can achieve an improvement effect of 100 times or more in reducing glitch noise. Further, according to this method, it is possible to use an equal-current type + R-2R ladder type D / A converter having a configuration in which glitch noise is small but is easily restricted by the number of bits.

The D / A converter selects any one of a plurality of reference value groups and outputs the selected one, thereby preventing a time difference between analog switches. For example, a reference value corresponding to −5 nm, −4 nm, −3 nm, −2
nm, -1 um, 0 nm, +1 nm, +2 nm, + 3u
Reference values corresponding to m and +4 μm are prepared, and one of them is selected and output according to an input code. This D / A converter has one analog switch that is turned ON at the same time, and has a structure in which glitch noise due to a time difference between a plurality of switches does not occur. Although the present D / A converter has little glitch noise, it is necessary to prepare a reference value corresponding to the number of bits due to its structure. Therefore, high Bi
It is not suitable for a D / A converter of t.

According to the electron beam lithography system having the tracking system of the present invention, the tracking range can be suppressed to be smaller than in the past.
The low glitch D / A converter can be used effectively. Therefore, as in the electron beam lithography apparatus of the present invention, the method can be used in a system in which the number of bits of the tracking D / A converter can be set to an arbitrary low bit, thereby eliminating the problem of glitch noise in the tracking deflection signal.

[0031]

As described above, in the electron beam lithography apparatus according to the present invention, the amount of movement of the sample stage when drawing a figure on the continuously moving sample stage is out of the preset allowable range. When the deviation is about to occur, the graphic drawing is suspended, the graphic drawing position data and the follow-up data of the shaped electron beam are reset, and the drawing is performed again. This makes it possible to keep the amount of follow-up deflection within the operating range of the follow-up D / A converter composed of low bits. Also, according to the method of the present invention,
An arbitrary low-bit D / A converter can be adopted as the tracking D / A converter, whereby the glitch noise of the D / A converter can be greatly improved, and high-precision tracking control can be realized. .

[Brief description of the drawings]

FIG. 1 is a block diagram of an electron beam drawing apparatus according to the present invention.

[Explanation of symbols]

1. Control computer, 2. Graphic data memory, 3. Restoring unit,
4: disassembly unit, 5: main deflection control circuit, 6: main deflection analog circuit, 7: sub deflection control circuit, 8: sub deflection analog circuit,
9: follow-up control unit, 10: moving amount comparison means in figure drawing, 1
DESCRIPTION OF SYMBOLS 1 ... Blanking control circuit, 12 ... Sample stage control part, 13
... Specimen stage drive unit, 14 Specimen stage length measuring instrument, 15 Electron optical body, 16 Main deflector, 17 Sub deflector, 18 Blanker, 19 Sample stage.

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2H097 BA03 CA16 LA10 5C033 GG03 5C034 BB04 BB06 BB07 5F056 AA20 CA09 CA28 CB40

Claims (3)

[Claims] A means for continuously moving a sample; a deflecting means for positioning an electron beam at a predetermined sample coordinate;
Deflecting means for drawing a figure on the sample, means for inputting the coordinates of the sample table which moves continuously when one figure is drawn, and means for feeding back the amount of movement of the sample table to a deflection signal. An electron beam lithography system for drawing figures on a continuously moving sample, comprising means for deflecting the drawing to follow the sample position, means for measuring and monitoring the figure drawing time when one figure is drawn, and Means for actually measuring the amount of movement of the sample table moving during the execution and determining the amount of movement within the figure drawing, and determining whether or not the amount of movement within the figure drawing is within a preset allowable range; In the case of deviation, the graphic drawing operation is temporarily stopped, the graphic drawing position data is corrected by adding the sample stage position information to the graphic drawing position data (X, Y), and the graphic drawing time is measured and monitored. Means to draw the figure An electron beam lithography apparatus comprising means for obtaining a remaining time of an image and drawing a figure of the remaining time. 2. An electron beam lithography apparatus according to claim 1, wherein:
In the D / A conversion means used for adding the feedback signal and the graphic drawing position data when the sample stage movement amount is fed back to the deflection signal, a reference value group including a plurality of different voltage values or current values is used. Using a D / A converter having means for selecting and switching only one of them based on the sample stage movement data to obtain an output, obtaining a feedback signal from the D / A conversion means, An electron beam lithography apparatus comprising means for performing addition with (X, Y). 3. An electron beam writing apparatus according to claim 1, wherein
If the figure drawing deviates from the preset allowable time range, the figure drawing operation is temporarily suspended, and the sample table position information is corrected and added to the figure drawing position data (X, Y) to correct the figure drawing position data. An electron beam lithography apparatus comprising: means for returning the correction amount of the sample stage follow-up correction to an initial value, and returning the amount of follow-up correction to an initial value every time a graphic drawing is performed.