JPH06124883A - Method for correcting charged beam and method for mark detection - Google Patents

Abstract

PURPOSE:To improve availability by using an optimization template having both functions of aperture design data and a noise filter as reference data used for calculating correlation. CONSTITUTION:An optimization template 102 is made by convolution of aperture design data 100 and a noise filter 101. Then a shift in beam position is detected at a peak position of a correlational coefficient calculated by the optimization template 102 and two-dimensional distribution of the beam. Then deflectors 25,26 are calibrated by offset voltage to eliminate the shift. Then this operation is repeated until there is no shift. When a direction of the beam is calibrated, the two-dimensional distribution of the beam is measured while an aperture 27b is rotated, and an amount of the aperture 27b rotation is determined so that a peak of the correlation calculated from the distribution and the optimization template is maximum. Thus a beam size, a shape and a slope can be rapidly and highly accurately calibrated.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a charged beam drawing technique for drawing a fine pattern of an LSI or the like on a sample, and in particular, the positional deviation, rotation, magnification and the like of a shaped beam projected on the sample by a character projection method. The present invention relates to a method of correcting astigmatism and the like and a method of detecting a mark formed on a sample.

[0002]

2. Description of the Related Art Conventionally, an electron beam exposure apparatus using a variable shaped beam such as a rectangle or a triangle has been used for drawing a desired pattern on a sample such as a semiconductor wafer. In such an electron beam exposure apparatus, when a pattern having a complicated shape is drawn, the number of figures per unit area increases, so that there is a problem that the drawing time increases in proportion to this and the throughput remarkably decreases. .

As a method for solving such a problem, L
Several kinds of complicated pattern figures that are repeatedly used in SI chips are processed and formed on the aperture mask, and each pattern figure on the aperture mask is selectively irradiated with a beam, and the beam pattern generated by passing through is sampled. There has been proposed an exposure apparatus of a method of reducing and projecting the image onto the projection (hereinafter referred to as "character projection method"). The pattern having a complicated shape is, for example, a combination of a plurality of rectangles or triangles or a pattern having an uneven portion.

In such a device, a beam pattern having a complicated shape in which a plurality of rectangles, triangles and the like are combined is used.
Since irradiation can be performed once, it is possible to significantly speed up drawing. However, using the character projection method, the LSI
In order to draw a pattern, a method of correcting the position, magnification, astigmatism, etc. of a beam having a complicated shape such as a character beam with high accuracy is indispensable.

Details of the character beam correction method will be described with reference to the drawings. FIG. 3 shows a schematic configuration diagram of the electron beam exposure apparatus. 10 is a sample chamber, and this sample chamber 10
A sample table 1 containing a sample 11 such as a semiconductor wafer inside
2 are housed. The sample stage 12 can be moved in the X direction and the Y direction by the sample stage drive circuit 31 that receives a command from the computer 30. The deflectors 25 and 26 are each composed of a beam scanning deflector for scanning the character beam on the sample 11 according to a deflection signal from the deflection control circuit 33.

An electron detector 37 for detecting backscattered electrons from the sample 11 is provided in the sample chamber 10. The electron detector 37 is used to detect backscattered electrons from a mark of a fine gold particle located on the sample 11. The mark may be of any material and shape as long as the beam shape can be measured by the emitted beam reflected electrons or the like, and there is no problem with regard to the arrangement location as long as the height is almost the same level as the sample surface.

Reference numeral 20 is an electron optical lens barrel, 21 is an electron gun, 22a to 22e are electron lenses, 23 is a blanking deflector, 24 is a beam shaping deflector, 27a and 27b are beam shaping apertures, and 28 is an axis. Alignment coil, 30 is a computer, 32 is a laser measuring system, 33 is a deflection control circuit, 3
Reference numeral 4 is a blanking control circuit, and 35 is a variable shaped beam size control circuit.

Next, the character projection method will be described with reference to FIGS. 3 and 4. A rectangular hole is formed in the first aperture 27a. The image of this hole can be formed by the lens 22c and the shaping deflector 24 at an arbitrary position on the second aperture 27b of the character aperture.

An LSI is provided on the character aperture 27b.
Since a plurality of characters 30a to 30d that are frequently used on the chip are processed, the beam can be formed into a desired character by changing the beam deflection direction by the forming deflector 24. Here, it is molded into 30a,
By irradiating the shaped character beam onto a desired position on the sample 11 by the deflectors 25 and 26, L
It shows how to draw an SI pattern. 30e is
By superimposing the beam with the rectangular aperture of 27a,
It is an aperture for forming a rectangular or triangular beam.

In the apparatus of this type, the deflector 25,
When the voltage of 26 is constant, the irradiation position on the sample greatly changes depending on the arrangement coordinates of the character graphic. Therefore, the fixed point of each character beam (beam reference position)
Must be defined, and different offset voltages (swing-back voltages) must be determined for each character beam so that they match on the sample surface.

Next, a method of measuring the two-dimensional distribution of the character beam will be described with reference to FIGS. 3 and 5. First, the character beams 30 are formed on the sample surface 11 by setting the offset voltages of the deflectors 25 and 26 of FIG. 3 to 0 V, and the beams are scanned on the gold fine particles 31 in the X direction. Next, the beam is shifted by a small amount in the Y direction by the deflectors 25 and 26 and scanned again in the X direction. By repeating such scanning, a two-dimensional distribution of the character beam shape as shown in FIG. 6A can be obtained. However, since the resolution of the beam is finite here, the measured beam edge has a blurred shape as shown in FIG. 6B.

Therefore, the design data of the size, shape, inclination and position of the character beam on the sample is shown in FIG.
Correlation between the aperture design data binarized with and without the beam as shown in (b) and the measurement data as shown in FIG. 7 (a) while changing the position, magnification, and rotation of the aperture design data. The function is obtained, and the point where the correlation is maximized is the position, magnification, and rotation angle of the measured beam. As for the astigmatism condition, the astigmatism amount can be determined by changing the blurring method in the astigmatism generation direction, blurring the aperture design data, and calculating the correlation with this. Based on the magnification, distortion (shape) and inclination of the measured data thus obtained, the exposure apparatus is fed back to correct each value.

Specifically, first, the design data A and the measurement data A'in FIG. 7 are made to match on a computer. This can be matched by applying a swing-back (offset) voltage corresponding to each character beam to the deflectors 25 and 26. Similarly, the correction amount of the rotation angle required for the aperture 27b can be known from the relatively long line segment in the character beam, for example, the angle between the line segment AB and the line segment A'B '. Furthermore, the amount of correction of the magnification required for the objective lens can be known from the difference in length. Also, at this time, the vertices of the aperture design data and the measurement data (for example, vertices C and C ′) may not match due to the astigmatism of the optical system. The direction and amount of can be determined.

By feeding back the correction amounts thus obtained to the exposure apparatus, even a beam having a complicated shape can be accurately measured, and as a result, drawing accuracy can be improved.

The resolution of the beam image detected by the above method is determined by the size of the mark. Therefore, in order to accurately measure the complicated uneven shape of the character beam, it is necessary to use a mark sufficiently smaller than the unevenness. However, as the mark becomes smaller, the S / N of the detection signal deteriorates and the position detection accuracy decreases, so it is necessary to effectively perform noise processing on the captured image data. Such noise processing causes a problem that the processing time increases as the amount of data increases.

On the other hand, in the electron beam exposure apparatus, the mark provided on the substrate is beam-scanned from above the resist to obtain the mark waveform at the time of overlay writing. At this time, local charge-up occurs depending on the resist material, the mark waveform becomes asymmetric, noise increases depending on the film thickness, and deposits adhere to the edge of the mark. The waveform of the mark edge that is detected as a result may be disturbed. Therefore, the mark detection accuracy is deteriorated.

As for noise, the average addition processing or the method of filtering after capturing the waveform is generally applied. For the disturbance (asymmetrical or the like) of the mark waveform, that portion is removed to calculate the mark position. Was there. However, there is a problem that such processing and calculation takes a lot of time.

[0018]

As described above, noise must be effectively removed in the method of performing highly accurate beam calibration from the two-dimensional beam pattern shape measured by using the minute marks on the sample surface. However, the current situation is that this increases the time required for the entire beam calibration, which in turn lowers the operating rate of the exposure apparatus. Therefore, there has been a demand for a method for calibrating the position, magnification, astigmatism, etc. of a beam having a complicated shape such as a character beam at high speed and with high accuracy. In addition, if the shape of the mark waveform to be detected is disrupted or noise increases during matching drawing,
There is a problem that the mark detection accuracy deteriorates.

The present invention has been made in consideration of the above circumstances, and an object thereof is a charged beam exposure capable of generating not only a rectangular shape and a rectangular shape but also a beam having a complicated shape such as a character beam. An object of the present invention is to provide a charged beam correction method capable of calibrating beam magnification, rotation, positional deviation, astigmatism, and the like at high speed and with high accuracy in an apparatus.

Another object of the present invention is to prevent the mark detection accuracy from deteriorating due to the collapse of the mark waveform and the increase of noise during the matching drawing, and to perform the mark detection at high speed and with high accuracy. An object of the present invention is to provide a mark detection method capable of performing the above.

[0021]

The essence of the present invention is to use a pattern obtained by convolving the design data of the beam pattern and a noise filter as a reference pattern.

That is, according to the present invention (Claim 1), a shaped beam is generated by irradiating an aperture mask having a predetermined aperture shape with a charged beam, and the shaped beam is deflected to draw at a desired position on a sample. A charged beam exposure apparatus, which measures a two-dimensional intensity distribution of a beam by scanning the beam on a minute mark at least once, and calculates a correlation coefficient between the intensity distribution and a reference pattern, and the calculation result In the method of adjusting and correcting various parameters of the electron optical system based on, a pattern obtained by convolving the beam design data and the noise filter function as a reference pattern is calculated in advance, and the pattern is used at the time of adjustment. And

According to the present invention (claim 2), the mark formed on the substrate is irradiated with a charged beam or light to measure the shape of the mark, and the correlation coefficient between the measured mark shape and the reference pattern is calculated. In the method of calculating and obtaining the mark position based on this calculation result, the design data of the mark and the data obtained by convolving the noise filter function as the reference pattern are calculated in advance as a template, and the template is used when measuring the mark. Characterize.
Here, the following are preferred embodiments of the present invention. (1) As the reference pattern, use a pattern obtained by convolving the distribution corresponding to the electronic reflectance of the minute mark and the design data. (2) When calibrating the beam based on the calculated displacement,
Compensate by moving the mechanism of the charged beam exposure system. (3) Use either a line-shaped one-dimensional mark or a dot-shaped two-dimensional mark as the minute mark.

(4) Instead of using the data obtained by convolving the mark design data and the noise filter function as a template, the mark waveform detected in the state where the resist is not applied, or the acceleration voltage and the mark material are calculated. Create a template using the mark waveform.

[0025]

According to the present invention (Claim 1), the reference pattern of the beam can have a noise filter function. Therefore,
By simply calculating the cross-correlation coefficient of the pattern with the noise filter function and the beam shape measured with fine particles,
It is possible to correct the character beam in the size, shape and direction according to the design data at high speed and with high accuracy.

Here, when comparing the design data and the measurement data, instead of calculating the pattern obtained by convolving the design data and the noise filter function in advance as in the present invention, noise measurement is performed on the measurement data as in the conventional case. It is also possible to perform highly accurate correction by applying. However, calculation for noise processing requires extra time, and when performing noise processing on measurement data, it is necessary to wait for the time required for noise processing during measurement. On the other hand, according to the present invention, since calculation for noise processing can be performed in advance, such waste of time can be eliminated.

Further, according to the present invention (claim 2), in the method of obtaining the mark position from the correlation coefficient between the measurement mark and the reference pattern, the reference pattern is provided with a noise filter function and the measured value has a high correlation. The ideal data can be obtained. Therefore, if such a template is calculated or actually measured in advance, even if the detected mark waveform is deteriorated due to noise, charge-up, mark processing, or film formation, high-precision mark It becomes possible to detect.

[0028]

The details of the present invention will be described below with reference to the illustrated embodiments. (First embodiment)

First, the same parts as those of the conventional example are designated by the same reference numerals and detailed description thereof will be omitted. A method of obtaining the size, shape inclination and position of the shaped beam different from the conventional example will be described in detail with reference to FIG.

In FIG. 1A, the size, shape, inclination and displacement amount are measured from the aperture design data and the correlation coefficient of the two-dimensional distribution of the measured beam using the binarized template of the conventional method. It is a block diagram for. On the other hand, FIG. 1B is a block diagram showing the measuring method according to the present embodiment. In this block diagram, a pattern 102 (hereinafter referred to as an optimization template) obtained by convolving the design data 100 and the noise filter 101 is obtained in advance. By doing so, the noise filter processing that was performed in the conventional example becomes unnecessary, and the time required for beam calibration can be greatly reduced. Here, if a function close to the electron reflectance of the fine particles is adopted as the distribution of the noise filter, the matching rate between the optimized template and the measured two-dimensional part increases and the detection accuracy further improves.

Next, the optimization template 102 described above.
A beam calibration method using will be described with reference to FIG. First, an optimization template 102 is created by convolution of the aperture design data 100 and the noise filter 101 (step a). Then, the deviation amount of the beam position is detected at the peak position of the correlation coefficient calculated from the optimization template 102 and the beam two-dimensional distribution. Then, the deflector 25,
Calibrate with a return voltage of 26. After that, the above-mentioned operation is repeated until the displacement amount is eliminated (step b).

When the beam direction is calibrated, the beam two-dimensional distribution is measured while rotating the second aperture 27b in FIG. 3, and the peak of the correlation coefficient calculated from the distribution and the optimization template becomes maximum. Thus, the rotation amount of the second aperture 27b is determined (step c). The astigmatism and magnification are calibrated by performing the same operation as the calibration of the direction on the astigmatism coil and the objective lens (step d) (step e).
Finally, it is checked whether the calibration is performed by the operations of (step b) to (step e), and if there is any one calibrated portion, the process returns to (step b) again.

As described above, according to the present embodiment, by using the optimization template having the function of the aperture design data and the function of the noise filter as the reference data used when calculating the correlation degree, the degree of beam distribution measurement is measured. It is possible to omit the noise processing required for. As a result, the beam size, shape, and inclination can be calibrated at high speed and with high precision for shaped beams of all shapes including rectangular and character projection beams.

Needless to say, the above correction method can be applied to a normal rectangular beam and to an exposure apparatus having one or a plurality of shaping apertures. Also,
The correction method does not depend on the method of measuring the two-dimensional distribution of the beam. That is, it can be applied to a two-dimensional distribution measured using a one-dimensional mark. Further, in this embodiment, the size, shape, and tilt of the obtained beam are fed back to various parameters of the electron optical system for correction, but the tilt is corrected by moving the rotary table of the sample table on which the sample is placed, for example. Obviously, it is okay. (Second Embodiment) Next, as a second embodiment of the present invention,
A method of detecting the mark formed on the sample will be described.

FIG. 8 is a block diagram for measuring the mark position from the mark design data and the correlation coefficient of the two-dimensional distribution of the measured mark waveform using the conventional binarized template. The detection data obtained by actually measuring the mark is used as input data, and this is passed through a noise filter to remove noise. Then, the degree of correlation between the noise-filtered detection data and the reference data (template) obtained from the design data is calculated, and the mark position is detected at the peak position of the correlation coefficient.

On the other hand, FIG. 9 is a block diagram showing the measuring method according to this embodiment. In this block diagram, a pattern 3 (optimization template) obtained by convolving the design data 1 and the noise filter 2 is obtained in advance.
This eliminates the need for noise filter processing at the time of measurement, which was performed in the conventional example, and the time required for mark detection can be greatly reduced.

Next, a mark detection method using the above-mentioned optimization template 3 will be described with reference to FIG.
First, as described above, the optimization template 3 is calculated from the convolution of the mark design data 1 and the noise filter 2. Then, the optimization template 3
The mark position is detected at the peak position of the correlation coefficient calculated from the detected three-dimensional profile (input data) of the mark.

At this time, the calculation for creating the optimization template may be performed in advance, and the calculation for noise processing is not necessary in the actual measurement. Therefore, it is possible to reduce the occupation time of the electron beam exposure apparatus in the mark detection and improve the operation rate of the apparatus.

As described above, according to this embodiment, the mark position is determined by using the optimization template having both the mark design data and the noise filter function as the reference data necessary for calculating the correlation. Noise processing required for each measurement can be omitted. As a result, the mark position can be detected at high speed and with high accuracy for marks of any shape. In this example, the beam is two-dimensionally scanned to obtain a three-dimensional mark waveform, but it is needless to say that it is applicable to a waveform obtained by one-dimensional (line) scanning. (Third embodiment)

In the mark detection using the correlation coefficient, it is ideal that the point of high accuracy is to use, as a template, data that is very similar to the detected mark waveform (that is, has a high correlation).

Therefore, in this embodiment, the width, depth, and
Based on the material, the thickness of the material, the accelerating voltage of the electron beam, etc., the energy of the electrons reflected by the substrate on which the mark is formed is obtained, and the mark waveform is calculated from this. Then, using this mark waveform as an optimization template, mark detection is performed in the same manner as in the previous embodiment. (Fourth embodiment)

When a mark covered with a resist or an insulating film is measured in overlay drawing, the mark waveform becomes asymmetric due to local charge-up, as shown in FIG. 11A, or the mark waveform shown in FIG. As shown in (3), the deposit may adhere to the side wall of the mark during film formation, and the detected edge waveform may deteriorate. Even in such a case, the methods of the second and third embodiments described above are effective, but a more effective method will be described.

In this embodiment, a typical mark waveform in a state where there is no resist or deposit is actually measured and obtained. Using this waveform as an optimization template, the correlation position with the measurement data is obtained and the mark position is calculated. Thereby, data having a higher correlation than the waveform obtained by calculation can be used as a template. As a matter of course, if the data obtained by the measurement in this way is convoluted with a sufficient average addition process or a noise filter function, and the data obtained as a result is used as a template, the accuracy can be improved.

In the second to fourth embodiments, the case where the electron beam exposure apparatus is used has been described, but the present invention is not limited to this, and when the ion beam exposure apparatus is used, further scanning with laser light or light irradiation is performed. It is also applicable to the case of irradiating with and detecting the image of the mark.

[0045]

As described above in detail, the present invention (Claim 1)
According to the authors, by using the optimization template that has both the aperture design data and the function of the noise filter as the reference data used when calculating the degree of correlation, the noise processing required each time the beam distribution is measured can be omitted. You can As a result, the beam size, shape, and inclination can be calibrated at high speed and with high precision for shaped beams of all shapes including rectangular and character projection beams, so that a charged beam exposure apparatus with a high operating rate can be realized.

Further, according to the present invention (claim 2), it is necessary for mark detection by using the optimization template having both the mark design data and the noise filter effect as the reference data used when calculating the correlation coefficient. Noise processing can be omitted. Further, even if the mark is covered with a resist or a film, by using the simulation result of the mark waveform detected by the optimized template or the measured value of the mark waveform with the substance covering the mark removed, The mark position can be accurately detected.

[Brief description of drawings]

FIG. 1 is a block diagram for explaining a first embodiment of the present invention.

FIG. 2 is a flowchart for explaining a beam calibration method according to the first embodiment.

FIG. 3 is a schematic configuration diagram showing an electron beam exposure apparatus used in a conventional calibration method.

FIG. 4 is a schematic diagram for explaining a character projection beam system.

FIG. 5 is a schematic diagram for explaining a beam scanning method.

FIG. 6 is a schematic diagram showing a measured beam intensity distribution.

FIG. 7 is a schematic diagram showing a method for comparing measurement data and aperture design data.

FIG. 8 is a block diagram for explaining a conventional example in which a mark position is detected using a correlation coefficient.

FIG. 9 is a block diagram for explaining an optimization template calculation method according to the second embodiment.

FIG. 10 is a block diagram illustrating a mark detecting method according to a second embodiment.

FIG. 11 is a signal waveform diagram for explaining the fourth embodiment and showing that the mark waveform is disturbed by the influence of a resist or a deposit.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 ... Sample chamber 11 ... Sample 12 ... Sample stand 20 ... Electron optical lens barrel 21 ... Electron gun 22a-22e ... Lens 23-26 ... Deflectors 27a, 27b ... Beam shaping aperture 30 ... Calculator 31 ... Sample stand drive circuit 32 Laser measurement system 33 Deflection control circuit 34 Blanking control circuit 35 Variable shaping beam size control circuit 100 Design data 101 Noise filter 102 Optimization template 1 Design data 2 Noise filter 3 Optimization template

Claims (2)

[Claims] 1. A charged beam exposure apparatus for irradiating an aperture mask having a predetermined aperture shape with a charged beam to generate a beam having the aperture shape and deflecting the beam to draw the beam at a desired position on a sample. Then, the two-dimensional intensity distribution of the beam is measured by scanning the beam on the minute mark at least once, and the correlation coefficient between the intensity distribution and the reference pattern is calculated, and based on the calculation result, In the method of adjusting and correcting various parameters of the electron optical system, a pattern in which the design data of the beam and a noise filter function are convoluted as the reference pattern is calculated in advance, and the pattern is used at the time of adjustment. Charged beam correction method. 2. A mark formed on a substrate is irradiated with a charged beam or light to measure the shape of the mark, a correlation coefficient between the measured mark shape and a reference pattern is calculated, and based on this calculation result In a method of obtaining a mark position, a mark detection method is characterized in that design data of the mark and data obtained by convolving a noise filter function are calculated in advance as a template as the reference pattern, and the template is used during mark measurement.