JP2005123427A - Method for measuring optical performance, exposing method, aligner, and mask - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To quickly and highly accurately measure the optical performance of a projecting optical system. <P>SOLUTION: A measuring pattern MP includes a wedge type pattern P1 of which the line width (width in a direction D2) is gradually changed along the direction D1, and a pattern P2 arranged in parallel with the patten P1 and setting the changing direction of its line width reversely to that of the pattern P1. The pattern MP is transferred to a wafer through the projecting optical system, and a shape change of a resist pattern formed on the wafer is measured and expressed as a value to find out the coma aberration of the projecting optical system. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an optical performance measurement method for measuring the optical performance of a projection optical system, an exposure method for exposing a substrate using a projection optical system whose optical performance is adjusted based on the measurement results of the method, and the optical of the projection optical system The present invention relates to an exposure apparatus having a function of measuring performance.

  In a photolithography process provided as one of the manufacturing processes of a microdevice such as a semiconductor element, a liquid crystal display element, an imaging device, and a thin film magnetic head, it is formed on a mask or a reticle (hereinafter collectively referred to as a mask). An exposure apparatus is used that projects and exposes the image of the pattern onto a substrate (a semiconductor wafer or glass plate coated with a photoresist) as an exposure target via a projection optical system. Recently, step-and-repeat type reduction projection exposure apparatuses (so-called steppers) or step-and-scan type exposure apparatuses are frequently used.

In recent years, in order to cope with higher integration of patterns formed on devices, it is desired to further increase the resolution of the projection optical system. The resolution of the projection optical system increases as the wavelength of the exposure light decreases and the numerical aperture of the projection optical system increases. For this reason, the wavelength of the exposure light used in the exposure apparatus has become shorter year by year, and the numerical aperture of the projection optical system has also increased. Focusing on the shortening of the exposure light wavelength, conventionally g-line (wavelength 436 nm) and i-line (wavelength 365 nm) were used, but now KrF excimer laser (wavelength 248 nm) and ArF excimer laser (wavelength 193 nm) are used. It has become mainstream, and practical application of F ₂ laser (wavelength 157 nm) and the like is also being studied.

  By the way, since the performance of the exposure apparatus mainly depends on the resolving power performance of the projection optical system, the projection optical system is designed and manufactured to minimize the aberration amount, but it is difficult to eliminate the aberration amount. . Therefore, the resolution performance can be improved by measuring the residual aberration of the projection optical system and correcting it.

  As a conventional method for measuring residual aberration of a projection optical system, as a pattern for aberration measurement, two or more patterns whose line widths are set uniformly in the longitudinal direction are arranged in the lateral direction. The projected image of the S (line and space) pattern projection optical system is imaged using a measuring instrument such as a CCD (Charge Coupled Device) arranged on the imaging surface, and the line width (dimension in the short direction) Is measured manually by an operator, and the measured line width is compared with the line width of a projected image projected in an ideal state.

  Also, the same aberration measurement pattern as described above is transferred onto the substrate coated with the photoresist, and the operator observes the pattern formed on the substrate using a scanning electron microscope (SEM) or the like. It is known to measure the width and compare the measured line width with the line width of a pattern formed on a substrate when transferred in an ideal state.

A coma aberration measuring method using an L / S pattern in which five lines are arranged is disclosed in Japanese Patent Laid-Open No. 2003-279341.
JP 2003-279341 A

  However, in the conventional residual aberration measurement method described above, an L / S pattern is used as the aberration measurement pattern, and the operator manually measures the projected image or the line width of the pattern transferred onto the substrate. Since these measurement results are obtained by comparing the line width of the projected image projected in the ideal state or the line width of the pattern transferred onto the substrate in the ideal state, these operations are extremely complicated, For this reason, there is a problem that the working time becomes long and a measurement error easily occurs.

  The present invention has been made in view of such problems of the prior art, and an object thereof is to enable high-precision measurement of the optical performance of a projection optical system in a short time.

  Hereinafter, in the description shown in this section, the present invention will be described in association with the member codes shown in the drawings representing the embodiments. However, each constituent element of the present invention is limited to the members shown in the drawings attached with these member codes. Is not to be done.

  In order to solve the above problems, according to a first aspect of the present invention, there is provided an optical performance measurement method for measuring the optical performance of a projection optical system (PL) that projects a pattern of a first surface onto a second surface, A first pattern (P1, P11) whose line width changes in the first direction (D1, D31) along the longitudinal direction and the first pattern are arranged side by side, and the change in the line width in the first direction is the first pattern. An arrangement step (S11, S21) of arranging a measurement pattern (MP, MP1) including a second pattern (P2, P12) that is opposite to one pattern in the first surface, and being projected on the second surface There is provided an optical performance measurement method including a measurement step (S12 to S17, S22 to S25) for measuring the optical performance of the projection optical system from the detection result of the image of the measurement pattern.

  In the present invention, a first pattern whose line width changes in the longitudinal direction as a measurement pattern and a second pattern whose line width changes in the opposite direction are arranged on the first surface, and a projection image by these projection optical systems. Are projected onto the second surface in a state where there is a difference in the change in length in the longitudinal direction according to the optical performance of the projection optical system (particularly, residual coma aberration). Thereby, for example, the optical performance of the projection optical system can be easily measured by detecting the change in the length in the longitudinal direction of the projected images of the first and second patterns.

  Further, by comparing (for example, ratios) the dimensional changes in the longitudinal direction of the projected images of the first and second patterns, the direction and size of the residual aberration including coma can be easily specified. For example, as will be described in an embodiment described later, since it is possible to automate the measurement of optical performance using an imaging device such as a CCD, the optical performance of the projection optical system can be measured with high accuracy in a short time. become able to.

  In the optical performance measurement method according to the first aspect of the present invention, the first pattern and the second pattern can be wedge-shaped ones whose line width gradually increases or decreases in the first direction, In this case, the shapes of the first pattern and the second pattern may be set so that the sum of the line widths in the second direction orthogonal to the first direction is constant along the first direction. preferable.

  In this case, the measurement step includes a detection step of detecting a projection image of the measurement pattern projected on the second surface to obtain a detection signal, and the detection signal obtained in the detection step is converted into the second direction. Integrating a step of integrating in a direction corresponding to the step of obtaining an integrated signal, and a numerical step of converting the optical performance of the projection optical system into a numerical value based on a distribution of the integrated signal in a direction corresponding to the first direction. be able to. Further, the measurement step includes a substrate placement step of placing a detection substrate on the second surface, a transfer step of transferring the measurement pattern to the detection substrate via the projection optical system, and a detection substrate. A pattern detection step for detecting the transferred pattern, and a digitization step for digitizing the optical performance of the projection optical system based on the detection result of the pattern detection step can be included.

  According to a second aspect of the present invention, in an exposure method for transferring a pattern (DP) formed on a mask (R) onto a substrate (W) via a projection optical system (PL), the pattern can be transferred. Prior to the optical performance measurement step of measuring the optical performance of the projection optical system using the optical performance measurement method described above, and the characteristics of adjusting the optical performance of the projection optical system according to the measurement results of the optical performance measurement step An exposure method including an adjusting step is provided.

  According to a third aspect of the present invention, in an exposure apparatus that transfers a pattern (DP) formed on a mask (R) onto a substrate (W) via a projection optical system (PL), the first along the longitudinal direction. The first pattern (P1, P11) whose line width changes in one direction (D1, D31) and the first pattern are arranged in parallel, and the change in the line width in the first direction is opposite to the first pattern. A measurement mask (TR) on which a measurement pattern (MP, MP1) including a second pattern (P2, P12) is formed is used as the mask, and the pattern formed on the measurement mask is determined by the projection optical system. A detection unit (20) for detecting a projected image, and an integration signal (AS) by integrating the detection signals of the detection unit in a direction (D12) corresponding to a second direction (D2, D32) orthogonal to the first direction. Corresponding to the first direction Countercurrent performance calculator to quantify the optical performance of the projection optical system based on the distribution of the integrated signal at the (D11) (12) and an exposure apparatus including a is provided.

  According to the present invention, the images of the first pattern and the second pattern arranged in the first surface are formed on the second surface in a state in which the length in the longitudinal direction changes according to the optical performance of the projection optical system (PL). An integrated signal obtained by integrating the detection signals projected and detected by the detection unit in the direction orthogonal to the longitudinal direction is obtained, and the optical performance of the projection optical system is quantified based on the distribution of the integrated signals.

  According to a fourth aspect of the present invention, there is provided a mask used for measuring the optical performance of a projection optical system (PL) that projects a pattern of a first surface onto a second surface, the first direction (D1) along the longitudinal direction. , D31) are provided adjacent to the first pattern (P1, P11) whose line width changes, and the change in the line width in the first direction is almost opposite to that of the first pattern. A mask (TR) having a measurement pattern including a second pattern (P2, P12) is provided.

  In this case, the measurement pattern may include a plurality of pairs of the first and second patterns arranged in parallel in a second direction orthogonal to the first direction. The first and second patterns may each have a wedge shape in which a line width in a second direction orthogonal to the first direction gradually increases or decreases in the first direction. Further, at least a part of the first and second patterns can be set such that the sum of the line widths in the second direction orthogonal to the first direction is substantially constant along the first direction. . Further, the measurement pattern is a plurality of pairs of the first and second patterns arranged apart from each other in a second direction orthogonal to the first direction so that the sum of the line widths in the second direction is substantially equal. Can be set. Furthermore, the measurement pattern may include a plurality of first and second patterns whose line widths change along the first direction and a direction different from the first direction.

  According to a fifth aspect of the present invention, there is provided an optical performance measuring method for measuring an optical performance of a projection optical system (PL) that projects a pattern of a first surface onto a second surface, wherein the fourth aspect of the present invention is described above. The measurement pattern (MP, MP1) measured on the mask (TR) according to the above is arranged on the first surface, and the projection optical system based on the detection result of the image of the measurement pattern projected on the second surface There is provided an optical performance measuring method for determining the optical performance of the optical performance.

  In this case, the optical performance of the projection optical system is obtained using detection information relating to the first direction of the image of the measurement pattern having a different length change between the first pattern and the second pattern during the projection. it can.

  According to the present invention, the operator's work is greatly reduced and the measurement by the operator's manual work can be omitted, so that the optical performance of the projection optical system can be measured with high accuracy in a short time. Can do.

  Further, since the optical performance of the projection optical system is adjusted based on the measurement result with high accuracy, the optical performance of the projection optical system can be brought closer to an ideal state.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

[First Embodiment]
FIG. 1 is a view showing the schematic arrangement of an exposure apparatus in which the optical performance measuring method according to the first embodiment of the present invention is used. In the exposure apparatus shown in FIG. 1, a wafer W as a substrate is placed on a wafer stage 8 which can be moved two-dimensionally, and the wafer W is stepped (stepped) by the wafer stage 8 so that a reticle as a mask. This is a step-and-repeat type exposure apparatus (so-called stepper) that repeats the operation of sequentially transferring the R pattern to each shot area on the wafer W.

  In the following description, an XYZ orthogonal coordinate system shown in the figure is set, and the positional relationship of each member will be described with reference to this XYZ orthogonal coordinate system. The XYZ orthogonal coordinate system is set so that the X axis and the Z axis are parallel to the paper surface and the Y axis is perpendicular to the paper surface. In the XYZ coordinate system in the figure, the XY plane is actually set to a plane parallel to the horizontal plane, and the Z-axis is set vertically upward.

  In FIG. 1, reference numeral 1 denotes an exposure light source, which is an ArF excimer laser light source (wavelength 193 nm) that emits exposure light EL that is a parallel light beam having a substantially rectangular cross section. The exposure light EL emitted from the exposure light source 1 enters the illumination optical system 2. The illumination optical system 2 includes, for example, a plurality of diffractive optical elements that are exchanged in the illumination optical path, a plurality of prisms with variable intervals, a molding optical system having a zoom optical system, an optical integrator (for example, a fly-eye lens, Illumination of the reticle R by shaping the exposure light EL emitted from the exposure light source 1 and making the illuminance distribution uniform, including an internal reflection integrator or diffractive optical element), a field stop, and a condenser lens system. Set conditions. Further, the illumination optical system 2 changes the light amount distribution of the exposure light EL on the pupil plane by the above-described shaping optical system, and thereby, in addition to normal illumination, for example, annular illumination, quadrupole deformation illumination, and small coherence. Lighting conditions such as lighting of a factor (σ value) are set.

  The exposure light EL emitted from the illumination optical system 2 is irradiated to the illumination area IA whose shape and size are set by a field stop (not shown) provided in the illumination optical system 2. The illumination area IA is basically set to a size corresponding to the shot area. By irradiating the exposure light EL in the illumination area IA, the pattern arranged in the illumination area IA in the pattern DP formed on the reticle R is illuminated with substantially uniform illuminance.

  The reticle R is mounted on a reticle stage 4 that can be finely moved in the direction of the optical axis AX of the projection optical system PL by the drive system 3 and that can be two-dimensionally moved and finely rotated in a plane perpendicular to the optical axis AX. ing. A movable mirror 5 that reflects the laser beam from the laser interferometer 6 is fixed to the end of the reticle stage 4, and the two-dimensional position of the reticle stage 4 is resolved by the laser interferometer 6 to a resolution of, for example, several nm. Always detected.

  The exposure light EL that has passed through the reticle R enters, for example, a telecentric projection optical system PL on both sides (or one side) and is projected onto the exposure area EA. After positioning one of the shot areas on the wafer W with respect to the exposure area EA, the illumination area IA of the reticle R is irradiated with the exposure light EL, and the pattern image is projected onto the exposure area EA via the projection optical system PL. As a result, the pattern is transferred to the shot area.

  Here, the surface (pattern surface) on which the pattern DP of the reticle R is formed is disposed on the object surface (first surface) of the projection optical system PL, and the surface of the wafer W is the image surface (second surface) of the projection optical system PL. Exposure is performed in a state of being disposed on the surface. The projection optical system PL has a pupil plane (not shown) that is substantially conjugate with the pupil plane of the illumination optical system 2, and the exposure apparatus of this example performs Koehler illumination. The projection optical system PL includes a plurality of optical elements such as lenses, and synthetic quartz, fluorite, etc. are used as the glass material of the optical elements (particularly refractive elements) according to the wavelength of the exposure light EL. The magnification is designed to be 1/5 or 1/4, for example.

  The wafer W is a semiconductor wafer having a diameter of about 300 mm, for example, and a photoresist as a photosensitive agent is applied on the surface thereof. The wafer W is placed on the wafer stage 8 via the wafer holder 7. A reference member 9 that determines the reference position of the wafer stage 8 is provided on the wafer stage 8 (wafer holder 7 in this example). This reference member 9 is used, for example, to measure a baseline that is the distance between the center of the exposure area EA on which the pattern image is projected and the center of the measurement field of view of the alignment sensor 15 described later.

  The wafer stage 8 includes an XY stage that two-dimensionally positions the wafer W in a plane perpendicular to the optical axis AX of the projection optical system PL, and a direction (Z direction) and X along the optical axis AX of the projection optical system PL. It can be finely moved in the rotation direction around the axis and the Y axis, and is configured by a fine movement stage that adjusts the position and inclination of the wafer W in the Z direction with respect to the image plane (or XY plane) of the projection optical system PL. The fine movement stage may be configured to be capable of fine movement in the rotation direction around the Z axis, or in addition to the X direction and the Y direction.

  An L-shaped movable mirror 10 is attached to the end (or side surface) of the wafer stage 8, and a laser interferometer 11 that emits a laser beam toward the mirror surface of the movable mirror 10 is provided. Although illustrated in a simplified manner in FIG. 1, the movable mirror 10 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 11 includes two X-axis laser interferometers that irradiate the moving mirror 10 with a laser beam along the X axis and a Y-axis that irradiates the moving mirror 10 with a laser beam along the Y axis. The X coordinate and the Y coordinate of the wafer stage 8 are measured by one laser interferometer for the X axis and the laser interferometer for the Y axis. Further, the rotation angle around the Z axis of the wafer stage 8 is measured by the difference between the measurement values of the two laser interferometers for the X axis.

  The two-dimensional coordinates of the wafer stage 8 are always detected by the laser interferometer 11 with a resolution of about several nanometers, for example, and the stage coordinate system (stationary coordinate system) of the wafer stage 8 is determined by the coordinates in the X-axis direction and the Y-axis direction. ) Is determined. That is, the coordinate value of the wafer stage 8 measured by the laser interferometer 11 is a coordinate value on the stage coordinate system. A position measurement signal PDS indicating the X coordinate, the Y coordinate, and the rotation angle measured by the laser interferometer 11 is output to the main control system 12. The main control system 12 outputs a control signal for controlling the position of the wafer stage 8 to the drive system 13 while monitoring the supplied position measurement signal PDS.

  Further, the exposure apparatus of the present embodiment includes a lens controller 14 that adjusts the imaging characteristics of the projection optical system PL. The lens controller 14 is based on a control signal from the main control system 12 while referring to a detection result of a sensor (for example, an atmospheric pressure sensor) that detects information related to the installation environment of the projection optical system PL or its temperature. Of a plurality of optical elements provided in the projection optical system PL, a predetermined number (for example, about 5) of optical elements are independently driven by three actuators (piezo elements, etc.), respectively, and the imaging performance of the projection optical system PL ( For example, magnification, distortion, curvature of field, spherical aberration, coma, etc.) are adjusted. The predetermined number of optical elements may not only move in the Z direction along the optical axis AX but also tilt or move in the X and Y directions.

  An off-axis alignment sensor 15 that measures position information of marks (alignment marks) formed on the wafer W is provided on the side of the projection optical system PL. As the alignment sensor 15, a mark image obtained by irradiating a mark formed on the wafer W with a detection beam is imaged with an imaging element such as a two-dimensional CCD (Charge Coupled Device) and converted into an image signal, for example. It is preferable to use a so-called FIA (Field Image Alignment) type alignment sensor that performs image processing on the image signal to measure mark position information. The measurement result of the alignment sensor 15 is output to the main control system 12.

  The main control system 12 stores a recipe consisting of a control command group for performing various processes necessary for exposure of the wafer W, and the main control system 12 controls each part in accordance with this recipe. The control performed by the main control system 12 includes, for example, light emission / stop of the exposure light source 1, control of the intensity / exposure amount of the exposure light EL, control of the positions and postures of the reticle stage 4 and the wafer stage 8, and connection of the projection optical system PL. For example, image performance control.

  Further, the main control system 12 positions information measured by the alignment sensor 15 on marks formed in association with each of several typical (3 to 9) shot areas preset on the wafer W. Then, EGA (enhanced global alignment) calculation is performed based on the design position information, and the regularity of the arrangement of all shot areas set on the wafer W is determined by a statistical method. The main control system 12 controls the wafer stage 8 based on the shot area arrangement (coordinate values) determined by such a method, and positions each shot area with high accuracy with respect to the exposure area EA. Perform exposure.

  Next, the principle of measuring the optical performance of the projection optical system PL will be described. In the present embodiment, a case where coma aberration is measured as an example of the optical performance of the projection optical system PL will be described as an example. 2 and 3 are diagrams for explaining the principle of measurement of coma remaining in the projection optical system PL.

  Now, a line-and-space pattern having a duty ratio of 50% is formed on the reticle R, and the reticle is arranged so that the line-and-space pattern is arranged in the illumination area IA. Assume that reticle R is held on stage 4. Further, when the reticle R is accurately positioned on the object plane of the projection optical system PL and the wafer W is accurately positioned on the image plane of the projection optical system PL, and the projection optical system PL has no aberration, the reticle R is used. The exposed exposure light EL travels on the optical path as designed in the projection optical system PL to expose the wafer W. For this reason, as shown in FIG. 2A, the resist pattern RP1 formed on the wafer W after the development processing is substantially similar to the line and space pattern formed on the reticle R, and the magnification of the projection optical system PL. The line width is multiplied by.

  However, even if the reticle R is accurately positioned on the object plane of the projection optical system PL and the wafer W is accurately positioned on the image plane of the projection optical system PL, if coma aberration occurs in the projection optical system PL, the reticle R passes through the reticle R. The projected light beam does not travel the designed optical path in the projection optical system PL, and forms an image at a position different from the designed position. For this reason, as shown in FIG. 2B, the resist pattern RP2 formed on the wafer W has a so-called line width abnormality in which the pattern widths at both ends are changed. This line width abnormality is caused by the image formation of the central pattern image on the wafer W with respect to the amount of deviation of the image formation position on the wafer W of the pattern images at both ends of the line and space pattern formed on the reticle R. Since the amount of positional deviation is large, the pattern image at the center is biased to one of the pattern images at both ends, resulting from the difference between the contrast at one end and the contrast at the other end.

  This phenomenon is not limited to a phenomenon that occurs in a line-and-space pattern composed of a plurality of line patterns and space patterns, and is also a phenomenon that occurs in a pattern composed of two line patterns and one space pattern shown in FIG. 3A shows a resist pattern RP3 formed on the wafer W when there is no coma aberration of the projection optical system PL, and FIG. 3B shows a wafer when the projection optical system PL has coma aberration. A resist pattern RP4 formed on W is shown.

  As shown in FIG. 3A, when there is no coma in the projection optical system PL, the line widths of the respective patterns forming the resist pattern RP4 are substantially equal, but there is a coma as shown in FIG. In some cases, one of the line widths of the pattern forming the resist pattern RP4 becomes thicker and the other becomes thinner. This is because a contrast bias contributing to image formation occurs due to the influence of coma remaining in the projection optical system PL. Although the amount of change in line width varies depending on the photosensitive characteristics of the resist applied on the wafer W, the direction of change in line width does not change, and the behavior is almost the same.

  The coma that remains in the projection optical system PL changes the line width of both ends of the line-and-space pattern or two line patterns because the three-beam interference shifts due to the shift of the optical axis, and the exposure amount The width of the resist pattern formed on the wafer W can be increased / decreased by increasing / decreasing or changing the line width of the pattern of the reticle R. In particular, in the case of a pattern thinner than the resolution limit, it is formed on the wafer W. The resist pattern disappears. In the present embodiment, coma aberration remaining in the projection optical system PL is measured using such properties.

  FIG. 4 is a diagram showing an example of a measurement pattern used for measuring the coma aberration of the projection optical system PL. As shown in FIG. 4, the measurement pattern MP is a direction in which a set pattern P0 formed by juxtaposing patterns P1, P2 (first and second patterns) having a longitudinal direction in the direction D1 in FIG. 4 is orthogonal to the direction D1. It is arranged in D2. FIG. 4 shows a case where the measurement pattern MP is composed of a set pattern P0 of three columns.

  The patterns P1 and P2 are wedge-shaped patterns in which the line width (the width of the direction D2) gradually changes along the direction D1, and the direction of the change is opposite between the patterns P1 and P2, that is, the pattern The line width of the pattern P2 decreases as the line width of P1 increases, and conversely, the line width of the pattern P2 increases as the line width of the pattern P1 decreases. The patterns P1 and P2 are set so that the sum of the line width of the pattern P1 and the line width of the pattern P2 at an arbitrary position in the direction D1 is constant.

  Hereinafter, a value obtained by dividing the maximum line width of the pattern in the direction D2 by the length of the pattern in the direction D1 is defined as a dimensional change rate of the pattern. In the patterns P1 and P2, for example, the thickest part of the line width is set to about 1 μm, and the length in the direction D1 is set to about 50 μm. In such a case, the dimensional change rate of the patterns P1 and P2 is 2%. Further, in order to obtain line width abnormality due to coma aberration, it is necessary to use a line and space pattern with a duty ratio of 50%. Patterns P1 and P2 shown in FIG. 4 both have a line width of 0.5 μm at an intermediate position in the longitudinal direction (direction D1). For this reason, in order to set the duty ratio to 50% at this position (that is, the line widths of the patterns P1 and P2 are equal to each other), the patterns P1 and P2 are arranged with an interval of 0.5 μm. Is desirable.

  FIG. 5 is a diagram showing an example of a resist pattern formed on the wafer W when the measurement pattern MP shown in FIG. 4 is transferred onto the wafer W via the projection optical system PL having coma aberration. The resist pattern RP10 shown in FIG. 5 includes three resist patterns rp0 formed by transferring the set pattern P0 shown in FIG. The resist pattern rp0 includes a resist pattern rp1 formed by transferring the pattern P1 and a resist pattern rp2 formed by transferring the pattern P2.

  Referring to FIG. 5, both of the resist patterns rp1 and rp2 are affected by coma aberration remaining in the projection optical system PL, and the line width changes, and the resist pattern rp1 has a thick line width. The resist pattern rp2 has a narrow line width. Further, the resist patterns rp1 and rp2 not only change the line width but also the length in the longitudinal direction, and the lengths thereof are also different from each other. This is because, in the pattern P1 shown in FIG. 4, the narrow line width at the tip is a line width near the resolution limit and is in an unresolved state on the wafer W, and the pattern P2 is the pattern P1. This is because the pattern disappears due to two effects of the same effect and the effect of reducing the line width due to the influence of coma aberration.

  Therefore, when the measurement pattern MP shown in FIG. 4 is transferred onto the wafer W via the projection optical system PL, changes in the shape (line width change and length change) of the resist pattern formed on the wafer W are measured. If it is converted into a numerical value, the direction and magnitude of coma aberration in the projection optical system PL can be obtained. However, it takes time to determine the shape change of each resist pattern, and the shape change often varies. Therefore, the resist pattern RP10 formed on the wafer W is imaged by an image sensor such as a CCD, and the obtained image signal is in a direction orthogonal to the longitudinal direction of the resist pattern (direction corresponding to the direction D2 in FIG. 4). The direction and magnitude of coma aberration are obtained from the integrated signal obtained by integrating the signals.

  As described above, the lengths of the patterns P1 and P2 shown in FIG. 4 are set to the same length of about 50 μm, and the line width of the pattern P1 and the line width of the pattern P2 at an arbitrary point in the direction D1. The sum is set to be constant. Therefore, when there is no coma aberration in the projection optical system PL, the amount of change in the length of the resist pattern formed by transferring the pattern P1 and the length of the resist pattern formed by transferring the pattern P2 are the same. Even if the exposure amount at the time of transfer of the patterns P1 and P2 changes, the length of the resist pattern formed by the transfer changes, but the change amount of the length is the same.

  Therefore, if no coma aberration is generated in the projection optical system PL, the above integrated signal does not change in the longitudinal direction. However, when coma aberration occurs in the projection optical system PL, the shape change of each resist pattern formed by the transfer of the patterns P1 and P2 is different, and thus the above integrated signal changes in the longitudinal direction of the resist pattern. It will be. For this reason, the coma aberration generation direction and magnitude of the projection optical system PL are obtained by measuring the integrated signal. Based on this principle, the present embodiment obtains the coma aberration generation direction and magnitude of the projection optical system PL.

  Next, a method for measuring coma aberration will be described. FIG. 6 is a flowchart illustrating a coma aberration measuring method according to the first embodiment. In order to measure the coma aberration of the projection optical system PL, first, the operator operates a keyboard, operation panel, etc. (not shown) connected to the main control system 12 in FIG. To do. When instructed, the main control system 12 outputs a control signal to a reticle loader (not shown), and unloads a measurement reticle having the measurement pattern MP shown in FIG. It arrange | positions on the stage 4 (step S11).

  FIG. 7 is a diagram illustrating an example of a measurement reticle. The measurement reticle TR shown in FIG. 7 has a plurality of measurement patterns MP so that the width directions of the patterns P1 and P2 are radial around the center, that is, the direction D2 shown in FIG. 4 is radial. Are arranged. The measurement pattern MP is formed on the measurement reticle TR by depositing a metal such as Cr (chromium) and patterning it in a wedge shape. Note that the arrangement of the pattern MP shown in FIG. 7 is merely an example, and may be an arbitrary arrangement.

  The main control system 12 controls a field stop (not shown) provided in the illumination optical system 2 and sets the size of the illumination area IA so that all the measurement patterns MP are located in the illumination area IA. The main control system 12 also outputs a control signal to a wafer loader (not shown) along with the arrangement of the measurement reticle TR, and carries the wafer W (measurement wafer) coated with resist into the exposure apparatus. W is arranged on the wafer stage 8 (step S12).

  When the arrangement of the measurement reticle TR and the wafer W is completed, the main control system 12 outputs a control signal to the drive system 13 to move the wafer stage 8 and position the wafer W at a predetermined position. When the positioning of the wafer W is completed, the main control system 12 outputs a control signal to the exposure light source 1 to start light emission. The exposure light EL emitted from the exposure light source 1 by the light emission of the exposure light source 1 illuminates the illumination area IA on the measurement reticle TR through the illumination optical system 2 with uniform illuminance. The exposure light EL that has passed through the measurement reticle TR is projected onto the exposure area EA on the wafer W through the projection optical system PL, whereby a plurality of measurement patterns MP are transferred onto the wafer W (step S13).

  When the measurement pattern MP is transferred onto the wafer W, the main control system 12 controls the unloader (not shown) to carry out the wafer W subjected to the exposure process from the exposure apparatus. The unloaded wafer W is transferred to a developing device (developer) (not shown) that is inlined with respect to the exposure device, and development processing is performed. By this development processing, a resist pattern having a shape corresponding to the shape of the measurement pattern MP and the coma aberration of the projection optical system PL is formed on the wafer W (step S14).

  Next, the operator sets the wafer W after the development processing to a measurement device (not shown), and uses this measurement device to measure the coma aberration of the projection optical system PL from the shape of the resist pattern formed on the wafer W. To do. The measuring device is a measuring device such as an overlay measuring device or a line width measuring device, for example, an input unit for inputting an operator's instruction, an imaging unit including an imaging device such as a CCD, and an image captured by the imaging device. An image processing unit that performs predetermined image processing on the signal and a calculation unit that digitizes the coma aberration of the projection optical system PL from the signal obtained by performing the image processing are included. Note that the functions of the image processing unit and the calculation unit included in the measurement apparatus may be realized by hardware or may be realized by software.

  When the wafer W is set in the measuring apparatus, first, an image of the portion where the resist pattern is formed on the wafer W is imaged by the imaging unit (step S15). Here, as shown in FIG. 7, since a plurality of measurement patterns MP are formed around the center of the measurement reticle TR, the resist pattern on the wafer W is a resist pattern RP10 shown in FIG. A plurality of patterns are formed around a point on the wafer W in the same arrangement as that of the measurement pattern MP.

  When imaging such a resist pattern, the operator may operate the input unit to set the imaging range of the imaging unit, and may image the resist pattern for each measurement pattern MP multiple times. An area including all of the resist patterns formed on the wafer W may be imaged collectively. When all the resist patterns are imaged collectively, the arrangement of the measurement patterns MP formed on the measurement reticle TR and the width direction of the patterns P1, P2 for each measurement pattern MP (in the direction D2 shown in FIG. 4). It is preferable to input information (measurement pattern information) related to (orientation) in advance to the measurement apparatus in performing subsequent processing.

  When the resist pattern is imaged, an imaging signal is output from the imaging unit and input to the image processing unit. The image processing unit performs predetermined image processing on the input image signal, and then integrates and integrates the image signal in a direction orthogonal to the longitudinal direction of the resist pattern (direction corresponding to direction D2 in FIG. 4). Processing for calculating a signal is performed (step S16). Here, the image processing performed by the image processing unit with respect to the input image signal includes processing for enlarging / reducing the image, processing for rotating the image, processing for cutting out the image based on measurement pattern information input in advance, and the like It is processing of. This process is performed in order to facilitate the process of calculating the integrated signal performed after the image processing.

  FIG. 8 is a diagram for explaining processing performed by the measurement apparatus when obtaining coma aberration. In FIG. 8, IS represents an image signal of a resist pattern included in an image signal subjected to image processing by the image processing unit. Since the resist pattern surface has a lower reflectance than the surface of the wafer W and further scatters incident light slightly, the resist pattern is observed darker than the surroundings. For this reason, when an area including the resist pattern is imaged, an image signal in which only the resist pattern portion has a lower signal intensity than the surrounding area can be obtained. In order to represent this state, the image signal IS of the resist pattern is hatched in FIG.

  In step S16, the image processing unit performs a process of calculating the integrated signal AS by integrating the image signals in a direction D12 orthogonal to the direction D11 corresponding to the longitudinal direction of the resist pattern. As shown in FIG. 8, in the regions R1 and R3 in which the image signal IS of the resist pattern is not included, there is almost no change in the image signal, so the integrated signal AS becomes a constant value. In contrast, in the region R2 including the image signal IS of the resist pattern, the intensity of the image signal IS of the resist pattern is lower than the surroundings, and the width in the direction D12 changes according to the position in the direction D11. For this reason, as shown in FIG. 8, the integrated signal AS whose intensity changes in the direction D11 is obtained.

  The integration signal AS is output from the image processing unit to the calculation unit. The calculation unit performs a process of converting the coma aberration of the projection optical system PL into a numerical value based on the change in the integrated signal AS (step S17). In this process, first, the end points E1, E2 at which the integrated signal AS changes abruptly and the distance L1 between the end points E1 and E2 are obtained. Note that the distance L1 obtained here is the total length of the actual resist pattern in consideration of the magnification of the imaging unit.

  Next, a predetermined slice level SL is set for the integrated signal AS, two intersections C1 and C2 between the integrated signal AS and the slice level SL are obtained, and a midpoint C0 of these intersections C1 and C2 is obtained. It is done. The midpoint C0 here is a point equidistant from the intersections C1 and C2, and is the midpoint C0 with respect to the slice level SL. The position of the midpoint C0 with respect to the slice level SL changes according to the coma aberration generation direction and magnitude of the projection optical system PL. Therefore, the coma aberration can be quantified by obtaining the positional relationship between the end points E1, E2 indicating both ends of the resist pattern and the midpoint C0 with respect to the slice level SL.

  In order to quantify the coma aberration, it is necessary to express the direction and magnitude of the coma aberration (coma aberration amount). Assuming that the projection optical system PL has no aberration, the midpoint C0 coincides with the midpoints of the end points E1 and E2, and the distance from the midpoint C0 to the end point E1 and the midpoint C0 to the end point E2 are the same. It becomes equal to the distance. On the other hand, when the projection optical system PL has coma aberration, the midpoint C0 is shifted in the direction of the end point E1 or the end point E2.

  For this reason, for example, the coordinates of the midpoint C0 when the midpoint C0 and the midpoints of the end points E1 and E2 coincide are set as the origin, the end point E1 side is set in the negative direction, and the end point E2 side is set in the positive direction. If set, the coma aberration generation direction can be expressed. Further, the distance from the end point E1 to the end point E2 is set to “100%”, the distance from the midpoint C0 to the end point E1 is assigned to “50%”, and the distance from the midpoint C0 to the end point E2 is assigned to “50%”. The magnitude of coma aberration can be expressed.

  When the above expression method is used, “0%” is expressed when there is no coma in the projection optical system PL. Further, as shown in FIG. 8, coma aberration when the midpoint C0 is on the end point E1 side and the ratio of the distance from the midpoint C0 to the end point E1 and the distance from the midpoint C0 to the end point E2 is 4: 6. Is expressed as “−10%”. In the above example, the distance between the end point E1 and the end point E2 was expressed as “100%”. By standardizing this distance to “1”, the coma aberration in the case shown in FIG. -0.1 ".

  In the foregoing, an example of a method for quantifying coma aberration has been described, but there are various expression methods other than the above expression method. For example, a method of expressing the distance from the end point E1 to the midpoint C0 as a percentage with respect to the distance from the end point E1 to the end point E2, and the ratio between the lowest signal strength at the end point E1 and the lowest signal strength at the end point E2. Or the signal strength of the integrated signal AS in the regions R1 and R3 not including the image signal IS of the resist pattern shown in FIG. 8 is “100%”, and the minimum signal strength at the end point E1 with respect to this signal strength and There are expression methods such as a method of expressing the minimum signal intensity at the end point E2 as a percentage.

  By using the above expression method, the direction and magnitude of coma aberration can be expressed, but the coma aberration can also be expressed as the line width abnormality described with reference to FIGS. As described above, the patterns P1 and P2 forming the measurement pattern MP shown in FIG. 4 have a line width of 0.5 μm at the middle position in the longitudinal direction (direction D1). It arrange | positions with the space | interval of 5 micrometers. For this reason, it is a line-and-space pattern with a duty ratio of 50% at an intermediate position in the longitudinal direction (direction D1), and an abnormal line width due to coma aberration can be obtained.

  Specifically, the line width abnormality is obtained from the target line width and dimensional change rate of the measurement pattern MP and the coma aberration amount. As described above, the target line width of the measurement pattern MP shown in FIG. 4 is 0.5 μm. Further, since the dimensional change rates of the patterns P1 and P2 are both 2%, the dimensional change rate of the measurement pattern MP is 4%. When the measurement result shown in FIG. 8 is obtained using such a measurement pattern MP and “−0.1” is obtained as the coma aberration amount, by multiplying each value, “−0. 2 μm ”is obtained.

  Since the processing described with reference to FIG. 8 is performed on the image signal of each resist pattern for each measurement pattern MP, the coma aberration amount is obtained around the optical axis AX of the projection optical system PL, and further the optical axis. Abnormal line width around AX is obtained. When the coma aberration amount of the projection optical system PL is obtained through the above processing, the result is output to a monitor such as a CRT or a liquid crystal display device. The operator inputs an instruction for reducing coma aberration by operating a keyboard, an operation panel (not shown) connected to the main control system 12 with reference to the display content of the monitor.

  When this instruction is input, a control signal is output from the main control system 12 to the lens controller 14. The lens controller 14 drives at least one optical element of the projection optical system PL based on a control signal from the main control system 12. Such processing reduces the coma aberration of the projection optical system PL.

  As described above, in this embodiment, the coma aberration is obtained by imaging the resist pattern formed by transferring the measurement pattern MP shown in FIG. As a result, the measurement time can be shortened. Further, since the operator's visual work is omitted, the coma aberration of the projection optical system can be measured with high accuracy. Further, the coma aberration amount is obtained from the integrated signal obtained by integrating the image signals of the plurality of resist patterns obtained by transferring the plurality of set patterns P0, and the shape variations of the individual patterns are averaged. Measurement reproducibility and stability can be improved.

  In this embodiment, the operator gives an instruction to reduce the coma aberration to the exposure apparatus with reference to the measurement result of the coma aberration displayed on the monitor of the measurement apparatus. For example, the measurement apparatus and the exposure apparatus May be connected via a communication line (wireless or wired), and the main control system 12 may adjust the projection optical system PL via the lens controller 14 based on the coma aberration measurement result transmitted from the measurement apparatus. In this embodiment, the measurement apparatus performs image signal processing of a resist pattern and calculation (quantification) of the coma aberration amount. However, a part of the function of the measurement apparatus is another apparatus, for example, an exposure apparatus or a host. You may give it to a computer. For example, the measurement apparatus may perform only image signal processing, and the processing result may be sent to the exposure apparatus so that the main control system 12 may calculate the coma aberration amount. Note that the measuring device may be connected inline to the coater / developer and the developed wafer may be automatically conveyed to the measuring device.

[Second Embodiment]
FIG. 9 is a view showing the schematic arrangement of an exposure apparatus in which the optical performance measuring method according to the second embodiment of the present invention is used. The overall configuration of the exposure apparatus shown in FIG. 9 is substantially the same as that of the exposure apparatus shown in FIG. 1, and the same members are denoted by the same reference numerals. In FIG. 9, illustration of some components such as the exposure light source 1 and the illumination optical system 2 shown in FIG. 1 is omitted.

  The exposure apparatus of the present embodiment is provided with an image measuring device 20 for measuring an optical image projected on the wafer stage 8 via the projection optical system PL, and the inside of the main control system 12. The configuration is different. The image measuring device 20 is provided at one end of the wafer stage 8 and includes an opening 21, relay lenses 22 and 23, and an image sensor 24 such as a CCD. The opening 21 is formed so that the position in the Z direction is substantially the same as the surface position of the wafer W.

  The relay lens 22 is arranged so that one focal point is located at the opening 21 and converts an incident light beam into a parallel light beam. The relay lens 23 is arranged so that one focal point is located on the image pickup surface of the image pickup device 24, and collects the light flux via the relay lens 22 and forms an image on the image pickup surface of the image pickup device 24. The image sensor 24 photoelectrically converts an optical image formed on the imaging surface to generate an image signal, and outputs the image signal to the main control system 12. The imaging surface of the imaging element 24 and the opening 21 are optically conjugate with respect to the relay lenses 22 and 23.

  The main control system 12 measures the resist pattern formed on the wafer W in the first embodiment described above and determines the coma aberration of the projection optical system PL. A configuration corresponding to a calculation unit is provided, and various processes such as image processing similar to those of the first embodiment are performed on the image signal output from the image sensor 24 to obtain the coma aberration of the projection optical system PL. That is, the exposure apparatus shown in FIG. 9 has the function for measuring the coma aberration in the exposure apparatus shown in FIG.

  In the first embodiment described above, the plurality of measurement patterns MP formed on the measurement reticle TR are transferred onto the wafer W, the resist pattern formed on the wafer W is imaged, and the coma aberration of the projection optical system PL is reduced. I was seeking. However, in this embodiment, an optical image of the measurement pattern MP projected onto the wafer stage 8 via the projection optical system PL is directly captured by the image measuring device 20 to obtain the coma aberration of the projection optical system PL. Hereinafter, a method for measuring coma aberration using the exposure apparatus shown in FIG. 9 will be described.

  FIG. 10 is a flowchart showing a coma aberration measuring method according to the second embodiment. Also in this embodiment, when measuring the coma aberration of the projection optical system PL, the operator first instructs the main control system 12 to start measurement, and the measurement reticle TR shown in FIG. 7 is placed on the reticle stage 4. Arrange (step S21). Next, the main control system 12 outputs a control signal to the drive system 13, moves the wafer stage 8, and arranges the opening 21 of the image measuring device 20 below the projection optical system PL (step S22).

  When the movement of the wafer stage 8 is completed, the main control system 12 starts light emission of the exposure light source 1 (not shown in FIG. 9). The illumination region of the measurement reticle TR is illuminated with uniform illuminance by the light emission of the exposure light 1, and the light transmitted through the measurement reticle TR passes through the projection optical system PL, so that a plurality of light beams are formed on the measurement reticle TR. An optical image of the measurement pattern MP is projected on the wafer stage 8.

  Since the opening 21 of the image measuring device 20 is disposed below the projection optical system PL, the light that has passed through the opening 21 enters the imaging surface of the image sensor 24 via relay lenses 22 and 23 in order. Since the aperture 21 and the imaging surface of the imaging device 24 are optically conjugate with respect to the relay lenses 22 and 23, the optical image of the measurement pattern MP projected on the wafer stage 8 on the imaging surface of the imaging device 24 is obtained. Reimage.

  The image sensor 24 photoelectrically converts the optical image formed on the imaging surface to generate an image signal, which is output to the main control system 12. In this way, an optical image projected through the projection optical system PL is measured (step S23). If all of the optical image of the measurement pattern MP projected on the wafer stage 8 is within the measurement field of view of the image measurement device 20 and re-imaged on the imaging surface, the process of step S23 is performed once. When the measurement is not within the measurement field of view, the wafer stage 8 is moved to sequentially measure while placing the openings 21 at positions where the respective measurement patterns MP are projected.

  When the measurement of the optical image is completed, the main control system 12 performs predetermined image processing on the image signal output from the image measurement device 20 in the same manner as in the measurement device of the first embodiment. A process of calculating the integrated signal by integrating the image signals in the direction orthogonal to the longitudinal direction of the optical image (the direction corresponding to the direction D2 in FIG. 4) is performed (step S24). Then, the same processing as that described with reference to FIG. 8 is performed to obtain a coma aberration amount obtained by quantifying the coma aberration of the projection optical system PL (step S25).

  When the coma aberration amount of the projection optical system PL is obtained through the above processing, the result is output to a monitor such as a CRT or a liquid crystal display device. Here, the operator may input an instruction for reducing coma aberration to the main control system 12 with reference to the display content of the monitor as in the first embodiment, but based on the obtained coma aberration amount. Thus, the main control system 12 may output a control signal to the lens controller 14 to automatically reduce coma.

  In the above description, the case where the image measuring device 20 is provided in the wafer stage 8 has been described as an example. However, even if a part of the image measuring device 20 is disposed outside the wafer stage 8. For example, an image measuring apparatus that guides an optical image projected on the wafer stage to the outside of the wafer stage by an optical transmission unit such as an optical fiber or a relay lens and measures the optical image may be used. Further, the image measuring device may be fixed to the wafer stage or may be removable. Further, the relay lenses 22 and 23 of the image measuring device 20 may be a unity magnification system, but an expansion system is preferable in consideration of the line width of the measurement pattern MP and the like.

  As described above, in this embodiment, since the optical image of the measurement pattern MP projected through the projection optical system PL is directly measured by the image measuring device 20 to obtain the coma aberration, the operator's manual operation is performed. Most of the time is reduced and the measurement time can be shortened. Further, since there is no operator's visual work, coma aberration of the projection optical system can be measured with high accuracy.

[Third Embodiment]
Next, a third embodiment of the present invention will be described. The exposure apparatus of the present embodiment has substantially the same configuration as the exposure apparatus of the second embodiment shown in FIG. 9, but in this embodiment, a wafer is used by using an alignment sensor 15 provided on the side of the projection optical system PL. The difference is that the resist pattern formed on W is measured, and the coma aberration amount of the projection optical system PL is measured from the measurement result. In this embodiment, the case where the alignment sensor 15 is an FIA type alignment sensor including an image sensor such as a CCD will be described as an example.

  The procedure for forming a resist pattern on the wafer W is the same as the procedure shown in FIG. That is, the measurement reticle TR is placed on the reticle stage 4 (step S11), the wafer W is placed on the wafer stage 8 (step S12), and the wafer W is positioned and then formed on the measurement reticle TR. The measurement pattern MP is transferred onto the wafer W via the projection optical system PL (step S13). Then, the wafer W that has been subjected to the exposure process is unloaded from the exposure apparatus, and development processing is performed with the developing apparatus inlined with respect to the exposure apparatus, thereby forming a resist pattern on the wafer W (step S14).

  Next, the wafer W on which the resist pattern is formed after the development process is carried back into the exposure apparatus and held on the wafer stage 8. When the above processing is completed, the main control system 12 moves the wafer stage 8 via the drive system 13 and arranges the resist pattern formed on the wafer W within the measurement field of view of the alignment sensor 15. When the alignment sensor 15 picks up an image of the resist pattern arranged in the measurement field of view, an image signal is output from the alignment sensor 15 to the main control system 12. If all the resist patterns on the wafer W do not fit within the measurement field of the alignment sensor 15, the wafer stage 8 is moved to place the resist pattern for each measurement pattern MP within the measurement field of the alignment sensor 15. While taking an image.

  When imaging of the resist pattern by the alignment sensor 15 is completed, the main control system 12 performs predetermined image processing on the image signal from the alignment sensor 15 and thereafter in the longitudinal direction of the resist pattern, as in the second embodiment. A process of calculating the integrated signal by integrating the image signals in the orthogonal direction (the direction corresponding to the direction D2 in FIG. 4) is performed (step S24 in FIG. 10). Then, the same processing as that described with reference to FIG. 8 is performed to obtain a coma aberration amount obtained by quantifying the coma aberration of the projection optical system PL (step S25). When the amount of coma is obtained, a process for reducing the coma of the projection optical system PL is performed by the lens controller 14 as in the second embodiment.

[Fourth Embodiment]
In the first and third embodiments described above, the image signal obtained by imaging the resist pattern formed on the wafer W is subjected to image processing, and in the second embodiment, the measurement is projected onto the wafer stage 8. The coma aberration amount of the projection optical system PL has been obtained by performing image processing on an image signal obtained by capturing an optical image of the pattern MP. On the other hand, the exposure apparatus of the present embodiment includes an LSA (Laser Step Alignment) type measurement apparatus, which irradiates the resist pattern on the wafer W with a laser beam such as He—Ne, The coma aberration of the projection optical system PL is measured by measuring the scattered light.

  In the present embodiment, when coma aberration is measured, first, a resist pattern is formed on the wafer W by performing processing similar to the processing in steps S11 to S14 shown in FIG. However, when the measurement pattern is transferred in step S13, the exposure amount is increased to separate the resist pattern corresponding to the pattern P1 and the resist pattern corresponding to the pattern P2 in FIG. FIG. 11 is a diagram illustrating an example of a resist pattern formed on the wafer W and a measurement signal of the resist pattern in the fourth embodiment.

  In FIG. 11, RP20 is a resist pattern formed on the wafer W. In the present embodiment, a measurement pattern is used in which three sets of set patterns each having two sets of set patterns P0 shown in FIG. 4 are arranged. By transferring the measurement pattern onto the wafer W, a resist pattern RP20 is formed. As shown in FIG. 11, the pattern is separated in the longitudinal direction (direction D21) of the resist pattern RP20 by increasing the exposure amount during exposure.

  Next, as in the third embodiment, the wafer W on which the resist pattern RP20 is formed is loaded again into the exposure apparatus and held on the wafer stage 8. When the above processing is completed, the main control system 12 moves the wafer stage 8 so that the resist pattern RP20 on the wafer W is directed to the irradiation position of the laser beam emitted from the LSA type measuring device. Then, the laser beam scattered by the resist pattern RP20 is measured by an LSA type measuring device. The cross-sectional shape of the laser light is a slit shape extending in a direction D22 orthogonal to the direction D21, and the moving direction (scan direction) of the resist pattern RP20 with respect to the laser light is a direction D21 in FIG.

  In FIG. 11, the curve with the symbol DS is a measurement signal obtained by measuring the resist pattern RP20. The measurement signal DS has a low signal intensity at a location where the resist pattern RP20 is not formed, and a high signal strength at a location where the measurement pattern DS is formed. Since the resist pattern RP20 is separated with respect to the direction D21, two peaks appear clearly in the measurement signal DS.

  In order to quantify the coma aberration from the measurement signal DS, for example, a predetermined slice level SL1 is set for the measurement signal DS, two widths L11 and L12 are obtained, and the ratio of the widths is determined as the coma aberration amount And Alternatively, the length L10 corresponding to the entire length of the resist pattern RP20 is obtained, the position of the midpoint C10 where the resist pattern RP20 is separated is obtained, and the relationship between the length L10 and the position of the midpoint C10 (for example, The ratio of the length L10 and the distance from one end point E10 to the midpoint C10) is the coma aberration amount. As described above, the coma aberration amount of the projection optical system PL can also be measured by measuring the resist pattern RP20 using an LSA type measuring apparatus.

[Other Embodiments]
In the first to fourth embodiments described above, the coma aberration amount of the projection optical system PL is determined using the measurement pattern MP having the set pattern P0 including the two patterns P1 and P2 shown in FIG. I was asking. However, the measurement pattern used for measuring the coma aberration amount of the projection optical system PL is not limited to the measurement pattern MP shown in FIG. 4, and a measurement pattern composed of three or more patterns can also be used.

  FIG. 12 is a diagram illustrating another example of the measurement pattern. The measurement pattern MP1 shown in FIG. 12A includes a pattern P11 having the same shape as the pattern P1, a pattern P12 having the same shape as the pattern P2, and a rectangular pattern P13 arranged between the patterns P11 and P12. . In the pattern P13, the length in the longitudinal direction (direction D31 in the drawing) is set equal to the lengths of the patterns P11 and P12, and the line width in the direction D32 orthogonal to the direction D31 is set constant. Accordingly, the sum of the line widths of the patterns P1 to P3 at any position in the direction D31 is constant.

  If the measurement pattern MP1 shown in FIG. 12A is transferred onto the wafer W via the projection optical system PL when the projection optical system PL has no aberration, a resist pattern similar to the measurement pattern MP1 is formed on the wafer W. Is formed. For this reason, for example, when the measurement method shown in the first embodiment is used, for example, an integrated signal AS1 shown in FIG. 12A is obtained. The integrated signal AS1 has a constant signal intensity at the position where the resist pattern is formed, and is lower than the signal intensity where the resist pattern is not formed.

  If the measurement pattern MP1 shown in FIG. 12A is transferred onto the wafer W via the projection optical system PL when the projection optical system PL has coma aberration, for example, a resist pattern RP30 shown in FIG. 12B is formed. The In the resist pattern RP30 shown in FIG. 12B, the line width of the portion corresponding to the pattern P11 is thickened and the length is shortened, and the line width of the portion corresponding to the pattern P12 is thinned and the length is shortened. However, the portion corresponding to the pattern P13 has no change in line width and length.

  For example, when the measurement method shown in the first embodiment is used for the resist pattern RP30, an integrated signal AS2 shown in FIG. 12B is obtained. Since this integration signal is a signal showing the same change as the integration signal AS shown in FIG. 8, the coma aberration of the projection optical system PL is determined in the same manner as described in the first embodiment with reference to FIG. Can be quantified. In FIG. 12A, the measurement pattern MP1 including three patterns P11 to P13 is illustrated, but the number of patterns forming the measurement pattern MP1 can be arbitrarily set. Further, this measurement pattern MP1 can be used in all of the first to fourth embodiments.

  In embodiments other than the second embodiment described above, the measurement pattern is transferred onto the wafer W via the projection optical system PL, and then developed to form a resist pattern on the wafer W and measure the resist pattern. Thus, the coma aberration amount of the projection optical system PL was obtained. However, the amount of coma aberration may be obtained by measuring a latent image on the wafer W without performing development processing. At this time, the material of the photosensitive layer on which the latent image of the measurement pattern is formed is not limited to the photoresist, and other materials such as a magneto-optical material may be used. Further, the photosensitive layer may be formed not only on the wafer but also on other members. Furthermore, instead of detecting a resist pattern or a latent image, a pattern after etching may be detected. Moreover, the shape and dimensional change rate of the pattern constituting the measurement pattern can be arbitrarily set.

  Further, in the above embodiment, the case where coma aberration is measured as an example of the optical characteristic of the projection optical system PL has been described as an example. You can also. When the position variation of the image plane of the projection optical system PL has occurred, the surface of the wafer W or the opening 21 of the image measuring device 20 is defocused with respect to the image plane of the projection optical system PL. In such a state, the image of the measurement pattern is projected on the wafer W or the image measurement device 21 in a state of being blurred regardless of the presence or absence of aberration of the projection optical system PL. In (Part), a disappeared part corresponding to the defocus amount appears. Since the disappearance portion increases as the defocus amount increases, the position of the image plane of the projection optical system PL can be specified by obtaining the position in the Z direction where the length in the longitudinal direction of the resist pattern or optical image is the longest. it can.

  Further, in each of the above embodiments, it is preferable that the surface of the wafer is accurately arranged on the image plane of the projection optical system PL at least at the projection position of the measurement pattern in the exposure area EA when the measurement pattern MP is transferred.

  Further, in each of the above embodiments, the number of measurement patterns MP is not limited to eight, and the measurement reticle may include at least one measurement pattern, but the width direction D2 of patterns P1 and P2 (that is, , Preferably including at least two measurement patterns having different length directions D1). Further, the measurement pattern MP of FIG. 4 has three pairs of patterns P1 and P2, but the number thereof may be one pair, two pairs, or four pairs or more. In FIG. 7, since the measurement pattern MP is exaggerated, only one set of eight measurement patterns MP is shown on the measurement reticle TR, but a plurality of sets are included in the measurement reticle TR. A plurality of measurement patterns MP described above may be formed in the above pattern, that is, at a plurality of locations.

  Moreover, in each embodiment except the said 2nd Embodiment, you may make it perform pattern detection using a scatterometry technique.

  The embodiment described above is described in order to facilitate understanding of the present invention, and is not described in order to limit the present invention. Therefore, each element disclosed in the above embodiment is intended to include all design changes and equivalents belonging to the technical scope of the present invention. For example, in the above embodiment, the step-and-repeat type exposure apparatus has been described as an example, but the present invention can also be applied to a step-and-scan type exposure apparatus.

In the above embodiment, the case where the exposure apparatus includes an ArF excimer laser as the exposure light source 1 has been described as an example. However, an ultrahigh pressure mercury lamp that emits g-line (wavelength 436 nm) and i-line (wavelength 365 nm); Alternatively, a KrF excimer laser (wavelength 248 nm), an F ₂ laser (wavelength 157 nm), a Kr ₂ laser (wavelength 146 nm), a YAG laser high-frequency generator, or a semiconductor laser high-frequency generator can be used. As the exposure light EL, a soft X-ray region generated from the SOR, for example, EUV (Extreme Ultra Violet) light having a wavelength of 13.4 nm or 11.5 nm may be used. Furthermore, you may use charged particle beams, such as an electron beam or an ion beam.

  The projection optical system PL may be any of a reflection optical system, a refractive optical system, and a catadioptric optical system. Furthermore, the present invention can also be applied when measuring the optical characteristics of a projection optical system for immersion exposure provided in an immersion exposure apparatus disclosed in International Publication No. WO99 / 49504.

It is a figure which shows schematic structure of the exposure apparatus in which the optical performance measuring method which concerns on 1st Embodiment of this invention is used. It is a figure for demonstrating the measurement principle of the coma remaining in a projection optical system. It is a figure for demonstrating the measurement principle of the coma remaining in a projection optical system. It is a figure which shows an example of the measurement pattern used in order to measure the coma aberration of a projection optical system. FIG. 5 is a diagram showing an example of a resist pattern formed when the measurement pattern shown in FIG. 4 is transferred onto a wafer via a projection optical system having coma aberration. It is a flowchart which shows the measuring method of the coma aberration in 1st Embodiment. It is a figure which shows an example of the reticle for a measurement. It is a figure for demonstrating the process performed with a measuring apparatus when calculating | requiring a coma aberration. It is a figure which shows schematic structure of the exposure apparatus in which the optical performance measuring method which concerns on 2nd Embodiment of this invention is used. It is a flowchart which shows the measuring method of the coma aberration in 2nd Embodiment. It is a figure which shows an example of the measurement signal of the resist pattern formed on a wafer in 4th Embodiment, and a resist pattern. It is a figure which shows the other example of a measurement pattern.

Explanation of symbols

DESCRIPTION OF SYMBOLS 12 ... Main control system 20 ... Image detection apparatus AS ... Integrated signal DP ... Pattern MP ... Measurement pattern MP1 ... Measurement pattern P1 ... 1st pattern P2 ... 2nd pattern P11 ... 1st pattern P12 ... 2nd pattern PL ... Projection optical system R ... Reticle TR ... Measurement mask W ... Wafer

Claims (17)

An optical performance measurement method for measuring optical performance of a projection optical system that projects a pattern of a first surface onto a second surface,
A first pattern whose line width changes in a first direction along the longitudinal direction, and a second pattern which is arranged in parallel with the first pattern and whose line width change in the first direction is opposite to the first pattern An arrangement step of arranging a measurement pattern including: within the first surface;
A measurement step of measuring the optical performance of the projection optical system from the detection result of the image of the measurement pattern projected onto the second surface.   The optical performance measurement method according to claim 1, wherein the first pattern and the second pattern have a wedge shape in which a line width gradually increases or decreases in the first direction.   The shapes of the first pattern and the second pattern are set so that a sum of line widths in a second direction orthogonal to the first direction is constant along the first direction. The optical performance measuring method according to claim 1 or 2. The measurement step includes a detection step of detecting a projection image of the measurement pattern projected on the second surface to obtain a detection signal;
An integration step of integrating the detection signals obtained in the detection step in a direction corresponding to the second direction to obtain an integration signal;
4. A quantification step of quantifying the optical performance of the projection optical system based on a distribution of the integrated signal in a direction corresponding to the first direction. The optical performance measuring method as described. The measurement step includes a substrate placement step of placing a detection substrate on the second surface,
A transfer step of transferring the measurement pattern to the detection substrate via the projection optical system;
A pattern detection step of detecting the pattern transferred to the detection substrate;
4. The optical performance measurement method according to claim 1, further comprising: a numericalization step of converting the optical performance of the projection optical system into a numerical value based on a detection result of the pattern detection step.   The optical performance measurement method according to claim 1, wherein the optical performance of the projection optical system includes coma aberration of the projection optical system. In an exposure method for transferring a pattern formed on a mask onto a substrate via a projection optical system,
Prior to the transfer of the pattern, an optical performance measurement step of measuring the optical performance of the projection optical system using the optical performance measurement method according to any one of claims 1 to 6,
And a characteristic adjustment step of adjusting the optical performance of the projection optical system according to the measurement result of the optical performance measurement step. In an exposure apparatus that transfers a pattern formed on a mask onto a substrate via a projection optical system,
A first pattern having a line width that changes in a first direction along the longitudinal direction, and a second pattern that is arranged in parallel with the first pattern and in which the change in the line width in the first direction is opposite to the first pattern; A detection unit for detecting a projection image of the pattern formed on the measurement mask by the projection optical system using a measurement mask on which a measurement pattern including
The detection signal of the detection unit is integrated in a direction corresponding to the second direction orthogonal to the first direction to obtain an integrated signal, and the projection optical is based on the distribution of the integrated signal in the direction corresponding to the first direction. An exposure apparatus comprising: a performance calculation unit that quantifies the optical performance of the system.   The exposure apparatus according to claim 8, further comprising a characteristic adjustment unit that changes an optical performance of the projection optical system according to a calculation result of the performance calculation unit. A mask used for measuring the optical performance of a projection optical system that projects a pattern of a first surface onto a second surface,
A first pattern whose line width changes in a first direction along the longitudinal direction and a first pattern provided adjacent to the first pattern, and a change in the line width in the first direction is substantially opposite to the first pattern. A mask having a measurement pattern including two patterns.   11. The mask according to claim 10, wherein the measurement pattern includes a plurality of pairs of the first and second patterns arranged side by side in a second direction orthogonal to the first direction.   The said 1st and 2nd pattern is a wedge shape from which the line | wire width of the 2nd direction orthogonal to the said 1st direction increases or decreases gradually in the said 1st direction, respectively. mask.   The said 1st and 2nd pattern is at least one part, The sum of the line | wire width of the 2nd direction orthogonal to the said 1st direction is substantially constant along the said 1st direction. 13. The mask according to any one of items 12.   The measurement pattern is a plurality of pairs of the first and second patterns arranged apart from each other in a second direction orthogonal to the first direction, and a sum of line widths in the second direction is substantially equal. The mask according to claim 13.   15. The measurement pattern according to claim 10, wherein the measurement pattern includes a plurality of the first and second patterns whose line widths change along a direction different from the first direction and the first direction. A mask according to any one of the above. An optical performance measuring method for measuring an optical performance of a projection optical system that projects a pattern of a first surface onto a second surface,
An optical performance of the projection optical system based on a detection result of an image of the measurement pattern projected on the second surface while arranging the mask according to any one of claims 10 to 15 on the first surface. An optical performance measurement method characterized by:   The optical performance of the projection optical system is obtained using detection information relating to the first direction of an image of the measurement pattern having a different length change between the first pattern and the second pattern during the projection. Item 17. The optical performance measurement method according to Item 16.

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