JP2016100590A - Focus control method, pattern transfer apparatus, and manufacturing method of article - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a focus control method advantageous in suppressing a focus measurement error.SOLUTION: A focus control method controls a focus operation in pattern transfer on the basis of a surface position measurement result of a plurality of regions to be transferred formed at an object during pattern transfer and a correction value according to positions in the regions to be transferred calculated on the basis of an advance measurement result prior to the pattern transfer. The focus control method includes: a measurement step of measuring surface positions at a plurality of measurement positions with respect to each of the plurality of regions to be transferred formed on the object; a determination step of determining abnormality of measurement values obtained in the measurement step; and a calculation step of calculating correction values by removing abnormal measurement values out of the plurality of measurement values obtained in the measurement step and measurement values at measurement positions in cancellation relations concerning an object deformation with respect to the measurement positions of the abnormal measurement values.SELECTED DRAWING: Figure 7

Description

  The present invention relates to a focus control method, a pattern transfer apparatus, and an article manufacturing method.

  A pattern transfer apparatus is used in a lithography process included in a manufacturing process of a semiconductor device or a liquid crystal display device. For example, an exposure apparatus as a pattern transfer apparatus transfers a pattern formed on an original (such as a reticle) onto a substrate (such as a wafer or glass plate having a resist layer formed on the surface) via a projection optical system or the like. . In such a conventional exposure apparatus, the surface position of the substrate is measured as preparation for accurately transferring the pattern onto the substrate.

  Patent Document 1 discloses a surface position measurement method for correcting a result measured by a measurement device so as to suppress measurement errors caused by a pattern structure formed in advance on a substrate in order to improve surface position measurement accuracy in an exposure apparatus. Is disclosed. Here, the correction value for suppressing the measurement error is derived from the result of the pre-measurement of the surface position acquired prior to the exposure, but the measurement result exceeding the predetermined threshold among the measurement results is It is determined as an abnormal value, and is excluded in advance from the measurement result used when calculating the correction value.

JP 2004-247476 A

  For example, the manufacturing process of a semiconductor device can generally be roughly divided into a pre-process for forming an integrated circuit on a substrate (wafer) and a post-process for completing an integrated circuit chip formed on the substrate in the pre-process as a product. In particular, in the pre-process, the substrate surface is polished in order to flatten the surface shape of the exposed substrate in addition to the step of exposing the substrate coated with the photosensitive agent using an exposure apparatus and the step of developing the substrate. Step (CMP). Here, the substrate that has undergone the previous process a plurality of times may be deformed by heat treatment in the development process or polishing by CMP. And the deformation | transformation at this time generate | occur | produces center-symmetrically from the special property that a board | substrate is circular. On the other hand, when the correction value is calculated using the technique disclosed in Patent Document 1, the deformation component can be canceled by performing the prior measurement of the surface position symmetrically with respect to the center position of the substrate. Since it can, the effect on the correction value is small.

  However, when a local foreign matter exists on the substrate in a deformed state, the foreign matter is determined as an abnormal value using the technique disclosed in Patent Document 1, and the surface position measurement result determined as the abnormal value is obtained. If excluded, the symmetry of the measurement result as described above is lost. That is, in this case, the deformation component cannot be canceled out, so that the correction value is influenced by the deformation component, and it becomes difficult to suppress a measurement error particularly related to the focus.

  The present invention has been made in view of such a situation, and an object of the present invention is to provide a focus control method that is advantageous in suppressing, for example, a focus measurement error.

  In order to solve the above problems, the present invention is calculated based on the surface position measurement results of a plurality of transferred regions formed on an object at the time of pattern transfer and the results of prior measurement prior to pattern transfer. A focus control method for controlling a focus operation in pattern transfer based on a correction value according to a position in a transfer area and a plurality of transfer areas formed on an object with respect to each of a plurality of transfer areas. A measurement process for measuring a surface position at a measurement position, a determination process for determining an abnormality of a measurement value obtained in the measurement process, and an abnormal measurement value determined as abnormal from a plurality of measurement values obtained in the measurement process And a calculation step of calculating a correction value by excluding the measurement value at the measurement position that has a canceling relationship with respect to the deformation of the object with respect to the measurement position of the abnormal measurement value. Further, according to another aspect of the present invention, the object to be calculated is calculated based on the surface position measurement results of a plurality of transfer regions formed on the object at the time of pattern transfer and the results of prior measurement prior to pattern transfer. A pattern transfer apparatus for controlling a focus operation in pattern transfer based on a correction value according to a position in a transfer area, and performing a plurality of measurements for each of a plurality of transfer areas formed on an object. Measuring means for measuring a surface position at a position; determination means for determining an abnormality of a measurement value obtained by the measuring means; storage means for storing at least two measurement positions in association with each other among a plurality of measurement positions; and measurement means Excludes the abnormal measurement value determined to be abnormal and the measurement value at the measurement position stored in association with the measurement position of the abnormal measurement value from the multiple measurement values obtained by Te, characterized by comprising calculating means for calculating a correction value.

  According to the present invention, for example, it is possible to provide a focus control method that is advantageous in suppressing a focus measurement error.

It is a figure which shows the structure of the exposure apparatus which concerns on one Embodiment of this invention. It is a figure which shows the shot area | region set on the wafer. It is a figure which shows the pattern structure on a specific shot area | region. It is a figure which shows the pattern structure to which the foreign material adhered with respect to FIG. It is a figure explaining the abnormal value determination with respect to the state shown in FIG. It is a figure which shows the pattern structure on the specific shot area | region on the deform | transformed wafer. It is a figure which shows the pattern structure to which the foreign material adhered to FIG. It is a figure explaining the abnormal value determination with respect to the state shown in FIG. It is a flowchart which shows the flow of the exposure method which concerns on one Embodiment of this invention. It is a figure which shows the shot area | region used as measurement object. It is a figure which shows the shot area | region used as measurement object.

  Hereinafter, embodiments for carrying out the present invention will be described with reference to the drawings.

  First, a description will be given of a configuration of a measurement apparatus used for measurement when executing a focus control method according to an embodiment of the present invention, and a lithography apparatus including the measurement apparatus. The measurement apparatus in the present embodiment is employed in a lithography apparatus used in a lithography process in a manufacturing process of an article such as a semiconductor device or a liquid crystal display device, and the surface position of a substrate to be processed (measurement object) or Tilt can be measured. Hereinafter, as an example, the measurement apparatus according to the present embodiment will be described as being used in an exposure apparatus as a pattern transfer apparatus used in a lithography process in a semiconductor device manufacturing process.

  FIG. 1 is a schematic diagram showing a configuration of an exposure apparatus 100 according to the present embodiment. The exposure apparatus 100 is a projection type exposure apparatus that exposes (transfers) an image of a pattern formed on the reticle R onto the wafer W (on the substrate) by, for example, a scan and repeat method. In FIG. 1, the Z axis is taken in parallel to the optical axis of the projection optical system 101, the X axis is taken in the scanning direction of the reticle R and the wafer W during exposure in the same plane perpendicular to the Z axis, and the X axis is taken as the X axis. The Y axis is taken in the orthogonal non-scanning direction. The exposure apparatus 100 includes an illumination system 106, a reticle stage 103, a projection optical system 101, a wafer stage 105, a measuring device 102, and a control unit 104.

  The illumination system 106 illuminates the reticle R by adjusting light emitted from a light source that generates pulsed light such as an excimer laser (not shown). The reticle R is an original made of, for example, quartz glass on which a pattern (for example, a circuit pattern) to be transferred is formed on the wafer W. The reticle stage 103 holds the reticle R and is movable in at least the X and Y axial directions. During exposure, the reticle stage 103 scans at a constant speed in the X-axis direction (arrow 103a) within a plane perpendicular to the optical axis AX of the projection optical system 101, while maintaining the target position. Correctly move in the Y-axis direction. The position information of the reticle stage 103 in each axial direction is always measured using the bar mirror 120 installed on the reticle stage 103 and the first interferometer 121 for the reticle stage. The projection optical system 101 projects the light that has passed through the reticle R onto the wafer W at a predetermined magnification (for example, 1/2 times). Here, the image plane of the projection optical system 101 is in a relationship perpendicular to the Z-axis direction. The wafer W is a substrate made of, for example, single crystal silicon, on which a resist (photosensitive agent) is applied. The wafer stage 105 holds the wafer W via a chuck (not shown) and can move (rotate) in the X, Y, and Z axial directions, and in the θx, θy, and θz directions that are the rotational directions of the respective axes. is there. The position information of each axis direction of the wafer stage 105 is always measured using the bar mirror 123 installed on the wafer stage 105 and the second interferometer 124 for the wafer stage.

  The measuring device (measuring means) 102 measures the position or inclination of the surface of the wafer W held on the wafer stage 105 in the Z-axis direction (hereinafter collectively referred to as “surface position”). Including a light projecting system and a light receiving system. First, a light projection system for projecting a measurement light beam onto the wafer W will be described. The measurement light source 110 is a light source such as a lamp or a light emitting diode. The collimator lens 111 converts the light beam emitted from the measurement light source 110 into a parallel light beam having a substantially uniform cross-sectional intensity distribution and emits the light beam. The slit member 112 is formed by bonding a pair of prisms so that their slopes face each other, and a light shielding film formed of chromium or the like having a plurality of openings (for example, nine pinholes) on the bonding surface. Is installed. The light projecting side optical system 113 is a telecentric optical system, and nine light beams individually passing through a plurality of pinholes formed in the slit member 112 are passed through the light projecting side mirror 114 on the wafer W. The light is guided to nine measurement points. Here, the plane having the pinhole and the plane including the surface of the wafer W satisfy the Scheimpflug condition for the light projecting side optical system 113. In the present embodiment, the incident angle Φ (angle formed with the optical axis) when each light flux from the light projecting system is incident on the wafer W is 70 ° or more. Further, each light beam from the light projecting system is θ ° (for example, 22 in the XY plane from the X axis direction) so that the following light receiving system can observe nine measurement points independently from each other in the wafer W. .5 °) is incident on the wafer W from the rotated direction.

  Next, a light receiving system that receives a light beam (reflected light beam) projected by the light projecting system and reflected by the wafer W will be described. The light-receiving side optical system 116 is a telecentric optical system that receives nine reflected light beams from the wafer W via the light-receiving side mirror 115. Although not shown, the light receiving side optical system 116 has a stopper stop therein. The stopper diaphragm is common to each of the nine measurement points, and cuts higher-order diffracted light (noise light) generated by a pattern that already exists on the wafer W. The correction optical system group 118 includes nine individual correction lenses, and passes the light beams that pass through the light receiving side optical system 116 and whose optical axes are parallel to each other to the measurement surface of the photoelectric conversion unit group 119 on the rear stage side. Thus, images are formed so as to be spot lights having the same size. The photoelectric conversion unit group 119 is, for example, a set of nine one-dimensional CCD line sensors, detects the intensity (light intensity) of the light beam incident on the detection surface, and outputs the detected intensity to the arithmetic circuit 126. However, as the photoelectric conversion means group 119, one in which a plurality of two-dimensional position measuring elements are arranged may be adopted. Here, the light receiving side optical system 116, the correction optical system group 118, and the photoelectric conversion means group 119 are tilted in advance so that each measurement point on the wafer W and the detection surface of the photoelectric conversion means group 119 are conjugate with each other. Corrections have been made. For this reason, there is no change in the position of the pinhole image on the detection surface due to the local inclination of each measurement point, and there is no change on the detection surface in response to the height change in the optical axis direction AX of each measurement point. The pinhole image changes.

  The control unit (control unit) 104 includes a main control unit 127, a reticle position control system 122, a wafer position control system 125, and an arithmetic circuit 126. The main control unit 127 is configured by, for example, a computer including a processor and a memory, and is connected to each component of the exposure apparatus 100 (a control system that controls them) via a line. Control the operation. The reticle position control system 122 controls the operation of the reticle stage 103 based on a drive command from the main control unit 127. Wafer position control system 125 controls the operation of wafer stage 105 based on a drive command from main controller 127. The arithmetic circuit 126 calculates the value of light intensity based on the detection result obtained from the photoelectric conversion means group 119. In particular, the main control unit 127 includes a position in the XY plane (a position in the X and Y axial directions and a rotation θ with respect to the Z axis) and a Z direction so as to form a slit image of the reticle R on a predetermined region of the wafer W. The axial position (rotations α, β and height Z on the Z axis relative to the X and Y axes) can be adjusted. Then, main controller 127 scans the reticle position control system 122 and the wafer position control system 125 to scan the reticle stage 103 and the wafer stage 105 synchronously while projecting the pattern on the reticle R onto the wafer W. (Scanning exposure) is performed. At this time, when the main control unit 127 scans the reticle stage 103 in the direction of the arrow 103a shown in FIG. 1, the main stage 127 moves the wafer stage 105 by the reduction magnification of the projection optical system 101 in the direction of the arrow 105a shown in FIG. Scan at the corrected speed. Further, the scanning speed of the reticle stage 103 is advantageous in apparatus productivity based on the width in the scanning direction of a masking blade (not shown) in the illumination system 106 and the sensitivity of the resist applied to the surface of the wafer W. Is determined in advance.

  Here, the control by the control unit 104 when aligning the pattern formed on the reticle R will be described. In the XY plane, the main control unit 127 includes position data of the stages 103 and 105 obtained from the first interferometer 121 and the second interferometer 124, and position data of the wafer W obtained from an alignment microscope (not shown). The control data is obtained based on Then, main controller 127 transmits a drive command to reticle position control system 122 and wafer position control system 125 based on the obtained control data, and appropriately sets the positions of reticle stage 103 and wafer stage 105 to desired positions. Change. On the other hand, in the Z-axis direction, the main control unit 127 transmits a drive command to the wafer position control system 125 based on the value of the light intensity obtained from the arithmetic circuit 126 as a focus operation control, and the wafer stage appropriately. The position (or posture) 105 is changed to a desired position. Specifically, the main control unit 127 obtains a position in the Z-axis direction based on a measurement result from the measurement device 102 (arithmetic circuit 126) arranged in the vicinity of the exposure slit with respect to the scanning direction. The main control unit 127 controls the wafer stage 105 based on the obtained position in the Z-axis direction so that the optimum image plane position is obtained at the exposure position.

  Note that the control unit 104 may be configured integrally with other parts of the exposure apparatus 100 (in a common casing), or separate from the other parts of the exposure apparatus 100 (in a separate casing). It may be configured. In the present embodiment, in addition to the control of the measuring apparatus 102, the main control unit 127 that controls the entire exposure apparatus 100 executes (also serves as) a determination unit, a storage unit, or a calculation unit described later. However, the present invention is not limited to this, and a control unit or the like for executing these, or a storage device as a storage unit may be configured separately from the main control unit 127.

  Next, a measurement method using the measurement apparatus 102 in the exposure apparatus 100 will be described. In general, when a surface position is measured using the optical measuring apparatus as described above, there may be a measurement error due to a pattern structure on the wafer surface or deformation of the wafer itself. Hereinafter, in order to clarify the characteristics of the measurement method according to the present embodiment, first, generation of a measurement error in the measurement method (focus control method) of the comparative example that does not implement the present invention, and a method of suppressing the generated measurement error Will be described.

  FIG. 2 is a schematic plan view showing a shot area (transfer target area) formed on the wafer W (on the object). It is assumed that a plurality of shot regions having the same pattern structure formed in the previous exposure process are regularly arranged on the wafer W as an exposure target. The pre-measurement of the surface position (hereinafter simply referred to as “pre-measurement”) performed when calculating the correction value for correcting the measurement value so as to suppress the measurement error as described above is selected in advance from all shot regions. Several shot areas that have been set are measured. In this embodiment, the control unit (main control unit) in the measurement device of the comparative example selects, for example, the six shot areas sam1 to sam6 shown in the arrangement example of FIG. Shall.

  FIG. 3 is a schematic diagram illustrating a cross-sectional view in the Y-axis direction of each shot region (first shot region sam1 to sixth shot region sam6) illustrated in FIG. 2 and a correction value obtained using the measurement method of the comparative example. FIG. Among these, FIG. 3A is a diagram in which cross sections in the Y-axis direction of the respective shot regions sam1 to sam6 are arranged in a line. In the drawing, the surface wp1 indicates the surface position of the wafer W, and the points s1 to s5 in the shot areas sam1 to sam6 indicate the measurement points of the surface position. Here, the measurement points are arranged so that the positions in the Y-axis direction in one shot area are substantially the same in each shot area. For example, the pattern structure p1 formed in the previous exposure process is present in advance on the surface of the wafer W at the measurement point s1. Similarly, pattern structures p2 to p5 exist in advance on the surface of the wafer W at the positions of the measurement points s2 to s5, respectively.

  FIG. 3B is a diagram illustrating correction values obtained using the measurement method of the comparative example. Here, as a measuring method of the comparative example, for example, there are the following methods. First, the control unit measures the surface position at each of the measurement points s1 to s5 corresponding to the position in each of the shot areas sam1 to sam6 (within the transferred area) (measurement process), and approximates the plane from the measurement result at that time. gt1 is calculated. Next, the control unit calculates a difference between the approximate plane gt1 and each measurement result regarding each measurement point s1 to s5, and averages the difference for each measurement point (averaging process). Next, the control unit normalizes the difference between the measurement results with reference to a portion (for example, measurement point s3) that requires the highest measurement accuracy in the shot area. And a control part determines the normalized difference value as a correction value, and correct | amends a measured value suitably using the determined correction value. In FIG. 3B, the correction value c31 is for the measurement value at the measurement point s1. Similarly, the correction values c31 to c35 are for the measurement values at the measurement points s2 to s5, respectively.

  Next, consider a case where a foreign object con exists in the vicinity of the measurement point s5 in the sixth shot region sam6 in the state shown in FIG. FIG. 4 shows a cross-sectional view in the Y-axis direction of each of the shot areas sam1 to sam6 and correction values obtained using the measurement method of the comparative example, as well as FIG. It is the schematic which shows these. Among these, FIG. 4A is a diagram showing a state in which the cross sections in the Y-axis direction of the respective shot regions sam1 to sam6 are arranged in a line and the foreign matter con exists as described above. In this case, the approximate plane calculated from the surface position results measured at the measurement points s1 to s5 of the shot areas sam1 to sam6 is an approximate plane gt2 under the influence of the foreign object con.

  FIG. 4B is a diagram illustrating correction values obtained using the measurement method of the comparative example in this case. When the correction value is calculated by the same method as that described with reference to FIG. 3B, the correction values for the measurement values at the respective measurement points s1 to s5 are the correction values c41 to c45.

  FIG. 4C is a diagram comparing the correction value c35 shown in FIG. 3B and the correction value c45 shown in FIG. 4B. As described above, both corrections to the measurement value at the measurement point s5 are performed. Value. The correction value c45 affected by the foreign object con changes from the correction value c35 calculated without the foreign object con by the difference diff34. Therefore, if the main control unit 127 corrects the measurement value obtained at the time of exposure using the correction value shown in FIG. 4B, overcorrection may occur and defocusing may occur in the exposure result. Therefore, in the measurement method of the comparative example, an abnormal value determination is further performed on the results measured at the measurement points s1 to s5 of the shot areas sam1 to sam6. In the abnormal value determination here, for example, an approximate plane is calculated for each measurement point, and when the difference between the calculated approximate plane and the measurement result exceeds a predetermined threshold, the measurement result at this measurement point is calculated. A method of determining an abnormal value (abnormal measurement value) can be adopted.

  FIG. 5 is a conceptual diagram when applying abnormal value determination with respect to the state shown in FIG. 4. Among these, Fig.5 (a) is a figure which shows the threshold value etc. at the time of applying abnormal value determination with respect to measurement point s5. The approximate plane lt1 is a plane calculated by approximating from the measurement result for each measurement point s5 in each of the shot areas sam1 to sam6. Each difference diff1 to diff6 is a difference between the approximate plane lt1 and each measurement result in each shot area sam1 to sam6. For example, as shown in FIG. 5A, the main control unit 127 predefines the upper limit of the threshold as thresh-U and the lower limit of the threshold as thresh-L. Here, the difference diff6 in the sixth shot region sam6 is larger than the differences diff1 to diff5 in the other shot regions sam1 to sam5 due to the presence of the foreign matter con, and exceeds the upper limit of the threshold value. In this case, the control unit determines that the measurement result of the measurement point s5 in the sixth shot region sam6 is an abnormal value, excludes the measurement result determined as the abnormal value, and newly adds an approximate plane gt1 (see FIG. 4A). ) Is calculated. Then, the control unit calculates the difference between the new approximate plane gt1 and the surface position measurement result of each of the measurement points s1 to s5, and averages it for each measurement point. In this averaging, the measurement result of the measurement point s5 in the sixth shot area sam6 determined to be an abnormal value is excluded.

  FIG. 5B shows correction values c41 ′ to c45 ′ obtained by normalizing the difference for each measurement point with reference to a portion (for example, measurement point s3) that requires the highest measurement accuracy in one shot area. FIG. Here, the correction values c41 'to c45' shown in FIG. 5B coincide with the correction values c31 to c35 shown in FIG. 3B.

  As described above, if the surface position of the wafer W is flat as indicated by the state of the surface position wp1, even if foreign matter is present on the wafer W, the abnormal value is determined and removed as described above. The correction value can be accurately obtained using the measurement method of the comparative example. However, if the surface shape of the wafer W is deformed, especially when foreign matter is present on the wafer W, even if the abnormal value determination and removal as described above are performed, correction is performed using the measurement method of the comparative example. The value cannot be determined accurately. Hereinafter, a measurement method of a comparative example when the surface shape of the wafer W is deformed and foreign matter is present on the wafer W will be described.

  FIG. 6 shows a cross-sectional view in the Y-axis direction of each of the shot areas sam1 to sam6 and a correction value obtained by using the measurement method of the comparative example based on the description of FIG. 3, and particularly the wafer surface position wp2. It is the schematic when the is deform | transforming. Among these, FIG. 6A is a diagram in which cross sections in the Y-axis direction of the respective shot regions sam1 to sam6 are arranged in a line. The approximate plane gt3 is a plane that is approximated and calculated from the results obtained when the surface position is measured at each of the measurement points s1 to s5 in each of the shot areas sam1 to sam6. Since the planar shape of the wafer W is circular, the deformation of the surface position wp2 occurs symmetrically with respect to the center. On the other hand, the arrangement of the shot areas sam1 to sam6 on the wafer W is also symmetrical with respect to the plane of the wafer W. Specifically, the first shot region sam1 and the sixth shot region sam6, the second shot region sam2 and the fifth shot region sam5, and the third shot region sam3 and the fourth shot region sam4 are arranged at the center of the wafer W, respectively. Symmetric with respect to position. Therefore, the correction value calculated as the average value of the surface position measurement results measured at the measurement points s1 to s5 in the shot areas sam1 to sam6 can cancel the deformation component. That is, the correction value in this case is not affected by the deformation of the surface position wp2 of the wafer W.

  FIG. 6B is a diagram showing correction values obtained using the measurement method of the comparative example in this case. When the correction value is calculated by the same method as that described with reference to FIG. 3B, the correction values for the measurement values at the respective measurement points s1 to s5 become the correction values c51 to c55, and the correction shown in FIG. It matches the values c31 to c35.

  Next, consider a case where a foreign object con exists in the vicinity of the measurement point s5 in the sixth shot region sam6 in the state shown in FIG. FIG. 7 shows a cross-sectional view in the Y-axis direction of each of the shot areas sam1 to sam6 and a correction value obtained by using the measurement method of the comparative example, as well as FIG. It is the schematic which shows these. Among these, FIG. 7A is a diagram illustrating a state where the cross sections in the Y-axis direction of the respective shot regions sam1 to sam6 are arranged in a line on the surface position wp2 of the wafer W, and the foreign matter con exists as described above. .

  FIG. 7B is a diagram illustrating correction values obtained using the measurement method of the comparative example in this case. When the correction value is calculated by a method similar to the method described with reference to FIG. 3B and abnormal value determination and removal are not performed as in the method described with reference to FIG. Correction values for the measurement values in s5 are correction values c61 to c65.

  FIG. 7C is a diagram comparing the correction value c55 shown in FIG. 6B and the correction value c65 shown in FIG. 7B. As described above, both corrections to the measurement value at the measurement point s5 are performed. Value. The correction value c65 affected by the foreign object con changes by a difference diff56 with respect to the correction value c55 calculated in a state where the foreign object con does not exist. Therefore, if the control unit corrects the measurement value obtained at the time of exposure using the correction value shown in FIG. 6B, overcorrection may occur and defocusing may occur in the exposure result.

  FIG. 8 is a conceptual diagram when applying abnormal value determination with respect to the state shown in FIG. 6. Among these, Fig.8 (a) is a figure which shows the threshold value etc. at the time of applying abnormal value determination with respect to measurement point s5. In this case, in order to suppress an erroneous determination of an abnormal value due to a local gradient in each of the shot areas sam1 to sam6, a primary gradient component is removed for each shot area. The approximate plane lt2 is a plane calculated by approximation after removing the primary inclination component from the measurement result for the measurement point s5 of each of the shot areas sam1 to sam6. The differences diff1 to diff6 are differences (relative amounts) between the approximate plane lt2 and the measurement results in the shot areas sam1 to sam6. Also in this case, for example, as illustrated in FIG. 8A, the control unit predefines the upper limit of the threshold as thresh-U and the lower limit of the threshold as thresh-L. Here, the difference diff6 in the sixth shot region sam6 exceeds the upper limit of the threshold as in the case of FIG. In this case, the control unit determines that the measurement result of the measurement point s5 in the sixth shot region sam6 is an abnormal value, excludes the measurement result determined as the abnormal value, and newly adds an approximate plane gt4 (see FIG. 7A). ) Is calculated. However, if the abnormal values are excluded in this way, the shot areas sam4 to each of the shot areas sam4 to sam4 existing on the right half of the drawing of the wafer W with respect to the respective measurement points of the shot areas sam1 to sam3 existing on the left half of the drawing of the wafer W. Each measurement point of sam6 is reduced. Therefore, the arrangement of the measurement points is asymmetric with respect to the center position of the wafer W, and it is difficult to sufficiently cancel the deformation component of the correction value calculated as it is.

  FIG. 8B is obtained by normalizing the difference for each measurement point with reference to a portion (for example, measurement point s3) that requires the highest measurement accuracy in one shot region in the asymmetric state as described above. It is a figure which shows each correction value c61'-c65 '. Here, the correction values c61 'to c65' shown in FIG. 8B are different from the correction values c41 'to c45' shown in FIG. 5B.

  FIG. 8C is a diagram comparing the correction value c45 ′ shown in FIG. 5B with the correction value c65 ′ shown in FIG. 8B, and as described above, both are measured values at the measurement point s5. Is a correction value for. In the deformed state as indicated by the surface position wp2 of the wafer W, the correction value c65 ′ affected by the foreign matter con is a correction value c45 calculated in a flat state as indicated by the surface position wp1 of the wafer W. It changes by “diff diff56” with respect to “. Therefore, when the control unit corrects the measurement value obtained at the time of exposure using the correction value shown in FIG. 8B, overcorrection occurs and defocusing may occur in the exposure result.

  As described above, when the surface position of the wafer W is deformed and the foreign matter con exists on the wafer W, the measurement method of the comparative example is performed even if the above abnormal value determination and removal are performed. The correction value cannot be obtained accurately using. This means that the measurement method of the comparative example cannot suppress measurement errors caused by the pattern structure of the surface of the wafer W, deformation of the wafer W itself, or the like. Therefore, in the present embodiment, when the surface position is measured, the above measurement error is suppressed by the following method.

  First, also in the present embodiment, a correction value for correcting a measurement value when the above measurement error occurs is obtained. Here, the main control unit 127 stores one or more different shot areas (measurement positions) corresponding to each of the shot areas (measurement positions) to be measured in advance as storage means, that is, among a plurality of measurement positions. Are registered (stored) in advance in association with each other. At this time, the other shot areas that are registered in advance are shot areas that have a canceling relationship with respect to the deformation of the wafer W, and are located, for example, at locations that have a symmetrical relationship (including substantially symmetrical) with respect to the circular shape of the wafer W. A shot area to be selected is selected. Hereinafter, with reference to FIG. 7, the main control unit 127 selects and registers other shot areas to be registered in advance as follows, for example. First, for the first shot area sam1, a sixth shot area sam6 located at a location that is symmetrical in the Y-axis direction with respect to the center position of the wafer W is registered. Similarly, the fifth shot area sam5 is registered for the second shot area sam2, and the fourth shot area sam4 is registered for the third shot area sam3. On the contrary, for the fourth shot area sam4, the third shot area sam3, for the fifth shot area sam5, for the second shot area sam2, and for the sixth shot area sam6, Each one-shot area sam1 is registered. In addition, the positional relationship of each measurement point in the cancellation relationship with respect to each shot region to which each measurement point as the measurement position in the cancellation relationship belongs is the abnormal value for each shot region to which the measurement position of the abnormal value described below belongs. It shall be substantially equal to the measurement position.

  Next, the main control unit 127 uses the same method as the method described with reference to FIG. 8A for the measurement results measured at the measurement points s1 to s5 in the shot areas sam1 to sam6 as the determination unit. Judgment is performed (determination step). As a result, the measurement result of the measurement point s5 in the sixth shot region sam6 is determined as an abnormal value. Here, as described above, the first shot area sam1 is associated and registered with the sixth shot area sam6 determined to be an abnormal value. Therefore, the main control unit 127 excludes the measurement results in the first shot area sam1 and the sixth shot area sam6 as calculation means, and uses the same measurement method as that described with reference to FIG. A correction value is calculated by a method (calculation step). As a result, the main control unit 127 makes the number of the shot areas on the left half surface in the drawing and the shot area on the right half surface in the drawing coincide with each other, that is, the symmetry. The correction value can be calculated while removing the influence of the foreign object con while maintaining the above.

  FIG. 8B is a diagram illustrating correction values obtained using the measurement method according to the present embodiment. When the correction value is calculated by such a method, the correction values for the measurement values at the respective measurement points s1 to s5 become the correction values c61 ″ to c65 ″, and the correction values c41 ′ to c45 shown in FIG. Matches'. The main control unit 127 can suppress measurement errors caused by the pattern structure and the like by appropriately correcting the measurement result of the surface position measured at the time of exposure using the correction value shown in FIG.

  Next, an exposure process that employs the above-described focus control method in the exposure apparatus 100 will be described. FIG. 9 is a flowchart showing the flow of the exposure process in the present embodiment. First, when the exposure process is started, the main control unit 127 carries the wafer W onto the wafer stage 105 by using a transfer hand (not shown) and sucks and holds the wafer W on the chuck (step S101). Next, the main control unit 127 performs pre-measurement and correction for global alignment in the following step S106 (pre-alignment step: step S102). Specifically, the main control unit 127 uses a low-magnification field alignment microscope (not shown) to enter a measurement range of a high-magnification field alignment microscope (not shown) used in global alignment, and a deviation amount such as a rotation error of the wafer W. Measure and correct.

  Next, the main control unit 127 uses the measurement apparatus 102 to measure the surface positions of the wafer W at a plurality of measurement positions, and calculates and corrects the overall inclination of the wafer W from the measurement results (global). Tilt process: Step S103). FIG. 10 is a plan view of the wafer W showing a measurement position (shot region) 801 to be measured at this time as an example.

  Next, the main control unit 127 performs pre-scan measurement for acquiring a correction value for correcting a measurement error that may occur at the time of surface position measurement during scan exposure (during pattern transfer) in step S107 below. Perform (pre-scan measurement step: step S104). The pre-scan measurement process includes, for example, adjustment of the light amount of the measurement light source 110, acquisition of correction values for correcting errors caused by the pattern structure on the surface of the wafer W, deformation of the wafer W itself, and the like. . In this pre-scan measurement, the pre-measurement included in the focus control method according to the present embodiment described above can be employed.

  Here, if the shot area used for calculating the correction value, specifically, the total number of measurement values is small, the averaging number decreases, and the calculation accuracy of the correction value may be reduced. Therefore, the main control unit 127 may further determine whether the correction value calculated by removing the shot area determined to be an abnormal value can be calculated with a desired accuracy. Specifically, the main control unit 127 first counts shot areas after exclusion based on the determination result in the determination step. Next, when the total number of shot areas after exclusion falls below a predetermined number (predetermined threshold), the main control unit 127 changes one or more shot areas used for calculating the correction value. Then, the main control unit 127 newly calculates a correction value after measuring a shot area where surface position measurement is not performed. Note that the threshold of the total number of shot areas after exclusion can be determined based on, for example, the required accuracy of the correction value derived from the focal depth of the wafer W to be exposed.

  FIG. 11 is a plan view of the wafer W showing shot areas that are changed when the total number of shot areas after exclusion falls below a predetermined threshold. In the example shown in FIG. 11, first, eight shot areas (seventh shot area sam7 to fourteenth shot area sam14) whose surface positions are measured prior to exposure for calculating a correction value are selected. . The other shot areas registered in advance are based on the above selection method, for example, the 14th shot area sam14 for the 7th shot area sam7 and the 11th for the 10th shot area sam10. Each shot area sam11 is selected. Further, it is assumed that the threshold value of the total number of shot areas after exclusion by the abnormal value determination is six. For example, it is assumed that the shot areas determined to be abnormal values are the seventh shot area sam7 and the tenth shot area sam10. In this case, according to the present embodiment, the main control unit 127 calculates the correction value by excluding a total of four shots in each of the shot areas sam7, sam14, sam10, and sam11. Here, by this exclusion, the total number of shot areas used for calculating the correction value is four, which is less than the six defined as threshold values. Therefore, the main control unit 127 first reselects the fifteenth shot area sam15 provided adjacently in the Y-axis direction, for example, instead of the seventh shot area sam7 determined to be an abnormal value. Similarly, the main control unit 127 reselects the sixteenth shot area sam16 adjacent in the Y-axis direction, for example, instead of the tenth shot area sam10 determined to be an abnormal value. However, in this state, the shot area that is the measurement target for calculating the correction value is not symmetrical with respect to the center position of the wafer W. Therefore, the main control unit 127 further replaces the fourteenth shot area sam14 with the eighteenth shot area adjacent in the Y-axis direction so that the selected shot area is symmetric with respect to the center position of the wafer W. Reselect sam18. Similarly, the main control unit 127 reselects the 17th shot area sam17 that is adjacent in the Y-axis direction, instead of the 11th shot area sam11. Then, the main control unit 127 measures the surface position for each of the shot areas sam15 to sam18 that are newly selected and for which the surface position measurement has not yet been performed, and recalculates the correction value.

  Returning to the flowchart of FIG. 9, next, the main control unit 127 calculates and corrects correction values such as the inclination and curvature of field of the projection lens in the projection optical system 101 (projection lens correction step: step S105). Although not shown, the correction value is calculated using a light quantity sensor and a reference mark installed on the wafer stage 105 and a reference plate installed on the reticle stage 103. Specifically, the main control unit 127 causes the light amount sensor to measure a change in the amount of exposure light when the wafer stage 105 scans in the XYZ axial directions. Then, the main control unit 127 calculates a deviation amount of the reference mark with respect to the reference plate based on the light amount change amount that is the output of the light amount sensor, and calculates a correction value for correcting the deviation amount.

  Next, the main control unit 127 uses an unillustrated high-magnification visual field alignment microscope to measure alignment marks on the wafer W, and calculates and corrects the deviation amount of the entire wafer W and the deviation amount common to each shot region. (Global alignment step: Step S106). Here, in order to measure the alignment mark with high accuracy, the contrast of the alignment mark must be at the best contrast position. For the measurement of the best contrast position, a measuring device 102 and an alignment microscope are used. Specifically, the main controller 127 moves the wafer stage 105 to a predetermined height (Z-axis direction), causes the alignment microscope to measure the contrast, and causes the measuring device 102 to measure the surface position. Repeat several times. At this time, the main control unit 127 associates and saves the contrast measurement result corresponding to each height and the surface position measurement result. Then, the main control unit 127 obtains the position with the highest contrast based on the obtained plurality of contrast measurement results, and determines it as the best contrast position.

  Next, the main control unit 127 causes the measurement apparatus 102 to measure the surface position of the shot area to be exposed. Next, the main control unit 127 corrects the measurement result of the surface position using the correction value for correcting the error caused by the pattern structure or the like acquired in step S104. Then, as the focus control, the main control unit 127 performs scan exposure while correcting and driving the wafer stage 105 to the optimum exposure image plane position based on the corrected measurement result (scan exposure process: step S107).

  The main control unit 127 then unloads the wafer W from the wafer stage 105 after completing the exposure for all the shot areas on the wafer W (step S108), and ends the series of exposure processes. .

  As described above, in the focus control method according to the present embodiment, the measurement value of the surface position is corrected using the correction value so that no measurement error appears. When the correction value is obtained, the foreign matter present on the wafer W is corrected. Therefore, abnormal value determination is performed in advance. At this time, if there is a shot area where an abnormal value is measured, the correction value is calculated after excluding that shot area and excluding other pre-registered shot areas corresponding to that shot area. Is done. Therefore, the calculated correction value is more accurate (high accuracy). As a result, for example, even when the surface position of the wafer W is not flat and is deformed, and there is a foreign object on the wafer W, it is possible to suppress measurement errors and perform highly accurate surface position measurement. it can.

  As described above, according to the present embodiment, it is possible to provide a focus control method that is advantageous for suppressing focus measurement errors. In addition, according to the pattern transfer apparatus using the focus control method according to the present embodiment, the surface position of the wafer W can be measured more accurately, so that highly accurate pattern transfer can be realized.

  In the above description, as other shot areas registered in advance, a shot area that is symmetrical with respect to the center position of the wafer W in the Y-axis direction is selected. This is because in the above example, it is assumed that each of the shot areas sam1 to sam6 to be measured in advance has a symmetrical relationship in the Y-axis direction. Therefore, for example, when the shot areas in this case are arranged so as to be symmetrical in the X-axis direction, as other shot areas registered in advance, shot areas that are symmetrical in the X-axis direction are used. Will be selected.

  Further, in the above description, the other shot areas registered in advance for each shot area to which the measurement position belongs are located at a symmetrical place with respect to the center position of the wafer W, that is, there is an offset relation regarding the deformation of the wafer W. A shot area having a symmetrical relationship is selected. However, the present invention is not limited to this.

  In the above description, one or more other shot areas are selected and registered in advance for each shot area. That is, although the object of the offset relationship has been described as a shot area, the present invention is not limited to this. For example, the same effect can be obtained when a measurement point belonging to each shot area is regarded as an object of cancellation relation, and one or more other measurement points are selected and registered in advance for each measurement point.

  In the above description, each shot area on the wafer W to be exposed is assumed to have a pattern (having a pattern structure) formed in advance by the previous exposure process. However, the present invention is not limited to this, and even if a pattern is not previously formed in each shot area on the wafer W, the wafer W can be an exposure target (measurement target). The pattern transfer apparatus is not limited to an apparatus having an original plate such as an exposure apparatus or an imprint apparatus. For example, the pattern transfer apparatus transfers electronic patterns using electronic data without using the original plate, such as a charged particle beam drawing apparatus. Including equipment.

(Product manufacturing method)
The method for manufacturing an article according to an embodiment of the present invention is suitable, for example, for manufacturing an article such as a microdevice such as a semiconductor device or an element having a fine structure. The method for manufacturing an article according to the present embodiment includes a step of transferring a latent image pattern to the photosensitive agent applied to the substrate using the pattern transfer device (step of exposing the substrate), and the latent image pattern is transferred in this step. And processing the processed substrate. Further, the manufacturing method includes other well-known steps (oxidation, film formation, vapor deposition, doping, planarization, etching, resist stripping, dicing, bonding, packaging, and the like). The method for manufacturing an article according to the present embodiment is advantageous in at least one of the performance, quality, productivity, and production cost of the article as compared with the conventional method.

  As mentioned above, although preferable embodiment of this invention was described, this invention is not limited to these embodiment, A various deformation | transformation and change are possible within the range of the summary.

102 Measuring Device 127 Main Control Unit

Claims (10)

Correction according to the position in the transfer area calculated based on the surface position measurement results of a plurality of transfer areas formed on the object at the time of pattern transfer and the results of prior measurement prior to the pattern transfer A focus control method for controlling a focus operation in the pattern transfer based on the value,
A measurement process for measuring the surface position at a plurality of measurement positions for each of a plurality of transfer areas formed on the object;
A determination step of determining an abnormality in the measurement value obtained in the measurement step;
From the plurality of measurement values obtained in the measurement step, the measurement value at the measurement position that is offset with respect to the abnormality measurement value determined to be abnormal and the measurement position of the abnormality measurement value with respect to the deformation of the object And calculating step for calculating the correction value,
A focus control method comprising:   The focus control method according to claim 1, wherein the calculating step includes an averaging process.   2. The focus control method according to claim 1, wherein the transferred area to which the measurement position in the canceling relationship belongs is different from the transferred area to which the measurement position of the abnormal measurement value belongs.   4. The transferred area to which the measurement position in the canceling relationship belongs is symmetrical to the transferred area to which the measurement position of the abnormal measurement value belongs with respect to the center position of the object. The focus control method described in 1.   The positional relationship of the measurement position in the cancellation relationship with respect to the transferred region to which the measurement position in the cancellation relationship belongs is the measurement position of the abnormal measurement value with respect to the transferred region to which the measurement position of the abnormal measurement value belongs. The focus control method according to claim 3, wherein the focus control method is substantially equal.   The method further includes a step of changing the plurality of transfer areas to be measured in the measurement step when the total number of the plurality of measurement values after exclusion is less than a predetermined number based on the determination result in the determination step. The focus control method according to claim 1, wherein: The pattern transfer is scan exposure,
The focus control method according to claim 1, wherein the pre-measurement is a pre-scan measurement prior to the scan exposure on the object. Correction according to the position in the transfer area calculated based on the surface position measurement results of a plurality of transfer areas formed on the object at the time of pattern transfer and the results of prior measurement prior to the pattern transfer A pattern transfer device for controlling a focus operation in the pattern transfer based on the value,
Measuring means for measuring the surface position at a plurality of measurement positions for each of a plurality of transfer areas formed on the object;
Determination means for determining an abnormality of the measurement value obtained by the measurement means;
Storage means for associating and storing at least two measurement positions among the plurality of measurement positions;
By excluding an abnormal measurement value determined as abnormal from the plurality of measurement values obtained by the measurement means and the measurement value at the measurement position stored in association with the measurement position of the abnormal measurement value Calculating means for calculating the correction value;
A pattern transfer apparatus comprising: The pattern transfer is scan exposure,
The pattern transfer apparatus according to claim 8, wherein the pre-measurement is a pre-scan measurement prior to the scan exposure on the object. Transferring the pattern onto the object using the pattern transfer apparatus according to claim 8 or 9,
And a step of processing the object to which the pattern is transferred.

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