JP4029180B2 - Projection exposure apparatus and projection exposure method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
  The present invention relates to a projection exposure apparatus and a projection exposure method, and more particularly to a projection exposure apparatus and a projection exposure method for projecting and exposing a pattern image formed on a mask onto a sensitive substrate via a projection optical system..
[0002]
[Prior art]
Conventionally, various exposure apparatuses have been used for manufacturing a semiconductor element or a liquid crystal display element in a photolithography process. Currently, a pattern of a photomask or a reticle (hereinafter, collectively referred to as “reticle”) is used. In general, a projection exposure apparatus that transfers an image onto a substrate such as a wafer or a glass plate (hereinafter, referred to as a “sensitive substrate” as appropriate) having a photosensitive material such as a photoresist coated on the surface via a projection optical system. in use. In recent years, as this projection exposure apparatus, a sensitive substrate is placed on a two-dimensionally movable substrate stage, and the sensitive substrate is stepped (stepped) by this substrate stage, so that the pattern image of the reticle is placed on the sensitive substrate. The so-called step-and-repeat type reduction projection exposure apparatus (so-called stepper), which repeats the operation of sequentially exposing each shot area, is the mainstream.
[0003]
Recently, a step-and-scan type projection exposure apparatus (for example, a scanning exposure apparatus as described in Japanese Patent Application Laid-Open No. 7-176468), which is an improvement on a static exposure apparatus such as a stepper, has also been developed. It has come to be used relatively frequently. This step-and-scan type projection exposure apparatus can expose a large field with a smaller optical system as compared with (1) a stepper, so that it is easy to manufacture the projection optical system, and a shot by large field exposure. By reducing the number, high throughput can be expected, and (2) there is an advantage in that the reticle and the wafer are scanned relative to the projection optical system, which has an averaging effect, and an improvement in distortion and depth of focus can be expected. Furthermore, as the integration density of semiconductor devices increases from 16M (mega) to 64M DRAM, and in the future to 256M, 1G (giga), and so on, the large field becomes essential, so it replaces the stepper. Therefore, it is said that scanning projection exposure apparatuses will become mainstream.
[0004]
[Problems to be solved by the invention]
Since this type of projection exposure apparatus is mainly used as a mass-production machine for semiconductor elements and the like, it is possible to improve the throughput, that is, the throughput of how many wafers can be exposed within a certain period of time. Is inevitably required.
[0005]
In this regard, in the case of a step-and-scan type projection exposure apparatus, when exposing a large field, as described above, the number of shots exposed in the wafer is reduced, so an improvement in throughput is expected. Since exposure is performed during constant-velocity movement by synchronous scanning of the reticle and wafer, an acceleration / deceleration area is required before and after the constant-velocity movement area, and a shot having the same size as the stepper shot size is temporarily exposed. In some cases, the throughput may be lower than that of the stepper.
[0006]
The flow of processing in this type of projection exposure apparatus is roughly as follows.
[0007]
(1) First, a wafer loading process is performed in which a wafer is loaded onto a wafer table using a wafer loader.
[0008]
(2) Next, a search alignment process is performed in which a rough position detection of the wafer is performed by the search alignment mechanism. Specifically, this search alignment process is performed, for example, based on the outer shape of the wafer or by detecting a search alignment mark on the wafer.
[0009]
{Circle around (3)} Next, a fine alignment step for accurately obtaining the position of each shot area on the wafer is performed. In this fine alignment process, an EGA (Enhanced Global Alignment) method is generally used. In this method, a plurality of sample shots in a wafer are selected, and an alignment mark (wafer mark) attached to the sample shot is selected. Are sequentially measured, and based on this measurement result and the design value of the shot arrangement, a statistical calculation is performed by a so-called least square method or the like to obtain all shot arrangement data on the wafer (Japanese Patent Laid-Open No. 61). -44429, etc.), the coordinate position of each shot area can be obtained with relatively high accuracy with high throughput.
[0010]
(4) Next, based on the coordinate position of each shot area obtained by the above-mentioned EGA method or the like and the baseline amount measured in advance, each shot area on the wafer is sequentially positioned at the exposure position, and the projection optical system is An exposure process for transferring the pattern image of the reticle onto the wafer is performed.
[0011]
(5) Next, a wafer unload process is performed in which the wafer on the wafer table subjected to the exposure process is unloaded using a wafer unloader. This wafer unloading step is performed simultaneously with the wafer loading step (1) for the wafer to be exposed. That is, (1) and (5) constitute a wafer exchange process.
[0012]
Thus, in the conventional projection exposure apparatus, four operations are repeatedly performed using one wafer stage, such as wafer exchange → search alignment → fine alignment → exposure → wafer exchange.
[0013]
Further, the throughput THOR [sheets / hour] of this type of projection exposure apparatus is given by the following equation when the wafer exchange time is T1, the search alignment time is T2, the fine alignment time is T3, and the exposure time is T4: It can be expressed as 1).
[0014]
THOR = 3600 / (T1 + T2 + T3 + T4) (1)
The operations from T1 to T4 are repeatedly executed sequentially (sequentially) in the order of T1, T2, T3, T4, T1, and so on. For this reason, if each element from T1 to T4 is speeded up, the denominator becomes smaller and the throughput THOR can be improved. However, the above-described T1 (wafer exchange time) and T2 (search alignment time) are relatively small since only one operation is performed on one wafer. In the case of T3 (fine alignment time), the throughput can be improved by reducing the number of shots when using the EGA method described above or by reducing the measurement time of a single shot. Since accuracy is degraded, T3 cannot be easily shortened.
[0015]
T4 (exposure time) includes a wafer exposure time and a stepping time between shots. For example, in the case of a scanning projection exposure apparatus such as the step-and-scan method, it is necessary to increase the relative scanning speed of the reticle and wafer by the amount that shortens the wafer exposure time, but the synchronization accuracy deteriorates. The scanning speed cannot be increased easily.
[0016]
In addition to the above throughput in this type of projection exposure apparatus, important conditions include (1) resolution, (2) depth of focus (DOF), and (3) line width control accuracy. . The resolution R is such that the exposure wavelength is λ and the numerical aperture of the projection lens is N.P. A. (Numerical Aperture), λ / N. A. And the depth of focus DOF is λ / (NA)²Is proportional to
[0017]
Therefore, in order to improve the resolution R (reduce the value of R), the exposure wavelength λ is reduced or the numerical aperture N.P. A. Need to be larger. In particular, the density of semiconductor elements has been increasing recently, and the device rule has become 0.2 μmL / S (line and space) or less, so illumination is necessary to expose these patterns. A KrF excimer laser is used as the light source. However, as described above, the degree of integration of semiconductor elements will inevitably increase in the future, and development of a device having a light source having a wavelength shorter than KrF is desired. As a candidate for a next-generation apparatus equipped with such a light source having a shorter wavelength, an apparatus using an ArF excimer laser as a light source, an electron beam exposure apparatus, and the like are representatively mentioned. In the case of an ArF excimer laser, oxygen In some places, light is hardly transmitted, high output is difficult to be output, laser life is short, and equipment costs are high, and in the case of electron beam exposure equipment, light exposure equipment In reality, it is difficult to develop next-generation machines with the main viewpoint of shortening the wavelength because of the disadvantage that the throughput is significantly lower than.
[0018]
As another method for increasing the resolution R, the numerical aperture N.I. A. Can be increased, but N.I. A. If is increased, there is a demerit that the DOF of the projection optical system is reduced. This DOF can be roughly divided into UDOF (User Depth of Forcus: part used on the user side: pattern step, resist thickness, etc.) and the total focal difference of the apparatus itself. Up to now, since the ratio of UDOF has been large, the direction in which the DOF is increased is the main axis of development of the exposure apparatus. For example, modified illumination has been put to practical use as a technique for increasing the DOF.
[0019]
By the way, in order to manufacture a device, a pattern in which L / S (line and space), isolated L (line), isolated S (space), CH (contact hole), etc. are combined is formed on the wafer. However, the exposure parameters for performing optimum exposure differ for each pattern shape such as L / S and isolated line. For this reason, conventionally, using a method called ED-TREE (excluding CHs with different reticles), the common is that the resolution line width is within a predetermined allowable error with respect to the target value and a predetermined DOF is obtained. Exposure parameters (coherence factor σ, NA, exposure control accuracy, reticle drawing accuracy, etc.) are determined and used as the specifications of the exposure apparatus. However, it is thought that there will be the following technical flow in the future.
[0020]
(1) Improvement in process technology (planarization on the wafer) will lead to a decrease in pattern step and a decrease in resist thickness, and UDOF may be in the range of 1 μm to 0.4 μm or less.
[0021]
(2) The exposure wavelength is shortened from g-line (436 nm) → i-line (365 nm) → KrF (248 nm). However, only light sources up to ArF (193) have been studied in the future, and the technical hurdles are high. Thereafter, the process shifts to EB exposure.
[0022]
(3) It is expected that scanning exposure such as step-and-scan will become the mainstream of steppers instead of static exposure such as step-and-repeat. This technique enables large field exposure with a projection optical system having a small diameter (especially in the scanning direction), and accordingly, a high N.D. A. It is easy to realize.
[0023]
Against the background of the technical trend as described above, the double exposure method has been reviewed as a method for improving the limit resolution, and this double exposure method is used in KrF and future ArF exposure apparatuses, and 0.1 μmL / S. Attempts have been made to expose to the maximum. In general, the double exposure method is roughly divided into the following three methods.
[0024]
(1) L / S and isolated lines with different exposure parameters are formed on separate reticles, and each is subjected to double exposure on the same wafer under optimum exposure conditions.
[0025]
(2) When the phase shift method or the like is introduced, the limit resolution is higher in the L / S with the same DOF than the isolated line. By utilizing this, all the patterns are formed with L / S by the first reticle, and an isolated line is formed by thinning out L / S with the second reticle.
[0026]
(3) Generally, the isolated line is smaller than the L / S. A. Can obtain a high resolution (however, the DOF becomes small). Therefore, all patterns are formed by isolated lines, and L / S is formed by a combination of isolated lines respectively formed by the first and second reticles.
[0027]
The above double exposure method has two effects of improving resolution and improving DOF.
[0028]
However, in the double exposure method, since it is necessary to perform the exposure process a plurality of times using a plurality of reticles, the exposure time (T4) is more than doubled as compared with the conventional apparatus, and the throughput is greatly deteriorated. In reality, the double exposure method has not been studied very seriously, and the resolution and depth of focus (DOF) can be improved by using ultraviolet exposure wavelength, modified illumination, phase shift reticle, etc. Has been done.
[0029]
However, when the double exposure method described above is used in KrF and ArF exposure apparatuses, exposure up to 0.1 μmL / S is realized, thereby developing next-generation machines aimed at mass production of 256M and 1G DRAMs. There is no doubt that it is a promising option, and the development of a new technology has been awaited for improving the throughput, which is a problem of the double exposure method that becomes a bottleneck for this.
[0030]
  The present invention has been made under such circumstances,FirstThe purpose is throughputAnd exposure accuracyImprovementPossibleTo provide a projection exposure apparatus.
[0031]
  BookInventionSecondThe purpose is throughputAnd exposure accuracyImprovementPossibleIt is to provide a projection exposure method.
[0032]
[Means for Solving the Problems]
  If the above four operations, ie, wafer exchange, search alignment, fine alignment, and exposure can be divided into at least two operations and performed in parallel, the throughput can be increased compared to the case where these four operations are performed sequentially. Can be improved. The present invention has been made paying attention to this point, and employs the following configuration. That is,
  According to a first aspect of the present invention, there is provided a projection exposure apparatus for projecting and exposing a pattern image formed on a mask (R) onto sensitive substrates (W1, W2) via a projection optical system (PL). A first substrate stage (WS1) capable of holding a sensitive substrate (W1) and moving in a two-dimensional plane; and holding a sensitive substrate (W2) in the same plane as the first substrate stage (WS1). A second substrate stage (WS2) movable independently of the first substrate stage (WS1); provided separately from the projection optical system (PL), on the substrate stage (WS1, WS2) or the substrate stage ( At least one alignment system (for example, 24a) for detecting marks on the sensitive substrates (W1, W2) held by WS1, WS2); receiving the sensitive substrate between the first substrate stage and the second substrate stage; Tooth and transport system (180 to 200) to perform; two simultaneously loadable mask stage the mask and (RST); wherein the first, one of the substrate stage of the second substrate stage,In a state where the mark on the one substrate stage can be detected by the alignment systemWith the transport systemofIn parallel with the transfer of the sensitive substrate and the first sequence for performing the mark detection operation by the alignment system, the mask stage and the other substrate stage are moved synchronously while using the plurality of masks. And a control means (90) for performing, in the other stage, a second sequence for performing double exposure of a plurality of shot areas on the sensitive substrate held on the other stage while changing the conditions.
[0033]
  According to this,Through parallel processing of the first sequence with one substrate stage and the second sequence with the other substrate stage, the throughput can be improved, and in the second sequence, two or more masks are used while changing the exposure conditions. Since multiple exposure is performed, an effect of improving high resolution and DOF (depth of focus) can be obtained.
[0036]
  In the projection exposure apparatus of the present invention, the first of the first substrate stage (WS1) from one side of the first axis passing through the projection center of the projection optical system (PL) and the detection center of the alignment system (24a). A first measuring axis (BI1X) for measuring the position in the axial direction and a length measuring the position in the first axial direction of the second substrate stage (WS2) from the other side in the first axial direction. At the second measurement axis (BI2X), the third measurement axis (BI3Y) perpendicular to the first axis at the projection center of the projection optical system (PL), and the detection center of the alignment system (24a) A fourth length measuring axis (BI4Y) perpendicularly intersecting the first axis, and two-dimensional of the first substrate stage and the second substrate stage (WS1 and WS2) by these length measuring axes (BI1X to BI4Y). Interferometer system that measures each position It may be provided with further.
  In this case, the alignment system may be provided with at least one alignment system separately from the projection optical system.2Two alignment systems (24a, 24b) may be arranged on one side and the other side in the first axis direction with the projection optical system (PL) interposed therebetween. When the alignment system is arranged in such a positional relationship, the sensitive substrate on the other substrate stage is exposed while the sensitive substrate on one substrate stage is exposed by the projection optical system located at the center (exposure operation). Can be detected using any alignment system (alignment operation). When switching between the exposure operation and the alignment operation, the substrate stage after the alignment operation can be moved under the projection optical system by simply shifting the two substrate stages in the first axis direction. The substrate stage can be moved to the position of the alignment system.
[0037]
  in this caseThe secondAn interferometer system (for example, a length measuring axis) so that each of the first substrate stage and the second substrate stage (WS1 and WS2) can perform an exposure operation by a projection optical system (PL) and a mark detection operation by an alignment system (for example, 24a). Control means (90) for independently controlling movement of the first substrate stage and the second substrate stage based on the measurement results of BI1X to BI4Y) may be further provided. According to this, the control means can interferometer system so that each of the first substrate stage and the second substrate stage can perform the exposure operation by the projection optical system (PL) and the mark detection operation by the alignment system (for example, 24a). Since the movement control of the first substrate stage and the second substrate stage is independently performed based on the measurement results of the measurement axes BI1X to BI4Y (for example, the measurement axes BI1X to BI4Y), the projection optical system is used for the sensitive substrate on any substrate stage. The exposure operation and the mark detection operation by the alignment system can be reliably performed.
[0038]
  In this case, if the distance between the length measuring axes BI3Y and BI4Y is too large, the length measuring axes BI3Y and BI4Y may be detached from the substrate stage when the first substrate stage and the second substrate stage are moved. If this is done, both stages will interfere with each other., SystemThe control means (90) interferes with each of the first substrate stage and the second substrate stage (WS1 and WS2) at the time of mark detection by the alignment system (for example, 24a) and at the time of exposure by the projection optical system (PL). The third measuring axis (BI3Y) and the fourth measuring axis (BI4Y) of the measuring system (for example, measuring axes BI1X to BI4Y) are switched so that the substrate stage may be removed from the measuring axis. Is desirable.
[0039]
In this case, the distance between the third length measurement axis (BI3Y) and the fourth length measurement axis (BI4Y) can be widened to prevent interference between both stages, and the first substrate stage and When the measurement axes BI3Y and BI4Y are disengaged from the substrate stage during the movement of the second substrate stage, each substrate at each processing position can be changed using the interferometer system by switching the measurement axis by the control means. It is possible to accurately measure the two-dimensional position of the stage.
[0043]
  In the projection exposure apparatus of the present invention, an exampleFor example, when there are two alignment systems apart from the projection optical system, two alignment systems (24a, 24b) are arranged on both sides of the projection optical system (PL) along a predetermined direction, and the control means (90) detects a mark on the first substrate stage (WS1) or on the sensitive substrate (W1) held on the first substrate stage (WS1) by one alignment system (24a), and the second substrate stage ( The mark on the sensitive substrate (W2) held on WS2) or the second substrate stage (WS2) may be detected by the other alignment system (24b).
[0044]
In this case, while the sensitive substrate on one substrate stage is exposed by the projection optical system located in the center (exposure operation), the sensitive substrate on the other substrate stage is moved to one alignment system. When the mark detection is performed (alignment operation) and the exposure operation and the alignment operation are switched, the two substrate stages are moved along the predetermined direction toward the other alignment system. Therefore, it is possible to easily move one substrate stage in the other alignment system position to the other alignment system position and move the other substrate stage in one alignment system position to below the projection optical system. Thus, two alignment systems can be used alternately.
[0049]
  According to a second aspect of the present invention, there is provided a projection exposure method for projecting and exposing a pattern image formed on a mask (R) onto a sensitive substrate (W1, W2) via a projection optical system (PL). Preparing two substrate stages (WS1, WS2) capable of holding the sensitive substrates (W1, W2) and independently moving in a two-dimensional plane, and a mask stage capable of mounting two of the masks simultaneously; In one of the two substrate stages,In a state where the mark on the one substrate stage can be detected by the alignment systemReplacing the sensitive substrate and markings on the substrate stage or on the sensitive substrate held on the substrate stageAccording to the alignment systemIn parallel with the first sequence for performing the detection operation, the mask stage and the other stage are moved synchronously, and are held on the other stage while changing the exposure conditions using the two masks. In the projection exposure method, a second sequence of double exposure of a plurality of shot areas on the sensitive substrate is performed on the other stage.
[0050]
  According to this,Through parallel processing of the first sequence with one substrate stage and the second sequence with the other substrate stage, the throughput can be improved, and in the second sequence, two or more masks are used while changing the exposure conditions. Since multiple exposure is performed, an effect of improving high resolution and DOF (depth of focus) can be obtained.
[0052]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an embodiment of the present invention will be described with reference to FIGS.
[0053]
FIG. 1 shows a schematic configuration of a projection exposure apparatus 10 according to an embodiment. The projection exposure apparatus 10 is a so-called step-and-scan type scanning exposure type projection exposure apparatus.
[0054]
The projection exposure apparatus 10 holds wafers WS1 and WS2 as first and second substrate stages that independently move in a two-dimensional direction while holding wafers W1 and W2 as sensitive substrates on a base board 12, respectively. The stage device provided, the projection optical system PL disposed above the stage device, and the reticle R as a mask above the projection optical system PL mainly in a predetermined scanning direction, here the Y-axis direction (the direction perpendicular to the plane of FIG. 1) ), A lighting system for illuminating the reticle R from above, a control system for controlling these parts, and the like.
[0055]
The stage device is levitated and supported on the base board 12 via an air bearing (not shown), and is independently 2 in the X-axis direction (the left-right direction on the paper surface in FIG. 1) and the Y-axis direction (the paper surface orthogonal direction in FIG. 1). Two wafer stages WS1 and WS2 capable of dimension movement, a stage drive system for driving these wafer stages WS1 and WS2, and an interferometer system for measuring the positions of the wafer stages WS1 and WS2 are provided.
[0056]
More specifically, air pads (not shown) (for example, vacuum preload type air bearings) are provided at a plurality of locations on the bottom surfaces of the wafer stages WS1 and WS2, and the air ejection force of the air pads and the vacuum prepressure are reduced. For example, it is levitated and supported on the base board 12 with an interval of, for example, several microns maintained by balance.
[0057]
On the base board 12, as shown in the plan view of FIG. 3, two X-axis linear guides extending in the X-axis direction (for example, a fixed side magnet of a so-called moving coil type linear motor) 122 , 124 are provided in parallel, and two X-axis linear guides 122, 124 are respectively attached with two moving members 114, 118 and 116, 120 that are movable along the X-axis linear guides. ing. Drive coils (not shown) are attached to the bottom portions of these four moving members 114, 118, 116, and 120 so as to surround the X-axis linear guide 122 or 124 from above and from the sides, respectively. And the X-axis linear guide 122 or 124 constitute moving coil type linear motors for driving the moving members 114, 116, 118, and 120 in the X-axis direction, respectively. However, in the following description, for the sake of convenience, the moving members 114, 116, 118, and 120 are referred to as X-axis linear motors.
[0058]
Two of these X-axis linear motors 114 and 116 are respectively provided at both ends of a Y-axis linear guide 110 (such as a fixed coil of a moving magnet type linear motor) 110 extending in the Y-axis direction. The remaining two X-axis linear motors 118 and 120 are fixed to both ends of a similar Y-axis linear guide 112 extending in the Y-axis direction. Therefore, the Y-axis linear guide 110 is driven along the X-axis linear guides 122 and 124 by the X-axis linear motors 114 and 116, and the Y-axis linear guide 112 is driven by the X-axis linear motors 118 and 120. 122 and 124 are driven.
[0059]
On the other hand, a magnet (not shown) surrounding one Y-axis linear guide 110 from above and from the side is provided at the bottom of wafer stage WS1, and wafer stage WS1 is moved to Y-axis by this magnet and Y-axis linear guide 110. A moving magnet type linear motor driven in the direction is configured. Further, a magnet (not shown) surrounding the other Y-axis linear guide 112 from above and from the side is provided at the bottom of the wafer stage WS2, and the wafer stage WS2 is moved to the Y-axis by this magnet and the Y-axis linear guide 112. A moving magnet type linear motor driven in the direction is configured.
[0060]
That is, in the present embodiment, the X-axis linear guides 122 and 124, the X-axis linear motors 114, 116, 118, and 120, the Y-axis linear guides 110 and 112, and the magnets (not shown) at the bottom of the wafer stages WS1 and WS2 are used. A stage drive system is configured to drive the wafer stages WS1 and WS2 independently in an XY two-dimensional manner. This stage drive system is controlled by the stage controller 38 in FIG.
[0061]
Note that by slightly varying the torque of the pair of X-axis linear motors 114 and 116 provided at both ends of the Y-axis linear guide 110, it is possible to generate or remove slight yawing in the wafer stage WS1. Similarly, by slightly varying the torque of the pair of X-axis linear motors 118 and 120 provided at both ends of the Y-axis linear guide 112, it is possible to generate or remove minute yawing in the wafer stage WS2. .
[0062]
On the wafer stages WS1 and WS2, the wafers W1 and W2 are fixed by vacuum suction or the like via a wafer holder (not shown). The wafer holder is finely driven in a Z-axis direction and a θ-direction (rotation direction about the Z-axis) orthogonal to the XY plane by a Z / θ drive mechanism (not shown). Further, on the upper surfaces of the wafer stages WS1 and WS2, fiducial mark plates FM1 and FM2 on which various fiducial marks are formed are installed so as to have almost the same height as the wafers W1 and W2, respectively. These reference mark plates FM1 and FM2 are used, for example, when detecting the reference position of each wafer stage.
[0063]
Further, a surface 20 on one side in the X-axis direction (left side surface in FIG. 1) and a surface 21 on one side in the Y-axis direction (surface on the back side in FIG. 1) 21 of the wafer stage WS1 are mirror-finished reflecting surfaces. Similarly, a surface 22 on the other side in the X-axis direction (the right side surface in FIG. 1) 22 and a surface 23 on the one side in the Y-axis direction of the wafer stage WS2 are mirror-finished reflecting surfaces. Yes. Interferometer beams of each length measuring axis (BI1X, BI2X, etc.) constituting an interferometer system, which will be described later, are projected onto these reflecting surfaces, and the reflected light is received by each interferometer, whereby a reference for each reflecting surface is obtained. The displacement from the position (generally a fixed mirror is arranged on the side surface of the projection optical system or the side surface of the alignment optical system, which is used as a reference surface) is measured, and thereby the two-dimensional positions of the wafer stages WS1 and WS2 are respectively determined. It has come to be measured. The configuration of the measurement axis of the interferometer system will be described in detail later.
[0064]
Here, as the projection optical system PL, there is used a refractive optical system composed of a plurality of lens elements having a common optical axis in the Z-axis direction and having a predetermined reduction magnification, for example, 1/5, on both sides telecentric. Yes. For this reason, the moving speed of the wafer stage in the scanning direction at the time of step-and-scan scanning exposure is 1/5 of the moving speed of the reticle stage.
[0065]
On both sides in the X-axis direction of the projection optical system PL, as shown in FIG. 1, off-axis type alignment systems 24a and 24b having the same function are provided. They are located at the same distance from the center (coincided with the projection center of the reticle pattern image). These alignment systems 24a and 24b have three types of alignment sensors, an LSA (Laser Step Alignment) system, an FIA (Filed Image Alignment) system, and an LIA (Laser Interferometric Alignment) system. It is possible to measure the position of the mark and the alignment mark on the wafer in the X and Y two-dimensional directions.
[0066]
Here, the LSA system is the most versatile sensor that irradiates a mark with a laser beam and measures the mark position using diffracted / scattered light, and has been conventionally used for a wide variety of process wafers. The FIA system is a sensor that measures the mark position by illuminating the mark with broadband light such as a halogen lamp and processing the image of the mark, and is effectively used for asymmetric marks on the aluminum layer and wafer surface. The In addition, the LIA system is a sensor that irradiates a diffraction grating mark with laser light having a slightly different frequency from two directions, causes the generated two diffracted lights to interfere, and detects the position information of the mark from the phase. Yes, it can be used effectively for low step and rough wafers.
[0067]
In the present embodiment, these three types of alignment sensors are properly used in accordance with the purpose, so-called search alignment in which the approximate position of the wafer is measured by detecting the positions of three-dimensional marks on the wafer, or on the wafer. Fine alignment or the like for performing accurate position measurement of each shot area is performed.
[0068]
In this case, the alignment system 24a is used for position measurement of the alignment mark on the wafer W1 held on the wafer stage WS1 and the reference mark formed on the reference mark plate FM1. The alignment system 24b is used for measuring the position of the alignment mark on the wafer W2 held on the wafer stage WS2 and the reference mark formed on the reference mark plate FM2.
[0069]
Information from each alignment sensor constituting the alignment systems 24a and 24b is A / D converted by the alignment control device 80, and a digitized waveform signal is arithmetically processed to detect a mark position. The result is sent to the main control device 90, and the main control device 90 instructs the stage control device 38 to correct the synchronization position at the time of exposure according to the result.
[0070]
Further, in the exposure apparatus 10 of the present embodiment, although not shown in FIG. 1, a reticle mark (not shown) on the reticle R is provided above the reticle R via the projection optical system PL as shown in FIG. ) And the marks on the reference mark plates FM1 and FM2 are provided with a pair of reticle alignment microscopes 142 and 144 composed of a TTR (Through The Reticle) alignment optical system using an exposure wavelength for simultaneously observing. Detection signals from these reticle alignment microscopes 142 and 144 are supplied to the main controller 90. In this case, the deflection mirrors 146 and 148 for guiding the detection light from the reticle R to the reticle alignment microscopes 142 and 144 are movably arranged, and when an exposure sequence is started, a command from the main controller 90 is also given. Thus, the deflecting mirrors 146 and 148 are retracted by a mirror driving device (not shown). Note that a configuration equivalent to the reticle alignment microscope 142, 144 is disclosed in, for example, Japanese Patent Laid-Open No. 7-176468, and therefore detailed description thereof is omitted here.
[0071]
Although not shown in FIG. 1, each of the projection optical system PL and the alignment systems 24a and 24b includes an autofocus / autoleveling measurement mechanism (hereinafter referred to as an in-focus position measuring mechanism) for checking the in-focus position as shown in FIG. , "AF / AL system") 130, 132, 134. Of these, the AF / AL system 132 projects the pattern formation surface on the reticle R and the exposure surface of the wafer W in order to accurately transfer the pattern on the reticle R onto the wafer (W1 or W2) by scanning exposure. Since it is necessary to be conjugated with respect to the optical system PL, it is detected whether or not the exposure surface of the wafer W matches the image plane of the projection optical system PL within the depth of focus range (whether it is in focus). This is what is provided. In the present embodiment, a so-called multipoint AF system is used as the AF / AL system 132.
[0072]
Here, the detailed configuration of the multipoint AF system constituting the AF / AL system 132 will be described with reference to FIGS.
[0073]
As shown in FIG. 5, the AF / AL system (multi-point AF system) 132 includes an optical fiber bundle 150, a condenser lens 152, a pattern forming plate 154, a lens 156, a mirror 158, and an irradiation objective lens 160. The optical system 151 includes a condensing objective lens 162, a rotational vibration plate 164, an imaging lens 166, and a condensing optical system 161 including a light receiver 168.
[0074]
Here, each part of the configuration of the AF / AL system (multi-point AF system) 132 will be described together with its operation.
[0075]
Illumination light having a wavelength that does not sensitize the photoresist on the wafer W1 (or W2) different from the exposure light EL is guided from an illumination light source (not shown) through the optical fiber bundle 150 and emitted from the optical fiber bundle 150. The light illuminates the pattern forming plate 154 through the condenser lens 152. The illumination light transmitted through the pattern forming plate 154 passes through the lens 156, the mirror 158, and the irradiation objective lens 160, and is projected onto the exposure surface of the wafer W. On the pattern forming plate 154 with respect to the exposure surface of the wafer W1 (or W2). The pattern image is projected and formed obliquely with respect to the optical axis AX. The illumination light reflected by the wafer W 1 is projected onto the light receiving surface of the light receiver 168 via the condenser objective lens 162, the rotation direction vibration plate 164 and the imaging lens 166, and on the light receiving surface of the light receiver 168 on the pattern forming plate 154. The pattern image is re-imaged. Here, the main controller 90 applies predetermined vibrations to the rotational direction vibration plate 164 via the vibration device 172, and a large number of light receivers 168 (specifically, the same number as the slit patterns of the pattern forming plate 154). Detection signals from the light receiving elements are supplied to the signal processing device 170. Further, the signal processing device 170 supplies a large number of focus signals obtained by synchronously detecting each detection signal with the drive signal of the vibration exciting device 172 to the main control device 90 via the stage control device 38.
[0076]
In this case, as shown in FIG. 6, for example, 5 × 9 = 45 vertical slit-like opening patterns 93-11 to 93-59 are formed on the pattern forming plate 154. The image of the aperture pattern is projected obliquely (45 °) with respect to the X axis and the Y axis on the exposure surface of the wafer W. As a result, a slit image having a matrix arrangement inclined at 45 ° with respect to the X axis and the Y axis as shown in FIG. 4 is formed. 4 indicates an illumination field on the wafer conjugate with an illumination area on the reticle illuminated by the illumination system. As is apparent from FIG. 4, the detection beam is irradiated onto an area that is two-dimensionally sufficiently larger than the illumination field IF under the projection optical system PL.
[0077]
The other AF / AL systems 130 and 134 are configured in the same manner as the AF / AL system 132. In other words, in the present embodiment, the detection beam can be irradiated by the AF / AL mechanisms 130 and 134 used when measuring the alignment mark in substantially the same area as the AF / AL system 132 used for focus detection during exposure. It has become. For this reason, when the alignment sensor 24a and 24b measures the alignment mark, the position of the alignment mark is measured while performing AF / AL measurement similar to that during exposure and autofocus / auto-leveling by control. Alignment measurement becomes possible. In other words, an offset (error) due to the posture of the stage does not occur between exposure and alignment.
[0078]
Next, the reticle driving mechanism will be described with reference to FIGS.
[0079]
The reticle driving mechanism includes a reticle stage RST that can move in a two-dimensional direction of XY while holding the reticle R on the reticle base board 32, a linear motor (not shown) that drives the reticle stage RST, and the reticle stage RST. And a reticle interferometer system for managing the position of the projector.
[0080]
More specifically, in the reticle stage RST, as shown in FIG. 2, two reticles R1 and R2 can be placed in series in the scanning direction (Y-axis direction). The RST is levitated and supported on the reticle base board 32 via an air bearing (not shown), and is driven minutely in the X-axis direction and minute in the θ direction by a drive mechanism 30 (see FIG. 1) including a linear motor (not shown). Rotation and scanning driving in the Y-axis direction are performed. The drive mechanism 30 is a mechanism that uses a linear motor similar to that of the stage device described above as a drive source, but is shown as a simple block in FIG. 1 for convenience of illustration and explanation. For this reason, the reticles R1 and R2 on the reticle stage RST are selectively used, for example, in double exposure, and any reticle can be scanned synchronously with the wafer side.
[0081]
On this reticle stage RST, a parallel plate moving mirror 34 made of the same material as the reticle stage RST (for example, ceramic) is extended in the Y axis direction at the other end of the X axis direction. A reflective surface is formed on the other surface of the mirror 34 in the X-axis direction by mirror finishing. An interferometer beam from an interferometer 36 indicated by a measurement axis BI6X is irradiated toward the reflecting surface of the movable mirror 34, and the interferometer receives the reflected light and performs the same as the wafer stage side with respect to the reference surface. By measuring the relative displacement, the position of reticle stage RST is measured. Here, the interferometer having the measurement axis BI6X actually has two interferometer optical axes that can be measured independently, and measures the position of the reticle stage in the X-axis direction and the yawing amount. Is possible. The measurement value of the interferometer having the length measurement axis BI6X is obtained based on the reticle and the Y position information of the wafer stages WS1 and WS2 from the interferometers 16 and 18 having the length measurement axes BI1X and BI2X on the wafer stage side. It is used to control the rotation of reticle stage RST in the direction in which the relative rotation (rotation error) of the wafer is canceled or to perform X-direction synchronization control.
[0082]
On the other hand, a pair of corner cube mirrors 35 and 37 are installed on the other side in the Y-axis direction (the front side in FIG. 1), which is the scanning direction (scanning direction) of reticle stage RST. A pair of double-pass interferometers (not shown) irradiate the corner cube mirrors 35 and 37 with interferometer beams indicated by measurement axes BI7Y and BI8Y in FIG. Are returned from the corner cube mirrors 35 and 37, and the reflected lights reflected there return on the same optical path and are received by the respective double-pass interferometers. The reference positions of the respective corner cube mirrors 35 and 37 (the reticle at the reference position). The relative displacement from the reflection surface on the base board 32 is measured. Then, the measurement values of these double pass interferometers are supplied to the stage control device 38 of FIG. 1, and the position of the reticle stage RST in the Y-axis direction is measured based on the average value. Information on the position in the Y-axis direction is obtained by calculating the relative position between the reticle stage RST and the wafer stage WS1 or WS2 based on the measurement value of the interferometer having the measurement axis BI3Y on the wafer side, and scanning during scanning exposure based on this. This is used for synchronous control of the reticle in the direction (Y-axis direction) and the wafer.
[0083]
That is, in this embodiment, a reticle interferometer system is configured by the interferometer 36 and a pair of double-path interferometers indicated by the measurement axes BI7Y and BI8Y.
[0084]
Next, an interferometer system for managing the positions of wafer stages WST1 and WST2 will be described with reference to FIGS.
[0085]
As shown in these figures, the X axis direction one side of the wafer stage WS1 is along a first axis (X axis) passing through the projection center of the projection optical system PL and the detection centers of the alignment systems 24a and 24b. The surface is irradiated with an interferometer beam indicated by a first measurement axis BI1X from the interferometer 16 of FIG. 1, and similarly, on the other surface in the X-axis direction of the wafer stage WS2 along the first axis. Is irradiated with an interferometer beam indicated by a second measuring axis BI2X from the interferometer 18 of FIG. The interferometers 16 and 18 receive these reflected lights, thereby measuring the relative displacement of each reflecting surface from the reference position and measuring the positions of the wafer stages WS1 and WS2 in the X-axis direction. . Here, as shown in FIG. 2, the interferometers 16 and 18 are three-axis interferometers each having three optical axes. In addition to the measurement in the X-axis direction of the wafer stages WS1 and WS2, tilt measurement and θ measurement is possible. The output value of each optical axis can be measured independently. Here, the θ stage (not shown) that performs θ rotation of the wafer stages WS1 and WS2 and the Z / leveling stage (not shown) that performs minute driving and tilt driving in the Z-axis direction are actually below the reflecting surface. All the driving amounts during tilt control of the wafer stage can be monitored by these interferometers 16 and 18.
[0086]
The interferometer beams of the first measurement axis BI1X and the second measurement axis BI2X always come into contact with the wafer stages WS1 and WS2 over the entire range of movement of the wafer stages WS1 and WS2, and accordingly, the X axis Regarding the direction, the position of the wafer stages WS1 and WS2 is the first length measurement axis BI1X and the second length measurement axis BI2X during exposure using the projection optical system PL and when the alignment systems 24a and 24b are used. It is managed based on the measured value.
[0087]
As shown in FIGS. 2 and 3, an interferometer having a third measurement axis BI3Y perpendicularly intersecting the first axis (X axis) at the projection center of the projection optical system PL, and alignment systems 24a and 24b. Interferometers each having measurement axes BI4Y and BI5Y as fourth measurement axes perpendicularly intersecting with the first axis (X axis) at the respective detection centers are provided. Only the long axis is shown).
[0088]
In the case of the present embodiment, in the Y-direction position measurement of the wafer stages WS1 and WS2 during exposure using the projection optical system PL, the interferometer of the measurement axis BI3Y passing through the projection center of the projection optical system, that is, the optical axis AX. In the measurement of the Y direction position of the wafer stage WS1 when the alignment system 24a is used, the measurement value of the interferometer of the measurement axis BI4Y passing through the detection center of the alignment system 24a, that is, the optical axis SX is used. The measurement value of the interferometer of the measurement axis BI5Y that passes through the detection center of the alignment system 24b, that is, the optical axis SX, is used for measuring the position of the wafer stage WS2 in the Y direction when the alignment system 24b is used.
[0089]
Accordingly, although the interference measurement major axis in the Y-axis direction deviates from the reflection surface of the wafer stages WS1 and WS2 depending on each use condition, at least one measurement axis, that is, the measurement axes BI1X and BI2X are the respective wafer stages. Since it does not deviate from the reflection surfaces of WS1 and WS2, the Y-side interferometer can be reset at an appropriate position where the interferometer optical axis to be used enters the reflection surface. A method for resetting the interferometer will be described in detail later.
[0090]
The Y measuring length measuring axes BI3Y, BI4Y, and BI5Y are two-axis interferometers each having two optical axes. In addition to the measurement in the Y-axis direction of the wafer stages WS1 and WS2, Tilt measurement is possible. The output value of each optical axis can be measured independently.
[0091]
In this embodiment, an interferometer system that manages the two-dimensional coordinate positions of the wafer stages WS1 and WS2 by a total of five interferometers including three interferometers having interferometers 16 and 18 and measurement axes BI3Y, BI4Y, and BI5Y. It is configured.
[0092]
In this embodiment, as will be described later, while one of the wafer stages WS1 and WS2 executes the exposure sequence, the other executes the wafer exchange and wafer alignment sequence. The movement of wafer stages WS1 and WS2 is managed by stage control device 38 in accordance with a command from main control device 90 based on the output value of each interferometer so that there is no interference.
[0093]
Next, the illumination system will be described with reference to FIG. As shown in FIG. 1, the illumination system includes a light source unit 40, a shutter 42, a mirror 44, beam expanders 46 and 48, a first fly-eye lens 50, a lens 52, a vibrating mirror 54, a lens 56, and a second fly. The lens includes an eye lens 58, a lens 60, a fixed blind 62, a movable blind 64, relay lenses 66 and 68, and the like.
[0094]
Here, each part of the illumination system will be described together with its operation.
[0095]
Laser light emitted from a light source unit 40 including a KrF excimer laser that is a light source and a dimming system (a dimming plate, an aperture stop, etc.) is transmitted through a shutter 42 and then deflected by a mirror 44 to be a beam expander 46, The beam is shaped into an appropriate beam diameter by 48 and is incident on the first fly-eye lens 50. The light beam incident on the first fly-eye lens 50 is divided into a plurality of light beams by two-dimensionally arranged fly-eye lens elements, and each light beam is again different by the lens 52, the vibrating mirror 54, and the lens 56. The light enters the second fly-eye lens 58 from an angle. The light beam emitted from the second fly-eye lens 58 reaches the fixed blind 62 installed at a position conjugate with the reticle R by the lens 60. After the cross-sectional shape is defined in a predetermined shape, the reticle R A predetermined shape defined by the fixed blind 62 on the reticle R as uniform illumination light that passes through the movable blind 64 disposed at a position slightly defocused from the conjugate plane of Here, the illumination area IA having a rectangular slit shape (see FIG. 2) is illuminated.
[0096]
Next, the control system will be described with reference to FIG. This control system is composed of an exposure amount control device 70, a stage control device 38, and the like, which are subordinate to the main control device 90, with a main control device 90 that controls the entire apparatus as a whole.
[0097]
Here, the operation at the time of exposure of the projection exposure apparatus 10 according to the present embodiment will be described focusing on the operations of the above-described components of the control system.
[0098]
The exposure amount controller 70 instructs the shutter driver 72 to drive the shutter driver 74 to open the shutter 42 before the synchronous scanning of the reticle R and the wafer (W1 or W2) is started. .
[0099]
Thereafter, the stage controller 38 starts synchronous scanning (scan control) of the reticle R and the wafer (W1 or W2), that is, the reticle stage RST and the wafer stage (WS1 or WS2) in accordance with an instruction from the main controller 90. The This synchronous scanning is performed by monitoring the measurement values of the measurement axis BI3Y and the measurement axis BI1X or BI2X of the interferometer system and the measurement axes BI7Y, BI8Y and the measurement axis BI6X of the reticle interferometer system, while controlling the stage control device. This is performed by controlling each of the linear motors constituting the driving system of the reticle driving unit 30 and the wafer stage by 38.
[0100]
When both stages are controlled at a constant speed within a predetermined tolerance, the exposure control device 70 instructs the laser control device 76 to start pulse emission. As a result, the rectangular illumination area IA of the reticle R whose pattern is chromium-deposited on the lower surface thereof is illuminated by illumination light from the illumination system, and an image of the pattern in the illumination area is 1/5 by the projection optical system PL. Projection exposure is performed on a wafer (W1 or W2) whose surface is reduced in size and coated with a photoresist on its surface. As is clear from FIG. 2, the slit width in the scanning direction of the illumination area IA is narrower than the pattern area on the reticle, and the reticle R and the wafer (W1 or W2) are synchronously scanned as described above. Thus, an image of the entire surface of the pattern is sequentially formed on the shot area on the wafer.
[0101]
Here, simultaneously with the start of the pulse emission described above, the exposure amount control device 70 instructs the mirror drive device 78 to drive the vibrating mirror 54 so that the pattern region on the reticle R is completely the illumination region IA (see FIG. 2). ), That is, until the image of the entire surface of the pattern is formed on the shot area on the wafer, this control is continuously performed to reduce the unevenness of interference fringes generated by the two fly-eye lenses 50 and 58. Do.
[0102]
Further, in order to prevent illumination light from leaking outside the light-shielding area on the reticle at the shot edge portion during the scanning exposure described above, the movable blind 64 is moved by the blind controller 39 in synchronization with the scanning of the reticle R and the wafer W. The drive control is performed, and a series of these synchronous operations are managed by the stage controller 38.
[0103]
By the way, the pulse light emission by the laser control device 76 described above needs to emit light n times (n is a positive integer) while an arbitrary point on the wafers W1 and W2 passes through the illumination field width (w). If the oscillation frequency is f and the wafer scan speed is V, the following equation (2) must be satisfied.
[0104]
f / n = V / w (2)
Further, when the irradiation energy of one pulse irradiated on the wafer is P and the resist sensitivity is E, the following equation (3) needs to be satisfied.
[0105]
nP = E (3)
In this way, the exposure amount control device 70 calculates all the variable amounts of the irradiation energy P and the oscillation frequency f, issues a command to the laser control device 76, and sets the dimming system provided in the light source unit 40. By controlling the irradiation energy P and the oscillation frequency f, the shutter driving device 72 and the mirror driving device 78 are controlled.
[0106]
Further, in the main controller 90, for example, when correcting the movement start position (synchronous position) of the reticle stage and the wafer stage that perform synchronous scanning during scan exposure, the correction amount with respect to the stage controller 38 that controls the movement of each stage. Instructs the correction of the stage position according to.
[0107]
Furthermore, the projection exposure apparatus of the present embodiment is provided with a first transfer system for exchanging wafers with the wafer stage WS1 and a second transfer system for exchanging wafers with the wafer stage WS2. ing.
[0108]
As shown in FIG. 7, the first transfer system performs wafer exchange with the wafer stage WS1 at the left wafer loading position as will be described later. The first transport system is attached to a first loading guide 182 extending in the Y-axis direction, a first slider 186 and a second slider 190 moving along the loading guide 182, and the first slider 186. A first wafer loader including a first unload arm 184, a first load arm 188 attached to a second slider 190, and the like, and three vertical moving members provided on the wafer stage WS1 And a first center-up 180 composed of
[0109]
Here, the wafer exchange operation by the first transfer system will be briefly described.
[0110]
Here, as shown in FIG. 7, a case will be described in which the wafer W1 'on the wafer stage WS1 at the left wafer loading position and the wafer W1 transferred by the first wafer loader are exchanged.
[0111]
First, main controller 90 turns off the vacuum of a wafer holder (not shown) on wafer stage WS1 via a switch (not shown) to release the wafer W1 '.
[0112]
Next, main controller 90 drives center-up 180 upward by a predetermined amount via a center-up drive system (not shown). As a result, the wafer W1 'is lifted to a predetermined position. In this state, main controller 90 instructs a wafer loader controller (not shown) to move first unload arm 184. Thereby, the first slider 186 is driven and controlled by the wafer loader control device, and the first unload arm 184 moves to the position above the wafer stage WS1 along the loading guide 182 and is positioned directly below the wafer W1 '.
[0113]
In this state, main controller 90 drives center up 180 downward to a predetermined position. During the downward movement of the center up 180, the wafer W1 'is transferred to the first unload arm 184, so the main controller 90 instructs the wafer loader controller to start vacuuming the first unload arm 184. As a result, the wafer W <b> 1 ′ is sucked and held on the first unload arm 184.
[0114]
Next, main controller 90 instructs the wafer loader controller to retract the first unload arm 184 and start moving the first load arm 188. As a result, the first unload arm 184 starts to move in the −Y direction in FIG. 7 integrally with the first slider 186, and at the same time, the second slider 190 and the first load arm 188 holding the wafer W1. The movement starts in the + Y direction integrally. When the first load arm 188 comes above the wafer stage WS1, the wafer loader control device stops the second slider 190 and releases the vacuum of the first load arm 188.
[0115]
In this state, the main controller 90 drives the center-up 180 upward, and the center-up 180 lifts the wafer W1 from below. Next, main controller 90 instructs wafer loader controller to retract the load arm. Thus, the second slider 190 starts moving in the −Y direction integrally with the first load arm 188, and the first load arm 188 is retracted. Simultaneously with the start of retraction of the first load arm 188, the main controller 90 starts to drive the center up 180 downward to place the wafer W1 on a wafer holder (not shown) on the wafer stage WS1, and vacuum the wafer holder. turn on. This completes a series of wafer exchange sequences.
[0116]
Similarly, as shown in FIG. 8, the second transfer system performs wafer exchange with the wafer stage WS2 at the right wafer loading position in the same manner as described above. The second transport system includes a second loading guide 192 extending in the Y-axis direction, a third slider 196 moving along the second loading guide 192, a fourth slider 200, and a third slider 196. A second wafer loader configured to include a second unload arm 194 attached, a second load arm 198 attached to the fourth slider 200, and the like, and a not-shown unit provided on the wafer stage WS2 It consists of the second center up.
[0117]
Next, parallel processing by two wafer stages, which is a feature of this embodiment, will be described with reference to FIGS.
[0118]
In FIG. 7, while the wafer W2 on the wafer stage WS2 is being exposed through the projection optical system PL, the wafer stage WS1 and the first transfer system are in the left loading position as described above. A plan view showing a state in which the wafers are exchanged between them is shown. In this case, an alignment operation is performed on the wafer stage WS1 as described later following the wafer exchange. In FIG. 7, the position control of the wafer stage WS2 during the exposure operation is performed based on the measured values of the measurement axes BI2X and BI3Y of the interferometer system, and the position of the wafer stage WS1 where the wafer replacement and alignment operations are performed. The control is performed based on the measurement values of the measurement axes BI1X and BI4Y of the interferometer system.
[0119]
At the left loading position shown in FIG. 7, the arrangement is such that the reference mark on the reference mark plate FM1 of the wafer stage WS1 comes directly under the alignment system 24a. For this reason, the main controller 90 resets the interferometer of the measurement axis BI4Y of the interferometer system before measuring the reference mark on the reference mark plate FM1 by the alignment system 24a.
[0120]
Subsequent to the wafer exchange and the interferometer reset described above, search alignment is performed. The search alignment performed after the wafer exchange is a pre-alignment performed again on the wafer stage WS1 because the position error is large only by the pre-alignment performed during the transfer of the wafer W1. Specifically, the positions of three search alignment marks (not shown) formed on the wafer W1 placed on the stage WS1 are measured using an LSA sensor or the like of the alignment system 24a, and the measurement is performed. Based on the result, the wafer W1 is aligned in the X, Y, and θ directions. The operation of each part during this search alignment is controlled by main controller 90.
[0121]
After this search alignment is completed, fine alignment is performed in which the arrangement of each shot area on the wafer W1 is obtained here using EGA. Specifically, the wafer stage WS1 is sequentially controlled based on design shot arrangement data (alignment mark position data) while managing the position of the wafer stage WS1 by the interferometer system (measurement axes BI1X, BI4Y). While moving, the alignment mark position of a predetermined sample shot on the wafer W1 is measured by an FIA sensor or the like of the alignment system 24a, and based on this measurement result and the design coordinate data of the shot arrangement, statistical calculation by the least square method is performed. , All shot array data are calculated. The operation of each part in the EGA is controlled by the main controller 90, and the above calculation is performed by the main controller 90. This calculation result is preferably converted into a coordinate system based on the reference mark position of the reference mark plate FM1.
[0122]
In the case of this embodiment, as described above, the position of the alignment mark is measured while performing the same AF / AL system 132 (see FIG. 4) measurement and control autofocus / auto leveling as in the exposure. Measurement is performed, and an offset (error) due to the attitude of the stage can be prevented from occurring between alignment and exposure.
[0123]
While the wafer exchange and alignment operations are being performed on the wafer stage WS1 side, the wafer stage WS2 side continuously uses the two reticles R1 and R2 as shown in FIG. 9 while changing the exposure conditions. Then, double exposure is performed by the step-and-scan method.
[0124]
Specifically, fine alignment by EGA is performed in advance in the same manner as on the wafer W1 side described above, and the shot arrangement data on the wafer W2 obtained as a result (the reference mark on the reference mark plate FM2 is used as a reference). ), The shot area on the wafer W2 is sequentially moved below the optical axis of the projection optical system PL, and then the reticle stage RST and the wafer stage WS2 are synchronized in the scanning direction each time each shot area is exposed. Scan exposure is performed by scanning. Such exposure for all the shot areas on the wafer W2 is continuously performed even after reticle replacement. As a specific exposure sequence of double exposure, as shown in FIG. 10A, each shot area of the wafer W1 is sequentially scanned and exposed from A1 to A12 using a reticle R2 (A pattern). The reticle stage RST is moved by a predetermined amount in the scanning direction using the drive system 30 to set the reticle R1 (B pattern) to the exposure position, and then the scan exposure is performed in the order of B1 to B12 shown in FIG. Do. At this time, since the exposure conditions (AF / AL, exposure amount) and the transmittance are different between the reticle R2 and the reticle R1, it is necessary to measure each condition during reticle alignment and change the conditions according to the result.
[0125]
The operation of each part during double exposure of the wafer W2 is also controlled by the main controller 90.
[0126]
In the exposure sequence and wafer exchange / alignment sequence that are performed in parallel on the two wafer stages WS1 and WS2 shown in FIG. 7 described above, the wafer stage that has been completed first enters a waiting state, and both operations are completed. At the time, the wafer stages WS1 and WS2 are controlled to move to the positions shown in FIG. The wafer W2 on the wafer stage WS2 for which the exposure sequence has been completed is replaced at the right loading position, and the wafer W1 on the wafer stage WS1 for which the alignment sequence has been completed is subjected to the exposure sequence under the projection optical system PL. Is called.
[0127]
In the right loading position shown in FIG. 8, the reference mark on the reference mark plate FM2 is arranged below the alignment system 24b as in the left loading position, and the wafer exchange operation and the alignment sequence described above are executed. Will be done. Of course, the reset operation of the interferometer of the measuring axis BI5Y of the interferometer system is executed prior to the mark detection on the reference mark plate FM2 by the alignment system 24b.
[0128]
Next, the reset operation of the interferometer by the main controller 90 when shifting from the state of FIG. 7 to the state of FIG. 8 will be described.
[0129]
After alignment at the left loading position, wafer stage WS1 is moved to a position where the reference mark on reference plate FM1 comes directly under the optical axis AX center (projection center) of projection optical system PL shown in FIG. However, since the interferometer beam of the measuring axis BI4Y is not incident on the reflecting surface 21 of the wafer stage WS1 during this movement, it is difficult to move the wafer stage to the position shown in FIG. 8 immediately after the alignment is completed. For this reason, in this embodiment, the following devices are devised.
[0130]
That is, as described above, in this embodiment, when the wafer stage WS1 is in the left loading position, the reference mark plate FM1 is set to be directly below the alignment system 24a, and the length measurement is performed at this position. Since the interferometer of the axis BI4Y has been reset, the wafer stage WS1 is once returned to this position, and the detection center of the alignment system 24a known in advance from that position and the optical axis center (projection center) of the projection optical system PL. Based on the distance (referred to as BL for convenience), the wafer stage WS1 is moved to the right in the X-axis direction by the distance BL while monitoring the measurement value of the interferometer 16 of the measurement axis BI1X where the interferometer beam does not break. As a result, wafer stage WS1 is moved to the position shown in FIG. Then, main controller 90 uses at least one of reticle alignment microscopes 142 and 144 to measure the relative positional relationship between the mark on reference mark plate FM1 and the reticle mark, and then an interferometer for measuring axis BI3Y. To reset. This reset operation can be executed when the next measuring axis to be used can irradiate the side surface of the wafer stage.
[0131]
As described above, the reason why high-precision alignment is possible even if the reset operation of the interferometer is performed is that the alignment mark on the reference mark plate FM1 is measured by the alignment system 24a, and then the alignment mark of each shot area on the wafer W1 is set. This is because the distance between the reference mark and the virtual position calculated by measuring the wafer mark is calculated by the same sensor. Since the relative distance between the reference mark and the position to be exposed is obtained at this point, if the correspondence between the exposure position and the reference mark position is obtained by the reticle alignment microscope 142 or 144 before the exposure, the value is added to the value. By adding the relative distance, even if the interferometer beam of the interferometer in the Y-axis direction is cut during the movement of the wafer stage and reset again, a highly accurate exposure operation can be performed.
[0132]
If the length measurement axis BI4Y cannot be cut while the wafer stage WS1 is moved from the alignment end position to the position shown in FIG. 8, the measurement values of the length measurement axes BI1X and BI4Y are monitored and after the alignment is completed. Of course, the wafer stage may be moved linearly to the position shown in FIG. In this case, the reset operation of the interferometer may be performed when the length measuring axis BI3Y passing through the optical axis AX of the projection optical system PL is applied to the reflecting surface 21 orthogonal to the Y axis of the wafer stage WS1.
[0133]
In the same manner as described above, the wafer stage WS2 may be moved from the exposure end position to the right loading position shown in FIG. 8 to perform the reset operation of the interferometer of the measurement axis BI5Y.
[0134]
FIG. 11 shows an example of the timing of an exposure sequence for sequentially exposing each shot area on the wafer W1 held on the wafer stage WS1, and FIG. 12 is performed in parallel with this. The timing of the alignment sequence on the wafer W2 held on the wafer stage WS2 is shown. In this embodiment, while the two wafer stages WS1 and WS2 are independently moved in the two-dimensional direction, the exposure sequence and the wafer exchange / alignment sequence are performed in parallel on the wafers W1 and W2 on each wafer stage. As a result, throughput is improved.
[0135]
However, when two operations are simultaneously performed using two wafer stages, the operation performed on one wafer stage may affect the operation performed on the other wafer stage as a disturbance factor. Conversely, there is an operation in which an operation performed on one wafer stage does not affect an operation performed on the other wafer stage. Therefore, in this embodiment, among the operations to be processed in parallel, each operation is performed so that operations that become disturbance factors or operations that do not become disturbance factors are performed at the same time by dividing into operations that do not become disturbance factors. The timing is adjusted.
[0136]
For example, during the scanning exposure, the wafer W1 and the reticle R are synchronously scanned at a constant speed, so that it does not become a disturbance factor, and it is necessary to eliminate other disturbance factors as much as possible. For this reason, during the scan exposure on one wafer stage WS1, the timing is adjusted so as to be stationary in the alignment sequence performed on the wafer W2 on the other wafer stage WS2. That is, the mark measurement in the alignment sequence is performed in a state where the wafer stage WS2 is stationary at the mark position, so that it is not a disturbance factor for the scan exposure, and the mark measurement can be performed in parallel during the scan exposure. 11 and 12, the scan exposure indicated by the operation numbers “1, 3, 5, 7, 9, 11, 13, 15, 17, 19, 21, 23” with respect to the wafer W1 in FIG. 12, the mark measurement operations at the respective alignment mark positions indicated by the operation numbers “1, 3, 5, 7, 9, 11, 13, 15, 17, 19, 21, 23” in FIG. You can see that it is done synchronously. On the other hand, even in the alignment sequence, during scanning exposure, since the motion is constant, it is possible to perform high-precision measurement without causing disturbance.
[0137]
The same thing can be considered at the time of wafer exchange. In particular, vibration generated when the wafer is transferred from the load arm to the center up can be a cause of disturbance. Therefore, acceleration / deceleration before scan exposure or before and after synchronous scanning is performed at a constant speed (disturbance factor) The wafer may be delivered according to the above.
[0138]
The timing adjustment described above is performed by the main controller 90.
[0139]
As described above, according to the projection exposure apparatus 10 of the present embodiment, the two wafer stages that respectively hold the two wafers independently are provided, and these two wafer stages are moved independently in the XYZ directions, Since the wafer exchange and alignment operations are performed on one wafer stage, the exposure operation is performed on the other wafer stage, and each operation is switched when both operations are completed. It becomes possible to greatly improve.
[0140]
In addition, according to the above embodiment, since at least two alignment systems that perform mark detection with the projection optical system PL interposed therebetween are provided, each alignment system can be used alternately by shifting the two wafer stages alternately. The alignment operation and the exposure operation to be performed can be performed in parallel.
[0141]
In addition, according to the above embodiment, since the wafer loader for exchanging the wafer is arranged in the vicinity of the alignment system, particularly at each alignment position, the transition from the wafer exchange to the alignment sequence is smoothly performed, and more High throughput can be obtained.
[0142]
Further, according to the above-described embodiment, the high throughput as described above can be obtained. Therefore, even if the off-axis alignment system is installed far away from the projection optical system PL, the influence of the throughput degradation is almost eliminated. For this reason, high N.I. A. It is possible to design and install a straight cylinder type optical system having a numerical aperture and a small aberration.
[0143]
Further, according to the above embodiment, each optical system has an interferometer beam from an interferometer that measures approximately the center of each optical axis of the two alignment systems and the projection optical system PL. In either case of pattern exposure via the projection optical system, the two wafer stage positions can be accurately measured without Abbe error, and the two wafer stages can be moved independently. It becomes possible.
[0144]
Furthermore, the measurement axes BI1X and BI2X provided from both sides along the direction in which the two wafer stages WS1 and WS2 are arranged (here, the X-axis direction) toward the projection center of the projection optical system PL are always the wafer stages WS1 and WS1. Since irradiation is performed on WS2 and the position of each wafer stage in the X-axis direction is measured, movement control can be performed so that the two wafer stages do not interfere with each other.
[0145]
In addition, the length measurement axes BI3Y, BI4Y, and the length measurement axes BI3Y, BI4Y in the direction perpendicular to the detection center of the alignment system and the projection center position of the projection optical system PL (here, the Y axis direction) with respect to the length measurement axes BI1X, BI2X, Even if the interferometer is arranged so as to irradiate BI5Y and the wafer stage is moved and the measurement axis deviates from the reflecting surface, the position of the wafer stage can be accurately controlled by resetting the interferometer. Become.
[0146]
Reference mark plates FM1 and FM2 are provided on the two wafer stages WS1 and WS2, respectively. The mark position on the reference mark plate and the mark position on the wafer are obtained by measuring in advance with an alignment system. By adding the distance from the correction coordinate system to the reference plate measurement position before exposure, the wafer position can be measured without performing baseline measurement to measure the distance between the projection optical system and the alignment system. As a result, the mounting of a large reference mark plate as described in JP-A-7-176468 becomes unnecessary.
[0147]
Further, according to the above embodiment, since double exposure is performed using a plurality of reticles R, an effect of improving high resolution and DOF (depth of focus) can be obtained. However, in this double exposure method, since the exposure process must be repeated at least twice, the exposure time becomes longer and the throughput is significantly reduced. However, the throughput is greatly improved by using the projection exposure apparatus of this embodiment. Therefore, high resolution and an improvement effect of DOF can be obtained without reducing the throughput. For example, in T1 (wafer exchange time), T2 (search alignment time), T3 (fine alignment time), and T4 (one exposure time), each processing time for an 8-inch wafer is T1: 9 seconds, T2: 9 seconds , T3: 12 seconds, T4: 28 seconds, throughput is THOR = 3600 / (T1 + T2 + T3 + T4 * 2) when double exposure is performed by a conventional technique in which a series of exposure processes are performed using one wafer stage. = 3600 / (30 + 28 * 2) = 41 [sheets / hour] The throughput of the conventional apparatus that performs the single exposure method using one wafer stage (THOR = 3600 / (T1 + T2 + T3 + T4) = 3600/58 = 62 [sheets] / Hour]), the throughput is reduced to 66%. However, in the case where double exposure is performed while T1, T2, T3, and T4 are processed in parallel using the projection exposure apparatus of this embodiment, the exposure time is longer, so that the throughput THOR = 3600 / (28 + 28) = Since it is 64 [sheets / hour], it is possible to improve the throughput while maintaining the effect of improving the high resolution and the DOF. Further, since the exposure time is long, the number of EGA points can be increased, and the alignment accuracy is improved.
[0148]
In the above embodiment, the case where the present invention is applied to an apparatus that exposes a wafer using the double exposure method has been described. However, the present invention can also be applied to stitching, which is a similar technique. Further, as described above, the apparatus of the present invention allows the wafer to be independently moved between two reticles on one wafer stage side (double exposure, stitching) on the other wafer stage side. This is because, when performing wafer exchange and wafer alignment in parallel, the throughput is higher than that of the conventional single exposure, and the resolving power can be greatly improved. However, the scope of application of the present invention is not limited to this, and the present invention can also be suitably applied when exposure is performed by a single exposure method. For example, assuming that the processing times (T1 to T4) of an 8-inch wafer are the same as described above, when performing exposure processing by a single exposure method using two wafer stages as in the present invention, T1, T2, and T3 are set as follows. When one group (30 seconds in total) and parallel processing with T4 (28 seconds) are performed, the throughput becomes THOR = 3600/30 = 120 [sheets / hour], and the single exposure method is performed using one wafer stage. Compared to the conventional throughput THOR = 62 [sheets / hour], it is possible to obtain a high throughput almost twice as high.
[0149]
In the above embodiment, the case where the scanning exposure is performed by the step-and-scan method has been described. However, the present invention is not limited to this, and the case where the stationary exposure is performed by the step-and-repeat method and the EB Of course, the present invention can also be applied to exposure apparatuses, X-ray exposure apparatuses, and stitching exposure in which chips are combined.
[0150]
【The invention's effect】
  As explained above,BookAccording to the invention, throughputAnd exposure accuracyTo improveThere is an effect that you can.
[Brief description of the drawings]
FIG. 1 is a diagram showing a schematic configuration of a projection exposure apparatus according to an embodiment.
FIG. 2 is a perspective view showing a positional relationship among two wafer stages, a reticle stage, a projection optical system, and an alignment system.
FIG. 3 is a plan view showing a configuration of a drive mechanism of the wafer stage.
FIG. 4 is a diagram showing AF / AL systems provided in the projection optical system and the alignment system, respectively.
FIG. 5 is a diagram showing a schematic configuration of a projection exposure apparatus showing a configuration of an AF / AL system and a TTR alignment system.
6 is a diagram showing the shape of the pattern forming plate of FIG. 5. FIG.
FIG. 7 is a plan view showing a state in which a wafer exchange / alignment sequence and an exposure sequence are performed using two wafer stages.
8 is a view showing a state where the wafer exchange / alignment sequence and the exposure sequence in FIG. 7 are switched. FIG.
FIG. 9 is a diagram showing a reticle stage for double exposure that holds two reticles.
10A is a view showing a state in which the wafer is exposed using the pattern A reticle of FIG. 9, and FIG. 10B is a view of performing the wafer exposure using the pattern B reticle in FIG. 9; FIG.
FIG. 11 is a diagram showing an exposure order for each shot area on a wafer held on one of two wafer stages.
FIG. 12 is a diagram showing a mark detection order for each shot area on a wafer held on the other of two wafer stages.
[Explanation of symbols]
10 Projection exposure equipment
24a, 24b alignment system
38 Stage control means
90 Main controller
180 Center up
182 First loading guide
184 First unload arm
186 first slider
188 First load arm
190 Second slider
192 Second loading guide
194 Second unload arm
196 Third slider
198 Second load arm
200 Fourth slider
W1, W2 wafer
WS1, WS2 Wafer stage
PL projection optical system
BI1X to BI4Y Measuring axis
RST reticle stage
R reticle

Claims (15)

A projection exposure apparatus that projects and exposes an image of a pattern formed on a mask onto a sensitive substrate via a projection optical system,
A first substrate stage capable of holding a sensitive substrate and moving in a two-dimensional plane;
A second substrate stage that holds a sensitive substrate and is movable independently of the first substrate stage in the same plane as the first substrate stage;
At least one alignment system that is provided separately from the projection optical system and detects a mark on the substrate stage or on a sensitive substrate held by the substrate stage;
A transfer system for delivering a sensitive substrate between the first substrate stage and the second substrate stage;
A mask stage capable of simultaneously mounting two of the masks;
One substrate stage of the first and second substrate stages delivers the sensitive substrate to and from the transfer system in a state where the mark on the one substrate stage can be detected by the alignment system, and the alignment In parallel with the first sequence for performing the mark detection operation by the system, the mask stage and the other substrate stage are moved synchronously, and the other mask is used while changing the exposure condition using the two masks. And a control means for performing a second sequence for performing double exposure on a plurality of shot areas on the sensitive substrate held on a stage on the other stage.   The control means waits for the stage in which the sequence ends first among the first sequence and the second sequence performed in parallel on the two substrate stages, and then both operations are completed. The projection exposure apparatus according to claim 1, wherein at the time, the first sequence in the other stage and the second sequence in the one stage are executed in parallel. A first measuring axis for measuring a position of the first substrate stage in the first axis direction from one side of a first axis passing through the projection center of the projection optical system and the detection center of the alignment system; A second length measurement axis for measuring the position of the second substrate stage in the first axis direction from the other side in the first axis direction intersects the first axis perpendicularly at the projection center of the projection optical system. A third length measuring axis and a fourth length measuring axis perpendicularly intersecting the first axis at the detection center of the alignment system, and two lengths of the first substrate stage and the second substrate stage are determined by these length measuring axes. An interferometer system for measuring each dimension position,
The alignment systems are respectively disposed on one side and the other side in the first axial direction across the projection optical system,
The control means detects a mark on the first substrate stage or the sensitive substrate held on the first substrate stage by one alignment system, and is held on the second substrate stage or the second substrate stage. The projection exposure apparatus according to claim 1, wherein the mark on the sensitive substrate is detected by the other alignment system.   The control means is configured to control the third measuring axis and the third measuring axis of the interferometer system for each of the first substrate stage and the second substrate stage during mark detection by the alignment system and during exposure by the projection optical system. 4. The projection exposure apparatus according to claim 3, wherein the four measuring axes are switched. The first and second substrate stages each have a reflection surface for an interferometer,
When the alignment operation for detecting the mark of the sensitive substrate on one of the first and second substrate stages is performed using the alignment system, the position of the one stage in the first axial direction is measured. When the exposure operation for exposing the sensitive substrate on the other stage is performed using the projection optical system, the position of the other stage in the first axis direction is measured. And a second measuring axis for measuring the position of the second stage perpendicular to the first axis direction of the other stage on which the exposure operation for the sensitive substrate is performed, so that the exposure operation can be performed. After the completion, the third length measuring axis deviating from the reflecting surface of the other stage and the position of the one stage in the second axis direction in which the alignment operation with respect to the sensitive substrate is performed in parallel with the exposure operation. It is measurable arranging, after completion of the alignment operation, the interferometer system and a fourth length-measuring axis which deviates from the reflecting surface of the one stage;
The projection exposure apparatus according to claim 1, further comprising: a stage drive system for driving the first and second substrate stages. The stage drive system includes a first drive system for driving the first substrate stage and a second drive system for driving the second substrate stage,
6. The projection exposure apparatus according to claim 5, wherein a part of the first drive system and the second drive system are common. The stage drive system includes a first motor member extending in the first axial direction and a first motor member extending in the first axial direction and spaced apart from the first motor member by a predetermined distance in the second axial direction. A second motor member disposed; first and second moving members movable in the first axial direction along the first motor member; and moving in the first axial direction along the second motor member. Possible third and fourth moving members, a third motor member extending in the second axial direction and provided with the first and third moving members at both ends, and extending in the second axial direction And a fourth motor member provided with the second and fourth moving members at both ends,
The first stage is provided so as to be movable in the second axial direction along the third motor member, and by moving the first and third moving members along the first and second motor members. It is also movable in the first axis direction,
The second stage is provided to be movable in the second axial direction along the fourth motor member, and the second stage and the fourth moving member are moved along the first and second motor members. The projection exposure apparatus according to claim 5, which is also movable in the first axis direction.   The first measuring axis is set to measure the position of the one substrate stage from one side in the first axis direction, and the second measuring axis is set from the other side in the first axis direction. The projection exposure apparatus according to any one of claims 5 to 7, which is set to measure the position of the other stage.   The projection exposure apparatus according to claim 5, wherein each shot region on the sensitive substrate is scanned and exposed while moving the sensitive substrate in the second axis direction. A base member,
The projection exposure apparatus according to claim 1, wherein the first and second substrate stages are independently movable in a two-dimensional direction on the base. A first focus / leveling measurement mechanism disposed in the vicinity of the projection optical system;
A second focus / leveling measurement mechanism disposed in the vicinity of the alignment system;
The projection exposure apparatus according to claim 1, further comprising:   The projection according to any one of claims 1 to 11, wherein the sensitive substrate held on the first substrate stage and the sensitive substrate held on the second substrate stage are alternately exposed via the projection optical system. Exposure device. A projection exposure method of projecting and exposing a pattern image formed on a mask onto a sensitive substrate via a projection optical system,
Preparing two substrate stages capable of holding a sensitive substrate and independently moving in a two-dimensional plane, and a mask stage capable of mounting two of the masks simultaneously;
Exchange operation of a sensitive substrate in a state where a mark on the one substrate stage can be detected by an alignment system on one of the two substrate stages, and a sensitive substrate held on or on the substrate stage In parallel with the first sequence in which the alignment mark is detected by the alignment system , the exposure condition is changed using the two masks while the mask stage and the other stage are moved synchronously. A projection exposure method in which a second sequence of performing double exposure of a plurality of shot areas on the sensitive substrate held on the other stage is performed on the other stage.   Of the first sequence and the second sequence performed in parallel on the two substrate stages, after placing the stage that has completed the sequence first in the waiting state, when both operations are completed, the other sequence The projection exposure method according to claim 13, wherein the first sequence at the stage and the second sequence at the one stage are executed in parallel.   The projection exposure according to claim 13 or 14, wherein the sensitive substrate held on one of the two substrate stages and the sensitive substrate held on the other of the two stages are alternately exposed via the projection optical system. Method.

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