JP2001284232A - Position detecting method based on position detection mark and exposure system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a position detecting device which is capable of restraining the position detection error of a position detection mark due to the asymmetry (WIS) of the mark. SOLUTION: A position detecting device is equipped with an exposure object holding means which holds a work 101 where a position detection mark 11 composed of sets each consisting of one or more position detection marks, a means 13 which irradiates partial regions included in the position detection mark 11 with detecting light, a means 15 which detects the intensity distributions of the diffracted light and reflected light from the position detection pattern produced by irradiation with the detection light, a mark symmetry calculating means 18 which calculates the symmetry of image signals formed on the basis of the intensity distributions of the diffracted light and reflected light, a means 19 which selects the most symmetrical partial region of the partial regions in comparison with the symmetry of the waveforms of image signals in each partial region, and a mark arrangement coordinate determining means 20.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a position detecting method and a position detecting device based on a position detecting mark, and more particularly, to a position detecting method and a position detecting device based on a position detecting mark formed on an object to be exposed. .

[0002]

2. Description of the Related Art As an example of a conventional position detection method based on position detection marks formed on an object to be exposed, a so-called FI is used.
An image processing method such as an A (Field Image Alignment) method is used to detect the position of a position detection mark.
The flowchart is shown in FIG.

As shown in FIG. 5, first, detection light of a wide wavelength is moved to the position of a position detection mark (position detection area) on a wafer, and the detection light is spread over the entire position detection mark 1 shown in FIG. Is irradiated vertically. The position detection mark 1 is 9
The rectangular position detection patterns 2 of a book are arranged so that their longitudinal directions are parallel and at appropriate intervals. Next, the reflected light and the diffracted light from the position detection pattern 2 are condensed through an image forming optical system, thereby obtaining FIG.
As shown in (b), the mark image is formed on the imaging surface of the image sensor, the imaging signal waveform (imaging image data) 3 generated from the mark image is processed, and the position is detected from the imaging signal waveform 3. The position coordinates of the mark 1 are detected. Specifically, as shown in FIG. 7, the edge of each position detection pattern 2 is detected, and the actual intersection of each position detection pattern 2 is determined by the intersection of the line of the slice level 40% and the edge of the position detection pattern 2. Is calculated.
Then, a temporary center line is set near the designed center of the entire position detection mark 1, and the distance ± Wi from the center line of each position detection pattern 2 is calculated. here,
The distance ± Wi is assigned a negative sign when it is on the left side of the temporary center line, and a positive sign when it is on the right side. These distances are added, and further divided by the number of center lines of each position detection pattern 2, and averaged to calculate a deviation ± ΔW from the temporary center line. The position where the temporary center line is shifted by ± ΔW is the coordinate Cr of the actually measured center position of the position detection mark 1.

In FIG. 6B, Cd indicates the design center coordinate of the position detection mark 1, and in FIG.
Cds indicates the designed center line of each position detection pattern 2. By the way, in recent years, CMP (Chemical-Mechanica)
l Low-level pattern is becoming a target of detection by adopting a flattening process such as l Polishment (chemical mechanical polishing).
When detecting the position of such a low step pattern in the position detection method based on the position detection mark of the conventional image processing method, it is necessary to form a mark image with as high a contrast as possible and good symmetry.

As described above, when the flattening step is adopted, it is difficult to improve the contrast using the step of the position detection pattern. Therefore, high contrast is obtained by using the multiple interference of light in the film layer. A method of fine tuning each film thickness structure of the device is used.

[0006]

However, as shown in FIG. 7, when the film thickness structure of the device changes, the contrast of the position detection pattern 2 changes greatly. If there is a change in the film thickness of the position detection pattern 2 in the detection mark 1, a mark asymmetry (WIS: Wafer Induced Shift) occurs as shown in FIG. In the position detection mark 1 where such a WIS exists, as shown in FIG. 7, the position detection result of the position detection pattern 2 includes a large measurement error, but as shown in FIG. TIS (Tool Induced
Shift), the positional deviation of the position detection pattern 2 becomes more remarkable, and the position detection result of the position detection mark 1 includes a very large error.

For this reason, after reducing the WIS, the TI
It is necessary to pursue the cause of S and improve the apparatus to obtain a better TIS. SUMMARY OF THE INVENTION The present invention has been made in view of the above-described problems of the conventional example, and has a mark asymmetry (WI
An object of the present invention is to provide a position detection method and a position detection device based on a position detection mark that can suppress the position detection shift of the position detection mark due to S).

[0008]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention relates to an exposure apparatus for holding an object to be exposed on which position detection marks each having at least one position detection pattern as a set are formed. Exposure object holding means, means for dividing the position detection mark into a plurality of partial areas and irradiating the partial areas with detection light, reflected light and diffraction light from the position detection pattern generated by the irradiation of the detection light Means for detecting the intensity distribution of the image signal, mark symmetry calculating means for calculating the symmetry of the image signal waveform generated from the intensity distribution of the reflected light and the diffracted light, and symmetry of the image signal waveform for each of the partial regions. And a mark arrangement coordinate detecting means for calculating the center coordinates of the selected partial area, the means for selecting the partial area having the best symmetry.

Further, in the position detecting method based on the position detecting mark of the present invention, the position detecting mark on the object to be exposed is divided into a plurality of partial areas, and the partial areas are irradiated with detection light, and the detection light is generated by irradiation of the detection light Detecting the intensity distribution of the reflected light and the diffracted light, and evaluating the symmetry of the imaging signal waveform generated from the intensity distribution for each partial area. Is characterized in that a partial region having the best symmetry is selected, and the center coordinates of the selected partial region are calculated.

In particular, when the position detection pattern has a rectangular shape and a set of position detection patterns is plural, the position detection patterns are arranged such that the longitudinal directions of the position detection patterns are parallel to each other. The mark symmetry calculating means is characterized in that the converted signal waveform is obtained by folding left and right the imaging signal waveform (imaged image data) obtained from the intensity distribution. The means for calculating the difference between the (converted image data) and the original imaging signal waveform by superimposing them, and for selecting the partial region having the best symmetry, detects the difference between the converted signal waveform and the imaging signal waveform by position detection. This is a means for comparing all partial areas in the mark and selecting a partial area having the smallest difference.

Next, the operation derived from the configuration of the present invention will be described. An exposure apparatus according to the present invention includes means for irradiating a position detection mark with detection light, and an image signal waveform (captured image data) obtained for each partial area of the position detection mark from an intensity distribution of reflected light or the like from the position detection pattern. Means for comparing the symmetry of the imaging signal waveforms based on the selected symmetry and selecting a partial region having the best symmetry.

Further, the position detection method of the present invention detects the intensity distribution of reflected light and diffracted light generated by irradiating the position detection mark with detection light, and obtains from the intensity distribution for each partial area of the position detection mark. The symmetry of the obtained imaging signal waveform (imaged image data) is evaluated, and a partial region having the best symmetry of the intensity distribution is selected. That is, in the present invention, the partial area having the best symmetry of the intensity distribution is selected from the plurality of partial areas in the position detection mark. Even though the asymmetry of the imaging signal waveform due to a variation in the thickness of the position detection pattern or the like is large in the entire position detection mark, the asymmetry of the imaging signal waveform is suppressed because the partial region is a narrow region. For this reason, the symmetry of the imaging signal waveform in the partial region is good, and the actually measured center of the partial region calculated based on the imaging signal waveform can be substantially matched with the designed center of the partial region.

Accordingly, the position detection deviation between the actually measured center coordinates of the entire position detection mark and the designed center coordinates of the entire position detection mark obtained by appropriately correcting the actually measured center coordinates of the partial area is corrected. It can be very small. That is, it is possible to suppress a position detection shift of the position detection pattern due to the mark asymmetry (WIS). In particular, the position detection pattern has a rectangular shape, and the averaging effect in the non-measurement direction can be enhanced by increasing the length of the rectangle.

[0014]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a side view showing an exposure apparatus having a position detection unit based on a position detection mark 11 formed on an object to be exposed 101 according to an embodiment of the present invention. The exposure apparatus includes a light source 13 for generating detection light, a half mirror 14, an imaging optical system such as an objective lens 12a and a condensing lens 12b, an optical system 12c such as a polarizer, and a wafer 101 as an object to be exposed. And a wafer mounting table (stage) on which is mounted.

FIG. 2 is a plan view showing the wafer mounting table 22 and the wafer 101 held thereon. As shown in FIG. 2, the position of the wafer mounting table 22 is specified by irradiating the mirrors 23a and 23b provided on the wafer mounting table 22 with laser light and detecting the reflected light. In addition, the position detection mark 11
Means for irradiating the (position detection area) with detection light from the light source 13 and a CC for detecting the intensity distribution of reflected light and diffraction light from the position detection pattern 24 generated by irradiation of the detection light
And a D camera 15.

The means for irradiating the position detection mark 11 with detection light from the light source 13 is not shown in FIG. 1, but, for example, the position detection mark 11 is divided into a plurality of partial areas, and the detection light is detected for each partial area. May be provided above the object to be exposed so that the irradiation area can be narrowed so that the light can be irradiated. Alternatively, it is not necessary to provide such a stop, and in this case, a unit capable of irradiating the entire position detection mark and acquiring an image for each partial region of the position detection mark may be provided, or Means may be provided for obtaining an image of the entire position detection mark at a time and thereafter obtaining a signal waveform for each scanning line, or performing signal processing such as cutting out a signal waveform of a partial region of the position detection mark. .

Further, an image processing means 16 for converting the intensity distribution of the reflected light and the diffracted light detected by the CCD camera 15 into digital data (image signal waveform (image data)), and an image memory for storing the image data 17
And a mark symmetry calculating unit 18 for calculating the symmetry of the captured image data for each partial area of the position detection mark 11, and comparing the symmetry of the captured image data for each partial area of the position detection mark 11, Means 1 for selecting the best partial area
9 and mark arrangement coordinate determination means 20 for calculating the center coordinate Crp of the selected partial area. further,
Offset coordinates (dx,
dy) adjusted and determined position detection mark 11
The exposure apparatus control means 21 outputs an alignment signal to the exposure apparatus based on the central coordinates Cr of the exposure apparatus.

Among these, the mark symmetry calculating means 18
A function of superimposing the folded intensity distribution (converted signal waveform (converted image data)) obtained by folding the imaged intensity distribution (imaged signal waveform (imaged image data)) left and right and the original intensity distribution and calculating the difference between the two. Having. The means 19 for selecting the partial area having the best symmetry compares the difference between the converted image data and the captured image data for all the partial areas in the position detection mark 11, and determines the difference between the converted image data and the captured image data. It has a function of selecting the smallest partial area.

FIG. 2 shows the exposure position of each chip formed by dividing the plane of the wafer 101. In FIG. 2, an ideal lattice connecting the designed center coordinates of the position detection mark 11 of each chip is shown by a solid line, and a real grid connecting the measured center coordinates of the position detection mark 11 of each chip is shown by a dotted line. Note that the position coordinates actually measured by the method of the present invention are represented by offset coordinates (d
x, dy), the actually measured center coordinates Cr of the chip position detection mark 11 are determined.

Then, the distance from the cross-shaped reference mark located at the lower right on the stage 22 to the coordinates of the corners of the specific real grid is determined in advance, and the measured position of each position detection mark 11 is set as the reference position. Exposure is performed by sequentially following the position coordinates of the real grid, which is the upper center coordinate Cr. Next, FIG.
A position detection method based on position detection marks formed on a wafer according to an embodiment of the present invention will be described with reference to FIGS.

FIG. 3 is a flowchart showing a position detection method according to an embodiment of the present invention. FIG. 4A is a plan view showing position detection marks (position detection areas), and nine position detection marks are provided. , And are arranged such that their longitudinal directions are parallel to each other and at appropriate intervals in the transverse direction. FIG.
4B is a diagram illustrating an image of the position detection mark detected by the detection light, and FIG. 4C is a diagram illustrating a method for evaluating the symmetry of the image data. In this embodiment, in order to acquire the image data of the partial area of the position detection mark, the image processing unit 16 irradiates the entire position detection mark with the detection light, collectively acquires the image of the entire position detection mark, and thereafter, And a function of performing signal processing of cutting out captured image data of a partial area of the position detection mark.

As shown in FIG. 3, first, the detection light of the broadband wavelength is moved to the position of the position detection mark (position detection area) 11 on the wafer 101 (P11). Subsequently, the detection light is applied to the position detection mark 11 vertically. Next, the reflected light and the diffracted light from the position detection pattern 24 are condensed via the imaging optical systems 12a and 12b and the optical system 12c, and as shown in FIG. To form a mark image showing its intensity distribution (P1
2). At this time, the position detection mark 11 may be divided into a plurality of partial areas, and a mark image may be acquired for each partial area. For example, a partial area is taken as shown in FIG.

In particular, the position detection pattern 24 has a rectangular shape, and the averaging effect in the non-measurement direction can be enhanced by lengthening the length of the rectangle. Note that the averaging effect means the following effects. That is,
It is advantageous to smooth the mark vertical structure (thickness difference, asymmetric) by enlarging the mark area so that the mark is still formed uniformly through a wafer process such as film formation and CMP, Alternatively, improvement of the S / N ratio can be expected by smoothing signal noise and mark fluctuation in a wide mark area.

Next, a digital signal waveform (imaging signal waveform (imaging image data)) is generated from the mark image by the image processing means 16 (P13). At this time, the position detection mark 11 is divided into a plurality of partial areas, and captured image data is acquired for each partial area. As shown in FIG. 4B, generation of captured image data is sequentially performed over all partial regions. The captured image data is stored in the image memory 17 (P14).

Next, as described below, the symmetry of the intensity distribution obtained for each partial area is calculated by the mark symmetry calculating means 18 (P15). For example, as shown in FIG. 4C, the intensity distribution (imaging signal waveform (imaged image data)) in the partial area is turned back to obtain a folded intensity distribution (converted signal waveform (converted image data)). And the difference is calculated. At this time, it is determined that the one with the smallest difference has the best symmetry.

Subsequently, as shown in FIG. 4C, a partial area having the smallest difference is selected (P16). Then, the sliced image is sliced at 40% of the maximum and minimum level difference of the intensity distribution with respect to the imaged intensity distribution acquired in the partial area.
From the intersection of the slice level and the intensity distribution, the center line of each position detection pattern 24 or the center line of the space that is the interval between adjacent position detection patterns 24 is obtained. Further, a temporary center line in the partial area is set, and distances -W1, + W2 between the center lines of the respective position detection patterns 24 are calculated from the temporary center line. Here, it is assumed that the temporary center line matches the designed center line Cdp in the partial area. Then, ΔW = (− W1 + W2) / 2 is calculated, and
The position obtained by moving the temporary center line by a deviation ΔW from the temporary center line is defined as the actually measured center coordinate Crp of the partial area.

In this embodiment, a total of three center lines Crs are calculated corresponding to the position detection pattern 24 of the partial area, and the center line Crp of the entire partial area is obtained from this. Large numbers are possible. For example, in the case of five lines, two center lines of the position detection pattern are formed on the left and right of the temporary center line of the entire partial area, and the distances (W1 to W4) from the temporary center line are calculated. . In this case, the left 2
ΔW = (− W1−W2 + W3 + W4) / 4 is calculated for −W1 and −W2 and the two right side + W3 and + W4, and the position coordinates of the temporary center line are corrected by ± ΔW. The position coordinates become the center coordinates Crp of the entire partial area.

Next, the distance between the designed center coordinate Cd of the entire position detection mark 11 and the actually measured center coordinate Crp of the partial area is calculated, and this is calculated as the offset coordinate (dx, d).
y) (P17). Since the actually measured center coordinates Crp of the partial area in each chip are generally different for each chip, the offset coordinates (d
x, dy) to calculate the center coordinates Cr of the position detection mark 11 in which the actually measured center coordinates Crp of the partial area are corrected,
The corrected center coordinates Cr of the position detection mark 11 must be used as reference coordinates common to the chips (P18).

When the position coordinates of all the position detection marks have been calculated in this way (P19), the position detection ends.
Thereafter, the alignment is performed sequentially based on the determined center coordinates Cr of the position detection marks 11, and exposure is performed. As described above, according to the embodiment of the present invention, the position detection mark 11
Of the plurality of partial regions, the partial region having the best symmetry of the intensity distribution is selected. Therefore, in the entire position detection mark 11, even if the asymmetry of the intensity distribution due to the fluctuation of the film thickness of the position detection pattern 24 is large. Since the partial area is narrow, the asymmetry of the intensity distribution is suppressed. Thereby, the symmetry of the intensity distribution in the partial area is good, and the actually measured center coordinates Crp of the partial area calculated based on the intensity distribution can be made to substantially match the designed center coordinates Cdp of the partial area. .

Accordingly, the actually measured center coordinates Cr of the partial area
The measured center coordinates Cr and the position detection mark 1 of the entire position detection mark 11 obtained by appropriately correcting p
(1) It is possible to make the position detection deviation from the center coordinate Cd in the overall design extremely small. That is, it is possible to suppress the position detection shift of the position detection mark 11 due to the mark asymmetry (WIS).

As described above, the present invention has been specifically described by the embodiments. However, the present invention is not limited to the examples specifically shown in the above embodiments, and the scope of the present invention does not depart from the gist of the present invention. Modifications of the embodiments are included in the scope of the present invention. For example, the distance between the reference coordinates and the actually measured center coordinates Crp of the partial area is set as offset coordinates (dx, dy) using the design center coordinates Cd of the entire position detection mark 11 as reference coordinates. When the center coordinates Cr of the mark 11 are not used as the reference coordinates, the position coordinates of a specific portion common to the position detection marks 11 of all chips are used as the reference coordinates, and the reference coordinates and the actually measured center coordinates Crp of the partial area are used. And the offset coordinate (d
x, dy). (Supplementary Note) (1) In the exposure apparatus according to claim 1 or 2, the mark symmetry calculating unit superimposes the conversion signal waveform obtained by folding the imaging signal waveform right and left and the imaging signal waveform, and calculates a difference between the two. Means for calculating, and means for selecting the partial area having the best symmetry, comparing the difference between the converted signal waveform and the imaging signal waveform for all the partial areas in the position detection mark, A means for selecting a partial area having the smallest difference between the waveform and the imaging signal waveform.

(2) In the position detection method based on the position detection mark according to claim 3 or 4, wherein the step of calculating the symmetry of the image signal waveform is performed by folding the image signal waveform right and left. And calculating the difference by superimposing the imaging signal waveform, and selecting the partial region having the best symmetry, the conversion signal waveform and the The method is characterized in that the step is a step of selecting a partial area having the smallest difference between the image signal waveforms.

[0033]

As described above, according to the present invention, the position detection mark is divided into a plurality of partial areas to obtain the captured image data, and the partial areas having the best intensity distribution symmetry among all the partial areas are obtained. Is selected. As a result, even if the intensity distribution has a large asymmetry due to a change in the thickness of the position detection pattern or the like in the entire position detection mark, since the partial region is a narrow region, the asymmetry of the intensity distribution is suppressed. Therefore, the symmetry of the intensity distribution in the partial region is good, and the actually measured center of the partial region calculated based on this intensity distribution can be substantially matched with the designed center of the partial region.

Therefore, the position detection deviation between the actually measured center coordinates of the entire position detection mark and the designed center coordinates of the entire position detection mark obtained by appropriately correcting the actually measured center coordinates of the partial area is determined. It can be very small. That is, it is possible to suppress the position detection deviation of the position detection mark due to the mark asymmetry (WIS).

[Brief description of the drawings]

FIG. 1 is a side view showing a position detecting device according to an embodiment of the present invention.

FIG. 2 is a plan view illustrating a position detection method according to the embodiment of the present invention.

FIG. 3 is a flowchart showing a position detection method according to the embodiment of the present invention.

FIG. 4A is a plan view showing a planar shape of a position detection pattern in a position detection mark used in the position detection method according to the embodiment of the present invention and their mutual arrangement,
(B) is a diagram showing intensity distributions of reflected light and diffracted light from position detection patterns in two different partial regions,
FIG. 3C is a diagram illustrating a method of calculating the actually measured center coordinates of the partial region based on the imaging signal waveform.

FIG. 5 is a flowchart illustrating a position detection method according to a conventional example.

FIG. 6A is a plan view showing a planar shape of a position detection pattern in a position detection mark used in a position detection method according to a conventional example and their mutual arrangement. (B) is a diagram showing a method of calculating the intensity distribution of reflected light and diffracted light from the position detection pattern in the position detection mark and the actually measured center coordinates of the position detection mark.

FIG. 7 shows a cross-sectional shape of a position detection pattern used in a position detection method according to a conventional example, an intensity distribution of reflected light and diffracted light from each position detection pattern, and actual measurement of each position detection pattern based on captured image data. It is a figure which shows the method of calculating an upper center coordinate.

FIG. 8 shows TIS and W in a position detection method according to a conventional example.
It is a figure explaining the relation with IS.

[Explanation of symbols]

 11 position detection mark, 12a objective lens (imaging optical system), 12b condenser lens (imaging optical system), 12c optical system, 13 light source, 14 half mirror, 15 CCD camera, 16 image processing means, 17 image memory, 18 mark symmetry calculation means, 19 partial area selection means, 20 mark arrangement coordinate limiting means, 21 exposure apparatus control means, 24 position detection patterns, 101 wafer (subject to be exposed), design center coordinates of Cds position detection patterns, Measured center coordinates of Crs position detection pattern, designed center coordinates of Cdp partial area, measured center coordinates of Crp partial area, designed center coordinates of Cd position detection mark, measured center coordinates of Cr position detection mark Center coordinates.

Continued on front page F term (reference) 2F065 AA03 AA14 BB01 BB28 CC19 DD03 FF01 FF42 FF61 HH13 JJ03 JJ26 LL00 MM03 PP12 QQ04 QQ13 QQ25 RR01 TT02 UU05 UU07 5F046 DB05 DB10 EB01 FC04 FC06

Claims (4)

[Claims] An exposure object holding unit configured to hold an exposure object on which a position detection mark having one or more position detection patterns as a set is formed; and wherein the position detection mark is divided into a plurality of partial areas. Means for irradiating the partial area with detection light, means for detecting the intensity distribution of reflected light and diffracted light from the position detection pattern generated by the irradiation of the detection light, and generation from the intensity distribution of the reflected light and diffracted light Mark symmetry calculating means for calculating the symmetry of the obtained imaging signal waveform, and means for comparing the symmetry of the imaging signal waveform for each of the partial areas, and selecting the partial area having the best symmetry, An exposure apparatus comprising: mark arrangement coordinate determination means for calculating center coordinates of the selected partial area. 2. The method according to claim 1, wherein the position detection pattern has a rectangular shape, and when a set of the position detection patterns is plural, the position detection patterns are arranged such that longitudinal directions of the position detection patterns are parallel to each other. 2. The exposure apparatus according to claim 1, wherein the position detection patterns are arranged at intervals in the short direction of the position detection patterns. 3. A step of preparing an object to be exposed on which a position detection mark having one or more position detection patterns as a set is formed, and dividing the position detection mark into a plurality of partial areas, and Means for irradiating the position detection mark with detection light; means for detecting the intensity distribution of reflected light and diffracted light from the position detection pattern generated by the irradiation of the detection light; and Calculating the symmetry of the generated imaging signal waveform; comparing the symmetry of the imaging signal waveform for each of the partial areas; and selecting the partial area having the best symmetry; and Calculating a center coordinate of the partial region. 4. The position detection pattern has a rectangular shape, and when a set of the position detection patterns is plural, the position detection patterns are arranged such that longitudinal directions of the position detection patterns are parallel to each other. 4. The position detection method based on a position detection mark according to claim 3, wherein the position detection patterns are arranged at intervals in the short direction.