JP3518826B2 - Surface position detecting method and apparatus, and exposure apparatus - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surface position detecting method for detecting the height and inclination of the surface of a flat plate-like object such as a wafer, and more particularly to the optical axis direction of a projection optical system in a slit scan type exposure apparatus. The present invention relates to a surface position detecting method for continuously detecting the position and inclination of a wafer surface.

[0002]

2. Description of the Related Art Recently, the size of memory chips has been gradually increasing due to the difference between the trend of resolution line width or cell size of an exposure apparatus and the trend of expansion of memory capacity. It is reported to be about 14 x 25 mm.

With this chip size, a reduction projection exposure apparatus (stepper) currently used as an exposure apparatus for a critical layer has an exposure area of 31 mm in diameter, and since only one chip can be exposed per exposure, the throughput decreases. Furthermore, there is a need for an exposure apparatus that enables a larger exposure area. As a large screen exposure apparatus, a reflection projection exposure apparatus has been widely used as a semiconductor device exposure apparatus for a rough layer, which is required to have a high throughput, or an exposure apparatus for a large screen liquid crystal display element such as a monitor. This is a so-called mask-wafer relative scanning slit-exposure device in which a mask is linearly scanned with illumination light in the shape of an arc slit and is exposed on a wafer all at once by a concentric reflection mirror optical system.

The focusing of the mask image in these devices is performed by adjusting the height of the mask image so that the exposure surface of the photosensitive substrate (wafer or glass plate coated with a photoresist or the like) is sequentially aligned with the best image forming surface of the projection optical system. Measurement and auto focus and auto leveling correction drive are continuously performed during scan exposure.

The height and surface position detection mechanism in these devices detects the reflected light from the photosensitive substrate as a positional deviation on the sensor by using, for example, a so-called oblique incidence optical system in which a light beam is obliquely incident on the wafer surface. There are methods such as a method using a gap sensor such as an air micro sensor or a capacitance sensor, and driving to correct the height and inclination when the measurement position passes through the exposure slit area from multiple height measurement values during scanning. The amount was calculated and corrected.

[0006]

The concept of the slit scan type exposure apparatus currently used is 256M.
When only the projection system is improved so that the resolution can be dealt with thereafter, the following problem occurs.

That is, as the NA of the reduction projection system is increased to cope with the miniaturization of the circuit pattern, the allowable depth of focus in the process of transferring the circuit pattern becomes narrower and narrower. Since the exposure equipment used in the current rough process has an allowable depth of 5 μm or more, the measurement error included in the measurement values continuously measured during scan exposure and the influence of the step inside the chip can be ignored. In consideration of the above, the permissible depth is 1 μm or less, and therefore the influence of the measurement error included in the measurement value and the step difference in the chip cannot be ignored. Also, in the conventional exposure sequence with the stepper method, since the processing shifts continuously (series) from the end of focus correction at the exposure position to the start of exposure, variations in focus measurement time did not affect accuracy. In the exposure sequence of the slit scan method, the exposure is performed even during the focus measurement, so that both processes are performed simultaneously (parallel). Therefore, the variation in the focus measurement time between shots affects the feedback loop of the entire focus correction system including the drive system as a time delay component, which causes deterioration of focus correction accuracy. In addition, there is a problem of unevenness on the chip surface as a subject for realizing highly accurate focus detection. As a process approach to the lack of allowable depth, a method for realizing a low step structure such as a recess array or CMP has been developed, but still 0.5
The unevenness of about μm remains until the end, and step-like steps remain, especially in the peripheral circuit portion and the scribe portion. In this step-like stepped portion, a gentle slope remains on the surface even after the resist application, resulting in the following problems. That is, when detecting a surface having a gentle slope as described above in the oblique incidence type height detection system, the intensity of the detection light may be extremely reduced. This is because the detection light path is limited so as to detect only the reflected light at almost the same angle as the incident angle for the purpose of removing other noise light. If the diameter of the light receiving diaphragm on the detection optical path side is increased, the intensity of noise light is also increased and a measurement error occurs. Therefore, the diameter of the light receiving diaphragm cannot be unnecessarily enlarged. Further, when the inclination region of the measurement target portion is smaller than the size of the detection beam, the shape of the detected waveform is asymmetrically collapsed, which causes a large measurement error. Such a phenomenon is
Compared to the chip area, it is more likely to occur in scribed areas where process control is not performed, and because reproducibility within the wafer is poor, correction by offset is also difficult. When the slit / scan focus measurement is performed in such a state, there is a problem that the focus detection cannot be performed during the scan exposure and the scan exposure is stopped or a large defocus is generated, which causes a chip defect. Occur. It is also possible to remove these troublesome measurement values during scan exposure measurement, but processing within the limited measurement time will lead to system complexity, and even if configured, the measurement time There is a risk that the focusing accuracy will deteriorate due to fluctuations in the image quality, a decrease in throughput, and the like. That is, in a system in which focus correction is performed in real time and exposure is performed at the same time, it is first that the cooperation between the units is smoothly performed. If the assumption is broken, offset correction timing deviation and correction system delay compensation are performed. However, a problem such as phase shift occurs, and the resolution performance as designed cannot be obtained.

The present invention has been made in view of the above conventional problems, and its purpose is to determine a measurement point to be scan-measured in advance and to determine the position of the wafer surface without being affected by the unevenness of the detection surface. An object of the present invention is to provide a surface position detecting method capable of detecting with high accuracy, and particularly to provide a surface position detecting method of high accuracy in a slit scan exposure method.

[0009]

In order to achieve the above object, a first surface position detecting method according to the present invention forms a first optical image on a surface to be detected at an oblique incidence and at the same time, detects the object to be detected. A surface position detecting method for detecting a second optical image obtained by re-forming the first optical image with a light beam obliquely emitted from a surface and detecting the position of the detected surface based on the position of the second optical image. ,
A first detection step of detecting the second optical image for each of a plurality of measurement points in a unit area on the detection surface;
The positions of the plurality of measured points are calculated based on the plurality of second optical images detected in the first detecting step, an approximate surface that approximates the positions of the plurality of measured points is calculated, and the plurality of measured points are calculated. Based on the position of the measurement point and the approximate surface , the plurality of
By selecting the measured point from among the measured points of
The determination step of determining the measured point in the unit area on the detected surface, and the position of the detected surface for each unit area on the detected surface.
In order to detect, it has the 2nd detection step which detects the 2nd optical image about the point to be measured determined in the above-mentioned determination step. Preferably, in the determining step, a feature amount of the signal of the second optical image is calculated, and based on the feature amount, one of the plurality of measured points is measured.
It is characterized in that the measured point is determined by selecting a measuring point. The feature amount is, for example, at least one of the signal magnitude, symmetry, high frequency component, and the like. Further, in the preferred embodiment of the first surface position detecting method, in the determination step, based on a deviation between each said approximate surface position of the plurality of the measurement points, before
Note Selecting a measured point from multiple measured points
More, and determines the target measurement points in the unit area on the detection surface. Further, the number of measured points in the first detecting step is set to be larger than the number of measured points possible in the second detecting step . A second surface position detecting method according to the present invention is a surface position detecting method for detecting a position of a detected surface, which is a first detection for detecting positions of a plurality of measured points in a unit area on the detected surface. And an approximate surface that approximates the positions of the plurality of measured points detected in the first detecting step, and based on the positions of the plurality of measured points and the approximate surface, the plurality of measured objects Out of the points
By selecting a measurement point, a determination step of determining the measured point in the unit area on the detected surface, and for each unit area on the detected surface, in order to detect the position of the detected surface, A second detection step of detecting the position of the measured point determined in the determination step.

A first surface position detecting apparatus according to the present invention is a surface position detecting apparatus for detecting the position of a surface to be detected, in which the first optical image is obliquely formed on the surface to be detected.
A detection unit that detects a second light image obtained by re-imaging the first light image by a light beam obliquely emitted from the detection target surface, and a plurality of detection targets in the unit area on the detection target surface. For the measurement points, first control means for detecting the second light image, and positions of the plurality of measurement points are obtained based on the plurality of second light images detected by the first control means,
Obtaining an approximate surface that approximates the positions of the plurality of measured points, based on the positions of the plurality of measured points and the approximate surface ,
Note Selecting a measured point from multiple measured points
From the determining means for determining the measured point in the unit area on the surface to be detected , and the detecting means for detecting the position of the surface to be detected for each unit area on the surface to be detected. A second control means for detecting the second optical image with respect to the measured point determined by the means.
Preferably, the determining means calculates a characteristic amount of the signal of the second optical image, and also based on the characteristic amount, the plurality of target objects are calculated.
It is characterized in that the measured point is determined by selecting the measured point from the measured points . The feature quantity is
For example, it is at least one of the magnitude, symmetry and high frequency component of the signal. Further, in a preferred embodiment of this first surface position detecting device, the determining means determines the plurality of measured points based on a deviation between each of the positions of the plurality of measured points and the approximate surface . Select the measured point from
By doing so, the measured point in the unit area on the detected surface is determined. Further, the number of measured points targeted by the first control means is larger than the number of measured points targeted by the second control means . A second surface position detecting device according to the present invention is a surface position detecting device for detecting a position of a detected surface, wherein the detecting means detects a position of a measured point on the detected surface, and the detecting means,
First control means for detecting the positions of a plurality of measured points in the unit area on the detected surface, and an approximate surface approximating the positions of the plurality of measured points detected by the first control means, A measured point is selected from the plurality of measured points based on the positions of the plurality of measured points and the approximate surface.
Thereby, the determination means for determining the measured point in the unit area on the detected surface, and the detection means, for each unit area on the detected surface, for detecting the position of the detected surface, It has a 2nd control means to detect the position of the measured point determined by the determination means.

The exposure apparatus according to the present invention projects a pattern
Exposure apparatus for exposing a substrate to a surface of the substrate
And a surface position detecting device having a surface to be detected as a surface to be detected.
And

In the above exposure apparatus, preferably the above
It is characterized in that the first control means and the determination means are operated only for a part of the substrates in the lot. Also, the above
At the position of the substrate surface detected by the surface position detection device
Based on the substrate in the projection direction of the pattern.
It is characterized by having a position control means for positioning.

[0013]

According to the above construction, the positions of a plurality of measured points can be determined.
The approximate surface to be approximated is calculated, and the positions of multiple measured points and the approximate surface
To determine the measured point on the detected surface based on
It was therefore possible to determine the target measurement point, excluding the abnormal point of discontinuity and the detection signal of the height data, such as the stepped portion,
Therefore, the position of the measurement point can be stably detected.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a partial schematic view of a slit-scan type projection exposure apparatus using a surface position detecting method according to an embodiment of the present invention. In FIG. 1, reference numeral 1 denotes a reduction projection lens, the optical axis of which is indicated by AX in the drawing, and its image plane is in a relationship perpendicular to the Z direction in the drawing. The reticle 2 is held on the reticle stage 3, and the pattern of the reticle 2 is reduced and projected to 1/4 to 1/2 at the magnification of the reduction projection lens 1 to form an image on its image plane. Reference numeral 4 denotes a wafer having a surface coated with a resist, in which a large number of exposed regions (shots) formed in the previous exposure process are arranged.
Reference numeral 5 denotes a stage on which a wafer is placed, a chuck for adsorbing and fixing the wafer 4 on the wafer stage 5, an XY stage horizontally movable in the X-axis direction and the Y-axis direction, and a Z-axis which is the optical axis direction of the projection lens 1. The leveling stage movable in the direction of rotation and rotatable about an axis parallel to the X-axis and Y-axis directions, the Z
It is composed of a rotary stage rotatable about an axis parallel to the axis, and constitutes a 6-axis correction system for matching the reticle pattern image with the exposed area on the wafer.

Reference numerals 10 to 19 in FIG. 1 denote respective elements of a detection optical system provided for detecting the surface position and inclination of the wafer 4. 10 is a light source, a white lamp,
Alternatively, it comprises an illumination unit configured to emit light of a high brightness light emitting diode having a plurality of different peak wavelengths. Reference numeral 11 denotes a collimator lens, which is a light source 10.
Is emitted as a parallel light flux whose cross-sectional intensity distribution is substantially uniform. Reference numeral 12 is a prism-shaped slit member, and a pair of prisms are attached to each other so that their slopes face each other. A plurality of openings (for example, 6 pinholes) are formed in the attachment surface using a light-shielding film such as chrome. Is provided. A lens system 13 is composed of both telecentric systems, and guides six independent light fluxes that have passed through the plurality of pinholes of the slit member 12 to six measurement points on the wafer 4 surface via the mirror 14. Although only two light fluxes are shown in FIG. 1, three light fluxes are parallel to each other in the direction perpendicular to the paper surface. At this time, the plane in which the pinhole is formed and the plane including the surface of the wafer 4 are set so as to satisfy the Scheimpflug's condition for the lens system 13.

In the present embodiment, the incident angle Φ of each light beam from the light irradiating means on the wafer 4 surface (the angle formed by the perpendicular to the wafer surface, that is, the optical axis) is Φ = 70 ° or more. Wafer 4
As shown in FIG. 3, a plurality of pattern areas (exposure area shots) are arranged on the surface. As shown in FIG. 2, the six light beams that have passed through the lens system 13 are incident on and imaged at the measurement points independent of each other in the pattern area. Further, the six measurement points are incident from the direction rotated by Θ ° (for example, 22.5 °) in the XY plane from the X direction (scan direction) so that they can be observed independently of each other on the wafer 4 surface. As a result, as proposed by the present applicant in Japanese Patent Application No. 3-157822, the spatial arrangement of each element is made appropriate to facilitate highly accurate detection of surface position information.

Next, the side from which the reflected light flux from the wafer 4 is detected, that is, 15 to 19 will be described. Reference numeral 16 denotes a light receiving lens which is composed of both telecentric systems and receives six reflected light beams from the surface of the wafer 4 via the mirror 15.
The stopper diaphragm 17 provided in the light receiving lens 16 is provided in common for each of the six measurement points, and cuts out the high-order diffracted light (noise light) generated by the circuit pattern existing on the wafer 4. There is. The light beams passing through the light-receiving lens 16 composed of both telecentric systems have their optical axes parallel to each other, and the six individual correction lenses of the correction optical system group 18 cause the light beams to be mutually detected on the detection surface of the photoelectric conversion means group 19. The light is re-imaged so that the spot light has the same size. Further, the light receiving side (16 to 18) is the wafer 4
Since the tilt correction is performed so that each measurement point on the surface and the detection surface of the photoelectric conversion means group 19 are conjugated with each other, the position of the pinhole image on the detection surface is caused by the local inclination of each measurement point. Does not change, and the pinhole image changes on the detection surface in response to the height change of each measurement point in the optical axis direction AX.

Here, the photoelectric conversion means group 19 is composed of six one-dimensional CCD line sensors. This is advantageous over the configuration of the conventional two-dimensional sensor in the following points. First, by forming the correction optical system group 18 by separating the photoelectric conversion means, the degree of freedom in arranging each optical member and mechanical holder is increased. Further, in order to improve the resolution of the detection, it is necessary to increase the optical magnification from the mirror 15 to the correction optical system group 18. In this respect as well, it is better to divide the optical path and make it incident on each sensor. It is possible to make it compact. Furthermore, in the slit scan method, continuous focus measurement during exposure is indispensable, and shortening the measurement time is an absolute issue. One of the reasons is that conventional 2D CCD sensors read more data than necessary. The read time is 10 times or more that of the dimensional CCD sensor.

Next, a slit scan type exposure system will be described. As shown in FIG. 1, after the reticle 2 is adsorbed and fixed to the reticle stage 3, the reticle 2 scans in the RX (X-axis direction) direction at a constant speed in a plane perpendicular to the optical axis AX of the projection lens 1, and the RY In (Y-axis direction: perpendicular to the paper surface), correction driving is performed so that the target coordinate position is always scanned. X direction and Y of this reticle stage
The positional information in the direction is obtained by using an external reticle interference system (X-axis) for the XY bar mirror 20 fixed to the reticle stage 3 in FIG.
Y) It is constantly measured by irradiating a plurality of laser beams from 21. The exposure illumination optical system 6 uses a light source that generates pulsed light such as an excimer laser, and uses a beam shaping optical system (not shown), an optical integrator,
It is composed of members such as a collimator and a mirror, and is made of a material that efficiently transmits or reflects pulsed light in the far ultraviolet region. The beam shaping optical system is for shaping the cross-sectional shape (including dimensions) of the incident beam into a desired shape, and the optical integrator makes the light distribution characteristics of the light flux uniform and illuminates the reticle 2 with uniform illuminance. It is a thing. A rectangular illumination area corresponding to the chip size is set by a masking blade (not shown) in the exposure illumination optical system 6, and a pattern on the reticle 2 partially illuminated by the illumination area is coated with a resist through the projection lens 1. It is projected on the formed wafer 4.

The main controller 27 shown in FIG. 1 positions the slit image of the reticle 2 on a predetermined area of the wafer 4 in the XY plane (X, Y positions and rotation Θ about an axis parallel to the Z axis).
The entire system is controlled so that scan exposure is performed while adjusting the position in the Z direction (rotation α, β around the axes parallel to the X and Y axes and the height Z on the Z axis). That is, for the alignment of the reticle pattern in the XY plane, control data is calculated from the position data of the reticle interferometer 21 and the wafer stage interferometer 24 and the wafer position data obtained from an alignment microscope (not shown) to control the reticle position. This is realized by controlling the system 22 and the wafer position control system 25. Figure 1 shows the reticle stage 3
When scanning in the direction of arrow 3a, the wafer stage 5
Is scanned in the direction of arrow 5a in FIG. 1 at a speed corrected by the reduction magnification of the projection lens. The scanning speed of the reticle stage 3 is determined so that the throughput is advantageous based on the width of the masking blade (not shown) in the scanning direction in the exposure illumination optical system 6 and the sensitivity of the resist coated on the surface of the wafer 4.

The alignment of the reticle pattern in the Z-axis direction, that is, the alignment to the image plane is performed based on the calculation result of the surface position detection system 26 that detects the height data of the wafer 4, and the leveling stage in the wafer stage. Is controlled via the wafer position control system 25. That is, the tilt in the vertical direction to the scanning direction and the height in the optical axis AX direction are calculated from the height data of the three wafer height measuring spot lights arranged near the slit in the scanning direction, and the height in the optical axis AX direction is calculated. The correction amount is corrected to the optimum image plane position.

A method of detecting the position of the exposed region of the wafer 4 by the surface position detecting method according to the present invention will be described below.
First, the outline of the correction method will be described with reference to the flowchart of FIG. Received start command at step 101, step 1
At 02, the wafer is loaded on the stage and fixed by suction onto a chuck. Then, in order to measure the surface shape inside the exposed region of the chip, prescan measurement is performed in a specific sample shot region in step 103. After that, in step 104, a measurement position that can measure an optimum focus detection value for correcting the exposed area to the exposure image plane position is selected using the measured scan focus detection value. When selection is complete, st
In ep 105, prescan measurement is performed again in a plurality of sample shot areas in order to determine a correction term that specifies the surface shape inside the exposed area of the chip. In step 106, a correction term for correcting the measured value during scanning to the distance to the optimum exposure image plane position is obtained using the measured scan focus detection value. When the calculation of the correction value is completed, the process moves to the scan exposure sequence at each exposed position in step 107,
While correcting the focus detection value at the selected measurement position with the correction value, correction amount calculation and correction drive for adjusting the exposure area to the exposure image plane are performed.

The method of selecting the measurement position that can measure the optimum focus detection value will be described in detail below. Before that, a method of determining a focus measurement point in the scan exposure method will be described. In the stepper method, the stage was stopped at the exposure position, so the objective could be achieved by performing focus / tilt measurement at at least one position common to all shots, that is, measuring and correcting the focus at that stop position. However, as described above, in the scanning method, the stage is always moving during the exposure of the shot, so that it is necessary to measure a plurality of points within the shot. In addition, the measurement position and timing must be determined in consideration of many factors such as cooperation with the drive system, slit width, and scan speed. Now, assuming that the slit width is Ws, the focus measurement time is Tm, the focus correction time is Td, and the scan speed of the stage is V as the determining factors, first, when the cycle of the unevenness of the surface of the exposure region is f,
Correction cycle 1 / (Tm
+ Td) needs to exceed 2f. In other words, as the cycle of the unevenness, for example, the cycle of the peripheral circuit is one cycle, and 3 mm
If so, the cycle time in the case of performing correction including detection or correction of the unevenness needs to be 3 / (2 × V) or less. This number is, for example, the scan speed V =
Cycle time is 15 ms when 100 mm / sec
Therefore, when the correction is included, it is difficult to realize in consideration of the response time of the drive system. As a realistic solution, it is conceivable to reduce the scan speed, but this is not preferable because it lowers the throughput. However, when this time is assigned only to the detection, the detection can be sufficiently performed and the surface state of the wafer can be detected. From this point, the method of detecting the surface condition by prescan to grasp the tendency of unevenness on the exposed surface, and determining the actual measurement position at the time of exposure, which is necessary for detection during actual exposure and can be corrected from the correction cycle time. According to this, it is possible to provide a scanning device that performs focus correction with high accuracy without reducing throughput. In addition, since the exposure area has a finite slit width of Ws during exposure, the relationship is such that focus measurement of one or more points can be performed in the slit, that is, Ws.
If / V> (Tm + Td) is satisfied, the same correction accuracy as that of the stepper can be obtained for each slit size. Needless to say, such a correction system is sufficient considering that the focus is averaged during scan exposure.

[0024]

Example 1 An example in which the focus value is scan-measured inside the exposed region of the wafer with the height correction system of the stage fixed is shown. FIG. 3B shows a measurement result when 13 points are measured while scanning the area in which the exposed area is divided into four areas as shown in FIG. 3A with the five focus measurement sensors a to e. Shown in. Figure 3 (b) for clarity
The measured values of b and d are not plotted in. The horizontal axis of the figure shows the position coordinate in the scanning direction, the vertical axis shows the focus measurement value, and the dot shows the measurement result at each measurement position of each sensor. The curve in the figure is calculated using the least squares method etc. Is the approximated curve. Originally, the unevenness of the wafer surface should be suppressed below the allowable depth of the projection lens, but the resist surface inclination as shown in FIG. 5 occurs in the scribe and peripheral circuit portions. In such a portion, the reflected light cannot be accurately collected, and a detection waveform such as P2 (asymmetric) or P3 (small peak) shown in FIG. The result is far from the value. In this way, the approximated curved surface was calculated from the measured values obtained by scanning measurement with the stage fixed, and the deviation between the actual measured value and the approximated curved surface was calculated at each measurement position, and the amount of deviation exceeded a predetermined value. In that case, accurate focus detection can be performed by removing the measurement point from the measurement point in the actual scan exposure. Further, as shown in the sensor measurement value of c in FIG. 3B, when the deviation amount is large over all the measurement values, all the measurement of the position is invalidated, and the correction amount of focus and tilt is calculated by the remaining sensors. Doing so is also effective. By selecting a position where the measurement result is stable as described above, it is possible to expect to obtain a stable measurement value over the entire surface of the wafer, and it is possible to perform accurate focus detection.

The correction sequence will be described with reference to FIG. First, in step 1, the wafer is loaded and fixed to the chuck by suction. Then, in step 2, the measurement points of prescan 1, that is, the prescan 2 or the shot candidate measurement points during exposure are calculated. Specifically, the necessary and sufficient number of measurement points is calculated from the relationship between the sampling theorem and the response time of the correction system described above. In this case, it is advantageous to take more measurement points than the number of measurement points at the time of exposure in order to determine measurement points in step 7 later. Except when the target is the first (1st) print, the alignment measurement of the entire wafer is performed here and the positioning is completed. Next, in step 3, a shot near the center in the wafer, which is less likely to be affected by the chuck, is selected as a shot to be measured in prescan 1 and focus position correction is performed at the shot center. After that, the stage moves only in the scanning direction and the Z direction is not corrected. step4
, Move to the first measurement point calculated in step 2, step
At 5, the focus measurement value Zij (j = 1 to 5) at that position is measured and stored. The loop confirmation in step 6 loops until the measurement of all n measurement points is completed. In step 7, from all measured values of Zi j stored in the memory,
As shown in (b), the approximate curve is calculated, and the deviation between the actual measurement value and the approximate curved surface is calculated at each measurement position.
When the amount of the deviation exceeds a predetermined value, the measurement point is removed from the measurement point in the actual scan exposure. The measurement point Pij recognized as having a large deviation is removed from the subsequent measurement points. In addition, the measurement point at the time of exposure is determined so as to minimize the deviation of the measurement point in consideration of the correction response speed. Specifically, the scribe is avoided and the correction cycle is selected to be almost periodic and the change in the measured value is gentle. There may be cases where the unevenness of the surface shape is extremely bad or there are cases where the measurement points cannot be selected, but in that case, it is not necessary that the measurement values at all five points be valid, and at least 2 if the span is sufficient. It is possible to calculate the tilt amount even in points. With respect to the final measurement point determined in this way, a prescan 2 is performed in step 8 to measure an offset caused by unevenness of the resist surface of the measurement system. Through the above processing, the optimum measurement point for accurately matching each exposed area with the focal plane of the projection system and the accurate measurement offset at that position are calculated. Based on the above data, wafer exposure is performed in the sequence of step 9 to step 16. After confirming the completion of exposure of all exposed shots in the wafer in step 16, the wafer is collected in step 17.

[0026]

[Embodiment 2] As in Embodiment 1, the focus value is scanned and measured inside the exposed region of the wafer with the stage height correction system fixed, and at the same time as the calculation of the measured value, the characteristic parameter of the detected waveform is measured. To calculate. As described above, in the height detection system of the oblique incidence method, the detection optical path is limited so as to detect only the reflected light at an angle substantially the same as the incident angle for the purpose of removing noise light, so When detecting a surface having a large inclination, the intensity of the detection light may be extremely reduced. For example, in the focus detection waveform in the first print, since no pattern is formed on the wafer at all, a well-balanced and symmetrical waveform as shown in FIG. 6A can be obtained, but it is a post-process. Then, as shown in FIG. 6B, the phenomenon that the asymmetry (P2) and the deterioration of the S / N (P3) in which the intensity of the detection light is extremely lowered (P3) becomes remarkable, which causes the measurement error and the variation. ing. In such a case, by calculating the characteristic amount of the waveform itself, that is, the reflected light amount and the symmetry of the waveform without statistically processing the measurement result, it is possible to determine whether or not the point is a point at which a stable measurement value can be obtained. At the time of focus measurement in step 5 of FIG. 7, the feature amount of the above waveform is simultaneously calculated and stored,
By making the determination in step 8 thereafter, the reliability of measurement point selection can be improved.

[0027]

[Third Embodiment] In the case of performing the measurement by the pre-scan 1, more measurement points can be obtained when the measurement time is shorter because of the above-mentioned relation, and as a result, the tendency of the uneven state in the exposure area is accurately grasped. It is possible, but the burden on the measurement system will increase. The scan speed at the time of exposure may change depending on the resist sensitivity and the required throughput, but the measurement of the pre-scan 1 only needs to be performed with the single shot of the first lot. No need to match. Rather, it is more convenient to select the position for focus measurement during exposure by measuring multiple points at low speed and increasing the number of sample points. That is, when determining the measurement candidate points in step 2 of FIG. 7, taking into consideration that the abnormal point calculation in step 7 is performed reasonably, the measurement points are determined so that the detection marks have a sufficient positional relationship, for example. , The scan speed in prescan 1 measurement is determined by giving priority to the response speed of the measurement system. When the abnormal value is determined from the measured value thus measured, the abnormal point can be easily selected and extracted by passing the measured value of a certain sensor through a high-frequency filter, for example. In addition, in order to improve the accuracy of the measurement value when determining the measurement point, waveform data is acquired N times per measurement of one point, the measurement value of each point is calculated after all the measurement points are acquired, and N times of 1 point is calculated. You may use the average value of each measurement value as the measurement value of that point, or measure the measurement data of more points than the measurement points at the time of actual exposure with a slow scan and calculate the average value for every few points ( Data for calculation of measurement candidate points may be obtained by performing so-called moving average.

[0028]

Fourth Embodiment Considering matching between a plurality of devices,
It is necessary to strictly manage the relationship between the focus beam position and the exposure position. For example, if the relationship in the scanning direction is different for each device, even if the calibration of the image plane position and the focus measurement origin is obtained by actually performing exposure, the value depends on the measurement position in the scanning direction. Accurate focus offset correction cannot be performed unless it is obtained for each device. In addition, if a mechanical adjustment mechanism is added in order to achieve matching between the above-mentioned devices, the structure or cost is enlarged. In such a case, if the relationship is obtained in advance and the relative difference is managed as an offset, it is possible to obtain matching between the corrected devices when selecting an actual measurement point,
It is possible to obtain the exposure condition by one device and apply the value to a plurality of other machines. This situation is shown in Figure 8.
This will be described using (a) to (b '). It is assumed that the focus origin of the apparatus a of FIG. 8A and the projection lens image plane are calibrated in the state of FIG. 8A, that is, in the relationship (Da) between the exposure slit position and the exposed position. If the correction value obtained here is applied to another device b (FIG. 8B), the position where the focus detection beam is observed with the lens pair stage positioned due to the relationship Da is the device. Unlike a, a position different from the position of the exposure slit position and the focus detection beam position, that is, a machine difference of the mounting position of the focus detection system is detected. As described above, although it is necessary to perform calibration for each device due to the machine difference of the mounting position, as shown in FIG. 8B ′, the machine position difference of the focus detection system is taken into consideration in FIG. If step 2 and step 7 are performed, it is not necessary to perform calibration for each device, and management is simple.

The pre-scan measurement for selecting the measurement position described above is performed in each process in which a pattern to be formed is different, but it is sufficient to perform measurement only on one sheet in the lot, and thereafter the same measurement is performed. Regarding the process, the original purpose can be sufficiently realized by storing the measurement position obtained for the first sheet of the lot in the memory and using it for each focus measurement and correction, and it is possible to achieve high accuracy without lowering the throughput. Leveling correction and exposure are performed. If it is expected that there will be large variations in wafers within a lot, pre-scanning will be performed on the first plurality of wafers to select measurement positions. Improvement of accuracy is expected.

[0030]

As described above, according to the present invention, the position of the measured point can be stably detected. example
For example, the pre-scan measurement of the exposed area on the wafer is performed before the exposure, and the position where the focus value is most accurately measured is obtained to detect the detection error and the surface caused by the IC pattern of the exposed area on the wafer. It is possible to reduce the occurrence of measurement instability and the like due to the step structure, and it is possible to accurately calculate the focus offset for each process and improve the reliability of the focus measurement value measured during scan exposure. In addition , for example, by selecting a point at which a stable measurement value can be obtained, exceptional processing will not occur due to unstable measurement during subsequent offset measurement or focus measurement during exposure, thus increasing the processing throughput. Can be improved. So in this case,
Even for a wafer that has progressed through a process such as a slit / scan exposure device to create a step on the surface, the original distortion component of the wafer is corrected without being affected by the step, and the exposed area is reliably positioned within the depth of focus. As a result, good pattern transfer can be performed with high throughput,
A more highly integrated chip after the 256M may construct stable.

[0031]

Scope of application of the invention In the above description, an example in which the present invention is mainly applied to a semiconductor exposure apparatus for exposing a semiconductor wafer has been described. However, the present invention applies to a semiconductor manufacturing apparatus other than the exposure apparatus or a semiconductor wafer other than the semiconductor wafer. It can also be applied to a flat object, for example, a device for subjecting a glass substrate of a liquid crystal display device to processing such as exposure.

[Brief description of drawings]

FIG. 1 is a partial schematic view of a slit-scan type projection exposure apparatus using a surface position detection method according to an embodiment of the present invention.

FIG. 2 is an explanatory diagram showing a positional relationship between an exposure slit and each measurement point in surface position detection by the detection optical system in FIG.

FIG. 3 is an explanatory diagram showing measurement points on a chip of the wafer in FIG. 1 and states of measurement values at the respective measurement points.

4 is a schematic flowchart showing a sequence from wafer loading to unloading in the apparatus of FIG.

5 is an explanatory diagram illustrating a phenomenon that occurs at a chip step portion of the wafer in FIG. 1. FIG.

6 is a schematic diagram of a detection signal detected in the device of FIG.

FIG. 7 is a flow chart diagram showing an outline of a sequence of drive of surface position correction upon selection of measurement points, measurement of offset, and exposure at each shot in the surface position detection method according to the embodiment of the present invention.

FIG. 8 is an explanatory diagram regarding a sensor mounting position error in the fourth embodiment.

[Explanation of symbols]

1: reduction projection lens, 2: reticle, 3: reticle stage, 4: wafer, 5: wafer stage, 6: exposure illumination optical system, 10: light source, 11: collimator lens, 12:
Prism-shaped slit members, 14, 15: bending mirrors, 19: photoelectric conversion means group, 21: reticle stage interferometer, 22: reticle position control system, 24: wafer stage interferometer, 25: wafer position control system, 26 : Surface position detection system, 27: Main controller.

─────────────────────────────────────────────────── ─── Continuation of the front page (58) Fields surveyed (Int.Cl. ⁷ , DB name) G01B 11/00 H01L 21/027

Claims (15)

(57) [Claims] 1. A first optical image is obliquely incident and formed on a surface to be detected, and a second optical image is formed by re-forming the first optical image by a light beam obliquely emitted from the surface to be detected. A surface position detecting method for detecting the position of the detected surface based on the position of the second optical image, wherein the second optical image is detected for each of a plurality of measured points in a unit area on the detected surface. Approximating the positions of the plurality of measured points based on the first detection step of detecting and the plurality of second optical images detected in the first detection step, and approximating the positions of the plurality of measured points A surface is obtained, and based on the positions of the plurality of measured points and the approximate surface , the plurality of
By selecting the measured point from among the measured points of
A determination step of determining a measured point in a unit area on the detected surface, and detecting the position of the detected surface for each unit area on the detected surface
In order to do so, a second detection step of detecting the second optical image with respect to the measured point determined in the determination step is included. Wherein in said determining step, calculating a feature quantity of the second light image signal, also based on the feature quantity, the
By selecting a measured point from multiple measured points
2. The measured point is determined according to
The surface position detection method described. 3. The surface position detecting method according to claim 2, wherein the feature quantity includes at least one of the magnitude, symmetry, and high frequency component of the signal. 4. In the determining step, a measured point is selected from the plurality of measured points based on the deviation between each of the positions of the plurality of measured points and the approximate surface.
It makes the surface position detecting method according to claim 1, wherein the determining the measured points in the unit area on the detection surface. 5. The surface position detection according to claim 1, wherein the number of measured points in the first detecting step is larger than the number of possible measured points in the second detecting step. Method. 6. A surface position detecting method for detecting a position of a detected surface, comprising: a first detecting step of detecting positions of a plurality of measured points in a unit area on the detected surface; and a first detecting step. Obtaining an approximate surface that approximates the positions of the plurality of measured points detected in, and based on the positions of the plurality of measured points and the approximate surface, the plurality of measured points
The step of determining the measured point in the unit area on the detected surface by selecting the measured point from among the above, and detecting the position of the detected surface for each unit area on the detected surface.
In order to do so, a second detection step of detecting the position of the measurement target point determined in the determination step is included. 7. A surface position detecting device for detecting the position of a surface to be detected, wherein a first optical image is obliquely formed on the surface to be detected and the first light image is obliquely emitted from the surface to be detected. A detection unit that detects a second light image obtained by re-forming the light image, and the detection unit that detects the second light image for each of a plurality of measured points in a unit area on the detected surface. A first control unit and an approximate surface that approximates the positions of the plurality of measured points by obtaining the positions of the plurality of measured points based on the plurality of second optical images detected by the first control unit. Obtained, based on the positions of the plurality of measured points and the approximate surface , the plurality of
By selecting the measuring point from among the measurement points, and determining means for determining a target measurement point in the unit area on the detection surface, the detection means, for each unit area on the detection surface, wherein Subject
A surface position detecting device, comprising: second control means for detecting the second optical image with respect to the measured point determined by the determining means in order to detect the position of the exit surface. 8. The determining means calculates a characteristic amount of a signal of the second optical image, and based on the characteristic amount, a plurality of the plurality of characteristic amounts are calculated .
The surface position detection device according to claim 7 , wherein the measured point is determined by selecting a measured point from among the measured points . 9. The surface position detection device according to claim 8 , wherein the feature amount includes at least one of the magnitude, symmetry, and high frequency component of the signal. Wherein said determining means, based on a deviation between each said approximate surface position of the plurality of the measurement points, before
Note Selecting a measured point from multiple measured points
More, the surface position detecting apparatus according to claim 7, wherein the determining the measured points in the unit area on the detection surface. The number of 11. the measured point of the first control means is intended, according to claim 7-1 0 said second control means is characterized by being greater than the number of the measurement points which may be of interest The surface position detection device according to any one of claims. 12. A surface position detecting device for detecting the position of a surface to be detected, wherein the detecting means detects a position of a measured point on the surface to be detected, and the detecting means includes a unit area on the surface to be detected. A first control means for detecting the positions of a plurality of measured points in the inside, and an approximate surface that approximates the positions of the plurality of measured points detected by the first control means, and the positions of the plurality of measured points Of the plurality of measured points based on
From by selecting the measurement point, and determining means for determining a target measurement point in the unit area on the detection surface, the detection means, for each unit area on the detection surface, the test
A surface position detecting device, comprising: second control means for detecting the position of the measured point determined by the determining means in order to detect the position of the projected surface. 13. The pattern is projected an exposure apparatus that exposes a substrate, including the surface position detecting apparatus according to the surface of the substrate to one of the claims 7-1 2, the detected face An exposure apparatus characterized by the above. 14. The exposure apparatus according to claim 13, wherein the first control unit and the determination unit are operated only on a part of the substrates in the lot. 15. Based on the detected position of the surface of the substrate by the surface position detecting apparatus, according to claim 1 3 or 1 4, characterized in that it comprises a position control means for positioning the substrate in the projection direction of the pattern The exposure apparatus described.