JPH0713938B2 - Electronic beam exposure method - Google Patents

Description

DETAILED DESCRIPTION [Outline] In electron beam exposure used for manufacturing a semiconductor device or the like, a drawing area is formed by using reflected electrons from a first mark of a heavy metal provided on a stage on which a substrate to be exposed is mounted. The first deflection distortion value of the entire area is obtained, and the first deflection distortion value is corrected by the second deflection distortion value of the specific point obtained using the second mark on the exposed substrate placed on the stage. Then, the correction value of the deflection distortion at the time of exposure is determined to ensure the accuracy of the deflection distortion correction for a long period of time.

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electron beam exposure method, and more particularly to a method for correcting deflection distortion of an electron beam.

Direct exposure technology, in which electron beams are deflected for writing, is used for pattern formation of miniaturized and highly densified LSIs and VLSIs.

In this case, in the exposure apparatus, even if the deflection system is operated to deflect the electron beam to a desired position, there is a deflection distortion in which the actual deflection point deviates from that position.

That is, for example, if the deflection system D (not shown) of the exposure apparatus is operated so that four sides of the rectangular drawing area 1 shown in FIG. The pattern drawn as shown in FIG. 3 becomes 3 and is shifted from the desired pattern 2 by the deflection distortion value 4 of the drawing caused by the deflection distortion.

Therefore, this deflection distortion deteriorates the pattern accuracy and requires correction when forming a fine pattern. Since the drawing deflection distortion value 4 changes as the exposure apparatus is used, as will be described later, it is desirable that this correction can follow the change.

[Conventional technology]

Since the deflection distortion value 4 differs depending on the drawing position, it is necessary to correct the deflection distortion over the entire drawing area 1.

FIG. 4 is a diagram (a) and (b) showing an example of a conventional correction method.
(A) is a correction value, (b) is a drawing pattern after correction.

Similar to FIG. 3, this figure shows a case where four sides of the drawing area 1 are set as the desired pattern 2.

In the conventional correction method, the deflection distortion value 5 (shown in FIG. (A)) for the entire drawing area 1 is obtained in advance by measurement using a mark, and this is stored in the controller memory of the deflection system D (not shown). Then, by applying the deflection distortion value 5 as the correction value 6 to the correction at the time of pattern drawing, the corrected drawing pattern 3a (shown in FIG. (B)) in which the desired pattern 2 is drawn is substantially matched with the desired pattern 2. I am letting you.

FIG. 5 is an explanatory diagram of a method for measuring the deflection distortion value 5.

The deflection distortion value 5 is the first deflection distortion value described later.

In the figure, 11 is a stage on which the substrate to be exposed in the exposure apparatus is placed, 12 is a mark made of heavy metal such as tantalum (Ta) and provided on the stage 11, B is an exposure electron beam, and E is an electron beam B. The reflected electrons are emitted from the irradiated part.

The deflection distortion value 5 at the desired position in the drawing area is measured as follows.

That is, first, the center of the mark 12 is aligned with the desired position by moving the stage 11. Next, while scanning the electron beam B, the backscattered electrons E from the mark 12 are detected by a backscattered electron detector (not shown) of the exposure device, and the deflection amount reaching the center of the mark 12 is obtained. This deflection amount is different from the deflection amount that the deflection system D (not shown) previously sees due to the deflection strain, and the difference is the deflection strain value 5 at that position.

Therefore, by drawing as many measurement points as possible in the drawing area 1 shown in FIG. 3, the deflection distortion value 5 of each measurement point is obtained by the above-mentioned measurement method, and between each measurement point is obtained by the interpolation method. The deflection distortion value 5 for the entire area 1 can be obtained.

Here, the material of the mark 12 is made of heavy metal so that the intensity of the backscattered electron E when the electron beam B irradiates the mark 12 is increased to surely and easily perform the above measurement.

Then, this measurement is usually performed immediately after disassembling and cleaning the column of the exposure apparatus. This is because the state of the column is changed and the deflection strain value 5 is changed by the above-mentioned disassembly.

[Problems to be solved by the invention]

The deflection distortion value 5 is the deflection distortion value immediately after the column is disassembled and cleaned, and coincides with the deflection distortion value 4 of the drawing shown in FIG. 3 at that time, and the accuracy of the correction for a while for the subsequent exposure. Can be secured.

However, if the use after the cleaning is continued for a long period of time, for example, the resist scattered from the exposure substrate adheres to the lower part of the column, and there is a charge (charge-up) at the time of exposure, which affects the deflection of the electron beam. Given that, as shown in FIG. 6A, the deflection distortion value 4 of drawing deviates from the deflection distortion value 5 (this deviation is called charge-up drift). The charge-up drift increases as the adhesion of the resist or the like increases, that is, as the number of exposures increases.

The accuracy of the deflection distortion correction is ensured when the correction value matches the drawing deflection distortion value 4.

Therefore, when the charge-up drift becomes noticeable, there is a problem that the conventional correction method using the deflection distortion value of 5 as a correction value cannot perform sufficient correction.

As a countermeasure against this, it is conceivable to remeasure the deflection distortion value 5 in the presence of charge-up drift. However, in this method, since the intensity of the reflected electrons E from the mark 12 which is a heavy metal is stronger by about one digit than in the actual exposure, the charge-up becomes large, and the deflection distortion value 5 obtained by the measurement is the sixth. As shown in FIG. 3B, the above-mentioned problem cannot be solved by deviating from the drawing deflection distortion value of 4.

Moreover, since the measurement of the deflection distortion 5 requires a considerable time,
It is not practical to do it relatively often.

Needless to say, the column may be disassembled and cleaned when the charge-up drift becomes large enough to cause a problem, but this is not desirable because it extremely reduces the operation of the exposure apparatus.

[Means for solving problems]

The above problem is that the first mark made of heavy metal is provided on the stage on which the substrate to be exposed in the electron beam exposure apparatus is mounted, and the first mark is formed by using the reflected electrons from the first mark by the electron beam irradiation. The first deflection distortion value in the entire drawing area is determined with reference to, and the second deflection distortion value at a specific position in the drawing area is further determined by using the second mark on the exposed substrate placed on the stage. And a correction value obtained by multiplying the ratio of the second deflection distortion value to the first deflection distortion value at the specific position by a proportional coefficient, and multiplying the first deflection distortion value in the entire drawing area by the proportional coefficient. Is solved by the electron beam exposure method of the present invention in which is the correction value of the deflection distortion during exposure.

According to the present invention, it is preferable that the specific position is set at four points in the center of each side of the rectangular drawing area, and the proportional coefficient is an average value of the ratios at the four points.

[Action]

Generally, the mark on the substrate to be exposed is formed by shape processing or the like and does not use heavy metal. Therefore, the above-mentioned second deflection distortion value is obtained under substantially the same conditions as in the case of exposure for the backscattered electrons that charge up the lower part of the column of the exposure apparatus, and even if there is a charge-up drift, it is approximately the same as the drawing deflection distortion value. Match.

However, since the direction of the second deflection distortion value is the same as the first deflection distortion value which is the same as the conventional correction value, the second deflection distortion value was measured only at the specific position. Even if, the new correction value obtained by the correction by multiplying the proportional coefficient is
Even at a position other than the specific position, the deflection distortion value of drawing substantially matches.

And since the measurement of the second deflection strain value can be performed more simply and frequently than the measurement of the first deflection strain value because it is only at the specific position, the measurement of the first deflection strain value of the column If it is performed after the disassembly and cleaning, even if the deflection distortion value of drawing changes due to charge-up drift, the correction can be performed in accordance with the change, and the accuracy of the deflection distortion correction can be ensured for a long period of time.

When measuring the deflection distortion value, if a mark such as a mark on the substrate to be exposed is used, it may be difficult to secure the measurement accuracy. Therefore, the use of the mark is avoided when obtaining the basic first deflection distortion value. Then, when obtaining the second deflection distortion value based on the second mark, the above-mentioned specific positions are made plural as described above, but are taken in four directions of the drawing area, thereby alleviating this problem. .

〔Example〕

FIG. 1 is a view showing an embodiment of the method of the present invention (a) to (d).
Where (a) is the first deflection distortion value, (b) is the second deflection distortion value, (c) is the correction value, and (d) is the corrected drawing pattern.
FIG. 2 is an explanatory diagram of the second method for measuring the deflection distortion value.

Similar to FIGS. 3 and 4, FIG. 1 shows a case where four sides of the drawing area 1 are formed into desired patterns.

That is, in FIG. 1, first, after disassembling and cleaning the column,
The deflection strain value (first deflection strain value) 5 (shown in FIG. 1 (a)) in the entire exposure area 1 is measured by the method shown in FIG.
It is put in the control unit memory (not shown). The mark 12 used for measurement corresponds to the first mark. This first deflection distortion value 5 is the same as the deflection distortion value 5 shown in FIG.

Next, when the substrate to be exposed is exposed, the second deflection strain values 8a to 8d at the specific positions 7a to 7d shown in FIG. 1B are measured by the method shown in FIG.

In FIG. 2, 11 and B and E are the above-mentioned stage, electron beam and backscattered electrons, and 13 is an exposed substrate such as a silicon wafer placed on the stage 11. Also, 14 is a substrate
Four specific locations on the center of each side of the drawing area 1 on 13 are specified positions 7a-
7d, which is, for example, a second mark formed on the wafer to measure the strain value at the specific position and which is, for example, a rectangular parallelepiped recess (size of about several μm), is used for detecting the position of the drawing area 1. It is similar to the marks provided at the four corners of the normal drawing area 1.

The measurement of the second deflection strain values 8a to 8d is performed as follows.

First, the substrate is formed by step and repeat of the stage 11.
13 drawing areas 1 are positioned at predetermined positions for exposure. Next, the drawing area 1 by the scanning of the electron beam B which is normally performed
And the respective positions of the second mark 14 are detected,
The amount of deflection to reach there is calculated. This detection is performed by the exposed substrate 13
This is performed by monitoring the backscattered electrons E from the above with a backscattered electron detector (not shown) of the exposure apparatus and detecting the change occurring at the stepped portion of the mark 14. By the way, the difference between the calculated deflection amount calculated from the position of the second mark 14 provided on the substrate 13 and the deflection amount by the above detection is the second deflection distortion values 8a to 8d.
become.

According to this method, the intensity of the reflected electrons E from the substrate to be exposed 13 is substantially the same as that at the time of drawing by exposure, so that even if there is a charge-up drift, the obtained second deflection distortion values 8a to 8d are obtained. Is substantially the same as the drawing deflection distortion value at the specific positions 7a to 7d.

After the measurement of the second deflection distortion values 8a to 8d, the first deflection distortion values 5a to 5d at the specific positions 7a to 7d (shown in FIG. 1 (a))
To calculate the ratio of the second deflection strain value 8a ~ 8d,
The average value is set as the proportional coefficient C, and this is put in the control unit register of the deflection system D.

Next, in drawing, the first deflection distortion value 4 of the drawing position is multiplied by the comparison coefficient C, and the obtained value is used as the correction value 6a (first
Drawing (c) (illustration) is performed after correction. Thus, when the desired pattern 2 is drawn, the drawn pattern 3b after correction substantially coincides with the desired pattern 2 as shown in FIG.

It is desirable to measure the second deflection distortion values 8a to 8d for each individual substrate to be exposed. By doing so, the deflection distortion correction can be made to always follow the change in the charge-up drift.

Even if the first deflection distortion value 5 is measured and the deflection distortion value 5 is applied in the state where there is charge-up drift for some reason, the present invention is effective from the principle.

Further, in the above embodiment, it is desirable to equalize the effect of the proportionality coefficient C over the entire drawing area 1 and reduce the number of specific positions for measuring the second deflection distortion value. However, the present invention is not limited to the above-mentioned setting of the specific position.

Further, the calculation for multiplying the comparison coefficient C is the second deflection distortion value.
Drawing area 1 before drawing after measurement of 8a to 8d
It is also possible to carry out for the entire area and store the result in the memory.

〔The invention's effect〕

As described above, according to the configuration of the present invention, in the electron beam exposure, the deflection distortion correction can be performed in accordance with the change in the deflection distortion value of drawing, and the accuracy of the deflection distortion correction can be ensured for a long period of time. Has the effect of

[Brief description of drawings]

FIG. 1 is a view showing an embodiment of the method of the present invention (a) to (d).
Where (a) is the first deflection distortion value, (b) is the second deflection distortion value, (c) is the correction value, (d) is the corrected drawing pattern, and FIG. 2 is the second deflection distortion value. FIG. 3 is an explanatory diagram of a value measurement method, and FIGS. 3A and 3B are explanatory diagrams of deflection distortion, where FIG. 4A is a desired pattern, FIG. 4B is a drawing pattern, and FIG. 4 is an example of a conventional correction method. In Figures (a) and (b),
(A) is a correction value, (b) is a drawing pattern after correction, FIG. 5 is an explanatory view of a first deflection distortion value measuring method, and FIG. 6 is a view showing problems of the conventional method (a) (b) ), In the figure, 1 is a drawing area, 2 is a desired pattern, 3 is a drawing pattern before correction, 3a and 3b are drawing patterns after correction, 4 is a deflection distortion value of drawing, and 5 is a deflection distortion value (first deflection distortion). Value), 5a-5d is 7a
First deflection distortion value of 7d, 6 is a conventional correction value, 6a is a correction value according to the present invention, 7a to 7d are specific positions, 8a to 8d are second deflection distortion values, 11 is a stage, and 12 is a mark. (First mark), 13
Is the substrate to be exposed, 14 is the second mark, B is the electron beam, E
Is the secondary electron ,.

Claims (2)

[Claims] 1. An electron beam exposure apparatus is provided with a first mark made of a heavy metal on a stage on which a substrate to be exposed is mounted, and drawing of the apparatus is performed by using reflected electrons from the first mark by electron beam irradiation. A first deflection distortion value in the entire area is calculated, and a second deflection distortion value at a specific position in the drawing area is calculated by using a second mark on the exposed substrate placed on the stage, A ratio of the second deflection distortion value to the first deflection distortion value at a specific position is set as a proportional coefficient, and a correction value obtained by multiplying the first deflection distortion value in the entire drawing area by the proportional coefficient is used. An electron beam exposure method, characterized in that a deflection distortion correction value is used. 2. The specific positions are four points in the center of each side of the rectangular drawing area, and the proportional coefficient is an average value of the ratios at the four points. The electron beam exposure method according to claim 1.