JP2007207822A - Measurement method, exposure method, device manufacturing method, measuring mark, and mask - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a measurement value approximate to a misalignment quantity of an actual device pattern image when the quantity of misalignment of the projected image of a specified mark is measured. <P>SOLUTION: A second mark image is overlaid on a first mark and they are exposed, and the misalignment is measured between the first mark and the second mark image. In this case, the second mark is provided with a plurality of line marks 36D and 36E of which transmission is lower than those of the periphery, and a width of the line mark 36D inside a specified edge 38A is set larger than that of the line mark 36E outside the edge 38A. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a measurement technique for exposing an image of a second mark on a first mark and measuring the amount of positional deviation between the first mark and the image of the second mark, and an exposure technique using the measurement technique. For example, in a lithography process for manufacturing a semiconductor device or the like, it can be applied when measuring an overlay error between two layers on an object such as a wafer.

  For example, in a lithography process for manufacturing a semiconductor device, a pattern of a reticle (or a photomask) is transferred to each shot area of a wafer (or a glass plate, etc.) coated with a resist via a projection optical system. An exposure apparatus such as a stepper or a scanning stepper is used. Semiconductor devices are formed by stacking multiple layers of circuits in a predetermined positional relationship on a wafer, and recently device patterns are becoming increasingly finer, so it is required to improve the overlay accuracy between different layers. Yes. In order to improve overlay accuracy, it is necessary to measure overlay error with high accuracy.

Conventionally, in order to measure an overlay error or distortion of a projection optical system that affects the overlay error, for example, a predetermined mark image is projected onto a wafer on which a plurality of first measurement marks are already formed. A plurality of second measurement marks are formed, and a positional deviation amount of the plurality of sets of two measurement marks is measured by a registration measurement device or the like. Conventionally, for example, a box-in-box mark is used as the measurement mark, and one mark of the box-in-box mark is formed by arranging, for example, one or more line marks in a rectangular frame shape. It was formed (for example, refer to Patent Document 1).
JP 2001-358059 A

  Conventional marks for overlay error measurement, for example, are generally defined in shape such as width irrespective of the device pattern that is actually exposed. Therefore, depending on the illumination conditions, the relative position between the measurement mark image and the actual device pattern image on the measurement target layer is projected to the design relative position (relative position on the reticle). There is a possibility that an error may occur between the measurement result of the overlay error and the positional deviation amount between the actual device patterns. If the device pattern is miniaturized as in recent years, the error may exceed the allowable range.

Further, when measuring distortion of the projection optical system or when performing alignment or the like, it is desirable that the deviation amount between the position measured by the measurement mark and the actual device pattern position is as small as possible.
In view of such a point, the present invention provides a measurement technique capable of obtaining a measurement value close to the positional deviation amount of a pattern image for a device when measuring the positional deviation amount of a projected image of a predetermined mark, and the measurement technique. An object of the present invention is to provide an exposure technique using the.

  In the measurement method according to the present invention, the image of the second mark (33A) is overlaid and exposed on the first mark (41A), and the amount of positional deviation between the first mark and the image of the second mark is measured. The second mark includes a plurality of line portions (36D, 36E) whose transmittance is lower than that of the surrounding portions, and the width of the line portion on the inner side with respect to the predetermined boundary portion (38A) is equal to that of the boundary portion. It is wider than the width of the outer line portion.

According to the present invention, since the second mark includes a plurality of line portions, the amount of positional deviation of the projected image is smaller than the position of the pattern image for the device as compared with the case of simply projecting a wide pattern image. Can be close to the amount of displacement.
Next, an exposure method according to the present invention is an exposure method for managing overlay when an image of a device pattern (32X) of another layer is exposed on one layer. A first step of forming a mark (41A) and exposing an image of a mask pattern in which a second mark (33A) is formed on the one layer together with the device pattern of the other layer; and A second step of measuring a positional shift amount between the first mark and the image of the second mark on one layer, wherein the second mark has a plurality of line portions whose transmittance is lower than that of a surrounding portion. (36D, 36E), and the width of the line portion inside the predetermined boundary portion (38A) is wider than the width of the line portion outside the boundary portion.

According to the present invention, since the second mark includes a plurality of line portions, the amount of misalignment of the projected image is smaller than that of simply projecting a wide pattern image. Close to quantity.
Next, the measurement mark according to the present invention is a measurement mark used for measuring the amount of positional deviation of the projected image, and includes a plurality of line portions (36D, 36E) whose transmittance is lower than the surrounding portions. And the width of the line portion inside the predetermined boundary portion (38A) is wider than the width of the line portion outside the boundary portion.

Next, the mask according to the present invention is a mask in which a device pattern is formed, and the measurement mark of the present invention is formed together with the device pattern.
Further, another mask according to the present invention is used for superimposing management when an image of a device pattern of another layer is exposed on one layer, and the measurement mark of the present invention is formed. . The measurement method or exposure method of the present invention can be used using the measurement mark or mask of the present invention.

  In addition, although the reference numerals in parentheses attached to the predetermined elements of the present invention correspond to members in the drawings showing an embodiment of the present invention, each reference numeral of the present invention is provided for easy understanding of the present invention. The elements are merely illustrative, and the present invention is not limited to the configuration of the embodiment.

Hereinafter, an example of a preferred embodiment of the present invention will be described with reference to the drawings.
FIG. 1 shows a schematic configuration of a scanning exposure type projection exposure apparatus (exposure apparatus) comprising a scanning stepper of this example. In FIG. 1, the projection exposure apparatus includes an exposure light source 6, an illumination optical system 5, a reticle stage. System, projection optical system PL, and wafer stage system. As the exposure light source 6, an ArF excimer laser light source (wavelength 193 nm) is used. As an exposure light source, an ultraviolet pulse laser light source such as a KrF excimer laser light source (wavelength 247 nm), an F ₂ laser light source (wavelength 157 nm), a harmonic generation light source of a YAG laser, or a harmonic generation of a solid-state laser (semiconductor laser, etc.) A device or a mercury lamp (i-line etc.) can also be used.

  Exposure light (exposure illumination light) IL as an exposure beam pulsed from the exposure light source 6 during exposure is mirror 7, a beam shaping optical system (not shown), a first lens 8A, a mirror 9, and a second lens 8B. Then, the cross-sectional shape is shaped into a predetermined shape, and enters the fly-eye lens 10 as an optical integrator (a homogenizer or a homogenizer), and the illuminance distribution is made uniform. On the exit surface of the fly-eye lens 10 (pupil surface of the illumination optical system), an illumination system aperture stop member 11 around which various aperture stops (σ stop) are arranged is rotatably arranged by a drive motor 12. The illumination condition is set by rotating the illumination system aperture stop member 11 and setting a desired aperture stop on the optical path of the exposure light IL.

  As an example, the illumination system aperture stop member 11 has an aperture stop 13A (σ stop) for normal illumination that increases the amount of exposure light in a variable circular region, and four regions that surround the optical axis of the illumination optical system. An aperture stop 13B for modified illumination, an aperture stop 13C for annular illumination, and an aperture stop 13D for first dipole illumination that increases the amount of light in two regions symmetric with respect to the optical axis in the first direction, A second dipole illumination aperture stop (not shown) or the like for increasing the amount of light in two regions symmetric with respect to the optical axis in a second direction orthogonal to the first direction is disposed. Instead of the illumination system aperture stop member 11, a molding optical system having a plurality of diffractive optical elements, a movable prism (such as an axicon), and a zoom optical system that are exchanged in the illumination optical system is used. The intensity distribution of the exposure light IL (reticle illumination conditions) on the pupil plane of the illumination optical system may be made variable by arranging the optical system upstream of the integrator 10 and using this shaping optical system.

  The exposure light IL that has passed through one aperture stop in the illumination system aperture stop member 11 passes through a beam splitter 14 and a relay lens 17A having a low reflectivity, and then a fixed blind 18A as a fixed field stop and a movable blind as a movable field stop. Pass through 18B sequentially. In this case, the movable blind 18B is arranged on a plane substantially conjugate with the pattern surface (reticle surface) of the reticle R as a mask, and defines the illumination area 21R on the reticle surface as a slit-like area elongated in the non-scanning direction. The fixed blind 18A is disposed on a surface slightly defocused from the plane conjugate with the reticle surface, and unnecessary portions are not exposed at the start and end of the scanning exposure for each shot area to be exposed. As described above, the illumination area 21R is used to control the center and width of the illumination area 21R in the non-scanning direction while opening and closing the illumination area 21R in the scanning direction. The exposure light IL that has passed through the blinds 18A and 18B illuminates the illumination region 21R of the pattern region of the reticle R with a uniform illuminance distribution through the sub-condenser lens 17B, the optical path bending mirror 19, and the main condenser lens 20.

  On the other hand, the exposure light reflected by the beam splitter 14 is received by the integrator sensor 16 formed of a photoelectric sensor via the condenser lens 15. The detection signal of the integrator sensor 16 is supplied to the exposure amount control system 3, and the exposure amount control system 3 detects the detection signal of the optical system from the beam splitter 14 measured in advance to the wafer W as an object (photosensitive substrate). Based on the transmittance and control information from the main control system 1 that controls the overall operation of the apparatus, the light emission operation of the exposure light source 6 is controlled so that an appropriate exposure amount is obtained on the wafer W. Mirrors 7 and 9, lenses 8A and 8B, fly-eye lens 10, illumination system aperture stop member 11, beam splitter 14, relay lens 17A, blinds 18A and 18B, sub-condenser lens 17B, mirror 19 and main condenser lens 20 are included. Thus, the illumination optical system 5 is configured.

  Under the exposure light IL, the pattern in the illumination area 21R of the reticle R is projected at a projection magnification β (β is a reduction magnification of, for example, 1/4, 1/5, etc.) via the bilateral telecentric projection optical system PL. The image is projected onto a slit-like exposure area 21W elongated in the non-scanning direction on one shot area SA on the wafer W coated with the photoresist. The projection optical system PL is, for example, a refractive system, but a catadioptric system or the like can also be used. The pattern surface (reticle surface) of the reticle R and the surface (wafer surface) of the wafer W correspond to the object surface and the image surface of the projection optical system PL, respectively. Hereinafter, in FIG. 1, the Z axis is taken in parallel to the optical axis AX of the projection optical system PL, and along a non-scanning direction orthogonal to the scanning direction of the reticle R and the wafer W during scanning exposure in a plane perpendicular to the Z axis. In the following description, the X axis is taken and the Y axis is taken along the scanning direction.

  The reticle R is sucked and held on the reticle stage 22, and the reticle stage 22 moves on the reticle base 23 at a constant speed in the Y direction, and finely moves in the X, Y, and rotational directions so as to correct the synchronization error. The reticle R is scanned. The position of the reticle stage 22 is measured by a movable mirror (not shown) and a laser interferometer (not shown) provided on the reticle stage 22, and based on the measured value and control information from the main control system 1, a stage drive system 2 controls the position and speed of the reticle stage 22 via a drive mechanism (not shown) such as a linear motor. A reticle stage system is composed of reticle stage 22, stage drive system 2, drive mechanism, laser interferometer, and the like. A reticle alignment microscope (not shown) for reticle alignment is disposed above the periphery of the reticle R.

  On the other hand, wafer W is sucked and held on wafer stage WST via wafer holder 24, and wafer stage WST moves on wafer base 27 at a constant speed in the Y direction and moves in steps in the X and Y directions. 26 and a Z tilt stage 25. The Z tilt stage 25 can control the position of the wafer W in the Z direction (focus position), the rotation angle around the X axis, and the rotation angle around the Y axis.

  Further, for example, there is provided an oblique incidence type multi-point autofocus sensor (not shown) composed of an irradiation system and a light receiving system as disclosed in JP-A-6-283403 and the like. The defocus amount of the test surface (for example, the surface of the wafer W) with respect to the image plane of the projection optical system PL and the inclination angles around the X axis and the Y axis can be obtained. The stage drive system 2 controls the Z tilt stage 25 based on the measurement value of the autofocus sensor so that the upper surface of the wafer W is focused on the image plane of the projection optical system PL during exposure.

  Further, the position of wafer stage WST in the XY plane and the rotation angles around the X, Y, and Z axes are measured by a laser interferometer (not shown), and the measured values and control information from main control system 1 are measured. Based on the above, stage drive system 2 controls the operation of wafer stage WST via a drive mechanism (not shown) (linear motor or the like). A wafer stage system is composed of wafer holder 24, wafer stage WST, stage drive system 2, drive mechanism, laser interferometer, and the like.

  Further, an off-axis type image processing type alignment sensor ALG for wafer alignment is arranged on the side surface of the projection optical system PL, and a detection signal of the alignment sensor ALG is processed by an unillustrated alignment signal processing system. Accordingly, for example, the amount of positional deviation of the test mark with respect to the detection center of the alignment sensor ALG in the X direction and the Y direction can be obtained. The main control system 1 aligns the wafer W based on the amount of positional deviation. The alignment sensor ALG can also be used as a sensor for measuring the amount of misalignment between two marks when measuring an overlay error or the like as necessary. Further, in the vicinity of wafer holder 24 on wafer stage WST, a dose monitor (not shown) having a light receiving surface larger than exposure area 21W and illuminance sensor 29 having pinhole-shaped light receiving unit 30A are fixed, Detection signals from these two sensors are supplied to the exposure amount control system 3.

  At the time of exposure, the reticle stage 22 and wafer stage WST are driven, the reticle R and one shot area on the wafer W are synchronously scanned in the Y direction while the exposure light IL is irradiated, and the wafer stage WST is driven. Then, the step of moving the wafer W stepwise in the X and Y directions is repeated. Thereby, the pattern image of the reticle R is exposed to each shot area on the wafer W by the step-and-scan method.

Next, in the projection exposure apparatus of this example, the Mth layer on the Nth layer (N is an integer of 1 or more, which is called the first layer (one layer)) on the wafer W. An example of the operation when measuring the overlay error of the circuit pattern of the layer (M is an integer greater than N, which is called the second layer (other layer)) will be described.
First, a pattern of a reticle R as a mask that can be used for overlay error measurement will be described with reference to FIGS.

  As shown in FIG. 2A, on almost the entire pattern area of the reticle R, there are I columns (I is an integer of 2 or more) at a predetermined interval in the X direction and J rows (J is a predetermined interval in the Y direction). A plurality of the same rectangular frame-shaped measurement marks 31 (i, j) (i = 1 to I, j = 1 to J) are formed at an integer of 2 or more. In addition, a large number of original pattern patterns (not shown) for actual semiconductor devices are densely formed between these measurement marks 31 (i, j). Among the original patterns, a dense line pattern 32X in the X direction composed of a line-and-space pattern (hereinafter referred to as an L & S pattern) having the smallest pitch in the X direction, and a shape obtained by rotating the dense line pattern 32X by 90 ° Only the dense line collection pattern 32Y in the Y direction is shown. For example, the dense line patterns 32X and 32Y have a duty ratio of 50% and a pitch of about 120 nm at the stage of the projected image. In FIG. 2A, the pitch is expressed to be large.

  As shown in the enlarged view of FIG. 2B, one measurement mark 31 (i, j) includes a pair of line mark groups 33A, 33B formed at predetermined intervals in the X direction and the Y direction, and The line mark 34A, 34B is formed of a pair of light shielding films and is parallel to the X axis. The measurement direction of the former line mark groups 33A and 33B is the X direction, and the measurement direction of the latter line marks 34A and 34B is the Y direction. The line mark groups 33A and 33B having the same shape are each formed by arranging a plurality of line marks made of a light shielding film parallel to the Y axis in the X direction with the transmissive portion as a background. For example, a halftone film (light-reducing film) having a transmittance of 6% can be used as the light-shielding film. Instead, an almost complete light-shielding film or a halftone film having a transmittance different from 6% is used. May be.

  4A shows an enlarged view of a part of one line mark group 33A in FIG. 2B in the Y direction. In FIG. 4A, the line mark group 33A is parallel to the Y axis. One or more (four in this example) line marks 36A, whose line widths are symmetrically the same or wider toward the edge portions 38A and 38B (boundary portions) in the ± X direction of the line mark 35 having the width D2, respectively. 36B, 36C, 36D and 37A, 37B, 37C, 37D (line portions) are formed densely, and one or more (three in this example) whose line width is gradually the same or wider symmetrically on the outside thereof The line marks 36E, 36F, 36G and 37E, 37F, 37G (line portions) are formed densely. In this case, the two edge portions 38A and 38B are the outer edges of the line marks 36D and 37D, respectively, and the width D1 (> D2) in the X direction defined by the edge portions 38A and 38B is shown in FIG. This is the same as the width in the Y direction of the line mark 34A (or 34B).

  The widths of the inner line marks 36D and 37D with respect to the edge portions 38A and 38B are formed wider than the widths of the outer line marks 36E and 37E with respect to the edge portions 38A and 38B, respectively. Furthermore, the pitch of the arrangement in the X direction of the line marks 36A to 36G and 37A to 37G is set to a common pitch P. In this example, the pitch P is the pitch in the X direction of the dense line pattern 32X in FIG. Is set to be approximately equal. The widths in the X direction of the plurality of line marks 36A to 36G and 37A to 37G are the same or gradually wider toward the edge portion inside the edge portions 38A and 38B, and outside the edge portions 38A and 38B. It is the same or gradually narrows toward the edge.

  Specifically, in the line mark group 33A in FIG. 4A, as an example, at the stage of the projected image, the width D2 of the center line mark 35 is 1040 nm, the pitch P is 120 nm, and the width D1 between the edge portions 38A and 38B. Is 2000 nm (2 μm), and the widths of the line marks 36A, 36B, 36C, 36D, 36E, 36F, and 36G (same for 37A to 37G) are set to 70 nm, 80 nm, 90 nm, 90 nm, 25 nm, 45 nm, and 45 nm, respectively. ing. Of the line marks 36A to 36G, at least only the line marks 36D and 36E are required, and the number of the line marks 36A to 36G may be an arbitrary number of two or more. Therefore, instead of the thick line mark 35 at the center, for example, an L & S pattern in which a plurality of line marks having substantially the same width as the line mark 36A are arranged in the X direction at substantially the pitch P may be used.

  5A shows a shot arrangement of the wafer W on which the pattern of the reticle R in FIG. 2A is exposed. In FIG. 5A, the surface of the wafer W is in the X direction and the Y direction. As shown in the enlarged view of FIG. 5B, the first layer of each shot area SA has already been subjected to the measurement of the reticle R of FIG. The arrangement of the measurement marks 40 (i) having a plurality of the same shapes, for example, convex or concave patterns, is an arrangement obtained by reducing the arrangement of the marks 31 (i, j) substantially by the projection magnification β of the projection optical system PL of FIG. , J) (i = 1 to I, j = 1 to J). Note that even if the projection optical system PL of FIG. 1 performs reverse projection, for the sake of convenience of explanation, it is assumed that the image of the reticle R by the projection optical system PL is an erect image.

  As shown in the enlarged view of FIG. 5C, one measurement mark 40 (i, j) includes a pair of line marks 41A and 41B that are formed at predetermined intervals in the X direction and are substantially parallel to the Y axis. , And a pair of line marks 42A and 42B substantially parallel to the X-axis formed at predetermined intervals in the Y direction. The measurement directions of the line marks 41A, 41B and 42A, 42B are the X direction and the Y direction, respectively. Instead of the line marks 41A and 41B, an L & S pattern or a mark formed by projecting the same mark as the line mark groups 33A and 33B in FIG. 2B may be used. For example, a resist is applied on the wafer W before the pattern is formed on the first layer in FIG. 5A, and the measurement marks 40 ((j, j)) in FIG. 5B is obtained by exposing each shot area SA on the wafer W to an image of another reticle pattern on which an original pattern i, j) is formed, and then performing a pattern formation process. The mark 40 (i, j) can be formed.

  Next, in order to set the illumination condition for the reticle R in FIG. 2A, the illumination system aperture stop member 11 in FIG. 1 is rotated and placed on the optical path of the exposure light IL for the bipolar illumination shown in FIG. An aperture stop 13D is installed. FIG. 3 shows an aperture stop 13D on the pupil plane of the illumination optical system 5 in FIG. 1, and the center thereof coincides with the optical axis of the illumination optical system 5. Further, the X direction and the Y direction in FIG. 3 correspond to the X direction and the Y direction on the reticle R in FIG. 2A, respectively, and two regions (2) having a large light amount across the optical axis of the aperture stop 13D. The next light source is separated in a direction corresponding to the measurement direction (X direction) of the line mark groups 33A and 33B of the measurement mark 31 (i, j) in FIG. As a result, the measurement mark 31 (i, j) is illuminated by the exposure light IL inclined symmetrically in the X direction by the dipole illumination method.

  When the measurement mark 31 (i, j) is a mark obtained by rotating the mark of FIG. 2B by 90 °, the dipole illumination obtained by rotating the aperture stop 13D of FIG. An aperture stop is used. Also, as the aperture mark in the case where the mark having a shape obtained by rotating the line mark groups 33A and 33B by 90 ° is used as the line marks 34A and 34B of the measurement mark 31 (i, j) in FIG. An aperture stop for modified illumination having four apertures (secondary light sources) separated in a direction that intersects the X axis and the Y axis at 45 ° around the optical axis may be used.

  Thereafter, a positive resist is applied onto the wafer W in FIG. 5A, and the exposure area 21W in FIG. 1 is relatively moved by the scanning exposure method along the locus 39 in FIG. 5A (actually). As the wafer W side moves, each shot area SA on the wafer W is sequentially exposed to the image RP of the pattern of the reticle R in FIG. 2A (first step). Next, by developing the resist on the wafer W, in the second layer of each shot area SA on the wafer W, as shown in FIG. 5C, the measurement marks 40 (i, j) (first A registration mark 31 (i, j) P for measurement as an image of the measurement mark 31 (i, j) (second mark) in FIG. 2B is formed outside the 1 mark). A box-in-box mark is formed from the inner measurement mark 40 (i, j) and the outer measurement registration mark 31 (i, j) P. The registration marks 31 (i, j) P for measurement include registration mark portions 33AP and 33BP composed of images of the line mark groups 33A and 33B in FIG. 2B, and registration marks 34AP composed of images of the line marks 34A and 34B. 34BP.

  Next, in a predetermined number of shot areas SA selected from the wafer W using, for example, a registration measurement apparatus, the measurement registration marks 31 with respect to the centers of the measurement marks 40 (i, j) in FIG. (I, j) The amount of displacement in the X and Y directions at the center of P is measured (second step). Then, for example, by using a plurality of measurement values of misregistration amounts in one shot area SA, a two-dimensional superimposition of the second layer device pattern on the first layer device pattern in the shot area SA on the wafer W is performed. The alignment error can be measured (third step). Further, for example, the position of the measurement mark 40 (i, j) in the shot area SA of the first layer in FIG. 5B is measured in advance with high accuracy, and the measurement for each measurement mark 40 (i, j) is performed. The dynamic distortion can be measured by measuring the positional deviation amount of the registration mark 31 (i, j) P, and the distortion of the projection optical system PL can be measured by measuring the positional deviation amount in a stationary state.

  In this case, the line mark group 33A of the measurement mark 31 (i, j) of this example includes a line mark 35 and a plurality of line marks 36A formed densely on both sides as shown in FIG. To 36G and 37A to 37G. Therefore, the developed registration mark portion 33AP corresponding to the image has thin line marks 36E, 36F, 36G and 37E outside the edge portions 38A and 38B in FIG. 4A, as shown in FIG. 4B. , 37F, and 37G have disappeared, and the registration marks 36AP to 36DP and 37AP to 37DP corresponding to the images of the thick line marks 36A to 36D and 37A to 37D inside thereof, and the resists corresponding to the images of the center line mark 35, respectively. Only the mark 35P is formed. In other words, the registration mark portion 33AP has registration marks 35P, 36AP to 36P of the width D1 × β (β is the projection magnification) inside the images 38AP and 38BP of the edge portions 38A and 38B of the line mark group 33A in FIG. It is formed only from 36DP and 37AP-37DP.

  As described above, the registration marks 36AP to 36DP and 37AP to 37DP similar to the dense line pattern image having the pitch P are formed on both sides in the measurement direction of the registration mark portion 33AP of the present example. When the center of the position in the X direction of 38AP and 38BP is obtained as the measurement position of the registration mark portion 33AP, the measurement position and the image of the dense line pattern 32X having a substantially pitch P, which is the device pattern of FIG. The positional relationship is exactly the positional relationship obtained by converting the positional relationship between the measurement mark 31 (i, j) on the reticle R (line mark group 33A in FIG. 2B) and the dense line pattern 32X by the projection magnification. Match. Therefore, the overlay error measured by the method of this example is exactly the overlay error between the circuit pattern of the first layer and the almost finest circuit pattern of the second layer corresponding to the image of the dense line pattern 32X. Overlay errors between actual circuit patterns between different layers can be measured with high accuracy. Based on the measurement result, high overlay accuracy can be obtained by adding an offset (correction information) that cancels the overlay error to the position of the wafer W at the time of the next exposure. As a result, semiconductor devices with fine patterns can be mass-produced with high yield and high accuracy.

Next, an example of the simulation result of the image of the line mark group 33A in FIG. 4A will be described with reference to FIGS. The simulation conditions are that the exposure wavelength is ArF (193 nm), the numerical aperture NA of the projection optical system PL is 0.92, and the coherence factor of the outer diameter of the aperture stop 13D for dipole illumination in FIG. 3 is 0.95.
6A and 6B show the image intensity distribution of a mark obtained by rotating one line mark 34A of FIG. 2B by 90 °, that is, a conventional mark, and the horizontal axis indicates the position of the projected image ( nm), and the vertical axis represents image intensity (arbitrary unit). 6A and 6B show image intensities when the defocus amounts are 0 and 100 nm, respectively.

  On the other hand, FIGS. 7A and 7B show the image intensity distribution of the line mark group 33A of FIG. 2B, that is, the mark of this example, corresponding to FIG. B) shows the image intensities when the defocus amounts are 0 and 100 nm, respectively. From the comparison between FIG. 6 and FIG. 7, the image intensity distribution of the mark of this example in FIGS. 7A and 7B is stable even when the defocus amount changes, and the position measurement accuracy Therefore, it can be seen that overlay error and the like can always be measured with high accuracy.

  FIG. 8 shows an example of a simulation result of wavefront aberration, and the horizontal axes of FIGS. 8A, 8B, and 8C show the 8 Zernike polynomials from the 7th to 34th order representing the wavefront aberration. The coefficients Z7, Z10, Z14, Z19, Z23, Z26, Z30, and Z34 are shown, and the vertical axis represents the Zernike sensitivity (nm / λ) (λ is the exposure wavelength) corresponding to the aberration represented by the coefficient of each Zernike polynomial. Show. 8A shows the wavefront aberration of the image of the dense line pattern 32X, which is the device pattern of FIG. 2A, and FIG. 8B shows one line mark 34A of FIG. FIG. 8C shows the wavefront aberration of the line mark group 33A of FIG. 2B, that is, the image of the mark of this example.

  Furthermore, the Zernike sensitivities of the Zernike polynomials Z7 to Z34 in FIGS. 8A to 8C are 0%, + 5%, respectively, when the exposure amount is set to −5% with respect to the appropriate exposure amount (graph 43A). The simulation results are shown for + 10%, + 25%, and + 50% (graph 43F). From these comparisons, the tendency of the wavefront aberration in FIG. 8A (dense line pattern) is greater than the wavefront aberration in FIG. 8B (conventional mark). It can be seen that the wavefront aberration tendency of the group 33A) is close. Therefore, by using the line mark group 33A of the present example, even when aberration remains in the projection optical system PL, it is superimposed with high accuracy close to the positional deviation amount of the dense line pattern image which is an actual device pattern. The alignment error can be measured.

  In the above embodiment, when a mark formed from an original mark similar to the line mark group 33A in FIG. 2B is used as the first layer line mark 41A in FIG. 5C, the original mark ( The line mark group 44A) and the line mark group 33A may be formed on the same reticle as shown in FIGS. 9A and 9B. In this case, the line mark group 33A in FIG. 9A and the line mark group 44A in FIG. 9B are formed on the reticle so as to be separated by a predetermined distance ΔX in the X direction, for example. When the image of the mark group 44A is exposed, the line mark group 33A is placed in the light shielding area 45B by the reticle blind, and when the image of the line mark group 33A is exposed on the second layer, the wafer side is placed on the wafer side. After the step movement corresponding to the predetermined interval ΔX, as shown in FIG. 9A, the line mark group 44A may be placed in the light shielding area 45A by the reticle blind.

  In the above-described embodiment, the measurement mark 31 (i, j) is provided on the reticle on which the original pattern transferred to the second layer is formed. However, the measurement mark 31 (i, j) is provided on a reticle different from the reticle having the original pattern. A mark 31 (i, j) may be provided. In this case, in addition to the exposure process of transferring the original pattern to the second layer, exposure is performed using a reticle having measurement marks 31 (i, j), and the overlay error is measured in the same manner as described above. . At this time, in the exposure process, it is preferable to expose the measurement marks under the same exposure conditions (including at least illumination conditions) as the original pattern, and the wafer on which the plurality of measurement marks 40 (i, j) described above are formed is used. It is done. When the measurement mark 31 (i, j) is provided on a measurement-dedicated reticle different from the device-manufacturing reticle, measurement marks suitable for a plurality of types of device patterns are formed on the same measurement-specific reticle. May be.

  In the above embodiment, the registration mark of the measurement mark 31 (i, j) formed on the wafer through the development process is detected. However, the mark image obtained through the etching process is further detected to detect the registration mark. The overlay error may be measured. In this case, even if the line width of the device pattern on the wafer fluctuates due to curing (heat treatment) performed between the development process and the etching process, the overlay error can be measured in consideration of the fluctuation.

  In addition, when a semiconductor device is manufactured using the projection exposure apparatus of the above-described embodiment, the semiconductor device includes a step of designing a function / performance of the device, a step of manufacturing a reticle based on the step, a wafer from a silicon material, A step of aligning with the projection exposure apparatus of the above-described embodiment to expose the reticle pattern onto the wafer, a step of forming a circuit pattern such as etching, a device assembly step (dicing process, bonding process, package process) ) And an inspection step.

  The present invention is not limited to a scanning exposure type projection exposure apparatus, but also includes a batch exposure type projection exposure apparatus, and an immersion type exposure apparatus disclosed in, for example, International Publication No. 99/49504 pamphlet. This can also be applied to the measurement. Further, instead of the reticle R of the above-described embodiment, a pattern generation device capable of forming a variable pattern such as a liquid crystal display may be used.

  Further, the present invention is not limited to a semiconductor device, for example, a liquid crystal display element formed on a square glass plate or a display device such as a plasma display, an imaging element (CCD etc.), a micromachine, a thin film magnetic head, and The present invention can be widely applied to an exposure apparatus for manufacturing various devices such as a DNA chip. Furthermore, the present invention can also be applied to an exposure process (exposure apparatus) when manufacturing a mask (photomask, reticle, etc.) on which mask patterns of various devices are formed using a photolithography process. As described above, the present invention is not limited to the above-described embodiment, and can have various configurations without departing from the gist of the present invention.

  According to the present invention, when an overlay error or the like is measured, a measurement value close to an actual device pattern error can be obtained. Therefore, by performing correction based on the measured value, various devices composed of fine patterns can be manufactured with higher accuracy.

It is a perspective view which shows the projection exposure apparatus of an example of embodiment of this invention. (A) is a plan view showing the arrangement of measurement marks on the reticle R, and (B) is an enlarged view showing the measurement marks. It is a figure which shows the aperture stop 13D for dipole illumination. (A) is an enlarged view showing the line mark group 33A, and (B) is an enlarged view showing a registration mark portion 33AP corresponding to the image of the line mark group 33A. (A) is a diagram showing the shot arrangement of the wafer W, (B) is a diagram showing the arrangement of measurement marks in the shot area, and (C) is an enlarged view showing the measurement marks. It is a figure which shows the simulation result of the image strength of the conventional mark. It is a figure which shows the simulation result of the image intensity of the mark of embodiment. It is a figure which shows the simulation result of the wavefront aberration of various marks. It is explanatory drawing in the case of forming two line mark groups on a reticle.

Explanation of symbols

  R ... reticle, PL ... projection optical system, W ... wafer, 1 ... main control system, 5 ... illumination optical system, 31 (i, j) ... measurement mark, 31 (i, j) P ... measurement registration mark, 33A ... Line mark group, 33AP ... Registration mark part, 40 (i, j) ... Measurement mark, 41A ... Line mark

Claims (17)

In the measurement method of overlaying and exposing the image of the second mark on the first mark, and measuring the amount of positional deviation between the image of the first mark and the second mark,
The second mark includes a plurality of line portions whose transmittance is lower than that of the surrounding portion,
The measurement method characterized in that the width of the line portion inside the predetermined boundary portion is wider than the width of the line portion outside the boundary portion.   The measurement method according to claim 1, wherein the arrangement pitches of the plurality of line portions are equal to each other.   The width of the plurality of line portions gradually increases toward the boundary portion inside the boundary portion and gradually decreases toward the boundary portion outside the boundary portion. Measurement method described in 1. The boundary is set at two locations so as to sandwich the center of the second mark in the measurement direction,
4. The second mark is illuminated with illumination light from two secondary light sources separated in a direction corresponding to the measurement method when exposing the image of the second mark. The measuring method as described in any one of. Obtaining correction information for overlay error of device patterns formed in different layers using the measurement method according to claim 1;
Transferring a device pattern onto a photoreceptor including the one layer and the other layer based on the correction information in order to form a device pattern on the other layer so as to be superimposed on the device pattern of the one layer; A device manufacturing method comprising: In an exposure method for managing superposition when an image of a device pattern of another layer is exposed on one layer,
A first step of forming a first mark on the one layer and exposing an image of a mask pattern in which a second mark is formed on the one layer together with the device pattern of the other layer; ,
A second step of measuring a displacement amount between the first mark and the image of the second mark on the one layer;
The second mark includes a plurality of line portions whose transmittance is lower than that of the surrounding portion,
An exposure method, wherein a width of the line portion inside the predetermined boundary portion is wider than a width of the line portion outside the boundary portion. The arrangement pitch of the plurality of line portions is equal to each other,
The exposure method according to claim 6, wherein the device pattern includes a line and space pattern having a pitch substantially equal to the arrangement pitch. The boundary is set at two locations so as to sandwich the center of the second mark in the measurement direction,
The width of the plurality of line portions gradually increases toward the boundary portion inside the boundary portion, and gradually decreases toward the boundary portion outside the boundary portion,
The mask pattern is illuminated with illumination light from two secondary light sources separated in a direction corresponding to the measurement method when an image of the mask pattern of the other layer is exposed. Or the exposure method of 7. The pattern of the other layer is projected through a projection optical system,
9. The method according to claim 6, further comprising a third step of obtaining distortion of the projection optical system or an overlay error between the one layer and the other layer based on a measurement result of the second step. The exposure method according to any one of the above.   A device manufacturing method comprising a step of transferring a device pattern onto a photoconductor using the exposure method according to claim 6. A measurement mark used for measuring the amount of misalignment of a projected image,
It has a plurality of line parts whose transmittance is lower than the surrounding part,
The measurement mark, wherein a width of the line portion inside the predetermined boundary portion is wider than a width of the line portion outside the boundary portion. The arrangement pitch of the plurality of line portions is equal to each other,
The width of the plurality of line portions gradually increases toward the boundary portion inside the boundary portion, and gradually decreases toward the boundary portion outside the boundary portion. Mark for measurement.   The measurement mark according to claim 11 or 12, wherein the boundary portion is set at two locations so as to sandwich the center of the measurement mark in the measurement direction. In the mask on which the device pattern is formed,
14. A mask, wherein the measurement mark according to claim 11 is formed together with the device pattern. A mask used for superimposition management when exposing an image of a device pattern of another layer on one layer,
A mask on which the measurement mark according to any one of claims 11 to 13 is formed.   The mask according to claim 15, wherein the measurement mark is used in an exposure process for the overlay management different from an exposure process of the device pattern. The arrangement pitch of the plurality of line portions is equal to each other,
17. The mask according to claim 14, wherein a line and space pattern having a pitch substantially equal to the arrangement pitch is included in the device pattern.

Images