JP2005300172A - Method and device for position measurement, exposure method using this position measuring method, exposure device provided with this position measuring device, position measuring program for performing this position measuring method and recording medium memorized with this position measuring program - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To measure the positional information of an alignment mark by applying an AGC on the detection signal of the alignment mark by finding out the detection signal buried in the noise signals. <P>SOLUTION: The image signal as the measuring signal is obtained by irradiating the area where the alignment mark AM1 of a wafer W is formed with the light flux of detection illumination light, the reflected light of which is focused on the imaging surface of the CCD camera 26. From the image signal obtained, the interval where the signal form almost flat continues more than the area of the alignment mark AM1 is extracted. The extracted signal part is amplified and determined whether the image signal is corresponding to the alignment mark AM1 or not based on the design value of the alignment mark AM1. If the image signal is determined as that of the alignment mark AM1, the alignment of the wafer W is executed. If the image signal does not corresponding to the alignment mark AM1, the interval other than the previous one is extracted, and the same acton is repeated so on. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  In the present invention, the amplitude of a signal for detecting a position detection mark such as an alignment mark is small, and even if it is buried in a noise signal or the like, it is searched for and subjected to AGC (automatic gain control) to The present invention relates to a position measurement method capable of measuring position information of a detection mark with high accuracy. Further, a position measuring apparatus for executing this position measuring method, an exposure method using this position measuring method, an exposure apparatus provided with this position measuring apparatus, a position measuring program for executing this position measuring method, and this position The present invention relates to a recording medium storing a measurement program.

  When manufacturing a semiconductor device, a liquid crystal display device, or the like using a lithography technique, an exposure illumination light (exposure light) is usually applied to a reticle as a mask on which a fine pattern is formed, and an image of this pattern is obtained. An exposure apparatus is used that repeatedly projects and exposes a photosensitive substrate such as a semiconductor wafer or a glass template coated with a photosensitive agent such as a photoresist via a projection optical system.

  In order to sequentially expose a circuit pattern drawn on a plurality of reticles on a wafer and superimpose them on a pattern that has already been formed, the positional relationship of the reticle with respect to the wafer stage coordinate system is accurately determined prior to exposure. Therefore, it is necessary to accurately perform alignment between the reticle and the wafer (circuit pattern in each shot area of the wafer). In order to perform this alignment, for example, the position of the alignment mark formed on the wafer is detected by an alignment sensor mounted on the exposure apparatus, and thereby the exact position of the circuit pattern in each shot area on the wafer. Is detected.

In recent years, along with the miniaturization of patterns, alignment accuracy has been strictly demanded, and various devices have been made for alignment. For example, in the alignment of a reticle, exposure light is used, and the exposure light is irradiated to an alignment mark formed on the reticle, while reflected light from the alignment mark is used as a CCD (Charge Coupled Device) or the like. VRA (Visual) that measures the position of the alignment mark by applying image processing to the image data obtained by imaging
(Reticle Alignment) method is known. In wafer alignment, a laser beam is irradiated onto a dot row alignment mark formed on the wafer, and the position of the alignment mark is determined using diffracted light or scattered light diffracted or scattered by the alignment mark. LSA to detect (Laser
The alignment mark is irradiated with light having a wide wavelength bandwidth using a step alignment) method, a halogen lamp, etc., while the reflected light from the alignment mark is imaged by the CCD, and the image data is subjected to image processing and the alignment mark FIA (Field
(Image Alignment) system or a diffraction grating-shaped alignment mark formed on a wafer is irradiated with laser light with slightly different frequencies from two directions, causing the two diffracted lights to interfere with each other, and the alignment mark LIA for measuring position (Laser
Interferometric Alignment) method is known.

  In these optical alignments, the alignment mark on the reticle is first detected and processed, and the position coordinates of the mark are measured. Next, the alignment mark on the wafer is detected and processed, and the position coordinates of the mark are measured to obtain the position of the shot area to be overlaid. Based on this, the wafer stage is moved so that the reticle pattern image overlaps with the shot region position on the wafer to move the wafer, and the reticle pattern image is projected and exposed.

  In any of the above-described methods, reflected light generated when illumination light is irradiated onto a mark formed on an object such as a wafer or a reticle is photoelectrically converted into an electrical signal (detection signal), and the converted signal is processed. Mark position information. However, there is a case where sufficient signal intensity for measuring the position information of the mark with high accuracy cannot be obtained due to reflected light from other than the mark when measuring the position information. This is because of the scattering of illumination light due to the shape of the pattern formed on the object, the difference in the light reflection and transmission characteristics of various materials laminated on the object (wafer), and the thickness of the photoresist applied to the object (wafer) surface. This is caused by the influence of multiple reflection based on the non-uniformity of the height or the difference in contrast between the bright part and the dark part of the detection signal.

  In order to cope with this, the sensor is equipped with an AGC (Automatic Gain Control) function. In this AGC, the detection signal is amplified to an intensity within a preset range. When the intensity of the detection signal is weak, the detection signal is amplified to a signal intensity necessary for obtaining position information.

  However, the signals detected by the sensor may include a false signal having a greater contrast than the alignment mark in addition to the alignment mark detection signal. Therefore, there is an inconvenience that the optimum AGC cannot be applied to the false signal. That is, when a noise signal including a false signal is superimposed on the alignment mark detection signal and the alignment mark detection signal is buried in the noise signal, AGC is applied to the original alignment mark detection signal. In addition, there is a disadvantage that AGC is applied to the false signal in the noise signal.

  The present invention has been made in view of such circumstances, and searches for an alignment mark detection signal buried in a noise signal and applies it to AGC (applying an AGC that is optimal for the mark signal). An object of the present invention is to provide a position measuring method and a position measuring apparatus for measuring position information of an alignment mark.

  It is another object of the present invention to provide an exposure method using the position measurement method and an exposure apparatus provided with the position measurement device.

  Furthermore, it aims at providing the recording medium which memorize | stored the position measurement program for performing the said position measurement method, and this position measurement program.

  The position measurement method according to claim 1 of the present invention that achieves the above object is provided on a measurement object (for example, a reticle as a wafer or a mask), and has a specified size on a design value with respect to a predetermined measurement direction. A position measuring method for measuring a pattern (for example, alignment marks AM1, AM2, etc.), wherein a measurement signal is obtained by photoelectrically detecting a measurement area including the specific pattern on the measurement object. (Step 601) and a state in which the difference between the maximum value and the minimum value of the measurement signal is less than or equal to a predetermined value and the difference is less than or equal to the predetermined value among the measurement signals obtained in the first step. A second step (step 602) for extracting a specific section that continues for the predetermined size or more in the measurement direction, and a third step for performing gain adjustment on the signal within the specific section extracted in the second step ( And step 603), and having a.

  That is, in order to find a measurement signal having a small signal amplitude and a specific pattern buried in a noise signal or the like, the difference between the maximum value and the minimum value of the measurement signal is equal to or less than a predetermined value, and the waveform of the measurement signal is almost flat. A section in which the portion continues for a predetermined size or more in the measurement direction is extracted, a signal in this section is regarded as a measurement signal of a specific pattern (for example, an alignment mark), and AGC is applied to this.

  In the position measuring method according to claim 1, when the specific pattern is not found, the second step and the third step may be repeated. That is, a fourth step (step 604) for identifying the presence / absence of the specific pattern based on the design value of the specific pattern from the signal in the specific section after gain adjustment in the third step is further performed. And when it is determined in the fourth step that the specific pattern does not exist in the specific section, the process returns to the second step, and is a section different from the specific section, and the difference is predetermined. The third and fourth steps may be repeated after extracting from the measurement signal a further section that is less than a value and whose state continues in the measurement direction for the predetermined size or more. reference).

  Further, in the position measurement method according to claim 1, when the difference between the maximum value and the minimum value of the measurement signal is equal to or less than a predetermined value, and there are a plurality of divided portions where the waveform of the measurement signal is substantially flat, That is, in the second step, when there are a plurality of sections satisfying the condition that becomes the specific section in the measurement signal, all the plurality of specific sections are extracted, and in the third step, The gain adjustment is performed on the signals of the plurality of specific sections extracted in the second step, and the specific pattern is obtained from the signals in the plurality of specific sections after the gain adjustment is performed in the third step. A fourth step of identifying the presence / absence of the specific pattern based on the design value may be provided (see claim 3 in FIG. 7).

  Further, in the third step, offset adjustment may also be performed on the extracted signal of the section (refer to claim 4 in FIG. 8).

  Further, when an error occurs in search measurement for searching for a specific pattern, the entire measurement signal obtained in the first step is performed after the first step and before performing the second step. Is further provided with a fifth step (step 903) for identifying the presence / absence of the specific pattern based on the signal after gain adjustment, wherein the presence of the specific pattern is identified in the fifth step. If not, the process may proceed to the second and subsequent steps (refer to claim 5 and FIG. 9).

  An exposure method according to a sixth aspect of the present invention is an exposure method in which a pattern is transferred and exposed onto a substrate to be exposed, and the exposure method is performed by the position measurement method according to any one of the first to fifth aspects. Position information relating to the substrate is obtained, and the positional relationship between the substrate to be exposed and the pattern is adjusted based on the position information.

  The position measuring device (12, 40) according to claim 7 of the present invention measures a specific pattern having a predetermined size on a design value with respect to a predetermined measurement direction, which is provided on an object to be measured (wafer W, reticle R). And a photoelectric detection means (CCD cameras 26 and 46) for photoelectrically detecting a measurement area including the specific pattern on the measurement object to obtain a measurement signal, and the photoelectric detection Among the measurement signals obtained from the means, the difference between the maximum value and the minimum value of the measurement signal is less than or equal to a predetermined value, and the state in which the difference is less than or equal to the predetermined value continues for the predetermined size or more in the measurement direction. Extraction means (position calculation unit 27, main control unit 10) for extracting a specific section to be performed, and signal processing means (amplifier 31, AGC) for performing gain adjustment on the signal in the specific section extracted by the extraction means Circuit 35) , Characterized by having a.

Identification means (main control unit 10) for identifying presence / absence of the specific pattern based on a design value of the specific pattern from a signal in the specific section after gain adjustment is performed by the signal processing means. May be.
Further, when the identification unit identifies that the specific pattern does not exist in the specific section, the specific section is different from the specific section, and the difference is equal to or less than a predetermined value and the state is in the measurement direction. After the further section that is continuous with the predetermined size or more is extracted from the measurement signal by the extraction means, the processing by the signal processing means and the identification means may be repeatedly executed.

  An exposure apparatus according to a ninth aspect of the present invention is an exposure apparatus that transfers and exposes a pattern (pattern on the reticle R) onto a substrate to be exposed (wafer W), and the position measurement according to the seventh or eighth aspect. The apparatus (12, 40) obtains positional information relating to the substrate to be exposed, and adjusts the positional relationship between the substrate to be exposed and the pattern based on the positional information.

  A position measurement program according to a tenth aspect of the present invention is a position measurement program for measuring a specific pattern having a predetermined size on a design value with respect to a predetermined measurement direction, which is provided in an object to be measured. The first step of photoelectrically detecting the measurement area including the specific pattern on the measurement object and outputting the measurement signal, and the measurement signal obtained in the first step, A second section for causing the extraction means to extract a specific section in which the difference between the maximum value and the minimum value of the measurement signal is equal to or smaller than a predetermined value and the state where the difference is equal to or smaller than the predetermined value continues in the measurement direction for the predetermined size or more. And a third step of causing the signal processing means to perform gain adjustment on the signal in the specific section extracted in the second step, the photoelectric detecting means, the extracting means, and the signal processing means, respectively. Fruit Characterized in that it allowed to.

  A computer-readable recording medium according to an eleventh aspect of the present invention stores the position measurement program according to the tenth aspect.

  According to the position measurement method of the first aspect of the present invention, a state in which the difference between the maximum value and the minimum value of the measurement signal is not more than a predetermined value and the difference is not more than the predetermined value among the measurement signals. Extracts a specific section that is continuous in a measurement direction by a predetermined size or more (second step), and performs gain adjustment on the signal in the specific section (third step), so that a false signal exists. Even if it is buried in the noise signal having this false signal, it is possible to search for a measurement signal (detection signal) of a specific pattern, apply AGC to this, and measure the position information of the specific pattern with high accuracy. Is possible.

  According to the position measurement method of the present invention, the presence / absence of the specific pattern is identified (determined) based on the design value of the specific pattern from the signal in the specific section after gain adjustment. (4th step), and when it is identified (determined) that the specific pattern does not exist in the specific section, the process returns to the second step and is a section different from the specific section, and the difference is a predetermined value. In the following, the third and fourth steps are repeated after extracting a further section in which the state continues for a predetermined size or more in the measurement direction from the measurement signal. Therefore, even if the first measurement is performed, a specific pattern is searched for. Even if it is not possible, it is possible to search for the specific pattern by repeating the second step, and to measure the position information by applying AGC to the measurement signal of this specific pattern.

  According to the position measurement method of claim 3 of the present invention, in the second step, when there are a plurality of sections satisfying a condition to be a specific section in the measurement signal, the plurality of specific sections are All are extracted, and in the third step, gain adjustment is performed on the signals of each of the plurality of specific sections extracted in the second step, and in the fourth step, the gain adjustment is performed in the plurality of specific sections after the gain adjustment is performed. Since the presence or absence of the specific pattern is identified (determined) based on the design value of the specific pattern from the signal, the difference between the maximum value and the minimum value of the measurement signal is equal to or less than a predetermined value. Even when there are a plurality of portions where the waveform is substantially flat, it is possible to search for a specific pattern and apply AGC to the measurement signal of this specific pattern to measure position information.

  Further, according to the position measurement method of claim 5 of the present invention, after the first step and before the second step, the entire measurement signal obtained in the first step is applied. A fifth step of performing gain adjustment and identifying (determining) the presence or absence of the specific pattern based on the signal after gain adjustment, and the presence of the specific pattern is not identified (determined) in the fifth step; In this case, since the process proceeds to the process after the second step, even if an error occurs in the search measurement of the specific pattern, the specific pattern is searched for and AGC is applied to the measurement signal of the specific pattern. Position information can be measured.

  According to the exposure method of claim 6 of the present invention, the position measurement method according to any one of claims 1 to 5 is used to obtain position information about the substrate to be exposed, based on the position information, Since the positional relationship between the substrate to be exposed and the pattern is adjusted, the positional relationship between the substrate to be exposed and the pattern can be set with high accuracy, and the yield of devices manufactured by this exposure method can be improved.

  According to the position measuring apparatus (12, 40) of the present invention, the specific pattern (alignment marks AM1, AM2, reticle alignment mark RM, etc.) on the measurement object (wafer W, reticle R), etc. ) Including a photoelectric detection means (CCD cameras 26 and 46) for photoelectrically detecting a measurement target region including a measurement signal to obtain a measurement signal, and the maximum value of the measurement signal from the measurement signals obtained from the photoelectric detection means Extraction means (position calculation unit 27, main control unit 10) for extracting a specific section in which the difference between the minimum value and the minimum value is equal to or smaller than a predetermined value and the difference is equal to or smaller than the predetermined value continues for a predetermined size or more in the measurement direction; Since the signal processing means (amplifier 31 and AGC circuit 35) for adjusting the gain of the signal in the specific section extracted by the extraction means is provided, a false signal exists and the noise having the false signal exists. Even if buried in the signal, finds the measurement signal of a specific pattern, contrast can apply AGC, it is possible to measure the positional information of the specific pattern with high precision.

  Further, according to the exposure apparatus of the ninth aspect of the present invention, the position measurement device (12, 40) according to the seventh or eighth aspect obtains position information regarding the substrate to be exposed (wafer W), and the position Since the positional relationship between the substrate to be exposed and the pattern (reticle R) is adjusted based on the information, the positional relationship between the substrate to be exposed and the pattern can be set with high accuracy, and the yield of devices manufactured by this exposure apparatus It is possible to improve.

  According to the position measurement program of claim 10 of the present invention, the photoelectric detection means (CCD cameras 26, 46) is caused to photoelectrically detect the measurement area including the specific pattern on the measurement object. The difference between the maximum value and the minimum value of the measurement signal is not more than a predetermined value among the first step for outputting the measurement signal and the measurement signal obtained in the first step, and the difference is not more than the predetermined value. A second step of causing the extraction means to extract a specific section in which the state below the value continues for a predetermined size or more in the measurement direction, and a gain adjustment for the signal in the specific section extracted in the second step to the signal processing means Since the photoelectric detection means, the extraction means, and the signal processing means are caused to execute the third step to be executed, if the position measuring device according to claim 7 is operated by this program, a false signal exists. Have this false signal Even if it is buried in a noise signal, a measurement signal (detection signal) of a specific pattern (such as an alignment mark) can be found and AGC can be applied to it, and the position information of the specific pattern can be measured with high accuracy. Is possible.

  Further, according to the recording medium according to claim 11 of the present invention, since the position measurement program according to claim 10 is stored, it is set in the control system of the position measurement device according to claim 7. For example, even if the position measuring device can be operated by the program according to claim 10 and a false signal exists and is buried in a noise signal having the false signal, the measurement signal of a specific pattern can be obtained. It is possible to search for (detection signal), automatically apply AGC to this, and measure position information of a specific pattern with high accuracy.

  Hereinafter, a position measurement method, a position measurement apparatus, an exposure method using the position measurement method, an exposure apparatus including the position measurement apparatus, a position measurement program for executing the position measurement method, and the position measurement program are stored. An embodiment of the recording medium will be described with reference to FIGS.

  FIG. 1 is an overall configuration diagram showing a first embodiment of a position measurement apparatus (FIA sensor: Field Image Alignment sensor VRA sensor: Visual Reticle Alignment sensor) and an exposure apparatus equipped with this position measurement apparatus according to the present invention. (A) is a plan view showing an example of an alignment mark as a specific pattern serving as a predetermined reference for position measurement, and FIG. (B) is a cross-sectional view taken along the line aa in FIG. ) Is a plan view of another alignment mark, FIG. 3D is a plan view of another alignment mark, FIG. 3 is an explanatory view showing an imaging surface of the CCD camera 26, and FIG. 4 is a diagram of the position calculation unit in FIG. FIG. 5 is a block diagram showing an outline, FIG. 5 is an explanatory diagram for explaining a process of searching for a measurement signal of an alignment mark buried in a false signal, and FIGS. 6 to 9 are flowcharts showing an embodiment of the position measurement program of the present invention.

  First, the overall configuration and operation of the position measurement apparatus and exposure apparatus of this embodiment will be described with reference to FIG.

  In the present embodiment, an exposure apparatus provided with the FIA sensor 12 and the VRA sensor 40 will be described as an example of the position measuring apparatus. In FIG. 1, the X axis and the Z axis are set in parallel with the paper surface, and the Y axis is set in a direction perpendicular to the paper surface.

  In FIG. 1, exposure light EL emitted from the illumination optical system 1 illuminates a reticle R as a mask with a substantially uniform illuminance. The reticle R is held on a reticle stage 3, and the reticle stage 3 is supported so that it can move and rotate in a two-dimensional plane on the base 4. A main control system 10 that controls the operation of the entire apparatus controls the operation of the reticle stage 3 via the drive device 5 on the base 4.

  The pattern image formed on the reticle R is projected onto each shot area on the wafer W as the substrate to be exposed through the projection optical system PL. On the wafer W, a plurality of shot areas are arranged in a state of being separated from each other by street lines (not shown). Alignment marks AM1 and AM2 as position measurement marks (specific patterns) are formed on the street line. In the present embodiment, the alignment marks AM1 and AM2 are of a line and space type for one-dimensional measurement. The alignment mark AM1 is for position measurement in the X-axis direction, and the alignment mark AM2 is for position measurement in the Y-axis direction. The alignment mark AM1 is formed of, for example, three rectangular mark elements am1, am2, and am3 arranged in parallel with each other at a predetermined interval as shown in FIG. 2A. Each mark element am1 , Am2 and am3 are formed from grooves having a rectangular cross section as shown in the cross-sectional view taken along the line aa in FIG. Similarly, the alignment mark AM2 is formed from a plurality of parallel mark elements arranged at predetermined intervals, and each mark element is formed from a groove having a rectangular cross section although not shown. In this embodiment, the alignment marks AM1 and AM2 are formed from three rectangular mark elements am1, am2, and am3 arranged in parallel with each other at a predetermined interval as shown in FIG. Although the one for one-dimensional measurement is used, for example, the one for two-dimensional measurement as shown in (C) or (D) of the figure may be used.

  The wafer W is placed on the wafer stage 7 via the wafer holder 6. The wafer stage 7 is an XY stage that two-dimensionally positions the wafer W in a plane perpendicular to the optical axis of the projection optical system PL, and the wafer W is placed in a direction parallel to the optical axis of the projection optical system PL (Z-axis direction). A Z stage for positioning, a stage for minutely rotating the wafer W, and the like are included.

  A movable mirror 8 is fixed on the upper surface of the wafer stage 7, and a laser interferometer 9 is disposed so as to face the movable mirror 8. Although not shown in detail, the movable mirror 8 includes a plane mirror having a reflecting surface perpendicular to the X axis and a plane mirror having a reflecting surface perpendicular to the Y axis. The laser interferometer 9 includes two X-axis laser interferometers that irradiate the moving mirror 8 with a laser beam along the X axis and a Y-axis that irradiates the movable mirror 8 with a laser beam along the Y axis. The laser interferometer. The X coordinate and Y coordinate of the wafer stage 7 are measured by one laser interferometer for the X axis and one laser interferometer for the Y axis. Further, the rotation angle of the wafer stage 7 is measured by the difference between the measurement values of the two X-axis laser interferometers.

  Information on the X coordinate, the Y coordinate, and the rotation angle measured by the laser interferometer 9 is sent to the main control system 10, and the main control system 10 monitors the sent coordinates and drives the wafer stage 7 via the drive system 11. Control the positioning operation. Although not shown, an interferometer system similar to that on the wafer side is also provided on the reticle side.

  An FIA sensor 12, which is a wafer position measurement system, is disposed on the side of the projection optical system PL. In this FIA sensor 12, illumination light IL from a light source 13 such as a halogen lamp that generates float band light is converted into parallel light by a collimator lens 14, reflected by a half mirror 15, and further reflected by a mirror 19. Then, the light reaches the objective lens 20 and is focused by the objective lens 20 to illuminate the alignment marks AM1 and AM2 on the wafer W. When the illumination light IL illuminates the alignment marks AM 1 and AM 2, the reflected light from the alignment marks AM 1 and AM 2 is reflected by the mirror 19 through the objective lens 20 and then enters the mirror 21 through the half mirror 15. The reflected light incident on the mirror 21 has its optical axis bent, proceeds in the Z-axis direction, and is imaged on the index plate 23 by the lens system 22. Although not shown, the indicator plate 23 is formed with an indicator mark (not shown) serving as a reference when measuring position information of the alignment marks AM1 and AM2. The index plate 23 is optically conjugate with the wafer W by the objective lens 20 and the lens system 22. The alignment marks AM1 and AM2 and the index mark on the wafer W are imaged on the imaging surface 26c of the CCD camera 26 as imaging means via the relay lens systems 24 and 25. In this embodiment, the indicator plate 23 is illuminated by the reflected light from the wafer W. However, the indicator plate 23 is illuminated by an illumination system different from the alignment marks AM1 and AM2 (indicator plate independent illumination method). You may do it.

  On the reticle R, a VRA sensor 40 that is a reticle position measurement system is arranged. In this VRA sensor 40, illumination light for exposure is used, and the light beam of the illumination light for detection is branched from the illumination optical system 1 through a light transmission optical system 47 such as an optical fiber to the VRA optical system 45. Led. The light beam of the detection illumination light is irradiated onto the reticle alignment mark RM formed on the reticle R via the mirror 44 and reaches the reference index plate FMB via the projection optical system PL. Thereafter, the luminous flux follows the reverse optical path from the reference indicator plate FMB to reach the VRA optical system 45 and is connected to the imaging surface of the CCD camera 46 as an imaging means via the imaging optical system in the VRA optical system 45. Image. At the time of this VRA measurement, the reference index plate FMB formed on the wafer stage 7 has a region where a mark on which the relative positional relationship with the mark formed on the reticle is measured is formed as a base. Used (positioned).

  The CCD cameras 26 and 46 convert an optical image formed on the imaging surface into an electric signal. FIG. 3 shows an image pickup surface of the CCD camera 26 as an example, and light receiving elements for receiving incident light and converting them into electric signals are arranged on the image pickup surface. The CCD cameras 26 and 46 sequentially scan the light receiving elements arranged on the imaging surface, thereby converting an image incident on the imaging surface into an image signal. The imaging surface is divided into a plurality of regions (14 from r1 to r14 in FIG. 4) in the non-scanning direction. For example, the light receiving elements arranged in the region r1 are sequentially scanned in the measurement direction, and the region r1 is scanned. When the scanning of all the arranged light receiving elements is completed, the light receiving elements arranged in the region r2 are sequentially scanned in the measurement direction. Similarly, the light receiving elements arranged in the regions r3 to r14 are sequentially scanned in the measurement direction. Image signals output from the CCD cameras 26 and 46 (image signals obtained by scanning the regions r1 to r14) are sent to the position calculation unit 27.

  The position calculation unit 27 performs various signal processing on the image signals output from the CCD cameras 26 and 46 to calculate the position information of the alignment marks AM1 and AM2 and the reticle alignment mark RM, and obtains this position information. Output to the control system 10. That is, each image signal obtained by scanning each of the regions r1 to r14 is integrated in the non-scanning direction in each of the regions r1 to r14 to obtain position information of the alignment mark AM1, AM2 or the reticle alignment mark RM.

  As shown in FIG. 4, the position calculation unit 27 includes a preamplifier 30, an amplifier 31, an A / D converter 32, an image signal memory 33, a control unit 34, an AGC (automatic gain control) circuit 35, a memory 36, and a position calculation unit. 37.

  The preamplifier 30 amplifies the image signal output from the CCD cameras 26 and 46 with a preset fixed amplification factor. The preamplifier 30 reduces noise generated when an image signal is directly amplified at a high amplification factor. The amplification factor of the amplifier 31 is controlled by the AGC circuit 35, and the image signal output from the preamplifier 30 is amplified (gain adjustment) to an image signal in a voltage range optimum for signal processing by the A / D converter 32. The A / D converter 32 performs A / D conversion processing on the image signal amplified by the amplifier 31 to convert it into a digital signal. The image signal memory 33 stores the digitized image signal.

  The control unit 34 reads the amplification factor and offset value of the amplifier 31 stored in the memory 36 based on the control signal from the main control unit 10, and performs the AGC so that the amplification factor and offset value read by the amplifier 31 are obtained. The circuit 35 is controlled. The control unit 34 also outputs a control signal that causes the position calculation unit 37 to calculate the position information of the alignment marks AM1 and AM2 and the reticle alignment mark RM based on the image signal stored in the image signal memory 33. .

  The main control system 10 drives the wafer stage 7 via the drive system 11 based on the position information of the alignment marks AM1 and AM2 from the position calculation unit 27, and projects the shot area set on the wafer W into the projection optical system. Adjust to the exposure position of PL. Further, the main control system 10 drives the reticle stage 3 via the driving device 5 on the base 4 based on the position information of the reticle alignment mark RM from the position calculation unit 27, and the reticle R is positioned. Thereafter, exposure light EL is exposed onto the reticle R, and an image of a pattern formed on the reticle R is transferred onto the wafer W to perform an exposure process.

  When measuring the positional information of the alignment marks AM1 and AM2 on the wafer W, sufficient signal intensity for measuring the positional information of the marks with high accuracy is obtained by reflected light from other than the alignment marks AM1 and AM2. In order to cope with this, the AGC circuit 35 controls the amplification factor of the amplifier 31 as described above to amplify the image signal in the voltage range optimum for signal processing by the A / D converter 32. Yes. However, in the signals (image signals) detected by the CCD camera 26, in addition to the detection signals (image signals) of the alignment marks AM1 and AM2, a false signal having a larger contrast than the alignment marks AM1 and AM2 is included. In this case, there is a disadvantage that AGC is not applied to the detection signals of the original alignment marks AM1 and AM2, but AGC is applied to the false signal. In order to solve this problem, in the present embodiment, the position calculation unit 27 and the like are controlled by the main control unit 10 based on the position measurement program having the contents shown in FIGS.

  Hereinafter, the contents of the position measurement program shown in FIGS. 6 to 9 will be described in detail.

  The position measurement program is recorded on the recording medium 50 that can be read by the main control unit 10, and the necessary position measurement program is read from the recording medium 50 based on a command from the main control unit 10, and this read The position calculation unit 27 and the like are controlled based on the position measurement program. As this recording medium 50, for example, a CD-ROM or the like is used.

  In the position measurement program shown in FIG. 6, first, the FIA sensor 12 is driven in step 601, and the illumination for detection is applied to the area where the alignment mark AM <b> 1 (or AM <b> 2) as the specific pattern is formed. The light beam is irradiated and the reflected light is imaged on the image surface of the CCD camera 26 to obtain an image signal as a measurement signal. Next, in step 602, the difference D (see FIG. 5) between the maximum value and the minimum value from the obtained image signal is equal to or smaller than a predetermined value, and the state where the difference D is equal to or smaller than the predetermined value is equal to or larger than a predetermined size in the measurement direction. A continuous specific section (between a and b in FIG. 5) is extracted. That is, in the obtained image signal, a portion where the signal waveform is substantially flat is an area of the alignment mark AM1 (or AM2) (“Mark Size” in FIG. 5), and X on the design value of the mark AM1. A section that is longer than (the length in the direction) is extracted (between “a” and “b” in FIG. 5). Next, in step 603, the extracted signal portion is amplified (gain adjustment) by the amplifier 31 to obtain an image signal in a voltage range optimum for signal processing by the A / D converter 32, and then by the A / D converter 32. In step 604, based on the design value of the alignment mark AM1 (or AM2), whether the image signal corresponds to the alignment mark AM1 (or AM2) (whether the alignment mark AM1 (or AM2) exists) ). When it is determined as an image signal of the alignment mark AM1 (or AM2), it is stored in the image signal memory 33. The controller 34 causes the position calculator 37 to calculate the position information of the alignment mark AM1 (or AM2) based on the image signal stored in the image signal memory 33. In step 605, the main control system 10 The wafer stage 7 is driven via the drive system 11 based on the position information of the alignment mark AM1 (or AM2) from the position calculation unit 27, and the shot area set on the wafer W is exposed to the projection optical system PL. Align to position (execute alignment of wafer W).

  If it is determined in step 604 that the image signal does not correspond to the alignment mark AM1 (or AM2), the process returns to step 602. In step 602, the difference D (see FIG. 5) between the maximum value and the minimum value in the section different from the previous specific section is a predetermined value or less, and the difference D is a predetermined value. A section in which the following state continues for a predetermined size or more in the measurement direction (between “second” ab in FIG. 5) is extracted, and steps 603 and 604 are repeated. That is, steps 602, 603, and 604 are repeated until the image signal (measurement signal) of the alignment mark AM1 (or AM2) is found.

  FIG. 5 illustrates the contents of the position measurement program of FIG. 6, where the left end of the region where the alignment mark AM1 (or AM2) (see FIG. 1) of the wafer W is expected to be formed is a, and the right end Is b. In the case shown on the left side of FIG. 5, the left end a is fixed, while the right end b is extended rightward, and the difference D between the maximum value and the minimum value of the signal in the region between a and b is less than or equal to a predetermined value. A region is searched, and it is confirmed (determined) whether or not ab is larger than the region (Mark Size) of the alignment mark AM1 (or AM2). When it is larger, AGC is applied to the region between a and b. In the case shown on the left side, the waveform of the signal after AGC is applied has only two peaks and does not correspond to the alignment mark AM1 (see FIG. 2A), so that the signal search has failed. Further, in order to search for an image signal corresponding to the alignment mark AM1 (or AM2), the left end a and the right end b are moved rightward (scanned on the image signal), and the same operation is repeated. At this time, it is performed while leaving the previously acquired signal. For example, by shifting the image signal that fits between a and b to the right by a predetermined number of pixels (for example, 1 pixel) of the CCD, the signal that fits the previous a and b regions and the current a and b regions are changed. Part of the fitted signal overlaps. In the case shown on the right side of FIG. 5, the left end a and the right end b are moved in this way, and the difference D between the maximum value and the minimum value of the signal in the region between a and b is not more than a predetermined value, A state in which the region between a and b is larger than the region (Mark Size) of the alignment mark AM1 (or AM2) (between “n” ab in FIG. 5) and AGC is applied to the signal in this region Is shown. The waveform of the signal after the AGC is applied has three peaks and corresponds to the alignment mark AM1 (see FIG. 2A), so that the signal search is successful.

  Next, the contents of the position measurement program shown in FIG. 7 will be described. In FIG. 7, the difference D (see FIG. 5) between the maximum value and the minimum value of the image signal is equal to or smaller than a predetermined value, and a signal in which the difference D is equal to or smaller than the predetermined value continues for a predetermined size or more in the measurement direction. This shows processing when there are a plurality of sections. In other words, the example shown in FIG. 7 is obtained after performing a certain amount of ab search rather than applying AGC each time one ab is specified. AGC is applied between a and b. In this case, in the same manner as in step 601 described above in step 701, the region of the wafer W that is the measurement target region, where the alignment mark AM1 (or AM2) is formed, is irradiated with the detection illumination light beam, and the reflected light is irradiated. An image signal as a measurement signal is obtained by forming an image on the image surface of the CCD camera 26. Next, in step 702, as in step 602 described above, a specific section in which the portion where the signal waveform is substantially flat continues from the obtained image signal more than the region (Mark Size) of the alignment mark AM1 (or AM2) is extracted. . Next, in step 703, it is determined whether or not there are a plurality of specific sections. When there are a plurality of specific sections, the process proceeds to step 704, and when only one specific section exists, the process proceeds to step 705.

  In step 704, each of the extracted signal portions is amplified (gain adjustment) by the amplifier 31 to obtain an image signal in a voltage range optimal for signal processing by the A / D converter 32, and then the A / D converter. Digitize by 32. Next, in step 706, it is determined whether each image signal corresponds to the alignment mark AM1 (or AM2). Among the plurality of image signals, the image signal determined to correspond to the alignment mark AM1 (or AM2) is stored in the image signal memory 33, and the position information is calculated by the position calculation unit 37. Next, in step 707, the main control system 10 drives the wafer stage 7 via the drive system 11 based on the position information of the alignment mark AM 1 (or AM 2) from the position calculation unit 27 and sets it on the wafer W. The shot area thus aligned is aligned with the exposure position of the projection optical system PL (alignment of the wafer W is executed).

  If it is determined in step 706 that each image signal does not correspond to the alignment mark AM1 (or AM2), the process returns to step 702, which is a section different from the previous specific section, and is the maximum from the obtained image signal. A section in which the difference D between the value and the minimum value (see FIG. 5) is equal to or smaller than a predetermined value and the state where the difference D is equal to or smaller than the predetermined value continues for a predetermined size or more in the measurement direction is extracted, and Steps 703 and 704706 are repeated. .

  When the process proceeds to step 705, the extracted signal portion is amplified (gain adjustment) by the amplifier 31 to obtain an image signal in a voltage range optimum for signal processing by the A / D converter 32, and then the A / D converter. In step 706, it is determined whether the image signal corresponds to the alignment mark AM1 (or AM2). When it is determined that the image signal corresponds to the alignment mark AM1 (or AM2), the image signal is stored in the image signal memory 33. The position information is calculated by the position calculation unit 37. Next, in step 707, the wafer W is aligned based on the position information of the alignment mark AM1 (or AM2).

  Next, the contents of the position measurement program shown in FIG. 8 will be described. 8 differs from the case shown in FIG. 6 in that the extracted signal portion is amplified (gain adjustment) and offset adjustment is performed in step 803, and steps 801, 802, 804, and 805 are respectively performed in step 601. , 602, 604, and 605. In the offset adjustment performed in step 803, an intermediate value between the maximum value (maximum value) and the minimum value (minimum value) of the image signal with respect to the zero signal level is adjusted.

  Next, the contents of the position measurement program shown in FIG. 9 will be described. In FIG. 9, the search measurement for finding the image signal (measurement signal) of the alignment mark AM <b> 1 (or AM <b> 2) can cope with an error, and between steps 601 and 602 in FIG. 6. Whether the entire image signal obtained in step 601 is amplified (gain adjustment) by the amplifier 31 and digitized by the A / D converter 32, and then whether or not this image signal corresponds to the alignment mark AM1 (or AM2). If not, the same processing as in steps 602, 603, 604, and 605 in FIG. 6 is performed. If applicable, position information is extracted from the amplified image signal and alignment is executed.

  That is, in step 901, an image signal is obtained by performing the same operation as in step 601 of FIG. 6 described above, and then the entire image signal obtained in step 902 is amplified (gain adjustment) by the amplifier 31 and A / D converted. After digitization by the device 32, it is determined in step 903 whether the mark corresponds to the alignment mark AM1 (or AM2). If it is determined that it corresponds to the alignment mark AM1 (or AM2), the process proceeds to step 907, and the same operation as in step 605 described above is performed to perform alignment of the wafer W.

  When the alignment mark AM1 (or AM2) does not correspond, the process proceeds to step 904, and the same operation as step 602 described above is performed, and the portion of the image signal having a substantially flat signal waveform is the alignment mark AM1 ( Alternatively, a section continuous beyond the area of AM2) is extracted. Next, in step 905, the same operation as in step 603 described above is performed, the extracted signal portion is amplified (gain adjustment), digitized by the A / D converter 32, and in step 906, similar to step 604 described above, Based on the design value of the alignment mark AM1 (or AM2), it is determined whether the image signal corresponds to the alignment mark AM1 (or AM2) (whether the alignment mark AM1 (or AM2) exists), and step 907. Then, the alignment of the wafer W is executed in the same manner as in step 605 described above.

  If it is determined in step 906 that the image signal does not correspond to the alignment mark AM1 (or AM2), the process returns to step 904. In step 904, a section different from the section extracted last time is extracted, and steps 905 and 906 are repeated.

  In the follow chart shown in FIG. 9, the processing from step 702 to 706 or the processing from step 802 to 804 may be executed instead of the processing from step 904 to 906.

  In the above-described embodiment, the case has been described in which image processing is performed on the image signals of the optical images of the alignment marks AM1 and AM2 captured by the CCD camera 26 using the FIA sensor 12 to measure the position information of the alignment marks AM1 and AM2. Without being limited thereto, the present invention can also be applied to, for example, an LSA type alignment sensor.

  In the above embodiment, the case where the position information of the alignment marks AM1 and AM2 formed on the wafer W is measured has been described. However, the present invention is also applicable to the case where the position information of the mark RM formed on the reticle R is measured. I can do it.

BRIEF DESCRIPTION OF THE DRAWINGS It is a whole block diagram which shows 1st embodiment of the position measuring apparatus (FIA sensor sensor VRA sensor) of this invention and the exposure apparatus equipped with this position measuring apparatus. (A) is a top view which shows an example of the alignment mark as a specific pattern used as the predetermined reference | standard in the case of position measurement. FIG. 2B is a cross-sectional view taken along line aa in FIG. (C) is a plan view of another alignment mark. (D) is a plan view of another alignment mark. 2 is an explanatory diagram showing an imaging surface of a CCD camera 26. FIG. It is a block diagram which shows the outline of the position calculation unit in FIG. It is explanatory drawing explaining the process which searches the measurement signal of the alignment mark buried in the false signal. It is a flowchart which shows one embodiment of the position measurement program of this invention. It is a flowchart which shows another embodiment of the position measurement program of this invention. It is a flowchart which shows another embodiment of the position measurement program of this invention. It is a flowchart which shows another embodiment of the position measurement program of this invention.

Explanation of symbols

10 Main control system 12 FIA sensor (position measuring device)
26 CCD camera (photoelectric detection means)
46 CCD camera (photoelectric detection means)
27 Position calculation unit 31 Amplifier 35 AGC circuit 34 Control unit 37 Position calculation unit 40 VRA sensor (position measurement device)
50 Recording medium AM1 Alignment mark AM3 Alignment mark RM Reticle alignment mark

Claims (11)

A position measurement method for measuring a specific pattern provided on a measurement object and having a predetermined size on a design value with respect to a predetermined measurement direction,
A first step of photoelectrically detecting a measurement area including the specific pattern on the measurement object to obtain a measurement signal;
Among the measurement signals obtained in the first step, the difference between the maximum value and the minimum value of the measurement signal is equal to or less than a predetermined value, and the state where the difference is equal to or less than the predetermined value is the predetermined value in the measurement direction. A second step of extracting a specific section that is continuous in size or more;
A third step of performing gain adjustment on the signal in the specific section extracted in the second step;
A position measurement method characterized by comprising: A fourth step of identifying presence / absence of the specific pattern based on a design value of the specific pattern from a signal in the specific section after gain adjustment is performed in the third step;
If it is determined in the fourth step that the specific pattern does not exist in the specific section, the process returns to the second step and is a section different from the specific section, and the difference is not more than a predetermined value. The position measuring method according to claim 1, wherein the third and fourth steps are repeated after a further section in which the state continues in the measurement direction by the predetermined size or more is extracted from the measurement signal. . In the second step, when there are a plurality of sections satisfying the condition to be the specific section in the measurement signal, all the plurality of specific sections are extracted,
In the third step, the gain adjustment is performed on the signals of the plurality of specific sections extracted in the second step, and
The method further comprises a fourth step of identifying presence / absence of the specific pattern based on a design value of the specific pattern from signals in the plurality of specific sections after gain adjustment is performed in the third step. The position measurement method according to claim 1.   The position measurement method according to claim 2 or 3, wherein in the third step, offset adjustment is also performed on the extracted signal of the section. After the first step and before the second step, the entire measurement signal obtained in the first step is subjected to gain adjustment, and the gain adjustment is performed based on the signal after the gain adjustment. A fifth step of identifying the presence or absence of the specific pattern;
5. The position measurement method according to claim 1, wherein when the presence of the specific pattern is not identified in the fifth step, the process proceeds to the processing after the second step. An exposure method for transferring and exposing a pattern onto a substrate to be exposed,
By the position measurement method according to any one of claims 1 to 5, position information relating to the substrate to be exposed is obtained,
An exposure method comprising adjusting a positional relationship between the substrate to be exposed and the pattern based on the position information. A position measurement device that is provided on a measurement object and measures a specific pattern having a predetermined size on a design value with respect to a predetermined measurement direction,
Photoelectric detection means for photoelectrically detecting a measurement area including the specific pattern on the measurement object and obtaining a measurement signal;
Among the measurement signals obtained from the photoelectric detection means, the difference between the maximum value and the minimum value of the measurement signal is equal to or less than a predetermined value, and the state where the difference is equal to or less than the predetermined value is the predetermined value in the measurement direction. Extraction means for extracting a specific section that is continuous in size or more;
Signal processing means for performing gain adjustment on the signal in the specific section extracted by the extracting means;
A position measuring device comprising: From the signal in the specific section after the gain adjustment by the signal processing means, further comprising identification means for identifying the presence or absence of the specific pattern based on the design value of the specific pattern,
When the identification means identifies that the specific pattern does not exist in the specific section, the specific section is different from the specific section, and the difference is equal to or less than a predetermined value and the state is the predetermined direction in the measurement direction. The position according to claim 7, wherein after the further section that is larger than the size is extracted from the measurement signal by the extraction means, the processing by the signal processing means and the identification means is repeatedly executed. Measuring device. An exposure apparatus for transferring and exposing a pattern onto a substrate to be exposed,
By the position measuring device according to claim 7 or 8, position information relating to the substrate to be exposed is obtained,
An exposure apparatus that adjusts a positional relationship between the substrate to be exposed and the pattern based on the position information. A position measurement program for measuring a specific pattern provided on a measurement object and having a predetermined size on a design value with respect to a predetermined measurement direction,
A first step of causing a photoelectric detection means to photoelectrically detect a measurement area including the specific pattern on the measurement object, and outputting the measurement signal;
Among the measurement signals obtained in the first step, the difference between the maximum value and the minimum value of the measurement signal is equal to or less than a predetermined value, and the state where the difference is equal to or less than the predetermined value is the predetermined value in the measurement direction. A second step of causing the extraction means to extract a specific section that is continuous in size or more;
A third step of causing a signal processing means to perform gain adjustment on the signal in the specific section extracted in the second step;
Is executed by the photoelectric detection means, the extraction means, and the signal processing means, respectively.   A computer-readable recording medium in which the position measurement program according to claim 10 is stored.

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