JP2006071440A - Position sensor, exposure system equipped with the position sensor, and exposure technique using the position sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a position sensor and the like for enhancing the throughput properties of alignment, maintaining measuring precision. <P>SOLUTION: In a CCD camera 61 of an AF sensor 60 as a two-dimensional CCD camera with the 96 lines in the non-measuring direction and the pixels (96×1024) of 1024 columns in the measurement direction, a method for processing the input measured signals contains a TDI measuring mode (cf. the step S101 reference) repeating sequential addition of the charges (signals), corresponding to the light quantity accumulated in the pixels on each line, on one by one line, at each predetermined time (the charges are transferred to added repeately) and a WA measuring mode (cf. the step S103) adding the charges (signals) to the light quantity accumulated in pixels on each line an amount corresponding to 96 lines at a time (charges are transmitted at one time to add), and switches this TDI measuring mode and the WA measuring mode fitting to the measuring conditions. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a position measurement apparatus that maintains measurement accuracy and improves throughput when imaging a position measurement pattern and measures the position of the position measurement pattern, an exposure apparatus including the position measurement apparatus, and The present invention relates to an exposure method using this position measuring apparatus.

  When a semiconductor device or a liquid crystal display device is manufactured using a lithography technique, an exposure illumination light (exposure light) is irradiated onto a reticle as a mask on which a pattern is formed, and an image of the pattern is projected onto a projection optical system. An exposure apparatus that performs projection exposure on a photosensitive substrate such as a semiconductor wafer or a glass template coated with a photosensitive agent such as a photoresist is used.

  In such an exposure apparatus, in general, circuit patterns drawn on a plurality of different reticles are sequentially overlapped on the wafer for exposure. Therefore, prior to exposure, the positional relationship of the reticle with respect to the wafer stage coordinate system is obtained with high accuracy. And the wafer (circuit pattern in each shot area of the wafer) need to be accurately aligned. 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.

  As one of the alignment sensors, for example, the alignment mark formed on the wafer is irradiated with broadband light having a long wavelength bandwidth using a halogen lamp as a light source (light in a band where the photosensitive agent is not exposed). An FIA (Field Image Alignment) sensor, which is a type of wafer alignment sensor, that captures reflected light from a mark with a CCD camera and performs image processing on the image signal to measure the position of the alignment mark is known.

  When the alignment mark is imaged by this FIA sensor, focus measurement and focusing operation are performed so that the reflected light image of the alignment mark is formed on the imaging surface of the CCD camera (the light receiving surface of the light receiving element) in advance. There is a need. This focus measurement and focusing operation is performed by using an alignment auto focus sensor (ALG-AF sensor: AF sensor) built in the FIA sensor to form the position of the light receiving surface of the light receiving element and the reflected light from the wafer surface. The amount of deviation in the focus direction from the position is measured, and the wafer stage is moved in the Z direction (height direction: focus direction) so that the amount of deviation becomes zero.

  As the AF sensor, for example, a light receiving element (CCD camera) having 96 (line) × 1024 (column) pixels and processing a measurement signal by TDI (Time Delay Integration) operation is employed. . In this AF sensor, in order to measure the amount of deviation, a focus measurement mark image (AF mark image) projected in the vicinity of the alignment mark on the wafer is imaged and measured, and this image pickup signal is subjected to image processing as a measurement signal. ing. Specifically, 1024 columns in the longitudinal direction are used for measuring the image position, and 96 lines in the non-measurement direction are used for sequentially integrating the signals, and accumulated in the pixels on each line. Charges (signals) are sequentially added to the next stage line at regular intervals, and finally all signals are added on one line (with a signal strength of 96 times per line). The amount of deviation is measured by image processing.

  By the way, in enhanced global alignment (EGA) using a statistical method in wafer alignment by the FIA sensor, a predetermined plurality of alignment marks formed in the vicinity of each shot area on the wafer are used. Select the alignment mark of the shot area, sequentially measure the position of the selected alignment mark to determine the residual rotation error of the wafer, linear expansion / contraction of the wafer, offset of the wafer, etc., and position all the shot areas of the wafer, In this case, if all the alignment marks to be measured are not measured in the same focus state, an error may occur in the measurement result of the alignment mark position. In general, the height distribution around the alignment mark is expected to be substantially the same in any shot area in the wafer, but there are actually variations. Further, the wafer stage movement path in the two-dimensional plane (XY plane) until the alignment mark enters the measurement field of view of the FIA sensor differs for each shot area. Therefore, measurement and adjustment of the AF slit image projected on the wafer image by the AF sensor while the alignment mark is in the measurement (detection) field of view of the FIA sensor so that the measurement conditions of the FIA sensor are constant between the alignment marks. It is desirable to perform (focus measurement, focusing operation). That is, for each alignment mark, it is desirable to perform the focus measurement and focusing operation immediately before performing the alignment measurement after moving the wafer stage in the XY direction so that the alignment mark falls within the measurement field of view of the FIA sensor.

  However, in such a case, measuring the AF slit image by the TDI operation (TDI mode measurement) described above significantly reduces the throughput. That is, in order to obtain an ideal measurement signal, it is necessary to perform measurement while the alignment mark is in the measurement field of view of the FIA sensor, so the wafer stage on which the wafer is mounted is maintained in the XY direction. In this stop state, the charges (signals) accumulated in the pixels of the light receiving element of the AF sensor are sequentially added to the next stage line at regular intervals, and a total of 96 stages are sequentially added to the AF slit. TDI mode measurement for measuring the position of an image takes time, and performing this for each measurement of a plurality of alignment marks takes time for wafer alignment, resulting in a decrease in throughput of wafer alignment.

  The present invention has been made in view of such circumstances, and a position measuring apparatus that maintains the measurement accuracy and improves the throughput of wafer alignment, an exposure apparatus including the position measuring apparatus, and the position measuring apparatus. An object is to provide an exposure method to be used.

  The position measuring apparatus according to claim 1 of the present invention that achieves the above object is provided in the two-dimensional plane of an object (wafer W) placed on a stage (wafer stage WST) that moves in the two-dimensional plane. Is a position measurement device that measures a position (XY position) at a position where the position is measured by an FIA sensor such as an alignment mark or an EGA measurement mark on the wafer W formed on the object. The measurement pattern) is irradiated with a measurement beam (broadband light from the FIA sensor), and the pattern beam (reflected light of the position measurement pattern) generated from the position measurement pattern upon receiving the measurement beam is received by the light receiving element (FIA). A pattern detection sensor (FIA) which receives light by a CCD camera 43, 44) for fine measurement of the sensor and outputs a photoelectric conversion signal according to the amount of light received. Sensor 30), and a focus state detection sensor (AF sensor 60) for measuring a shift amount in the focus direction (Z-axis direction) between the position of the light receiving surface of the light receiving element and the image forming position of the pattern beam. The focus state detection sensor can be used in a plurality of measurement modes (TDI measurement mode, WA measurement mode), and depending on the use conditions when the focus state sensor is used for measurement, It is characterized by being switched to an arbitrary measurement mode among a plurality of measurement modes.

  2. The position measurement apparatus according to claim 1, wherein the use condition includes, for example, a first measurement condition for performing detection by the focus state detection sensor in parallel with a movement operation of the stage in the two-dimensional plane, and the stage. And a second measurement condition for performing detection by the focus state detection sensor while the vehicle is stationary (claim 2).

  Under the second measurement condition, it is desirable that the position measurement pattern is positioned within a detection visual field of the pattern detection sensor.

  The focus state detection sensor is a sensor that measures the amount of deviation by detecting a plurality of line images projected on the object and having different line widths, and the use condition is a condition among the plurality of line images. You may make it include the 1st measurement condition which detects the line image whose line width is larger than a predetermined value, and the 2nd measurement condition which detects the line image whose said line width is below the said predetermined value (Claim 4).

  The use condition may include a first measurement condition that is allowed with an accuracy of a predetermined level or less as a detection accuracy of the deviation amount, and a second measurement condition that requires an accuracy of the predetermined level or more. Item 5).

The focus state detection sensor includes pixels of n lines × m columns (n and m are natural numbers of 2 or more), and the measurement mode outputs a signal corresponding to the amount of light accumulated in the pixels in each line. A first measurement mode (TDI (Time Delay Integration) measurement mode) in which addition is sequentially performed by predetermined lines every predetermined time, and a signal corresponding to the amount of light accumulated in the pixels of each line is added for n lines at a time. 2 Measurement mode (WA (Wide
It is preferable that the first measurement mode is set when the first measurement condition is set, and the second measurement mode is set when the second measurement condition is set (Claim 6).

  An exposure apparatus according to claim 7, which achieves the above object, illuminates a mask pattern (pattern formed on a reticle R) and mounts an image of the mask pattern on a stage (wafer stage WST). An exposure apparatus for transferring onto a substrate to be exposed (wafer W), comprising the position measuring device according to any one of claims 1 to 6, wherein the position measurement is formed on the substrate to be exposed. An image of the mask pattern is transferred onto the positioned substrate to be exposed based on the result of measuring the pattern for use with the position measuring device.

  8. The exposure apparatus according to claim 7, wherein the focus state detection sensor provided in the position measuring device measures the amount of deviation by detecting a plurality of line images projected on the substrate to be exposed. The longitudinal direction of each of the plurality of line images projected onto the substrate to be exposed (the axis of the line image along the longitudinal direction) is a region to which the image of the mask pattern on the substrate to be exposed is transferred ( It is desirable to incline 10 to 35 degrees or 55 to 80 degrees with respect to the street lines between the shot areas.

  The exposure method according to claim 9 of the present invention, which achieves the above object, illuminates a mask pattern (pattern formed on a reticle R) and mounts an image of the mask pattern on a stage (wafer stage WST). A position measuring apparatus according to claim 1, wherein the position measuring pattern is formed on the substrate to be exposed, wherein the position measuring pattern is transferred onto the substrate to be exposed (wafer W). And an image of the mask pattern is transferred onto the substrate to be exposed positioned based on the result of measurement using the position measuring device.

  According to the position measuring apparatus of the first aspect of the present invention, the focus state detection sensor can be used in a plurality of measurement modes (TDI measurement mode, WA measurement mode), and the focus state sensor is used for measurement. Depending on the usage conditions at the time of measurement, it is set to be switched to an arbitrary measurement mode among the plurality of measurement modes. Therefore, the measurement is performed immediately before the position detection pattern measurement (for example, EGA measurement) by the pattern detection sensor. By switching the measurement mode of the focus state detection sensor from the TDI measurement mode to the WA measurement mode in which the time required for measurement is shorter than the TDI mode, the position of the light receiving surface of the light receiving element and the pattern beam are changed. The amount of deviation in the focus direction from the image forming position can be measured in a short time, resulting in measurement accuracy Maintain and shorten the time measured by the pattern detection sensor, it is possible to result improve the throughput properties.

  According to the position measurement apparatus of the second aspect, the use condition is the first measurement condition in which detection is performed by the focus state detection sensor in parallel with the movement of the stage in the two-dimensional plane, and the focus is set while the stage is stationary. Since the second measurement condition for detecting by the state detection sensor is included, for example, when measuring the average height of the object surface, the measurement is performed in parallel with the movement operation of the stage in the two-dimensional plane as the first measurement condition. For example, in focus measurement performed before EGA measurement, measurement can be performed while the stage is stationary as the second measurement condition, and in any case, measurement can be performed in an optimum state.

  According to the position measuring apparatus of the third aspect, since the position measurement pattern is positioned within the detection visual field of the pattern detection sensor under the second measurement condition, the pattern detection sensor is in focus. Each position measurement pattern can be measured. For example, EGA measurement can be performed in an ideal state.

  According to the position measuring apparatus of the fourth aspect, since the focus state detection sensor measures the amount of deviation by detecting a plurality of line images having different line widths projected on the object, one line A first measurement condition for detecting a line image having a smaller measurement error than the case of measuring an image, having measurement reliability, and having a line width larger than a predetermined value among a plurality of line images; The second measurement condition for detecting a line image whose line width is less than or equal to the predetermined value is included. Therefore, the average height of the object surface can be measured by detecting a line image whose line width is larger than the predetermined value. For example, focus measurement immediately before EGA measurement can be performed by detecting a line image having a line width of a predetermined value or less.

  According to the position measuring apparatus of the fifth aspect, the usage condition is the first measurement condition that is allowed with an accuracy of a predetermined level or less as the detection accuracy of the deviation amount, and the second that requires an accuracy of a predetermined level or more. Since the measurement conditions are included, for example, a rough average surface measurement of the object surface is performed under the first measurement conditions, and focus measurement that requires accuracy just before the EGA measurement is performed under the second measurement conditions, for example. I can do it.

According to the position measurement device of claim 6, the focus state detection sensor includes n lines × m columns of pixels, and the measurement mode outputs a signal corresponding to the amount of light accumulated in the pixels in each line for a predetermined time. A first measurement mode (TDI (Time Delay Integration) measurement mode) in which addition is sequentially performed for each predetermined line every time, and a second measurement mode in which a signal corresponding to the amount of light accumulated in the pixels of each line is added for n lines at a time. (WA (Wide
Aperture) measurement mode), and the first measurement mode is set at the first measurement condition, and the second measurement mode is set at the second measurement condition. For example, this is performed immediately before the EGA measurement. By measuring the amount of deviation in the focus direction in the second measurement mode (WA measurement mode), the measurement can be completed in a short time (1 / n time when measuring in the TDI measurement mode). For example, EGA measurement time Can be shortened.

  According to the exposure apparatus of the seventh aspect, the position measurement apparatus according to any one of the first to sixth aspects is provided, and based on the result of measuring the position measurement pattern using the position measurement apparatus. Since the mask pattern image is transferred onto the substrate to be exposed, the measurement time for the amount of deviation in the focus direction, which is performed immediately before the position measurement of the position measurement pattern, is shortened, and the throughput of the apparatus is improved. In addition, the position measurement pattern, for example, EGA measurement can be performed in a focused state (in-focus state), and as a result, the mask pattern overlay accuracy can be improved.

  According to the exposure apparatus of the eighth aspect, the focus state detection sensor measures a shift amount by detecting a plurality of line images projected on the substrate to be exposed, and thus measures one line image. There are few measurement errors compared to the case, there is measurement reliability, and each longitudinal direction of a plurality of line images projected on the substrate to be exposed is between regions where the mask pattern image on the substrate to be exposed is transferred. 10 degrees to 35 degrees or 55 degrees to 80 degrees with respect to the street line, even if a part of the line image may overlap the mask pattern image, the measurement signal deformation caused by this The amount is small, and as a result, the influence on the measurement accuracy can be reduced.

  According to the exposure method of claim 9, the position measurement pattern formed on the substrate to be exposed is measured using the position measurement device according to any one of claims 1 to 6, and this measurement is performed. Since the image of the mask pattern is transferred onto the substrate to be exposed positioned based on the result, the measurement time of the shift amount in the focus direction performed immediately before the position measurement of the position measurement pattern is shortened, and the exposure process is performed. Throughput can be improved. In addition, position measurement patterns such as EGA measurement can be performed in a focused state (in-focus state), and as a result, mask pattern overlay accuracy can be improved.

  Embodiments of a position measuring apparatus, an exposure apparatus including the position measuring apparatus, and an exposure method using the position measuring apparatus according to the present invention will be described below with reference to FIGS.

  FIG. 1 is an overall configuration diagram showing an embodiment of a position measuring apparatus (FIA (Field Image Alignment) sensor 30 and AF (Alignment Auto Focus) sensor 60) and an exposure apparatus equipped with this position measuring apparatus according to the present invention. FIG. 3 is a flowchart showing an embodiment of the exposure method of the present invention performed using the position measuring apparatus and exposure apparatus of FIG. 1, and FIG. 3 is a schematic diagram of a light transmission system of an AF sensor as a focus state detection sensor shown in FIG. 4 is a schematic diagram of a light receiving system of the AF sensor, FIG. 5 is a diagram for explaining the principle of displacement amount measurement by the AF sensor, and FIG. 6 is a circuit pattern, position measurement patterns (alignment marks AM1, AM2) and AF marks (line). FIG. 7 is a detailed view of the slit image, FIGS. 8A to 8C are detailed views of the position measurement pattern, and FIG. ) Is an explanatory diagram for explaining a reduction in signal deformation error caused by inclining the slit image by 30 degrees with respect to the street lines between the shot areas, and FIG. 9B shows a slight (3 FIG. 10 is an explanatory diagram for correcting and processing the measurement signal of the AF sensor when only tilting is performed.

  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 10 provided with a position measurement device (FIA sensor 30 and AF sensor 60) will be described as an example. The exposure apparatus 10 uses a circuit pattern as a mask pattern formed on a reticle R as a mask as an object or a substrate to be exposed through the projection optical system PL by a step-and-repeat method or a step-and-scan method. 2 is a reduction projection type exposure apparatus that sequentially exposes and transfers each shot area of the wafer W. 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, the exposure light EL emitted from the illumination optical system 11 illuminates the reticle R as a mask with a substantially uniform illuminance. The reticle R is held on a reticle stage RS, and the reticle stage RS is supported so that it can move and rotate in a two-dimensional plane (XY plane) on the base 12. A main control system 50 that controls the operation of the entire apparatus controls the operation of the reticle stage RS via the drive device 15 on the base 12.

  The image of the circuit pattern formed on the reticle R is projected onto each shot area on the wafer W via the projection optical system PL. On the wafer W, alignment marks (for position measurement) for position measurement in the X-axis direction and for position measurement in the Y-axis direction (for two-dimensional measurement), for example, as shown in FIG. Pattern) AM1 and AM2 are formed. 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 includes two sets of a plurality of (for example, three) linear mark elements (line patterns) parallel to each other and extending in the Y-axis direction, which are arranged at relatively small intervals along the X-axis direction. Each mark element is formed from a groove having a rectangular cross section. The mark elements are formed with a relatively wide interval along the X-axis direction. Similarly, for the alignment mark AM2, two sets of a plurality of (for example, three) linear mark elements extending in the X-axis direction and arranged in a relatively narrow space along the Y-axis direction, Each mark element is formed of a groove having a rectangular cross section. As the alignment marks AM1 and AM2, other than the one shown in FIG. 8A, for example, the one shown in FIG. 8B or the one shown in FIG. 8C may be used.

  Wafer W is placed on wafer stage WST via wafer holder 16. Wafer stage WST includes an XY stage 17 that two-dimensionally positions wafer W in a plane perpendicular to the optical axis of projection optical system PL, and wafer W in a direction parallel to the optical axis of projection optical system PL (Z-axis direction). Are constituted by a Z stage 18 for positioning the wafer and a stage (not shown) for rotating the wafer W slightly.

  A movable mirror 19 is fixed on wafer stage WST (XY stage 17), and a laser interferometer 20 is arranged so as to face this movable mirror 19. Although not shown in detail, the movable mirror 19 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 20 includes two X-axis laser interferometers that irradiate the moving mirror 19 along the X axis and two laser beams that irradiate the moving mirror 19 along the Y axis. It is composed of a Y-axis laser interferometer. The X coordinate and Y coordinate of wafer stage WST are measured by one laser interferometer for X axis and one laser interferometer for Y axis. Further, the rotation angle of wafer stage WST is measured by the difference between the measurement values of the two laser interferometers for the X axis.

  Information on the X coordinate, the Y coordinate, and the rotation angle measured by the laser interferometer 20 is sent to the main control system 50. The main control system 50 monitors the sent coordinates from the control unit 52 via the drive system 21. Then, the positioning operation of wafer stage WST is controlled. Although not shown, an interferometer system similar to that on the wafer side is also provided on the reticle side.

  An FIA sensor 30 is disposed on the side of the projection optical system PL. In this FIA sensor 30, illumination light IL from a light source 31 such as a halogen lamp that generates broadband light is converted into parallel light by a collimator lens 32, reflected by a half prism 33, and further reflected by a mirror 34. It reaches the objective lens 35 and is focused by the objective lens 35 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 34 through the objective lens 35, then passes through the half prism 33 and enters the mirror 36. The reflected light incident on the mirror 36 has its optical axis bent, proceeds in the Z-axis direction, and is imaged on the index plate 38 by the lens system 37. Although not shown, the indicator plate 38 is formed with an indicator mark (not shown) serving as a reference when measuring positional information of the alignment marks AM1 and AM2, and this indicator mark is an infrared light source (not shown). Illuminated by infrared light from (LED). The index plate 38 is optically conjugate with the wafer W by the objective lens 35 and the lens system 37. The reflected light image and the index mark image of the alignment marks AM1 and AM2 on the wafer W are passed through relay lens systems 39, 40, and 41 and a half prism 42, and CCD cameras 43 and 44, which are light receiving elements, and an index not shown. Each image is formed on the imaging surface of the camera (CCD). That is, a part of the light from the relay lens system 39 is reflected by the half prism 42 and the imaging surface of the CCD camera 43 which is an X-axis fine measurement CCD camera that images the alignment mark AM1 through the relay lens system 40. The other part passes through the half prism 42 and is led to the imaging surface of the CCD camera 44 which is a CCD camera for Y-axis fine measurement that images the alignment mark AM2 through the relay lens system 41.

  The CCD cameras 43 and 44 and the index camera convert an optical image formed on the imaging surface into an electrical signal (photoelectric conversion), and send this as an image signal (measurement signal) to the position calculation unit 51 of the main control system 50 ( Output).

  The position calculation unit 51 performs various signal processing on the image signals output from the CCD cameras 43 and 44 to calculate the position information of the alignment marks AM1 and AM2, and obtains the position information from the main control system 50. To the unit 52.

  The control unit 52 drives the wafer stage WST via the drive system 21 based on the position information of the alignment marks AM1 and AM2 from the position calculation unit 51, and projects the shot area set on the wafer W into the projection optical system PL. Set to the exposure position. Thereafter, the exposure light EL is exposed to the reticle R, and an image of the circuit pattern formed on the reticle R is transferred onto the wafer W to perform an exposure process.

  Next, an AF sensor (focus state detection sensor) 60 that is a characteristic part of the present invention will be described.

  The AF sensor 60 is built in the FIA sensor 30 described above, and before the measurement of the alignment marks AM1 and AM2, the position of the imaging surface (light receiving surface) of the CCD cameras 43 and 44 and the surface position of the wafer W are determined. The amount of deviation in the focus direction is measured.

  A measurement signal of the shift amount by the AF sensor 60 is sent to the control unit 52 of the main control system 50. The control unit 52 performs focusing by moving the wafer stage WST (Z stage 18) in the Z direction via the drive system 21 based on the measurement signal from the AF sensor 60.

  5A and 5B show the measurement principle of the pupil division method, and the shift in the focus direction between the position of the imaging surface of the CCD camera and the image formation position of the reflected light image from the surface of the wafer W is shown. The amount (defocus amount) is detected as a change in the interval D of the slit image SI imaged on the light receiving surface of a CCD camera which is a light receiving element of the AF sensor. From the state shown in FIG. 5A where there is no deviation, for example, as shown in FIG. 5B, when defocused in the minus (−) direction (the direction away from the light receiving surface of the CCD camera), the pupil division mirror PD Thus, the interval between the slit images divided into two is reduced from the interval D to the interval d. On the other hand, when defocusing is performed in the plus (+) direction (direction approaching the light receiving surface of the CCD camera), the interval between the slit images divided into two by the pupil division mirror PD is widened. Therefore, the amount of deviation can be measured by measuring the interval between the slit images imaged on the light receiving surface of the CCD camera.

  The AF sensor 60 used in this embodiment is an application of the principle of the pupil division method shown in FIG. 5, and instead of using the pupil division mirror PD, the AF slit image SI (see FIG. 7) differs in two directions. Then, the slit image is projected obliquely onto the wafer W, and the slit image is received by one CCD 61 (AF sensor 60).

  In the present embodiment, the AF sensor 60 includes two independent light transmission systems 63 and two light receiving systems 62, and irradiates each slit light to one point of the wafer W from two directions, while the two directions from the one point. However, the two optical axes are coupled at the position of the pupil. In this way, the two light transmission systems 63 and the two light receiving systems 62 are provided, the light is irradiated to one point from the two directions, and the reflected light is branched from the one point to the two directions. This is because even if the position is temporarily moved, the slit image can be collected and the amount of deviation can be accurately measured.

  Next, the light transmission system (illumination system) 63 and the light receiving system 62 will be described with reference to FIGS.

  As shown in FIG. 3, a part of the illumination light IL branched from the light source 31 of the FIA 30 is divided into two via ride guides 64a and 64b made of optical fibers of the light transmission unit 63, and this divided illumination The light IL passes through the multi-slits 66a and 66b via the illumination condenser lenses 65a and 65b, respectively, and becomes slit light. These two slit lights are further transmitted to the light transmission lenses 67a and 67b, and the prisms 68a, 68b, 69a, 69b, and Two slit images SI (see FIG. 7) are projected on two appropriate positions on the surface of the wafer W (see FIG. 6). Is done.

  FIG. 6 shows a slit image SI projected on the surface of the wafer W. The slit image SI is projected in the vicinity of the position measurement patterns AM1 and AM2 formed on the street line SL between the shot areas. The slit image SI is projected in the vicinity of the position measurement patterns AM1 and AM2. The focus measurement and focusing operations are performed when the position measurement patterns AM1 and AM2 are in the measurement field (detection field) of the FIA sensor 30. This is because the position measurement patterns AM1 and AM2 can be measured in a state where the FIA sensor 30 is in focus (in a focused state).

  As shown in FIG. 4, the reflected light of the two slit images SI projected on the wafer W in a superimposed manner is divided into two parts, which are the slit combining lens 70, prisms 69a, 69b, 68a, 68b, and light transmission, respectively. The optical path passes through the same optical path as the light transmission path with the lenses 67a and 67b. Further, the optical path is bent by the prisms 71a, 71b, 72a and 72b of the light receiving system 62, and is imaged and photoelectrically converted on the light receiving surface of the CCD camera 61. It becomes an imaging signal (measurement signal). This imaging signal is sent from the CCD camera 61 to the control unit 52 as described above, and the control unit 52 makes the shift amount zero from the interval between the two slit images (the shift amount in the optical axis direction). ) Is calculated.

  As shown in detail in FIG. 7, the slit image SI projected onto the wafer W is composed of a plurality of line images (seven in FIG. 7) that are parallel to each other and have different line widths. The line width of the image is larger than a predetermined value, and the line widths of the inner five line images are set to be equal to or smaller than the predetermined value.

  In rough measurement that is allowed with an accuracy of a predetermined level or less (a kind of first measurement condition to be described later), two line images having a wide line width on both sides are used, and a predetermined level of measurement is required. In measurement and the like (a kind of second measurement condition described later), five line images having a narrow inner line width are used. That is, the slit image SI can be adapted to both rough measurement and fine measurement.

  Further, as shown in FIGS. 6 and 7, the slit image SI is aligned with the street lines SL between shot areas of the wafer W or alignment marks AM1, AM2 formed along (in parallel with) the street lines SL. For example, it is inclined at an angle of 30 degrees (60 degrees). The reason why the slit image SI is largely inclined with respect to the street line SL and the like in this way is that the signal deformation error is small even when a part of the slit image SI is projected onto the pattern already transferred onto the wafer W. It is for doing so. FIG. 7 also shows a measurement visual field F when performing fine alignment measurement.

  FIG. 9 shows signal deformation caused when a part of the slit image SI overlaps the pattern already transferred to the wafer W.

  As shown in FIG. 9B, if the slit image SI is slightly inclined with respect to the street line SL or the alignment marks AM1 and AM2 (see FIGS. 6 and 7), a part of the slit image SI becomes a wafer. When overlapped with the pattern already transferred to W, the signal obtained by photoelectrically converting the slit image SI is greatly deformed as shown in FIG.

  On the other hand, as shown in FIG. 9A, the slit image SI is greatly inclined at an angle of, for example, 30 degrees (60 degrees) with respect to the street line SL or the alignment marks AM1 and AM2 (see FIGS. 6 and 7). As a result, even if a part of the slit image SI overlaps the pattern already transferred to the wafer W, the signal obtained by photoelectrically converting the slit image SI is less deformed as shown in FIG. As a result, the adverse effect on the measurement accuracy is small.

Next, the CCD camera 61 will be described. The CCD camera 61 is a two-dimensional CCD camera having 96 rows (lines) in the non-measurement direction and 1024 columns of pixels (96 × 1024) in the measurement direction. As a method of processing signals, charge (signal) corresponding to the amount of light accumulated in pixels on each line is sequentially added one line at a predetermined time (charges are sequentially transferred and repeated). TDI (Time Delay Integration) measurement mode as a measurement mode, and charge (signal) corresponding to the amount of light accumulated in the pixels on each line is added for 96 lines at a time (charge is transferred and added at once). WA (Wide as second measurement mode)
Aperture) measurement mode, and the TDI measurement mode and WA measurement mode can be switched according to the measurement conditions.

  The measurement conditions include a first measurement condition in which detection by the AF sensor 60 is performed in parallel with the movement operation in the two-dimensional plane of the XY stage 17 moving in the two-dimensional plane, and an AF sensor while the XY stage 17 is stationary. There is a second measurement condition for performing detection by 60, the TDI measurement mode that is the first measurement mode is adopted in the first measurement condition, and the WA measurement mode that is the second measurement mode is adopted in the second measurement condition. .

  In the case where the measurement (detection) of the surface of the wafer W is performed in the TDI measurement mode in parallel with the movement operation of the XY stage 17, the wafer W over the range in which the XY stage 17 has moved within the measurement time for 96 lines. The average height of the surface is measured. Therefore, the influence of the local shape of the wafer W can be suppressed.

  When measuring the approximate height of the surface of the wafer W immediately after the wafer W is loaded on the wafer stage WST, an average variation (about ± 20 μm) in the thickness of the wafer W is measured. The TDI measurement mode that can measure a wide range on average is more advantageous. For example, if the measurement time in the WA measurement mode is 1 msec and the XY stage 17 is moving at a constant speed of 500 mm / sec in the XY direction, only 0.5 mm can be averaged in the WA measurement mode. In the TDI measurement mode, it can be averaged over 48 mm. However, when the measurement is performed in the TDI measurement mode, the measurement is started after the wafer W enters the measurement region of the AF sensor 60. Therefore, the AF sensor 60 outputs the measurement result of the wafer W. The time for measuring signals for 96 lines at the shortest after the end of W enters the measurement area of the AF sensor 60 (for example, 96 mmsec has passed if the measurement time in the above-described WA measurement mode is 1 msec). After that.

  In the measurement performed while the XY stage 17 is moving, a high-accuracy measurement result cannot be obtained. Therefore, when the measurement is permitted with an accuracy of a predetermined level or less, for example, as described above, the average height of the surface of the wafer W is set. It is preferable to apply when measuring.

  When measurement (detection) is performed in the WA measurement mode while the XY stage 17 is stationary, since the XY stage 17 is stationary, high-precision measurement can be expected, and measurement at a predetermined level is required. In this case, for example, it is preferable to apply the focus measurement immediately before measuring the alignment marks AM1 and AM2 by EGA measurement.

  FIG. 10 shows a correction calculation process for the signal measured by the CCD sensor 61. The signal measured by the CCD sensor 61 includes a flare of the optical system of the AF sensor 60. When the measurement signal is sent from the CCD camera 61 to the control unit 52, the control unit 52 should remove this flare. A correction calculation process is performed. That is, the flare signal is removed from the original signal of the CCD camera 61, and at the time of this removal, correction calculation processing is performed in consideration of the sensor exposure time, and then used for position measurement (focus measurement). The flare signal is a measurement signal obtained when measurement is performed without the wafer W. The flare signal is collected in advance and stored in the memory of the control unit 52. The flare signal is read from the memory and used when correction processing is performed. Since the corrected measurement signal is divided on the pupil plane, it is divided into two signal components as shown in FIG. Since the CCD sensor 61 itself may include high-frequency noise that does not change with time as fixed noise, this fixed noise is previously collected in the same manner as the flare signal and stored in the memory of the control unit 52. When the measurement signal is subjected to correction calculation processing, it can be removed.

  Next, an embodiment of the exposure method of the present invention will be described with reference to FIG.

  In step S100, wafer W is loaded onto wafer stage WST.

  Next, in step S101, the measurement mode of the AF sensor 60 is switched to the TDI measurement mode, and the slit image SI is projected onto the surface of the wafer W while the XY stage 17 is moved in the XY plane (two-dimensional plane). Rough measurement of the image SI is performed. That is, among the slit images SI, reflected light images from two wide line images located on both sides are sequentially picked up by the CCD camera 61, and this picked-up signal (measurement signal) is arithmetically processed. A rough height distribution on the W surface (average height of the wafer W surface) is obtained. Specifically, a charge (signal) corresponding to the amount of light accumulated in each line is sequentially added one line at a predetermined time to obtain a measurement signal, and this measurement signal is sent to the control unit 52. The average height of the surface of the wafer W is obtained by performing arithmetic processing at 52.

  Next, in step S102, a control signal is sent from the control unit 52 to the drive system 21 based on the measurement result of the height distribution of the surface of the wafer W in step S101, and the drive system 21 moves the Z stage 18 in the Z-axis direction. By driving, the surface of the wafer W is drawn near the center of the effective measurement area (range) in the Z direction of the FIA sensor 30 and the AF sensor 60.

  The average height of the wafer W is obtained in step S101, and the surface of the wafer W is drawn near the center of the effective measurement area (range) of the FIA sensor 30 and the AF sensor 60 in step S102. Immediately after loading on wafer stage WST, the surface of wafer W may be out of the measurement range of the various sensors of exposure apparatus 10 by the thickness error (variation). Since the sensor 30 and the AF sensor 60 have a limited range in the Z-axis direction in which accurate measurement is possible, the surface of the wafer W is drawn near the center of the effective measurement range such as the FIA sensor 30 before measurement. This is necessary.

  Next, in step S103, the XY stage 17 is driven so that the alignment marks AM1 and AM2 on the wafer W are the imaging surface of the FIA sensor 30 (detection field of CCD cameras 43 and 44 / measurement field F when performing fine alignment measurement). The measurement mode of the AF sensor 60 is switched to the WA measurement mode. In this state, the XY stage 17 is stopped, the slit image SI is projected onto the surface of the wafer W in the vicinity of the alignment marks AM1 and AM2, which are position measurement patterns, and the slit image SI is finely measured. That is, among the slit images SI, reflected light images from five line images having a narrow line width located inside are picked up on the light receiving surface of the CCD camera 61, and an image pickup signal (measurement signal) obtained by photoelectric conversion is obtained. At this time, the signal corresponding to the amount of light accumulated in each line is not added one line at a time every predetermined time, but is added for 96 lines at a time to obtain a measurement signal. Then, this measurement signal is arithmetically processed by the control unit 52, and in the focus direction between the position of the imaging surface (light receiving surface) of the CCD cameras 43 and 44 and the imaging position of the reflected light image of the alignment marks AM1 and AM2. The shift amount is measured (focus measurement), and a control signal is sent from the control unit 52 to the drive system 21 based on the shift amount, and the drive stage 21 moves the Z stage 18 in the Z direction to perform a focusing operation.

  As described above, when processing the imaging signal in the WA measurement mode, the signal strength equivalent to that in the TDI measurement mode can be obtained in the charge transfer time for one line, so that the measurement time can be greatly shortened. . In other words, for example, when the number of pixels on the light receiving surface of the CCD camera 61 is 96, the measurement time can be theoretically reduced to 1/96 as compared with the TDI measurement mode.

  Next, in step S104, the positions of the alignment marks AM1, AM2 are measured in a focused state.

  The measurement of the positions of the alignment marks AM1 and AM2 is not performed for all the alignment marks AM1 and AM2 formed in each shot area, but some of the shot areas are selected and the selected shot area is selected. Measurement is performed for the alignment marks AM1 and AM2 in the (sample shot area) (EGA measurement).

  In the EGA measurement, measurement is performed for the alignment marks AM1 and AM2 of a plurality of target (selected) shot areas. Before the measurement of the alignment marks AM1 and AM2, the focus is always set in step S103. Measure and focus. That is, the alignment marks AM1 and AM2 are measured in the same focus state (measurement is performed so that the measurement conditions of the FIA sensor 60 are constant between the alignment marks AM1 and AM2).

  Next, in step S105, the remaining rotation error of the wafer W, linear expansion / contraction of the wafer W, offset of the wafer W, and the like are obtained based on the measurement results of the alignment marks AM1 and AM2 performed in step S104, and all shots of the wafer W are obtained. Position the area.

  Next, in step S106, an exposure process for exposing and transferring the circuit pattern on the reticle R onto the shot area of the wafer W is performed. In step S107, it is determined whether or not to continue the exposure process. Returning to S106, the exposure process is performed, and if not continued, the exposure process ends.

  As described above, according to the exposure method of the present embodiment, the measurement mode of the AF sensor 60 (CCD camera 61) is switched in accordance with the measurement conditions. For example, the surface of the wafer W performed immediately after the wafer W is loaded. When measuring the average height, measure in the TDI measurement mode, and in the focus measurement that requires measurement accuracy before the measurement of the alignment marks AM1 and AM2, perform it in the WA measurement mode. Can do. That is, measurement can be performed in an optimal measurement mode that meets the measurement conditions.

  Further, in the focus measurement performed before the measurement of the alignment marks AM1 and AM2, since the measurement is performed in the WA measurement mode, the measurement can be performed with high accuracy and in a short time, and is performed before the measurement of the alignment marks AM1 and AM2. Since focus measurement is performed for each alignment mark AM1, AM2, the number of times of measurement is very large, and the measurement time can be shortened by this focus measurement, which leads to a significant reduction in wafer alignment time. Throughput will be improved.

  In the above-described embodiment, the case where the two-dimensional CCD camera 61 is used as the light receiving element of the AF sensor 60 is shown, but the slit image SI only moves in one direction according to the amount of deviation (measurement in FIG. 5). The output from the sensor may be a one-dimensional signal, or a simple line sensor that can obtain this one-dimensional signal.

  However, it is preferable to use the above-described two-dimensional CCD camera 61 that can measure with high sensitivity (high signal intensity) in a short time as shown in the present embodiment.

  Moreover, although the case where the slit image SI was inclined 30 degrees (60 degrees) with respect to the street line SL was shown, it is not limited to this. In short, if the inclination is within a range of 10 to 35 degrees or 55 to 80 degrees, the deformation of the measurement signal is minimized as much as possible even if a part of the slit image SI overlaps the already transferred pattern. be able to. This is because a normal device pattern is often a pattern orthogonal to the slit line (0 degrees, 90 degrees) or an inclined pattern of 45 degrees, and by tilting the slit image at the above angle, This is because measurement errors due to the influence of the device pattern can be reduced.

  Moreover, although the case where it switched to WA measurement mode in the case of the focus measurement in the case of EGA measurement was shown, it is not limited to this. It is possible to switch to the WA measurement mode also in other focus measurements that require measurement accuracy.

1 is an overall configuration diagram showing an embodiment of a position measuring apparatus (FIA 30 and AF sensor 60) of the present invention and an exposure apparatus equipped with the position measuring apparatus. It is a flowchart which shows one Embodiment of the exposure method of this invention performed using the position measuring apparatus and exposure apparatus of FIG. It is the schematic of the light transmission system of AF sensor shown in FIG. FIG. 2 is a schematic diagram of a light receiving system of the AF sensor shown in FIG. 1. It is explanatory drawing of the measurement principle of the deviation | shift amount by AF sensor. It is explanatory drawing which shows the arrangement | positioning relationship of a circuit pattern, a position measurement pattern, and AF mark (a plurality of line images having different line widths: slit images). It is a detailed view of a slit image. (A) It is a detailed view of the pattern for position measurement. FIG. 4B is a detailed view of a position measurement pattern. (C) It is a detail drawing of the pattern for position measurement. (A) is explanatory drawing explaining reduction of the signal deformation | transformation error brought about by inclining a slit image 30 degree | times with respect to the street line between shot areas. (B) is an explanatory diagram of a signal deformation error in the case where the slit image is inclined only slightly (about 3 degrees) with respect to the street line. It is explanatory drawing which carries out correction | amendment calculation processing of the measurement signal of AF sensor.

Explanation of symbols

10 Exposure Device 17 XY Stage 18 Z Stage 30 FIA Sensor (Pattern Detection Sensor)
43 CCD camera (light receiving element)
44 CCD camera (light receiving element)
50 Main control system 60 AF sensor (focus state detection sensor)
61 CCD camera AM1 alignment mark (pattern for position measurement)
AM2 alignment mark (position measurement pattern)
SI Slit image R Reticle W Wafer

Claims (9)

A position measuring device for measuring the position of an object placed on a stage moving in a two-dimensional plane in the two-dimensional plane,
A position measurement pattern formed on the object is irradiated with a measurement beam, and the pattern beam generated from the position measurement pattern is received by the light receiving element after receiving the measurement beam. A pattern detection sensor that outputs a conversion signal;
A focus state detection sensor for measuring a shift amount in a focus direction between the position of the light receiving surface of the light receiving element and the imaging position of the pattern beam;
The focus state detection sensor can be used in a plurality of measurement modes, and is set to be switched to an arbitrary measurement mode in the plurality of measurement modes according to use conditions when the focus state detection sensor is used for measurement. A position measuring device characterized by that.   The use condition includes a first measurement condition in which detection by the focus state detection sensor is performed in parallel with a movement operation of the stage in the two-dimensional plane, and detection by the focus state detection sensor while the stage is stationary. The position measurement device according to claim 1, further comprising: a second measurement condition.   The position measurement apparatus according to claim 2, wherein the position measurement pattern is positioned within a detection visual field of the pattern detection sensor under the second measurement condition. The focus state detection sensor is a sensor that measures the amount of deviation by detecting a plurality of line images with different line widths projected on the object,
The use condition includes a first measurement condition for detecting a line image having a line width larger than a predetermined value among the plurality of line images, and a second measurement condition for detecting a line image having the line width equal to or less than the predetermined value. The position measuring device according to claim 1, comprising:   The use condition includes a first measurement condition that is allowed with an accuracy of a predetermined level or less as a detection accuracy of the deviation amount, and a second measurement condition that requires an accuracy of the predetermined level or more. The position measuring device according to claim 1. The focus state detection sensor includes pixels of n lines × m columns (n and m are natural numbers of 2 or more),
The measurement mode corresponds to a first measurement mode in which a signal corresponding to the light amount accumulated in the pixels in each line is sequentially added by a predetermined line every predetermined time, and a light amount accumulated in the pixels in each line. A second measurement mode for adding n lines of signals to be performed at a time,
6. The position measurement according to claim 2, wherein the first measurement mode is set when the first measurement condition is set, and the second measurement mode is set when the second measurement condition is set. apparatus. An exposure apparatus that illuminates a mask pattern and transfers an image of the mask pattern onto an exposure substrate mounted on a stage,
It has the position measuring device according to any one of claims 1 to 6,
An image of the mask pattern is transferred onto the exposure substrate positioned based on a result of measuring a position measurement pattern formed on the exposure substrate using the position measurement device. Exposure device. The focus state detection sensor provided in the position measurement device is a sensor that measures the shift amount by detecting a plurality of line images projected on the substrate to be exposed,
Each longitudinal direction of the plurality of line images projected on the substrate to be exposed is 10 degrees to 35 degrees or 55 degrees with respect to a street line between regions where the image of the mask pattern on the substrate to be exposed is transferred. The exposure apparatus according to claim 7, wherein the exposure apparatus is tilted by 80 degrees to 80 degrees. An exposure method for illuminating a mask pattern and transferring an image of the mask pattern onto an exposure substrate mounted on a stage,
A position measurement pattern formed on the substrate to be exposed is measured using the position measurement device according to any one of claims 1 to 6,
An exposure method, comprising: transferring an image of the mask pattern onto the substrate to be exposed positioned based on a result measured using the position measuring device.

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