JPH06196386A - Projection aligner - Google Patents

Abstract

PURPOSE:To enhance the throughput of an aligner by a method wherein a height position is detected in advance during a movement to a next exposure region and a focusing operation is performed during the movement or immediately after the finish of the movement on the basis of information on the detected height position. CONSTITUTION:Information on the target position of an X-Y stage 21 in a next exposure operation or on the position of a desired measuring point for a region to be exposed next is input to an MCU 30 from a host computer or the like via an input means 31. A height position is found during the movement on the basis of a detection output signal FS by a prescribed light-receiving cell when the X-Y stage 21 has reached a prescribed position. In addition, a desired measuring point which does not pass a pattern image during a movement to a next exposure region and which cannot be measured during the movement is measured at a point of time when the desired measuring point has reached a point which is sufficiently close to the pattern image. In this manner, it is known in advance on the basis of a design item before starting an exposure operation and on the basis of known information whether the height of which position can be measured when the X-Y stage 21 has reached which position.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a projection exposure apparatus,
In particular, it relates to a projection exposure apparatus used in a semiconductor manufacturing process.

[0002]

2. Description of the Related Art Conventionally, in a projection exposure apparatus in a semiconductor manufacturing apparatus, as disclosed in Japanese Patent Laid-Open No. 168112/1985, a semiconductor wafer arranged at a position where a mask pattern should be transferred by a projection lens. On the other hand, an oblique incidence type focus position detection device that emits detection light from an oblique direction is used.

This focus position detecting device uses the surface of a semiconductor wafer, which is a photosensitive substrate, as a surface to be inspected, projects a slit-shaped pattern on the surface to be inspected in a direction in which its longitudinal direction is perpendicular to the incident surface, and The reflected light is re-imaged on the detection means formed of a photoelectric conversion element, and the incident position of the reflected light on the detection means can be detected.

By the way, in recent years, LSI (Large
With higher integration of (Scale Integration), it is desired to transfer a fine pattern to the exposure area (shot area) of the wafer, and in order to cope with this, the numerical aperture NA (Numerial Aparture) of the projection lens is large. It is configured. As a result, the depth of focus of the projection lens becomes shallower,
It is desired to position the exposure region more accurately and surely at the focal position (within the depth of focus) of the projection lens without lowering the throughput.

In addition, the size of the exposure area of the projection exposure apparatus is increasing. As a result, the exposure area of the LSI chip itself is increased by one exposure, or a plurality of LSI chips are printed by one exposure. For this reason, it is desired to more accurately and surely position the entire size of the exposure area at the focus position (within the depth of focus) of the projection lens without lowering the throughput.

[0006]

In the conventional projection exposure apparatus having the focus position detection system described above, after the exposure area on the wafer is positioned at a predetermined position within the projection field of the projection optical system by moving the XY stage, The height position at a predetermined measurement point in the exposure area is detected, and the Z stage is appropriately driven based on the detected height position information to position the exposure surface (for example, surface) of the exposure area within the depth of focus of the projection optical system. Since the focus exposure has to be carried out and projection exposure has to be carried out, there is a disadvantage that the throughput is lowered.

Further, there has been proposed a method of focusing while detecting the height position at a predetermined point in the next exposure area while the XY stage is moving, but the height position information detected during the movement is tentative. In this method, the final focus must be made based on the height position information newly detected after the next exposure area is moved to a predetermined position and stopped. In addition, there was an inconvenience that the throughput was not good.

The present invention has been made in view of the above problems, and detects the height position in advance during the movement to the next exposure area, and during the movement or after the movement is completed based on the detected height position information. It is an object of the present invention to provide a projection exposure apparatus which can perform focusing immediately and has improved throughput.

[0009]

In order to solve the above-mentioned problems, in the present invention, an exposure means for transferring a mask pattern to each of a plurality of exposure areas on a photosensitive substrate via a projection optical system ( PL) and a substrate stage (21, 22) capable of holding the photosensitive substrate and moving two-dimensionally in a plane perpendicular to the optical axis of the projection optical system and moving in the direction along the optical axis. A projection exposure apparatus for transferring the pattern of the mask for each of the exposure areas by causing the image formation surface of the projection optical system and the exposure surface of the exposure area to substantially coincide with each other. A position for forming an image and photoelectrically detecting the light reflected from the photosensitive substrate to detect the position in the optical axis direction of the projection optical system at each of a plurality of predetermined measurement points in the exposure area. Detection means (1 16), and while the substrate stage is moving, output from the position detecting means when each of a plurality of measurement points in the next exposure region to which the pattern of the mask is to be transferred coincides with or comes close to the pattern image. Calculating means (31, PSD17, MCU30) for calculating the amount of deviation in the optical axis direction between the image plane of the projection optical system and the exposure surface of the next exposure area based on the detected signal, and the detection A projection exposure apparatus comprising: a control unit (18 to 20, 30) for controlling the movement of the substrate stage so that the amount of shift thus obtained becomes substantially zero.

Further, according to a preferred embodiment of the present invention, the pattern image is two slit images intersecting on the photosensitive substrate surface or three slit images arranged substantially parallel to each other on the photosensitive substrate surface.

[0011]

The present inventor has found that rectangular LSI chips, which are exposure regions, are arranged vertically and horizontally on a circular wafer, and the movement to the next exposure region is performed by using two orthogonal axes parallel to each side of the rectangular chip. It is necessary to measure the height position of the exposure surface at multiple points that cover the exposure area evenly and comprehensively because there is a step on the exposure surface of the LSI chip in advance due to the overprinting process. Observe the fact that an oblique incident light type focus position detection device that forms a pattern image of a predetermined shape on the surface to be detected and detects height positions at a plurality of points on the pattern image has already been developed. However, while moving to the next exposure area, some of the desired measurement points on the next exposure area should pass the pattern image of the above-mentioned predetermined shape, and other measurement points that do not pass the pattern image should also be moved before the end of movement. Be sufficiently close to the pattern image. Paying attention to, and conceived the present invention.

That is, in the projection exposure apparatus of the present invention, the height position is successively detected when a desired measurement point in the next exposure area passes through the pattern image while moving to the next exposure area, For other desired measurement points that do not pass through the pattern image, the height position can be detected when they approach each other during movement. In this way, the height position can be detected in advance during the movement to the next exposure region, and focusing can be performed during the movement or immediately after the movement ends based on the detected height position information.

[0013]

Embodiments of the present invention will be described with reference to the accompanying drawings. FIG. 1 is a schematic diagram of an oblique incident light type A according to an embodiment of the present invention.
It is a figure which partially shows the structure of the projection exposure apparatus provided with the F (autofocus) system. The AF system (1 to 1 shown in FIG.
5) is a multi-point AF system in which measurement points for measuring the positional deviation (so-called focal deviation) of the wafer W in the optical axis direction are provided at a plurality of positions within the projection visual field of the projection lens PL.

In FIG. 1, the illumination light IL, which is non-photosensitive to the resist applied on the wafer W, illuminates the slit plate 1. The light transmitted through the slit formed in the slit plate 1 obliquely irradiates the wafer W through the lens system 2, the mirror 3, the diaphragm 4, the projection objective lens 5, and the mirror 6. A halogen lamp or the like is used as the light source.

When the surface of the wafer W is at the best image plane Fo, that is, at the best focus position of the projection lens PL, the image of the slit of the slit plate 1 is formed on the surface of the wafer W by the action of the lens system 2 and the objective lens 5. It is imaged. The angle between the optical axis of the objective lens 5 reflected by the mirror 6 and the wafer surface is set to about 5 to 12 degrees, and the center of the slit image of the slit plate 1 is such that the optical axis AX of the projection lens PL is the surface of the wafer W. Located at the intersection with.

The slit image light beam reflected by the wafer W is re-formed on the light receiving slit plate 14 via the mirror 7, the light receiving objective lens 8, the lens system 9, the vibrating mirror 10 and the plane parallel plate 12. It is imaged. The vibrating mirror 10 has a function of slightly vibrating a slit image formed on the light-receiving slit plate 14 in a direction orthogonal to the longitudinal direction thereof.

The plane parallel 12 has a function of shifting the relative relationship between the slit of the slit plate 14 and the vibration center of the reflection slit image from the wafer W in a direction orthogonal to the slit longitudinal direction. Further, the vibrating mirror 10 is vibrated by a mirror drive unit (M-DRV) 11 driven by a drive signal output from an oscillator (OSC) 16.

When the slit image vibrates on the light-receiving slit plate 14, the light flux transmitted through the slits of the slit plate 14 is received by the array sensor 15. The array sensor 15 is
In the slit plate 14, the longitudinal direction of the slit is divided into a plurality of minute regions, and individual photocells are arranged in each minute region. As the array sensor, for example, a silicon photodiode, a phototransistor or the like can be used.

A signal from each light receiving cell of the array sensor 15 is sent through a selector circuit 13 to a synchronous detection circuit (PSD).
Enter in 17. An AC signal having the same phase as the drive signal from the OSC 16 is input to the PSD 17, and synchronous rectification is performed with the phase of this AC signal as a reference.

The PSD 17 is provided with a plurality of detection circuits for individually synchronously detecting the output signals of a plurality of light receiving cells selected from the array sensor 15. The detection output signals FS are so-called S-curve signals. It is called zero level when the slit center of the light receiving slit plate 14 and the vibration center of the reflection slit image from the wafer W coincide with each other, and is positive when the wafer W is displaced above the zero level. Level, a negative level when the wafer W is displaced below the zero level. Therefore, the height position of the wafer W at which the output signal FS becomes zero level is detected as the focus point.

However, in such an oblique incident light system, there is no guarantee that the height position of the wafer W at the in-focus point (the output signal FS is at the zero level) always always coincides with the best coupling surface Fo. That is, in the oblique incident light system, the system itself has a virtual reference plane, and the wafer W is placed on the reference plane.
The output signal FS of the PSD becomes zero level when the surfaces of the two are coincident with each other. Therefore, the reference surface and the best image forming surface Fo are set so as to coincide as much as possible at the time of manufacturing the device, but for a long period of time. There is no guarantee that they will agree. Therefore, by tilting the plane parallel 12 in FIG. 1, the virtual reference plane can be displaced in the optical axis AX direction so that the reference plane and the best imaging plane Fo can be matched.
That is, the calibration is possible.

In FIG. 1, the MCU 30 receives the output signal KS of the photoelectric sensor 45 to calibrate the multipoint AF system of the oblique incident light system, the function to set the inclination of the plane parallel 12, and the multipoint AF. A function of outputting a command signal DS to a circuit (Z-DRV) 18 that drives a drive motor 19 of a Z stage 20 based on each output signal FS of the system, and a drive unit that drives an XY stage 21 (motor and its control 22) (including a circuit) and the like to output a command signal.

Further, in FIG. 1, a leveling stage 23 is provided on the Z stage 20, and the leveling stage 23 is provided.
The reference numeral 30 also has a function of outputting a command signal to the leveling stage drive unit 24 (including the motor and its control circuit) that drives the leveling stage 23, based on each output signal FS of the multipoint AF system. By appropriately driving the leveling stage 23, the wafer surface can be tilted as a whole by a desired amount.

On the Z stage 20, the best image plane F
A fiducial mark FM for determining o is provided. A plurality of slit-shaped openings are provided on the surface of the mark FM, and the mark FM is illuminated from below (from the Z stage side) with light having substantially the same wavelength as the exposure light via the fiber 41. The height of the surface of the mark FM is configured to substantially match the height of the surface of the wafer W. The light transmitted through the slit-shaped opening of the mark FM is reflected by a reticle (mask) (not shown) via the projection lens PL, and is incident on the photoelectric sensor 45 provided below the opening through the opening. The Z stage 20, that is, the surface of the mark FM is moved in the height direction (optical axis AX direction),
The position of the surface of the mer FM at which the contrast of the light received by the photoelectric sensor 45 is highest (that is, the voltage value of the output signal KS is the peak) is the best image forming surface (best focus position) Fo. Therefore, the mark FM is positioned at each of a plurality of points in the projection field of the projection lens PL (for example, a plurality of measurement points of the multipoint AF system should be matched), and the above measurement is repeated to project the image. The best image plane of the lens PL can be obtained.

FIG. 2 shows the projection field If of the projection lens PL.
FIG. 6 is a diagram showing the positional relationship between the light projection slit image ST of the AF system and the AF system on the wafer W surface. The projection visual field If is generally circular, and the pattern area PA of the reticle R has a rectangular shape included in the circle. The slit image ST is 45 with respect to each of the moving coordinate axes X and Y of the XY stage 21.
Two intersecting slit images ST1 and ST2 that are inclined by about °
Is formed on the wafer as. Each slit image ST1, S
T2 is a pair of oblique incident light type multipoints A described above.
It is formed by the F system. Therefore, both the optical axis AF of the light-projecting objective lens 5 and the light-receiving objective lens 8 of one AF system
x1 is a slit ST1 on the wafer surface, and both optical axis AF of the projection objective lens 5 and the reception objective lens 8 of the other AF system.
On the wafer surface, x2 extends in a direction orthogonal to the slit ST2.

Further, the centers of the slit images ST1 and ST2 are positioned so as to substantially coincide with the optical axis AX.

Generally, in the exposure area (shot area) on the surface of the wafer W on which the pattern is projected and exposed, a circuit pattern to be superimposed on the pattern image is already formed. A stack type memory IC or the like has a large step shape on the wafer surface for high integration. Further, in the shot area, a change in the unevenness becomes noticeable each time the device manufacturing process is performed, and a large unevenness may exist in the longitudinal direction of the slit image ST. For this reason, the slit image ST is configured to extend as long as possible within the projection area of the pattern area PA, in other words, to cover the slit area ST evenly and comprehensively.

In this embodiment, each slit image is divided into five parts, and five measurement points shown in FIG. 2 are selected.
How to arrange the slit images, how to divide each slit image, to select the measurement point at which division part, and to which position of the division part to select the measurement point depends on the pattern to be exposed, The number of chips to be exposed at one time and their arrangement,
It depends on conditions such as a step already formed before exposure.
All these conditions are known before each projection exposure step and relate to so-called modifiable design considerations.

The operation of the projection exposure apparatus of the present invention constructed as above will be described below. Information such as the target position of the XY stage 21 at the time of the next exposure and the desired measurement point position of the next exposure area is input to the MCU 30 from the host computer or the like via the input means 31. XY stage 21
Of the present position, the next target position, and the corresponding position of each light receiving cell of the array sensor 15 on the photosensitive substrate surface, that is, the height measurable position on the pattern image of the multipoint AF system, and the like, from the next exposure area. It is determined which measurement point of the desired measurement positions in the next exposure area passes through the pattern image during the movement to, and as a result, the measurement during the movement is possible.

In this way, the desired measurement point that can be measured during the movement to the next exposure area is set at the height position from the detection output signal FS of the predetermined light receiving cell when the XY stage 21 reaches the predetermined position. Can be requested on the move. Also, during the movement to the next exposure area does not pass through the pattern image,
Therefore, for the desired measurement point that cannot be measured during movement, the measurement is performed when the desired measurement point is sufficiently close to the pattern image. In other words, for other desired measurement points that do not pass through the pattern image, measurement is performed while moving at a position sufficiently close to the desired measurement point.

As described above, based on the design items and known information before the start of exposure, when the XY stage 21 reaches the position, the height of the position in the exposure area from the detection output signal FS of which light receiving cell is measured. You can know in advance if you can.

That is, the MCU 30 uses the XY-DRV 22.
The next target position is set to, and the XY stage 21 is started to move to the next exposure area, and the position information during the movement is XY-D.
It is sequentially input from the RV 22 to the MCU 30. The position information of the XY stage 21 that is sequentially input is compared with the measurement position information that is obtained in advance, and a plurality of height position information is obtained during movement from the detection output signal FS of a predetermined light receiving cell at the time when the positions match. be able to. The height shift from the focus position of the exposure area is obtained from the obtained plurality of height position information, and the MCU 30 outputs the control signal DS to the Z-DRV 18 to move the Z stage 20 by a predetermined amount. The leveling stage 23 is also driven as necessary to position the exposure area at an appropriate position within the depth of focus of the projection lens PL.

Next, the measurement timing during the movement to the next exposure area will be specifically described with reference to FIG. FIG. 3A shows the first exposure area P after projection exposure.
It shows a state in which A1 and the second exposure area PA2 to be projected and exposed next are juxtaposed. Five points 51 to 55 shown in the first exposure area PA1 are measurement points at height positions. Five points 61 to 65 shown in the next exposure area PA2
Is a desired measurement point. When the projection exposure of the first exposure area PA1 is completed, the first projection shown in FIG.
The XY stage 21 is driven in the direction of the arrow in the drawing until the second exposure area PA2 is moved to the position of the exposure area PA1.

In the figure, 61 out of the desired measurement points to be measured
And 62 are points that pass the slit image ST during movement, more specifically, points that coincide with the measurement points 54 and 55 during movement, and the other three points 63 to 65 pass through the slit image ST during movement. The point is not.

As shown in FIG. 3B, the slit image ST
The desired measurement points 61 and 62 passing through can be measured during the movement when they coincide with the measurement points 51 and 52, respectively. In addition, as shown in FIG.
The desired measurement points 63 to 65 that do not pass through the slit image ST can be measured during movement when they are sufficiently close to the measurement points 53 to 55.

That is, 61 and 62 of the five desired measurement points can be measured during movement at desired positions, and 63 to 65 can be measured during movement at positions slightly deviated from the desired position to the left side in the drawing.

Although the present embodiment has been described without considering the inclination (irregularities) of the image forming surface, in reality, the best image formation of the projection optical system is caused due to inaccuracy of holding the reticle. The face is not necessarily a plane. That is, the measurement points 51 to 55
The in-focus points at the respective positions do not necessarily exist in one plane, and are distributed unevenly as a whole. For this reason, the plane parallel 12 is used to calibrate the inclination of the entire image plane on average.

In the present invention, the height positions to be originally measured at the measurement points 51 and 52 are pre-read at the measurement points 54 and 55 and measured. Therefore, measuring points 51 and 5
4 or the offset amount of Δz due to the inclination of the image plane between the measurement points 52 and 55 needs to be considered. More specifically, the measurement point 54 or 5 is caused by the inclination of the image plane.
If it is calibrated that the focal point of 5 is located Δz above the focal point of the measurement point 51 or 52, it is necessary to offset the actual measurement value at the measurement point 54 or 55 by Δz. . Further, the values measured at points close to the measurement points 53 to 55 can be corrected by an appropriate method such as linear interpolation if necessary.

Although the present embodiment has been described by using the pattern image composed of two intersecting slit images, a pattern image composed of a plurality of slit images, preferably three slit images, which are substantially parallel to each other may be used. Further, an AF system may be used in which a bright / dark pattern is projected on almost the entire exposure area and the light reflected here is imaged on the light receiving surface of the image sensor (CCD camera or the like). This AF system obtains the height position of the exposure area by detecting the amount of deviation of the position (or pitch) of the pattern image on the light receiving surface from a predetermined reference position, and the greatest feature is the exposure. The height position can be detected at any point in the area. Therefore, if such an AF system is used, there is an advantage that even if conditions such as the step structure in the exposure area and the shape thereof change, a plurality of optimum measurement points can be selected according to the conditions. For example, even if at least one of the plurality of points whose height positions are to be measured is different between two adjacent exposure areas, the measurement point can be appropriately selected and changed by using the AF system.

In this embodiment, a wafer used in a semiconductor manufacturing process is taken as an example of the photosensitive substrate, but it is obvious that the present invention can be applied to any other photosensitive substrate. . Furthermore, as a modified example of the present invention, without deviating from the range, the obtained height position information is averaged or a weighted averaging is performed to average the sum of weighting factors to obtain a target focal plane, and It is obvious that the optimal travel route can be selected and controlled.

The exposure area located at the outermost periphery of the wafer W may be partially cut off. When the reticle pattern is transferred to such an exposure area, the number of measurement points for measuring the height position in the area can naturally be reduced. Therefore, before moving to the area, a measurement point to be used in the area is selected from a plurality of measurement points of the multipoint AF system, and at least one selected measurement point and a plurality of points of the multipoint AF system are selected. It is desirable to detect the height position when any of the measurement points of (1) and (2) coincide with each other or are close to each other.

[0042]

As described above, in the projection exposure apparatus of the present invention, the pattern image has such a shape that a plurality of measurement points can be comprehensively and averagely selected on the exposure area. Therefore, while moving to the next exposure area, the height position is successively detected when a desired measurement point in the next exposure area passes the pattern image, and another desired measurement that does not pass the pattern image is performed. Since the height position of a point can be detected when moving and approaching, the height position can be detected in advance while moving to the next exposure area, and the height position can be detected based on the detected height position information during or after the movement. Throughput can be significantly improved since focusing can be done immediately.

[Brief description of drawings]

FIG. 1 is a diagram partially showing a configuration of a projection exposure apparatus according to an embodiment of the present invention.

FIG. 2 is a diagram showing a positional relationship between a projected visual field and a pattern image.

FIG. 3 is a diagram illustrating timings at which a desired measurement point that passes a pattern image and a desired measurement point that does not pass the pattern image are measured during movement.

[Explanation of symbols]

 2, 9 Lens system 3, 6 Mirror 4, Aperture 5 Projection objective lens 9 Imaging optical system 10 Oscillating mirror 11 Mirror drive unit 12 Parallel plane 13 Selector 14 Slit plate 15 Array sensor 17 Synchronous detection circuit

Claims (3)

[Claims] 1. An exposure unit for transferring a pattern of a mask to each of a plurality of exposure regions on a photosensitive substrate via a projection optical system, and holding the photosensitive substrate and perpendicular to an optical axis of the projection optical system. And a substrate stage movable in the direction along the optical axis while moving two-dimensionally in the plane, and for each of the exposure areas, an image plane of the projection optical system and an exposure surface of the exposure area. In a projection exposure apparatus that transfers the pattern of the mask in a substantially coincident manner, a pattern image of a predetermined shape is formed on the photosensitive substrate, and the light reflected from the photosensitive substrate is photoelectrically detected to detect the light in the exposure area. Position detection means for detecting a position in the optical axis direction of the projection optical system at each of a plurality of predetermined measurement points, and during movement of the substrate stage, within the next exposure area to which the pattern of the mask is to be transferred plural Based on the detection signal output from the position detection means when each of the measurement points coincides with or comes close to the pattern image, the image formation surface of the projection optical system and the exposure surface of the next exposure area are described above. A projection exposure apparatus comprising: a calculation unit that calculates a shift amount in the optical axis direction; and a control unit that controls the movement of the substrate stage so that the detected shift amount becomes substantially zero. 2. The pattern image is two slit images intersecting each other on the surface of the photosensitive substrate.
The projection exposure apparatus according to. 3. The projection exposure apparatus according to claim 1, wherein the pattern image is three slit images arranged substantially parallel to each other on the surface of the photosensitive substrate.