JP2006013310A - Exposure method and exposure apparatus - Google Patents

Abstract

An object of the present invention is to perform reticle pattern surface measurement in a scanning exposure apparatus without increasing the apparatus inspection time before exposure processing.
In a scanning exposure method in which an image of a pattern formed on a reticle is scanned and exposed on a substrate via a projection optical system, another inspection process for scanning the reticle stage and the substrate stage in the same stage driving state as at the time of exposure And reticle pattern surface measurement in parallel.
[Selection] Figure 1

Description

  The present invention relates to a scanning exposure method and a scanning exposure apparatus used when a reticle pattern is exposed on a substrate such as a wafer in a lithography process for manufacturing, for example, a semiconductor element or a liquid crystal display element.

  When manufacturing semiconductor elements and the like, in addition to a batch exposure type projection exposure apparatus such as a stepper, a scanning type projection exposure apparatus (scanning type exposure apparatus) such as a step-and-scan method is being used. . In the projection optical system of this type of exposure apparatus, a resolution close to the limit is required. Therefore, factors affecting the resolution (for example, atmospheric pressure, environmental temperature, etc.) are measured, and the imaging characteristics are determined according to the measurement results. A mechanism for correcting the above is provided. In addition, since the numerical aperture of the projection optical system is set to be large in order to increase the resolution, and as a result, the depth of focus is considerably shallow, projection of irregularities on the surface of the wafer as the substrate is performed by the surface position measurement system of the oblique incidence method. An autofocus mechanism is provided that measures the position of the optical system in the optical axis direction (wafer pattern surface measurement) and aligns the wafer surface with the image surface of the projection optical system during exposure based on the measurement result. Supplementing the wafer pattern surface measurement using the oblique incidence optical system in the scanning exposure apparatus, since the measurement is performed while scanning the wafer stage during exposure, the reflectivity of the wafer measurement position fluctuates and the received light signal is too large. If the light receiving system is saturated or conversely too small and the S / N deteriorates, the surface position measurement accuracy deteriorates. Therefore, as proposed in Japanese Patent Laid-Open No. 10-64980, the reflectivity at the wafer measurement position is measured by scanning the wafer stage in advance before exposure, and the wafer measurement position at scan exposure is measured. Pre-exposure processing is performed such that the amount of light emitted from the light projecting means is set according to the reflectance. Note that the pre-exposure processing performed before exposure is not limited to this, and the position of the wafer placed on the wafer chuck on the stage as proposed in Japanese Patent Laid-Open No. 2000-260699 is correctly measured, and the reticle and In order to manage the offset data for the step data resulting from the wafer pattern structure as proposed in Japanese Patent Application Laid-Open No. 9-45608 and the processing called alignment for positioning so that the positioning error is within an allowable range. For example, a process of measuring the wafer pattern surface in advance before the exposure.

  By the way, conventionally, measurement of unevenness in the optical axis direction of the projection optical system on the reticle pattern surface (reticle pattern surface measurement) has not been regarded as important as measurement of unevenness on the surface of the wafer. This is because the deviation of the reticle pattern surface in the optical axis direction in the projection optical system is 1 / (the square of the magnification of the projection optical system) on the image plane. For example, when the magnification of the projection optical system is 4, a 50 nm shift in the optical axis direction of the projection optical system on the reticle pattern surface is approximately 3 nm when converted to a shift in the image plane. However, in recent years, the numerical aperture of the projection optical system has been set to be larger in order to increase the resolving power, the depth of focus has become shallower, and the imaging error due to the unevenness of the reticle pattern surface cannot be ignored. Therefore, in order to obtain higher imaging performance in the exposure system, the pattern surface is measured not only on the wafer but also on the reticle side, and the wafer surface position and the image plane of the projection optical system are aligned during exposure, including the measurement results. It is necessary to indent. Therefore, an oblique incidence type focal position detection system for measuring the wafer pattern surface is also arranged on the reticle stage side.

Reticle pattern surface measurement and correction value calculation are performed as follows. Prior to shipment, a reference reticle is prepared, and the reticle stage and wafer stage are in the same state as during exposure, and measurement is performed at a plurality of points on the reticle pattern surface. An approximate surface of the reticle pattern surface is obtained from this measured value. Next, the position of the image plane of the projection optical system is obtained by exposing the surface of the wafer to the height of the wafer surface, and stored in correspondence with the approximate surface of the reticle pattern surface. When exposure is performed after shipment, measurement is performed at a plurality of points on the reticle pattern surface used by the user as pre-exposure processing, and an approximate surface of the reticle pattern surface is calculated from the measurement result. The approximate surface is compared with the approximate surface of the reference reticle pattern surface obtained in advance before shipment, and the amount of deviation is obtained and converted to the amount of deviation of the image plane position of the projection optical system. This conversion can be obtained theoretically. For example, assuming that the magnification of the projection optical system is 4 and the amount of deviation of the reticle pattern surface in the optical axis direction of the projection optical system is 160 nm, as described above, the amount of deviation of the image plane position is 1 / (of the projection optical system. Since it is the square of the magnification), it is 10 nm.
JP-A-10-64980 JP 2000-260699 A JP-A-9-45608

  Since the respective states of the reticle stage, the wafer stage, and the housing on which the projection optical system is mounted have an influence on each other, an attitude difference occurs depending on the respective states. For example, the postures of the reticle stage and the housing are different between when the wafer stage is scanning and when it is stationary. For this reason, even if the reticle pattern surface is measured with the wafer stage stationary before exposure, the position of the reticle pattern surface relative to the projection optical system when scanning the wafer stage during exposure is different. Therefore, also in reticle pattern surface measurement before exposure, it is necessary to scan the wafer stage in the same way as during exposure.

  However, if the above is realized, the reticle pattern surface measurement cannot be performed in parallel with the other pre-exposure processing described above, so that the preprocessing time corresponding to the reticle pattern surface measurement time increases.

  A step of detecting a wafer stage scanning process from the existing pre-exposure processing in the same manner as during exposure and a step of scanning the reticle stage and performing reticle pattern surface measurement in synchronization with this processing are provided.

  A step is provided for detecting whether or not the wafer stage needs to be scanned at the time of measuring the reticle pattern as in the case of exposure. What must be measured at the same time is the case of measurement for exposure correction. What is not necessary to be measured at the same time is the case of foreign object pinching inspection between the reticle holder and the reticle.

  According to the present invention, it is possible to perform highly accurate reticle pattern surface measurement without reducing the throughput. Since the image plane position of the projection optical system can be calculated based on this measurement result, there is an advantage that an accurate and stable image of the reticle pattern can be obtained without reducing the throughput.

  Hereinafter, embodiments of the invention will be described in detail with reference to examples.

  FIG. 2 is a partial schematic view of a slit-scan type projection exposure apparatus using the scanning exposure method of the present invention.

  In FIG. 2, a reticle R is illuminated with a uniform illuminance by a rectangular slit-shaped illumination area 21 by a light source 1 and an illumination optical system composed of an illumination light shaping optical system 2 to a relay lens 8, and within the slit-shaped illumination area 21. The circuit pattern image of the reticle R is transferred onto the wafer W via the projection optical system 13. As the light source 1, an excimer laser light source such as an F2 excimer laser, an ArF excimer laser or a KrF excimer laser, a pulse light source such as a metal vapor laser light source or a harmonic generator of a YAG laser, or a combination of a mercury lamp and an elliptical reflector A continuous light source having a different configuration can be used.

  In the case of a continuous light source, ON / OFF of exposure is switched by a shutter in the illumination light shaping optical systems 2-8. However, in this embodiment, since a movable blind (variable field stop) 7 is provided as will be described later, the exposure may be switched on and off by opening and closing the movable blind 7.

  In FIG. 2, the illumination light from the light source 1 reaches the fly-eye lens 3 with the light beam diameter set to a predetermined size by the illumination light shaping optical system 2. A large number of secondary light sources are formed on the exit surface of the fly-eye lens 3, and illumination light from these secondary light sources is collected by a condenser lens 4, and a movable blind (variable field stop) through a fixed field stop 5. 7 is reached. In FIG. 2, the field stop 5 is arranged on the condenser lens 5 side with respect to the movable blind 7, but it may be arranged on the reverse side of the relay lens system 8.

  A rectangular slit-shaped opening is formed in the field stop 5, and the light beam that has passed through the field stop 5 enters the relay lens system 8. The longitudinal direction of the slit is a direction perpendicular to the paper surface. The movable blind 7 includes two blades (light-shielding plates) 7A and 7B that define the width in the scanning direction (Y direction), which will be described later, and two blades (not shown) that define the width in the non-scanning direction perpendicular to the scanning direction. It is made up of. The blades 7A and 7B that define the width in the scanning direction are supported by the drive units 6A and 6B so that they can be moved independently in the scanning direction, and the two blades that define the width in the non-scanning direction (not shown) are also independent. It is supported so that it can be driven. In this embodiment, illumination light is irradiated only within a desired exposure area set by the movable blind 7 in the slit-shaped illumination area 21 on the reticle R set by the fixed field stop 5. The relay lens system 8 is a bilateral telecentric optical system, and the telecentricity is maintained in the slit-shaped illumination region 21 on the reticle R.

  Reticle R is held on reticle stage RST. The position of reticle stage RST is detected by interferometer 22 and driven by reticle stage drive unit 10. The optical element G1 is held below the reticle R, and is scanned together with the reticle R during reticle stage RST scanning driving. An image of the circuit pattern on the reticle R in the slit-shaped illumination area 21 and defined by the movable blind 7 is projected and exposed on the wafer W via the projection optical system 13.

  In a two-dimensional plane perpendicular to the optical axis of the projection optical system 13, the scanning direction of the reticle R with respect to the slit-shaped illumination region 21 is defined as the + Y direction (or −Y direction), and the direction horizontal to the optical axis of the projection optical system 13 Is the Z direction.

  In this case, the reticle stage RST is driven by the reticle stage driving unit 10 to scan the reticle R in the scanning direction (+ Y direction or −Y direction), and the driving units 6A and 6B of the movable blind 7 and the driving for the non-scanning direction. The operation of the unit is controlled by the movable blind control unit 11. The main control system 12 that controls the operation of the entire apparatus controls the operations of the reticle stage driving unit 10 and the movable blind control unit 11.

  Between the optical element G1 held on the reticle stage RST and the projection optical system 13, a reticle surface position detection system RO is configured.

  On the other hand, the wafer W is held after being transferred to the wafer stage WST by a wafer transfer device (not shown), and the wafer stage WST positions the wafer W in a plane perpendicular to the optical axis of the projection optical system 13 and also moves the wafer W. XY stage that scans in the ± Y direction, and a Z stage that positions the wafer W in the Z direction. The position of wafer stage WST is detected by interferometer 23. Above the wafer W, an off-axis type alignment sensor 16 is configured. An alignment mark on the wafer is detected by the alignment sensor 16, processed by the control unit 17, and sent to the main control system 12. Main control system 12 controls positioning operation and scanning operation of wafer stage WST via wafer stage drive unit 15.

  When the pattern image on the reticle R is exposed to each shot area on the wafer W through the projection optical system 13 by the scan exposure method, the slit-shaped illumination area 21 set by the field stop 5 in FIG. In contrast, the reticle R is scanned at a speed VR in the −Y direction (or + Y direction). Further, assuming that the projection magnification of the projection optical system 13 is β, the wafer W is scanned in the + Y direction (or −Y direction) at the speed VW (= β · VR) in synchronization with the scanning of the reticle R. As a result, the circuit pattern image of the reticle R is sequentially transferred to the shot area on the wafer W.

  The reticle surface position detection system RO will be described with reference to FIG. First, the basic detection principle of the reticle surface position detection system will be described. The reticle pattern surface, which is the test surface, is irradiated with a light beam from an oblique direction, and the incident position of the light beam reflected by the test surface on the predetermined surface is positioned. Detection is performed by a detection element, and position information in the Z direction (the optical axis direction of the projection optical system 13) of the surface to be detected is detected from the position information. In this figure, only one system will be described, but a plurality of light beams set in a direction substantially orthogonal to the scanning direction are projected onto a plurality of measurement points on the surface to be measured, and the positions in the Z direction obtained at the respective measurement points The tilt information of the test surface is calculated using the information. Further, by scanning the reticle R, position information in the Z direction at a plurality of measurement points can also be measured in the scanning direction. From these position information, the surface shape of the pattern surface of the reticle R can be calculated.

  Next, each element of the reticle surface position detection system will be described. In FIG. 3, reference numeral 30 denotes a light source unit of a reticle surface position detection system. Reference numeral 31 denotes a light source for detecting the reticle surface position. The light source 31 is an LED that emits visible to infrared light in order to obtain a sufficient amount of reflected light at an oblique incidence with respect to the reticle material. Reference numeral 32 denotes a drive circuit, which is configured so that the intensity of light emitted from the light emitting light source 31 can be arbitrarily controlled.

  The light emitted from the light emitting light source 31 is guided to a light transmission means 35 such as an optical fiber by a collimator lens 33 and a condenser lens 34.

  The light beam emitted from the light transmission means 35 illuminates the slit 37 by the illumination lens 36. A surface position measuring mark 37A on the pattern surface of the reticle R is provided on the slit 37, and the mark 37A is projected onto the pattern surface of the reticle R, which is the test surface, by the imaging lens 38 via the mirror 39. Has been. By the imaging lens 38, the slit 37 and the surface of the pattern surface of the reticle R have an optical conjugate relationship. In the figure, only the chief ray is shown for easy explanation. The light beam based on the mark image formed on the pattern surface of the reticle R is reflected on the pattern surface of the reticle R, and the mark image is re-imaged on the most image formation position 42 by the imaging lens 41 via the mirror 40. A light beam based on the mark image re-imaged at the re-image position 42 is condensed by the magnifying optical system 43 and is substantially imaged on the light-receiving element 44 for position detection. A signal from the light receiving element 44 is measured and processed by a reticle surface position signal processing system (not shown), and is processed as information on the Z and inclination of the pattern surface of the reticle R, which is the test surface.

  FIG. 3 shows a cross-sectional view, and only one system is shown. However, a plurality of systems can be actually arranged. Further, in FIG. 3, the incident direction of the reticle surface position detection system detection light to the reticle R pattern surface is shown from a direction parallel to the scanning direction. However, the present invention is not limited to this, and the direction orthogonal to the scanning direction or arbitrary It is also possible to adopt a configuration in which the light enters from the direction of the angle.

  Next, the outline of the reticle pattern surface measuring method of the present invention will be described with reference to the flowchart of FIG.

  In step 1, a start command is received, and in step 2, reticle R is carried and fixed onto reticle stage RST by a reticle conveying means (not shown).

  In the control program for executing the pre-exposure process in step 3, it is determined whether there is a process for scanning the wafer stage WST in the same or similar state as that during the exposure from the pre-exposure processes to be performed this time. To supplement the pre-exposure process, the pre-exposure process that can use the result of the previous exposure is not performed because of time reduction. For example, in the pre-exposure processing in which the reflectance at the wafer measurement position as described above is measured by scanning the wafer stage WST in advance, the measurement result of the first wafer is the second and subsequent wafers. Can also be used, so the second and subsequent measurements can be omitted. Therefore, this pre-exposure processing is set as pre-exposure processing for each lot. Thus, each pre-exposure process is set as a process for each wafer and a process for each lot. Therefore, specifically, the pre-exposure processing set in advance or not in the control program is selected, the processing for scanning the wafer stage WST is selected, and the wafer stage WST is driven. It is determined by comparing whether there is a process in which parameters such as acceleration and speed are the same as or similar to those at the time of this exposure. The state close to the time of exposure means that the reticle stage RST and the wafer stage WST are scanned in synchronization with the reticle stage RST and wafer stage WST in the same manner as during exposure when scanning the reticle stage RST and measuring the reticle R pattern surface. A state in which the difference in the position of the R pattern surface can be ignored. For example, the difference in the scanning speed of the wafer stage within a range in which the difference in behavior of the reticle R pattern surface can be ignored. If parameters such as acceleration and speed for driving wafer stage WST are the same as or similar to those at the time of the current exposure, the process proceeds to step 4. If parameters such as acceleration and speed for driving wafer stage WST are the same as or similar to those at the time of this exposure, step 5 is proceeded to.

  In step 4, a pre-exposure process is performed in which the reticle stage is measured by scanning the reticle stage in parallel with the process in which the wafer stage WST is scanned in a state similar to or close to that at the time of exposure.

  When proceeding to step 5, it is determined whether the object of reticle R pattern surface measurement is limited to foreign object detection. Supplementing the necessity of measuring the reticle R pattern surface, one of the purposes of measuring the reticle R pattern surface is a foreign object pinching inspection between the reticle holder and the reticle. For example, when a single wafer is exposed with a plurality of reticles, the reticle is frequently exchanged. In such a case, the foreign object pinching inspection may occur at every exchange, so that the foreign object inspection by the reticle R pattern surface measurement is necessary every time. However, the measurement for correcting the exposure is performed at the time of exposure for the second and subsequent wafers. Since reticle R pattern surface information already exists, it is not always necessary.

  On the other hand, as described above, the pre-exposure processing for the second and subsequent wafers is less because many data can be substituted for the data for the first wafer. That is, it is unlikely that the existing pre-exposure process includes a process in which wafer stage WST scans in a state close to that at the time of exposure. Therefore, reticle R pattern surface measurement cannot be performed in parallel with the existing preprocessing. However, in detecting foreign object pinching, the degree of deformation (decrease in flatness) of the reticle R is important, and the positional relationship between the projection optical system and the reticle R pattern surface is not so important. That is, in detecting foreign object pinching, it is not always necessary to bring wafer stage WST into the same state as exposure in synchronization with measurement of reticle stage RST.

  If attention is paid to this point, when the object of reticle R pattern surface measurement is foreign object pinching detection, the wafer stage is not scanned during the pre-exposure processing in the same way as during exposure, but in parallel with the existing pre-exposure processing. Thus, the preprocessing time can be shortened by measuring the reticle R pattern surface.

  If the purpose of the reticle R pattern surface measurement is limited to foreign object detection, the process proceeds to step 6. If the objective of reticle R pattern surface measurement is not limited to foreign object detection, the process proceeds to step 7.

  In step 6, in parallel with the other exposure processes, a pre-exposure process is performed in which the reticle stage RST is scanned to measure the reticle R pattern surface.

  In the case of proceeding to step 7, in order to improve reticle R pattern surface measurement accuracy, pre-exposure processing for performing reticle R pattern surface measurement by scanning not only reticle stage RST but also wafer stage WST in the same state as during exposure. To implement.

  In step 8, the reticle R pattern surface measurement timing for the purpose of foreign object detection is determined. It is performed in parallel with the existing pre-exposure processing at a timing that does not affect the measurement of both wafer stage WST and reticle stage RST.

  In step 9, the foreign object pinching is determined from the reticle R pattern surface measurement result.

  The following modifications can be considered in the above embodiment.

  Of the pre-exposure processing described above, it is conceivable that the processing for scanning wafer stage WST in a state similar to or close to that of exposure is changed in advance as follows. The processing is changed so that the reticle R pattern surface measurement is also performed by scanning the reticle stage RST synchronously unconditionally. That is, the process of scanning wafer stage WST in a state similar to or close to the exposure is changed to a new process that combines the process of measuring the reticle R pattern surface. In this way, it is not necessary to select a process for scanning wafer stage WST in a state similar to or close to the exposure from the pre-exposure processes each time, and to change the reticle pattern surface measurement in synchronization.

The flow of the Example of this invention. Explanatory drawing of the exposure apparatus of this invention. Explanatory drawing of a reticle surface position detection system.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Light source 2 Illumination system shaping optical system 3 Fly eye lens 4 Condenser lens 5 Field stop 6A, 6B Movable blind drive part 7A, 7B Movable blind 8 Relay lens 10 Reticle stage control part 11 Movable blind control part 12 Main control part 13 Projection optics System 15 Wafer stage control unit 16 Off-axis alignment sensor 17 Control unit 21 Illumination area 22, 23 Interferometer 30 Light source unit of reticle surface position detection system 31 Light emission source for reticle surface position detection 32 Drive circuit 33 Collimator lens 34 condensing lens 35 light transmission means 36 illumination lens 37 slit 37A mark 38, 41 imaging lens 39, 40 mirror 42 maximum imaging position 43 magnifying optical system 44 light receiving element RST reticle stage WST wafer stage G1 correcting optical element The reticle W wafer RO reticle surface position detecting system

Claims (6)

  In a scanning exposure method in which an image of a pattern formed on an original is scanned and exposed on a substrate via a projection optical system, the original stage and the substrate stage are scanned in the same stage driving state as during exposure when not exposed, and the original pattern surface is measured. Performing a scanning exposure method.   In a scanning exposure method in which an image of a pattern formed on an original is scanned and exposed on a wafer via a projection optical system, the above-mentioned program is used to control a plurality of inspection items for inspecting the apparatus state of the exposure apparatus before the exposure operation. 2. The scanning exposure method according to claim 1, wherein an inspection item scanned by the substrate stage in the same stage driving state as that at the time of exposure is detected, and an original pattern surface measurement is performed in synchronization with the operation of the detected inspection item. .   In a scanning exposure method in which an image of a pattern formed on an original is scanned and exposed on a substrate via a projection optical system, an inspection item in which the substrate stage is in the same stage driving state as during exposure is detected from the control program. 3. The scanning exposure method according to claim 2, wherein when there is not, the substrate stage is brought into the same stage driving state as during exposure in synchronization with the measurement of the original pattern surface.   In a scanning exposure method in which an image of a pattern formed on an original is scanned and exposed on a substrate via a projection optical system, whether or not the substrate stage needs to be in the same stage driving state as during exposure for measuring the original pattern surface The scanning exposure method according to claim 2, wherein if necessary, the original pattern surface measurement is performed at an appropriate timing during execution of the inspection item.   5. The scanning exposure method according to claim 4, wherein the original pattern surface measurement is performed in parallel with the inspection item when the original pattern surface measurement is not required to be performed in the same stage driving state as that during exposure.   A scanning exposure apparatus to which the scanning exposure method according to claim 1 is applied.

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