JP2006234768A - Position detecting method and position measuring apparatus - Google Patents

Abstract

【Task】
Provided is a position detection method capable of detecting a mark position without hindrance even when a plurality of alignment marks are present in a detection visual field of an imaging optical system.
[Solution]
When detecting the position of the alignment mark AM on the substrate W, it is used to detect the coordinates in the alignment direction as the mark position from the positional relationship in the alignment direction of the line portions L, L,. When a plurality of alignment marks AM, AM,... Are aligned at a predetermined interval in the alignment direction of the line portion and are placed in the detection visual field 35f of the detection optical system 35, one of the alignment marks AM, AM,. The position of the mark is detected by obtaining the coordinates in the direction orthogonal to the alignment direction of the line portion L from the positional relationship between both ends YT and YB of the line portion L of one alignment mark AM.
[Selection] Figure 6

Description

  The present invention relates to a position detection method for detecting the position of an alignment mark formed on a substrate, and a position measuring apparatus provided with a detection means for detecting the position of the alignment mark.

  In a lithography process for forming a semiconductor pattern on a wafer, a plurality of patterns are stacked one by one on a wafer on a stage using a plurality of photomasks (reticles) on which patterns corresponding to the respective processes are formed. In order to form a semiconductor pattern by laminating a plurality of patterns, the lower layer pattern formed on the wafer placed on the stage and the upper layer pattern laminated thereon by exposure using a photomask are correct. It needs to be positional. For this reason, an alignment mark for detecting the position of the wafer or reticle is formed, and the exposure apparatus measures a position measurement device for measuring the position information of the substrate and the reticle by measuring the position information of these marks. It is prepared for.

  The alignment mark formed on the wafer is generally provided outside the shot area, for example, on a scribe line extending in the vertical and horizontal directions between the shot areas. As shown in FIGS. 3 and 4, such an alignment mark AM may be formed by a so-called line and space pattern in which a plurality of line portions L, L,. An alignment mark (hereinafter also referred to as an X direction mark) XM in which line portions L, L,... Are aligned in the X direction on a scribe line (hereinafter also referred to as an X direction line) XL extending in the illustrated arrow X direction is indicated by an arrow in the drawing. On a scribe line (hereinafter also referred to as Y direction line) YL extending in the Y direction, an alignment mark (hereinafter also referred to as Y direction mark) YM in which line portions L, L,.

  The position of the alignment mark is optically detected by processing the image of the alignment mark in the field of view of the imaging optical system. The position measuring device for detecting the position of the alignment mark includes an illumination optical system that illuminates the alignment mark formed on the wafer, an imaging optical system that forms an image of reflected light from the alignment mark on the imaging surface, From a photoelectric conversion element that has an image formation surface and outputs a signal based on an image formed on the image formation surface, a signal processing unit that processes a signal from the photoelectric conversion element and obtains position information of the alignment mark Composed.

In the exposure apparatus provided with this position measuring apparatus, as shown in FIG. 7, first, the wafer is placed on the stage, and mechanical positioning is performed using an orientation flat formed on the outer edge of the disk-shaped wafer. (Mechanical alignment), tracking the position of the alignment mark using a low magnification imaging optical system (pre-alignment), and then accurately detecting the position of the alignment mark AM using a high magnification imaging optical system (Global alignment). A low-magnification imaging optical system used in pre-alignment allows observation in a wide area, and a high-magnification imaging optical system used in global alignment allows observation in a narrow area. For example, FIG. As shown in FIG. 4, the size is such that only one alignment mark is accommodated in the detection field.
JP 2003-92248 A

  In the conventional position detection method, for the X direction mark XM, the X coordinate of the mark is detected based on the signal waveform with respect to the X direction in the processing of the image signal in the signal processing unit. The Y coordinate of the mark is detected based on the signal waveform with respect to the direction. However, when observing with a low-magnification imaging optical system at the time of pre-alignment, as shown in FIG. 5, a plurality of alignment marks arranged on the scribe line (in the figure, the X direction mark XM arranged on the X direction line XL is illustrated). May fall within the field of view. As described above, when a plurality of alignment marks for performing position detection in this alignment direction are arranged in the alignment direction of the line portion, it is not known which X coordinate of the alignment mark is calculated, and the image signal from the photoelectric conversion element There is a problem that the mark position cannot be calculated based on the signal waveform in the alignment direction by the received signal processing unit. For this reason, there is a problem that the subsequent accurate detection of the position of the alignment mark by the high-magnification imaging optical system is hindered.

  The present invention has been made in view of such problems, and an object of the present invention is to provide a position detection method capable of detecting the position of a mark without any trouble even when a plurality of alignment marks are present in the detection field of the imaging optical system. And It is another object of the present invention to provide a position measuring device that can similarly detect the position of a mark.

  In order to achieve the above object, a position detection method according to the present invention has a detection optical system for imaging an alignment mark formed on a substrate, and the alignment mark is detected based on an image of the alignment mark in the detection visual field of the detection optical system. In the position detection method for detecting the position, the alignment mark is composed of a plurality of equal-length line portions formed on the substrate at equal intervals and aligned in parallel with each other, and is detected by the detection optical system. When images of a plurality of alignment marks are obtained in the field of view, based on any of the images of the plurality of alignment marks from which the images were obtained, The position in the direction orthogonal to the alignment direction of the line part is detected.

  Note that it is preferable to calculate orthogonal positions at both ends of the line portion based on the image, and to detect the center of the orthogonal positions at both ends as the orthogonal position of the alignment mark.

  At this time, by comparing each of the plurality of alignment mark images in the detection visual field with a reference image of the alignment mark stored in advance, a matching score for each of the plurality of alignment mark images with respect to the reference image is calculated and matched. It is preferable to detect the position in the orthogonal direction of the alignment mark having the best score.

  Further, the position measuring apparatus according to the present invention is mounted with a semiconductor substrate on which an alignment mark composed of a plurality of line portions formed at equal intervals and in parallel with end portions aligned with each other is horizontally moved. Possible stage, imaging means for imaging the alignment mark and outputting the image signal of the alignment mark, and image signals at both ends of the plurality of line portions when measuring the position of the semiconductor substrate using the image signal of the alignment mark And detecting means for detecting a position in a direction orthogonal to the alignment direction of the line portions.

  According to such a position detection method according to the present invention, when detecting the position of the alignment mark on the substrate, the coordinates of the alignment direction are determined from the positional relationship of the alignment direction of the line portion formed by a so-called line and space pattern. With respect to the alignment mark used for detection as the mark position, the position of the mark is detected by obtaining the coordinates in the direction orthogonal to the alignment direction of the line portion from the positional relationship between both ends of the line portion of the mark. For this reason, even if a plurality of alignment marks arranged in the line part alignment direction are present in the field of view, the coordinates in the direction orthogonal to the line part alignment direction are the same in each alignment mark. By calculating as the position, the position of the mark can be detected without any trouble even when a plurality of alignment marks are stored in the field of view.

  Further, the position measuring device according to the present invention can measure the position of the mark without any trouble even when a plurality of alignment marks are stored in the field of view, as in the case of the position detecting method.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings. FIG. 1 shows an exposure apparatus 80 provided with a position measuring apparatus 10 in which the position detection method according to the present invention is used. First, an outline of the exposure apparatus 80 will be described. An exposure apparatus 80 used in a photolithography process in a semiconductor manufacturing process optically projects a device pattern precisely drawn on a photomask (reticle) onto a semiconductor wafer or glass substrate coated with a photoresist. And transcribe. Such an exposure apparatus 80 includes an exposure light source 81, an illumination optical system 82, a mask support base 84 that supports a photomask 83, a projection optical system 85, and a stage 86 on which the wafer W is placed and held. The

  In this exposure apparatus 80, exposure light output from the exposure light source 81 is input to the illumination optical system 82, and is irradiated onto the entire surface of the photomask 83 supported by the mask support base 84 through the illumination optical system 82. The light irradiated in this way and passed through the photomask 83 has an image of a device pattern drawn on the photomask 83, and the wafer W is absorbed by the chuck 87 via the projection optical system 85. The predetermined position is irradiated. At this time, the projection optical system 85 reduces the image of the device pattern of the photomask 83 onto the wafer W and forms and exposes the image on one shot area SA. This is scanned over the entire wafer, and semiconductor patterns are formed for each of the shot areas SA, SA,.

  The stage 86 is an XY stage that two-dimensionally positions the wafer in a plane (XY plane) perpendicular to the optical axis of the projection optical system 85, and a Z stage that positions the wafer in a direction parallel to the optical axis of the projection optical system 85. , A stage that rotates the wafer W minutely, a stage that changes the angle with respect to the Z-axis to adjust the inclination of the wafer W with respect to the XY plane, and the like. Movement, rotation in the XY plane and tilt about the Z axis can be adjusted respectively.

  A movable mirror (not shown) having a length longer than the movable range of the stage 86 is attached to one end of the upper surface of the stage 86, and a laser interferometer (not shown) is disposed at a position facing the mirror surface of the movable mirror. Has been. The moving mirror is composed of a moving mirror having a reflecting surface perpendicular to the Z axis and a moving mirror having a reflecting surface perpendicular to the Y axis. The laser interferometer includes an X-axis laser interferometer that irradiates the moving mirror with a laser beam along the X-axis, and a Y-axis laser interferometer that irradiates the movable mirror with a laser beam along the Y-axis. The X and Y coordinates of the stage 86 are measured by one laser interferometer for the X axis and one interferometer for the Y axis. Further, the rotation angle of the stage 86 in the XY plane is measured by the difference between the measurement values of the two laser interferometers. Information on the X coordinate, Y coordinate, and rotation angle measured by the laser interferometer is output to the main control system 6 as stage position information. Further, an oblique focus type autofocus device (not shown) for detecting the position of the wafer W along the Z-axis direction is provided, and the position detection result of the wafer W by the autofocus device is sent to the main controller 6. Is output. Based on the detection results of the laser interferometer and the autofocus device, the drive control of the stage drive mechanism 7 is performed by the main control unit 6, and the position of the stage 86 along the XYZ-axis direction is adjusted. The above-described stage 86, main controller 6 and stage drive mechanism 7 constitute a positioning device 90.

  In the lithography process, the positional relationship between the lower layer pattern formed on the wafer and the pattern of the photomask 83 needs to be accurate. Therefore, an alignment mark for detecting a positional deviation between the wafer W placed on the stage 86 and the photomask 83 held on the mask holding table 84 is formed on the wafer W. As shown in FIGS. 3 and 4, the alignment mark AM formed on the wafer W is formed by a line-and-space pattern in which the ends of the plurality of line portions L, L,. In the wafer W, it is provided outside the shot areas SA, SA,. In this embodiment, it is provided on the scribe line SL extending in the vertical and horizontal directions between the shot areas SA, SA,..., And the scribe line (X direction line) XL extending in the X direction includes the line portions L, L,. An alignment mark (X direction mark) XM having an alignment direction of X in the X direction is aligned with a scribe line (Y direction line) YL extending in the Y direction with the alignment direction of the line portions L, L,. A mark (Y direction mark) YM is provided.

  FIG. 5 shows an enlarged portion of the wafer W where the alignment mark AM is formed. As shown in FIG. 5, on the X-direction line XL, there is a portion where a plurality of X-direction marks XM, XM,. Although not shown in the drawing, there is a portion where a plurality of Y-direction marks are provided in a line with both ends of the line portion L of each mark aligned in the same manner in the Y-direction line YL. This is caused by the fact that marks positioned in the lower layer pattern can be seen through.

  The exposure apparatus 80 includes a position measurement apparatus 10 that detects the position of the alignment mark AM by the position detection method according to the present invention. As shown in FIG. 2, the position measuring apparatus 10 includes a stage 86 on which a wafer W is placed and a light source 1 that irradiates illumination light onto an alignment mark AM formed on the wafer W placed on the stage 86. The illumination optical system 2 that guides the illumination light from the light source 1 to the wafer W and irradiates the wafer W perpendicularly, and the reflected light (including diffracted light) from the illumination optical system 2 is formed on the imaging planes 41 and 46. An imaging optical system 3 that forms an image on the CCD, CCDs (Charge Coupled Devices) 40 and 45 that have the imaging surfaces 41 and 46, convert the reflected light received by the imaging surface into electrical signals, and output the electrical signals; The signal processing unit 5 detects the position of the alignment mark AM by processing the signals from the CCDs 40 and 45, and is a FIA type position measuring device. The projection optical system 85 of the exposure device 80 is Directly on the wafer W without going through And it is configured as an off-axis method which measures the over click position.

  The light source 1 is composed of, for example, a halogen lamp, and emits light having a wide wavelength range of 530 to 800 nm that does not expose a photosensitive agent such as a resist for lithography process applied on the wafer W.

  Irradiation light from the light source 1 is converted into a parallel light beam by the collector lens 21. Irradiated light converted into a parallel light beam by the collector lens 21 is a filter group including a wavelength selection filter 22a including an infrared absorption filter, a short wavelength cut filter, a long wavelength cut filter, and the like, and a neutral density filter 22b capable of moving back and forth with respect to the optical path. The wavelength range and intensity required for the measurement light are selected. In addition, the incident end 24a of the light guide 24 is positioned at the imaging position of the condenser lens 23, and the illumination light that passes through the filter group 22 and is collected by the condenser lens 23 enters the light guide 24 from the incident end 24a. Is incident on. The light beam incident on the light guide 24 propagates through the light guide 24 and exits from the exit end 24b. Thus, the light source 1 to the incident end 24 a of the light guide 24 are configured as the light source unit 11 integrated with the light source 1.

  An exit end 24b of the light guide 24 is provided in the sensor unit 12. Irradiation light emitted from the exit end 24b of the light guide 24 is limited via an illumination aperture stop (not shown) and is applied to the condenser lens 25. Incident. Light irradiated through the condenser lens 25 is once condensed in the vicinity of an illumination field stop (not shown) and enters the illumination relay lens 26 through the illumination field stop. The illumination light that has become a parallel light beam via the illumination relay lens 26 passes through the half prism 27 and enters the objective lens 28. The illumination light condensed by the objective lens 28 is reflected downward by the reflecting surface of the reflecting prism 29 and incidentally illuminates the alignment mark AM formed on the wafer W. As described above, the illumination optical system 2 is configured by the collector lens 21 to the reflecting prism 29.

  Reflected light from the alignment mark AM obtained by irradiating the light emitted from the light source 1 enters the half prism 27 via the reflecting prism 29 and the objective lens 28. The reflected light incident on the half prism 27 is reflected upward in the figure, and an image of the alignment mark AM is formed on the indicator plate 34 via the objective lens 33a. A magnification switching mirror 31 configured to be movable on the optical path indicated by a solid line and outside the optical path indicated by a two-dot chain line is provided above the indicator plate 34 in the figure. When the magnification switching mirror 31 is on the optical path, the light from the relay lens 33b is reflected, enters the CCD 40 via the imaging relay lens (high magnification lens) 32, and the image of the alignment mark AM on the imaging surface 41 of the CCD 40. Then, an image of the index mark from the index plate 34 is formed.

  When the magnification switching mirror 31 is out of the optical path, the light from the relay lens 33 b is reflected by the reflecting mirror 36 above the magnification switching mirror 31 and enters the CCD 45 via the imaging relay lens (low magnification lens) 37. The imaging relay lens 37 forms a field of view that is lower than the imaging relay lens 32 described above. The light enters the CCD 45, and an image of the alignment mark AM and an image of the index mark from the index plate 34 are formed on the imaging surface 46 of the CCD 45. As described above, the imaging optical system 3 is configured by the reflecting prism 29 to the imaging relay lenses 32 and 37, and the imaging optical system 3 is connected to the high magnification lens 32 via the magnification switching mirror 31 on the optical path from the reflecting prism 29. The high-magnification imaging system 30 that reaches the zoom lens and the low-magnification imaging system 35 that leads from the reflecting prism 29 to the low-magnification lens 37 have two imaging systems having different magnifications.

  The CCDs 40 and 45 that receive the reflected light from the alignment marks AM on the imaging surfaces 41 and 46 by the imaging optical system 3 photoelectrically convert the images of the alignment marks AM and index marks formed on the imaging surfaces 41 and 46, respectively. The image signal is generated, and the image signal is output to the signal processing unit 5. The signal processing unit 5 performs image processing on the image signals output from the CCDs 40 and 45 to obtain, for example, the center of the image of the alignment mark AM and the center position of the image of the index mark, and the alignment mark AM from these relative relationships. The position information of is calculated.

  In the position measuring apparatus 10 configured as described above, the detection visual field 30f obtained by imaging the reflected light on the imaging surface 41 by the high magnification imaging system 30 on the optical path indicated by the solid line of the magnification switching mirror 31 is shown in FIG. As shown in FIG. 4, the size is such that one alignment mark AM (X direction mark XM is illustrated in the figure) is accommodated. Further, a detection visual field 35f obtained by imaging the reflected light on the imaging plane 46 by the low magnification imaging system 35 outside the optical path indicated by the dotted line with the magnification switching mirror 31 is a scribe line SL as shown in FIG. (In the figure, the X direction line XL is illustrated) A plurality of alignment marks AM arranged on the upper side are accommodated.

  Hereinafter, the flow of detecting the position of the alignment mark using the position measuring apparatus 10 will be described with reference to the flowcharts shown in FIGS.

  First, a rough flow from when the wafer W is supplied to the exposure apparatus 80 until it is exposed will be described with reference to the flowchart of FIG. When the wafer W is supplied to the exposure apparatus 80 (step S1), mechanical alignment is performed using the outer periphery of the wafer W and the orientation flat OF (step S2). Next, the wafer W is placed on the chuck 87, and the pre-alignment by the low magnification imaging system 35 is performed with the magnification switching mirror 31 positioned outside the optical path (step S3), and the mark position of the alignment mark AM is obtained. Further, the magnification switching mirror 31 is positioned on the optical path, and global alignment is performed by the high magnification imaging system 30 (step S4), and the position of the wafer W and the position of the exposure shot are accurately obtained.

  Now, the position detection method according to the present invention is used in the signal processing unit 5 at the time of pre-alignment, and calculation processing at the time of pre-alignment will be described with reference to the flowchart of FIG. Note that, by pre-alignment, images of a plurality of X-direction marks XM, XM,... Aligned in the X-direction line XL are formed on the detection field 35f of the low-magnification imaging system 35 as shown in FIG. . The X-direction mark XM in which the alignment direction of the line portions L, L,... Is the X-axis direction is an alignment mark originally formed for detecting the X-direction coordinate as described above.

  At this time, the signal processing unit 5 performs pattern matching between the image output from the CCD 45 and the template image (reference image) of the X-direction mark XM stored in advance (step S31). This image processing by pattern matching is a known technique, but the template image is moved with respect to the image output from the CCD 45, and the matching score is calculated by the signal processing unit 5 sequentially in this moving process. At this time, the higher the matching score, the higher the matching of the target image with the template image.

  Next, the obtained matching scores are rearranged in order of score (step S32), and an image corresponding to the highest score is extracted (step S33). That is, by these steps, an image obtained as a result that the matching with the template image is the highest is selected and acquired from the image output from the CCD 45.

  Then, the positions of the upper end YT and the lower end YB of the line portion L are calculated for the X direction mark XM selected as the image with the highest matching (step S34).

  Further, based on the calculated positions of both ends YT, YB of the line portion L, the Y coordinate of the center YO of the positions of both ends YT, YB is calculated, and the Y coordinate of this center YO is the position detection result of the X direction mark XM. (Step S35). Then, the position detection result of the X direction mark XM is output from the signal processing unit 5 to the main control unit 6.

  Even when images of a plurality of Y direction marks YM, YM,... Aligned in the Y direction line YL are formed on the detection visual field 35f of the low magnification imaging system 35, the coordinates in the X direction are the same as described above. Can be requested. That is, the highest value obtained by pattern matching between the image output from the CCD 45 and the template image (reference image) of the Y-direction mark YM stored in advance to obtain a matching score, and rearranging in order of the score. The image of the Y direction mark corresponding to the score is taken out. Then, the positions of the left end and right end of the line portion L are calculated with respect to the field image of the Y direction mark corresponding to the highest value score. Furthermore, based on the calculated positions of both ends of the line portion L, the X coordinate of the center of the positions of both ends is calculated, and this X coordinate of the center is used as the position detection result of the Y direction mark YM.

  As described above, according to the position detection method of the present invention, when detecting the position of the alignment mark AM formed on the wafer W for alignment of the exposure apparatus 80, it is formed by a line-and-space pattern and is originally a line. For the alignment mark for detecting the coordinate in the alignment direction from the positional relationship in the part alignment direction, the position of the mark is detected by obtaining the coordinate in the direction orthogonal to the alignment direction of the line part from the positional relationship at both ends of the line part. I am doing so. Therefore, even if a plurality of alignment marks AM arranged in the line portion alignment direction are present in the detection visual field 30f, the coordinates in the direction orthogonal to the line portion alignment direction are the same in each alignment mark AM. The position of the mark can be detected without any trouble even when a plurality of alignment marks are within the field of view. Similarly, the position detection device that detects the position by such a position detection method can detect the position of the mark without any trouble when a plurality of alignment marks are stored in the field of view.

  Furthermore, when there are a plurality of alignment marks AM, more accurate position detection can be performed by performing the pattern matching process and representing the coordinates represented by the image that best matches the predetermined template image. Can do.

  Further, in this embodiment, it is performed when a plurality of alignment marks having a size that can be accommodated in the detection field 30f of the high-magnification imaging system 30 are arranged side by side in the detection field 35f of the low-magnification imaging system 35. Thus, by performing the position detection method according to the present invention in pre-alignment, it is possible to perform position detection sufficient to shift to subsequent global alignment.

It is a block diagram which shows the schematic structure of the exposure apparatus provided with the position measuring apparatus which detects a position with the position detection method which concerns on this invention. It is a block diagram which shows schematic structure of the said position measuring apparatus. It is a top view of a wafer. It is a figure which shows the alignment mark for X directions when forming an image in the detection visual field of a high magnification imaging system. It is a figure which shows the alignment mark for X directions when forming an image in the detection visual field of a low magnification imaging system. It is a flowchart which shows the position detection method which concerns on this invention. It is a flowchart shown about the outline of an alignment process.

Explanation of symbols

AM alignment mark XM X direction mark YM Y direction mark L Line part W Wafer (substrate)
DESCRIPTION OF SYMBOLS 1 Light source 2 Illumination optical system 3 Imaging optical system 5 Signal processing part (detection means)
6 Main control unit 7 Stage drive mechanism 10 Position measuring device 30 High magnification imaging system 35 Low magnification imaging system 30f, 35f Detection field of view 40, 45 CCD (imaging means)
41, 46 Imaging surface 80 Exposure device 86 Stage

Claims (4)

In a position detection method that has an imaging optical system that images an alignment mark formed on a substrate and detects the position of the alignment mark based on an image of the alignment mark in the field of view of the imaging optical system.
The alignment mark is composed of a plurality of equal-length line portions formed on the substrate at equal intervals and aligned in parallel with the ends of each other,
When obtaining images of the plurality of alignment marks in the field of view, based on the image of any of the plurality of alignment marks obtained images, the positional relationship between the both ends of the line portion of the alignment mark A position detection method for detecting a position in a direction orthogonal to the alignment direction in a plurality of alignment marks.   The position in the orthogonal direction at each of both ends of the line portion is calculated based on the image, and the center of the position in the orthogonal direction at the both ends is detected as the position in the orthogonal direction of the alignment mark. The position detection method according to claim 1. A matching score for each of the plurality of alignment mark images is calculated by comparing each of the plurality of alignment mark images obtained within the field of view with a reference image of the alignment mark stored in advance. And
The position detection method according to claim 2, wherein the position in the orthogonal direction in the alignment mark having the best matching score is detected. A stage on which a semiconductor substrate on which an alignment mark composed of a plurality of line portions formed at equal intervals and aligned with each other in parallel is arranged, is mounted, and can be moved horizontally,
Imaging means for imaging the alignment mark and outputting an image signal of the alignment mark;
Detection means for detecting positions in a direction orthogonal to the alignment direction of the line portions from image signals at both ends of the plurality of line portions when measuring the position of the semiconductor substrate using the image signals of the alignment marks And a position measuring device.

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