JP3146568B2 - Pattern recognition device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[Table of Contents] The present invention will be described in the following order. BACKGROUND OF THE INVENTION Problems to be Solved by the Invention Means for Solving Problems (FIGS. 1 to 6) Operation (FIGS. 1 to 6) Example (1) Principle of Example (2) First Embodiment (FIGS. 1 to 6) (3) Second Embodiment (FIGS. 7 to 9) (4) Another Embodiment (FIG. 10) Effects of the Invention

[0002]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pattern recognition apparatus, and more particularly, to a pattern recognition apparatus suitable for use in the positioning of a wafer or a glass plate used in a manufacturing process of a semiconductor element or a liquid crystal device, and the detection of a mark during alignment.

[0003]

2. Description of the Related Art Conventionally, wafers used for manufacturing semiconductor devices and the like are processed through various apparatuses. In particular, an exposure apparatus (an aligner, a stepper, etc.) for transferring a circuit pattern of a mask or a reticle onto the wafer. In such a case, it is necessary to detect an alignment mark formed together with a circuit pattern on the wafer and accurately align the mask or reticle with the wafer.

Usually, this work is called "alignment", but at present, its meaning is interpreted in a broad sense, and the work up to simply detecting a mark on a wafer and specifying its position (position with respect to a reticle). Is sometimes called “alignment”. In the case of a stepper or the like, the operation of actually aligning the reticle and the wafer is sometimes called “stepping”.

For this alignment, various types of alignment sensors are mounted on the exposure apparatus, and most of the exposure apparatuses which are currently in practical use in semiconductor device manufacturing lines have an optical automatic alignment system. In particular, a spot light such as a laser beam is irradiated on the wafer, and the spot light and the wafer are relatively scanned to obtain light information (scattered light) from a fine alignment mark provided at a specific position on the wafer. , Diffracted light, etc.) have been widely used at present as an alignment method capable of obtaining good detection accuracy.

The alignment method detects a position where optical information from an alignment mark is obtained on a scanning position between a spot light and a wafer based on a signal detected by photoelectric detection, thereby forming a mask (or a wafer) on the wafer. (Reticle). Further, this alignment method is divided into two types. One is to binarize an analog photoelectric signal at a predetermined slice level, and to digitally change a mark position based on the binarized signal and a clock pulse corresponding to a scanning position. The other is to digitally sample an analog photoelectric signal according to a scanning position, store a signal waveform on a memory, and calculate a mark position from a feature on the signal waveform. .

As an alignment sensor of another detection system, a mark on a wafer is observed with a microscope, an enlarged image is photoelectrically detected by an image pickup device such as a vidicon, a CCD or the like, and an image (video) signal corresponding to the mark is processed. In some cases, the mark position is detected. In this case, since the image sensor receives an image of a local area including a mark on the wafer surface in a frame unit composed of a plurality of scanning lines, it extracts a video signal corresponding to one or a plurality of scanning lines, and extracts a pixel ( After digitally sampling the signal level for each pixel and storing it in a memory as a waveform, the mark position is calculated by digital arithmetic processing.

[0008] Such an image processing type alignment sensor normally receives a mark image in a bright field, but has a space on a pupil plane (Flier plane or a front focal plane of an objective lens) in an optical system path to an image pickup device. By providing a filter or providing an illumination system for performing night vision illumination on an imaging area on a wafer, a video signal may be obtained by receiving a mark image in a dark field.

The above-described spot light scanning type alignment sensor can also photoelectrically detect light information from a mark or the like by a bright field method. Regardless of which method is used, the mark is detected on the wafer. A mark is recognized by generating an analog signal corresponding to a change in optical or physical characteristics in the direction of detecting the position of a local area including the mark, and analyzing the analog signal.

[0010]

However, in the alignment sensor having such a configuration, since a local area (or an image thereof) on a wafer is scanned by spot light (or a scanning line), dust, a scratch, or the like is formed on a scanning locus. If surface irregularities (irregularities) or the like similar to the mark are present, optical information equivalent to the optical information from the mark is also generated from these defective portions, and this is erroneously recognized as the mark.

Another problem is that the mark cannot be detected unless the wafer and the alignment sensor are pre-aligned so that the mark on the wafer is located within the scanning range (measurement range). In particular, when a circuit portion having a fine pattern structure exists near the alignment mark, a problem arises when misalignment occurs when the precision of pre-alignment is deteriorated.

The present invention has been made in view of the above points, and it is an object of the present invention to propose a pattern recognition device capable of accurately and quickly identifying a specific mark (pattern) without erroneous recognition. .

[0013]

According to a first aspect of the present invention, a pattern M having substantially the same shape is provided.
Holding means ST for holding an object W formed at predetermined intervals in a direction in which a plurality of M1, M2 and M3 are to be detected, and a predetermined range on the object W including a plurality of patterns M1, M2 and M3 in the position detection direction Scanning means 1, 2, 3, 4, 5, 6, 7, 8, 9 for scanning and outputting an analog signal whose level changes in accordance with an optical characteristic change within a predetermined range; Is analyzed to obtain a plurality of patterns M1,
In a pattern recognition device for recognizing the position of a specific pattern M2 among M2 and M3, storage means for storing a waveform of an analog signal obtained by scanning by the scanning means 1 to 9 in correspondence with a scanning position on the object M. 12 and storage means 12
A differentiating means 18 (SP10) for reading out the waveform of the analog signal stored in the
1) and a waveform obtained by shifting the differentiated waveform in the scanning direction by an amount Fa, Fb corresponding to a predetermined interval between the plurality of patterns M1, M2, M3 and the original waveform are combined to correspond to a specific pattern M2. The waveform synthesizing means 18 (SP103) for outputting a synthesized waveform in which the waveform portion emphasized by the waveform portions corresponding to the other patterns M1 and M3, and specifying the detected waveform portion by detecting the emphasized waveform portion. Pattern M2
And an identification means 17 for identifying the position of the image.

In the second invention, the holding means ST for holding an object W formed by forming a plurality of patterns M1, M2, M3 of substantially the same shape at predetermined intervals in a direction in which the position is to be detected.
Scanning means 1 for scanning a predetermined range on an object W including a plurality of patterns M1, M2, M3 in the position detection direction and outputting an analog signal whose level changes according to a change in optical characteristics within the predetermined range. And a pattern recognition device for recognizing the position of a specific pattern M2 among a plurality of patterns M1, M2, M3 by analyzing an analog signal. Storage means 12 for storing the waveform of the analog signal obtained in correspondence with the scanning position on the object M; reading the waveform of the analog signal stored in the storage means 12; obtaining the differential waveform of the analog signal; Waveform shaping means 18 (SP101, S
P102), a waveform obtained by shifting the weighted differential waveform in the scanning direction by an amount Fa, Fb corresponding to a predetermined interval of the plurality of patterns M1, M2, M3 and the original waveform, and
A waveform synthesizing means 18 (SP103) for outputting a synthesized waveform in which a waveform portion corresponding to a specific pattern M2 is emphasized by waveform portions corresponding to other patterns M1 and M3, and detecting a emphasized waveform portion of the synthesized waveform. Thus, the identification means 17 for identifying the position of the specific pattern M2 is provided.

[0015]

The waveform of an analog signal obtained by the relative scanning of the scanning means 1 to 9 is weighted in addition to differentiation or differentiation as preprocessing for pattern recognition, and then a plurality of patterns M1, M2, M3 or a simple pattern is obtained. By adding (or multiplying) the waveform shifted in the interval direction and the waveform before the shift by the interval amounts Fa and Fb designed by the edge by adding (or multiplying), the waveform corresponding to the position of the specific pattern M2 on the waveform is obtained. Only the partial waveform can be emphasized, and thus, even when there is much noise superimposed on the original analog signal, the S / N ratio is relatively improved on the composite waveform, and the specific pattern M2 can be formed at high speed and with high accuracy. Can recognize.

[0016]

BRIEF DESCRIPTION OF THE DRAWINGS FIG.

(1) Principle of the Embodiment In the present invention, the following two items are basically assumed. That is, a plurality (two or more) of patterns (or simple edges) having substantially the same shape are formed on the object at predetermined intervals determined in the position detection direction in the position detection direction. In order to obtain an analog signal corresponding to a change in optical or physical characteristics of each pattern.

Although the present invention can be applied to any field in principle as long as it has this configuration, the present embodiment is limited to the case where the present invention is applied to an alignment sensor of a semiconductor manufacturing apparatus or a semiconductor inspection apparatus. Will be described. An alignment method for a projection exposure apparatus having such a configuration is as follows.
For example, it is disclosed in JP-A-60-256002.
Since it is publicly known, an alignment sensor will be briefly described below with reference to FIGS.

(2) First Embodiment FIG. 1 shows a configuration of a projection exposure apparatus to which a pattern recognition apparatus according to a first embodiment of the present invention is applied as an alignment sensor, and a reticle R having a circuit pattern and a wafer W.
A projection lens PL at least on the wafer side (image side) is provided between the projection lens PL and the wafer W during step-and-repeat exposure or alignment.
It is placed on the stage ST so as to move x and y in a dimension. A mark WM composed of, for example, a plurality of diffraction grating marks is formed on the wafer W for alignment with the reticle R.

FIG. 2 shows a mark arrangement on the wafer W.
Here, three marks M1 of the same shape extending in the y direction,
It is assumed that M2 and M3 are formed at intervals D1 and D2 in the x direction. Each of the marks M1, M2, and M3 is a diffraction grating in which minute rectangular elements (projections or depressions) are arranged in a line at a 1: 1 duty in the y direction. , Y-axis and z-axis (perpendicular to the wafer surface) to obtain diffracted light that is spread and reflected.

In FIG. 1, the laser beam LB from the laser light source 1 actually enters the center of the pupil ep of the projection lens PL via the cylindrical lens 2, the beam splitter 3, and the objective lens 4 and the mirror 5. The projection lens PL vertically irradiates the laser beam LB onto the wafer W, and forms a sheet-like (or slit-like) spot light SP extending in the y-direction as shown in FIG. I do.

Light information generated from a spot light irradiating portion on the wafer W travels backward through the original illumination light path via the projection lens PL, is reflected by the beam splitter 3 via the mirror 5 and the objective lens 4, and is relayed. Through the system 6 the space filter 7 is reached. The relay system 6 forms an image of the pupil ep of the projection lens PL at the position of the spatial filter 7, and the spatial filter 7 is arranged conjugate with the pupil ep. The spatial filter 7 outputs the mark WM (M1, M1) of the optical information from the wafer W.
2, M3) spatially separate and extract only the diffracted light (or scattered light) of a specific order from M3), and the extracted diffracted light and the like are received by a photoelectric element (photometric) 9 by a condenser lens 8 Collected on the surface.

An amplifier (AMP) 10 amplifies the photoelectric signal from the photoelectric element 9 by a fixed amount, and inputs the amplified photoelectric signal to an analog-to-digital converter (ADC) 11 to convert the signal into a digital value corresponding to the signal level. Is done. This digital value is stored in a memory (RAM) 12 for storing (capturing) the signal waveform.
Are sequentially stored. The conversion timing of the ADC 11 and the RA
The address setting of M12 is performed by a counter circuit (CNT) 13.

The CNT 13 receives an up-down pulse signal from the laser interferometer 14 for measuring the position of the stage ST (for example, a signal that becomes one pulse every time the stage ST moves by 0.01 [μm]) via the stage controller 15. Enter The movement of the wafer stage ST is performed by the motor 16 under the control of the stage controller 15, and the movement of the stage ST is determined by the main control unit (CPU).
This is performed by exchanging commands and information between the stage controller 17 and the stage controller 16. A processor (BSP) 18 dedicated to high-speed calculation calculates the position of the mark WM at high speed based on the characteristics of the signal waveforms taken into the RAM 12 and outputs the result to the CPU 17.

The CPU 17 moves the stage ST to an arbitrary position while monitoring the measurement coordinate value of the interferometer 14 based on the determined position. Specifically, the positioning is performed so that the projected image of the circuit pattern of the reticle R matches a predetermined area (shot area) on the wafer W. The address designation of the RAM 12 by the CNT 13 is performed by the ADC.
This is done only when writing the waveform data from
When reading data from M12, BSP18 is CNT1
Specify an address instead of 3. 1, two sets of spot light SP of the laser beam LB for the X direction and for the Y direction are supplied to the wafer W via the projection lens PL.
The interference 14 is also provided with two axes, one for the X direction and one for the Y direction.

FIG. 3 shows spot light S for the X and Y directions.
This figure shows the plane arrangement of the PX and SPY in the projection lens field IF, assuming that the point through which the optical axis of the projection lens PL passes is the origin of the XY coordinate system, and measures the length of the laser interferometer on each of the X and Y axes. Assume that the axes match. The spot light SPX extending in the Y direction is fixed to the periphery in the field IF on the Y axis, and the spot light SPY extending in the X direction is fixed to the periphery in the field IF on the X axis. Is also not accurate.

On the other hand, the circuit pattern area PA of the reticle R
Of the projection lens PL due to the residual error during reticle alignment and the system offset.
(The origin of the coordinate system). Then, after the reticle R is mounted on the stepper and aligned, the shift amount ΔBX between the center Rc of the reticle R and the spot light SPX in the X direction and the shift amount ΔBY between the center RC and the spot light SPY in the Y direction are calculated by: The measurement is performed in advance using another alignment sensor or a reference mark on the stage SP. The shift amount (ΔBX, ΔBY) is called a baseline amount, and is maintained until the reticle R is converted or the baseline amount is measured again.
It is stored as a constant in the PU 17.

The analog signal waveform generated from the photoelectric element 9 by the relative scanning of the spot light SP and the mark WM is stored as digital data in the RAM 12, and the range of the relative scanning is the mark WM in FIG. Is determined in consideration of the total width in the X direction and the pre-alignment accuracy of the wafer W. The CPU 17 determines the coordinate position of the stage ST (X
0) is stored. The address value of the waveform data written in the RAM 12 in this manner is 0.01 [μ] of the stage ST.
m].

The BSP 18 processes the waveform data. In this embodiment, the BSP 18 performs all the calculations by using programmed software. Hereinafter, in this embodiment, the center mark M2 in the mark WM is considered as a specific pattern to be detected, and as shown in FIG. 2, the center distance D1 between the marks M1 and M2 in the X direction, the mark M2, and The center interval D2 of M3 is set to a different value (here, D1 <D2) so as to be advantageous in pattern recognition.

More preferably, each mark M1, M2, M
When the width in the X direction of No. 3 is L, it is preferable to satisfy the condition of D1 <D2 + L. Of course, each mark M1, M2, M3
The values of the mark width L, the width of the spot light SP, and the distances D1 and D2 are determined so that the signal waveform portions corresponding to the above are all separated.

Next, the waveform processing of the BSP 18 will be described with reference to FIGS. FIG. 4 shows the flow of the processing algorithm in the BSP 18, and FIG. 5 shows the waveform data in the RAM 12 and the state of the processing. FIG. 5A shows waveform data obtained in the RAM 12 when the spot light SP relatively scans from the mark M1 to the mark M3 in order as shown in FIG. 2, and is hereinafter referred to as original waveform data. In FIG. 5, the horizontal axis represents the address value (0.01 [μm] per address) of the RAM 12 corresponding to the scanning position in the X direction, and the vertical axis represents the signal strength S.

As shown in FIG. 5A, it is assumed that the original waveform data is stored between the address values MS and MS + SD in the RAM 12 with the number of sampling points as SD. In the RAM 12, an area for storing a pattern recognition waveform that has been subjected to pre-processing (differential processing and weighting processing) for pattern recognition of the original waveform and waveform data that has been subjected to shift addition are secured. It is assumed that the value is between M0 and M0 + SD.

In the BSP 18, a plurality of address pointers IXn (n = n
0, 1, 2, 3,...). Further, in the BSP 18, the number of points (the number of addresses) Fa corresponding to the center interval D1 [μm] between the position of the mark M and M2
And the number of points Fb corresponding to the center distance D2 [μm] between the marks M2 and M3 are preset.

As shown in FIG. 4, in step SP100, the BSP 18 sets the start address value MS on the original waveform data in the pointer IX0 and the start address value M of the pattern recognition waveform in the pointer IX1 in step SP100.
S 'is set, the value (MS'-Fa) obtained by subtracting the number of points Fa from the start address value MS' on the pattern recognition waveform data is set in the pointer IX2, and the start on the pattern recognition waveform data is set in the pointer IX3. A value obtained by adding the number of points Fb to the address value MS '(M
S '+ Fb), a start address value M0 for storing the waveform data resulting from the addition and synthesis is set in the pointer IX4, and the number of processing points S
The register r for counting D is set to zero.

Next, the BSP 18 executes R in step SP101.
The original waveform data stored in the AM 12 is converted into differential waveform data. Si is the i-th data of the original waveform, Dj is the j-th coefficient of the differential filter, and Si 'is the data after the differentiation of the i-th data of the original waveform. Subsequently, the BSP 18 weights the data sequence of the differential waveform obtained in the next step 102. Wi is a weighting coefficient to be multiplied by the i-th of the differential waveform data, and Si ″ ′ is differential weighting data after weighting. Here, the weighting coefficient may be set arbitrarily, for example, a weighting coefficient using a Gaussian waveform. Is set, waveform data in which the central portion of the differential waveform data sequence is emphasized and the influence of the peripheral portion is weakened is obtained.

The BSP 18 further includes a step SP103.
The data RAM (IX1 +) stored at three address values from the original waveform data stored in the RAM 12
r), RAM (IX2 + r), and RAM (IX3 + r) are read and added, and the added value is obtained as data DT. Then, the BSP 18 stores the data DT in the address (IX4 +
r), the register r is incremented (r +
1) Yes.

Subsequently, the BSP 18 proceeds to step SP105.
It is determined whether or not the count number of the register r has become larger than SD. If it is smaller, the operation from step SP103 is executed again. In this step SP105, r
If> SD is determined to be true, all the shift addition operations are terminated, and the addresses M0 to M0 + SD of the RAM 12 are stored in the addresses M0 to M0 + SD of the pattern recognition waveform data of FIG. 5B as shown in FIG. 5 (C) shifted to the right by Fa and the waveform data of FIG. 5 (D) shifted to the left by Fb are stored. Note that this flowchart is an example, and any algorithm may be used as long as it performs the same function.

Thereafter, the BSP 18 obtains a point position PX having the largest peak value from the waveform data of FIG. 5E, and determines a point position (address value) on the original waveform data corresponding to the point position PX. . In order to actually determine the center position of the mark M2, there are two cases, one using the waveform data of FIG. 5E and the other using the original waveform data of FIG. 5A.

When the synthesized waveform shown in FIG.
Since the addition is performed after the differentiation of the waveform portions corresponding to each of the marks M1, M2, and M3, the distortion of the composite waveform portion may increase due to the influence of each waveform distortion. Therefore, in order to accurately detect the position of the mark M2, it is preferable to perform a waveform analysis based on the original waveform data. The synthesized waveform of FIG. 5E is used only for searching (recognizing) a true mark. It is better to use it only for.

If the waveform distortion is small, the mark position may be determined by analyzing the waveform of the composite waveform.
In general waveform analysis using the original waveform, the slice is performed at the level corresponding to the steepest part at the rise and fall of a specific mark waveform part, and the slice level, the waveform rise part, and the waveform fall A method of calculating each intersection position of the portion and calculating the middle point thereof as the center position of the mark M2, comparing the rising and falling of the mark waveform portion with a lower slice level to determine the two intersection positions, and calculating the center of gravity of the waveform between them There is a method in which (the position where the integral value is reduced to １ ／) is set as the center position.

In this embodiment, the marks M1, M2, M
Since the intervals D1 and D2 of FIG. 3 have different values, the combined waveform of the waveform data obtained by shifting the pattern recognition waveform data by Fa in the positive direction and the waveform data shifted by Fb in the negative direction is 3 at the position PX only. The two mark waveform portions are combined and emphasized, and recognition becomes extremely easy.

Of course, even when the mark interval is D1 = D2, the specific mark can be recognized in the same manner. However, when there is a signal strength difference between the three mark waveform portions,
Alternatively, when strong noise is generated in a portion other than the marks M1, M2, and M3, the detection capability (waveform enhancement) may be reduced. In addition, at least two search marks
If a book is used, emphasis can be similarly performed by waveform synthesis. However, as in the present embodiment, when at least three marks are arranged at different intervals, an extremely strong recognition ability is obtained.

An example will be described with reference to FIG. That is, FIG. 6A shows the original waveform data, in which the level of the waveform portion corresponding to the specific mark M2 is
1 and M3, and the waveform portion due to the noise N has a signal intensity (mark M) at a position of -2Fa with respect to the specific mark M2.
It is assumed that extremely poor conditions are present, that is, they are mixed at the same level as (1, M3).

When the mark M2 is to be recognized by analyzing only the original waveform data as in the prior art, the mark M1 is erroneously recognized as the mark M2 with a very high probability. However, as in the present embodiment, after the differentiation processing (FIG. 6B), the pattern recognition waveform (FIG. 6D) obtained by multiplying the differential waveform by the weighting coefficient (FIG. 6C) is applied in the positive direction. 6 is obtained by adding the waveform data of FIG. 6 (E) shifted by Fa and the waveform data of FIG. 6 (F) shifted by Fb in the negative direction.
(G) is obtained, and the maximum value S is obtained at the position C0.
0 is obtained.

Here, as is clear from FIGS. 6D, 6B and 6F, at the position C0, all three partial waveforms of the marks M1, M2 and M3 are synthesized. E)
The next largest composite waveform appearing on the left side of the position C0 is obtained by combining the partial waveforms of the mark M1 and the noise N. As shown in FIG. Since it is shifted by (Fa-Fb) therefrom, it does not contribute to the synthesis.

Therefore, even if the large noise N happens to appear at a position separated by the design interval (Fa or Fb), it is very easy to recognize the specific mark by using the waveform synthesizing method according to this embodiment. Can be.

(3) Second Embodiment Next, a second embodiment of the present invention will be described with reference to FIG. 7, FIG. 8, and FIG. In this embodiment, an alignment sensor of a type in which a pattern on a wafer W is detected by an image sensor and a video signal thereof is subjected to waveform analysis is used. The same applies to an image pickup tube such as a vidicon as an image pickup device. Here, a two-dimensional CCD camera is used.

As shown in FIG. 7, the pattern on the wafer W is transmitted through a telecentric objective lens 30, a beam splitter 31, an imaging lens system 32, a conjugate index plate 33, and a re-imaging lens 34. An enlarged image is formed on the imaging surface of the CCD camera 35. The wafer W is illuminated by the Koehler illumination method in which the exit end of the fiber bundle 36 is arranged on the pupil plane ep of the objective lens 30. Further, the index plate 33 is formed by forming an index mark on a transparent glass with a light shielding layer.
When the video signal from the CD camera 35 is displayed on the CRT, it is observed as shown in FIG.

In FIG. 8, index marks RMa and RMb are located on the left and right of the frame FR, and prealignment is performed so that the marks MA and MB on the wafer W exist between them.
Assuming that horizontal scanning lines of the CCD camera 35 are SL1... SLn, index marks RMa and RMb and wafer marks MA and
The MB is constituted by a linear edge in a direction orthogonal to the horizontal scanning line. The widths of the marks MA and MB in the scanning line direction are determined to be different from each other, and the space width between the marks MA and MB is also determined to be different from the mark width.

The alignment here is performed by using the coordinate value (X) of the stage ST when the wafer W is positioned as shown in FIG.
0, Y0), and the index marks RMa and R
The amount of displacement (Δx) in the scanning line direction between the midpoint of Mb and the midpoint of the space between the marks MA and MB, for example, is determined by waveform processing, and the previously stored coordinate value X0 is calculated by Δx. It is completed by correcting.

FIG. 9 shows an example of a video signal waveform obtained along one horizontal scanning line, and it is assumed that the scanning direction coincides with the x direction. On the left and right sides of the video waveform, waveform portions RE corresponding to index marks RMa and RMb (black level)
a and REb are generated. This waveform portion always appears with a good contrast, almost irrespective of the optical characteristic change on the wafer W.

However, the pattern on the wafer W does not always have a clear waveform due to the wavelength of the illumination light, the material of the pattern, the surface treatment, and the like. In FIG. 9, the video waveforms have bottom waveforms AEl and AEr at the left and right edges of the mark MA, and have bottom waveforms BEl and BEr at the left and right edges of the mark MB. The bottom of the mark edge in this way is the case of bright-field observation. For example, in dark-field observation in which a spatial filter for specularly reflected light (zero-order light) is inserted in the pupil plane ep in the observation optical path, the mark edge is observed. It becomes a peak waveform at the point.

When a CCD camera is used, if the signal level is converted into a digital value for each pixel in the horizontal scanning line and stored in a frame memory or the like, the subsequent processing is exactly the same as in the first embodiment. Can be executed. When a video signal from a CCD camera is used, a process of adding and averaging video waveforms corresponding to each of two or more horizontal scanning lines in a frame FR for pixels in a vertical direction is usually performed.

Therefore, it is preferable to extract only the waveform between the bottom waveforms REa and REb from the averaged video waveform, and perform the horizontal shift synthesis in the same manner as in the first embodiment. As an example, when the number of horizontal pixels Qa corresponding to the width of the mark MA, the number of horizontal pixels corresponding to the width of the mark MB is Qb, and the number of pixels corresponding to the space width between the marks MA and MB are Qc, Qb /Qc=1.5, Qa / Qc
= 2.0 is assumed. After performing pre-processing using FIG. 9 as an original waveform, a right-shifted waveform shifted to the right (in the direction of increasing addresses) by the number of pixels Qc,
The bottom waveform B on the original waveform is obtained by adding the left waveform shifted to the left by the number of pixels Qb to the original waveform, respectively.
At the position El, the bottom waveform AEr on the right shift waveform and the bottom waveform BEr on the left shift waveform are overlapped and emphasized, and no other bottom waveform is generated at other positions.

Therefore, in this example, the bottom waveform BE1 is recognized as a specific mark edge position. If this position is known, the position of the bottom waveform AEr is also changed, so that the midpoint between the bottom waveforms AEr and BEl on the original waveform may be obtained.
Here, one bottom waveform portion is considered to correspond to one edge of the mark. However, when the mark width itself becomes extremely small, the left and right edges of the mark appear as one bottom waveform, so that a very thin linear mark is formed. Exactly the same processing is possible even with a plurality of lines.

According to the above-described configuration, a second camera such as a CCD camera can be used.
When a two-dimensional image sensor is used, averaging of video waveforms from many scanning lines and horizontal shift addition can be mixed. For example, when a video waveform for 30 horizontal scanning lines is extracted in the frame FR, the video waveforms for every other 10 lines are used as the original waveforms, and the video waveforms for every other 10 lines are, for example, the right side. The shift waveform is used, and the remaining 10 video waveforms are used as the left shift waveform, and even if the video waveforms of a total of 30 video lines are added and synthesized, the waveform emphasized by a specific mark or a specific edge is similarly used. Is obtained. However, in order to determine the mark position more precisely, it is preferable to analyze only the original waveform signal again.

FIG. 10 shows a modified example of another mark shape. In FIG. 10, SL1, SL2 and SL3 denote scanning spots (sheet-like or simple circle) of a laser beam or horizontal scanning lines of a television camera. The mark MC is trapezoidal and the left and right edges E1 and E2 are at 45 ° to the scanning line.
Just leaning. Three scanning lines SL1, SL2, SL3
Are separated by a constant interval K in a direction orthogonal to the scanning.

Therefore, for example, to recognize the edge E1,
The signal obtained along the scanning line SL1 is used as an original waveform, the signal waveform obtained along the scanning line SL2 is shifted to the right by K, and the signal waveform obtained along the scanning line SL3 is shifted to the right by 2K.
, And may be combined after the preprocessing. To recognize the edge E2, a left shift may be performed in the same manner.

(4) Other Embodiments In each of the above embodiments, a case where a photoelectric signal (video signal) is processed has been described. Instead, a spot of an electron beam is scanned on an object to perform a specific operation. The same can be applied to the case of recognizing a pattern or an edge position. In this case, since the amount of secondary electrons and scattered electrons generated from the object changes according to the scanning position of the electron beam,
A similar analog signal is obtained.

As a format for obtaining a similar analog signal, a method of scanning an enlarged mark image via an objective lens with a minute slit, and photoelectrically detecting the transmitted light of the slit with a photometer or the like, and the slit is fixed. A method in which the light beam of the mark image from the objective lens is swung by a mirror or the like in the width direction of the slit while being kept intact is similarly applied. Further, the laser beam may be deflected by a rotating polygon mirror, a carbano mirror, or the like, focused on spot light via a telecentric objective lens, and one-dimensionally scanned. In this case, if a sampling pulse is generated in synchronization with the deflection angle (deflection position) of the laser beam, signal waveform data corresponding to the scanning position is extracted to the memory.

Further, in the above-described embodiment, shift addition is performed to obtain a composite waveform. However, similar effects can be obtained by multiplying the shifted waveform by the waveform before the shift. However, there is a disadvantage that it takes a little longer in software program processing than simple addition.

[0062]

As described above, according to the present invention, a high pattern recognition ability can be always provided even for a pseudo signal due to a change in the intensity of a detected analog signal, noise, or the like. A pattern recognition device that can reliably detect only a specific pattern from an area can be realized.

[Brief description of the drawings]

FIG. 1 is a schematic perspective view showing the overall configuration of a projection exposure apparatus to which a pattern recognition device according to a first embodiment of the present invention is applied.

FIG. 2 is a schematic plan view for explaining a mark arrangement according to the first embodiment;

FIG. 3 is a schematic plan view showing an arrangement of spot light in a projection visual field in the pattern recognition device of the first embodiment.

FIG. 4 is a flowchart illustrating an operation according to the first embodiment.

FIG. 5 is a characteristic curve diagram showing waveform data processed according to the operation shown in FIG. 4;

FIG. 6 is a characteristic curve diagram showing a state of processing on another signal waveform.

FIG. 7 is a schematic diagram illustrating a configuration of a pattern recognition device according to a second embodiment of the present invention.

FIG. 8 is a schematic diagram for explaining the operation of the pattern recognition device.

FIG. 9 is a characteristic curve diagram showing a signal waveform of the pattern recognition device of the second embodiment.

FIG. 10 is a plan view showing a modification of the mark shape.

[Explanation of symbols]

W: Wafer, WM, MA, MB, MC: Wafer mark, M1, M2, M3: Mark element, SP, SPX,
SPY: Spot light, 10: Amplifier, 11: A /
D converter, 12 memory (RAM), 18 high-speed arithmetic processor, 35 imaging device.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-61-236117 (JP, A) JP-A-62-273402 (JP, A) JP-A-63-229307 (JP, A) JP-A-63-229 247602 (JP, A) JP-A-2-103401 (JP, A) JP-A-4-283917 (JP, A) JP-A-3-209812 (JP, A) (58) Fields investigated (Int. ⁷ , DB name) H01L 21/027 G01B 11/24 G03F 1/08 G03F 9/00 G06T 7/00

Claims (2)

(57) [Claims] 1. A holding means for holding an object in which a plurality of patterns of substantially the same shape are formed at predetermined intervals in a direction in which position detection is to be performed, and a predetermined range on the object including the plurality of patterns in the position detection direction. Scanning means for scanning and outputting an analog signal whose level changes in accordance with a change in optical characteristics within the predetermined range, and analyzing the analog signal to specify one of the plurality of patterns. A pattern recognition device for recognizing a position of the pattern, wherein a storage means for storing a waveform of the analog signal obtained by scanning by the scanning means in correspondence with a scanning position on the object; Differentiating means for reading a waveform of the analog signal and obtaining a differential waveform of the analog signal; and calculating the differential waveform by an amount corresponding to a predetermined interval of the plurality of patterns. Waveform synthesizing means for synthesizing a waveform shifted in the scanning direction and an original waveform, and outputting a synthesized waveform in which a waveform portion corresponding to the specific pattern is emphasized by a waveform portion corresponding to another pattern. And a discriminating means for detecting a position of the specific pattern by detecting an emphasized waveform portion of the composite waveform. 2. A holding means for holding an object in which a plurality of patterns having substantially the same shape are formed at predetermined intervals in a direction in which position detection is to be performed, and a predetermined range on the object including the plurality of patterns is set in the position detection direction. Scanning means for scanning and outputting an analog signal whose level changes in response to an optical characteristic change within the predetermined range, and analyzing the analog signal to thereby obtain an analog signal out of the plurality of patterns. A pattern recognition device for recognizing a position of a specific pattern; a storage unit configured to store a waveform of the analog signal obtained by scanning by the scanning unit in correspondence with a scanning position on the object; Waveform shaping means for reading out the waveform of the analog signal, obtaining a differential waveform of the analog signal, and transmitting a weighted differential waveform for weighting the differential waveform. Combining the original waveform and a waveform obtained by shifting the weighted differential waveform in the scanning direction by an amount corresponding to a predetermined interval of the plurality of patterns, and forming a waveform portion corresponding to the specific pattern into another pattern. Waveform synthesizing means for outputting a synthesized waveform emphasized by a waveform portion corresponding to the above, and identification means for identifying the position of the specific pattern by detecting the emphasized waveform portion of the synthesized waveform. A pattern recognition device characterized by