WO1999005707A1 - Focusing method, exposure method, and aligner - Google Patents

Abstract

An exposure method wherein a focus measuring pattern is successively projected onto focus-measuring points on a wafer (W) while changing the position of the wafer (W) along the optical axis (AX). Then, from the results of projection exposure of the focus measuring pattern, the position of the best image formation plane of a projection optical system (PL) at each measurement point is determined. By using the positions of the best image formation planes, the target focus level of a multi-point autofocus sensor is calibrated. Even when the environment of the projection optical system changes, a high detection precision of the multi-point autofocus sensors can be maintained for each sensor. This exposure method is particularly effective in aligners using a projection optical system with a large numerical aperture.

Description

 Description Focusing method, exposure method and exposure apparatus

Technical field

 The present invention relates to a method of focusing a sensitive substrate on a focal plane of a projection optical system when projecting a pattern on a mask onto a sensitive substrate using a projection optical system. The best imaging position in the optical axis direction of the projection optical system is detected for each of a plurality of detection points defined in the projection area on the substrate, thereby focusing the sensitive substrate on the focal plane of the projection optical system. The present invention relates to a method for performing the focusing method, an exposure method using the focusing method, and an exposure apparatus. The focusing method and exposure method of the present invention are suitable for a projection exposure apparatus used in a photolithographic process for manufacturing a semiconductor device or a liquid crystal display device.

Background art

Various exposure apparatuses are used in a photolithography process for manufacturing a semiconductor device or a liquid crystal display device. In a typical exposure apparatus, a circuit pattern formed on a photomask or a reticle (hereinafter, collectively referred to as a “reticle” as appropriate) is converted into a silicon wafer or glass having a surface coated with a photosensitive agent such as a photo resist. The substrate is exposed by projecting it onto a sensitive substrate such as a plate (hereinafter referred to as “wafer” or “substrate”) using a projection optical system. For example, in a reduction projection exposure apparatus for manufacturing semiconductor devices, a projection lens system having a large numerical aperture (N.A.) is used. A mechanism to match the image plane on the substrate side is indispensable. A mechanism for adjusting the position of the wafer surface in the optical axis direction of the projection lens system as a mechanism for matching the wafer surface with the image plane on the substrate side of the projection lens system. A focus mechanism is provided. The focus mechanism is located within each exposure area.

It has a function to focus one point, but the in-plane inclination is not negligible as the target line width becomes smaller, so a repelling mechanism to make the wafer surface perpendicular to the optical axis of the projection lens system. Is also provided. In order to perform the gain focusing, for example, an oblique incident light type gain focusing mechanism using an optical system different from the projection lens of the projection exposure apparatus is known. In this mechanism, the light emitted from a light source such as an erogen lamp passes through a slit, and then a slit image is projected onto the wafer surface from obliquely above. The projected image is vibrated by a vibrating mirror and detected by a detector via a light receiving slit. The position of the slit image moves left and right on the light receiving slit according to the top and bottom of the wafer surface. For this reason, if the wafer position (target position) when the slit image accurately overlaps the light receiving slit is set in advance so as to be a true focal point, the detection signal is raised and lowered while moving the wafer position up and down.

By observing the (focus signal), the focus can be realized. Conventionally, a target position of a wafer for setting a true focal point in this autofocus mechanism is disclosed in, for example, Japanese Patent Application Laid-Open Nos. 1-187178 and 2-30112. And U.S. Pat.No. 4,908,656 as disclosed in U.S. Pat.No. 4,908,656, by subjecting a mask pattern to test exposure on a sensitive substrate and determining the best image plane position obtained from the result. Had been decided. However, the projection lens system can change its image plane due to various factors such as changes in the surrounding environment such as temperature and absorption of a single laser beam for exposure. Therefore, in the oblique incident light type focus mechanism, the target position once set as described above (ie, the wafer position where the gain signal becomes zero level) is actually Deviates from the best imaging plane of the projection lens system. Therefore, it is necessary to verify in some time whether or not the talent focus signal indicates the true focus, and if necessary, the focus indicated by the talent focus mechanism becomes the true focus. Like The detector in the focus mechanism must be adjusted. In other words, it was necessary to reset or calibrate the detection signal level at the true focal point (hereinafter referred to as the target focus level) by adding an offset to the detection signal of the detector. Conventionally, a method of determining the true focal point (the best image plane position) by checking the in-focus state of the wafer with respect to the projection lens system is disclosed in, for example, Japanese Patent Application Laid-Open Nos. Focus measurement at the reticle center (the position on the reticle that almost coincides with the optical axis of the projection optical system) as disclosed in US Pat. No. 3,010,656 and US Pat. No. 4,908,656. There is known a method using a measurement reticle on which a measurement pattern is arranged. In this method, the wafer is exposed by the pattern of the measurement reticle while gradually changing the position of the wafer with respect to the projection lens in the direction of the optical axis and sequentially stepping the wafer. Then, the exposure pattern of the wafer is observed visually or by using a pattern line width measuring device or the like, and the position in the optical axis direction of the wafer where the exposure result is the best is determined as the best imaging plane position. In recent years, as a mechanism for simultaneously detecting the position and the inclination of the projection lens system on the wafer surface in the optical axis direction, for example, many types of oblique incident light systems disclosed in Japanese Patent Application Laid-Open No. 5-190423 have been proposed. A point focus position detection system or a multi-point focus sensor is known. In an exposure apparatus equipped with this multipoint focus position detection system, when exposing a plurality of shot areas partitioned in a wafer, three or more measurement points are set in each shot, and the measurement points are measured. By measuring the position of the point in the optical axis direction, the local inclination in the shot can be obtained, and the imaging plane can be adjusted to the optimum plane for each shot. In such a multipoint focal position detection system of the oblique incident light system, it is necessary to verify and calibrate the true focal point as in the conventional focal position detection system at one point. In particular, in the case of a multi-point focal position detection system, the exposure area in the shot (the area on the wafer that is illuminated with the exposure light, the area illuminated by the reticle and the projection lens system) (A region on the wafer conjugate with respect to), and these measurement points are illuminated via different optical paths of the projection lens system during exposure. Therefore, if the refractive index distribution of the projection lens system is different due to environmental changes or absorption of exposure light, for example, if the projection lens system has a curvature of field or an inclination of the field, measurement will be performed. Focus must be verified and calibrated for each point. The present invention has been made under such circumstances, and an object thereof is to provide a method of measuring a true focus position for each of a plurality of focus measurement points existing in an exposure area on a substrate. It is in. A further object of the present invention is to measure a true focus position for each of a plurality of focus measurement points existing in the exposure area plane on the substrate, and use the measurement results to determine the position and inclination of the substrate in the optical axis direction. It is an object of the present invention to provide an exposure method capable of exposing a substrate in a state in which the temperature is adjusted. Still another object of the present invention is to provide a sensor that measures the positions in the optical axis direction of a plurality of focus measurement points existing in the exposure area plane, for example, a target focus level of a multipoint gain focus sensor, It is an object of the present invention to provide an exposure apparatus capable of calibrating the exposure and a method of manufacturing the same. DISCLOSURE OF THE INVENTION According to a first aspect of the present invention, when a predetermined pattern formed on a mask is projected onto a sensitive substrate by a projection optical system, the position of the sensitive substrate is adjusted to the focal point of the projection optical system. A focusing method is provided. In this focusing method, a plurality of measurement points are determined in a projection area on the sensitive substrate on which the pattern of the mask is projected, and a focus measurement pattern is formed at a position on the mask corresponding to the plurality of measurement points. Using a Mask, In the first step, the sensitive substrates are respectively exposed while changing the positions of the sensitive substrates in the optical axis direction of the projection optical system to various positions. As a second step, the best imaging position by the projection optical system is determined for each measurement point from the exposure results of the sensitive substrate at the various optical axis positions. In the method of the present invention, a focus measurement mask having a focus measurement pattern formed at a position on the mask corresponding to the plurality of measurement points is used. By using this focus measurement mask, in the first step, the focus measurement pattern is exposed on all the measurement points in the exposure area. The obtained exposure patterns are also obtained at various positions along the optical axis. In the second step, it is determined for each measurement point which exposure pattern is best focused. This judgment is made by visually observing the line width of the pattern exposed on the sensitive substrate or by observing with a measuring device. Thus, the best imaging position is obtained for each measurement point. The best imaging position usually differs for each measurement point. This reflects the imaging characteristics of the projection optical system, such as curvature of field and tilt of the field. Therefore, by using the method of the present invention, the in-focus position can be accurately determined not only for the position passing through the optical axis of the projection optical system but also for the light beam passing around or outside the position. Therefore, the present invention is suitable for use in focusing a certain area in a substrate, and is particularly effective for focusing a projection optical system having a large numerical aperture, that is, a small depth of focus. In the present invention, each measurement point on the sensitive substrate is irradiated with light using light from a projection system different from the projection optical system, and the position of each measurement point in the optical axis direction is determined from the reflected light. The position in the optical axis direction can be calibrated by the best imaging position. In other words, it is useful for calibration of the obliquely incident light type multi-point focusing position detection mechanism (multi-point focusing sensor). According to a second aspect of the present invention, a predetermined pattern formed on a mask is projected onto a projection optical system. An exposure method for exposing a sensitive substrate by projecting it on a sensitive substrate by a system,

 A plurality of measurement points are defined in a projection area on the sensitive substrate on which the pattern of the mask is projected, and a focus measurement mask having a focus measurement pattern formed at a position on the mask corresponding to the plurality of measurement points Using;

 Exposing the sensitive substrate with the focus measurement pattern while changing the position of the sensitive substrate in the optical axis direction of the projection optical system to various positions;

 From the exposure results of the sensitive substrate at the various positions in the optical axis direction, the best imaging position by the projection optical system is obtained for each measurement point;

An exposure method is provided wherein the sensitive substrate is positioned with respect to the projection optical system based on the obtained best imaging position, and exposure is performed using a mask on which the predetermined pattern is formed. The exposure method of the present invention is characterized in that preliminary exposure is performed using a focus measurement mask on which a plurality of focus measurement patterns are formed. The plurality of focus measurement patterns formed on the mask correspond to the plurality of measurement points defined in the exposure area (projection area) of the sensitive substrate. By performing the preliminary exposure while changing the substrate position in the optical axis direction, it is possible to determine which optical axis direction position is the best focus position for each measurement point. Using this result, the exposure area of the substrate can be accurately focused, and leveling can be performed. In the exposure apparatus of the present invention, each measurement point on the sensitive substrate can be irradiated with light using light from a projection system different from the projection optical system. That is, at the time of actual exposure, the focus position is detected by using a projection system different from the projection optical system, for example, an oblique incident light type multi-point autofocus sensor. Can calibrate the target position of the substrate detected by the sensor using the best focus position (true focus position) obtained by the preliminary exposure. Therefore, the exposure δ When the refractive index distribution of the projection optical system changes due to a change in the environment of the apparatus or the absorption of the exposure light from the projection optical system, a signal indicating the target position of the substrate indicated by the sensor, that is, The scum level can be adjusted. The method of the present invention is directed to a scanning exposure method, that is, when exposing the mask on which the predetermined pattern is formed, irradiating the mask with slit-like illumination light while applying the mask and the sensitive substrate to a projection optical system. This method is suitable for a method of exposing a sensitive substrate by moving the photosensitive substrate synchronously. In this method, the projection area is an area conjugate with the illumination area formed on the mask and irradiated with the slit-like illumination light with respect to the projection optical system. According to a third aspect of the present invention, there is provided an exposure apparatus for exposing a projection area on a sensitive substrate by projecting a predetermined pattern formed on a mask onto the sensitive substrate by a projection optical system.

 A substrate stage for moving the sensitive substrate in the direction of the optical axis of the projection optical system; and a projection system separate from the projection optical system, wherein light is respectively transmitted to a plurality of measurement points in a projection area on the sensitive substrate. A focus detection system having a projection system for irradiating, and a focus detector for detecting the position of each measurement point in the optical axis direction by detecting light reflected from each measurement point on the sensitive substrate;

 A control device for storing information on the best imaging position for each measurement point and controlling the exposure device;

The exposure apparatus is characterized in that the control device controls the substrate stage based on the stored best imaging position and the value detected by the focus detector, and positions the sensitive substrate at the best imaging position. Is done. In the exposure apparatus according to the present invention, the control device stores information on the best imaging position for each measurement point in the exposure area (projection area). This control device is The information on the position can be used to calibrate the target focus level of a focus detector, for example, an oblique incidence type multipoint gain focus sensor. If the detector has multiple detectors that detect the optical axis position at each measurement point, the target focus level can be calibrated for each detector. Therefore, it is compensated that the focus position obtained by the focus detection system is accurate. Therefore, even if the optical characteristics of the projection optical system, for example, the curvature of field and the inclination of the image plane change due to the environmental change of the exposure apparatus, the force position following the change is determined by each of the exposure areas. It can be obtained for each measurement. The exposure apparatus further includes an image focus position measurement pattern provided on the substrate stage, an image of the pattern formed by a projection optical system illuminating the pattern, and projecting the image on the mask. The apparatus may further include a focus position detection system that receives the reflected light via the projection optical system, for example, an aerial image focus position detection system. Since the best imaging position can be calibrated by this focal position detection system, it is not necessary to perform the pre-exposure every predetermined period. According to a fourth aspect of the present invention, in a method of manufacturing an exposure apparatus, there is provided a substrate stage for moving a projection optical system and a sensitive substrate in an optical axis direction of the projection optical system;

 A projection system that is different from the projection optical system and irradiates a plurality of measurement points in a projection area on a sensitive substrate with light, and detects light reflected from each measurement point on the sensitive substrate. A focus detector having a focus detector for detecting the position of each measurement point in the optical axis direction;

A control device that stores information on the best imaging position for each measurement point and controls an exposure device, and controls a substrate stage based on the stored best imaging position and a detection value of a focus detector. Providing a control device for positioning the sensitive substrate at the best imaging position; A method is provided for manufacturing an exposure apparatus that includes connecting the focus detector to a control device. In the present invention, the exposure apparatus exposes the sensitive substrate by moving the mask and the sensitive substrate synchronously with respect to the projection optical system while irradiating the mask with slit-like illumination light. ■ A scanning exposure apparatus is suitable. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a diagram schematically showing a configuration of a projection exposure apparatus according to an embodiment to which a focus position detection method according to the present invention is applied.

 FIG. 2A is a plan view showing the pattern forming plate of FIG. 1, FIG. 2B is a diagram showing an arrangement of a pattern image formed on an exposure surface of the wafer, and FIG. 2C is a drawing showing a light receiving slit plate. It is a figure which shows arrangement | positioning of the slit.

 Fig. 3 is a graph showing the relationship between the Z-axis position of each detection point for a plurality of detection points obtained as a result of the line width measurement on the horizontal axis and the pattern line width of the resist image on the vertical axis. It is.

FIG. 4 is an enlarged view of one curve shown in FIG. 3, and is a view for explaining a method of determining an optimum pattern line width. BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, an embodiment of the present invention will be described with reference to FIGS. FIG. 1 shows a schematic configuration of a projection exposure apparatus 10 according to an embodiment to which a surface position detection method according to the present invention is applied. The projection exposure apparatus 10 is a so-called step-and-repeat type reduction projection exposure apparatus. The projection exposure apparatus 10 holds a wafer W as a substrate and XY stage device 14 equipped with a substrate table 18 as a sample stage that can move in two axes directions and perpendicular to the reference plane, and perpendicular to the reference plane, and in the Z axis direction, and perpendicular to the reference plane. The projection optical system PL disposed above the XY stage device 14 with the Z-axis direction as the direction of the optical axis AX, and a mask disposed perpendicular to the optical axis AX above the projection optical system PL And a reticle holder 36 for holding a reticle R as a reticle. The XY stage device 14 includes a base 11, a Y stage 16 that can reciprocate on the base 11 in the Y direction (left-right direction in FIG. 1) on the base 11, and a Y stage 16 on the Y stage 16. It has an X stage 12 that can reciprocate in an X direction (a direction perpendicular to the paper) perpendicular to the direction, and a substrate table 18 provided on the X stage 12. A wafer holder 25 is placed on the substrate table 18, and the wafer W is held by the wafer holder 25 by vacuum suction. The substrate table 18 is positioned on the X stage 12 in the XY direction, and is mounted in such a manner that movement in the Z axis direction, inclination with respect to the XY plane, and rotation around the Z axis (zero rotation) are allowed. A movable mirror 27 is fixed on the substrate table 18, and the positions of the substrate table 18 in the X, Y, and 0 directions (the rotation direction around the Z axis) are fixed by an interferometer 31 disposed outside. The position information monitored by the high accuracy (for example, with a resolution of several nm) and obtained by the interferometer 31 is supplied to the main controller 44. The main controller 44 controls the positioning operation of the Y stage 16, the X stage 12, and the substrate table 18 via the driving device 21 as a driving system, etc., and controls the operation of the entire device. Control. The driving of the substrate table 18 in the Z-axis direction, the inclination with respect to the XY plane, and zero rotation are performed by the driving device 21 via a Z-axis driving mechanism (not shown). In addition, one end of the substrate table 18 is provided with an off-axis The reference mark plate FM on which various reference marks are formed for measuring the distance from the detection center of the element detection system to the optical axis of the projection optical system PL is fixed. The reticle holder 36 has vacuum suction portions 34 at four corners on the upper surface thereof, and the reticle R is held on the reticle holder 36 via the vacuum suction portions 34. The reticle holder 36 has an opening (not shown) corresponding to the pattern area PA where the circuit pattern on the reticle R is formed, and is driven in the X, Y, and Θ directions by a drive mechanism (not shown). (Rotational direction around the Z axis), so that the reticle R can be positioned so that the center (reticle center) of the pattern area PA passes through the optical axis AX of the projection optical system PL. It has a configuration. In the projection exposure apparatus 10, the reticle R and the wafer W are aligned (aligned) by the main controller 44 based on a detection signal of an alignment detection system (not shown). Based on the detection signal of the detection system, the pattern surface of the reticle R and the surface of the wafer W are conjugate with respect to the projection optical system PL, and the focal plane (substrate-side image surface) of the projection optical system PL and the surface of the wafer W The main controller 44 controls the driving of the substrate table 18 via the driving device 21 in the Z-axis direction and the tilt direction so that the surface position is adjusted. With the positioning and focusing performed in this manner, the pattern area PA of the reticle R is substantially uniform by the exposure light EL emitted from the illumination optical system including the mirror 97 and the main condenser lens 99. When illuminated with illuminance, a reduced image of the pattern of the reticle R is formed on the wafer W having the surface coated with a light resist through the projection optical system PL. Here, although not shown, the illumination optical system includes a light source such as a mercury lamp, An elliptical mirror for condensing the exposure light emitted from the light source, an input lens for converting the collected exposure light into a substantially parallel light beam, and a light beam output from the input lens being incident upon the input lens. Rear (reticle side) A fly-eye lens that forms a number of secondary light sources on the focal plane, and a condenser that collects exposure light emitted from these secondary light sources and illuminates the reticle R with uniform illuminance. It can be configured to include a lens system and the like. In the present embodiment, the illumination optical system includes a movable blind as a variable field stop having two L-shaped movable blades 45A and 45B (hereinafter, this movable blind is appropriately referred to as a movable blind). “Movable blinds 45 A, 45 B” are provided, and the arrangement surface of the movable blinds 45 A, 45 B is conjugate with the butter surface of the reticle R. In addition, near the movable blinds 45A and 45B, fixed blinds 46 having fixed openings are arranged. The fixed blind 46 is, for example, a field stop that surrounds a rectangular opening with four knife edges, and the rectangular opening defines an area that can be exposed by the projection optical system. The movable blinds 45A and 45B are driven in the X and Z directions in the XZ plane by the movable blind drive mechanism 43A and 43B, thereby fixing the blinds.

46 Part of the illumination area on reticle R specified in 6 is masked, and the illumination area is set to a rectangular shape of any shape (including size). The exposure area on the conjugate wafer W is also set as a rectangular area of any shape (including size). That is, in the present embodiment, the movable blind 45 A, 4 A

The exposure area E f on the wafer W (see FIG. 2 (B)) is set by 5B. The operation of drive mechanisms 43A and 43B is controlled by main controller 44 based on the reticle information. Furthermore, in the present embodiment, when the wafer W is positioned within the pattern projection area by the projection optical system PL, oblique incidence is performed to detect the position of the surface of the wafer W in the Z direction (optical axis AX direction). One of the optical focus detection systems is a multi-point position detection system. Is provided. This multipoint focus position detection system includes an irradiation optical system 40 including an optical fiber bundle 81, a condenser lens 82, a pattern forming plate 83, a lens 84, a mirror 85, and an irradiation objective lens 86, Condensing objective lens 87, rotating direction diaphragm 88, imaging lens 89, slit plate 93 for receiving light, and a number of photosensors as photodetectors (silicon type die or type transistor) Etc.) and a light receiving optical system 42 comprising a light receiver 90 having Here, the operation of each component of the multi-point focus position detection system will be described. Illumination light having a wavelength that does not expose the photoresist on the wafer W, which is different from the exposure light EL, is transmitted from an illumination light source (not shown) to an optical fiber bundle. Guided through 8 1. The illumination light emitted from the optical fiber bundle 81 illuminates the pattern forming plate 83 via the condenser lens 82. The illumination light transmitted through the pattern forming plate 83 is projected onto the exposure surface of the wafer W via the lens 84, the mirror 85 and the irradiation objective lens 86, and the exposure surface of the wafer W is projected onto the pattern forming plate 83. Is projected and imaged. The illumination light (beam of the pattern image) reflected by the wafer W passes through the converging objective lens 87, the rotating diaphragm 88, and the imaging lens 89, and is received by the light receiver arranged in front of the receiver 90. The image of the pattern on the pattern forming plate 83 is projected on the slit plate 93 for light reception, and is re-imaged on the slit plate 93 for light reception. Here, the main controller 44 has a built-in oscillator (OSC.), And the rotation direction diaphragm 88 is vibrated by the vibrating device 92 driven by the drive signal from the 0 SC. Thus, when the slit image vibrates on the light receiving slit plate 93, the light flux transmitted through the many slits of the slit plate 93 is received by the many photo sensors of the light receiver 90. Then, detection signals (photoelectric conversion signals) from many photo sensors of the light receiver 90 are supplied to the signal processing device 91 via the sensor selection circuit 92. this The signal processing device 91 has a built-in synchronous detection circuit (PSD) to which an AC signal having the same phase as the drive signal from the OSC is input. Then, the signal processing device 91 performs synchronous detection of each detection signal based on the phase of the AC signal described above, and outputs a large number of detection output signals, that is, a large number of focus position detection signals FS to the main control device 44. Output. Here, the pattern on the pattern forming plate 83 based on FIG. 2, the image of this pattern formed on the exposure surface of the wafer W, and the light receiving slit plate 93 on which this image is re-imaged will be further described. It will be described in detail. FIG. 2A shows a pattern forming plate 83. As shown in FIG. 2A, the pattern forming plate 83 has 3 X 3 at equal intervals in the vertical and horizontal directions, that is, in the directions of the four sides (X, Y directions) of the nine pattern forming plates 83 in total. The slit-shaped opening patterns P11 to P33 inclined by 45 degrees with respect to each other are formed, and the images of these slit-shaped opening patterns P are projected on the exposure surface of the wafer W. Here, in the present embodiment, the image light flux from the irradiation optical system 40 irradiates the wafer W surface (or the reference mark plate FM surface) from a direction inclined by a predetermined angle with respect to the optical axis AX in the YZ plane. The reflected light flux of the image light flux from the surface of the wafer W travels in a direction inclined by a predetermined angle symmetrically to the image light flux from the irradiation optical system 40 with respect to the optical axis AX in the YZ plane to receive light. The light is received by the system 42 as described above. That is, when viewed in a plan view, the image light flux and the reflected light flux from the irradiation optical system 40 travel from one side to the other along the Y axis. For this reason, as shown in FIG. 2B, a 3 × 3 matrix-like arrangement inclined by 45 ° with respect to the X-axis and the Y-axis is provided in the exposure area E f on the surface of the wafer W. 3. A total of nine slit-shaped aperture pattern images (hereinafter, “slit images”) S11 to S33 are formed at regular intervals along the X-axis and Y-axis directions. Note that this embodiment In this example, 3 × 3 (= 9) slit images are arranged in the exposure area E f, but the number of the slit images S is not limited. FIG. 2C shows a slit plate 93 for receiving light. On the light receiving slit plate 93, the slits Q11 to Q33 are arranged in a matrix of 3 rows and 3 columns corresponding to the slit images S11 to S33. Each slit D is arranged at an angle of 45 degrees to the X-axis and Y-axis, respectively. Photosensors D11 to D33 (not shown) are arranged behind the light receiving slit plate 93, respectively, and the slit images S11 to S33 re-formed on the slit plate 93 are formed. 33 light beams are photoelectrically detected by the photosensors D11 to D33 via the slits Q11 to Q33. Then, as described above, the light reflected on the exposure surface of the wafer W is rotationally vibrated by the rotational direction vibration plate 88, so that the position of each re-imaged image on the slit plate 93 is shown in FIG. Oscillates in the direction of arrow RD. Therefore, the detection signals of the photosensors D11 to D33 are synchronously detected by the signal processing device 91 via the sensor selection circuit 94 by the signal of the rotational vibration frequency as described above. Each of the focus position detection signals FS is called a so-called S-curve signal, and becomes zero level when the center of the slit of the light-receiving slit plate 93 coincides with the center of vibration of the slit image reflected from the wafer W. When the wafer W is displaced upward from that state, the level is positive, and when the wafer W is displaced downward, the level is negative. Therefore, the height position (position in the optical axis direction) of the wafer W at which the focus position detection signal FS becomes zero level is detected as the focal point. However, in such an oblique incident light method, there is no guarantee that the height position of the wafer W at the focal point (the signal FS is zero level) always coincides with the best image plane. That is, the focus position detection signal FS is the reference mark plate FM or This signal is a signal indicating the position of the projection optical system PL in the optical axis direction, and is a signal indirectly indicating the focus position. Therefore, using the focal position detection signal FS, the amount of positional deviation in the optical axis direction from the focal point (best image plane) at the projection position of each slit image S (hereinafter, appropriately referred to as “detection point”). In order to detect the focus, the focus state of the reference mark plate FM or the wafer W with respect to the projection optical system PL is directly checked in advance, and the level of the focus position detection signal FS at or near the true focus point is determined. The offset of each photo sensor is adjusted (calibration of each photo sensor) so as to be a predetermined level (target level), and thereafter, each signal FS and each target are adjusted. The difference from the focus level is recognized as the amount of displacement (defocus amount) in the optical axis direction from the best imaging plane position at each detection point, and based on this, the movement of the substrate table 18 in the Z direction and the tilt direction is determined. Control it . For example, zero (0) is used as the target focus level. In such a case, there are optical and electrical methods for setting a predetermined threshold at the level of the focus position detection signal FS at the time of focusing and calibrating each of the gate sensors. However, here, it is assumed that a method is used in which the main controller 44 electrically offsets the value of the signal FS so as to be at the in-focus level. Next, the best results at each detection point, which is a prerequisite for calibration of the photosensors Dll to D33, corresponding to each detection point of the above-mentioned multipoint focus position detection system (40, 42). A method for detecting the image plane position will be described. It is assumed that the main controller 44 sets the same focus level as the target focus level of all the photosensors D11 to D33 corresponding to the respective detection points of the multipoint focus position detection system (40, 42). Is set. In addition, on the reticle stage 36, the exposure area (pattern projection area) E f on the wafer W A measurement reticle R1 as a measurement mask on which a focus position measurement pattern projected on each of the lith images S11 to S33, that is, all the detection point positions, is placed, and the reticle alignment is performed. Mention has been completed. The pattern on the measurement reticle R1 is not particularly limited, but in this embodiment, any pattern may be used as long as the pattern is formed at the positions of the slit images S11 to S33.

① In this state, first, the main controller 44 uses the multi-point focus position detection system (40, 42) to position it at five detection points, specifically, four corners in the exposure area E f Wafers at a total of five detection points: four detection points, which are the positions of the slit images S11, S13, S3K, S33, and the detection points, which are the position of the slit image S22, which is located at the center Measure the position of the W surface in the optical axis direction. In the following description, for the sake of convenience, each detection point will be referred to with the same reference sign S11 to S33 as the reference sign of the slit image S corresponding to each detection point. In this case, only the photosensors D11, D13, D22, D31, and D33 are connected to the signal processing device 91 via the sensor selection circuit 94 by the main controller 44, and five of the nine detection points are detected. Of the detection points are being selected.

② Next, the main controller 44 calculates the average value of the detection results of the above five points in the Z-axis direction, and monitors each focus position detection signal from the multi-point focus position detection system (40, 42), The drive device 21 and the Z-not-shown (not shown) are set so that the Z-axis coordinates of the five detection points S11, S13, S22, S3K 0 Drive control (feedback control) of the substrate table 18 via the drive mechanism. Thereby, the inclination of the exposure area E f on the wafer W is corrected. In order to correct the tilt of the exposure area Ef on the wafer W, the Z-axis position (1) described above may be detected at all (9 in this case) detection points S in the exposure area. Only needs to detect the Z-axis position with at least three detection points. ③ Next, the main controller 44 keeps the inclination of the board table 18 adjusted in the above ①, so that the Z-axis coordinates can be set arbitrarily based on the average of the Z-axis detection values obtained earlier. After driving the substrate table 18 in the Z-axis direction via a drive device 21 and a Z ■ 0 drive mechanism (not shown), the opening / closing of a shirt (not shown) in the illumination system is controlled to obtain the measurement reticle. The projection of R1 is projected into the exposure area Ef on the wafer W. As a result, the focus position measurement pattern is exposed at the positions of the detection points S11 to S33 in the exposure area Ef. As described above, the first exposure area E f (hereinafter, referred to as “E f 1”) When the exposure is completed, the main controller 44 outputs the X stage 12 and the Y stage via the driving device 21. Driving both or one of 16 is performed to step the wafer W by a predetermined amount. The above operations (1) to (3) are performed on the next second exposure area E f (hereinafter, referred to as “E f 2”). In the exposure, the Z-axis position at the time of exposure is different from that of the exposure area E f 1 by a predetermined pitch {ii ia (<_5 or later. On the other hand, the above-mentioned stepping and the above-mentioned operations (1) to (3) are performed while changing the Z-axis position at the time of exposure in (3) above at a fixed pitch, so that the Z-axis position within a predetermined range is determined. When the exposure is completed, the operation of exposing the focus position measurement pattern on the measurement reticle R1 to the wafer W ends, in this case, it is assumed that the exposure has ended in the n-th exposure area E fn. The wafer W that has been exposed is transferred to a developing device (not shown), Performed, registration of the respective detection point position of each exposure area E f 1 to E fn on the wafer W By measuring the line width of the storage pattern, for example, with a line width measuring device, the relationship between the Z-axis position and the pattern line width of the resist image at each of the detection points S11 to S33 is obtained.

1 o In Fig. 3, the horizontal axis represents the Z-axis position of each of the multiple detection points obtained as a result of the above line width measurement, and the vertical axis represents the pattern line width of the resist image. A graph showing the relationship is shown. FIG. 4 shows an arbitrary curve in FIG. First, a method for detecting a focal position (best image plane position) at an arbitrary detection point will be described with reference to FIG. In FIG. 4, the pattern line width of the resist image is largest at the position where the Z-axis coordinate value is Za. The Z-axis coordinate value of the point where the line width of the resist image becomes maximum is determined as the best image plane position. By detecting such a best imaging plane position based on a graph showing the relationship between the Z-axis position for each detection point and the pattern line width of the resist image as shown in FIG. 3, each detection point is obtained. the nine points of S. 11 to S 33, the best imaging plane position Z of each detection _{point, Ζ 12, Ζ, 3,} Ζ 21, τ η, Z ", to detect a _{Z 31, Z 32, Z 33} . Note Depending on the focus measurement pattern, the operator may visually detect the pattern line width and determine the best imaging plane position for each detection point based on the result. Shows only the graphs of the four detection points S11, S13, S22, S31, and S33 at the four corners and the center in the exposure area, but similar graphs are used for the other detection points. Obviously, the best image plane position is obtained in the same manner as described above. Image plane position _{Ζ π, Ζ 12, Ζ Ι3} , Ζ

„, Τ _η , ζ„, 、 ₃₁ , ζ _3?か ら₃₃ are input from an input device (not shown), and the main controller 4

18 Store in the internal memory of 4. In the main controller 44, the best imaging plane positions Z „, Z, ₂ , and

Z _U s L _M n, Z _{! 3} s Z _{3 3 33} (Photo sensor D11 to D33 corresponding to each detection point of SIJ multi-point, focus position detection system (40, 42) performing calibration. That is, the main controller 44, the best imaging plane _{iiim π Ζ 12, Ζ 13,} Ζ ίΙ arm _{", Ζ 23, Ζ 3,} ν L, or厶, t respectively Fotose capacitors D11, D12, D13, D2K Offset adjustment of the photosensors D11 to D33 so that the target level of each of the D22, D23, D31, D32, and D33 is achieved (calibration calibration). The structure and calibration method of the photosensor are described in, for example, Japanese Patent Application Laid-Open Nos. 1-18778, 2-301112 and U.S. Pat. No. 4,908,656. As disclosed, this disclosure is incorporated herein by reference to the extent permitted by national law of the designated State of the International Application. In the subsequent exposure, when the surface position is detected by the multi-point focus position detection system (40, 42), the above-mentioned image plane position and wafer W are detected from the photo sensor D corresponding to each detection point S. Since the focus detection signal (defocus signal) FS indicating the difference from the position in the optical axis direction of the surface is obtained, the main controller 44 controls the focus position of the wafer W and the wafer surface tilt correction control based on this. This enables high-precision focus and repelling control based on high-precision focus position detection. In the main controller 44, the best imaging plane position Z, _{Z l2, 13, Z 21,} Z 22, Z 23, ZL 32. rather suspended in Z _33, without calibrating the photosensors D. 11 to D 33 of the upper §d, certain reference position is first set Detected value of Z-axis position based on (target position) A measured value), in advance internal memory best image plane stored in the position Z u, Z ヽ * ~ ヽ ヽ ヽ The difference between the Z _33, recognized as the amount of deviation from the focal position at the respective detection points, it is also possible to implement the focus position location control and Ueno \ plane inclination correction control. By the way, as described above, the focus position detection signal FS is a signal indicating an in-focus point indirectly, so that the position of the best image forming plane (focal point) of the projection optical system PL previously detected due to exposure light absorption or the like changes. In this case, in this case, a difference occurs between the focal point at which the signal FS is at the target focus level and the actual focal point. In consideration of such a case, it is most preferable that the focus position is periodically detected based on the exposure result using the measurement reticle R 1 described above. It is difficult to adopt it because of the labor involved. Therefore, as a next best measure, means capable of detecting a change in the focal position without actually performing exposure, for example, Japanese Patent Application Laid-Open No. 5-190423 and the corresponding US Pat. A light emitting mark is formed on a reference plate FM on a substrate table 18 (wafer stage) as disclosed in No. 2, 311 and the light emitting mark is illuminated from below with light having the same wavelength as the exposure light. The light-emitting mark is projected onto the reticle pattern surface via the projection optical system PL, and the reflected light from the reticle pattern surface is projected onto the light-emitting mark on the reference plate FM via the projection optical system PL, and the substrate table 18 An internal light receiving sensor is used to detect each image at each detection point using a spatial image focal position detection system (TTL type focal position detection system) that photoelectrically detects the image projected on the light-emitting mark. Periodically detect the corresponding best image plane position. It can be considered. According to such an aerial image focus position detection system, the best imaging plane position at an arbitrary point (image height) of the projection optical system PL is changed in the Z direction on the substrate table 18, and the contrast of the image detected at that time is changed. Can be detected based on the data. To the extent permitted by the national legislation of the designated country designated in this international application, the disclosure of Japanese Patent Application Laid-Open No. 5-190423 and the corresponding US Patent No. 5,502,311 Incorporation of text Part of However, since such an aerial image focus position detection system sensor may include a sensitivity error, it is necessary to perform the <focus position detection based on the exposure result using the measurement reticle R 1 described above before the start of exposure. The result is compared with the detection result of the aerial image focus position detection system at the X 丫 coordinate position of each detection point, and if there is a difference between the two, it is used as a device constant and the internal memory in the main controller 44 To memorize it. After that, every time the aerial image focal position detection system detects the best imaging plane position at the XY coordinate position of each detection point, the actual best imaging plane position is calculated in consideration of the above device constant. It is desirable to readjust the offset of each photosensor D of the multipoint focus position detection system (40, 42) based on the value. Further, as described above, the best imaging plane position Z, which is stored in the internal memory, based on to Z _33, if not the offset adjustment of Bok each follower Tosensa D is stored in the internal memory What is necessary is just to correct the data of the focal position that is set. This enables highly accurate wafer surface detection and surface position adjustment even when the position of the best imaging plane (focal point) of the projection optical system PL previously detected due to exposure light absorption or the like changes. . As described above, according to this embodiment, the best imaging plane position is detected based on the actual exposure result for each detection point position in the pattern projection area (exposure area) on the wafer W. Even if the projection optical system PL has a curvature of field, an inclination of the image plane, and the like, it is possible to simultaneously detect the true best imaging plane position Z at each detection point S in consideration of these factors. The multi-point focus detection system (40, 42) detects the true best imaging plane position Z at each detected point S and the optical axis direction position of each detected point S of the wafer W detected thereafter. Based on the photoelectric detection result, the displacement of the projection optical system PL from the best imaging plane position Z in the optical axis direction can be accurately determined for each detection point S. Can be detected. Therefore, if the position and inclination of the wafer W in the optical axis direction are adjusted based on this detection result, it is possible to ensure that the projection area of the wafer W matches the focal depth of the best imaging plane of the projection optical system P. it can. Further, according to the present embodiment, it is needless to say that the influence of the displacement due to the backlash in the Z-axis direction due to the manufacturing accuracy of the stage and the like at the time of the focus position detection as in the prior art described above is of course eliminated. . Further, in the above embodiment, when detecting the best imaging plane position at each detection point by exposure using a measurement reticle, in the above-mentioned step (1), the multi-point imaging is performed.

—Electroscopic detection of at least three of the plurality of detection points S11 to S33 on the wafer W in the optical axis direction of the projection optical system PL using the residue position detection system (40, 42); Since the tilt adjustment of the wafer W is performed using the result, there is no need to separately provide another leveling sensor or the like. Further, in the above embodiment, the case where the surface position detection method according to the present invention is applied to a step-and-repeat type projection exposure apparatus has been described. However, the present invention is not limited to this, and US Patent Nos. 5,448, The present invention can also be suitably applied to the step exposure apparatus disclosed in No. 3 32 and the .-scan type projection exposure apparatus, and only to the extent permitted by national laws and regulations of the designated country specified in the international application. The disclosure of US Patent No. 5,448,333 is incorporated herein by reference. Industrial applicability

As described above, according to the focusing method of the present invention, the best imaging of the projection optical system is performed for each of the plurality of measurement points defined in the projection area of the projection optical system, that is, the exposure area on the substrate. The surface can be measured accurately. Using this method, the output level of a multipoint smart focus sensor such as an oblique incidence type of exposure apparatus can be easily compared. The correct focus position of the substrate is compensated even in different environments where the projection optical system is placed. In particular, the present invention is extremely useful for a projection exposure apparatus and a projection exposure apparatus using a projection optical system having a large numerical aperture.

Claims

The scope of the claims 1. When the predetermined pattern formed on the mask is projected onto the sensitive substrate by the projection optical system, the focusing method for focusing the position of the sensitive substrate on the projection optical system includes:  Using a mask in which a plurality of measurement points are defined in a projection area on the sensitive substrate on which the pattern of the mask is projected, and a focus measurement pattern is formed at a position on the mask corresponding to the plurality of measurement points;  Exposing the sensitive substrate with a focus measurement pattern while changing the position of the sensitive substrate in the optical axis direction of the projection optical system to various positions;  A focusing method, wherein the best imaging position by a projection optical system is determined for each measurement point from the exposure results of the sensitive substrate at the various positions in the optical axis direction. 2. Each measurement point on the sensitive substrate is irradiated with light using light from a projection system other than the projection optical system, and the position of each measurement point in the optical axis direction is determined from the reflected light. The focusing method according to claim 1, wherein the position in the optical axis direction is calibrated based on the best imaging position. 3. The focusing method according to claim 2, wherein an in-focus position of each measurement point on the sensitive substrate is detected using a multi-point focusing position detection mechanism of an oblique incident light system. 4. Using the oblique incident light type multi-point focus position detection mechanism, detect the focus positions of the measurement points on the sensitive substrate in advance, find the average focus position, and calculate the average focus position. The method according to claim 3, wherein the sensitive substrate is exposed while changing the position of the sensitive substrate in the optical axis direction of the projection optical system to various positions after positioning the substrate. Focusing method. 5. The focusing method according to claim 1, wherein the best imaging position at each measurement point is determined by observing the line width of the pattern exposed on the sensitive substrate. 6. The focusing method according to claim 1, wherein a pattern for focus measurement is formed on the mask at a center of the mask through which the optical axis of the projection optical system passes, and at a plurality of positions around the center. 7. The focusing method according to claim 1, wherein each time the position in the optical axis direction is changed, the sensitive substrate is moved in a direction orthogonal to the optical axis direction to change the projection area. 8. An exposure method for exposing a sensitive substrate by projecting a predetermined pattern formed on a mask onto the sensitive substrate by a projection optical system,  A plurality of measurement points are defined in a projection area on the sensitive substrate on which the pattern of the mask is projected, and a focus measurement mask having a focus measurement pattern formed at a position on the mask corresponding to the plurality of measurement points Using;  Exposing the sensitive substrate with the focus measurement pattern while changing the position of the sensitive substrate in the optical axis direction of the projection optical system to various positions;  From the exposure results of the sensitive substrate at the various positions in the optical axis direction, the best imaging position by the projection optical system is obtained for each measurement point;  An exposure method, comprising: positioning a sensitive substrate with respect to a projection optical system based on the obtained best image forming position; and performing exposure using a mask on which the predetermined pattern is formed. 9. Further, each measurement point on the sensitive substrate is irradiated with light using light from a projection system different from the projection optical system, and the position of the sensitive substrate in the optical axis direction is obtained from the reflected light. 9. The exposure method according to claim 8, wherein the calculated position in the optical axis direction is calibrated based on the best imaging position. 10. The exposure method according to claim 9, wherein an in-focus position of each measurement point on the sensitive substrate is detected by using a multi-point in-focus position detection mechanism of an oblique incident light system. 1 1. In advance, the in-focus multi-point in-focus position detection mechanism is used to detect the in-focus position of each measurement point on the sensitive substrate, and determine the average in-focus position. 10. The method according to claim 10, further comprising: exposing the sensitive substrate while changing the position of the sensitive substrate in the optical axis direction of the projection optical system to various positions after positioning the substrate. Exposure method. 12. The exposure method according to claim 8, wherein the best imaging position at each measurement point is determined by observing the line width of the pattern exposed on the sensitive substrate. 13. The exposure method according to claim 8, wherein a pattern for focus measurement is formed on the mask at a center of the mask through which the optical axis of the projection optical system passes and at a plurality of positions around the center of the mask. . 14. When exposing the mask on which the predetermined pattern is formed, the mask and the sensitive substrate are moved synchronously with respect to the projection optical system while irradiating the mask with slit-like illumination light. Exposing the transparent substrate, wherein the projection region is a region conjugated to the projection optical system with the illumination region formed on the mask by irradiation with the slit-like illumination light. The exposure method according to claim 9, wherein the exposure is performed. 15. Further, the image of the pattern formed by the projection optical system is projected onto the mask by illuminating the image focus position measurement pattern provided on the substrate stage, and the reflected light from the mask is projected by the projection optical system. 9. The exposure method according to claim 8, further comprising calibrating the determined best imaging position by receiving light through a system. 16. An exposure apparatus that exposes a projection area on a sensitive substrate by projecting a predetermined pattern formed on a mask onto the sensitive substrate by a projection optical system, wherein the sensitive substrate is connected to the optical axis of the projection optical system. A substrate stage for moving in a direction; a projection system separate from the projection optical system, the projection system irradiating light to a plurality of measurement points in a projection area on the sensitive substrate; A focus detection system including a focus detector for detecting the position of each measurement point in the optical axis direction by detecting light reflected from each measurement point;  A control device for storing information on the best imaging position for each measurement point and controlling the exposure device;  An exposure apparatus, wherein the control device controls a substrate stage based on the stored best imaging position and a detection value of a focus detector to position a sensitive substrate at the best imaging position. 17. The best imaging position is determined by using a measurement mask in which a focus measurement pattern is formed at a position on the mask corresponding to the plurality of measurement points, and determining the position of the sensitive substrate in the optical axis direction of the projection optical system. 17. The exposure apparatus according to claim 16, wherein the position is determined from an exposure result obtained by exposing the sensitive substrate while changing to various positions. 18. The exposure apparatus according to claim 16, wherein the control device calibrates a target focus level of a focus detector using information on the best imaging position. 19. The exposure apparatus according to claim 16, wherein the control device corrects a detection result of a focus detector using information on the best imaging position. 20. The exposure according to any one of claims 16 to 18, wherein the focus detector has a plurality of detectors that detect a position in an optical axis direction for each measurement point. 21. The exposure apparatus according to claim 20, wherein the focus detector is an oblique incidence type multipoint focus sensor. 22. Further, an image focus position measurement pattern provided on the substrate stage, and an image of the pattern formed by the projection optical system by illuminating the pattern and projecting the image on the mask, and reflecting light from the mask. The exposure apparatus according to claim 16, further comprising a focus position detection system that receives light via a projection optical system, wherein the focus position detection system calibrates the best imaging position. 23. The exposure apparatus exposes the sensitive substrate by moving the mask and the sensitive substrate synchronously with respect to the projection optical system while irradiating the mask with slit-like illumination light. A scanning type exposure apparatus, wherein the projection area is an area conjugate to an illumination area formed on a mask by being irradiated with the slit-like illumination light and a projection optical system. Item 16. An exposure apparatus according to Item 16. 24. In the manufacturing method of the exposure apparatus, Providing a substrate stage for moving the projection optical system and the sensitive substrate in the direction of the optical axis of the projection optical system;  A projection system separate from the projection optical system, which irradiates a plurality of measurement points in a projection area on the sensitive substrate with light, and detects light reflected from each measurement point on the sensitive substrate. Thereby providing a focus detection system including a focus detector for detecting the position of each measurement point in the optical axis direction;  A system for storing information on the best imaging position for each measurement point and controlling the exposure apparatus. 2 S A control device for controlling a substrate stage based on the stored best imaging position and a detection value of a focus detector to position a sensitive substrate at the best imaging position;  A method of manufacturing an exposure apparatus, comprising connecting the focus detector to a control device. 25. The stored best imaging position is sensitive in the optical axis direction of the projection optical system using a measurement mask having a focus measurement pattern formed at a position on the mask corresponding to the plurality of measurement points. The method according to claim 24, wherein the position is determined from an exposure result obtained by exposing the sensitive substrate while changing the position of the substrate to various positions. . 26. The method according to claim 24, wherein the exposure apparatus is a step-and-scan type exposure apparatus.